Understanding Mechanistic Differences between 3-Diazoindolin-2-lmines and N-Sulfonyl-1,2,3-Triazoles in the Rh_(2)(ll)-Catalyzed Reactions with Nitrosoarenes

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)(ll)-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)(ll)-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 differ-ences for the reactions of nitrosoarenes with a-imino rhodium carbene species I and II are discussed.