Diels-Alder reactions of (E)-2-Phenyl-4-[(S)-2,2-dimethyl-1,3-dioxolan-4-ylmethylen]-5(4H)-oxaz olone with heterogeneous catalysts

Article abstract of DOI:10.1016/0957-4166(96)00295-9

Diels-Alder reactions of (E)-2-Phenyl-4-[(S)-2,2-dimethyl-1,3-dioxolan-4-ylmethylen]-5(4H)-oxaz olone with 2,3-dimethylbutadiene, cyclopentadiene, and 2-methyl-1,3-butadiene (isoprene) are catalysed by silica gel and aluminium, titanium, and zinc catalyst supported on silica gel. l conversion and asymmetric induction are obtained with very low percentages of E/Z isomerisation. The best results are obtained with ZnCl₂ supported on silica gel, and by carrying out the reaction without a solvent. The stereochemistry of the major cycloadducts has been determined by single crystal X-ray structure determination and AM1 calculations of the corresponding transition structures.