Aerobic Oxidation of a Tertiary Aliphatic Amine Under Visible-Light Photocatalysis: Facile Synthesis of Methylene-Bridged Bis-1,3-dicarbonyl Compounds

摘要

The development of new synthetic methodologies that utilize carbon-hydrogen (C-H) bonds as substrates is of great interest due to the challenges associated with selective C-H bond functionalization and the potential to streamline synthesis by the elimination of pre-activated coupling partners. The cross-dehydrogenative coupling (CDC) reaction of the C-H bond adjacent to a nitrogen atom represents a remarkably successful strategy towards the realization of an efficient synthetic method for carbon-carbon (C-C) bond formation. The mode of activation for the CDC reactions with tertiary amines occurs through the oxidative formation of a reactive iminium intermediate, which is then subsequently trapped by a variety of nucleophiles to generate the desired C-C bond. An underappreciated but similar oxidative transformation with tertiary amines is their use as a carbon source through a sequential CDC reaction/carbon-nitrogen (C-N) bond cleavage process to generate new C-C bonds (Scheme 1). Following the initial report of an iron-catalyzed protocol for the synthesis of methylene-bridged bis-1,3-dicarbonyl compounds by Li et al. using tert-butyl hydroperoxide (TBHP) as a sacrificial oxidant and N,N-dimethylaniline as the methylene donor, a variety different synthetic procedures for the use of tertiary amines as methylenation and acylation reagents have been reported. However, despite these recent advances in the use of amines as methylene and acyl donors, new synthetic methodologies to perform these reactions under mild aerobic conditions are highly desirable.