Synthesis of (Carboxymethylidene)cyclopentenedione Derivatives via the Oxidative Cleavage of the Allylic Double Bond in 2-Allyl-2,4-dichloro-5-(2,4,6-trimethoxyphenyl)cyclopent-4-ene-1,3-dione

The oxidative cleavage reactions of the allylic double bond in 2-allyl-2,4-dichloro-5-(2,4,6-trimethoxyphenyl)cyclopent-4-ene-1,3-dione in the OsO4–NaIO4 and KMnO4–Et3BnN+Cl– systems were studied. The periodate cleavage of the starting 2-allylcyclopentene-1,3-dione gave an aldehyde, whose oxidation with the Jones reagent followed by HCl elimination resulted in the formation of the target 2-(carboxymethylidene)cyclopent-4-ene-1,3-dione. In the alternative approach, the permanganate oxidation of the starting 2-allylcyclopentene-1,3-dione led to the corresponding diol in a moderate yield.