A mixture of (10c), (2.30 g, 6.94 mmol) and pyridinium dichromate (10.62 g, 28.2 mmol) in 20 mL of N,N-dimethylformamide is stirred under argon for 18 h. The reaction mixture is diluted with 100 mL of water and extracted with ethyl acetate (3×40 mL). The organic layer is separated, washed with water and brine, dried and evaporated to give 1.87 g of a residual brown liquid. The liquid is purified by chromatography using 1:6 ethyl acetate/hexane to give 997 mg of the desired product as an oil. NMR δ0.83 (s, 9H), 1.61 (m, 2H), 2.22 (t, 2H), 2.23 (s, 3H), 3.82 (dd, 1H), 4.09 (dd, 1H), 4.57 (m, 1H), 6.42 (brd, 1H); MS (FAB) m/z 330 (M+H calc'd for C17H36NO3Si 330).
