Ethylenetricarboxylates, 1-allylic 2,2-dimethyl Diels-Alder reactions

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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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

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