Ethylenetricarboxylates, 1-allylic 2,2-dimethyl

Kelly found that intramolecular ene reaction of triester (62) occurs rapidly at room temperature to give (63). Snider and coworkers investigated the scope of this reaction and found that 1-allylic 2,2-dimethyl ethylenetricarboxylates undergo intramolecular cyclization reactions at 80-140 C to give mixtures of ene adducts and dhydropyrans resulting from inverse electron Diels-Alder reactions in which the a, -unsatuiated ester functions as the diene. The rrans-crotyl triester (64a) reacts at 135 C for 2(X) h giving... 

Until recently, the reaction of a,p-unsatuiated esters with electron-rich alkenes has been reported to provide cyclobutane [2 + 2] cycloaddition products. Amice and Conia first proposed the intermediacy of [4 + 2] cycloadducts in the reaction of ketene acetals with methyl acrylate, and the first documented example of the 4ir participation of an a,3-unsaturated ester in a Diels-Alder reaction appears to be the report of Snider and coworkers in their description of the reversible, intramolecular [4 + 2] cycloaddition reaction of l-allylic-2,2-dimethyl ethylenetricarboxylates. Subsequent efforts have demonstrated that substitution of an a, -unsaturated ester with a C-3 electron-withdrawing substituent may permit their well-behaved 4ir participation in LUMOdiene-controlled Diels-Alder reactions (equation 3). ... 

In studies which represent the first carefully documented example of the 4-n participation of an a,/3-unsaturated ester in a [4 + 2] cycloaddition,142 Snider and co-workers systematically investigated the competing thermal, intramolecular Diels-Alder and ene reactions of l-allylic-2,2-dimethyl ethylenetricarboxylates [Eq. (39)].142... 

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