Enantioselective Synthesis of Bicyclo[4.4.1]undecane-2,7-dione via Samarium(II)-Mediated Fragmentation of a Cyclopropane Precursor

An efficient six-step synthesis of bicyclo[4.4.1]undecane-2,7-dione was elaborated. Key steps include an enantioselective oxazaborolidine-catalyzed borane reduction (CBS reduction) of 2,3,4,6,7,8-hexahydronaphthalene-1,5-dione to the corresponding diol, and a subsequent (syn-diastereoselective) cyclopropanation. Oxidation then gives tricyclo[4.4.1.01,6] undecane-2,7-dione (>99% ee) which on treatment with two equivalents of samarium(II) iodide undergoes cleavage of the central cyclopropane bond to yield the target compound without any loss of stereochemical information.