Engaging 2-methyl indolenines in a tandem condensation/1,5-hydride transfer/cyclization process: construction of a novel indolenine–tetrahydroquinoline assembly

Abstract

New reactivity and application of 2-methyl indolenines have been established by their engagement in a tandem condensation/1,5-hydride transfer/cyclization process. Under the catalysis of BF₃·Et₂O, the condensation of easily available 2-methyl indolenines with o-amino benzaldehydes occurred readily, followed by a facile redox neutral 1,5-hydride shift/cyclization process in a one-pot manner, leading to the construction of a novel indolenine–tetrahydroquinoline assembly in good yield with high levels of diastereoselectivity. This synthetic protocol tolerates a broad range of substrates in terms of both the indolenine and o-amino benzaldehyde partners. The reaction can be readily scaled up and the indolenine moiety of the product can be facilely reduced to the indoline scaffold.