Equilibration of the [2+2] Cycloaddition of Silyl Enol Ethers Catalyzed by Ethylaluminium Dichloride: Diastereoselectivity Switch in the Synthesis of Fused Cyclobutanes

The process by which the reaction between silyl enol ethers and acrylates reached equilibrium through an EtAlCl2-catalyzed [2+2] cycloaddition was characterized. The mechanism and substrate scope of the retro [2+2] cycloaddition were investigated. The trans or cis isomers can be selectively obtained by controlling the reaction temperature, although the substrate scope was found to be limited.