Synthetic and Theoretical Studies on the Reduction of Electron Withdrawing Group Conjugated Olefins Using the Hantzsch 1,4-Dihydropyridine Ester

The Hantzsch 1,4-dihydropyridine ester (1) has been observed to be a useful selective reducing
agent for the reduction of electron-withdrawing conjugated double bonds. The rate of this reaction
was observed to be dependent upon the nature of the conjugated substituents and, consequently,
the electronic nature of the unsaturated double bond. Theoretical calculations confirmed the
importance of the HOMO−LUMO gap for this reaction and implicated a hydride transfer, agreeing
with the experimentally observed reaction rate order. The calculations also revealed the importance
of a boatlike structure of the 1,4-dihydropyridine nucleus as well as a trans arrangement of the
ester groups to facilitate the hydride transfer.