16021-08-2

The synergistic combination of three catalytic processes – photoredox, enamine and hydrogen atom transfer (HAT) catalysis – enabled the β-isomerization of 2-decalones towards the thermodynamically most stable trans-isomers. A library of iridium (III) complexes and organic dyes were screened in combination with cyclic amines and thiols which after optimization gave the desired trans-2-decalones with high trans/cis ratios of 60 : 40 up to 98 : 2.

Spin states of iron often direct the selectivity in oxidation catalysis by iron complexes using hydrogen peroxide (H2O2) on an oxidant. While low-spin iron(III) hydroperoxides display stereoselective C-H bond hydroxylation, the reactions are nonstereoselective with high-spin iron(II) catalysts. The catalytic studies with a series of high-spin iron(II) complexes of N4 ligands with H2O2 and Sc3+ reported here reveal that the Lewis acid promotes catalytic C-H bond hydroxylation with high chemo- and stereoselectivity. This reactivity pattern is observed with iron(II) complexes containing two cis-labile sites. The enhanced selectivity for C-H bond hydroxylation catalyzed by the high-spin iron(II) complexes in the presence of Sc3+ parallels that of the low-spin iron catalysts. Furthermore, the introduction of multimetal centers enhances the activity and selectivity of the iron catalyst. The study provides insights into the development of peroxide-dependent bioinspired catalysts for the selective oxygenation of C-H bonds without the restriction of using iron complexes of strong-field ligands.

Ozonolysis is used for oxidation of a model cyclic molecule-decalin, which may be consid-ered as an analog of saturated cyclic molecules present in heavy oil. The conversion of decalin exceeds 50% with the highest yield of formation of acids about 15–17%. Carboxylic acids, ketones/aldehydes, and alcohols are produced as intermediate products. The methods of UV-visible, transmission IR, at-tenuated total reflection IR-spectroscopy, NMR and mass-spectrometry were used to identify reaction products and unravel a possible reaction mechanism. The key stage of the process is undoubtedly the activation of the first C-H bond and the formation of peroxide radicals.

The present invention relates to the field of organic synthesis and more specifically to the isomerization of the β position of a β?trisubstituted C3-C70 carbonyl compound.

The popularity of NHCs in transition metal catalysis has prompted the development of chiral versions as electron-rich neutral stereodirecting ancillary ligands for enantioselective transformations. Herein we demonstrate that cyclic (alkyl)(amino)carbene (CAAC) ligands can also engage in asymmetric transformations, thereby expanding the toolbox of available chiral carbenes.

The use of a peroxidase-mimicking Fe complex has been reported on the basis of the biuret-modified TAML macrocyclic ligand framework (Fe-bTAML) as a catalyst to perform selective oxidation of unactivated 3° C-H bonds and activated 2° C-H bonds with low catalyst loading (1 mol %) and high product yield (excellent mass balance) under near-neutral conditions and broad substrate scope (18 substrates which includes arenes, heteroaromatics, and polar functional groups). Aliphatic C-H oxidation of 3° and 2° sites of complex substrates was achieved with predictable selectivity using steric, electronic, and stereoelectronic rules that govern site selectivity, which included oxidation of (+)-artemisinin to (+)-10β-hydroxyartemisinin. Mechanistic studies indicate FeV(O) to be the active oxidant during these reactions.

A preorganised ligand scaffold is capable of coordinating multiple Fe(II) centres to form an electrophilic CH oxidation catalyst. This catalyst oxidises unactivated hydrocarbons including simple, linear alkanes under mild conditions in good yields with selectivity for the oxidation of secondary CH bonds. Control complexes containing a single metal centre are incapable of oxidising unstrained linear hydrocarbons, indicating that participation of multiple centres aids the CH oxidation of challenging substrates.

A non-heme, iron(iii)/THA(thymine-1-acetate) catalyst together with H2O2 as an oxidant is efficient in oxidative C-H activation of alkanes. Although having a higher preference for tertiary C-H bonds, the catalyst also oxidizes aliphatic secondary C-H bonds into carbonyl compounds with good to excellent conversions. Based on the site selectivity of the catalyst and our mechanistic studies the reaction proceeds via an Fe-oxo species without long lived carbon centered radicals.

The present invention relates to novel alpha-hydrogen substituted nitroxyl compounds and their corresponding oxidized (oxoammonium cations) and reduced (hydroxylamine) forms, and to the use of such compounds, inter alia, for (1) oxidation of primary and secondary alcohols to aldehydes and ketones, respectively; (2) resolution of racemic alcohols; (3) desymmetrization of meso-alcohol; (4) as radicals and spin trapping reagents; and (5) as polymerization agents. The present invention further relates to processes for preparing the novel nitroxyl/oxoammonium/ hydroxylamine compounds from the corresponding amines, and to certain novel amine derivatives and their uses. The compounds of the invention as well as the amine precursors are also useful as ligands for transition metals and as organocatalysts in e.g., aldol reactions.

In this work, we report the discovery of a carboxyl-containing iron catalyst 1 (FeII-DCBPY, DCBPY = 2,2′-bipyridine-4,4′- dicarboxylic acid), which could activate the C-H bonds of cycloalkanes with high secondary (2°) C-H bond selectivity. A turnover number (TN) of 11.8 and a 30% yield (based on the H2O2 oxidant) were achieved during the catalytic oxidation of cyclohexane by 1 under irradiation with visible light. For the transformation of cycloalkanes and bicyclic decalins with both 2° and tertiary (3°) C-H bonds, 1 always preferred to oxidise the 2° C-H bonds to the corresponding ketone and alcohol products; the 2°/3° ratio ranged between 78/22 and >99/1 across 7 examples. 18O isotope labelling experiments, ESR experiments, a PPh3 method and the catalase method were used to characterize the reaction process during the oxidation. The success of 1 showed that, in addition to using a bulky catalyst, high 2° C-H bond selectivity could also be achieved using a less bulky molecular iron complex as the catalyst.

Many are called but few are chosen: A nonheme iron complex catalyzes the oxidation of alkyl C-H bonds by using H2O2 as the oxidant, showing an enhanced selectivity for secondary over tertiary C-H bonds (see scheme). Copyright

A versatile, solvent free aerobic alcohol oxidation system has been established in the presence of benzaldehyde based on a heterogenous cobalt catalyst supported on nanoshell carbon (Co/NSC), which was prepared through the pyrolysis of a mixture of Co(II) phthalocyanine and phenol resin. The established system features equal efficiency toward both benzylic alcohols and aliphatic alcohols. The nanoshell carbon has been demonstrated to be a better supporting material for the present reaction than some other carbon materials, e.g., activated carbon. Mechanistic studies suggest that Co/NSC can catalyze the formation of oxidative intermediate peroxybenzoic acid as efficiently as homogeneous cobalt catalyst, and moreover, suppress the undesired Baeyer-Villiger side reaction. Co/NSC also exhibits good reusability, i.e., it can be reused for at least 10 times without significant loss of performance. Crown Copyright

High SN2′ selectivity in the allylic substitution of cyclohexylidene ethyl picolinates with copper reagents prepared from RMgBr and CuBr·Me2S was realized by addition of ZnX2 (X = I, Br, Cl). Furthermore, ZnX2 accelerated the reaction with the bulky iPr reagent. The Royal Society of Chemistry 2010.

Direct functionalization of alkanes by oxidation of C-H bonds to form alcohols under mild conditions is a challenge for synthetic chemistry. Most alkanes contain a large number of C-H bonds that present difficulties for selectivity, and the oxidants employed often result in overoxidation. Here we describe a divanadium-substituted phosphotungstate that catalyses the stereo- and regioselective hydroxylation of alkanes with hydrogen peroxide as the sole oxidant. Both cyclic and acyclic alkanes were oxidized to form alcohols with greater than 96% selectivity. The bulky polyoxometalate framework of the catalyst results in an unusual selectivity that can lead to the oxidation of secondary rather than the weaker tertiary C-H bonds. The catalyst also avoids wasteful decomposition of the stoichiometric oxidant, which can result in the production of hydroxyl radicals and lead to non-selective oxidation and overoxidation of the desired products.

A novel regeneration system for oxidized nicotinamide cofactors (NAD + and NADP+) is presented. By combining 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid (ABTS)-catalyzed oxidation of NAD(P)H with laccase-catalyzed utilization of molecular oxygen as terminal oxidant, a simple chemo-enzymatic NAD(P)+ regeneration method is achieved. Thus, the advantages of both worlds, chemical oxidation of reduced nicotinamide cofactors and laccase-catalyzed utilization of oxygen from air are combined in a simple and generally applicable new approach for biooxidation catalysis. This new application of the well-known laccase-mediator system (LMS) is successfully used to promote alcohol dehydrogenase-catalyzed oxidation reactions of primary and secondary alcohols. Already under non-optimized conditions, high turnover numbers of > 300 and > 16000 were obtained for the nicotinamide cofactor and ABTS, respectively. In this communication, we present the proofof-principle and initial characterization of the proposed new regeneration system.

(Chemical Equation Presented) The development of an efficient and stereoselective trans-Diels-Alder paradigm is described. A central element of this transformation is the introduction of a temporary dienophilic functionality (A), which serves both to acti

GaCl3 catalyzes the aromatic alkylation of naphthalene or phenanthrene using cycloalkanes. The C-C bond formation predominantly takes place at the least hindered positions of the substrates, and equatorial isomers regarding the cycloalkane moiety are generally obtained. The reaction of bicyclo[4.4.0]decane and naphthalene occurs at the 2-position of naphthalene and at the 2- or 3-carbons of the cycloalkane, and the products possess a trans configuration at the junctures and an equatorial configuration at the naphthyl groups. Notably, cis-bicyclo[4.4.0]decane turns out to be much more reactive than the trans isomer, and a turnover number "TON" up to 20 based on GaCl3 is attained. 1,2-Dimethylcyclohexane reacts similarly, and the cis isomer is more reactive than the trans isomer. Monoalkylcycloalkanes react at the secondary carbons provided that the alkyl group is smaller than tert-butyl. Adamantanes react at the tertiary 1-position. The alkylation reaction is considered to involve the C-H activation of cycloalkanes with GaCl3 at the tertiary center followed by the migration of carbocations and electrophilic aromatic substitution yielding thermodynamically stable products. The stereochemistry of the reaction reveals that GaCl 3 activates the equatorial tertiary C-H bond rather than the axial tertiary C-H bond.

The two-carbon ring expansion of cycloalkanones is now possible in a two-step procedure. This procedure is based on an unusual cascade reaction that consists of a [2,3]-sigmatropic rearrangement (Mislow-Braverman-Evans rearrangement) of an allylic sulfoxide followed by a radical fragmentation-cyclization process (see scheme; AIBN = azobisisobutyronitrile).

Under Gif conditions using ascorbic acid as reductant and oxygen as oxidant in pyridine, the selectivity for secondary hydrogen functionalization is exceptional. EDTA (ethylenediamine-tetra-acetic acid) is not needed as a ligand for iron.

The oxidation of cyclohexene with hydrogen peroxide catalyzed by a vanadium complex and pyrazine-2-carboxylic acid (PCA) in air results in the formation of cyclohex-2-enyl hydroperoxide as the main product and cyclohex-2-enol, cyclohex-2-enone, cyclohex-3-enyl hydroperoxide, cyclohex-3-enol, cyclohexanol, cyclohexane, and 1,2-epoxycyclohexane in lesser amounts. The composition of the products of oxidation of decalin isomers with the system in question is similar to those obtained in the photochemical oxidation with hydrogen peroxide in air and in the oxidation with air in the presence of anthraquinone. A proposed mechanism for the oxidation includes the initiation by hydroxyl radicals generated from hydrogen peroxide under the action of the V - PCA system.

A variety of alcohols are oxidised to the corresponding carbonyl compounds in excellent yields by chromium trioxide-H-ZSM 5 in dichloromethane at room temperature.

The total synthesis of (±)2,3-dimethoxyhexahydroberbine 7 key compound transhexahydroisochroman-3-one 5 has been reported.

α,β-Unsaturated ketones can be hydrogenated conveniently under catalytic hydrogenation conditions using ammonium formate / Pd-C (10percent) in refluxing methanol.

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Two types of processes are described which involve the selective transformation of unactivated carbon-hydrogen bonds in a ketone, cis-2-decalone, cis-1, which possesses conventionally far more reactive bonds. The first type of process involves irradiation of decatungstate, W10O324- in the presence of cis-1 producing, trans-2-decalone, trans-1, the product resulting from epimerization of an unactivated tertiary C-H bond remote from the carbonyl group, in high selectivity at high conversion of substrate, eq 1. The second type of reaction involves irradiation of the heteropolytungstate, α-P2W18O626- or α-PW12O403-, in the presence of cis-1 producing two monounsaturated ketones (octalones) in high selectivity with the nonthermodynamic isomer, 2, in comparable or greater quantity than the conventional thermodynamic (conjugated) isomer, 3, eq 2. Both types of processes are independent of wavelength over the principal range of absorption of the complexes (250-380 nm). The reactions are first order in W10O324- under optically dilute conditions. The primary kinetic isotope of the corresponding decalin hydrocarbons evaluated under the same reaction conditions as eq 1, kcis-decalin-H18/kcis-decalin-D18 ～ 2, and the solvent kinetic isotope effect, kCH3CN/kCD3CN = 1.0. The photochemical reaction of decatungstate with α,α,α′,α′-D4-cis-1 leads exclusively, even at moderate conversion of substrate (25%), to α,α,α′,α′-D4-trans-1. These data, an isotope crossover experiment in which decatungstate was irradiated in the presence of a 50/50 molar mixture of deuterated and protiated cis-decalin in CD3CN, reactions of cis-1 and cis-decalin with an authentic localized ground-state radical, t-BuO?, and a number of other experiments are consistent with initial H atom abstraction in all cases. The dramatically different products seen with the different polyoxometalate systems are dictated by the relative rates of epimerization, oxidation, and escape of the cisoid tertiary bridgehead radicals in the initial radical cage and, to a lesser extent, by the rates of conventional radical-radical reactions and other processes.

Alicyclic α,β-unsaturated ketones react with lithium in ethylenediamine, followed by Jones oxidation, to give cyclic ketones in good yield.The stereoselectivity at the β position parallels that observed with lithium in liquid ammonia.

The reaction of methyl(trifluoromethyl)dioxirane (1b), a novel dioxirane species, with two open-chain, four cyclic, and five polycyclic saturated hydrocarbons and two aralkyl hydrocarbons in CH2Cl2/1,1,1-trifluoropropanone has been studied; under mild conditions (-22 to 0 deg C), it gives alcohols and/or ketones (deriving from further oxidation of secondary alcohols) in high yields and within very short reaction times.Primary C-H bonds are not appreciably oxidized and high regioselectivities were determined for attack at tertiary over secondary C-H bonds, with theexception of norbornane, which showed opposite regioselectivity.The reaction is also highly stereoselective, since hydroxylations of cis- and trans-decalin and of cis- and trans-1,2-dimethylcyclohexane were found to be in each case stereospecific with retention.From kinetic data, Ea = 14.3 kcal mol-1 and log A = 9.9 were estimated for cyclohexane oxidation.Relative rates change in the order cyclohexane (0.78) octane (9.2) adamantane (146); cis-1,2-dimethylcyclohexane was observed to be 7-fold more reactive than its trans isomer, demonstrating remarkable discrimination for equatorial vs axial C-H attack (also noticed in the case of cis- and trans-decalin).The relative rate of oxidation of cumene vs ethylbenzene was found to be ca. 3.1 (after statistical correction), i.e., in sharp excess over values usually recorded in classical radical H-atom abstraction from benzylic position.Rate constants determined for the reactions of cumene and of ethylbenzene show the title dioxirane (1b) is more reactive than dimethyldioxirane (1a) by factors of ca. 600 and over 700, respectively.The whole of theobservations is better accommodated by an "oxenoid" mechanism, involving concerted O-atom insertion by dioxirane into C-H bonds of hydrocarbons.

Six saturated hydrocarbons (cyclohexane, 3-ethylpentane, methylcyclopentane, cis- and trans-decalin and adamantane) were oxidised by the Gif system (iron catalyst, oxygen, zinc, carboxylic acid) and its electrochemical equivalent (Gif-Orsay system).Results obtained using various solvents (pyridine, acetone, pyridine-acetone mixtures) were similar for both systems.Total or partial replacement of pyridine with acetone affects the selectivity for secondary positions and lowers the ketone/secondary alcohol ratio.The formation of the same ratio of cis- and trans-decal-9-ol from both cis- and trans-decalin clearly demonstrates that tertiary alcohols result from a mechanism essentially radical in nature.

The excited states of a representative heteropolytungstate, α-PW12O40(3-), and a representative isopolytungstate, W10O32(4-), accessible with near UV or blue light, oxidize alkanes and conventionally far more reactive organic molecules including alcohols, alkenes, N-alkylacetamides, and ketones, at comparable rates.One or more of the latter three types of compounds are produced upon irradiation of acetonitrile solutions containing the polyoxotungstate and alkane substrate under anaerobic conditions.Comparison of alcohol versus alkane reactivities under absolute and competitive kinetic conditions indicates that alcohol-polyoxotungstate preassociation can be important in these processes.Reaction of cis- and trans-decalones in these systems indicates that functionalization of unactivated positions (primarily incorporation of the olefinic unit) remote from the usually activating ketone group can be accomplished.

Reduction of various α,β-unsaturated ketones (3a-g) and (4a-d) in methanol by the benzothiazoline (1) in the presence of aluminium chloride gives, in all cases, the corresponding saturated ketones (5a-g) and (6a-d)without any of the unsaturated or saturated alcohol.Reduction of α,β-unsaturated esters (7a,b) similarly gives the saturated esters (9a,b), while reaction of cinnamaldehyde (8) with compound (1) does not occur at all.Among the Lewis acids examined, aluminium chloride gives the best results.Reduction of 2'-azachalcone (21) with 2-phenylbenzothiazoline reveals that, in the reduction product, the deuterium atom is located at the β-position with respect to the carbonyl group.The result obtained from the reduction of the same substrate with compound (1) in methanol shows that no incorporation of a hydrogen atom from the solvent takes place and suggests (indirectly) that the introduced hydrogen atom at the α-position of the product comes from the benzothiazoline (1).The reaction of (Z)-1,2-dibenzoyl-1,2-diphenylethylene (30) with compound (1) in the presence of aluminium chloride stereospecifically yields meso-1,2-dibenzoyl-1,2-diphenylethane (31).This shows that the transfer of two hydrogens from compound (1) to the carbon-carbon double bond of the enone proceeds via cis-addition.Experiments with ethyl phenylpropiolate (28) also support cis-reduction for the present conjugate reduction.These results are interpreted in terms of a mechanism involving synchronous transport of a pair of hydrogens from the benzothiazoline (1); i.e a cyclic addition of the two hydrogens either in exact or nearly exact concurrence.

The preparations of ten decalindiones for investigation as substrates of horse liver alcohol dehydrogenase are reported.The structure characterizations include clarifications of some ambiguities in the decalin literature.

The oxidation of trans-decahydronaphthalene (1) was carried out in acetic anhydride with oxygen in the presence of Co(OAc)2, Ce(OAc)3, and NH4Br.Decahydronaphthyl acetates were obtained as main oxidation products in a selectivity of 81 molpercent at 120 degC.In addition, relative reactivities of hydrogen atoms of 1 were determined at temperatures from 90 to 120 degC.

Carbonyl compounds were selectively reduced by diphenylstibine in the presence of Lewis acid.

Cleavage of N,N-dimethylhydrazones is cleanly effected with good yield in dichloromethane using the extremely inexpensive clay-supported ferric nitrate.

The triflates 8,9,12,17,19, and 23 have been synthesized to investigate their solvolysis products in absol. 2,2,2-trifluoroethanol (TFE) (Table 1).The kinetics of the solvolysis in 50percent ethanol have been measured as well.The rate constants give a straight correlation line when we apply an approximate Taft's equation, from which we deduce that the solvolyses take place by a kc mechanism; one exception is 12, as it reacts with S-O bond cleavage.We also deduce that the value of ρ* does not depend on steric factors.Relations between structure and rearrangement of vinyl cations are discussed.Mechanisms for the formation of reaction products are proposed.

Catalytic hydrogenation of 2-naphthol (NL) with the six platinum metals has been studied in t-BuOH at 80 degree C and 4-5 MPa H//2 pressure. Selectivities for formation of 1,2,3,4- and 5,6,7,8-tetrahydro-2-naphthols (ac- and ar-TLs) have been determined by application of a kinetic equation. ar-TL was formed more predominantly than ac-TL over all the metals. The hydrogenation of ac- and ar-TLs has also been studied under the same conditions for comparison. The hydrogenation of NL and ar-TL was accompanied by extensive hydrogenolysis to give decalins over Os, Ir, and Pt, whereas the hydrogenolysis occurred only slightly over Ru, Rh, and Pd. In general the hydrogenolysis occurred to much lesser extents with ac-TL. The amounts of 2-decalone formed in hydrogenation of ar-TL have been determined by application of the kinetic equation.

Novel covalent vandium(V) oxo peroxo complexes of general formula VO(O//2)(O-N)LL prime and anionic complexes with the general formula left bracket VO(O//2)(Pic)//2 right bracket ** minus A** plus L were synthesized and characterized by physicochemical methods and X-ray crystallography. The crystal structure of VO(O//2)(Pic) multiplied by (times) 2H//2O (Ia) revealed a pentagonal-bipyramidal environment, with a significant hydrogen bonding between the peroxo moiety and the equatorial water molecule. Protonated type II complexes (A** plus equals H** plus ) are dissociated in an aqueous solution and have an acidic nature (pK//a equals 1. 8) but are undissociated in a nonprotic solution, with a presumably peracid-like oxohydroperoxo structure. It is shown that vanadium peroxo complexes are effective oxidants in nonprotic solvents under mild conditions. They transform olefins to epoxides and cleavage products in a nonsteoroselective fashion (cis-2-butene gave a mixture of cis and trans epoxides). More interestingly, they hydroxylate aromatic hydrocarbons to phenols and alkanes to alcohols and ketones.

Δ1,9octalone, Δ1,9-10-methyl octalone and testosterone were reduced by NBu4BH4, alone or in the presence of tetramethylethylenediamine (TMEDA), in THF and in toluene.With TMEDA, the first step of the reduction is the regioselective 1,4 attack by BH4(1-) which leads either to the saturated ketones or to the corresponding saturated alcohols.The results observed under different conditions were interpreted by the intervention of various reductive species: diborane, enoxyborohydrides in the absence of TMEDA, amine-borane in its presence.

Hydrocyanation at sites other than ring junctions does not exhibit the same stereoselectivity in the keto-3 Δ1-steroid series as in analogous bicyclic compounds.Irrespective of the presence or the absence of an angular methyl group, the kinetic product has always an axial cyano group; however a stereoelectronic control of the reverse reaction explains why under thermodynamic conditions, only enones of the decalin series give both axial and equatorial epimers.A conformational analysis based on the conservation of the torsion angle and the maximum overlap of orbitals accounts for these facts.

The methyl acetals of 2-hydroxy-3-oxa-trans-decalin were synthesized as models for conformationally rigid methyl glycosides.The compounds were prepared by Baeyer-Villiger oxidation of trans-hexahydrohydrindan-2-one followed by reduction of the resulting lactone with diisobutylaluminum hydride.Treatment of the hemiacetal with methanol and an acid catalyst afforded a mixture of acetals which were separated by chromatography and identified by NMR.Hydrolytic studies were carried out under a range of acid concentrations and temperatures.The mechanistic implications of the relative hydrolysis rates (axial/equatorial ratio of 1.51+/-0.22) and activation parameters are discussed.

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Tetraethyl- and tetrabutylammonium permanganate are less prone to explosive decomposition when heated than are benzyl(triethyl)ammonium and methyl(triphenyl)phosphonium permanganate and are about equally effective as oxidants for the conversion of alkanes into alcohol and ketones.