Synthesis of 7-Deamidocephalosporin Lactone. Preliminary Communication

Condensation of azetidinone 1 with mercaptan 3 gave compound 5 . Bromination of 5 afforded two isomeric bromohydrins 11a and 11b which differ in the configuration at C(4). Acetylation and reduction with zinc and acetic acid of the above bromohydrins gave 7-deamidocephalosporin lactone ( 14 ).     

On the Structure of Oxirane Molecular Cation. Preliminary Communication

A recent controversy on the interpretation of the ESR spectrum of ionized oxirane is clarified on the basis of the electronic absorption spectra of ionized tetramethyloxirane and 9,10-octalineoxide. The results favour a ring-opened structure for oxirane molecular cation, resulting from C? C bond cleavage and being iso-π-electronic to allyl radical.     

New Indigo Syntheses. Preliminary Communication

Three novel routes for the preparation of the dyestuff indigo are described. Two of the methods use isatoic anhydride, the third one styrene as starting materials. Key reactions are acylation of both dimsyl and nitromethane anions, Pummerer rearrangement and Nef reaction. A novel nitration of styrene is the basis of the third method.     

Building Blocks for the Synthesis of Maytansinoids. Preliminary Communication

The dienal 14 and the ketone 19 , both potential building blocks of maytansinoids, were synthesized starting from ethyl vanillate ( 2 ) via the aldehyde 9 . It could be shown in a preliminary experiment that the dienal 14 can be coupled with 2-lithio-1,3-dithiane to afford compound 16 which exhibits the correctly substituted aromatic part of maytansine as well as its C(9) to C(15) moiety.     

Studies Directed to the Total Synthesis of Cepacin A. Preliminary Communication

The synthesis of the bromoallenyl‐substituted epoxide derivative 34 related to cepacin A ( 1 ) starting from D ‐arabinose as a chiral pool is reported.     

Highly Stereoselective Photochemical Oxidative Addition Reactions. Preliminary Communication

Cyclometallated complexes of the type cis-bis(2-phenylpyridine)platinum(II) (C₂₂H₁₆N₂Pt) and cis-bis(2-(2′-thienyl)pyridine)platinum(II) (C₁₈H₁₂N₂S₂Pt) undergo thermal or photochemical oxidative addition (TOA or POA) reactions with a number of substrates. TOA (with CH₃I, CH₃CH₂I etc.) yield mixtures of several isomers which rearrange slowly (within ca. one week at room temperature) to one of the possible cis-isomers. CH₂Cl₂, CHCl₃, or (E)? ClCH?CHCl, e.g., do not react thermally. POA yield directly complexes of Pt(IV) with the halide and a σ-bonded C-atom in cis-position. The configuration, as assigned by extensive use of ¹H-NMR data, can be characterized for the two chelating ligands C …? N and C′ …? N′ by C,C′-cis; N,N′-cis and C(chelate), Cl-trans.     

The First Asymmetric Intramolecular Stetter Reaction. Preliminary Communication

The first asymmetric intramolecular Stetter reaction is reported, using the chiral triazolium salt 1 as catalyst. Starting from the easily accessible 4-(2-formylphenoxy)but-2-enoates 2 , this protocol opens up an enantioselective pathway to the benzo-annulated pyran-4-ones (chroman-4-ones) 3a–h with good yields and enantiomeric excesses of up to 74%.     

Dendrophanes: Novel Steroid-Recognizing Dendritic Receptors. Preliminary Communication

The H₂O-soluble dendritic cyclophanes (dendrophanes) 3–5 of first to third generation with molecular weights up to nearly 20 kD were synthesized, purified, and characterized. Cyclophane 2 , which served as the initiator core (generation zero), was prepared from tetrabromocyclophane 10 in a four-step sequence which involved as the first transformation a high-yielding, four-fold Pd(0)-catalyzed Suzuki cross-coupling reaction with 4-(benzyloxy)-phenyl-boronic acid to give 18 . The X-ray crystal-structure analysis of tetrabromocyclophane 10 displayed an open, nearly rectangular box with opposite aromatic walls being 8.3 and 11.4 Å apart and of suitable size for the incorporation of steroidal substrates. ¹H-NMR Binding titrations in borate-buffered D₂O/CD₃OD 1:1 showed that cyclophane-tetracarboxylate 2 forms 1:1 inclusion complexes with steroids (Table 2). Complexation was found to be enthalpically driven with higher binding affinities measured for the more apolar substrates. ¹H-NMR Titrations in the same solvent also provided clear evidence for core-selective complexation of testosterone ( 21 ) by the dendrophanes 3 (1st), 4 (2nd), and 5 (3rd generation) carrying up to 108 carboxylate surface groups. The stability of the corresponding 1:1 complexes was hardly affected by the size of the dendritic shell, although some generation-dependent conformational changes in the receptor cavity seemed to take place. Remarkably, host-guest exchange kinetics in all recognition processes were fast on the ¹H-NMR time scale.     

Preliminary Communication. Refractive index of a sheared cholesteric polymer

Abstract

After unwinding a cholesteric solution of a mesomorphic polymer by shear, we investigate the evolution of the refractive index. Two mechanisms with different time constants are observed, one corresponding to the cholesteric rewinding, the other to the reorientation of the cholesteric axes.     

Preliminary Communication. Refractive index of a sheared cholesteric polymer

After unwinding a cholesteric solution of a mesomorphic polymer by shear, we investigate the evolution of the refractive index. Two mechanisms with different time constants are observed, one corresponding to the cholesteric rewinding, the other to the reorientation of the cholesteric axes.     

Photochemical Synthesis of 2-Alkylidene-1,3-cyclocalkanediones. Preliminary Communication

Photolysis (λ = 254 nm) of 4-(tert-butyl)-4,6,7,8-tetrahydro-7,7-dimethy-2H-1-benzopyran-2,5(3H)-dione ( 3a ) in t-BuOH affords 2-(2,2-dimethylpropylidene)-5,5-dimethyl-1,3-cyclohexanedione ( 1a ) in 80% yield via homolysis of the lactone O? CO bond and subsequent ketene elimination.     

CuI‐Mediated Trifluoromethylations with Stannanes. Preliminary Communication

(Trifluoromethyl)stannane reagents such as Bu₃SnCF₃ are effective in CuI‐mediated trifluoromethylation reactions of aryl iodides. The reactions proceed via the intermediacy of [CuCF₃] species.     

On the stereochemistry of allylmetal-aldehyde condensations. Preliminary communication

The stereochemical course of the intramolecular allylsilane-aldehyde condensation of 1a has been investigated. A modest preference for the product arising from a synclinal orientation of double bonds was observed with Lewis-acid catalysts. Cyclization induced by fluoride ion resulted in stereochemical reversal.     

Cycloaddition of Carbodiimides and Triphenylketen-imine to Allenic Acids. Preliminary Communication

Allenic acids are found to add to dicyclohexylcarbodiimide affording, in the presence of secondary amines, the 1,3-oxazine-4-ones. 5 . Under neutral conditions, they add to diaryl- or aryl(cyclohexyl)carbodiimides and triphenylketen-imine to give the corresponding tricyclo[5.2.2.0^1,5]undecatriene-3-ones 7–9 and 12 .     

Chlorine Dioxide as an Electron-Transfer Oxidant of Olefins. Preliminary Communication

The kinetics and product studies of oxidation of eight olefins 1 - 8 by ClO₂ in H₂O in the pH range 3-7 are described. The reaction is faster as the pH decreases. At pH < 4, ClO₂ reacts equimolarly with olefins to yield isomeric mixtures of chlorohydrines and 1,2-dioxygenated products, following the equation: The order of reactivity is: (E)-stilbene > indene > β-methylstyrene > acenaphthylene > α-methylstyrene > styrene > cyclohexene > allylbenzene. A multi-stage radical-cation mechanism is proposed, in which an initial reversible protonation: is followed by an electron-transfer stage (rate-determining): The cation-radical thus produced, adds rapidly an additional ClO₂ to form dioxygenated products. The chlorohydrines most likely arise from HClO additions to the olefinic double bonds, which, in turn, generate from dismutation of 2 HClO₂ into HClO + H⁺ + ClO.     

Carbon-chain polymers and copolymers Communication 7. Kinetics of the polymerization of alkoxystyrenes

Summary The rate constants for the polymerization of thirteen alkoxystyrenes at 100° were determined, and it was found that the size of the alkoxy group affects the rate of polymerization only in the case of o-alkoxystyrenes and has no effect on the rate of polymerization of p-alkoxystyrenes.     

论经济学的非历史性—重读马克思《哲学的贫困》

对《资本论》的性质和方法的研究,在今天仍是马克思研究领域中一个基本而重要的课题,这是因为,在《资本论》中展开的学说,对于分析和洞察当代资本主义的经济现象、趋势和危机,仍然具有非常深刻的启发和指导意义。《资本论》对于资本主义研究具有不可取代的作用,《哲学的贫困》的思想内容可看作整个《资本论》学说的一个导言。《资本论》学说是马克思运用感性辩证法所建构的一门历史科学。其关于具有批判和革命性质的历史科学的思想,以及对经济学的非历史性的批判,早在1847年的《哲学的贫困》中就得到了阐发。     

On the Nature of the Positronic Bond

Recently it has been proposed that the positron, the anti-particle analog of the electron, is capable of forming an anti-matter bond in a composite system consists of two hydride anions and a positron [Angew. Chem. Int. Ed. 57 , 8859–8864 (2018)]. In order to dig into the nature of this novel bond the newly developed multi-component quantum theory of atoms in molecules (MC-QTAIM) is applied to this positronic system. The topological analysis reveals that this species is composed of two atoms in molecules, each containing a proton and half of the electronic and the positronic populations. Further analysis elucidates that the electron exchange phenomenon is virtually non-existent between the two atoms and no electronic covalent bond is conceivable in between. On the other hand, it is demonstrated that the positron density enclosed in each atom is capable of stabilizing interactions with the electron density of the neighboring atom. This electrostatic interaction suffices to make the whole system bonded against all dissociation channels. Thus, the positron indeed acts like an anti-matter glue between the two atoms.