N‐Insertion of Diazonium Salts into Ketone Derivatives

We report a new oxidative nitrogen insertion into cyclic ketones using readily available diazonium salts. In the case of indanones, the reaction is promoted by auto‐catalytically generated Brønsted acid and proceeds via sequential α‐diazenylation and ring expansion through an N‐iminoaziridinium intermediate. For less α‐acidic ketones, a complementary strategy employing silyl enol ethers was developed: catalyzed by HNTf2, efficient nitrogen insertion occurred into silyl enol ethers derived from a broad range of four‐ to seven‐membered cyclic ketones. The resulting N‐aminoamides exhibit broad synthetic utility in various downstream transformations. Notably, a ring expansion, followed by N‐N bond cleavage offers a powerful tool for skeletal editing, converting indanones into isoquinol‐inones, as demonstrated by the scaffold modification of donepezil.