Investigation of Diastereomeric Induction in the Diels-Alder Reactions of Acylnitroso Dienophiles

Oxidation of hydroxamic acids, and also related N-hydroxyureas and N-hydroxycarbamates, gives acylnitroso dienophiles. These are highly reactive species and cannot be isolated, however they can be trapped with dienes, undergoing hetero Diels-Alder reactions to give cycloadducts. The aim of this project was to investigate diastereomeric induction in the hetero-Diels-Alder reactions of acylnitroso dienophiles by attaching them to chiral auxiliaries. The chiral auxiliaries used were mainly based on 1,2-trans-cyclohexylamines or 1,2-trans-cyclohexanols and used a large equatorial 2-substituent to shield one face of the dienophile. It was hoped that intramolecular hydrogen bonding in nitrosoformamide dienophile 234 would restrict the rotation of the dienophile and hence increase the diastereoselectivity of the cycloaddition, in comparison with nitrosoformate dienophiles 238 and 292 which cannot have this intramolecular hydrogen bonding. These hetero Diels-Alder reactions were carried out at both