N-heterocyclic carbene-catalyzed single-electron-transfer radical processes for reductive coupling reactions
Year: 2018
Type: dissertation
Abstract: This thesis focuses on exploring single-electron-transfer (SET) reductive coupling reactions catalyzed by N-heterocyclic carbene (NHC) organocatalysts.It contained five chapters: Chapter 1 gives a brief introduction to NHC-catalyzed electron-pair transfer reactions involving different key intermediates, and recent discoveries on NHC-catalyzed SET process and relating reactions.Chapter 2 describes a carbene-catalyzed reductive coupling reaction for β-nitroalkenes.The reaction pathway includes SET process mimicking the thiamine pyrophosphate (TPP)catalyzed oxidative decarboxylation of pyruvate in living systems.The SET process starts from Breslow intermediate of nitroalkene to generate corresponding nitroalkene radical anion for further transforming to homocoupling product.For the first time, the presence of radical anion intermediate in NHC-organocatalytic system is revealed.Chapter 3 introduces a carbene-catalyzed reductive cross-coupling of nitrobenzyl bromides with nitroalkenes via SET process and formal 1,4-addition.Control experiments prove that the reaction initiates from the SET process between nitrobenzyl bromide and Breslow intermediate.The nitrobenzyl bromide first obtains one electron, and the elimination of bromide takes place during the following generation of corresponding nitrobenzyl radical intermediate for further transformation.The bromo group serves as a leaving group in this reaction.The reaction pathway shows a new activation mode in NHCorganocatalysis.Chapter 4 describes a carbene-catalyzed reductive cross-coupling of nitrobenzyl bromides with ketones or imines via SET process and formal 1,2-addition.This reaction utilizes the nitrobenzyl radical intermediate, which generates via single-electron reduction of nitrobenzyl bromide and elimination of bromide, to react with α,β-unsaturated ketoesters,
DOI: 10.32657/10356/73859
Author: Wang, Yuhuang
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W2800190044