Theoretical insights into the reaction mechanism and solvation effect of conjugate addition of dimethyl propanedioate to 1-nitroprop-1-ene catalyzed by cinchona alkaloids

Abstract

The conjugate addition reaction of dimethyl propanedioate to 1-nitroprop-1-ene catalyzed by cinchona alkaloid derivatives (QD-R″) is investigated using density functional theory calculations in this paper. The geometry optimizations and frequency calculations were carried out at the B3LYP/6-31G(d,p) level, and the accurate energetic parameters were obtained by the B3LYP/6-311++G(2df,2p) method. Our calculations find that cinchona alkaloids with –NCONHPh and –NH electron-withdrawing substituents in the quinuclidine show stronger activation on the system than that with –CH2 electron-donating substituent. The NBO charge analysis for the tertiary amine nitrogen of the quinuclidine affirms that the electron-withdrawing substituents decrease the negative charges on the tertiary amine nitrogen atom, which is favorable for the second proton transfer from the catalyst to α-carbon of 1-nitroprop-1-ene. As a result, the calculations show that the charge distribution of the tertiary amine nitrogen affects the catalytic efficiency of the system. Furthermore, a detailed analysis of the effects of the solvent on the system further revealed the regularity.