To a solution of tert-butyl 1-vinyl-2-hydroxy-8-azaspiro[4.5]decane-8-carboxylate (0.462 g, 1.64 mmoL) from Step A in DMF (8 mL) was added imidazole (0.335 mg, 4.92 mmol) and then tert-butyldimethylsilyl chloride (0.370 g, 2.4 mmol). The reaction was stirred at room temperature for 20 h and then diluted with ether and sodium bicarbonate solution. The mixture was extracted twice with ether. The combined ether layers were washed with brine, dried over sodium sulfate, filtered, and concentrated. The residue was purified by flash chromatography eluting with 5% ethyl acetate in hexanes to afford the title compound (0.56 g) as a mixture of isomers.
