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N‐Heterocyclic Carbene–Betaine Interconversions: Tautomeric Equilibria of Imidazolium‐Indolates and Indole‐Substituted Imidazol‐2‐ylidenes
Author(s) -
Pidlypnyi Nazar,
Uhrner Fabian,
Nieger Martin,
Drafz Martin H. H.,
Hübner Eike G.,
Namyslo Jan C.,
Schmidt Andreas
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201300728
Subject(s) - chemistry , tautomer , carbene , pyridine , imidazole , medicinal chemistry , deprotonation , adduct , benzimidazole , indole test , stereochemistry , organic chemistry , catalysis , ion
Indol‐2‐yl‐hetarenium salts of imidazole, benzimidazole, imidazo[1,5‐ a ]pyridine, imidazo[1,2‐ a ]pyridine, (pyridin‐2‐yl)imidazole, and 2,5‐bis(imidazol‐1‐yl)pyridine were prepared. On deprotonation, hetarenium‐indolates were formed that belong to the subclass of ylides of heterocyclic mesomeric betaines. The stabilities of these ylides depend on the substitution pattern. The ylides are in tautomeric equilibrium with the N‐heterocyclic carbenes (indol‐2‐yl)imidazol‐2‐ylidenes, which were trapped as thiones on reaction with sulfur. The N‐heterocyclic carbene derived from imidazo[1,5‐ a ]pyridine could also be trapped as its zwitterionic borane adduct by reaction with triethylborane. Results of two single‐crystal X‐ray analyses and DFT calculations are presented.