The Role of the Sulfinyl Group on the Course of the Reactions of 3-p-Tolylsulfinylfuran-2(5H)-ones with Nitrones. Synthetic Uses of Cycloreversion Processes

The reaction of enantiopure 3-p-tolylsulfinylfuran-2(5H)-ones (2a and 2b) with cyclic (4) and acyclic (6) nitrones afforded furoisoxazolidines (5 and 7) in high yields under mild conditions. The reactivity of the dipolarophile was dramatically enhanced by the sulfinyl group, which modulated the π-facial selectivity (it was complete for reactions from 2b, yielding only the anti adducts) and was the main controller of the endo/exo selectivity. Cycloreversion processes from the resulting sulfinyl furoisoxazolidines proceeded readily and were to be considered to account for an improvement in the selectivity (facial and endo/exo) and even for an inversion of it when the composition of the reaction mixtures obtained under kinetic and thermodynamic conditions were quite different.