First Example of a Lewis Acid-Promoted [2 + 1] Cycloaddition of a 1-Thio-2-silylethene

First Example of a Lewis Acid-Promoted [2 + 1] Cycloaddition of a 1-Thio-2-silylethen

[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 benzenesulfonylacrylates 3 in the presence of SnCl4 at −78 °C gave sulfone-substituted cyclopropanes 4 as single stereoisomers. The structure of one of these crystalline cyclopropane products was elucidated by X-ray crystallographic analysis. The relative stereochemistry of the cyclopropane ring carbon (C2) and selenosilylmethyl group was determined as R,R and S,S, which is consistent with previous mechanical considerations and the NOE determination. 2-Sulfinyl acrylate 2 did not undergo this cycloaddition. 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−SnCl4 complexes and activation energies in the synclinal addition of 1 to the complexes