Theoretical Study on Hetero‐Diels–Alder Reaction of Butadiene with Benzaldehyde Catalyzed by Chiral InIII Complexes

Abstract

AbstractThe mechanism of the hetero‐Diels–Alder reaction of butadiene with benzaldehyde catalyzed by chiral N,N′‐dioxide/In(OTf)3 complexes was studied theoretically by using density functional theory (DFT) and model system. The computational results indicate that the catalyzed reaction proceeded through a concerted mechanism via a highly zwitterionic transition state. The lowest energy barrier was 11.8 kJ mol–1, which is 63.0 kJ mol–1 lower than that of the uncatalyzed reaction. The results indicate that the endo approach is advantageous over the exo approach, because exo transitions states suffer from more steric hindrance than the endo transitions states as a result of interactions among the substrates, the trifluoromethanesulfonic group and the R4 groups of the ligand. The (S) configuration was observed predominantly over the (R) form, because there is no distinguishable repulsion between butadiene and the exo amino side or the endo amino side of the ligand. Besides, the interactions between the terminal hydrogen atoms of butadiene and the oxygen atoms of the trifluoromethanesulfonic group make the structure more stable. Thus, the experimental results were explained well by calculation of the chiral N,N′‐dioxide/In(OTf)3 complex catalyzed hetero‐Diels–Alder reaction at the molecular level.