Photoinduced Copper-Catalyzed Asymmetric Acylation of Allylic Phosphates with Acylsilanes

We report a visible-light-induced copper-catalyzed highly enantio-selective umpolung allylic acylation reaction with acylsilanes as acyl anion equivalents. Triplet-quenching experiments and DFT calculations supported our reaction design, which is based on copper-to-acyl metal-to-ligand charge transfer (MLCT) photoexcitation that generates a charge-separated triplet state as a highly reactive intermediate. According to the calculations, the allylic phosphate substrate in the excited state undergoes novel molecular activation into an allylic radical weakly bound to the copper complex. The allyl radical fragment undergoes copper-mediated regio- and stereocontrolled coupling with the acyl group under the influence of the chiral N-heterocyclic carbene ligand.

Automated summary

We present a copper-catalyzed enantioselective umpolung allylic acylation reaction under visible light. The reaction involves the use of acylsilanes as acyl anion equivalents and is supported by triplet-quenching experiments and DFT calculations. The reaction mechanism involves a charge-separated triplet state intermediate generated by copper-to-acyl metal-to-ligand charge transfer photoexcitation.