Mimicking a biocatalytic system has been one of the prevalent strategies for the design of novel and efficient chemical transformations. Among the enzyme-catalyzed reactions, the cooperative interplay of Lewis- and Brønsted-acidic functionalities at active sites represents a common feature in activating reactants. Employing MIL-101(Cr) as a biomimetic platform, we customize a sulfonic group (SO3H) into its hierarchical pores to generate a heterogeneous catalyst for transfer hydrogenation of imines by using Hantzsch ester as the reductant. Both aldimines and ketimines were efficiently converted to their hydrogenated counterparts in a manner similar to metal enzymes. The Cr3+ node and sulfonic acid functionality encapsulated in MOF cages worked cooperatively in promoting this transformation, resulting in an enhanced reactivity as compared to its homogeneous analogue. Furthermore, MIL-101(Cr)-SO3H could be recycled for many times without considerable loss in reactivity.Keywords: biomimetic catalyst; Brønsted acid; Hantzsch ester; hydrogenation; imine; metal−organic frameworks;

•An improved protocol for N-dealkylative addition of trialkylamines with DMAD.•High efficiency under mild oxygen-free conditions.•Good to excellent yield and better substrate tolerance.Herein we present a continuous improvement of visible-light mediated N-dealkylative addition of tertiary amines to dimethyl acetylenedicarboxylates (DMAD) using alkyl halogenides as external oxidants together with base additives. This method is highlighted by excellent tolerance with various tertiary amines and good to excellent yields in short reaction time under mild conditions.Download high-res image (76KB)Download full-size image

Thiourea-based hydrogen bond donor has been recently disclosed by our group to be an efficient organocatalyst for cross-dehydrogenative coupling (CDC) reactions. Here we present a detailed mechanistic study of this reaction using NMR spectroscopy and kinetic isotope effect experiment. The results revealed that α-amino peroxide is the true intermediate within the catalytic cycle, formed via a thiourea-catalyzed rate-determining hydrogen atom transfer (HAT) process. These experimental investigations not only provide somewhat insight into the mechanism of thiourea-catalyzed CDC reactions but also promote their further applications.Download high-res image (169KB)Download full-size image

•First expanding application of cyclopentadiene-based Brønsted acid catalyst.•Attractive approach with mild reaction conditions and low catalyst loading.•Enantioselective reduction of 2-substituted quinolines.A simple and readily available cyclopentadiene-based Brønsted acid was employed to catalyze the transfer hydrogenation of 2-substituted quinolines using Hantzsch ester as the hydrogen source. This conceptually new designed organocatalyst demonstrates remarkably high efficiency for this transformation and a variety of substituted 1,2,3,4-tetrahydroquinoline derivatives were afforded in excellent yields under mild reaction conditions.This study reports on the first transfer hydrogenation of 2-substituted quinolines promoted by cyclopentadiene-based Brønsted acid catalyst with Hantzsch 1,4-dihydropyridine as the hydrogen source.Download high-res image (115KB)Download full-size image

The Suzuki–Miyaura reaction is one of the most popular and efficient routes for the formation of carbon–carbon bonds in both laboratorial and industrial synthetic processes. Here, we report for the first time that a Au–Pd/TiO2 catalyst could be utilized efficiently for Suzuki–Miyaura reactions at ambient conditions under visible light with high activity and reusability. Mechanistic investigation by means of experimental methods revealed that through the strong local surface plasma resonance of Au under the visible light, the hot electrons of Au could be injected into Pd in the bimetallic nanoparticles, thus facilitating activation of the aryl halides. Meanwhile, the electropositive Au tended to gain electrons from TiO2, resulting in the separation of the photogenerated electron/hole pairs of TiO2, which enabled the holes to activate aryl boronic acids. This Au–Pd/TiO2 catalyst not only expands the application scope of Suzuki–Miyaura reactions under mild conditions but will also inspire further exploitation of the direct harvesting of visible light by nanomaterials for a wide range of chemical reactions.

Over the last decade, the use of (thio)urea derivatives as organocatalysts in organic chemistry has increased rapidly. One of the key features is their ability to activate substrates and subsequently stabilize partially developing negative charges (e.g., oxyanions) in the transition states employing explicit double hydrogen bonding. Among (thio)urea-based catalysts, N,N′-bis[3,5-bis(trifluoromethyl)phenyl]thiourea developed by Schreiner's group (abbreviated here as Schreiner's thiourea) has played a very important role in the development of H-bond organocatalysts. Nowadays it is used extensively in promoting organic transformations, and the 3,5-bis(trifluoromethyl)phenyl motif thereof is used ubiquitously in H-bond catalysts. This review summarizes the key developments of Schreiner's thiourea-mediated reactions with the aim to further expand the applications of (thio)urea-based catalysts.

This study reports on the first transfer hydrogenation of 2-substituted quinolines promoted by a thiourea catalyst with Hantzsch ester as the hydrogen source. A wide range of quinoline derivatives, including 2-alkylquinolines and 2-arylquinolines, were efficiently reduced to give 1,2,3,4-tetrahydroquinolines with good to excellent yields. The operational simplicities and conveniences of this reaction pathway render this protocol considerably promising in the preparation of biologically active tetrahydroquinoline derivatives.

Over the last decade, the use of (thio)urea derivatives as organocatalysts in organic chemistry has increased rapidly. One of the key features is their ability to activate substrates and subsequently stabilize partially developing negative charges (e.g., oxyanions) in the transition states employing explicit double hydrogen bonding. Among (thio)urea-based catalysts, N,N′-bis[3,5-bis(trifluoromethyl)phenyl]thiourea developed by Schreiner's group (abbreviated here as Schreiner's thiourea) has played a very important role in the development of H-bond organocatalysts. Nowadays it is used extensively in promoting organic transformations, and the 3,5-bis(trifluoromethyl)phenyl motif thereof is used ubiquitously in H-bond catalysts. This review summarizes the key developments of Schreiner's thiourea-mediated reactions with the aim to further expand the applications of (thio)urea-based catalysts.