FACILE CONSTRUCTION OF TERPENOID FRAMEWORKS BY CYCLOADDITIONS WITH METHYL 2-CHLOROCYCLOPROYLIDENACETATE

Article abstract of DOI:10.1016/S0040-4020(01)90289-3

Methyl 2-chlorocyclopropylidenacetate (2-Cl) smoothly <2+4>cycloadds to cyclopentadiene and 2,3-dimethylbutadiene at room temperature.With the donorsubstituted cyclohexadienes 6, 9 at elevated temperatures (60, 120 deg C respectively) 2-Cl reacts without any observable regioselectivity.In contrast, 2-Cl, when treated with lithium cyclohexadienolates 13 undergoes completely regioselective iterative Michael additions with subsequent intramolecular γ-elimination to give tricyclic γ-ketoesters 16 in good to excellent yields.The products 16 can readily be transformed to multifunctional bicyclo<2.2.2>octane as well as bicyclo<3.2.1>octane derivatives 17.A rationalization of the unprecedented reactovity of 2-Cl on the basis of its available structural features (IP(?), ¹J_C,C', C=C bond length) is offered.