Gold(I)/(III)-catalyzed synthesis of 2-substituted piperidines; valency-controlled cyclization modes

Strategic use of hard gold(III) and soft gold(I) catalysts provides facile access to two types of 2-substituted piperidines from propargylic alcohols. Thus, heating propargylic alcohols in the presence of AuBr3 results in cyclization to furnish piperidines having an acetylenic moiety, due to activation of the propargylic hydroxyl group by coordination of gold(III). On the other hand, the catalyst [Ph3PAuNTf2](2)PhMe induces Meyer-Schuster rearrangement of propargylic alcohols to give alpha,beta-unsaturated ketones, which undergo intramolecular aza-Michael addition to afford piperidines bearing a carbonyl group, due to activation of the triple bond by coordination of gold(I). (C) 2015 Elsevier Ltd. All rights reserved.