Lewis-Acid-Catalyzed Cyclization of Bicyclo[1.1.0]butanes with Alkenyl Cyclic Dithioacetals for the Synthesis of 11-Membered Bicyclic Medium-Sized Rings

Medium-sized rings are valuable synthetic scaffolds yet challenging to construct. Herein, we report a Lewis-acid-catalyzed (8 + 3) cycloaddition of bicyclo[1.1.0]butanes with alkenyl cyclic dithioacetals that provides efficient access to previously inaccessible 11-membered bicyclo[8.1.1] skeletons. Driven by strain release and catalyzed by Lu(OTf) 3, this ring expansion proceeds under mild conditions, exhibits a broad substrate scope, and delivers products in excellent yields (46 examples, with yields up to 94%). Mechanistic studies and DFT calculations support a pathway involving sequential nucleophilic attack, ring opening, and regioselective intramolecular 1,4-addition.