Studies on reductive alkylation. Regiocontrolled synthesis of anthracene derivatives

Abstract

Reductive alkylation of 2,5-dimethoxybenzoic acid, its 4-methyl derivative, and 3,5-dimethoxybenzoic acid with methyl 2-iodomethyl-6-methoxybenzoate furnished acids (I), (2) and (3),respectively. Oxidative decarboxylation followed by hydrolysis led to diphenylmethane acids (4),(5) and (6). Cycloacylation of (4) and (5) gave 1,4,8-trimethoxyanthracen-9-ol (7) and its 2-methyl derivative (8), thereby serving as models for a regiocontrolled synthesis of anthracyclines. Cycloacylation of (6) could only be achieved with concomitant C-acylation, to give 4-acetyl-1,3,8-trimethoxyanthracen-9-yl acetate (9).