Studies on intramolecular Friedel–Crafts cyclisation. Part II. Synthesis of 7-methoxy-8-methyl-1-tetralone

Abstract

Friedel–Crafts cyclisation of the mixture of isomeric 4-(2- and 3-bromo-4-methoxy-5-methylphenyl)butyric acids (IVb and d) furnished three isomeric tetralones: 5- and 6-bromo-7-methoxy-8-methyl-1-tetralone (Va and c), and 8-bromo-7-methoxy-6-methyl-1-tetralone (VIa). Similar cyclisation of the corresponding chloro-acid mixture (IVc and e) afforded the equivalent isomeric chlorotetralones (Vb and d), and (VIb). The influence of bromine and chlorine on the course of the cyclisations of the acids (IVb and c) is discussed in terms of steric and polar effects. Catalytic dehalogenation of the tetralones (Va—d) gave 7-methoxy-8-methyl-1-tetralone (I).