Catalytic Enantioselective Synthesis of 3-Piperidines from Arylboronic Acids and Pyridine.

Piperidines are frequently found in natural products and are of importance to the pharmaceutical industry. A generally useful asymmetric route to enantiomerically enriched 3-substituted piperidines remains elusive. Here we report a cross-coupling approach to enantioenriched 3-piperidines from pyridine- and sp²-hybridized boronic acids. The key step involves a Rh-catalyzed asymmetric reductive Heck reaction of aryl, heteroaryl, or vinyl boronic acids and phenyl pyridine-1(2<i>H</i>)-carboxylate to provide 3-substituted tetrahydropyridines in high yield and excellent enantioselectivity with a wide functional group tolerance. A three-step process involving i) partial reduction of pyridine, ii) Rh-catalyzed asymmetric carbometalation, and then iii) another reduction provides access to a wide variety of enantioenriched 3-piperidines, including clinically used materials such as Preclamol and Niraparib.