-DIMETHYL-1,3-DIOXOLAN-4-YLMETHYLEN]-5(4H)-OXAZONE AS THE DIENOPHILE IN ASYMMETRIC DIELS-ALDER REACTIONS

Diels-Alder reactions of dimethyl-1,3-dioxolan-4-ylmethylen]-5(4H)oxaz olone and several cyclic and open chain dienes are studied. Less-react ive dienes required longer reaction times and led to isomerization of the Z-oxazolone and isolation of products derived from the E-isomer; L ewis acid catalysts were used to shorten the reaction times. In all ca ses high diastereofacial selectivity is observed and Diels-Alder adduc ts can be obtained in high optical purity. The stereochemistry of addu cts has been elucidated by single crystal X-ray structure determinatio ns, H-1-NMR analysis and mechanistic considerations.