Synthesis of Simple Derivatives of (2Z,4Z)-3-Methyl-2,4-hexadienedioic Acid

Article abstract of DOI:10.1021/jo00346a014

Methanolysis of 4-methyl-2,7-oxepindione yields a mixture of both monomethyl esters of (2Z,4Z)-3-methyl-2,4-hexadienedioic acid. 4-Methyl-1,2-benzoquinone is oxidized by lead(IV) acetate in methanol-benzene to give dimethyl (2Z,4Z)-3-methyl-2,4-hexadienedioate.The 6-monomethyl ester, but not the 1-monomethyl ester or dimethyl ester, spontaneously stereomutates to the 2Z,4E isomer.The monoesters also cyclize to lactone esters.The disodium salt of (2Z,4Z)-3-methyl-2,4-hexadienedioic acid, prepared by saponification of the corresponding dimethyl ester or cyclicanhydride, is stable in the presence of excess base but immediately gives (2Z,4E)-3-methyl-2,4-hexadienedioic acid upon acidification.The results fit the general mechanism of stereomutation of 3-substituted (2Z,4Z)-2,4-hexadienedioic acids and derivatives.