Asymmetric imino-acylation of alkenes enabled by HAT-photo/nickel cocatalysis.

Abstract

By merging nickel-mediated facially selective aza-Heck cyclization and radical acyl C-H activation promoted by tetrabutylammonium decatungstate (TBADT) as a hydrogen atom transfer (HAT) photocatalyst, we accomplish an asymmetric imino-acylation of oxime ester-tethered alkenes with readily available aldehydes as the acyl source, enabling the synthesis of highly enantioenriched pyrrolines bearing an acyl-substituted stereogenic center under mild conditions. Preliminary mechanistic studies support a Ni(i)/Ni(ii)/Ni(iii) catalytic sequence involving the intramolecular migratory insertion of a tethered olefinic unit into the Ni(iii)-N bond as the enantiodiscriminating step.