Asymmetric Knoevenagel‐Phospha‐Michael Tandem Reaction Synergistically Catalyzed by Achiral Silanols and Grafted Chiral Amines on Mesoporous Silica

Abstract

Highly efficient and enantioselective asymmetric Knoevenagel-phospha-Michael tandem reactions have been achieved on bifunctional heterogeneous catalysts with inherent silanols as acidic sites and immobilized chiral amines as basic sites. Final products were afforded in yields of up to 99% and ee values of up to 99%. The effects of substituents on benzaldehyde and molecular dimensions of phosphites have also been investigated. Larger substrates can access the catalytic site inside larger mesoporous pores, thereby improving both of yield and ee of final products.

Heterogeneous Synergistic Catalysis for Promoting Aza-Michael–Henry Tandem Reaction for the Synthesis of Chiral 3-Nitro-1,2-Dihydroquinoline

“…Immobilized acid and base active sites could supply efficient synergistic catalysis as previously reported [36][37][38][39][40][41]. Our group more recently reported efficient synergistic catalysis achieved with inherent achiral silanols of mesoporous silica as acidic sites and immobilized chiral amines as basic sites in the direct asymmetric aldol condensation [42], the asymmetric Henry-Michael one-pot reaction [43], oxa-Michael-Michael cascade reaction [44] and Knoevenagel-phospha-Michael tandem reaction [45]. The heterogeneous bi-functional catalysts were not only demonstrated effective in the synergistic catalysis, but also were easy to be separated and recycled.…”

Application of chiral recyclable catalysts in asymmetric catalysis

“…This catalyst 37 (20 mol%), consisting of Si-lanol hydroxyl group and chiral amine, was employed to catalyze the tandem reaction of aromatic aldehyde, malononitrile, and phosphite ( Scheme 37 ). 126 The resulting product exhibited a yields of 99% and an ee of 99% ee . Furthermore, the researchers investigated the impact of benzaldehyde substituents and phosphite molecular size.…”

One‐pot oxidant‐free dehydrogenation‐Knoevenagel tandem reaction catalyzed by a recyclable magnetic base‐metal bifunctional catalyst

“…[ 44 ] In recent years, some bifunctional catalysts have been developed and exhibit high catalytic activity in a series of tandem reactions. [ 45–61 ] For example, Dong et al . prepared a bifunctional heterogeneous catalyst Pd(0)@UiO‐68‐AP, which was applied to catalyze oxidation–Knoevenagel condensation tandem reaction from benzyl alcohols.…”

“…[44] In recent years, some bifunctional catalysts have been developed and exhibit high catalytic activity in a series of tandem reactions. [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61] For example, Dong et al prepared a bifunctional heterogeneous catalyst Pd(0)@UiO-68-AP, which was applied to catalyze oxidation-Knoevenagel condensation tandem reaction from benzyl alcohols. [62] In 2017, Gu et al synthesized a hollow sphericalstructured HCP − A − B catalyst with acidic and basic sites for catalyzing one-pot hydrolysis-Henry and hydrolysis-Knoevenagel reactions.…”