Asymmetric hetero-Diels-Alder reactions. Mechanism of the reaction of alkenyloxazolines with isocyanates

Diastereomerically pure oxazolo[3,2-c]pyrimidines can be readily prepared by the reaction of alkenyloxazolines with isocyanates. These compounds undergo epimerisation upon prolonged heating. The mechanism of this transformation has been investigated experimentally and computationally. Diastereomerically pure oxazolo[3,2-c]pyrimidines can be prepared by hetero-Diels-Alder reaction of alkenyloxazolines. The mechanism of the formation and isomerisation of these compounds is discussed.