Mesyl synthesis (via hydroxyl group): 


To a solution of 25c (1.5 g, 0.006 mol) and Et3N (1.6 g, 0.016 mol) in dry DCM (6 ml) was added dropwise MsCI (1.5 g, 0.015 mol) at 0°C under N2 gas. After the addition, the reaction mixture was stirred at room temperature overnight.The reaction mixture was diluted with EtOAc (50 ml), washed with 5% aqueous citric acid (100 ml), 5% aqueous Na2CO3 (100 ml) and brine (100 ml) in sequence.Then the organic layer was dried over Na2SO4 and concentrated in vacuo which gave the title compound 25d as brown oil (1.8 g, 90%).


Patent reference: WO2010016005 (Pfizer)