By the action of ozone, sodium cyanoborohydride and the optically active benzylic amines 2, the 1-substituted cyclopentenes 1, 5 and 9 were converted to a diastereoisomeric mixture of 1, 2-disubstituted piperidines (3, 6 and 10), respectively. Hydrogenation of these compounds and the following work-up yielded optically active 2-alkylpiperidines (4, up to 68% ee.), pipecolic acid (7, 84% ee.) and 2-(hydroxymethyl) piperidine (11, up to 85% ee.). ...