Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst [Cp*Ir(2,2′-bpyO)(H2O)] without using base

An efficient catalytic system for hydrogenation of ketones and aldehydes using a Cp*Ir complex [Cp*Ir(2,2′-bpyO)(H₂O)] bearing a bipyridine-based functional ligand as catalyst has been developed. A wide variety of secondary and primary alcohols were synthesized by the catalyzed hydrogenation of ketones and aldehydes under facile atmospheric-pressure without a base. The catalyst also displays an excellent chemoselectivity towards other carbonyl functionalities and unsaturated motifs. This catalytic system exhibits high activity for hydrogenation of ketones and aldehydes with H₂ gas.     

Reduction of Aldehydes and Ketones with Potassium Borohydride as Reductant

A series of aldehydes and ketones were reduced by potassium borohydride in an ionic liquid/water ([bmim]PF6/H2O) biphasic system to afford corresponding alcohol with high purity in excellent yields. The ionic liquid/water biphasic system could promote the chemoselectivity and the substituents such as nitro group and chlorine remained intact. Aromatic ketones were not as active as aromatic aldhydes and cyclic ketones owing to their higher steric hindrance. The ionic liquid could be recycled and reused. This protocol has notable advantages of no need of phase transfer catalyst and organic solvents, mild conditions, simple operation, short reaction time, ease work-up, high yields and recycling of the ionic liquid.     

Monodisperse CuPt alloy nanoparticles assembled on reduced graphene oxide as catalysts in the transfer hydrogenation of various functional organic groups

We present herein a new nanocatalyst, namely binary CuPt alloy nanoparticles (NPs) supported on reduced graphene oxide (CuPt‐rGO), as a highly active heterogeneous catalyst for the transfer hydrogenation (TH) protocol that is demonstrated to be applicable over the reduction of various unsaturated organic compounds (olefins, aldehydes/ketones and nitroarenes) in aqueous solutions at room temperature. CuPt alloy NPs were synthesized by the co‐reduction of metal (II) acetylacetonates by borane‐tert‐butylamine (BTB) complex in hot oleylamine (OAm) solution and then assembled on reduced graphene oxide (rGO) via ultrasonic‐assisted liquid phase self‐assembly method. The structure of yielded CuPt NPs and CuPt‐rGO nanocatalyst were characterized by TEM, XRD and ICP‐MS. The activity of Cu₇Pt₃‐rGO nanocatalysts were then tested for the THs that were conducted in a commercially available high‐pressure tube using water as sole solvent and ammonia borane as a hydrogen donor at room temperature. The presented catalytic TH protocol was successfully applied over nitroarenes, olefines and aldehydes/ketones, and all the tested compounds were converted to corresponding reduction products with the yields reaching up to 99% under ambient conditions. Moreover, the Cu₇Pt₃‐rGO nanocatalyst was also reusable in the TH by providing 99% yield after five consecutive runs in TH of nitrobenzene as an example.     

Chemoselectivity in the Reaction of 2‐Diazo‐3‐oxo‐3‐phenylpropanal with Aldehydes and Ketones

The chemoselectivity in the reaction of 2‐diazo‐3‐oxo‐3‐phenylpropanal ( 1 ) with aldehydes and ketones in the presence of Et₃N was investigated. The results indicate that 1 reacts with aromatic aldehydes with weak electron‐donating substituents and cyclic ketones under formation of 6‐phenyl‐4H‐1,3‐dioxin‐4‐one derivatives. However, it reacts with aromatic aldehydes with electron‐withdrawing substituents to yield 1,3‐diaryl‐3‐hydroxypropan‐1‐ones, accompanied by chalcone derivatives in some cases. It did not react with linear ketones, aliphatic aldehydes, and aromatic aldehydes with strong electron‐donating substituents. A mechanism for the formation of 1,3‐diaryl‐3‐hydroxypropan‐1‐ones and chalcone derivatives is proposed. We also tried to react 1 with other unsaturated compounds, including various olefins and nitriles, and cumulated unsaturated compounds, such as N,N′‐dialkylcarbodiimines, phenyl isocyanate, isothiocyanate, and CS₂. Only with N,N′‐dialkylcarbodiimines, the expected cycloaddition took place.     

Tetrahydro‐1,5‐benzoxazepines and tetrahydro‐1H‐1,5‐benzodiazepines by a tandem reduction‐reductive amination reaction

A tandem reduction‐reductive amination reaction has been applied to the synthesis of (±)‐4‐alkyl‐2,3,4,5‐tetrahydro‐1,5‐benzoxazepines and (±)‐4‐alkyl‐1‐benzoyl‐2,3,4,5‐tetrahydro‐1H‐1,5‐benzodiazepines. The nitro aldehydes and ketones required for 1,5‐benzoxazepine ring closures were prepared by nucleophilic aromatic substitution of the alkoxides from several 3‐buten‐1‐ol derivatives with 2‐fluoro‐1‐nitrobenzene followed by ozonolysis. Precursors for the 1,5‐benzodiazepines were prepared by similar addition of N‐(3‐butenyl)benzamide anions to 2‐fluoro‐1‐nitrobenzene followed by ozonolysis. Catalytic hydrogenation of the nitro carbonyl compounds using 5% palladium‐on‐carbon in methanol then gave the target heterocycles by a tandem reduction‐reductive amination sequence. The 1,5‐benzoxazepines were isolated in high yield following chromatographic purification; the 1,5‐benzodiazepines were isolated as solids directly from the hydrogenation mixture and possessed differentiated functionality on the two nitrogen atoms.     

Selective Hydrogenation and Hydrodeoxygenation of Aromatic Ketones to Cyclohexane Derivatives Using a Rh@SILP Catalyst

Rhodium nanoparticles immobilized on an acid‐free triphenylphosphonium‐based supported ionic liquid phase (Rh@SILP(Ph₃‐P‐NTf₂)) enabled the selective hydrogenation and hydrodeoxygenation of aromatic ketones. The flexible molecular approach used to assemble the individual catalyst components (SiO₂, ionic liquid, nanoparticles) led to outstanding catalytic properties. In particular, intimate contact between the nanoparticles and the phosphonium ionic liquid is required for the deoxygenation reactivity. The Rh@SILP(Ph₃‐P‐NTf₂) catalyst was active for the hydrodeoxygenation of benzylic ketones under mild conditions, and the product distribution for non‐benzylic ketones was controlled with high selectivity between the hydrogenated (alcohol) and hydrodeoxygenated (alkane) products by adjusting the reaction temperature. The versatile Rh@SILP(Ph₃‐P‐NTf₂) catalyst opens the way to the production of a wide range of high‐value cyclohexane derivatives by the hydrogenation and/or hydrodeoxygenation of Friedel–Crafts acylation products and lignin‐derived aromatic ketones.     

Copper(II) tetrafluoroborate as an extremely efficient catalyst for 1,3-dithiolane/dithiane formation from carbonyl compounds under solvent-free conditions at room temperature

Copper(II) tetrafluoroborate hydrate is a new and extremely efficient catalyst for 1,3-dithiolane/dithiane formation from aromatic, heteroaromatic and aliphatic aldehydes and cyclic saturated ketones in 1-5 min under solvent-free conditions at room temperature. The reaction is compatible with other functionalities such as ether, ester, hydroxyl, halide, nitro and cyano groups and exhibits excellent chemoselectivity. α,β-Unsaturated aldehydes/ketones lead to selective formation of 1,3-dithiolanes instead of Michael addition products. For substrates bearing an aldehyde and a ketone carbonyl group, chemoselective dithiolane formation takes place with the aldehyde.     

Aspects of Electrochemical Behavior of Aldehydes and Ketones in Protic Media

Reduction of carbonyl group in aldehydes and ketones, as well as oxidation of numerous aldehydes is discussed, as well as those reductions of organic compounds where the C?O group activates cleavage of an adjacent C? X bond where X is a good leaving group like halogen, OH, NH₂ or SR or activates hydrogenation of an adjacent C?C group. Survey involves aliphatic and aromatic aldehydes, aryl alkyl and diaryl ketones, as well as α‐ketoacids, 1,2‐diketones and compounds where the carbonyl group is a part of a ring. The role of acid–base, hydration–dehydration and in some cases keto–enol equilibria on electrochemical behavior is pointed out, as well as the role of buffer kind and concentration and the nature of the cation of supporting electrolyte. Better understanding of these factors promises finding of best conditions for electroanalytical procedures.     

REDUCTION OF CARBONYL COMPOUNDS TO THE CORRESPONDING ALCOHOLS WITH ISOPROPANOL ON DEHYDRATED ALUMINA UNDER MICROWAVE IRRADIATION

ABSTRACT

The reduction of different types of aldehydes and ketones were performed in the presence of isopropylalcohol (as solvent and hydride source) under microwave irradiation. It is proved that dehydrated Woelm chromatographic alumina supported KOH catalyses these transformations. Regioselectivity was observed in the reduction of cinnamaldehyde and chemoselectivity was observed in the reduction of carbonyl in the presence of nitro group.     

Chemoselective Hydrogenation of Functionalized Nitroarenes and Imines by Using Carbon Nanofiber‐Supported Iridium Nanoparticles

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with Ir₄(CO)₁₂ in mesitylene at 165 °C provided the corresponding CNF‐supported iridium nanoparticles, Ir/CNFs (Ir content=2.3–2.6 wt. %). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size‐controlled Ir nanoparticles (average particle size of 1.1–1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF‐T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 atm of H₂, and the catalyst is reusable. Ir/CNF‐T was also effective for the reductive N‐alkylation of anilines with carbonyl compounds.     

KF/clinoptilolite nanoparticles as a novel catalyst for the green synthesis of chromens using three component reactions of 4‐hydroxycoumarins: Study of antioxidant activity

In this research, the green synthesis of chromen derivatives in good yields is described via three‐component reactions of 4‐hydroxycumarine, aldehydes or ketones, and methyl ketones in the presence of KF/clinoptilolite nanoparticles (KF/CP‐NPs) under solvent‐free conditions at 50°C in low time. The present methodology suggests some advantages such as low reaction time, easy and simple procedure, green method, inexpensive catalyst, high yield of product, and existence of different substrates for performing these reactions. In addition, it should be mentioned that antioxidant activity was studied for some prepared compounds, such as 4a–4d, by DPPH radical trapping and reducing potential tests of ferric ion and then comparing results with TBHQ and BHT as synthetic antioxidants. In this study, compounds 4c was shown to have moderate DPPH radical trapping, and compounds 4b and 4d displayed good reducing power of ferric ion.     

Chemoselective Synthesis of Substituted Imines,Secondary Amines,and β‐Amino Carbonyl Compounds from Nitroaromatics through Cascade Reactions on Gold Catalysts

Substituted imines, α,β‐unsaturated imines, substituted secondary amines, and β‐amino carbonyl compounds have been synthesized by means of new cascade reactions with mono‐ or bifunctional gold‐based solid catalysts under mild reaction conditions. The related synthetic route involves the hydrogenation of a nitroaromatic compound in the presence of a second reactant such as an aldehyde, α,β‐unsaturated carbonyl compound, or alkyne, which circumvents an ex situ reduction process for producing the aromatic amine. The process is shown to be highly selective towards other competing groups, such as double bonds, carbonyls, halogens, nitriles, or cinnamates, and thereby allows the synthesis of different substituted nitrogenated compounds. For the preparation of imines, substituted anilines are formed and condensed in situ with aldehydes to provide the final product through two tandem reactions. High chemoselectivity is observed, for instance, when double bonds or halides are present within the reactants. In addition, we show that the Au/TiO₂ system is also able to catalyze the chemoselective hydrogenation of imines, so that secondary amines can be prepared directly through a three‐step cascade reaction by starting from nitroaromatic compounds and aldehydes. On the other hand, Au/TiO₂ can also be used as a bifunctional catalyst to obtain substituted β‐amino carbonyl compounds from nitroaromatics and α,β‐unsaturated carbonyl compounds. Whereas gold sites promote the in situ formation of anilines, the intrinsic acidity of Ti species on the support surface accelerates the subsequent Michael addition. Finally, two gold‐catalyzed reactions, that is, the hydrogenation of nitro groups and a hydroamination, have been coupled to synthesize additional substituted imines from nitroaromatic compounds and alkynes.     

First and Efficient Method for Reduction of Aliphatic and Aromatic Nitro Compounds with Zinc Borohydride as Pyridine Zinc Tetrahydroborato Complex: A New Stable Ligand‐Metal Borohydride

Pyridine zinc tetrahydroborate, [(Py)Zn(BH₄)₂], as a new stable ligand‐metal borohydride, is prepared quantitatively by complexation of 1:1 zinc borohydride and pyridine at room temperature. This reagent efficiently reduces different aromatic and aliphatic nitro compounds to their primary amines in refluxing THF. In addition, the reduction shows chemoselectivity for aliphatic nitro compounds over the aromatic nitro compounds.     

Reduction processes biocatalyzed by Vigna unguiculata

Whole cells from the Brazilian beans feijão de corda (Vigna unguiculata) have been employed as biocatalysts in different bioreduction processes. Good to excellent selectivities can be obtained in the reduction of aromatic and aliphatic ketones, as well as β-ketoesters, depending on the conversions and the chemoselectivity on the substrate structure. This biocatalyst was also able to reduce the nitro moiety of different aromatic nitro compounds, showing as well enoate reductase activity, and chemoselectively catalyzing the double bond reduction of 4-phenyl-3-buten-2-one with moderate conversion.     

Allylation of Carbonyl Compounds Mediated by Aluminum/Fluoride Salts in Water

A novel mediator (Al/KF) has been developed and employed in the Barbier‐type alkylations of various aldehydes and ketones with alkyl halide in water. The carbonyl compounds could be effectively converted into corresponding homoallylic alcohol in good yields only when allyl bromides or substituted allyl bromides were used as halides. Aromatic aldehydes could afford homoallylic alcohols in high yields, unfortunately, the allylation of aromatic aldehyde substituted by nitro‐ or amino‐group could not proceed smoothly, and the allylation yields of ketones and aliphatic carbonyl compounds were lower under the same condition. The diastereoselectivity and regioseletivity of the reaction have also been studied, the predominant products preferred the erythro‐ or anti‐isomer in dominant γ‐adduct by using Al/KF mediated allylation of benzaldehydes with cinnamyl bromide and ethyl 4‐bromo‐2‐butenoate in water.     

Highly efficient metal-free one-pot synthesis of α-aminophosphonates through reduction followed by Kabachnik–fields reaction using three-component system

One-pot synthesis of α-aminophosphonates directly from aryl nitro compounds, aldehydes/ketones, and diethyl phosphite using sodium dithionite through reduction and followed by Kabachnik–Fields reaction under metal-free conditions is reported. The major advantages are excellent yield, high chemoselectivity, neutral reaction medium, and simple experimental procedure. This methodology consists of the following steps: 1) amine formation from nitro compound, 2) imine formation from amine and aldehyde/ketone, 3) phosphate addition to imine.     

Reductive Amination of Aldehydes and Ketones with Sodium Triacetoxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures(1)

Sodium triacetoxyborohydride is presented as a general reducing agent for the reductive amination of aldehydes and ketones. Procedures for using this mild and selective reagent have been developed for a wide variety of substrates. The scope of the reaction includes aliphatic acyclic and cyclic ketones, aliphatic and aromatic aldehydes, and primary and secondary amines including a variety of weakly basic and nonbasic amines. Limitations include reactions with aromatic and unsaturated ketones and some sterically hindered ketones and amines. 1,2-Dichloroethane (DCE) is the preferred reaction solvent, but reactions can also be carried out in tetrahydrofuran (THF) and occasionally in acetonitrile. Acetic acid may be used as catalyst with ketone reactions, but it is generally not needed with aldehydes. The procedure is carried out effectively in the presence of acid sensitive functional groups such as acetals and ketals; it can also be carried out in the presence of reducible functional groups such as C-C multiple bonds and cyano and nitro groups. Reactions are generally faster in DCE than in THF, and in both solvents, reactions are faster in the presence of AcOH. In comparison with other reductive amination procedures such as NaBH(3)CN/MeOH, borane-pyridine, and catalytic hydrogenation, NaBH(OAc)(3) gave consistently higher yields and fewer side products. In the reductive amination of some aldehydes with primary amines where dialkylation is a problem we adopted a stepwise procedure involving imine formation in MeOH followed by reduction with NaBH(4).     

Silver nanoparticles supported on ionic‐tagged magnetic hydroxyapatite as a highly efficient and reusable nanocatalyst for hydrogenation of nitroarenes in water

A novel chemically modified magnetic hydroxyapatite (MHAp) was prepared and used as support and stabilizer for the synthesis of silver nanoparticles. First, 1,4‐diazabicyclo[2.2.2]octane (DABCO) was successfully grafted onto the surface of MHAp, and then silver nanoparticles were homogeneously loaded on mesoporous MHAp‐DABCO (ionic‐tagged MHAp) nanocomposite by in situ chemical reduction of silver nitrate using sodium borohydride. The structure and properties of the resulting MHAp‐DABCO‐Ag nanocomposite were confirmed using various techniques. The catalytic activity of ionic‐tagged MHAp‐Ag nanocatalyst was investigated for the hydrogenation reaction of nitroarenes in aqueous media. The results reveal that the Ag‐containing inorganic–organic nanocomposite is highly efficient for the reduction of a wide range of aromatic nitro compounds under green conditions. The superparamagnetic nature of the nanocatalyst leads to its being readily removed from solution via application of a magnetic field, and it can be easily stored and reused.     

Silica Phenyl Sulfonic Acid as a Solid Acid Heterogeneous Catalyst for Chemoselective Thioacetalization of Carbonyl Compounds and Dethioacetalization under Mild Conditions

Silica phenyl sulfonic acid (SPSA) is an effective catalyst for chemoselective thioacetalization of aldehydes in the presence of ketones under neutral conditions. In addition, a simple and an efficient procedure for deprotection of 1,3‐dithianes and 1,3‐dithiolanes of aromatic, aliphatic, and α,β‐unsaturated aldehydes and ketones in the solvent‐free to the corresponding parent carbonyl compounds was successfully carried out with SPSA in excellent yields.     

A Regioselective Biginelli‐like Reaction Controlled by the Size of Alicyclic Mono‐ketones

A regioselective Biginelli‐like reaction of alicyclic mono‐ketones, aromatic aldehydes, and urea in ionic liquid [BPY]BF₄ has been investigated. The process is controlled by the size of alicyclic mono‐ketones and the steric hindrance of aromatic aldehydes. The reaction of cyclopentanone with urea and aromatic aldehydes afforded 7‐arylidene‐3,4,6,7‐tetrahydro‐4‐aryl‐1H‐cyclopenta[d]pyrimidin‐2(5H)‐ones ( 4 ). When cyclohexanone was used as the source of active methylene to react with urea and aldehydes with slight steric hindrance groups under the same condition, 8‐arylidene‐3,4,5,6,7, 8‐hexahydro‐4‐arylquinazolin‐2(1H)‐ones ( 6 ), a homologue of 4 , were yielded, whereas 4,8‐bisaryloc‐tahydro‐1H‐pyrimido[5,4‐i]‐quinazoline‐2,10(3H,11H)‐diones ( 7 ) were obtained via the simple one‐pot reaction of cyclohexanone, urea, and aromatic aldehydes with high steric hindrance groups. The possible transitional states and mechanism of the regioselective process were discussed.