Synthesis of four methoxy-substituted 1,8-naphthalic anhydrides and of the three monomethyl-1,8-naphthalic anhydrides
Cason, J; Weiss, A; Monti, SA
The 2-, 3-, and 4-methoxy-1,8-naphthalic anhydrides were synthesized by starting, respectively, with a Friedel-Crafts reaction on,β-methoxynaphthalene, sulfonation of 1,8-naphthalic anhydride, and nitration of acenaphthene. 2,3-Dimethoxy-1,8-naphthalic anhydride was prepared in very low yield via the Friedel-Crafts reaction of diphenyloxalimide chloride with 2,3-dimethoxynaphthalene. The 2-and 4-methyl-1,8-naphthalic anhydrides were prepared, respectively, via the Friedel-Crafts reaction on β-methylnaphthalene and bromination of acenaphthene. Synthesis of 3-methyl-1,8-naphthalic anhydride via Friedel-Crafts methylation of acenaphthene failed. Although ethylation of acenaphthene yields 4-ethylacenaphthene, methylation yields 5-methylacenaphthene. Successful synthesis of 3-methyl-1,8-naphthalic anhydride followed the discovery that diborane reduction of 3-bromo-1,8-naphthalic anhydride yields 5-bromo-2,1,3-pm-naphthopyran. After the bromine had been converted into methyl via the carboxylic acid, oxidation yielded the 3-methyl-1,8-naphthalic anhydride. Numerous attempts to synthesize 3,4-dimethoxy-1,8-naphthalic anhydride failed. In the nmr spectra of the anhydrides, resonance for the methyl hydrogens in both the methyl-substituted and methoxy-substituted anhydrides followed the same pattern, highest field for the 3 position and lowest field for the 2 position. © 1968, American Chemical Society. All rights reserved.