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Electrospray ionisation mass spectrometry (ESI-MS) has been used to study the relative gas-phase proton and alkali metal (Li, Na, K and Cs) binding affinities of three different resorcin[4]arenes using the kinetic method. Collision-induced dissociation (CID) was used to study the fragmentation of resorcin[4]arene heterodimer sandwich complexes, allowing the relative binding affinity order to be established. All the alkali metal cations have the same gas-phase binding affinity order with the resorcin[4]arene host molecules. At collision energies of = 13 eV, one of the [resorcin[4]arene + Metal]+, (Metal = Li, Na, K) ions fragmented through break-up of the resorcin[4]arene, whilst the other host resorcin[4]arene remained intact, causing an apparent change in binding affinity at high collision energy. This effect was not observed with caesium, since all complex ions dissociated readily under CID by displacement of the caesium cation. The binding affinity for the protonated resorcin[4]arenes was found to be different from the alkali metal cation binding affinity because of the higher proton affinity of the nitrogen-containing resorcin[4]arenes. It is shown that resorcin[4]arenes containing an oxazine ring can be converted into a ring-opened derivative via an Eschweiler–Clarke reaction in the presence of formic acid. A second ring-opening process also occurs, including a hydrolysis reaction that results in apparent losses of 12 mass units from the intact resorcin[4]arene. Both these reactions occur in solution before mass spectrometric investigation and cannot be achieved by CID. This observation was confirmed by inducing the Eschweiler–Clarke reaction in a model benzoxazine compound.

The conversion of axially chiral tetraalkoxyresorcin[4]arenes (cyclochiral resorcinarenes) into the related tetrakis(triflates) in high yields is described; this provides an efficient source of chiral materials for use in palladium‐catalyzed transformations, including the reductive removal of triflate groups and the synthesis of compounds that are formally derived from 3‐aminophenol, providing axially chiral derivatives that are nitrogen‐substituted on the upper rim.

A number of stable new NH oxaziridines have been designed and prepared, and their reactivity as electrophilic sources of nitrogen investigated. 3tertButyl3phenyloxaziridine is the most efficient and stable and has potential for use as a general reagent for this purpose.

Enantiomerically enriched epoxides are useful intermediates that have found many applications in asymmetric synthesis, and development of efficient catalysts for asymmetric epoxidation has received considerable attention. In this manuscript we describe the design, preparation, and use of new highly selective iminium salt organocatalysts for asymmetric epoxidation, based around a chiral binaphthalene motif coupled with a chiral substituted dioxane moiety. The new catalysts have been tested in the catalytic asymmetric epoxidation of unfunctionalized alkenes, and provide up to 95  ee. © WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

Iminium salt organocatalysts can provide high selectivity and high efficiency in catalytic asymmetric epoxidation. They are normally used in conjunction with Oxone as the stoichiometric oxidant. Oxone, however, has limited stability and is insoluble in most organic solvents; we report here for the first time the development of a reaction system driven by hydrogen peroxide as the stoichiometric oxidant, involving an unusual double catalytic cycle.

The preparation of a series of diastereoisomeric tetracamphorsulfonates derived from racemic tetramethoxyresorcin[4]arenes was achieved by reactions with an excess of (S)-(+)-10-camphorsulfonyl chloride in pyridine followed by isolation using flash chromatography. Tetradeprotonation of a number of tetramethoxyresorcin[4]arenes using n-butyllithium in tetrahydrofuran, followed by reactions using (S)-(+)-10-camphorsulfonyl chloride, gave the same tetracamphorsulfonates. Mono-, di- and tricamphorsulfonates were also prepared following selective deprotonation. In the reactions with tetraisopropyloxy- and tetracyclopentyloxyresorcin[4]arenes, only the mono- and dicamphorsulfonates were formed. X-ray crystallographic analysis established the absolute configurations of three diastereoisomerically pure tetracamphorsulfonates, including a diastereoisomer prepared from 6,12,18,24-tetramethoxy-2,8,14,20-tetrakis(2-methylpropyl)resorcin[4]arene. An additional pair of diastereoisomers was also prepared using (R)-(–)-10-camphorsulfonyl chloride and 6,12,18,24-tetramethoxy-2,8,14,20-tetrakis(2-methylpropyl)resorcin[4]arene, for one of which the structure was confirmed by an additional X-ray structure determination. Hydrolytic removal of the camphorsulfonyl residue(s) from the various diastereoisomers gave enantiomers of known absolute configurations. In some cases, the chiral nonracemic tetraalkoxyresorcin[4]arenes were converted into known tetrabenzoxazine derivatives by using N,N-bis(methoxymethyl)[(S)-(–)-(α-methylbenzyl)]amine in thermal or microwave-assisted reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The measurement of the pKa of racemic tetramethoxyresorcin[4]arenes explains the failure to obtain good yields in attempted Mannich reactions of these substrates under classical reaction conditions. The failure is related to the lack of adequate concentrations of the iminium ions that results from the reduced acid strength of tetraalkoxyresorcin[4]arenes compared with that of the parent octahydroxyresorcin[4]arenes. However, the preparation of a series of Mannich bases derived from racemic tetraalkoxyresorcin[4]arenes was accomplished under microwave-assisted aprotic reaction conditions and the use of preformed iminium ion intermediates. When the reactions were carried out with the use of chiral bis(aminol) ethers, mixtures of diastereomers were obtained that could be separated by flash chromatography. The absolute configurations of the enantiomerically pure tetrabenzoxazine derivatives were established in some cases by X-ray crystallographic analysis and by a comparison of the nuclear magnetic resonance spectroscopic data. The alkylation of racemic tetramethoxyresorcin[4]arenes was achieved with the use of an excess of 2-bromo-N-[(R)-(+)-(α-methylbenzyl)]acetamide in acetonitrile containing potassium carbonate. Enantioselective ligand-assisted reactions of aromatic aldehydes are also reported with the use of dialkylzinc reagents both in the absence and in the presence of terminal alkynes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A highly enantioselective iminium salt catalyst has been prepared and tested in the catalytic asymmetric epoxidation of unfunctionalized alkenes, giving up to 95% ee, the highest ee yet reported for iminium salt-catalyzed epoxidation. Catalyst loadings as low as 0.1 mol % may be used.

No Abstract

The voltammetry of the water-insoluble redox liquids para-N,N,N‘,N‘-tetraalkylphenylenediamines (TAPDs; A = butyl, hexyl, heptyl, octyl, and nonyl) at the TAPD|electrode|electrolyte interface is studied. The ion-transfer processes between the aqueous and the organic phase&sbd;consequent of the necessity to maintain charge neutrality during electrochemical oxidation and reduction reactions in the organic phase&sbd;are elucidated as a function of the Gibbs free energy of transfer of the electrolyte anions, of the concentration of TAPD in the organic phase, and of the length of the alkyl chain of the phenylenediamines. Two conditions are considered:  the voltammetry of microdroplets of the pure redox liquids and the voltammetry of the TAPDs dissolved in nitrobenzene, either deposited as microdroplets at an electrode surface. The oxidation of the neutral redox liquids, accompanied by the uptake of anions from the adjacent aqueous solution leads to the formation of ionic liquid phases, TAPD⁺X^- and TAPD²⁺X^-2 (X^- = monovalent electrolyte anions). Despite the high concentration of redox centers in the microdroplets, the redox potentials of the TAPDs are exclusively determined by the Gibbs free energy of the electrochemically driven transfer of anions between the aqueous and the redox liquid phase. There is no evidence for ion pair formation of the TAPD⁺ and TAPD²⁺ with the transferred anions X^- either in the pure redox liquid phase or in the nitrobenzene matrix. Depending on the Gibbs energy of transfer of the electrolyte anions two different reaction mechanisms are observed:  At low ΔG values, a reversible transfer of electrolyte anions across the liquid/liquid interface as a consequence of the redox process takes place. However, anions with high transfer energies do not enter the organic phase. Instead, upon oxidation TAPD mono- and dications are transferred from the organic into the aqueous phase, which leads to the diminution of the voltammetric signals due to the loss of material from the droplets. From the voltammetric data, the Gibbs energy of transfer of the different TAPD cations and of the hexafluoroarsenate anion were derived for the water|nitrobenzene interface. Whereas the oxidation of the TAPD in the nitrobenzene droplets due to its low concentration does not measurably affect the properties of the nitrobenzene|water interface of the droplet, the oxidation of the pure redox liquids leads to a considerable change of the liquid|liquid interface upon ionic liquid formation. This change depends on the nature of the inserted anion:  the more hydrophilic the inserted anion is, the less hydrophobic the ionic liquid becomes.

A synthesis of the tricyclic ring system of the daphnane and tigliane diterpenes, incorporating C-18 and the C-13 oxygen functionality found in phorbol and related compounds is described. The convergent synthesis utilizes an intramolecular Diels-Alder reaction as the key stereocontrolling step.

The leaching of Ti from the redox molecular sieve TS-1 when used as a catalyst for the oxidation of crotyl alcohol with hydrogen peroxide is described and discussed. The crystallisation time of the TS-1 is found to be the critical preparation parameter. TS-1 prepared using a 2 day crystallisation period leaches Ti, whereas TS-1 prepared using a 10 day crystallisation period is inert to leaching. Silanisation of the external surface of the 2 day preparation effectively stops the leaching of Ti, without significantly affecting the catalytic performance. Similarly, treatment of the 2 day TS-1 with sodium azide also minimises leaching of Ti but with a reduction in catalytic activity. The Ti leaching is shown to be caused by the reaction of a triol with TS-1 in the presence of hydrogen peroxide from the surface of the 2 day TS-1. A possible mechanism is proposed in which the triol by-product chelates the Ti, thereby breaking Ti–O–Si framework bonds and causing leaching to form a Ti species in solution. The reactivity of this Ti species in solution is modelled using the reaction of crotyl alcohol with hydrogen peroxide in the presence of titanyl acetylacetonate, and it is found that this effectively catalyses the formation of triol. Hence, it is concluded that, once initiated, Ti leaching will be catalysed by the reaction products of the solution Ti species that is formed.

Manganese-exchanged Al-MCM-41 modified by the chiral salen ligand [(R,R)-(−)-N,N '-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamine] has been investigated as a heterogeneous catalyst for the enantioselective epoxidation of (Z )-stilbene using iodosylbenzene as oxygen donor, with particular interest in the effect of reaction conditions on the cis∶trans ratio of the epoxide product. Immobilisation of the chiral Mn–salen complex in Al-MCM-41 increases the cis∶trans ratio of the epoxide product when compared to the non-immobilised complex under the same conditions. Increasing the level of Mn-exchange in the Al-MCM-41 increases the amount of trans-epoxide, whereas increasing the iodosylbenzene∶substrate ratio increases the amount of cis product formed. Increasing the reaction temperature also increases the amount of trans-epoxide for the homogeneous Mn-complex under the same conditions. A series of experiments is described in which the external ion-exchange sites on Al-MCM-41 are preferentially silanised, which enables the cis/trans selectivity for external and internal sites to be determined. Mn–salen immobilised on the external surface of Al-MCM-41 gives the same cis∶trans ratio as that observed with the non-immobilised Mn–salen complex in solution, whereas Mn–salen immobilised within the pores gives the cis-epoxide preferentially. The enantioselection of the immobilised chiral Mn–salen complex is shown to decrease with reaction time at −10 °C, but the cis∶trans epoxide ratio remains unchanged; whereas for the non-immobilised complex in solution the enantioselection is independent of reaction time. Iodobenzene, a decomposition product formed from iodosylbenzene, is found to act as a poison for the immobilised catalyst, leading to a slower reaction and lower enantioselection.

A combined experimental and molecular simulation study of the oxidation of thioethers with hydrogen peroxide using Ti-containing zeolites as catalysts is described and discussed. Two aspects of reaction selectivity were explored. First, regioselectivity was studied for the oxidation of allyl methyl thioether with TS-1 as catalyst, and only products for the oxidation at sulfur, i.e., the sulfoxide and sulfone, were observed. Second, shape-selective oxidation was studied using four isomeric butyl methyl thioethers. For n-, iso- and sec-butyl methyl thioethers the dominant product in the TS-1 catalysed reaction was the sulfone, but for tert-butyl methyl thioether, the dominant product was from partial oxidation to the sulfoxide. Molecular simulations were used to investigate the origin of this effect. For all substrates used in this study, the oxidation of the thioether to the sulfoxide was found to occur readily by a non-catalysed solution reaction and this was studied in detail. However, the oxidation of the sulfoxide to the sulfone was only observed in the catalysed reactions. It was observed that the non-catalysed reaction can be suppressed by carrying out the catalysed reaction in the presence of a base, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), that is too large to diffuse into the intracrystalline pore structure of TS-1. In the presence of DBU, the rate of reaction with TS-1 as catalyst was much lower and the relative ratios of the sulfoxide and sulfone products can be explained through a combination of intramolecular steric hindrance and the shape selectivity of the zeolite.

Copper-exchanged zeolite Y (CuHY) is found to be a highly effective heterogeneous catalyst for the aziridination of alkenes using [N-( p-tolylsulfonyl)imino]phenyliodinane (PhI&z.dbd6;NTs) as the nitrogen source. Exchange of zeolite Y with other cations (Ag⁺, Co²⁺, Fe³⁺, Mg²⁺, Ni²⁺, Zn²⁺) was found to be ineffective. This is considered to be due to the ability of these metals to catalyse the breakdown of the PhI&z.dbd6;NTs reagent into iodobenzene and toluene sulfonamide. Modification of the CuHY catalyst with bis(oxazolines) leads to preparation of the first heterogeneous enantioselective aziridination catalyst and the results showing the effect of temperature and modifier concentration are described and discussed. A pyridine-bridged bis(oxazoline) was observed to give the highest enantioselectivity of 61% ee for the aziridination of styrene using acetonitrile as solvent and at −10 °C.

Members of a series of α,ω-di(adenosin- N6-yl)alkanes, comprising two adenosine residues linked with alkyl bridges from 1 to 14 methylene units in length, were found to be inhibitors of rat liver and BHK cell adenosine kinase. The inhibition was competitive with respect to adenosine and non-competitive with respect to ATP. The corresponding α,ω-di(cytidin-N4-yl) alkanes were not inhibitors and N6-alkyladenosines inhibited only weakly.

Polymerizations of methyl methacrylate initiated by organocuprates in tetrahydrofuran solution have been investigated. The heterocuprate lithium n-butylcyanocuprate was found to be an effective initiator at - 78°C, and lithium di-n-butylcuprate was confirmed as an effective initiator; both species give rapid polymerization to virtually complete conversion of monomer. Polydispersities (Mw/Mn) are about 1.5. Polymerizations have an inherent termination reaction and a low initiator efficiency. Polymerization of methyl vinyl ketone is virtually uncontrollable, and polymerizations of methyl methacrylate are inhibited by styrene.

Sulphides are efficiently oxidized to either sulphoxides or sulphones as required by treatment with acetonitrile/hydrogen peroxide and potassium carbonate in methanolic solution.

A key intermediate 14 for the synthesis of lactacystin 1 has been constructed in four steps and 33% overall yield. The key steps involve cyclization of a suitably functionalized glutamic acid derivative and concomitant alkylation of the resulting β,β-diketoester system, C-acylation of the cyclic α-amidoketone 9, and decarboxylbenzylation of 12. Alkylation of a related β,β-diketoester 5 was additionally achieved with several electrophiles.

New iminium salt organocatalysts for catalytic asymmetric epoxidation based upon dibenzazepinium salts are reported, providing ee of up to ca 60%.

Triols, formed as by-products from the titanium silicalite (TS-1) catalysed epoxidation of allylic alcohols, can cause leaching of Ti from the microporous framework.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.