Copper-catalyzed remote C(sp³)-H azidation and oxidative trifluoromethylation of benzohydrazides.

ABSTRACT: The Hofmann-Löffler-Freytag (HLF) reaction is a prototypical example of radical-based remote functionalization of unactivated C(sp³)-H bond. While 1,5-hydrogen atom transfer (1,5-HAT) of the amidyl radical is thermodynamically favorable and is well-established, the method for the subsequent functionalization of the translocated carbon radical is still limited. We report herein two catalytic remote C(sp³)-H functionalization protocols. Cu(MeCN)₄PF₆-catalyzed reaction of 2-alkyl benzohydrazides 3 with TMSN₃ in the presence of MeCO₂OtBu affords the ?-azido amides 4, while CuCl-catalyzed reaction of 3 with Togni's reagent provides 2-(?-trifluoromethylvinyl)benzamides 5 via an oxidative ?-trifluoromethylation of the alkyl group. Mechanistic studies suggest that the ?-azidation of benzohydrazides 3 goes through 1,5-HAT followed by a Cu-mediated azido transfer cascade, while the oxidative ?-trifluoromethylation of 3 proceeds via, after 1,5-HAT process, a radical-polar crossover mechanism.

SUBMITTER: Bao X 

PROVIDER: S-EPMC6377619 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature