FREE-RADICAL RING EXPANSION OF FUSED CYCLOBUTANONES - STEREOSPECIFIC CONSTRUCTION OF 5,7-CIS-FUSED, 6,7-CIS-FUSED, 7,7-CIS-FUSED, 8,7-CIS-FUSED, AND 5,8-CIS-FUSED BICYCLIC SYSTEMS

A new method of appending seven- and eight-membered rings to cycloalkenes is described. Treatment of selected alkene precursors with an omega-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.