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[摘要]：On decarboxylation, 1,2-dimethylindazolium-3-carboxylate forms the N-heterocyclic carbene, 1,2-dimethylindazol-3-ylidene, which deprotonates a-halo ketones. The resulting indazolium salt and the corresponding enolate give 1:1 adducts, which undergo a ring enlargement to cinnolines. Reaction with 2-bromo-2,3-dihydro-1H-inden-1-one gives a 4-hydroxyspiro[cinnoline-3,2'-inden]-1'-one by ring enlargement reaction [x-ray crystal structure anal.: monoclinic, space group P21/c, a 11.815(1), b 10.113(1), c 13.162(2) ? b 113.72(1)? V 1439.8(3) ?, Z 4]. Vicinal dibromides undergo debromination under these conditions to give alkenes, and substrates with 1,2-dibromoethene partial structure give acetylenes. As 3-bromoindazole is found as the second product of this reaction, an E1cb mechanism, initiated by Br+ abstraction by the N-heterocyclic carbene of indazole, is suggested. |
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