Synthesis of homofascaplysin B, C and analogues by the photocyclization of 3-acyl-2-chloro-1-[2-(indol-3-yl)ethyl]indoles

Two routes for the synthesis of homofascaplysin B, C and analogues have been established using the photocyclization as the key step. The first route is based on sequential photocyclization and photochemical dehydrogenation reactions of 2-chloro-3-acyl-1-[2-(indol-3-yl)ethyl]indoles in Cu(OAc)2- and air-saturated acetone; and the second is based on the two-step reactions, namely, photocyclization of 2-chloro-3-acyl-1-[2-(indol-3-yl)ethyl]indoles in acetone and DDQ-mediated dehydrogenation of 13-acyl-6,7-dihydro-pyrido[1,2-a;3,4-b′]diindoles in benzene at room temperature. Comparatively, the two-step route for the synthesis of homofascaplysin B, C and analogues is more efficient than the one-pot route.