New cyclodimerization reaction of (3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)acetic acid

(3,5-Di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)acetic acid la underwent on heating a new cyclodimerization reaction affording a 1 : 1 mixture of th e racemic cis- and trans-isomeric lactone-acids 2. The decisive structure e lucidation of 2 was carried out after its mild esterification with diazomet hane and separation of the racemic isomeric methyl esters 3a and 3b. The at tempted esterification of 2 with methanol and sulfuric acid gave only the m ethyl diarylacetate 4. In contrast to la, which contains the carboxylic aci d functionality no cyclodimerization was observed with the corresponding me thyl ester 1b or nitrile 1c.