Facile aromatisation of abscisic acid

Abstract

Treatment of abscisic acid (ABA) or its methyl ester either with acetic anhydride and toluene-p-sulfonic acid or with lithium diisopropylamide and methyl chloroformate led to aromatisation of the cyclohexene ring. A mechanism for the reaction is proposed which involves the initial formation of the 4′,5′-enol followed by a carbocationic rearrangement initiated by loss of the 1′-tertiary alcohol. Analogues of ABA with a saturated side chain do not undergo this aromatisation process.