Lewis acid catalyzed intramolecular [3+2] cross-cycloaddition of donor-acceptor cyclopropanes with carbonyls: a general strategy for the construction of acetal[n.2.1] skeletons.

Build a bridge: The first catalytic intramolecular [3+2] cycloaddition of monodonor-monoacceptor cyclopropanes (see scheme) provides a general and efficient strategy for construction of structurally diverse acetal[n.2.1] and 1,4-dioxygen-substituted cyclic skeletons, which are widely distributed in biologically important natural products.