Understanding Mechanistic Differences Between 3‐diazoindolin‐2‐imines and N‐Sulfonyl‐1,2,3‐Triazoles in the Rh2(II)‐Catalyzed Reactions with Nitrosoarenes

Main observation and conclusionThe 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 Rh2(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 Rh2(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.