Elemental steps of the thermodynamics of dihydropyrimidine: a new class of organic hydride donors

Abstract

25 Dihydropyrimidine derivatives, a new class of organo-hydrides, were designed and synthesized by the Biginelli reaction. For the first time, the thermodynamic driving forces of the six elemental steps to obtain a hydride in acetonitrile were determined by isothermal titration and electrochemical methods, respectively. The effects of molecular structures and substituents on these thermodynamic parameters were examined, uncovering some interesting structure–reactivity relationships. Both the thermodynamic and kinetic studies show that the hydride transfer from dihydropyrimidines to 9-phenylxanthylium (PhXn⁺ClO₄⁻) prefers a concerted mechanism.