Asymmetry induction on the [4C(4π)+3C(2π)] cycloaddition reaction of C2-functionalized furans: influence of the chiral auxiliary nature

The study of the π-facial diastereoselectivity in the [4+3] cycloaddition reaction of thirteen different chiral 2-substituted furans with oxyallyl cations, under sonochemical and/or thermal conditions, is presented. In almost all studied furans, a cis diastereoselectivity and a high endo diastereoselectivity is observed. Decreasing the distance between the closest stereocenter of the chiral auxiliary and the reactive C2-carbon of the furan ring, increases the π-facial diastereoselectivity, especially by using chiral furyl-sulfoxides.