Concise Synthesis of Alkaloid (−)-205B

Described herein is a short total synthesis of alkaloid (−)-205B (<b>1</b>) by means of an anti-selective S_N2′ alkylation of an attractively functionalized cyclopropanol and diastereoselective cyclization of the resulting aminoallene adduct for bicyclic ring formation. The synthesis features a general route to <i>cis</i>- or <i>trans</i>-2,6-disubstituted piperidines by lithium aluminum hydride reduction of the imine intermediate by an appropriate choice of solvent and <i>cis</i>- or <i>trans</i>-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