INTRA-MOLECULAR REACTIONS OF 1-ALLYLIC 2,2-DIMETHYL ETHYLENETRICARBOXYLATES

1-Allylic 2,2-dimethyl ethylenetricarboxylates undergo intramolecular cyclization reactions at 80-140 °C giving mixtures of ene adducts and dihydropyrans in which the α,β-unsaturated ester functions as diene in an inverse electron demand 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 m-crotyl triester 12 gives the same ene adduct 8 and the Diels-Alder adduct 13. The cinnamyl triester 14 undergoes a reversible Diels-Alder reaction at 80-120 °C with ΔH= -14.3 keal/mol and ΔS = -41 eu. The ene adducts are of value as α-methylene lactone precursors while the pyrans will be of value in synthesis of iridoids and their analogues. © 1979, American Chemical Society. All rights reserved.