Rhodium-catalyzed asymmetric cyclodimerization of oxabenzonorbornadienes and azabenzonorbornadienes: scope and limitations.

Cationic rhodium(I)-catalyzed cyclodimerization of oxabenzonorbornadienes produced naphtho[1,2-b]furan ring systems in a single step with excellent yields and excellent enantioselectivities. The effect of various Rh(I) catalysts, Ag(I) salts, solvents, and phosphine ligands on the yield and enantioselectivity of the reaction was investigated, and the scope and limitations of this reaction with various oxabicyclic alkenes were studied. Similar results were obtained with the azabenzonorbornadiene analogues, providing the corresponding cyclodimerization products in excellent yields and excellent enantioselectivities.