Functionalized SBA-15 and its Catalytic Applications in Selective Organic Transformations

Ordered, mesoporous SBA-15 functionalized with organic and inorganic moieties exhibits efficient catalytic activity in a variety of organic transformations. In this account, reviewing our own work, three-sets of surface-modified SBA-15 materials have been investigated. The first-set of materials consists of SBA-15 modified with organo-acidic (propyl thiol and propyl sulfonic acid) and basic (propyl amine and propyl adenine) moieties. The second-set of materials was prepared by grafting Mn complexes to the organo-functionalized SBA-15. The third-set composes of nanocrystalline metal oxides supported on SBA-15. All these catalysts have been characterized by structural and spectroscopic techniques. Catalytic activities of the first-set of solid materials have been investigated in acid/base-catalyzed reactions viz., ring-opening of epoxides with amines (producing β-amino alcohols), esterification, three-component-Mannich reactions and cycloaddition of CO₂ to epoxides. The Mn complexes grafted on organofunctionalized SBA-15 are efficient catalysts for the chemo-, regio- and stereoselective aerial oxidation of monoterpenes at ambient conditions. TiO_x, VO_x, MoO_x and WO_x supported on SBA-15 catalyzed biomimetic oxyhalogenation of aromatic compounds. In all these reactions, the functionalized SBA-15 showed high selectivity.     

Aza-Michael reactions in water using functionalized ionic liquids as the recyclable catalysts

Some recyclable SO₃H-functionalized ionic liquids have been used as catalysts in water for the aza-Michael reactions of amines with ??,??-unsaturated compounds to produce ??-amino compounds. High yields of the products, short reaction times, mild reaction conditions, simple experimental procedure, reusable catalysts and no obvious loss of the catalytic activity make this protocol a contribution to organic chemistry.     

[HP(HNCH2CH2)3N]NO3: an efficient homogeneous and solid-supported promoter for aza and thia-Michael reactions and for Strecker reactions

In the presence of a catalytic amount of an azaphosphatrane nitrate salt, amines and thiols react readily with Michael acceptors. The salt is also an efficient promoter for the one pot synthesis of α-amino and α-amidonitriles. By anchoring the salt to Merrifield Resin, a reusable heterogeneous catalyst is obtained for these reactions. Evidence is presented for catalysis being attributable solely to the NO₃⁻ ion.     

Palladium-assisted multicomponent synthesis of 2-aryl-4-aminoquinolines and 2-aryl-4-amino[1,8]naphthyridines

A palladium-mediated multicomponent domino reaction leading to 2-aryl-4-amino-quinolines and 2-aryl-4-amino[1,8]naphthyridines is reported. The scope of the reaction was examined using carbon monoxide, two 2-ethynyl-arylamines, four aryl iodides, and 10 primary amines as substrates. The selection of the appropriate catalytic system was achieved testing several palladium/phosphine systems and overrides previously reported drawbacks associated with the use of primary amines in related reactions. Moreover several features concerning the role of both palladium [(0) and (II)] and phosphines are reported.     

Synthetic Aspects of Metal-Catalyzed Oxidations of Amines and Related Reactions

The metabolism of amines is governed by a variety of enzymes such as amine oxidase, flavoenzyme, and cytochrome P-450. A wide variety of compounds are produced such as ammonia and alkaloids in selective and clean oxidation reactions that proceed under mild reaction conditions. Simulation of the functions of these enzymes with simple transition metal complex catalysts may lead to the discovery of biomimetic, catalytic oxidations of amines and related compounds. Indeed, metal complex catalyzed oxidations have been found to proceed with high efficiency. The first section of this review discusses the dehydrogenative oxidations of amines with transition metal catalysts by transition metal catalysts that simulate amine oxidase. The second section highlights the catalytic oxidation of secondary amines to nitrones by simulation of flavoenzymes. The third section describes the simulation of the function of cytochrome P-450 with lowvalent ruthenium complexes and peroxides. Biomimetic ruthenium-catalyzed oxidations of tertiary amines, secondary amines, and other substrates such as amides, β-lactams, nitriles, alcohols, alkenes, ketones, and even nonactivated hydrocarbons can be performed selectively under mild conditions. These three general approaches provide highly useful strategies for synthesis of fine chemicals and biologically active compounds such as alkaloids, amino acids, and β-lactams.     

Microwave-enhanced bismuth triflate-catalyzed epoxide opening with aliphatic amines

In the presence of a catalytic amount of Bi(OTf)₃·4H₂O and under microwave irradiation, neat mixtures of epoxides and amines afforded smoothly the corresponding 2-amino alcohols. A wide variety of aliphatic amines were reacted with cycloalkene oxide, styrene oxide, and stilbene oxide. The reaction proceeded rapidly and afforded the 2-amino alcohols in high up to quantitative yields. All products could be obtained without aqueous work-up by simple filtration.     

Development of aqueous oxidative Ugi-type reactions by copper-catalyzed surfactant-promoted C(sp)–H direct functionalization in water

Direct assembly of α-amino amides from N-alkyl amines and isocyanides through oxidative Ugi-type reactions in aqueous conditions, has been achieved in a Cu(I)–TBHP–surfactant catalysis system. Various N-alkyl amines and isocyanides could be tolerated in this reaction and furnish α-amino amides in moderate yields.     

Biomimetic monoacylation of diols in water. Lanthanide-promoted reactions of methyl benzoyl phosphate

The direct monoacylation of diols by acyl phosphate monoesters in water is a biomimetic analogy to the enzymic aminoacylation of tRNA by aminoacyl adenylates. Without catalysis, acyl phosphate monoesters react rapidly with amines but very slowly with water and alcohols. Lanthanide ions dramatically and selectively facilitate the base-catalyzed monoacylation of diols in water by methyl benzoyl phosphate (MBP), a typical acyl phosphate monoester, in neutral solutions where reactive amines are protonated and unreactive. The reaction patterns and reactivity of various diols with MBP in the presence of lanthanides are consistent with a mechanism that involves internal addition from the conjugate base of the bis-bidentate complex of the lanthanide with the diol and MBP. The method is also applicable to reactions of nucleosides as evidenced by the selective monoacylation of the 2'- or 3'-hydroxyl group of adenosine, without reaction of the 5'-hydroxyl group or the 6-amino group. Analogues of adenosine without the diol are unreactive. This suggests that the method will selectively monoacylate the hydroxyl groups at the unique diol in tRNA that forms the 3'-terminus.     

Behaviour of enaminomalonates and enamidomalonates under various reductive conditions: a novel synthetic approach to N-acetyl-N-aryl β-amino acids

The behaviour of enaminomalonates and their deprotection to amines under various reductive conditions is described. A new synthetic approach to N-aryl-N-acetyl-β-amino acids using heterogeneous catalytic hydrogenation has been discovered.     

Enantioselective biomimetic transamination of α-keto acids catalyzed by H4-naphthalene-derived axially chiral biaryl pyridoxamines

Asymmetric biomimetic transamination is a highly attractive method for synthesis of chemically and biologically important chiral amino acids and chiral amines. Development of chiral pyridoxamines/pyridoxals is the key for the reaction. New axially chiral biaryl pyridoxamines based on H₄-naphathene skeleton have been developed. The pyridoxamines display good enantioselectivity and high catalytic activity in asymmetric biomimetic transamination of α-keto acids, affording various optically active unnatural amino acids in 61–98% yields with up to 91% ee’s.     

The stereoselective syntheses and reactions of 5,6-epoxy-perhydroisoindolines

Stereo-selective syntheses of 2,5,6-trisubstituted perhydroisoindolines are achieved by preparation of the three diastereoisomeric 5,6-epoxy-perhydroisoindolines and their reactions with nucleophiles, e.g. amines. The transformation of trans-amino alcohols obtained in this way into cis-amino alcohols is described.     

A Bioinspired Catalytic Aerobic Oxidative CH Functionalization of Primary Aliphatic Amines: Synthesis of 1,2‐Disubstituted Benzimidazoles

Aerobic oxidative C?H functionalization of primary aliphatic amines has been accomplished with a biomimetic cooperative catalytic system to furnish 1,2‐disubstituted benzimidazoles that play an important role as drug discovery targets. This one‐pot atom‐economical multistep process, which proceeds under mild conditions, with ambient air and equimolar amounts of each coupling partner, constitutes a convenient environmentally friendly strategy to functionalize non‐activated aliphatic amines that remain challenging substrates for non‐enzymatic catalytic aerobic systems.     

Bismuth(III) chloride-catalyzed one-pot Mannich reaction: three-component synthesis of β-amino carbonyl compounds

A simple and efficient method has been developed for the one-pot Mannich reaction of β-amino carbonyl compounds from aromatic aldehydes, aromatic ketones and aromatic amines in the presence of a catalytic amount of bismuth trichloride.     

Direct α-Functionalization of Saturated Cyclic Amines

Recent advances in synthetic methods for the direct α-functionalization of saturated cyclic amines are described. Methods are categorized according to the in situ formed reactive intermediate (α-amino cation, α-amino anion, and α-amino radical). Transition-metal-catalyzed reactions involving other intermediates have been treated as a separate and fourth class.     

ZrCl4 as a new and efficient catalyst for the opening of epoxide rings by amines

Zirconium(IV) chloride catalyses the nucleophilic opening of epoxide rings by amines leading to the efficient synthesis of β-amino alcohols. The reaction works well with aromatic and aliphatic amines in short times at room temperature in the absence of solvent. Exclusive trans stereoselectivity is observed for cyclic epoxides. Aromatic amines exhibit excellent regioselectivity for preferential nucleophilic attack at the sterically less hindered position during the reaction with unsymmetrical epoxides. However, in case of styrene oxide, selective formation of the benzylic amine was observed during the reactions with aromatic amines.     

Synthesis and structure of an air-stable hypervalent organobismuth (III) perfluorooctanesulfonate and its use as high-efficiency catalyst for Mannich-type reactions in water

An air-stable hypervalent organobismuth (III) perfluorooctanesulfonate was synthesized and characterized by spectroscopic and X-ray crystallographic techniques, and found to exhibit high catalytic efficiency towards one-pot Mannich-type reaction of ketones with aromatic aldehydes and aromatic amines in water. This catalyst also shows good recyclability and reusability. This catalytic system would provide a simple, efficient and ‘green’ avenue towards the synthesis of β-amino ketones.     

Trifluoroethanol as a metal-free, homogeneous and recyclable medium for the efficient one-pot synthesis of α-amino nitriles and α-amino phosphonates

Trifluoroethanol is found to be an efficient and recyclable medium in promoting one-pot, three-component coupling reactions of aldehydes or ketones, amines and trimethylsilyl cyanide or trimethyl phosphite to afford the corresponding α-amino nitriles or α-amino phosphonates in high yields. This protocol does not require the use of an acid or base catalyst.     

Biomimetic reductive amination under the continuous-flow reaction conditions

This study present a full account of continuous-flow reaction conditions for biomimetic reductive amination of fluorinated carbonyl compounds to corresponding amines and amino acids of biomedical importance. We demonstrate that simple silica-adsorbed DBU can be used as efficient catalysts for on-column 1,3-proton shift reaction, a key transformation in the biomimetic reductive amination process. This new on-column process features operationally convenient conditions, higher chemical yields, enantioselectivity and purity of the corresponding products as compared with traditional in-flask reactions. Moreover the removal of base-catalyst, the most delicate problem of the in-flask reactions, is not an issue in the on-column process, as the silica-adsorbed DBU or polymer-bound guanidine remains on the column and can be reused. This feature renders the overall process substantially more economical and synthetically efficient, in particular, for large-scale synthesis of the corresponding fluorinated amines and amino acids target.     

聚苯乙烯负载氯化铁催化一锅法合成β-氨基酮类衍生物

制备了聚苯乙烯负载型氯化铁催化剂(PS-FeCl3),并通过红外光谱、X射线衍射、扫描电子显微镜等技术手段进行了表征。 在PS-FeCl3催化下,以苯乙酮、芳醛和芳胺为原料,采用一锅法Mannich反应合成了一系列β-氨基酮衍生物。 制备的催化剂性能稳定,使用4次仍保持较高活性。     

Highly enantioselective organocatalytic addition of unmodified aldehydes to N-Boc protected imines: one-pot asymmetric synthesis of β-amino acids

Highly enantioselective catalytic routes to Boc protected β-amino aldehydes, β-amino acids and γ-amino alcohols are presented. The organocatalytic asymmetric reactions between unmodified aldehydes and N-Boc protected aryl imines proceed with excellent chemo- and enantioselectivities to give the corresponding compounds in high yields with up to >19:1 dr and 93% to >99% ee.