One perverted rearrangement: a detailed quantum-chemical study of Thiemann-type SO2-mediated conversion of nitrile oxide into isocyanate

Abstract

Isocyanates play an essential role in modern manufacturing processes, especially in polyurethane production. There are numerous synthesis strategies for isocyanates both in industrial and laboratory conditions, which do not prevent searching for alternative highly efficient synthetic protocols. Here, we report a detailed theoretical investigation of the mechanism of sulfur dioxide-catalyzed rearrangement of the phenylnitrile oxide into phenyl isocyanate, which was first reported in 1977. The DLPNO-CCSD(T) method and up-to-date DFT protocols were used to perform a highly accurate quantum-chemical study of the rearrangement mechanism. An overview of various organic and inorganic catalysts has revealed other potential catalysts, such as sulfur trioxide and selenium dioxide. Furthermore, the present study elucidated how substituents in phenylnitrile oxide influence reaction kinetics. This study was performed by a self-organized collaboration of scientists initiated by a humorous post on the VK social network.