NEW ACCESS TO DI-EXO-METHYLENECYCLOBUTANES VIA [2+2] CYCLOADDITION OF 3-METHYLTHIO-4-TRIMETHYLSILYL-1,2-BUTADIENE WITH ALKENES MEDIATED BY A LEWIS-ACID
Methylthio-substituted allenylmethylsilane, a kind of allylsilane, undergoes only [2 + 2] cycloaddition reaction with alkenes mediated by a Lewis acid to afford the corresponding methylenecyclobutanes which are readily converted to di-exo-methylenecyclobutanes by rite sequential oxidation-1,2-elimination in good yield. Di-exo-methylenecyclobutane is also successfully applied to construct a bicyclo[5.2.0]nonenone skeleton by the reaction with 2-oxyallyl cation.