2-Benzopyrylium salts. 29. A new approach to the synthesis of the natural alkaloid salsolidine using 2-benzopyrylium salts

The reaction of 6,7-dimethoxy-1-methyl-2-benzopyrylium salt with ammonia forms the corresponding isoquinoline, and its reaction with methylamine and benzylamine forms mixtures of the corresponding isoquinolinium salts and naphthylamines. The reduction of 2-benzyl-1-methyl-6,7-dimethoxyisoquinolinium perchlorate with sodium tetrahydroborate has given the corresponding tetrahydroisoquinoline, the hydrogenolysis of which has led to salsolidine. The products have been characterized by elementary analyses and IR and PMR spectroscopy.