Photocyclization of aryl enaminones. An efficient route to indole alkaloid synthons

The photocyclization of enaminones was extended to aryl enaminones bearing a substituent on the aromatic moiety. This reaction was studied in order to achieve the synthesis of indole alkaloid synthons. Trials of regioselectivity control were made by using groups with enhanced steric hindrance. The reactivity of secondary enaminones was tested, and the ratio of C-alkylation to N-alkylation was shown to be dependent on the nature of the aromatic substituent. During this work, new hexahydrocarbazolones were synthesized, with substituents on the A ring or the modified C ring. Keywords: photocyclization, aryl enaminones, indole alkaloids, hexahydrocarbazolones-4, cyclopenta[b]indoles.