Catalytic Hydrogenation of Aliphatic Nitro Compounds with Polysilane/Bone Charcoal‐Supported Palladium Catalysts under Continuous‐Flow Conditions

Reductive N-Alkylation of Amines with Ketones Using Heterogeneous Polysilane-Palladium Catalysts under Continuous-Flow Conditions

This work reports a continuous-flow reductive N-alkylation of amines with ketones using molecular hydrogen. The reaction, performed with highly active polysilane-modified heterogeneous palladium catalysts, enables the efficient synthesis of diversely substituted amines under mild flow conditions. The developed catalyst exhibits sustained activity for 5 days (turnover number of >2400). Moreover, the utility of the method is demonstrated by the synthesis of a key intermediate of the active pharmaceutical ingredient teneligliptin.

Catalytic Hydrogenation of Nitrocyclohexane with CuCo/SiO2 Catalysts in Gas and Liquid Flow Reactors

Catalytic hydrogenation of nitrocyclohexane proved to be an attractive alternative source of various chemical compounds: cyclohexanone oxime, cyclohexanone, cyclohexanol, cyclohexylamine and dicyclohexylamine. A growing interest in this reaction has been observed in the last few years. Herein, we present the catalytic performance of Cu/SiO2, Co/SiO2 and CuCo/SiO2 in gas and liquid flow nitrocyclohexane hydrogenation. The analysis of synthesized catalysts morphology (BET, TPR, XRD, TEM) in terms of their catalytic behavior allows us to draw general conclusions and determine the optimal conditions for the production of desired products. Application of the monometallic copper leads to the formation of cyclohexanone as the main product, but with low activity. On the other hand, Co/SiO2 shows high activity but gives cyclohexylamine. Bimetallic system CuCo(3:1)/SiO2 allows for the efficient production of 100% cyclohexanone at 5 bar and 75 °C.

Value-added materials recovered from waste bone biomass: technologies and applications

As the world population increases, the generation of waste bones will multiply exponentially, increasing landfill usage and posing health risks. This review aims to shed light on technologies for recovering valuable materials (e.g., alkaline earth material oxide such as CaO, hydroxyapatite, beta tri-calcium phosphate, phosphate and bone char) from waste bones, and discuss their potential applications as an adsorbent, catalyst and catalyst support, hydroxyapatite for tissue engineering, electrodes for energy storage, and phosphate source for soil remediation. Waste bone derived hydroxyapatite and bone char have found applications as a catalyst or catalyst support in organic synthesis, selective oxidation, biodiesel production, hydrocracking of heavy oil, selective hydrogenation and synthesis of bioactive compounds. With the help of this study, researchers can gather comprehensive data on studies regarding the recycling of waste bones, which will help them identify material recovery technologies and their applications in a single document. Furthermore, this work identifies areas for further research and development as well as areas for scaling-up, which will lead to reduced manufacturing costs and environmental impact. The idea behind this is to promote a sustainable environment and a circular economy concept in which waste bones are used as raw materials to produce new materials or for energy recovery.

Continuous-Flow Synthesis of (R)-Tamsulosin Utilizing Sequential Heterogeneous Catalysis

We describe the continuous-flow synthesis of (R)-tamsulosin, a blockbuster therapeutic drug employed for dysuria associated with urinary stones and benign prostatic hyperplasia, by utilizing sequential heterogeneous catalysis. Two heterogeneous catalysts have been developed for the synthesis, and the key step involves reductive amination of nitriles using dimethylpolysilane-modified Pd on activated carbon/calcium phosphate. Overall, (R)-tamsulosin was obtained in 60 % yield and 64 % ee (99 % ee after recrystallization) in a flow stream through four catalytic transformations without the need for the isolation or purification of any intermediates or byproduct.

Tandem H/D Exchange-SET Reductive Deuteration Strategy for the Synthesis of α,β-Deuterated Amines Using D2O

α,β-Deuterated amines are crucial for the development of deuterated drugs. We intend to introduce the novel tandem H/D exchange-single electron transfer (SET) reductive deuteration strategy with high pot- and reagent-economy by the synthesis of α,β-deuterated amine using nitrile as the precursor. The H/D exchange of the -CH₂CN group was achieved by D₂O/Et₃N, which were also the required reagents in the tandem SmI₂-mediated SET reductive deuteration of the α-deuterated nitrile. The potential application of this method was further showcased by the synthesis of bevantolol-d₄.

Development of Robust Heterogeneous Chiral Rhodium Catalysts Utilizing Acid-Base and Electrostatic Interactions for Efficient Continuous-Flow Asymmetric Hydrogenations

Heterogeneous chiral Rh catalysts based on acid-base and electrostatic interactions have been developed. The robust catalysts demonstrate high activity and selectivity in the continuous-flow asymmetric hydrogenation of a wide variety of enamides and dehydroamino acids, providing optically active amides without leaching of metal species. The chiral environments can be easily tuned by changing the chiral ligands, demonstrating the high versatility of the heterogeneous catalysts. By applying these efficient catalysts, continuous synthesis of several active pharmaceutical ingredient intermediates was achieved.

Enantioselective Sequential-Flow Synthesis of Baclofen Precursor via Asymmetric 1,4-Addition and Chemoselective Hydrogenation on Platinum/Carbon/Calcium Phosphate Composites

Continuous-flow synthesis of baclofen precursor (2) was achieved using achiral and chiral heterogeneous catalysts in high yield with high enantioselectivity. The key steps are chiral calcium-catalyzed asymmetric 1,4-addition of a malonate to a nitroalkene and chemoselective reduction of a nitro compound to the corresponding amino compound by using molecular hydrogen. A dimethylpolysilane (DMPS)-modified platinum catalyst supported on activated carbon (AC) and calcium phosphate (CP) has been developed that has remarkable activity for the selective hydrogenation of nitro compounds.

Reworking Organic Synthesis for the Modern Age: Synthetic Strategies Based on Continuous-Flow Addition and Condensation Reactions with Heterogeneous Catalysts

While organic synthesis carried out in most laboratories uses batch methods, there is growing interest in modernizing fine chemical synthesis through continuous-flow processes. As a synthetic method, flow processes have several advantages over batch systems in terms of environmental compatibility, efficiency, and safety, and recent advances have allowed for the synthesis of several complex molecules, including active pharmaceutical ingredients (APIs). Nevertheless, due to several reasons related to the difficulties arising from byproduct formation during the flow process, such as lower yields, poor selectivities, clogging of columns due to poor solubility, catalyst poisoning, etc., successful examples of continuous-flow synthesis of complex organic molecules are still limited. In order to solve this bottleneck, the development of selective and atom-economical continuous-flow organic transformations are needed. This perspective highlights examples of atom-economical addition and condensation reactions with heterogeneous catalysts under continuous-flow conditions and their applications for the synthesis of complex organic molecules such as natural products and APIs. In order to realize new continuous-flow methodologies, based on addition and condensation reactions, in place of substitution reactions, the development of novel reactions and heterogeneous catalysts is required.

Selective formation of γ-lactams via C-H amidation enabled by tailored iridium catalysts

Intramolecular insertion of metal nitrenes into carbon-hydrogen bonds to form γ-lactam rings has traditionally been hindered by competing isocyanate formation. We report the application of theory and mechanism studies to optimize a class of pentamethylcyclopentadienyl iridium(III) catalysts for suppression of this competing pathway. Modulation of the stereoelectronic properties of the auxiliary bidentate ligands to be more electron-donating was suggested by density functional theory calculations to lower the C-H insertion barrier favoring the desired reaction. These catalysts transform a wide range of 1,4,2-dioxazol-5-ones, carbonylnitrene precursors easily accessible from carboxylic acids, into the corresponding γ-lactams via sp³ and sp² C-H amidation with exceptional selectivity. The power of this method was further demonstrated by the successful late-stage functionalization of amino acid derivatives and other bioactive molecules.

Hydrogenolysis of C-O Chemical Bonds of Broad Scope Mediated by a New Spherical Sol-Gel Catalyst

The new spherical sol-gel hybrid material SiliaCat Pd0 selectively mediates the hydrogenolysis of aromatic alcohols, aldehydes, and ketones by using an ultralow catalytic amount (0.1 mol % Pd) under mild reaction conditions. The broad reaction scope as well as the catalyst's superior activity and pronounced stability open the route to green and convenient reductive deoxygenation processes of primary synthetic relevance in chemical research as well as in the fine chemical and petrochemical industries.

Selective Hydrogenation of Nitriles to Primary Amines Catalyzed by a Polysilane/SiO2-Supported Palladium Catalyst under Continuous-Flow Conditions

Hydrogenation of nitriles to primary amines with heterogeneous catalysts under liquid‐phase continuous‐flow conditions is described. Newly developed polysilane/SiO₂‐supported Pd was found to be an effective catalyst and various nitriles were converted into primary amine salts in almost quantitative yields under mild reaction conditions. Interestingly, a complex mixture was obtained under batch conditions. Lifetime experiments showed that this catalyst remained active for more than 300 h (TON≥10 000) without loss of selectivity and no metal leaching from the catalyst occurred. By using this continuous‐flow hydrogenation, synthesis of venlafaxine, an antidepressant drug, has been accomplished.