Tetrahedron Asymmetry

Editorial board ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12
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Graphical contents list ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12
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Contributors to this issue ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12
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Nucleophilic substitution at phosphorus: stereochemistry and mechanisms ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Oleg I. Kolodiazhnyi, Anastasy Kolodiazhna This review is devoted to the stereochemistry of nucleophilic substitution reactions at phosphorus. The study of the reactions of phosphoryl group transfer is important for biological and molecular chemistry. The stereochemistry and mechanisms of SN1(P) monomolecular and SN2(P) bimolecular nucleophilic substitution reactions of organophosphorus compounds are discussed. It has been shown that hydrolysis of many natural phosphates proceeds according to the monomolecular SN1(P) mechanism via the formation of metaphosphate intermediate (PO3 −). SN2(P) nucleophilic substitution at chiral trivalent or pentavalent phosphorus compounds proceeds via the formation of penta-coordinated transition state or pentacoordinate intermediate. Graphical abstract image
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Chiral enantiopure organosilane precursors for the synthesis of periodic mesoporous organosilicas ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Orit Cohen, Raed Abu-Reziq, Dmitri Gelman The manuscript describes synthesis of new chiral organosilica networks starting from modified readily available enantiopure substances such as sugars and amino acids. We report on the successful preparation of robust all-chiral organosilicas by polymerization of the homochiral monomers. When the homochiral organosilane monomers were polymerized in mixtures of polar organic solvents and water in the presence of hydrochloric acid or tetrabutylammonium fluoride as catalysts, mainly spherical microparticles were obtained due to emulsification of the hydrophobic monomers in these mixtures. Polycondensation of the chiral organosilanes in the presence of Pluronic P123 as a template produced ordered mesoporous networks. The new all-chiral materials were characterized by SEM, STEM, BET, SAXS, IR, NMR and TGA. Graphical abstract image
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Four new norlignan glycoside isomers from the twigs of Cephalotaxus oliveri Mast. ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Fan-Cheng Meng, Hui Liu, Xiao-Jun Huang, Yu Chang, Dai Ren, Li-Gen Lin, Qing-Qian Zeng, Qing-Wen Zhang Four novel isomers of norlignan glycoside were isolated from Cephalotaxus oliveri Mast.. Their structures were elucidated as 3S-4″-O-β-d-glucopyranosylnyasol 1, 3S-4′-O-β-d-glucopyranosylnyasol 2, 3S-4″-O-β-d-glucopyranosylhinokiresinol 3, 3S-4′-O-β-d-glucopyranosylhinokiresinol 4 by extensive spectroscopic methods including 1D and 2D NMR experiments (1H, 13C, DEPT, 1H–1H COSY, HSQC, HMBC, ROESY) along with HR-ESIMS and comparison to literature data. Their absolute configurations were elucidated through CD spectra coupled with the quantum chemical CD calculations. Graphical abstract image
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Amidation of carboxylic acids via the mixed carbonic carboxylic anhydrides and its application to synthesis of antidepressant (1S,2R)-tranylcypromine ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Tetsuya Ezawa, Yuya Kawashima, Takuya Noguchi, Seunghee Jung, Nobuyuki Imai Primary amidations of carboxylic acids 1 or 3 with NH4Cl in the presence of ClCO2Et and Et3N were developed to afford the corresponding primary amides in 22% to quantitative yields. Additionally, we have applied the amidation to the preparation of various amides containing hydroxamic acids and achieved the synthesis of (1S,2R)-tranylcypromine as an antidepressant medicine via Lossen rearrangement. Graphical abstract image
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Stereoselective sulfoxidation catalyzed by achiral Schiff base complexes in the presence of serum albumin in aqueous media ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Jie Tang, Pengfei Yao, Fuping Huang, Meiyi Luo, Yi Wei, Hedong Bian Four coordination complexes ML derived from an achiral Schiff base ligand (H2L = 2,2′-[(1,2-ethanediyl)bis(nitrilopropylidyne)]bisphenol) have been synthesized and characterized. A method is described for the enantioselective oxidation of a series of aryl alkyl sulfides using the coordination complexes in the presence of serum albumins (SAs) in an aqueous medium at ambient temperature. The mixture of metal complexes with serum albumins is useful for inducing asymmetric catalysis. The complex, albumin source and substrate influence stereoselective sulfoxidation. At optimal pH with the appropriate oxidant, some of ML/SA systems are identified as very efficient catalysts, giving the corresponding sulfoxides in excellent chemical yield (up to 100%) and good enantioselectivity (up to 94% ee) in certain cases. UV–visible spectroscopic data provide evidence that stronger binding between the complex and serum albumin lead to higher enantioselectivity. Graphical abstract image
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Enantioselective synthesis of chiral 4H-pyran derivatives through [3+3] tandem reaction over a squaramide catalyst ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Zhonghe Wang, Yali Zhu, Jing Zhang, Jiawei Li, Min Wu, Xilong Yan, Yang Li, Ligong Chen An efficient [3+3] tandem reaction between 1-phenyl-3-methyl-5-pyrazolones and 2-(1-alkynyl)-2-alken-1-ones over a tertiary amine–squaramide catalyst is described. The pyran fused pyrazolone derivatives were successfully obtained in 53–88% yields and with 62–84% ee by this synthetic methodology. This methodology involves easily accessible starting material, mild condition, satisfied yields and ee values. Additionally, when enynes were used as the substrates for the [3+3] cascade reaction, isomerized target products could be obtained directly. Graphical abstract image
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Lipase-catalyzed kinetic resolution approach toward enantiomerically enriched 1-(β-hydroxypropyl)indoles ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Paweł Borowiecki, Iwona Justyniak, Zbigniew Ochal In a route towards enantiomerically enriched 1-(β-hydroxypropyl)indoles, which are potentially useful building blocks for high value-added chemicals synthesis, a kinetic resolution approach by means of lipase-catalyzed enantioselective acylation as well as hydrolysis/methanolysis has been elaborated for the first time. The enzymatic resolution of chiral N-substituted indole-based sec-alcohols was successfully accomplished, yielding both enantiomeric forms of the employed derivatives with up to >99% enantiomeric purity via an enantioselective transesterification under mild reaction conditions. The most selective resolutions were obtained using fungal (CAL-B and TLL) and bacterial (PFL and BCL) lipases and vinyl acetate as the acyl group donor. The synthetic protocol described herein is very simple, user-friendly and efficient, thus paving the way for future access towards more complex compounds of this type. The absolute configurations of novel enantiomeric derivatives, and thus stereoselectivity of the described enzymatic reactions were confirmed by application of CDA-based NMR methodology and single-crystal X-ray diffraction analysis. Graphical abstract image
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Asymmetric aminocarbonylation of iodoalkenes in the presence of α-phenylethylamine as an N-nucleophile ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Gábor Mikle, Borbála Boros, László Kollár Iodoalkenes, such as 2-iodo-bornene, 17-iodoandrost-16-ene, 3-methoxy-17-iodoestra-1,3,5(10),16-ene, 3β-hydroxy-20-iodopregna-5,20-diene and 3β-hydroxy-12-iodo-5α,25R-spirost-11-ene were aminocarbonylated with enantiomerically pure and racemic α-phenylethylamine as the N-nucleophile in the presence of palladium(0) catalysts. Monodentate and bidentate (chiral and achiral) phosphines were used as ligands in the catalytic system. All diastereoisomers of the corresponding carboxamides were characterised as pure stereoisomers using both α-phenylethylamine and iodoalkene in enantiomerically pure form. The diastereoisomers were obtained in moderate to high yields in a chemoselective reaction, i.e., carboxamides due to single carbon monoxide insertion were formed exclusively, with no double CO insertion leading to 2-ketocarboxamides. Diastereoselectivities of the aminocarbonylation were investigated using the N-nucleophile in racemic form by the systematic variation of the catalyst. Graphical abstract image
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New functional chiral P-based ligands and application in ruthenium-catalyzed enantioselective transfer hydrogenation of ketones ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Nermin Meriç, Cezmi Kayan, Nevin Gürbüz, Mehmet Karakaplan, Nil Ertekin Binbay, Murat Aydemir Metal-catalyzed asymmetric transfer hydrogenation is a powerful and practical method for the reduction of ketones to produce the corresponding secondary alcohols, which are valuable building blocks in the pharmaceutical, perfume, and agrochemical industries. Hence, a series of novel chiral β-amino alcohols were synthesized by chiral amines with regioselective ring opening of (S)-propylene oxide or reaction with (S)-(+)-2-hydroxypropyl p-toluenesulfonate by a straightforward method. The chiral ruthenium catalytic systems generated from [Ru(arene)(μ-Cl)Cl]2 complexes and chiral phosphinite ligands based on amino alcohol derivatives were employed in asymmetric transfer hydrogenation of ketones to give the corresponding optically active alcohols; (2S)-1-{[(2S)-2-[(diphenylphosphanyl)oxy]propyl][(1R)-1-phenylethyl]amino}propan-2-yldiphenylphosphinitobis[dichol-oro(η6-benzene)ruthenium(II)] acts an excellent catalyst in the reduction of α-naphthyl methyl ketone, giving the corresponding alcohol with up to 99% ee. The substituents on the backbone of the ligands were found to have a remarkable effect on both the conversion and enantioselectivity of the catalysts. Furthermore, this transfer hydrogenation is characterized by low reversibility under these conditions. Graphical abstract image
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Synthesis of polyhydroxylated bicyclic tetrahydrofurans and tetrahydropyrans via a stereoselective domino cyclization/reduction reaction ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Michał Malik, Piotr Cmoch, Mykhaylo A. Potopnyk, Sławomir Jarosz A novel reaction cascade involving a Lewis acid-induced migration of an isopropylidene protecting group followed by the formation of a pyranose or furanose ring and subsequent reduction of the hemiacetal is described. Depending on the reaction conditions, as well as, the stereochemistry of the substrate, polyhydroxylated tetrahydrofurans or tetrahydropyrans can be obtained in reasonable yields. The synthons used in this transformation were prepared via a highly stereoselective one-pot tandem reaction, consisting of a 1,4-Michael addition of vinylmagnesium bromide to d-glucose-derived cyclohexenone followed by aldol reaction with 2,3-O-isopropylidene-d-glyceraldehyde. Graphical abstract image
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Asymmetric syntheses of the N-terminal α-hydroxy-β-amino acid components of microginins 612, 646 and 680 ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Stephen G. Davies, Ai M. Fletcher, Abigail R. Hanby, Paul M. Roberts, James E. Thomson The asymmetric syntheses of the N-terminal α-hydroxy-β-amino acid components of microginins 612, 646 and 680 are reported. Conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to the requisite (E)-α,β-unsaturated ester followed by in situ enolate oxidation with (−)-(camphorsulfonyl)oxaziridne (CSO) gave the corresponding anti-α-hydroxy-β-amino esters. Sequential Swern oxidation followed by diastereoselective reduction gave the corresponding syn-α-hydroxy-β-amino esters. Subsequent N-debenzylation (i.e., hydrogenolysis for microginin 612, and NaBrO3-mediated oxidative N-debenzylation for microginins 646 and 680) followed by acid catalysed ester hydrolysis gave the corresponding syn-α-hydroxy-β-amino acids, the N-terminal components of microginins 612, 646 and 680, in good yield. An analogous strategy for elaboration of the enantiopure anti-α-hydroxy-β-amino esters facilitated the asymmetric synthesis of the corresponding C(2)-epimeric α-hydroxy-β-amino acids. Graphical abstract image
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Solid supported Hayashi–Jørgensen catalyst as an efficient and recyclable organocatalyst for asymmetric Michael addition reactions ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Piotr Szcześniak, Olga Staszewska-Krajewska, Bartłomiej Furman, Jacek Mlynarski A comparison of three different catalytic systems for the efficient, asymmetric synthesis of N-({(3R,4R)-4-[(benzyloxy)methyl]pyrrolidin-3-yl}methyl)-N-(2-methylpropyl)benzenesulfonamide 1 (BZN) is described. The presented strategy is based on the organocatalytic Michael addition of aldehyde 2 to trans-nitroalkene 3, and subsequent reductive cyclization. High yields, enantio-, and diastereoselectivities were achieved in the Michael addition by application of a POSS- or Wang resin-supported Hayashi–Jørgensen catalyst. Graphical abstract image
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Highly enantioselective asymmetric reactions involving zinc ions promoted by chiral aziridine alcohols ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Szymon Jarzyński, Greta Utecht, Stanisław Leśniak, Michał Rachwalski Enantiomerically pure, chiral secondary and tertiary aziridine alcohols (including the aziridine analogue of ProPhenol—AziPhenol) have proven to be highly effective catalysts for enantioselective asymmetric reactions in the presence of zinc ions, including arylation of aromatic aldehydes, epoxidation of chalcone and addition of diethylzinc to aldehydes, leading to the desired chiral products in high chemical yields (up to 90%) and with ee’s up to 90%. A higher catalytic activity of Prophenol-type bis(aziridine alcohol) in the aforementioned asymmetric transformations has been demonstrated. Graphical abstract image
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Chiral ethylene-bridged flavinium salts: the stereoselectivity of flavin-10a-hydroperoxide formation and the effect of substitution on the photochemical properties ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Jiří Žurek, Eva Svobodová, Jiří Šturala, Hana Dvořáková, Jiří Svoboda, Radek Cibulka A series of chiral non-racemic N 1,N 10-ethylene bridged flavinium salts 4 was prepared using enantiomerically pure 2-substituted 2-aminoethanols (R = isopropyl, phenyl, benzyl, 4-methoxybenzyl, 4-benzyloxybenzyl) derived from amino acids as the sole source of chirality. The flavinium salts were shown to form 10a-hydroperoxy- and 10a-methoxy-adducts with moderate to high diastereoselectivity depending on the ethylene bridge substituent originating from the starting amino acid. High diastereoselectivities (dr values from 80:20 to >95:5) were observed for flavinium salts bearing benzyl substituents attached to the ethylene bridge. The benzyl group preferred the face-to-face (syn) orientation relative to the flavinium unit; thereby effectively preventing nucleophilic attack from one side. This conformation was found to be the most stable according to the DFT calculations. Consequently, the presence of benzyl groups causes intermolecular fluorescence quenching resulting in a significant decrease in the fluorescence quantum yield from 11% for 4a bearing an isopropyl substituent to 0.3% for 4c containing a benzyl group and to a value lower than 0.1% for the benzyloxybenzyl derivative 4e. Graphical abstract image
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Stereoselection in the Betti reaction of valine methyl esters ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Maria Annunziata M. Capozzi, Cosimo Cardellicchio The multi-component Betti reaction of 2-naphthol, benzaldehyde and (S)-amines, that usually provides highly valuable aminobenzylnaphthol bearing two stereogenic centers, yielded a completely racemic product, when (S)-valine methyl ester was employed as the amine in the usual reaction protocol. The cause of this drawback, that appears to be overlooked in the literature, was investigated. As a result, new reaction conditions were set up, that were able to yield the expected useful product, having two fully resolved stereogenic centers. Furthermore, when the effect of substituents on the phenyl ring was preliminarily studied, we found that 4-fluoro- and 4-chlorobenzaldeyde gave stereoisomerically pure compounds also in the original reaction protocol. Graphical abstract image
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Synthesis of chiral carbosilane dendrimers with l-cysteine and N-acetyl-l-cysteine on their surface and their application as chiral selectors for enantiomer separation by capillary electrophoresis ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Sara Quintana, María Ángeles García, María Luisa Marina, Rafael Gómez, F. Javier de la Mata, Paula Ortega The synthesis of chiral carbosilane dendrimers functionalized with cysteine and N-acetylcysteine groups is presented. These dendrimers were obtained through thiol–ene addition reactions and their application as chiral selectors in capillary electrophoresis was investigated. Four drugs used as model compounds were analyzed under different experimental conditions observing that the use of a first generation dendrimer containing 4 terminal N-acetyl-l-cysteine groups enabled the enantiomeric discrimination of razoxane with a discrimination power similar to that obtained with other powerful chiral selectors such as cyclodextrins. Graphical abstract image
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A convergent approach towards the synthesis of the 2-alkyl-substituted tetrahydroquinoline alkaloid (−)-cuspareine ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): M.V. Madhubabu, R. Shankar, T. Krishna, Y. Satish Kumar, Y. Chiranjeevi, Ch. Muralikrishna, H. Rama Mohan, Satish S. More, M.V. Basaveswara Rao, Raghunadh Akula A convergent approach towards the synthesis of the 2-alkyl-substituted tetrahydroquinoline alkaloid (−)-cuspareine via enantiospecific construction of the (R)-benzyl 2-formyl-3,4-dihydroquinoline-1(2H)-carboxylate. We have achieved an efficient enantiospecific synthesis of (−)-cuspareine starting from known key starting materials. The reactions employed for individual transformations are simple and high yielding, and the strategy could potentially be easily extended. Graphical abstract image
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Synthesis of enantiomerically pure 2-(N-aryl, N-alkyl-aminomethyl)aziridines: a new class of ligands for highly enantioselective asymmetric synthesis ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Szymon Jarzyński, Stanisław Leśniak, Michał Rachwalski A simple and effective synthesis of enantiomerically pure 2-(N-aryl-, N-alkyl-aminomethyl)aziridines from (2S)-N-tritylaziridine-2-carboxylic acid methyl ester has been developed. Treating of this key ester with several primary and secondary amines in the presence of AlMe3 provided the corresponding chiral N-trityl-2-carboxamides, and their reduction performed with different reagents resulted in the formation of the expected 2-(aminomethyl)aziridines. The choice of reaction conditions allows to either keep or leave the trityl substituent in the product. Such 2-(aminoalkyl)aziridines have shown very high catalytic efficiency in the asymmetric arylation of aldehydes and in other testing asymmetric reactions. On the other hand, homochiral N-trityl-2-carboxamides are interesting building blocks for the synthesis of various biologically active compounds. Graphical abstract image
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O-(α-Phenylethyl)hydroxylamine as a ‘chiral ammonia equivalent’: synthesis and resolution of 5-oxopyrrolidine- and 6-oxopiperidine-3-carboxylic acids ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Ihor Kleban, Andriy V. Tymtsunik, Yuliya V. Rassukana, Oleksandr O. Grygorenko An approach to the synthesis and resolution of five- and six-membered lactams (i.e., 5-oxopyrrolidine- and 6-oxopiperidine-3-carboxylic acids) is described. The method relies on the one-pot Michael reaction—cyclization of itaconic acid or diethyl homoitaconate and enantiopure O-(α-phenylethyl)hydroxylamine as a ‘chiral ammonia equivalent’. It is shown that this chiral auxiliary can be used for the separation of diastereomeric lactam products and then easily removed by catalytic hydrogenolysis. Graphical abstract image
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Absolute configuration assignment of caffeic acid ester derivatives from Tithonia diversifolia by vibrational circular dichroism: the pitfalls of deuteration ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Gari V. Ccana-Ccapatinta, Bruno L. Sampaio, Fernando M. dos Santos, João M. Batista, Fernando B. Da Costa Recently, it was observed that infrared (IR) and vibrational circular dichroism (VCD) calculations including deuterated hydroxyl groups in phenolic and saccharide moieties improved significantly the agreement with experimental data obtained in methanol-d 4. In the present study, the relative and absolute configurations of three methanol-soluble caffeic acid ester derivatives 1–3, isolated from Tithonia diversifolia, were established by a combined use of experimental and calculated 13C NMR chemical shifts, as well as electronic circular dichroism (ECD) and VCD spectroscopies. Interestingly, the attempt to reproduce the deuteration pattern arising from possible isotopic exchange in methanol-d 4 solution led to nearly mirror image calculated VCD spectra for 1 when compared to the non-deuterated molecule with the same absolute configuration. This latter fact can potentially lead to absolute configuration misassignments. A closer inspection of the vibrational chiroptical properties of 1 revealed that the deuteration status of the tertiary hydroxyl group at C-2 is critical for the correct reproduction of experimental VCD data in protic solvents. Therefore, in the case of stereochemical analysis of polar chiral natural product molecules, a combination of VCD and ECD is recommended. Graphical abstract image
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Efficient lipase-catalysed route for the kinetic resolution of salsolidine and its ß-carboline analogue ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Barbara Kovács, Rita Megyesi, Enikő Forró, Ferenc Fülöp Racemic 1-methyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline 1 and 1-methyl-1,2,3,4-tetrahydro-ß-carboline 3 were resolved through lipase-catalysed asymmetric acylation on the secondary amino group. High enantioselectivities (E >200) were observed when the acylation of racemic 1 was performed with phenyl allyl carbonate in the presence of Candida rugosa lipase in toluene at 40 °C or with Candida antarctica lipase B in tert-butyl methyl ether at 50 °C. Excellent enantioselectivity (E >200) characterised the CAL-B-catalysed acylation of racemic 3 with phenyl allyl carbonate in the presence of triethylamine in tert-butyl methyl ether at 50 °C. The product (R)-carbamates (ee >97%) were hydrolysed into the corresponding (R)-enantiomers of the free amines 1 and 3 (ee = 99%) with the use of Pd2(dba)3·CHCl3 catalyst. Graphical abstract image
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Synthesis and stereochemical assignment of geraniol- and nerol-derived Cygerol enantiomers ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Anna A. Sukhanova, Ilya A. Puchkin, Andrei A. Vasil'ev, Sergei G. Zlotin The enantiomers (up to 99% ee) of both geraniol- and nerol-derived 2-cyclohexyl-5,9-dimethyldeca-4,8-dienoic acid, the active ingredient of the wound healing medication Cygerol, were prepared via a low-temperature alkylation, basic hydrolysis, derivatization with (S)-4-benzyloxazolidin-2-one and chromatographic separation steps. The absolute configuration of stereocenters in the antipodes having an (E)- or (Z)-geometry of the internal double bond was determined based on characteristic 1H NMR signals of the corresponding (S)-4-benzyloxazolidin-2-one-derived imides and on conversion to the known diethyl (S)-2-cyclohexylsuccinate and (S)-2-cyclohexylbutane-1,4-diol with reported specific rotations. Graphical abstract image
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The conjugate addition of enantiomerically pure lithium amides as chiral ammonia equivalents part III: 2012–2017 ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12 Author(s): Stephen G. Davies, Ai M. Fletcher, Paul M. Roberts, James E. Thomson This review covers further applications of the conjugate addition of enantiomerically pure lithium amides as chiral ammonia equivalents in asymmetric synthesis and provides an update since our last review of this area, which was published in 2012. Graphical abstract image
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Stereochemistry abstracts ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12
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Tetrahedron: Asymmetry Reports ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12
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Cumulative author index ()
Publication date: 15 December 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 12
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Editorial board ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11
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Graphical contents list ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11
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Contributors to this issue ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11
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Review on asymmetric synthetic methodologies for chiral isoquinuclidines; 2008 to date ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Muhammad Faisal, Danish Shahzad, Aamer Saeed, Bhajan Lal, Shomaila Saeed, Fayaz Ali Larik, Pervaiz Ali Channar, Parvez Ali Mahesar, Jamaluddin Mahar Isoquinuclidines constitute the central structural nucleus of numerous biologically active natural products, for example, iboga alkaloids such as ibogamine and catharanthine as well as non-indole-containing alkaloids such as the dioscorine and the cannivonines. Furthermore, in medicinal and pharmaceutical chemistry, the isoquinuclidine core is commonly employed as a rigid azabicyclic scaffold, thus providing significant precursors in the synthesis of numerous valuable alkaloids. Summarizing well-organized approaches to access the chiral isoquinuclidine structural centerpiece signifies a significant endeavor not only for developing biologically active natural products but also enhancing biological researches that can lead to possible drug discovery. Over time, the values and methodologies for the asymmetric synthesis of chiral isoquinuclidines are increasing; hence to advance asymmetric synthesis, this review combines and discusses the pros and cons of each synthesis techniques from 2008. This review should be helpful for promoting further developments of asymmetric synthetic methodologies and for medicinal chemistry. Graphical abstract image
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Recent developments in the enantioselective synthesis of polyfunctionalized pyran and chromene derivatives ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Kamal Usef Sadek, Ramadan Ahmed H. Mekheimer, Mohamed Abd-Elmonem, Afaf Abdel-Hameed, Mohamed Hilmy Elnagdi Recent developments in the synthesis of 4H- and 2H-pyrans as well as structurally related chromene derivatives that have enabled the enantioselective synthesis of these scaffolds have been surveyed. The role of chiral catalysts in orienting initial reactions of active methylenes, methines and methyl ketones, to unsaturated ketones and nitriles in multi-component reactions or Friedel–Craft alkylations of phenols is discussed to show their involvement in transition states leading to end products. Chromene synthesis via [4+2] cycloadditions, [3+3] and [4+2] annulations as well as ring opening and recyclization leading to high enantio- and diasteroselectivity is also demonstrated. The enantioselectivity in such catalytic asymmetric reactions despite starting with non-chiral starting materials is discussed. On the other hand, in surveying ring opening and recyclization, the starting materials are chiral and the chiral center was not part of the reaction leading to the final product. Graphical abstract image
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Cystoseira algae (Fucaceae): update on their chemical entities and biological activities ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Carolina Bruno de Sousa, Katkam N. Gangadhar, Jorge Macridachis, Madalena Pavão, Thiago R. Morais, Lenea Campino, João Varela, João Henrique G. Lago Cystoseira (Sargassaceae) is a genus of marine brown algae composed of about 40 species, which is distributed along the Eastern Atlantic and Mediterranean coasts. The biological potential of the Cystoseira genus has been investigated and several activities have been reported. Chemically, this genus contains a wide variety of secondary metabolites, such as terpenoids, steroids, phlorotannins and phenolic compounds. Additionally, other chemical components as, for instance, carbohydrates, triacylglycerols/fatty acids, pigments as well as vitamins have been identified in the studied species. Some of the isolated compounds were associated with the reported pharmacological properties, as for example antioxidant, anti-inflammatory, cytotoxicity, anticancer, cholinesterase inhibition, anti-diabetic, activities but also antibacterial, antifungal and anti-parasitic activities. In this review, we provide a comprehensive overview of the compounds isolated and identified after 1995 from the different species of Cystoseira, compiling more than 200 compounds isolated, together with their therapeutic potential. Graphical abstract image
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Applications of Danishefsky’s dienes in asymmetric Oxo-Diels-Alder reactions ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Afsaneh Taheri kal Koshvandi, Majid M. Heravi Applications of Danishefsky’s dienes in catalytic asymmetric hetero-Diels-Alder (AHDA) reactions or specifically, their asymmetric Oxo-Diels-Alder (AOxo-DA) reactions with appropriate dienophiles are highlighted in detail, including the preparation of catalysts with discussion from a mechanistic points of view. Danishefsky’s dienes are effective and useful compounds for the synthesis of optically active six-membered rings such as dihydropyrones, dihydropyridones and dihydropyrans. Due to the broad range of the overall subject, we have limited ourselves, to the recent developments in the utility of Danishefsky’s dienes in the reaction with carbonyl compounds (aldehydes, ketones and 1,2-dicarbonyl compounds) in asymmetric Oxo-Diels-Alder (AOxo-DA) reactions. Graphical abstract image
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Thermal racemization of biaryl atropisomers ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Darshan C. Patel, Ross M. Woods, Zachary S. Breitbach, Alain Berthod, Daniel W. Armstrong Many biaryl compounds possess atropisomerism due to the steric hindrance of substituents at the ortho-position of the two aromatic moieties. Upon heating, atropisomers may have enough energy to surpass the rotational energy barrier and racemize. The thermal stability of five atropisomers was studied using chiral chromatography by following the change in enantiomeric excess ratio at different temperatures. The first order racemization reaction rate was obtained at a given temperature as the slope of the change in enantiomeric excess ratio versus time. For each atropisomer, the racemization rates at different temperatures led to the value of the rotational energy barrier for racemization, ΔG ‡, and to the racemization half lifetime, t 1/2, indicating the atropisomer thermal stability. Binaphthol started to racemize significantly at temperature of 190°C and above while binaphthyldiamine was much more stable showing little or very minor racemization up to 210°C. A chloro-substituted phenylamino-naphthol was very sensitive to thermal racemization starting at a low 40°C. Graphical abstract image
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Concise asymmetric synthesis of the sex pheromone of the tea tussock moth ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Zhi-Feng Sun, Lu-Nan Zhou, Yifei Meng, Tao Zhang, Zhen-Ting Du, Huaiji Zheng A concise asymmetric total synthesis of the sex pheromone of the tea tussock moth has been achieved from commercially available starting materials. The chiral moiety was introduced by Evans’ template and the key CC bond construction was accomplished through Julia-Kocienski coupling and Wittig olefination. The salient characteristic of our synthetic route is that it is protecting a group free. Graphical abstract image
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A fast, new method to enhance the enantiomeric purity of non-racemic mixtures: self-disproportionation of enantiomers in the gas antisolvent fractionation of chlorine-substituted mandelic acid derivatives ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Márton Kőrösi, János Madarász, Tamás Sohajda, Edit Székely Gas antisolvent precipitation is a particle formation technique, when typically pressurized carbon dioxide is added to an organic solution resulting in immediate and high oversaturation and precipitation of fine particles. Provided that a reasonable share of the originally dissolved material remains dissolved in the carbon dioxide – organic mixed solvent, these components can be extracted during the washing phase. This method is called gas antisolvent fractionation. Gas antisolvent fractionation has been applied for the first time to enantiomeric enrichment of non-racemic mixtures, and demonstrated on the example of chlorinated mandelic acid derivatives. Due to self-disproportionation of enantiomers, the precipitated solid and the extracted fractions have different enantiomeric excesses if gas antisolvent fractionation is carried out on a non-racemic mixture. However, there is a limit in the enantiomeric excess (ee) that can be achieved correlating strongly with the atmospheric melting eutectic behavior of the compounds. Thus, if initial enantiomeric mixtures have a higher than eutectic ee, a >99% ee can be reached in the crystalline product. The strong correlation between the high-pressure experiments and the atmospheric melting eutectic behavior suggest that despite the very large oversaturation during the antisolvent precipitation, the composition of the products (i.e., the crystalline and the extracted phases) is thermodynamically determined. Technological advantages such as short operational time, or the possibility of controlling the crystal morphology suggest that the development of an efficient technique of enantiomeric purification is possible based on gas antisolvent fractionation. Graphical abstract image
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anti-Selective aldol reactions of chiral alcohol substituted γ-benzyloxyl vinylogous urethanes and the synthesis of 3-benzyloxyl-4-hydroxylalkan-2-ones ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Yu-Jang Li, Chuan-Chung Chung, Pin-Zu Chen The anti-selective aldol reaction of chiral alcohol-substituted γ-benzyloxy vinylogous urethanes is described. The use of (1S,2R,4R)-1-(hydroxydiphenylmethyl)-7,7-dimethylbicyclo[2,2,1]-heptan-2-ol as a chiral auxiliary in the aldol reaction of a vinylogous urethane enolate was found to provide anti-products in good yields with moderate to excellent enantioselectivities. The major anti-vinylogous urethane lactones were transformed into 3-benzyloxyl-4-hydroxylalkan-2-ones in good yields. Graphical abstract image
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An asymmetric synthesis of (+)-monomorine I ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Masaki Asai, Yukiko Takemoto, Ayaka Deguchi, Yasunao Hattori, Hidefumi Makabe The synthesis of (+)-monomorine I, an indolizidine alkaloid isolated from Monomorium pharaonis, has been achieved. The 2,6-cis-piperidine ring moiety of (+)-monomorine I was constructed using diastereoselective aminopalladation. Chain elongation via cross-metathesis using Hoveyda-Grubbs 2nd catalyst followed by deprotection of the Cbz group and cyclic reductive hydroamination afforded (+)-monomorine I. Graphical abstract image
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Efficient 1H NMR chiral discrimination of sulfoxides caused by the dynamic nature of (R,R)-3′,3″-biBINOL ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Toshio Kawanami, Kentaro Ishizuka, Hiroshi Furuno, Yoshihito Shiota, Kazunari Yoshizawa, Junji Inanaga A chiral BINOL dimer, (R,R)-3′,3″-BiBINOL, which possesses both rigid (atropos) and dynamic (tropos) axial chiralities, was found to work as an effective NMR chiral solvating reagent for the determination of the enantiomeric purities of various chiral sulfoxides. The unique chiral discrimination mechanism was also revealed by using DFT calculations and X-ray crystallographic analysis. Graphical abstract image
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A highly enantioselective [4+2] cycloaddition involving aldehydes and β,γ-unsaturated-α-keto esters ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Nanda Kumar Katakam, Yejin Kim, Allan D. Headley A stereoselective inverse electron demand oxo-Diels-Alder reaction involving electron poor dienes (γ-aryl-β,γ-unsaturated-α-keto ester) and electron rich dienophiles has been studied. These cycloaddition reactions are extremely useful for the construction of O-, N-, S-centered heterocyclic compounds, which are routinely used in both synthetic organic and medicinal chemistry. The [4+2] hetero cycloaddition reactions involving various aldehydes and β,γ-unsaturated-α-keto esters were carried out in which three different types of substituted proline catalysts were examined. For these reactions, high selectivities (enantiomeric excess 93–98%) were obtained using catalyst 3. Due to the bulkiness of catalyst 3, compared to the other catalysts tested, it is more efficient at catalyzing these type reactions. Graphical abstract image
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Catalytic asymmetric synthesis of Leukotriene B4 ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Pengfei Yang, Jiangchun Zhong, Kaijie Ji, Jingwei Yin, Shuoning Li, Siyuan Wei, Yun Zhou, Lifeng Wang, Min Wang, Qinghua Bian Leukotriene B4 1 was prepared from two chiral synthons 8 and 14. The chiral secondary alcohols of 8 and 14 were constructed by BINOL/Ti(OiPr)4 catalyzed enantioselective alkynylzinc addition to aldehydes. Graphical abstract image
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Synthesis of the four enantiomers of diethyl 1,2-di(N-Boc-amino)propylphosphonates ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Iwona E. Głowacka, Dorota G. Piotrowska, Andrzej E. Wróblewski, Aleksandra Trocha A simple and efficient synthetic strategy to all four enantiomerically pure diethyl 1,2-di(N-Boc-amino)propylphosphonates has been elaborated starting from the corresponding N-[(R)-(1-phenylethyl)]aziridine-(2S)- and N-[(S)-(1-phenylethyl)]aziridine-(2R)-carboxaldehydes, employing a one-pot three-components Kabachnik-Fields reaction followed by the hydrogenolytic removal of the chiral auxiliary and aziridine ring opening with simultaneous protection of the amino groups as the N-Boc derivatives. Graphical abstract image
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Highly enantioselective organocatalysis of the Michael addition of benzyloxyacetaldehyde to nitroolefins ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Sripragna Burugupalli, Yupu Qiao, Allan D. Headley A novel category of di(N,N-dimethylbenzylamine)prolinol silyl ether catalyst, which when used in conjunction with an acidic co-catalyst, generates an ammonium salt supported organocatalyst. This catalytic system is shown to be very effective for the Michael reaction of benzyloxyacetaldehyde and various nitroolefins in isopropanol. Excellent enantioselectivities (up to 99%) and diastereoselectivities (syn/anti of 75:25) and short reaction times were obtained. The presence of the bulky OTMS group combined with the presence of two large N,N-dimethylbenzyl ammonium ion groups accounts for the effectiveness of this catalytic system. Graphical abstract image
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Immobilization of Lecitase® ultra on recyclable polymer support: application in resolution of trans-methyl (4-methoxyphenyl)glycidate in organic solvents ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Thenkrishnan Kumaraguru, Tirunagari Harini, Shalini Basetty Lecitase® Ultra was immobilized on epoxy-activated polymer (DILBEAD-VWR) functionalized with polyethyleneimine via adsorption and crosslinking with glutaraldehyde. The resolution of methyl trans-(±)-3-(4-methoxyphenyl) glycidate was carried out in xylene (e.e. >99%, conversion 50%). The enzyme is not inhibited by the 4-methoxy phenyl acetaldehyde produced during hydrolysis and the immobilized enzyme with 7% moisture content works efficiently in an organic phase. While the immobilized enzyme can be recycled several times, the polymer support can also be recycled after removing the immobilized enzyme by washing with 1 M HCl. Graphical abstract image
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Pd(II) complexes of monodentate deoxycholic acid derived binaphthyl diamido phosphites as chiral catalysts in the asymmetric Suzuki-Miyaura cross-coupling ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Grazia Iannucci, Vincenzo Passarelli, Alessandro Passera, Anna Iuliano Chiral binaphthyl diamidophosphites derived from deoxycholic acid were synthesized and used as ligands for the preparation of mononuclear Pd(II) complexes, which were employed as catalysts in the asymmetric Suzuki-Miyaura cross-coupling of arylboronic acids with aryl bromides. Among the different reaction parameters, the substrate concentration emerged as being crucial for the outcome of the reaction: the reaction was faster in a concentrated reaction mixture, and could be performed at 0°C, where the reaction promoted by the Pd-complexes was more enantioselective affording cross-coupling products with ee up to 70%. Graphical abstract image
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Asymmetric epoxidation of enones using cumyl hydroperoxide and in situ generated zinc complexes of chiral pyrrolidinyl alcohols ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Halide Sedef Karaman, Hamdullah Kılıç, Engin Şahin The homogeneous asymmetric epoxidation of a range of enones was carried out using cumyl hydroperoxide, diethylzinc, and chiral pyrrolidinyl alcohol-containing ligands to afford the corresponding epoxy ketones with enantioselectivities of ≤97% ee. Examination of the enantioselectivities obtained in the asymmetric epoxidation of enones using a range of chiral ligands indicated that synergy between the sterically bulky bicyclo[2.2.2]octane skeleton and the substituents attached to the carbinol moiety played an important role in determining the reaction enantioselectivity. The position and nature of the substituent on the aromatic ring of the enone also had a pronounced effect on the observed enantioselectivity. Graphical abstract image
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Tartaric acid-derived chiral phosphite-type P,N-ligands: behavioural features in Pd-catalyzed asymmetric transformations ()
Publication date: 15 November 2017 Source:Tetrahedron: Asymmetry, Volume 28, Issue 11 Author(s): Konstantin N. Gavrilov, Sergey V. Zheglov, Ilya V. Chuchelkin, Marina G. Maksimova, Ilya D. Firsin, Andrew N. Fitch, Vladimir V. Chernyshev, Alexander V. Maximychev, Alexander M. Perepukhov A practical synthesis of new phosphoramidite, phosphite and diamidophosphite P,N-ligands derived from (R,R)-tartaric acid was carried out. A study of these chiral inducers showed them to provide up to 93% ee in the Pd-catalyzed asymmetric allylations of (E)-1,3-diphenylallyl acetate, up to 84% ee in the Pd-catalyzed asymmetric alkylation of cinnamyl acetate with ethyl 2-oxocyclohexane-1-carboxylate and up to 63% ee in the Pd-catalyzed desymmetrization of N,N′-ditosyl-meso-cyclopent-4-ene-1,3-diol biscarbamate. The effects of the structural modules, such as the nature of the phosphorus-containing ring or exocyclic substituent as well as of the nature of palladium source on the catalytic activity and enantioselectivity were investigated. Graphical abstract image
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