Mechanism of the Fe(iii)-catalyzed synthesis of hexahydropyrimidine with α-phenylstyrene: a DFT study.

It is very important to develop multiple C-H substitution reactions of simple alkenes to obtain complex unsaturated components. The present study focuses on a theoretical investigation of the plausible mechanism in the Fe(OTf) 3 -catalyzed tandem amidomethylative reactions of α-phenylstyrene. Bis(tosylamido)methane is activated by Fe(OTf) 3 to form tosylformaldimine and its Fe(OTf) 3 -adduct. The Fe(OTf) 3 -adduct undergoes an intermolecular aza-Prins reaction with α-phenylstyrene to form allylamide. The DFT data support the formation of the hexahydropyrimidine derivative from allylamide, and "condensation/iminium homologation/intramolecular aza-Prins" is the optimal reaction path. At the same time, a possible reaction pathway for the conversion of the hydrolysate 1,3-diamide derivative to the hexahydropyrimidine (HHP) derivative is given. This work is thus instructive for understanding Fe(iii)-based tandem catalysis for the amidomethylative multiple-substitution reactions of alkenes.