Asymmetric Induction in Nitrile Oxide Cycloadditions to Optically Active Acrylates. Comparisons of Acrylate Conformations in Thermal and Acid-Catalyzed 1,3-Dipolar and Diels-Alder Cycloaddition Transition States

Article abstract of DOI:10.1021/jo00387a004

Nitrile oxides undergo cycloadditions to several different chiral acrylates to give 0-56percent ?-facial stereoselectivity.In cases where stereoselectivity is significant, the structure of the major product is consistent with transition state with an s-cis conformation of the acrylate.Thermal Diels-Alder reactions of cyclopentadiene with these acrylates have also been studied, since the literature only gives results of catalyzed reactions.The major products are consistent with transition states which involve a small s-cis preference, by contrast to the substantial s-trans preferences required to explain results found by Oppolzer for the catalyzed reactions of the same acrylates.Model theoretical calculations also are in accord with these models, favoring an s-cis preference in the thermal reaction and an s-trans in the catalyzed.