Development of a Formal Catalytic Asymmetric [4 + 2] Addition of Ethyl-2,3-butadienoate with Acyclic Enones

Allene esters are unique not only as excellent electrophiles but also because of their ability for subsequent reactivity after the initial nucleophilic attack. A mechanistically inspired cyclization using ethyl-2,3-butadienoate and acyclic enones to provide dihydropyrans in excellent yields and enantioselectivity under solvent-free conditions at room temperature is reported.