To a suspension of zinc dust (12.2 g) in THF (200 mL) and diiodomethane (5 mL) at 0° C. was added trimethylaluminium (2M in hexanes, 6 mL). After the addition the reaction was carefully warmed to room temperature (exothermic reaction!). The reaction was then cooled with an ice bath and a solution of tert-butyl (2R,5R)-5-{[tert-butyl(dimethyl)silyl]oxy}-2-formylpiperidine-1-carboxylate (Intermediate 189, 6.84 g) in THF (40 mL) was added. After 6 hours it was warmed to room temperature, the reaction was diluted with ethyl acetate and slowly quenched with a saturated aqueous solution of NaHCO3. The organic phase was collected and washed with NaHCO3 and brine, dried (Na2SO4), filtered and concentrated. Chromatography on silica gel with a gradient of 0-100% methylene chloride in hexanes gave 3.96 g of product.
