Chiral (E,E)-1,4-dialkoxy-1,3-butadienes. 2. Conformational studies and Diels-Alder reactions with symmetric dienophiles
摘要:
The first examples of Diels-Alder reactions of chiral, C-2-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 Id, 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. (C) 1999 Elsevier Science Ltd. All rights reserved.