Pseudo-Cross-Conjugated Mesomeric Betaines and <i>N</i>-Heterocyclic Carbenes of Indazole

Abstract

1,2-Dimethylindazolium-3-carboxylates are pseudo-cross-conjugated mesomeric betaines (PCCMB) and derivatives of the indazole alkaloid Nigellicin. They decarboxylate on heating to give intermediary N-heterocyclic carbenes of indazole that can be trapped with iso(thio)cyanates to amidates. Alternatively, 1,2-di­methylindazolium-3-amidates can be prepared starting from the corresponding 1H-indazol-3-carboxylic acid which is converted into its chloride, reacted with anilines and deprotonated on anion exchange resin. The heterocumulene moieties of these amidates, which are new representatives of pseudo-cross-conjugated mesomeric betaines, can be exchanged to 3,5-dichlorophenyl isocyanate via the N-heterocyclic carbene.