The reaction of arylcoppermagnesium and other organometallic reagents with phthalic anhydride

Abstract

Arylcoppermagnesium reagents, prepared from 5ArMgX + 2.5CuI, (Ar = 4-CH 3C 6H 4, 4-CH 3OC 6H 4, 4-ClC 6H 4, 2-C 4H 3S react with one equivalent of phthalic anhydride in ether or THF at −5'C for 2.5 h to give 2-aroylbenzoic acids in 83–98% yields. The phenylcopperma reagent (Ar  C 6H 5 under similar conditions gives 2-benzoylbenzoic acid and 3,3-diphenylphthalide in 40–42% and 42–45% yield, respec The yield of the 2-benzoylbenzoic acid rises to 93% in the presence of dimethyl sulphide. Under these conditions no phthalide is formed. Lithium diphen reacts with phthalic anhydride in ether-hexane to give 92% of 2-benzoylbenzoic acid and 7% of 3,3-diphenylphthalide. The reaction of phenylcopper reage from PhMgBr + CuI, under similar conditions is slow and gives 2-benzoylbenzoic acid in 15% yield. The reaction of phenylmagnesium bromide in the presen of catalytic amounts of copper(I) iodide gives unsatisfactory results. Use of two equivalents of phenyllithium with one equivalent of phthalic anhydrid hand, affords 3,3-diphenylphthalide in 77% yield. The mechanisms of these reactions are discussed.