Enantioselective Syntheses of 2-Alkyl- and 2,6-Dialkylpiperidine Alkaloids: Preparations of the Hydrochlorides of (-)-Coniine, (-)-Solenopsin A, and (-)-Dihydropinidine.

[reaction: see text] Sequences of lithiation-substitution, enantioselective hydrogenation, and diastereoselective lithiation-substitution provide efficient highly enantioselective syntheses of 2-substituted and cis and trans 2,6-disubstituted piperidines. The methodology is demonstrated by syntheses of (-)-coniine, (-)-solenopsin A, and (-)-dihydropinidine as their hydrochlorides.