Concise Synthesis of Alkaloid (-)-205B

摘要

Described herein is a short total synthesis of alkaloid (-)-205B (1) by means of an anti-selective S_N2' alkylation of an attractively functionalized cyclo-propanol and diastereoselective cyclization of the resulting aminoallene adduct for bicyclic ring formation. The synthesis features a general route to cis- or trans-2,6-disubstituted piperidines by lithium aluminum hydride reduction of the imine intermediate by an appropriate choice of solvent and cis- or trans-2,5-disubstituted pyrrolidines by an exceptional level of chirality transfer from a pendant allene. Particularly noteworthy are the brevity and convergence made possible by a segment-coupling strategy.