Stereoselective synthesis of nipecotic acid derivatives via palladium-catalyzed decarboxylative cyclization of gamma-methylidene-delta-valerolactones with imines.

A new synthetic method of multisubstituted nipecotic acid (piperidine-3-carboxylic acid) derivatives has been developed by way of palladium-catalyzed decarboxylative cyclization of gamma-methylidene-delta-valerolactones with imines. By employing the diethoxyphosphinoyl group as the N-protecting group for imines, the reaction proceeds smoothly with high diastereoselectivity. The products thus obtained can be further derivatized with high efficiency under simple reaction conditions.