DFT study of thermal 1,3-dipolar cycloaddition reactions between alkynyl metal(0) fischer carbene complexes and 3 H-1,2-dithiole-3-thione derivatives

The thermal 1,3-dipolar cycloaddition reaction between alkynyl metal(0) Fischer carbenes and 5-methyl-3H-1,2-dithiole-3-thione to yield 1,3-dithiafulvene has been studied computationally within the Density Functional Theory framework. The transformations involving Fischer carbene complexes and their isolobal analogues (organic esters and corresponding Lewis acid complexes) were compared in terms of regioselectivity, barrier and reaction energies, synchronicity, and aromaticity of the corresponding transition states. These reactions are found to be concerted and completely regioselective toward the formation of the Z-1,3-dithiafulvene isomer, which is kinetically favored. DFT calculations are in good agreement with the experimental outcome of the process, which can be explained by means of the corresponding frontier molecular orbitals of reactants and their electrostatic potentials. © 2010 American Chemical Society.