[2+1] cycloaddition reactions of a 1-seleno-2-silylethene to 2-sulfonylacrylates: Stereoselective synthesis of sulfone-substituted cyclopropanes

Reaction of 1-(phenylseleno)-2-(trimethylsilyl)ethene 1 and methyl or ethyl 2-p-toluene- or benzene-sulfonylacrylates 3 in the presence of SnCl4 at -7 8 degrees C gave sulfone-substituted cyclopropanes 4 as single stereoisomer s. The structure of one of these crystalline cyclopropane products was eluc idated by X-ray crystallographic analysis. The relative stereochemistry of the cyclopropane ring carbon (C-2) and selenosilylmethyl group was determin ed as R,R and S,S, which is consistent with previous mechanical considerati ons and the NOE determination. 2-Sulfinyl acrylate 2 did not undergo this c ycloaddition. The difference in reactivity of the sulfoxide 2 and sulfones 3 toward 1 was explained by comparison of LUMO levels of 2-SnCl4 and 3-SnCl 4 complexes and activation energies in the synclinal addition of 1 to the c omplexes.