Enantioselective Formal [3+3] Annulation for the Direct Construction of Bicyclic Skeletons with Four Stereogenic Centers

An enantioselective formal [3+3] annulation reaction of cyclic ketones with enones has been developed. In the presence of 20 mol % of
pyrrolidine-thiourea 1a or N-(pyrrolidin-2-ylmethyl)trifluoromethanesulfonamide 1i, the reactions afford bicyclo [3.3.1] adducts in moderate to
good yields with good to high enantioselectivities under mild conditions.