A NEW SYNTHETIC METHOD FOR CYCLOPENTANONES VIA FORMAL [3+2] CYCLOADDITION REACTION

A new synthetic method for cyclopentanone derivatives via formal [3+2] cycloaddition reaction of 2-oxyallyl cation and an alkene was develop ed. Under the influence of EtAlCl(2) or AlCl3, xy-1-(methylthio)-2-(tr iisopropylsiloxy)-1-propene or 1-acetoxy- 3-(methylthio)-2-(triisoprop ylsiloxy)-2-tridecene reacted with various kinds of alkenes to afford 2-(methylthio)cyclopentanone derivatives in good yield. The reaction w as highly regioselective to yield the sterically more hindered regiois omer, which indicates that the initial C-C bond formation reaction bet ween an alkene and the (1-(methylthio)-2-siloxy)allyl cation intermedi ate occurs at the gamma-position of sulfur.