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.