Lewis Acid Catalyzed Intramolecular [4+2] and [3+2] Cross‐Cycloaddition of Alkynylcyclopropane Ketones with Carbonyl Compounds and Imines

One brick, two bridges: The choice of the catalyzing Lewis acid (LA, π: π-electrophilic, σ: σ-electrophilic) determines the pathway ([4+2] or [3+2]) of catalytic intramolecular cycloaddition reactions (IMCCs) of alkynylcyclopropane (ACP) ketone. This method provides a general strategy for stereoselective construction of structurally diverse bridged oxa-/aza-[n.3.1] and oxa-/aza-[n.2.1] skeletons (see scheme).