The synthesis of 8-methyl-4,6,6a,7,8,9-hexahydroindolo[4,3-fg]isoquinoline, the 9,10-didehydro-7-methyl-7-aza analogue of ergoline

Abstract

The title compound has been synthesised by ring expansion of the cyclopentenone 4-acetyl-4,5,5a,6,6a,7-hexahydro-8H-indeno[6,5,4-cd]indol-8-one (5c). Compound (5c) was prepared from the readily available 1-benzoyl-2,2a-3-4-tetrahydrobenz[cd]indol-5(1H)-one (3). An unexpected isomerisation was observed on N-methylation of the 7-aza lactam, the double bond having migrated from Δ^9,10 to Δ^5,6. Hydrogenation of the Δ^9,10 lactam (7c) and the Δ^5,6 lactam (8a) gave rise to different dihydro derivatives whose configurations are discussed on the basis of their 360 MHz ¹H n.m.r. spectra.