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A Lewis acid catalyzed intramolecular [3 + 2] cross cycloaddition of cobalt-alkynylcyclopropane 1,1-diesters with carbonyls has been successfully developed. Together with simple and efficient postcycloadditions of the cobalt-alkyne moiety, a general and efficient strategy for construction of structurally complex and diverse medium-sized skeletons and related polycycles was supplied successfully.

A novel Lewis acid promoted formal intramolecular [3 + 2] parallel/cross-cycloaddition of cyclopropane 1,1-diesters with allenes has been successfully developed, in which the two C═C of allenes were involved respectively. This provides a general and efficient strategy for the construction of structurally diverse [4.3.0]nonane and [3.2.1]octane skeletons.

The title reaction is successfully developed, and applied to the total synthesis of the tetracyclic diterpenoids phyllocladanol (XX) and phyllocladene (XXI).

The Lewis acid-regulated selective title cycloadditions are developed by using common starting materials and under mild conditions.

A novel Lewis acid catalyzed formal intramolecular [3 + 3] cross-cycloaddition (IMCC) of cyclopropane 1,1-diesters has been successfully developed. This supplies an efficient and conceptually new strategy for construction of bridged bicyclo[2.2.2]octane skeletons. This [3 + 3]IMCC could be run up to gram scale and from easily prepared starting materials. This [3 + 3]IMCC, together with our previously reported [3 + 2]IMCC strategy, can afford either the bicyclo[2.2.2]octane or bicyclo[3.2.1]octane skeletons from the similar starting materials by regulating the substituents on vinyl group.

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.