Synthesis of 3,4-bridged indoles by photocyclisation reactions. Part 2. Photocyclisation of halogenoacetyl tryptophol derivatives and α-chloro indol-3-ylalkanoate esters

Abstract

Irradiation of the trichloroacetates 2, 4 and 5, derived from the corresponding tryptophols, in methanolic acetonitrile results In photocyclisation to the indole 4-position, and the formation of the pyrrolobenzoxocines 9–11. Attempted photocyclisation of the ‘reversed’α-chloro esters 15a, 15b and 18 was thwarted by readily occurring elimination of HCl, although the dimethyl compound 15c did cyclise to give the cycloheptaindole 20 upon irradiation in acetonitrile.