Diastereofacial Selectivity Studies on 3-Alkeny1-4,5-dipheny1-4,5-dihydroisoxazoles

Abstract

Epoxidation of 3-(l-phenylethenyl)-4,5-diphenyl-4,5-dihydroisoxazole and 3-ethenyl-4,5-diphenyl-4,5-dihydroisoxazole occurred with 74% diastereomer excess (de) and 66% de, respectively. Catalytic cis-hydroxylation of the 3-(l-phenylethenyl)dihydroisoxazole afforded a diol with 80% de. Cycloaddition reactions of the same alkenyl dihydroisoxazoles with bromonitrile oxide and phenylsulfonylcarbonitrile oxide occurred with 10-46% de; opposite diastereomers were preferred in the reactions of 3-ethenyl- and 3-(l-phenylethenyl)dihydroisoxazoles. These results are rationalized based on a combination of two factors: a preference for the s-trans heterodiene conformer and a preference for attack anti to the C-4 phenyl group in all but one case. The s-trans conformer of 3-ethenyl-4,5-dihydroisoxazole was determined by the ab initio method to be 2.8 kcal/mol more stable than the s-cis conformer. © 1990, American Chemical Society. All rights reserved.