Stereo- and regioselectivity in nitrile oxide cycloaddition reactions to norethisterone acetate as dipolarophile

: Benzo- and anthracenenitrile oxides undergo 1,3-dipolar cycloaddition reactions with 17 α- acetate norethisterone affording the expected isoxazoline and isoxazoles derivatives in good yields and as single regioisomers. The structures of all the new compounds were elucidated on the basis of the corresponding analytical and spectroscopic data, which were presented and discussed. The stereo- and regiochemical outcome of the cycloadditions were also accounted on the basis of 1,3-dipolar cycloaddition theory and computational investigations. Electronic (Frontier Orbital theory) and steric effects are at work in orienting selectively the cycloaddition to specific regioisomeric steroids.