Chiral (E,E)-1,4-dialkoxy-1,3-butadienes. 2. Conformational studies and diels-alder reactions with symmetric dienophiles

Article abstract of DOI:10.1016/S0040-4020(99)00086-1

The first examples of Diels-Alder reactions of chiral, C₂-symmetric (E,E)-1,4-dialkoxy-1,3-butadienes are described. The cycloadditions with maleic anhydride lead in all instances to the exclusive formation of the endo adducts. C(2h)-Symmetric dienophiles such as fumaronitrile and diethyl fumarate react with variable diastereoselectivities; best results are obtained with the camphor-derived diene 1d, whose reaction with diethyl fumarate takes place with complete facial selectivity. A theoretical analysis, using the SCF-MO procedure AM1, of the conformations of the dialkoxydienes has been used to rationalize the steric course of the cycloadditions.