Lewis Acids Promoted Formal Intramolecular [3+2] Parallel and Cross-Cycloadditions of Cyclopropane 1,1-Diesters with Allenes

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.