Ya. S. Kayukov, I. N. Bardasov, O. Kayukova
Sep 10, 2010
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Journal
Russian Journal of Organic Chemistry
Abstract
Tetracyanocyclopropyl ketones obtainable via modified Wideqvist reaction are accessible and convenient precursors of a number of heterocyclic systems [1–3]. Reactions of cyclopropyl ketones Ia–Ic with alkoxides give rise to 2-[2-alkoxy-5-amino-4-cyano-2-phenylfuran-3(2H)-ylidene]malononitriles [3]. We anticipated that replacement of the ketone acetal fragment in the latter by more labile semiacetal moiety should facilitate recyclization of the furan ring into pyrrole. Such transformation could be promoted using hydroxide ion instead of alkoxide in reactions with cyclopropyl ketones Ia–Ic. The above assumption was verified by studying the reaction of cyclopropyl ketones Ia–Ic with aqueous sodium hydroxide. We found that this reaction involves not only expected recyclization of furan ring into pyrrole but also annelation of pyridine ring. The structure of compounds IIa–IIc isolated by neutralization of the reaction mixture with a solution of sulfuric acid was confirmed by the H NMR and mass spectra. The H NMR spectra contained singlets at δ 7.12– 7.69 and 8.78–9.02 ppm, which were assigned to the hydroxy and NH protons, respectively, in the pyrrole ring. The NH proton in the pyridine ring resonated as