“Abnormal” Addition of NHC to a Conjugate Acid of CAAC: Formation of N ‐Alkyl‐Substituted CAAC

The addition reactions of N‐heterocyclic carbenes (NHCs) are mostly known to occur through the carbenic centre (C2), which leads to a “normal” adduct. Herein, we report the “abnormal” addition of NHC Dip 1 (1,3‐(2,6‐ i Pr 2 C 6 H 3 )‐imidazole‐2‐ylidene) to a conjugate acid of cyclic (alkyl)(amino)carbene 2 (CAAC i Pr =1‐ i Pr‐3,3,5,5‐Me 4 ‐pyrrolinium triflate). Mechanistic study revealed that this reaction proceeded through the in situ formation of 1,3‐(2,6‐ i Pr 2 C 6 H 3 )‐imidazolium cation 4 and N‐i Pr‐substituted CAAC 5 followed by the oxidative addition of compound 5 across the C4−H bond (alias backbone C−H) of compound 4 . The in situ formation of compound 5 was also proven by the oxidative addition of it to the N−H group of i PrNH 2 . DFT calculations also supported the mechanistic findings. A different methodology for the in situ generation of compound 5 by using TMPLi is also described.