Diastereofacial Selectivity Studies on 3-Alkenyl-4,5-diphenyl-4,5-dihydroisoxazoles

Article abstract of DOI:10.1021/jo00297a018

Epoxidation of 3-(1-phenylethenyl)-4,5-diphenyl-4,5-dihydroisoxazole and 3-ethenyl-4,5-diphenyl-4,5-dihydroisoxazole occurred with 74percent diastereomer excess (de) and 66percent de, respectively.Catalytic cis-hydroxylation of the 3-(1-phenylethenyl)dihydroisoxazole afforded a diol with 80percent de.Cycloaddition reactions of the same alkenyl dihydroisoxazoles with bromonitrile oxide and phenylsulfonylcarbonitrile oxide occurred with 10-46percent de; opposite diastereomers were preferred in the reactions of 3-ethenyl- and 3-(1-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.