Esters (via hydroxyl group, Mitsunobu reaction):  


To a stirred solution of triphenylphosphine (23.2 g, 0.089 mol) in THF (300 ml) was added DIAD (17.9 g, 0.089 mol) with stirring under nitrogen at 0°C. The resulting pale yellow suspension was stirred for 40 min, then a solution of Hydroxyl compound (15 g, 0.059 mol) and 4-nitrobenzoic acid (16.2 g, 0.089 mol) in THF (200 ml) was added slowly over 1.5 h. The resulting orange solution was warmed to room temperature and stirred for 48 h. The mixture was concentrated under reduced pressure, and the residual oil was purified by column chromatography (EtOAc: petroleum ether = 1 :40 to 1 :10) which gave the title ester compound as a yellow oil (30 g, 30%). 


Patent reference: WO2010016005 (Pfizer)

Mitsunobu reaction








Esters (via carboxylic acid): 


To a stirred solution of (R)-3-cyclopentyl-2-hydroxypropanoic acid (2.36 g) in anhydrous methanol (15 ml) at room temperature was added SOCI2 (1.64 ml). The resulting mixture was heated at reflux for 2 hours. It was then cooled and concentrated under reduced pressure. The residue was partitioned between ethyl acetate and aqueous saturated NaHCO3 solution. The biphasic mixture was separated and the aqueous portion was extracted with ethyl acetate. The combined extracts were dried over MgSO4, filtered and the filtrate was concentrated under reduced pressure. The resulting residue was purified by flash column chromatography (silica gel, heptanes/ethyl acetate) to provide (R)-methyl S-cyclopentyl^-hydroxypropanoate as clear oil (1.5 g). 


Patent reference: WO2010013161 (Pfizer)