Stereoselectivesynthesis of chiral sulfinylcyclopropane derivatives and stereochemistry of the asymmetric 1,2-rearrangements are described. Heating of each stereoisomeric mesylate of (Ss)-1-(1-hydroxy-1-phenylethyl)-1-p-toluenesulfinylcyclopropane, followed by reduction of the sulfinyl group with acetyl chloride, provided (R)-(−)-4-methyl-4-phenyl-1-p-toluenesulfenylcyclobutene. In contrast, the same