Recent Advances in the Chemistry of Pyrazoles. Part 2. Reactions and N-Heterocyclic Carbenes of Pyrazole

Organic Synthesis with N‐Heterocyclic Carbenes of Indazole: Synthesis of Benzo(thio)imidates, Benzo[d][1,3]thiazines and Quinazoline‐4‐thiones

“…[31] (Scheme 2) To the best of our knowledge, 2-anilinobenzothioimidates have not been described before, as we were not able to find any examples in the literature. In view of the synthetic potential of N-heterocyclic carbenes of pyrazole [32][33][34] and indazole, [34,35] we envisaged the first synthetic approach as outlined in Scheme 3. We used indazolium salts I as protonated precursors of the N-heterocyclic carbenes II (indazol-3-ylidenes) which can be trapped as thiones or rhodium complexes.…”

Recent advances in neutral and anionic N-heterocyclic carbene – betaine interconversions. Synthesis, characterization, and applications

“…Thus, the chemistry of pyrazole-ylidenes and indazolylidenes has been summarized. 25 More general review articles deal with syntheses, properties, and biological activities of pyrazoles 26,27 and indazoles, 28 including betaines and carbenes. This interesting area of overlap will serve as strong impetus for additional research in that field.…”

“…The chemistry of N-heterocyclic carbenes and mesomeric betaines of pyrazole and indazole has been reviewed recently, 25 and reviews dealing with syntheses, properties, and biological activities of pyrazoles 26,27 and indazoles 28 appeared as well. Therefore, only a brief overview will be given here.…”

Synthesis of a Pyrazol-3-ylidene Palladium Complex, Pyrazolium Salts and Mesomeric Betaines of Pyrazole as N-Heterocyclic Carbene Precursors

“…N-Heterocyclic carbenes of pyrazole and of its relative, indazole, have so far stood in the shadow of the impressive development of pyrazole [26,27] and indazole chemistry [28] taking place during the last decade. However, some very interesting structures and applications have been published recently.…”

“…Several pyrazol-3-ylidene complexes have been described, the structures of which are summarized in a recent review on pyrazole chemistry [27]. Palladium pyrazol-3-ylidene complexes have been obtained by oxidative addition of 3-chlorotetramethylpyrazolium chloride and 3-chloro-1,5-dimethyl-2,4-diphenylpyrazolium chloride to a palladium(0) complex [30].…”