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.
Key words
carbenes - nigellicin - nitrogen heterocycles - indazolium salts - decarboxylation