Synthesis of 5-ethyl-11H-pyrido[3,4-a]carbazole by two routes and conversion of uleine into 5-ethyl-1,2,3,4-tetrahydro-2-methyl-11H-pyrido[3,4-a]carbazole

Abstract

Syntheses of 5-ethyl-11H-pyrido[3,4-a]carbazole and derivatives as potential intermediates for a synthesis of the furopyridocarbazole alkaloid subincanine are described. In one approach 5-ethylisoquinoline was prepared and the indole ring was built up via 5-ethyl-8-hydrazinoisoquinoline. An alternative approach utilised the oxidative photocyclisation of a 1-(indol-3-yl)-2-(4-pyridyl)but-1-ene. Finally, the conversion of the 1,5-methanoazocino-[4,3-b]indole uleine into 5-ethyl-1,2,3,4-tetrahydro-2-methyl-11H-pyrido[3,4-a]carbazole is described.