Computational insights into the S3 transfer reaction: A special case of double group transfer reaction featuring bicyclically delocalized aromatic transition state geometries.

An unusual pericyclic process that involves the intermolecular transfer of thiozone (S3 ) is computationally described. The process can be considered as a special case of double group transfer reaction whereby the two migrating groups are connected to the same substituent, taking place in a concerted manner via transition states featuring two five-membered C2 S3 rings fused together. Analysis of the aromaticity at the TS geometries by computing NICS values at the (3,+1) RCPS as well as ACID calculations confirms the aromatic character of each C2 S3 ring, thus resulting in bicyclically delocalized aromatic structures. The free energy barriers for the transfer of S3 are relatively similar (40-50 kcal mol-1 ) to those computed for typical double H group transfer reactions. The similarities and differences between these processes have been further analysed by applying ASM-EDA and NBO approaches to the model reactions between ethene and ethane, and ethene and 1,2,3-trithiolane. © 2017 Wiley Periodicals, Inc.