Synthesis of three-dimensional fused and spirocyclic oxygen-containing cyclobutanone derivatives

An approach to fused and spirocyclic oxygen-containing cyclobutanone derivatives based on ketene [2+2] cycloaddition with vinyl ethers is described. Using alicyclic chloroanhydrides as ketene sources as well as cyclic vinyl ethers in the reaction resulted in the formation of three-dimensional conformationally restricted building blocks of interest to medicinal chemistry and organic synthesis. In particular, 2-oxaspiro(bicyclo[3.2.0]heptane-7,1′-cycloalkane)-6-ones and 2-oxaspiro(bicyclo[4.2.0]octane-8,1′-cycloalkane)-6-ones were obtained. The procedure involves readily available and inexpensive starting materials and allows construction of complex molecular architectures on a large scale in a single run.