Copper(I)-catalyzed addition of Grignard reagents to in situ-derived N-sulfonyl azoalkenes: an umpolung alkylation procedure applicable to the formation of up to three contiguous quaternary centers.

The alpha-alkylation of N-sulfonyl hydrazones via in situ-derived azoalkenes provides an umpolung approach to ketone alpha-alkylation that has considerable potential with regard to catalysis and the direct incorporation of functionality not amenable to the use of enolate chemistry. Herein, we describe the first Cu(I)-catalyzed addition of Grignard reagents to in situ-derived N-sulfonyl azoalkenes. This method is remarkable in its ability to deliver highly sterically hindered compounds that would be difficult or impossible to synthesize via traditional enolate chemistry, including those having up to three contiguous quaternary centers.