Thermal [2 + 2]-Cycloaddition of Ketenes with Chiral Enol Ethers: Route to Densely Substituted Cyclobutanones

Access to chiral
polysubstituted cyclobutanones by [2 + 2]-cycloaddition
of ketenes with chiral acyclic enol ethers is reported. A wide variety
of easily accessible di- and monosubstituted ketenes were found to
react with a very high degree of stereoselectivity with chiral, Stericol
derived, acyclic enol ethers. This combination of simple reagents
provides straightforward entry to highly substituted enantioenriched
cyclobutanones.