“…Known pseudo‐cross‐conjugated heterocyclic mesomeric betaines, which form N‐heterocyclic carbenes by in situ decarboxylation, are presented in Figure 2. The alkaloid Homarine ( III , R 1 = R 2 = R 3 = H),25 and quinolinium ( III , R 1 = H, R 2 –R 3 = –CH=CH–CH=CH–), as well as isochinolinium derivatives ( III , R 1 –R 2 = –CH=CH–CH=CH–,R 3 = H),26 imidazolium‐2‐carboxylates IV ,27 pyrazolium‐3‐carboxylates V ,28 as well as indazolium‐3‐carboxylates V (R 1 –R 2 = –CH=CH–CH=CH–)29 were found to undergo thermal fragmentation to CO 2 and the correspondinghetarene ylidenes. Extrusions of isocyanates and isothiocyanates have been reported as well 29.…”