Tris(trimethylsilyl)silyl-governed aldehyde cross-aldol cascade reaction

The use of the tris(trimethylsilyl)silyl (TTMSS) group in aldehyde-derived silyl enol ethers affords aldehyde cross-aldol products with high yields and allows for unprecedented reactivity. The reaction is catalyzed by 0.05 mol % of HNTf2, and can easily be managed to give beta,delta-bis-, beta,delta,gamma-tris-, and beta,delta,zeta-tris-hydroxy-aldehydes with extremely high selectivity by simple stoichiometric control. High diastereoselectivity is obtained in all cases, and the use of chiral aldehydes affords Felkin products when there are nonchelating substituents, chelation products when there is a chelating sbustituent, and syn products when there is beta-substitution. HNTf2 is proposed to be an initiator, and highly Lewis acidic TTMSSNTf2 is the true catalyst.     

The cross-aldol reaction of hexafluoroacetone (HFA) with ketones catalyzed by an acid

The cross-aldol reactions of hexafluoroacetone (HFA) and ketones using an acid catalyst are reported. When concentrated sulfuric acid was employed as the catalyst, HFA reacted regioselectively with various ketones at 50-100 °C to give the aldol adducts (6) in good yields. The reaction is initiated by an acid-catalyzed transformation of the ketone into the corresponding enol that reacts with HFA. The obtained adducts (6) can be reduced with hydrogen under a Ru/C catalyst to lead to the corresponding fluorine-containing diols (13).     

Germanium(II)-mediated reductive cross-aldol reaction of bromoaldehydes with aldehydes: NMR studies and ab initio calculations

A highly practical reductive cross-aldol reaction of alpha-bromoaldehydes with various aldehydes has been developed using Ge(II)Cl 2 to produce aldehyde germanium(IV) aldolates, which were directly transformed to various multifunctionalized compounds. A remarkable change in stereoselectivity depended on the alpha-bromoaldehydes employed; secondary alpha-bromoaldehydes gave syn selectivities, while tertiary alpha-bromoaldehydes accomplished the synthesis of anti-selective aldol products with a quaternary carbon center. NMR studies and X-ray analysis strongly suggested the formation of germanium enolate in the reaction of alpha-bromoaldehyde 2h with GeCl 2-dioxane. Detailed mechanistic studies, including NMR analysis and ab initio calculations, revealed the generation of stable germanium aldolates, which was due to the remarkably low Lewis acidity of the germanium(IV).     

Chromium (II) chloride : a new reagent for cross-aldol reactions

The proposed cross aldolization of α-bromoketones with aldehydes in presence of Chromium (II) chloride is an excellent stereospecific reaction. One exception to the stereospecific orientation is reported.     

Reductive dechlorination of atrazine using sodium-borohydride catalysed by cobalt(II) phthalocyanines

A series of functional metallophthalocyanines have been synthesized to study their role as a catalyst towards the reductive dechlorination of atrazine using sodium borohydride as a mild reducing agent. The cobalt(II) phthalocyanine bearing nitro groups at the peripheral position is the most efficient catalyst with exceptionally high catalytic activity in comparison to other functional cobalt(II) phthalocyanines.     

Water-acetic acid mediated an efficient and eco-friendly protocol for the one-pot synthesis of bis-isoxazolyl amino dihydro-1H-indol-4(5H)-ones under mild reaction conditions

A cost-effective and eco-friendly straightforward synthesis of new bis-isoxazolyl amino dihydro-1H-indol-4(5H)-ones is successfully achieved via one-pot three-component reaction of N-isoxazolyl enaminone, aryl glyoxal monohydrates and 4-amino-3-methyl-5-styrylisoxazoles by using water as a reaction medium and acetic acid (AcOH) as cheap and green promoter. The protocol proves to be an efficient and environmentally benign in terms of high yields, low reaction time, operational simplicity, metal-free and wide substrates scope. Most important of all, this reaction process is green.     

Modified asymmetric strecker reaction of aldehyde with secondary amine: a protocol for the synthesis of s-clopidogrel (an antiplatelet agent)

A first approach for catalytic asymmetric Strecker reaction of aldehydes with a secondary amine in the presence of sodium fluoride using hydroquinine as chiral catalyst was developed. The catalytic system gave α-aminonitriles in excellent yields (up to 95%) and high enantioselectivities (er up to 94:6). The efficacy of the chiral product was successfully fulfilled in the improved synthesis of (S)-clopidogrel (an antiplatelet agent).     

Synthesis of highly functionalized piperidines by one-pot multicomponent reaction using tetrabutylammonium tribromide (TBATB)

Tetrabutylammonium tribromide (TBATB) has been found to be an efficient catalyst for the one-pot synthesis of highly substituted piperidines through a combination of 1,3-dicarbonyl compounds, aromatic aldehydes, and various amines in ethanol at room temperature. Atom economy, good yields, environmentally benign, and mild reaction conditions are some of the important features of this protocol.     

Rhodium catalyzed three-component reaction of aldehyde,boronic acid,and sulfonamides: a facile one-pot synthesis of diarylmethylamines

Rhodium(I) catalyzed three-component reaction for the one pot synthesis of diarylmethylamines in excellent yields were achieved by using aldehyde, boronic acid, and sulfonamides. The use of hyper-valent bis(trifluoroacetoxy)iodobenzene as an additive plays a key role in the chemo selective formation of amines instead of alcohols.     

Reductive heterocoupling mediated by Cp*2U(2,2'-bpy)

Trivalent Cp*(2)U(2,2'-bpy) (2) (Cp* = C(5)Me(5), 2,2'-bpy = 2,2'-bipyridine), which has a monoanionic bipyridine, was treated with p-tolualdehyde (a), furfuraldehyde (b), acetone (c), and benzophenone (d). Reduction of the C[double bond, length as m-dash]O bond followed by radical coupling with bipyridine forms the U(iv) derivatives [Cp*(2)U(2,2'-bpy)(OCRR')] (3a-d).     

Organocatalytic tandem three-component reaction of aldehyde, alkyl vinyl ketone, and amide: one-pot syntheses of highly functional alkenes

An EtPPh(2)- or PPh(3)-catalyzed tandem three-component reaction of aldehyde, alkyl vinyl ketone, and amide is developed. Its further application in one-pot syntheses of highly functional alkenes starting from aldehydes, alkyl vinyl ketones, and amides is realized. A wide variety of highly functional α,β-unsaturated ketones can be furnished in 68-99% yields with high stereoselectivity (E/Z up to 98 : 2) within overall 3-29.5 h.     

A Copper(II) Thiolate from Reductive Cleavage of an S-Nitrosothiol

S-Nitrosothiols RSNO represent circulating reservoirs of nitric oxide activity in the plasma and play intricate roles in protein function control in health and disease. While nitric oxide has been shown to reductively nitrosylate copper(II) centers to form copper(I) complexes and ENO species (E = R(2)N, RO), well-characterized examples of the reverse reaction are rare. Employing the copper(I) β-diketiminate [Me(2)NN]Cu, we illustrate a clear example in which an RS-NO bond is cleaved to release NO(gas) with formation of a discrete copper(II) thiolate. The addition of Ph(3)CSNO to [Me(2)NN]Cu generates the three-coordinate copper(II) thiolate [Me(2)NN]CuSCPh(3), which is unstable toward free NO.     

Reductive and oxidative DNA damage by photoactive platinum(II) intercalators

Several photoactive platinum alpha-diimine intercalators have been prepared to develop new probes of DNA oxidation and reduction chemistry. Five water-soluble bis(mes')Pt(II) complexes (mes' = N,N,N,3,5-pentamethylaniline) with various aromatic alpha-diimine ligands (dppz = dipyridophenazine, np = naphtha[2,3-f][1,omega]phenanthroline, CN-np = naphtho[2,3-f][1,10]phenanthroline-9-carbonitrile, CN(2)-np = naphtho[2,3-f][1,10]phenanthroline-9,14-dicarbonitrile, and bp = benzo-[f][1,10]phenanthroline) were synthesized. The complex [(np)Pt(mes')(2)]Cl(2) was also characterized by X-ray crystallography, and the crystal structure shows that the ortho-methyl groups of the mes' ligands conveniently block substitution at the vacant sites of platinum without overlapping with the intercalating alpha-diimine ligand. The Pt(II) complexes were found to have excited-state oxidation and reduction potentials of -0.6 to -1.0 and 1.0 to 1.5 V versus NHE, respectively, making them potent photoreductants as well as photooxidants. Many of the complexes are found to promote the photooxidation of N(2)-cyclopropyldeoxyguanosine (d(Cp)G). Photoexcited [(dppz)Pt(mes')(2)](2+) is found to be most efficient in this photooxidation, as well as in the photoreduction of N(4)-cyclopropylcytidine ((Cp)C); these modified nucleosides rapidly decompose in a ring-opening reaction upon oxidation or reduction. Photoexcited [(dppz)Pt(mes')(2)]Cl(2), upon intercalation into the DNA pi stack, is found, in addition, to promote reductive and oxidative damage within the DNA duplex, as is also probed using the kinetically fast electron and hole traps, (Cp)C and (Cp)G. These Pt complexes may therefore offer useful reactive tools to compare and contrast directly reductive and oxidative chemistry in double helical DNA.     

Synthesis of pentacene-, tetracene- and anthracene bisimides using double-cyclization reaction mediated by bismuth(III) triflate

Novel bisimide-fused acenes were synthesized via bismuth triflate mediated double-cyclization reaction of acid chlorides and isocyanates. Their optical and electrical properties revealed significantly smaller HOMO-LUMO gaps compared with those of their parent acenes. Fabricated OFET based on tetracene bisimide showed n-type OFET outputs.     

Reductive coupling reaction of aldehydes using indium(III) triflate as the catalyst

A reductive coupling reaction was effectively developed to convert an aldehyde to its symmetrical ether. The successful reactions required Et₃SiH and CH₂Cl₂ as the suitable solvent in the presence of a catalytic amount of In(OTf)₃. Various aldehydes were subjected to the method, and each afforded the expected ethers in good to excellent yields.     

Crystal structure of germanium(II) dichloride solvated by tetrahydrofuran

The thermally highly unstable tetrahydrofuran solvate of germanium(II) dichloride (GeCl₂ · 2THF) was crystallized, and its crystal structure was determined. It consists of a chain of GeCl₂ units connected by secondary Cl···Ge contacts [3.846(2) Å] in which each Ge atom is coordinated to two molecules of THF. Two weak hydrogen bonds of the C H ··· Cl Ge type in GeCl₂ · 2THF were also detected both with lengths of 2.90(3) Å. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:361–363, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20105     

Hydrated nickel (II) halides mediated ring opening reaction with N-tosylaziridines

An efficient and water tolerant method for the synthesis ofβ-haloamines is described utilizing hydrated nickel（Ⅱ） halides （NiX₂ⅩnH₂O X = Cl,Br,I） and aziridines as starting materials.N-Tosylaziridines reacted with NiCl₂·6H₂O or NiI₂·6H₂O givingβ-chloro -orβ-iodoamines in high yields（73-99%） within a short time,but 10 mol%of n-Bu₄NBr should be added in the reactions of N-tosylaziridines with NiBr₂·3H₂O in order to obtain the high yields of correspondingβ-bromoamines.Solvent played an important role in the reactions.The proper solvent for the reaction of NiCl₂·6H₂O was DMF,while NiBr₂·3H₂O or NiI₂·6H₂O proceeded well in 1,4-dioxane.     

The hydroformylation reaction: catalysis by platinum(II)-tin(II) systems

The complexes [Pt(ER₃)(CO)Cl₂] (E = P, As; R = aryl, alkyl) are active precursors for the catalytic hydroformylation of olefins in the presence of added tin(II) chloride. The yield of aldehyde may be maximized by systematic parameter variation and is shown to be limited by the degree of steric crowding at the metal centre. Terminal aliphatic monoenes are hydroformylated readily with a high n : iso ratio; hindered internal olefins, cyclic and conjugated aromatic olefins are less readily hydroformylated, but with no competing hydrogenation. The catalyst system is active under mild conditions of temperature and pressure.     

Beyond Samarium Diiodide: Vistas in Reductive Chemistry Mediated by Lanthanides(II)

Reactions proceeding through open-shell, single-electron pathways offer attractive alternative outcomes to those proceeding through closed-shell, two-electron mechanisms. In this context, samarium diiodide (SmI(2) ) has emerged as one of the most important and convenient-to-use electron-transfer reagents available in the laboratory. Recently, significant progress has been made in the reductive chemistry of other divalent lanthanides which for many years had been considered too reactive to be of value to synthetic chemists. Herein, we illustrate how new samarium(II) complexes and nonclassical lanthanide(II) reagents are changing the landscape of modern reductive chemistry.