N-Heterocyclic Carbenes of Indazole: Ring Enlargement Reactions by α-Halo Ketones and Dehalogenations of Vicinal Dihalides

Content Provider	Scilit
Author	Schmidt, Andreas Snovydovych, Bohdan Gjikaj, Mimoza
Copyright Year	2008
Description	On decarboxylation, 1,2-dimethylindazolium-3-carboxylate forms the N-heterocyclic carbene, 1,2-dimethylindazol-3-ylidene, which deprotonates α-halo ketones. The resulting indazolium salt and the corresponding enolate form 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 analysis). 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 $E_{1cb}$ mechanism, initiated by $Br^{+}$ abstraction by the N-heterocyclic carbene of indazole, is suggested.
Related Links	http://www.thieme-connect.de/products/ejournals/pdf/10.1055/s-2008-1067215.pdf
Ending Page	2804
Page Count	7
Starting Page	2798
ISSN	00397881
e-ISSN	1437210X
DOI	10.1055/s-2008-1067215
Journal	Synthesis
Issue Number	17
Volume Number	2008
Language	English
Publisher	Georg Thieme Verlag KG
Publisher Date	2008-08-06
Access Restriction	Open
Subject Keyword	Journal: Synthesis Organic Chemistry N-heterocyclic Carbene Vicinal Dihalides
Content Type	Text
Resource Type	Article
Subject	Organic Chemistry Catalysis