ADDITION OF METHANOL TO HEXYNEDIOIC ESTERS . SNTHESIS OF CYCLOPENTANEDIONES AND MUCONATES

Sodium methoxide reacts with hexynedioic esters in a manner that is determined by the structure of the ester and by the solvent medium. Treatment of 4,4-dimethyl-2-hexynedioic acid dimethyl ester (2a) with sodium methoxide in dry tetrahydrofuran gives 4,4-dimethyl-3-methoxy-2-carbomethoxy-2-cyclopenten-1-one (5), an over-all trans addition to the triple bond. In methanol ester 2a reacts to give iraras-4,4-dimethyl-3-methoxy-2-hexenedioic acid dimethyl ester (9), cis-4,4-dimethyl-3-methoxy-2-hexenedioic acid dimethyl ester (10), and 4,4-dimethyl-3-methoxy-5-carbomethoxy-2-cyclopenten-1-one (8); a net cis addition occurs. The distribution of these products varies with time. Hydrolysis and decarboxylation of esters 5 and 8 lead to 4,4-dimethylcyclopentane-1,3-dione (6). For 4-n-propyl-2-hexynedioic acid diethyl ester (2b) and 2-hexynedioic acid dimethyl ester (2c), rearrangement to muconates competes with base-catalyzed alcohol addition and is the principal reaction pathway. The structures of all products are proven by a combination of analysis, spectral identification, and chemical transformation and synthesis. The mechanisms of these reactions are discussed. © 1968, American Chemical Society. All rights reserved.