Dicobalt hexacarbonyl complexes of conjugated enynes as equivalents of tetradentate synthons for the preparation of bicyclo [3.3.0] octanes

Abstract

A method has been developed for the acylation of dicobalt hexacarbonyl (DCHC) complexes of conjugated enynes with α, β-unsaturated acylium salts as a general route to DCHC complexes of 3-keto-1,6-enynes. Conditions have been found for the selective Grignard reaction or hydride reduction of the carbonyl group of the latter. The method has been found to be applicable to [2+2+1]-cycloaddition at a sorbent surface for the DCHC complexes of a variety of functionally substituted 1,6-enyne substrates. A novel convergent strategy is proposed for the synthesis of substituted bicyclo[3.3.0]octanes by steps involving cationic acylation of the DCHC complexes of conjugated enynes with α,β-unsaturated acylium salts, modification of the carbonyl function in the resulting adducts and intramolecular [2+2+1]-cycloaddition.