Synthesis of Highly Oxidized Quinolizidine via Reduction of Acylpyridinium Cations, and Total Syntheses of Quinolizidines 207I and 1-epi-207I

A new strategy for synthesizing quinolizidine skeletons by reductive cyclization via acylpyridinium cations was developed. Several functional groups, including carbonyl, silyl, and acetal, were tolerated under mild reaction conditions. The reaction was successfully extended to a one-pot synthesis of a bicyclic compound, and the synthetic strategy was applied to concise total syntheses of quinolizidines 207I and 1-epi-207I, without protecting groups.