A comparison of Friedel–Crafts acylations of acenaphthene and 1,8-dimethylnaphthalene. Methyl migration and acyl rearrangements accompanying acylations

Abstract

Acylations of acenaphthene afford mixtures of 5-and 3-(but no 4-)acylacenaphthenes. The 5-acylacenaphthene : 3-acylacenaphthene ratio varies from 2 to 40 for acetylations, and from 3 to 13 for benzoylations, according to the solvent used. From benzoylations of 5-acetylacenaphthene two isomeric diketones could be isolated: 6-acetyl-3-benzoyl- and 3-acetyl-6-benzoyl-acenaphthene, the latter a product of acyl rearrangement. 1,8-Dimethylnaphthalene affords mixtures of 2-,3-, and 4-acetyl-1,8-dimethylnaphthalenes, together with two isomeric ketones, 3- and 4-acetyl-1,7-dimethylnaphthalenes, which result from methyl migration of the substrate. From competitive acetylations, the relative positional reactivities could be estimated for chloroform solution at 20 °C 1-naphthyl 1.0, 2-naphthyl 0.45, 1,8-dimethyl-4-naphthyl 60, 3-acenaphthenyl 6.4, and 5-acenaphthenyl 94.