Synthetic studies on indoles and related compounds. XXXI. Chemical confirmation of the synthetic route for the benz[f]indole skeleton and its application

To confirm the structure of ethyl 9-methoxybenzf]indole ( 8a ) prepared from ethyl pyrrole-2-carboxylate ( 4 ) via a new synthetic route, the following chemical correlation work was performed. Ethyl 9-methoxybenzf]in-dole ( 8a ) was converted to 1-benzyl-3-methyl-5,6,7,8-tetrahydrobenzf]indole ( 25 ), which was alternatively and authentically synthesized from ethyl 3-methylpyrrole-2-carboxylate ( 11 ). On the basis of the established route to the benzf]indole nucleus, two representative benzf]indoles, benzf]indole ( 1 ) and 4,9-dioxobenzf]indole ( 26 ) were synthesized.