The dipolar 3+2-cycloaddition reactions of 3-aroylpyrrolo2,1-c1,4benzothiazine-1,2,4-triones with diarylnitrones lead to the formation of benzobisoxazolo5',4':2,3pyrrolo1,2-d1,4thiazines. The reaction proceeds stereoselectively to form exclusively the (2aS*,3R*,5aS*) diastereomers. Density functional theory computations for the model reaction showed that the (2aS*,3R*,5aS*) diastereomers are both kinetically and thermodynamically preferred over the alternative (2aS*,3S*,5aS*) diastereomers. At room temperature in solution, the resulting cycloadducts dissociate into the starting reagents, with stability highly dependent on the electronic properties of the substituents in the nitrone moiety.
Khramtsova et al. (Thu,) studied this question.