The elimination of an alkoxy group in the photo-Graebe–Ullmann conversion of 1-(2,5-dialkoxyphenyl)triazolopyridines into carbolines, and the preparation of α-, γ- and δ-carboline quinones

Abstract

Photochemical decomposition of 1-(2,5-dialkoxyphenyl)triazolopyridines 7a, 21 and 33 resulted in elimination of an alkoxy group to give the alkoxycarbolines 9a and 35 in addition to the expected dialkoxycarbolines. The carbolines having either a methoxy and a isopropoxy substltuent 22, 34a and 34b or two methoxy groups 41 were oxidised with ceric ammonium nitrate to yield the α-, γ- or δ-carboline p-quinones 37, 38 and 42.