Diastereoselective synthesis of methylated alpha-methoxy-beta-oxabicyclo[3.2.1]oct-6-en-3-ones. Contrathermodynamic introduction of methoxy group by low temperature [4+3]-cycloaddition

A series of alpha,alpha-dimethoxysilyl enol ethers has been prepared and sh own to undergo diastereoselective [4+3]-cycloaddition with furan and cyclop entadiene in the presence of catalytic trimethylsilyl triflate. The alpha-m ethoxy group of the resulting title oxabicyclics preferentially adopts the contrathermodynamic equatorial position.