title: Organocatalytic enantioselective β-functionalization of aldehydes by oxidation of enamines and their application in cascade reactions.
abstract: Iminium catalysis, involving the transformation of iminium ions to enamines, has been extensively studied in the context of a number of organic processes. However, the reverse of this process involving conversion of enamines to iminium species has not been realized. Here, we describe a new transformation-'oxidative enamine catalysis'-in which direct oxidation of an enamine occurs to generate an iminium species. We show that the use of o-iodoxybenzoic acid as an oxidant in the presence of a secondary amine catalyst serves as effective system for promoting rapid conversion of enamines to iminium ions. The preparative power of this process has been demonstrated in the context of direct asymmetric β-functionalization of simple aldehydes. Moreover, a variety of enantioselective cascade transformations, including triple and quadruple cascades, have been developed for the 'one-pot' synthesis of versatile chiral building blocks and structural frameworks starting with simple aldehydes.
authors.affiliation: State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Shi-Lei
authors.initials: SL
authors.lastname: Zhang
authors.forename: He-Xin
authors.initials: HX
authors.lastname: Xie
authors.forename: Jin
authors.initials: J
authors.lastname: Zhu
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.forename: Xin-Shuai
authors.initials: XS
authors.lastname: Zhang
authors.forename: Jian
authors.initials: J
authors.lastname: Li
authors.forename: Wei
authors.initials: W
authors.lastname: Wang