Synthesis of 3-Phenyl-4-oxopyrano[2,3-a]carbazoles (Indoloisoflavones)

Phenacylation of 1-hydroxycarbazoles 1 with phenylacetic acid in the presence of zinc chloride and phosphorous oxychloride afforded 2-phenacyl- and 2,4-diphenacyl-1-hydroxycarbazoles (2 and 3). Further, 2-phenacyl-1-hydroxycarbazoles 2 on Claisen condensation reaction followed by cyclisation with H+/EtOH yielded 3-phenyl-4-oxopyrano[2,3-a]carbdzoles 4.