Condensed thiophen ring systems. Part VIII. Intramolecular cyclisation of azido- and nitro-substituted 2-arylbenzo[b]thiophens; new routes to 10H-[1]benzothieno[3,2-b]indoles

Abstract

10H-[1]Benzothieno[3,2-b]indole (1) and some of its derivatives have been prepared by reductive cyclisation of a 2-(2-nitroaryl)- or a 2-aryl-3-nitro-benzo[b]thiophen with triethyl phosphite. The parent compound (1) has been prepared also by thermolysis of either 3-azido-2-phenyl- or 2-(o-azidophenyl)-benzo[b]thiophen in bis-(2-methoxyethyl) ether. 2-(o-Nitrophenyl)benzo[b]thiophen and its 5-methyl derivative have been prepared by reaction of the corresponding 2-benzo[b]thienyl-lithium compounds with o-nitrofluorobenzene. The scope of the reaction of benzo[b]thienyl-lithium compounds with other fluoroaromatic compounds has been studied, and the preparations of starting materials are also reported. Bromination of compound (1) gave the 2-bromo-derivative.