The thioacyl isocyanate-acyl isothiocyanate rearrangement

The title rearrangement, involving a 1,3-shift of a substituent on an acyl(thioacyl) group is investigated computationally at ab initio and DFT levels of theory (G2(MP2,SVP) and B3LYP/6-31G*). The computed order of migratory aptitudes is Br > Cl > NMe2> F, SCH3, SH > OMe, NH2> OH>>H>>Me, in good agreement with experimental data reported by Goerdeler. The acyl isothiocyanates are of lower energy than the thioacyl isocyanates, but in many cases an equilibrium between the two is achievable