Induction of asymmetry on the [4+3] cycloaddition reaction of C2-functionalized furans

A study of the induction of asymmetry on the [4+3] cycloaddition reaction of some 13 C2-substituted furan derivatives with 2-oxyallyl cation is presented. The asymmetry was induced by a chiral auxiliary on C2 of furan. A cis diastereospecificity and a high endo diastereoselectivity are observed in almost all studied cases. On decreasing the distance between the stereocenter of the chiral auxiliary and the reactive C2-carbon of the furan ring, the π-facial diastereoselectivity is increased, especially by using chiral furyl-sulfoxides.