Photoinduced Nickel-Catalyzed Reductive Acyl Cross-Coupling: Facile Access to All Carbon Quaternary Aliphatic Ketones

Abstract

Sterically hindered α-tertiary dialkyl ketones are difficult to synthesize via traditional organometallic approaches. Recently developed reductive acyl-coupling strategy provides an access to α-tertiary dialkyl ketones with using either tertiary acyl electrophiles or tertiary alkyl radical precursors. However, due to the large steric hindrance effect, tertiary acyl donors or alkyl donors are largely restricted to highly strained ring system, thus limited the broad substrate scope of more general tertiary alkyl carboxylic acid derivatives. Herein, we develop a photoinduced nickel-catalyzed reductive acyl-coupling reaction with two different carboxylic acid esters to synthesize steric bulky dialkyl ketones in the absence of exogenous photocatalyst or stoichiometric metal reductant. Various unstrained tertiary acyl electrophiles can couple with 1o, 2o, 3o alkyl radical to afford all carbon quaternary aliphatic ketones including α-tertiary amino ketones with satisfactory yields under mild conditions, which have been previously difficult to access or not yet to be explored in literature.