Abstract
1 -Allylic 2,2-dimethyl ethylenetricarboxylates undergo intramolecular cyclization reactions at 80-140 °C giving mixtures of ene adducts and dihydropyrans in which the ,/3-unsaturated ester functions as diene in an inverse electron de- mand Diels-Alder reaction. The trans-crotyl triester 6 reacts at 135 °C giving a 1:1 mixture of the cis-substituted ene adduct 8 and the Diels-Alder adduct 7. The tis-crotyl triester 12 gives the same ene adduct 8 and the Diels-Alder adduct 13. The cin- namyl triester 14 undergoes a reversible Diels-Alder reaction at 80-120 °C with AH = -14.3 kcal/mol and AS = —41 eu. The ene adducts are of value as -methylene lactone precursors while the pyrans will be of value in synthesis of iridoids and their analogues.