Asymmetric Hydrogenation of Pyridinium Salts with an Iridium Phosphole Catalyst

Iridium-catalyzed asymmetric hydrogenation of Nalkyl-2-alkylpyridinium salts provided 2-aryl-substituted piperidines with high levels of enantioselectivity. Simple benzyl and other alkyl groups successfully activated the challenging pyridine substrates toward hydrogenation. The use of the unusual chiral-phosphole-based MP2-SEGPHOS was the key to the success of this approach which provides a versatile and practical procedure for the synthesis of chiral piperidines.