[2+2] Cycloaddition Reaction between Allenyl Sulfides and Electron Deficient Olefins Promoted by Lewis Acids

Methylenecyclobutane derivatives are prepared by the Lewis acid promoted [2+2] cycloaddition reactions of 1-substituted-1-methylthio-1,2-propadienes and electron deficient olefms. The asymmetric [2+2] cycloaddition of the allenyl sulfides also proceeds in high enantioselectivity by the use of a chiral titanium reagent.