Understanding Mechanistic Differences between 3‐Diazoindolin‐2‐Imines and N ‐Sulfonyl ‐1,2, 3‐Triazoles in the Rh 2 ( II )‐Catalyzed Reactions with Nitrosoarenes

Main observation and conclusion The employment of α‐iminometallocarbenes to construct valuable N ‐containing compounds has attracted significant research interest. Herein, the nucleophilic addition of nitrosoarenes with the α‐imino rhodium carbene species (I), which is derived from Rh 2 (II)‐catalyzed denitrogenation of 3‐diazoindolin‐2‐imines, to produce synthetically useful 2‐iminoindolin‐nitrones is described. Mechanistically, the N‐attack of nitrosoarenes with the carbene site of I is proposed. For the analogous Rh 2 (II)‐catalyzed reaction of nitrosoarenes with N ‐sulfonyl‐1,2,3‐triazoles reported by Li and co‐workers ( Org . Lett . 2014, 16 , 6394), however, the O‐attack of nitrosoarenes with the carbene site of α‐imino rhodium carbene species (II) is more favorable to occur than the N‐attack. The subsequent transformation to yield the product of N ‐acylamidines is rationalized based on computational studies. The mechanistic differences for the reactions of nitrosoarenes with α‐imino rhodium carbene species I and II are discussed.