The first enantioselective organocatalytic Mukaiyama-Michael reaction: a direct method for the synthesis of enantioenriched gamma-butenolide architecture

The first enantioselective organocatalytic Mukaiyama-Michael reaction using alpha,beta-unsaturated aldehydes has been accomplished. The use of iminium catalysis has provided a new strategy for the enantioselective addition of 2-silyloxy furans to unsaturated aldehydes to generate a variety of butenolide systems, an important chiral synthon found among many natural isolates. The (2S,5S)-5-benzyl-2-tert-butyl-imidazolidinone amine catalyst has been found to mediate the conjugate addition of a wide variety of substituted and unsubstituted silyloxy furans to unsaturated aldehydes. A diverse range of aldehyde substrates can be accommodated in this new organocatalytic transformation. Application of this new asymmetric technology to the enantioselective total synthesis of spiculisporic acid and the corresponding 5-epi-spiculisporic acid analogue is also discussed.     

THE EFFECT OF RED AND FAR-RED LIGHT ON NUCLEIC ACID METABOLISM IN RYE SEEDLING SHOOTS

Abstract— The quantitative changes in the levels of RNA and DNA in shoots treated with red and/or far-red light are presented.
The results indicate that red light, but not far-red light, stimulated cell division. The changes in RNA are discussed in relation to the nature of the light treatment.     

A simple molecular-orbital study of theβ-,α-, and p-bands in triphenylenes

Clar has observed that the spectra of annellated derivatives of triphenylene such as II, III, IV below show remarkable resemblance to those of the phenes defined by the central ring of the triphenylene and its two longest acene limbs, II resembling tetraphene I, and III and IV pentaphene V. We show that this observation can be explained in terms of a simple modification of the Hückel molecular-orbital method.

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Zusammenfassung Eine Beobachtung von Clar hat gezeigt, daß die Spektren der Benzologen des Triphenylens, wie z. B. II, III, IV außerordentlich ähnlich sind denen der Phene, die ausgehend vom zentralen Ring und den beiden längsten Armen der obigen Systeme gebildet werden. Daher ähnelt das Spektrum von II stark dem des Tetraphens I und die von III und IV dem des Pentaphens V. Es wird gezeigt, daß dieser Beobachtung durch eine einfache Modifikation der Hückelschen MO-Theorie Rechnung getragen werden kann.

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Résumé Clar a observé que les spectres d'absorption des dérivés annelés du triphénylène tels que, II, III et IV montrent une ressemblance extraordinaire à ceux des phènes définis par l'anneau central du triphényléne et ses deux armes les plus longues. Ainsi le spectre de II ressemble à celui du tétraphène et ceux de III et de IV à celui du pentaphène V. Nous avons démontré qu'on peut expliquer cette observation par une modification simple de la méthode des orbitales moléculaires d'Hückel.

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We gratefully acknowledge many helpful discussions with Dr. E. Clar and Dr. J.-F. Guye-Vuilléme and the award of a D. S. I. R. Maintenance Grant to one of us (D. A. M.-B.). Chemistry Department, University of Glasgow.     

Bi- and poly-metallic cyanide-bridged complexes of the redox-active cyanomanganese nitrosyl unit [Mn(CN)(PR3)(NO)(eta-C5H4Me)

Cationic nitrile complexes and neutral halide and cyanide complexes, with the general formula [MnL1L2(NO)(eta-C5H4Me)]z, undergo one-electron oxidation at a Pt electrode in CH2Cl2. Linear plots of oxidation potential, Eo', vs. nu(NO) or the Lever parameters, EL, for L1 and L2, allow Eo' to be estimated for unknown analogues. In the presence of TlPF6, [MnIL'(NO)(eta-C5H4Me)] reacts with [Mn(CN)L(NO)(eta-C5H4Me)] to give [(eta5-C5H4Me)(ON)LMn(mu-CN)MnL'(NO)(eta5-C5H4Me)][PF6] which undergoes two reversible one-electron oxidations; DeltaE, the difference between the potentials for the two processes, differs significantly for stable cyanide-bridged linkage isomers. Novel pentametallic complexes such as [Mn[(mu-NC)Mn(CNBut)(NO)(eta5-C5H4Me)]4(OEt2)][PF6]2 and [Mn[(mu-NC)Mn(CNXyl)(NO)(eta5-C5H4Me)]4(NO3-O,O')][PF6], containing a trigonal bipyramidal and a distorted octahedral Mn(II) centre, respectively, result either from slow decomposition of the binuclear cyanide-bridged species or from the reaction of anhydrous MnI2 with four equivalents of [Mn(CN)L(NO)(eta5-C5H4Me)] in the presence of TlPF6.     

Chemical control of peptide material phase transitions

Progressive solute-rich polymer phase transitions provide pathways for achieving ordered supramolecular assemblies. Intrinsically disordered protein domains specifically regulate information in biological networks via conformational ordering. Here we consider a molecular tagging strategy to control ordering transitions in polymeric materials and provide a proof-of-principle minimal peptide phase network captured with a dynamic chemical network.

Substrate initiated assembly of a dynamic chemical network.     

La and Zn promotion of Ru Fischer-Tropsch catalysts

An investigation of the use of La- and Zn-promoters for Ru/SiO₂ F-T catalysts has been carried out. It was found that, while the use of a La-promoter did not result in any improvement over the use of a K one, Zn-promotion resulted in much higher yields of olefins. The CH₄ and olefin selectivities of the Zn-promoted Ru/SiO₂ were essentially insensitive to temperature over the range 250–320 °C. The Zn-promoted catalyst was found to have many of the same catalytic properties previously found for Ru/ZnO, but was much more active. Thus, it is possible to achieve certain interesting catalytic properties for Ru by the use of Zn-promotion without having to make use of the low surface area support ZnO.

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La Zn- Ru/SiO₂ F-T. , , La- - , Zn- . CH₄ Zn- Ru/SiO₂ , -, 250–320°C. Zn- , Ru/ZnO, . Ru, Zn- ZnO .

     

Identification and characterization of monoanionic tripodal tetradentate ligand complexes of copper(I) and copper(II) involved in halogen atom transfer reactions

The copper(I) complex of bis-(2-(2-pyridyl)-ethyl)-(2-(N-p-toluenesulfonamido)-ethyl)amine (PETAEA), a monoanionic, tripodal tetradentate ligand, was prepared, characterized, and shown to be an effective catalyst for atom transfer radical polymerization (ATRP). A model atom transfer reaction of Cu(PETAEA) with 1-phenylethyl bromide and TEMPO radical trapping agent was studied. The copper(II) complex formed in this reaction was identified by comparison of its spectroscopic data with that of Cu(PETAEA)Br prepared by an independent synthesis. Kinetic and spectroscopic data indicated that the reaction mechanism involved simple atom transfer from the alkyl halide to the Cu(PETAEA) to form the Cu(PETAEA)Br, and no other intermediates were involved. The solid-state structures of the copper(I) and (II) complexes appeared to be maintained in solution, so this system is an atom transfer reaction in which all of the reactive species are identified and characterized.     

Decomposition rates of radiopharmaceutical indium chelates in serum

The rates at which six small aminopolycarboxylate chelates of trivalent¹¹¹In and three protein-bound chelates of¹¹¹In deliver indium to the serum protein transferrin have been studied in sterile human serum at pH 7.3, 37°C. Sterically hindered chelates containing a substituent on an ethylene carbon of EDTA decompose with rates in the range 0.03 to 0.11% per day—one to two orders of magnitude slower than other chelates. Only small differences are observed between rates of decomposition for low-molecular-weight chelates and for protein-bound chelates having analogous structures.     

The mechanism of the norrish type II reaction of α-keto-acids and esters

Methyl-α-keto-octanoate undergoes a Type II reaction to give pent-1-ene and photophysical measurements show that this and the Type II reactions of α-keto-acids occur, contrary to previous claims, from the excited singlet state.     

Near- and far-field emission distributions of mesa stripe geometry double heterostructure lasers

Mesa stripe geometry double heterostructure lasers have been made with cavity widths down to 16 μm. The lowest threshold current values are down to 75 mA but more typical values are 110 mA, and the slope efficiencies are typically 40%. Measurements of near- and far-field distributions have shown that the problem of high order mode structure parallel to the junction is not as serious as expected although emission is normally in the lowest order only for very low drive currents. Improved mode control is demonstrated by a hybrid mesa-contact stripe geometry device which gave a pulse power output of 30 mW in the lowest order mode at a drive current of 310 mA.