Nickel-Catalyzed Cross-Dehydrogenative Aldehyde Allylation

Nucleophilic additions to aldehydes play a central role in synthetic chemistry. Additions of organometallic nucleophiles are commonly employed, and alternative catalytic processes using cross-electrophile couplings and reductive couplings involving various π-systems have been developed and extensively used. In this study, we describe a complementary approach for aldehyde-alkene coupling that involves the direct nickel-catalyzed cross-dehydrogenative coupling of aldehydes and alkenes. The process utilizes a combination of zinc powder and di-tert-butyl peroxide, which enables the cross dehydrogenative coupling to allow the synthesis of beta,gamma--unsaturated ketones through the catalytic union of acyl radicals and allylic radicals generated from the aldehyde and alkene substrates. An array of substrate combinations are demonstrated, and experimental and computational work supports the involvement of a double hydrogen-atom-transfer (HAT) mechanism.