A simple route to spiro[indene-2,1′-isoquinoline]s, a spiro[indene-2,1′-β-carboline], and hexadehydroyohimbane

Abstract

1′,2,2′,3,3′,4′-Hexahydro-5,6,6′,7′-tetramethoxyspiro[indene-2,1′-isoquinolin]-1-one (13) and its 6′-benzyloxyanalogue (14) were synthesised from 3,4-dihydro-1-(1,2-dihydro-4,5-dimethoxybenzocyclobuten-1-yl)isoquinolines [(6) and (7)]. Autoxidation of the 1-(1,2-dihydrobenzocyclobuten-1-yl)-β-carboline (26) gave the spiro[indene-2,1′-β-carbolin]-1-one, which was converted photochemically into the hexadehydroyohimbane (29).