Studies on Seven-membered Ring Compounds. XXII. Preparation of Tropylium Ions Having Fused Heterocyclic Systems

Abstract

The preparation of tropylium ions having a fused oxazole, imidazole or thiazole nucleus is described. The heating of 2-benzoylaminotropone (I) and dimethyl sulfate produced 2-phenyloxazolotropylium ion (IIIa). The disproportionation reaction of IIIa with aqueous alkali gave 2-phenyl-6H-cycloheptoxazole (V) and 2-phenyl-6H-cycloheptoxazol-6-one (IV), The structures of which were proved by the reactions shown in Chart 1 and by examination of the spectra. 2-Phenylthiazolotropylium ion (XVIIb) and 1-p-tolyl-2-phenylimidazolotropylium ion (XXI) were prepared, respectively, by the simple dissolution of 2-benzoylaminotroponthion (XVI) and 2-benzoylamino-N-p-tolyltroponeimine (XX) in dilute hydrochloric acid. Treatment of both ions XVIIb and XXI with aqueous alkali resulted in the disproportionation reaction in which the former gave XVIII and XIX and the latter XXII and XXIII. The NMR spectra of the ions, XVII and XXI, showed the significant contribution of the tropylium ion structure of these compounds.