Aromatic annelation by reaction of aryl radicals with dimethyl acetylenedicarboxylate and related compounds

Abstract

Phenyl radicals derived from N-nitrosoacetanilide, dibenzoyl peroxide, or di-t-butyl peroxide–triphenylarsine react with dimethyl acetylenedicarboxylate (DMAD) to give tetramethylnaphthalene-1,2,3,4-tetracarboxylates, the maximum yield being 0·5 mol per mol of radical source, obtained in the case of dibenzoyl peroxide. Substituted dibenzoyl peroxides [(XC₆H₄CO₂)₂; X = 2-NO₂, 2-Cl, 3-Cl, 3-Br, 3-Me, 4-Cl, 4-Br, 4-Me, or 4-CN] undergo this annelation less successfully to give the corresponding tetramethyl X-naphthalene-1,2,3,4-tetracarboxylates. Di-2-naphthoyl peroxide similarly gave a mixture of tetramethylanthracene- and phenanthrene-1,2,3,4-tetracarboxylates, and dibenzoyl peroxide in ethyl propiolate gave a mixture of diethyl naphthalenedicarboxylates.

That the annelation probably proceeds via reaction of first-formed styryl radicals with DMAD followed by cyclisation is indicated by the additional formation of dimethyl diphenyl-maleate and -fumarate when dibenzoyl peroxide decomposed in a mixture of benzene and DMAD. In accord with this, decomposition of bis-α-methylcinnamoyl peroxide in DMAD gave a small yield of dimethyl 3-methylnaphthalene-1,2-dicarboxylate.

Di-2-thenoyl peroxide behaved differently on decomposition in DMAD, giving dimethyl thenoylmaleate (20%), the trans-isomer being absent, and trimethyl 5-methoxyfuran-2,3,4-tricarboxylate (5%). A mechanism is advanced.