Free-Radical Ring Expansion of Fused Cyclobutanones: Stereospecific Construction of 5,7-, 6,7-, 7,7-, 8,7-, and 5,8-Cis-Fused Bicyclic Systems

Article abstract of DOI:10.1021/jo00052a034

A new method of appending seven- and eight-membered rings to cycloalkenes is described.Treatment of selected alkene precursors with an ω-bromoalkyl ketene or a keteniminium salt leads to haloalkyl cyclobutanone formation.Tri-n-butyltin hydride promoted ring expansion then yields the annulated product.Since the initial cyclobutanone is cis fused, the final product is also produced stereospecifically with a cis ring fusion.