Intramolecular Diels−Alder Reaction by Self-Assembly of the Components on a Lewis Acid Template

Diels-Alder reactions of 2,4-hexadienol or its O-methyl ether with acrylate derivatives at 120 degrees C give mixtures of the four possible adducts with low selectivity. At ambient temperature and in the presence of Mg(II) or Al(III) Lewis acids, reactions of the dienol (but not the ether) are highly selective. Control experiments suggest that the Lewis acid serves both to tether the diene and dienophile and to induce an "intramolecular" reaction of the resulting "self-assembled" intermediate.