1,3-cycloaddition of nitrile oxides to cyclic and open-chain 4-oxo-2-sulfinylbut-2-enoic acid derivatives

The reactions of tert-butyl (E)-4,4-diethoxy-2-p-tolylsulfinylbut-2-enoate with benzonitrile, acetonitrile, and bromoformonitrile oxides yield isoxazo les. However, (S-5,S-S)- and (R-5,S-S)-5-ethoxy-3-p-tolylsulfinylfuranones with benzonitrile oxide afford isoxazolines. The reactivity of the double b ond as a dipolarophile is strongly increased by the sulfinyl group. This is also the case of the regioselectivity, which usually is opposite to that e xhibited by dipolarophiles lacking the sulfinyl group. Electrostatic intera ctions seemingly explain this behaviour. The pi-facial selectivity of the r eactions with the cyclic dipolarophiles is dependent on steric effects, but some role seems to be exerted by electrostatic attraction. (C) 1999 Elsevi er Science Ltd. All rights reserved.