Formation of selenaphosphole isomers from 1,2,4-selenadiphosphole by cycloaddition reaction. A synthetic and ab initio quantum chemical study

Abstract

The reaction of 1,2,4-selenadiphosphole with dimethyl acetylenedicarboxylate resulted in a mixture of 1,2-selenaphosphole and 1,3-selenaphosphole at 110 °C in boiling toluene. The mechanism has been interpreted by quantum chemical calculations. A cycloreversion process of the 1,2,4-selenadiphosphole has been ruled out on the basis of the high energy of the selenaphosphirene intermediate. A [4 + 2] cycloaddition of the acetylene on the selenadiphosphole results in the 1,2-selenaphosphole via an intermediate. A [3 + 2] cycloaddition via a single transition structure results in the 1,3-selenaphosphole. While the energies of the products differ considerably, transition structures on the two cycloaddition routes are predicted to have similar energies, explaining the observed 1 : 1 product ratio.