Regio- and face-selective cycloaddition of benzonitrile oxide and C,N-diphenylnitrone to 6,8-dioxabicyclo[3.2.1]oct-3-ene

Abstract

Benzonitrile oxide, generated by dehydrochlorination of benzohydroximoyl chloride, undergoes regioand face-selective cycloaddition to 6,8-dioxabicyclo[3.2.1]oct-3-ene 5 yielding a 4:1 mixture of 4,5-dihydroisoxazoles 6 and 7. Both products have exo-stereochemistry resulting from approach of the nitrile oxide from the face opposite the methyleneoxy bridge. The structures of the adducts were determined by ¹H NMR spectroscopy and, in the case of compound 6, by X-ray crystallography. The corresponding reaction with C,N-diphenylnitrone yielded three of the eight possible isoxazolidines, the major isomer being exo,endo-adduct 16.