DIELS-ALDER REACTIONS OF IMETHYL-1,3-DIOXOLAN-4-YLMETHYLEN]-5(4H)-OXAZOLONE WITH HETEROGENEOUS CATALYSTS

Diels-Alder reactions of imethyl-1,3-dioxolan-4-ylmethylen]-5(4H)-oxaz olone with 2,3-dimethylbutadiene, cyclopentadiene, and 2-methyl-1,3-bu tadiene (isoprene) are catalysed by silica gel and aluminium, titanium , and zinc catalyst supported on silica gel. Overall conversion and as ymmetric induction are obtained with very low percentages of E/Z isome risation. The best results are obtained with ZnCl2 supported on silica gel, and by carrying out the reaction without a solvent. The stereoch emistry of the major cycloadducts has been determined by single crysta l X-ray structure determination and AM1 calculations of the correspond ing transition structures. Copyright (C) 1996 Elsevier Science Ltd