ORGANOTIN TRIFLATE AS PRACTICAL CATALYST FOR MICHAEL ADDITION OF ENOL SILYL ETHERS

Dibutyltin bis(triflate) is a mild Lewis acid which catalyzes clean Michael addition of enol silyl ethers. The new catalyst allows to employ various labile acceptors such as methyl vinyl ketone and 2-cyclopentenone which do not undergo smooth reaction with conventional Lewis acids. A variety of enol silyl ethers are also employable and thus 2-(trimethylsiloxy)propene, the simplest one in this class of compounds, can be used. The adducts of enol silyl ethers of cycloalkanones with vinyl ketones are readily cyclized to give the desired annulated enones free from isomers. Consequently, a practical version of the Robinson annulation has been realized.