To a solution of (R)-tert-butyl 2-(((tert-butyldiphenylsilyl)oxy)methyl)-5-oxopyrrolidine-1-carboxylate (D29) (6 g, 13.23 mmol) in THF (80 ml) cooled at −70° C., LiHMDS 1M solution in THF (17.2 ml) was added dropwise over a period of minutes. The reaction was kept at −78° C. for 1 h before adding (iodomethyl)trimethylstannane (6.04 g, 19.84 mmol) over a period of 5 minutes. The mixture was allowed to warm at −35 and stirred at this temperature for 2 hrs. NH4Cl sat. sol (15 ml) was added and the mixture diluted with EtOAc (40 ml). The organic layer was separated and the aqueous phase acidified to pH˜4 with 0.5N HCl and the latter re-extracted with EtOAc (3×50 ml). The organic phases were combined, dried over Na2SO4 and evaporated in vacuo. The residue was purified by Biotage SNAP-Si (50 g) eluting with a mixture cHex/EtOAc from 100/0 to 90/10. Collected fractions after solvent evaporation afforded the title compound (D30) as diastereoisomer mixture (3.2 g).
