REACTION OF PHOSPHOLE SULFIDES WITH DIAZOALKANES AS A NEW ROUTE TO PHOSPHININES

The reaction of ethyl diazoacetate with 1-(methylthio)-3,4-dimethylphosphole 1-sulfide (6) in refluxing xylene leads to the corresponding diene-carbene [2 + 1] cycloadduct 7. The sterochemistry of 7 was established by X-ray crystal structure analysis. Compound 7 is converted into 2-(ethoxycarbonyl)-4,5-dimethylphosphinine (4) upon reaction with triphenyl phosphite at 160-degrees-C. On the basis of the X-ray data, the proposed mechanism includes the opening of the cyclopropane ring of 7 with selective phosphorus-assisted migration of the ethoxycarbonyl group. This kind of chemistry can be transposed to a 2,2'-biphosphole to prepare a 2,2'-biphosphinine.