Reactions of methyl 2-(1-oxo-2,3,4,9-tetrahydro-1H-carbazol-2-yl) oxoacetates. Synthesis of methyl isoxazolo[5,4-a]carbazole-3-carboxylates

Abstract

The reaction of methyl 2-(1-oxo-2,3,4,9-tetrahydro-1 H-carbazol-2-yl)oxoacetates (1a-e) with hydroxylamine hydrochloride in alcoholic KOH afforded 1-hydroxyimino-2,3,4,9-tetrahydro-1 H-carbazoles (2a-e), and in acetic acid methyl isoxazolo[5,4- a]carbazole-3-carboxylates (3a-e). Ketoesters 1a-e with urea and thiourea under acidic conditions yielded a mixture of the respective 1-hydroxycarbazoles (6a-e) and 2,3,4,9-tetrahydro-1 H-carbazol-1-ones (7a-e), but under basic conditions the respective 1-carbimido- and 1-thiocarbimido-2,3,4,9-tetrahydro-1 H-carbazoles (8a-e and 9a-e) were formed. Plausible mechanisms are proposed.