Hydrogen bonding NH/pi interactions between betacarboline and methyl benzene derivatives

In the presence of benzene, toluene, m-xylene, mesitylene and durene, the pyrrolic NH stretching band of betacarboline, 9H-pyrido[3,4-b]indole, and its 1-methyl derivative, harmane, in tetrachloroethane diminishes in intensity while a new red-shifted band grows up. The shifts of the associated bands increase linearly with the pi-electron density of the substrates. These spectral changes are attributed to the formation of 1:1 molecular association complexes between the betacarbolines and the benzenoid substrates. The complexes are stabilized by the hydrogen-bonding interaction between the pyrrolic NH group of betacarboline and the pi-delocalized electrons of the benzene derivatives. The influence of these NH/pi hydrogen-bonding interactions in the fluorescence spectra of betacarboline is discussed.     

Scalable synthesis of methyl ent-isocopalate and its derivatives

An efficient and convenient synthetic route was developed to prepare the tricycle diterpene intermediates 1-3 starting from commercially available (−)-sclareol. This improved approach involving four-step reactions provides large-scale (30-40 g) methyl ent-isocopalate in 61% overall yield, which could supply sufficient material for the synthesis of marine natural products containing tricyclic diterpenes.     

Wurtz-Fittig syntheses of mixed trideuteromethyl and methyl derivatives of benzene

In the Wurtz-Fittig reaction of an aryl bromide with methyl iodide no rearrangement products are produced. All reaction mechanisms involving radical intermediates are contrary to experimental results and should be rejected. Selective or even specific adsorption dominates the sequence of the Wurtz-Fittig reactions:

Aryl tribromide aryl dibromide aryl monobromide alkyl iodide, although chemical reactivity with sodium is in the reverse order, the higher ranking molecule reacting much slower. This effect may be important in other surface-localized reactions also.

By the method described, it is possible to introduce any number of trideuteromethyl groups at predetermined locations in the phenyl nucleus. Thus fifteen trideuteromethyl derivatives and mixed trideuteromethyl and methyl derivatives of benzene have been prepared (see Tables).     

Radical cyclization of exo-methylene furanose derivatives: an expedient approach to the synthesis of chiral tricyclic nucleosides and benzannulated oxepine derivatives

Tributyltin radical mediated cyclization of the glucose derived exo-methylene furanose derivatives 5a-c led to the highly functionalized cis-fused bicyclic ethers 6a-c. The product could subsequently be transformed to the optically active tricyclic nucleoside analogue 8 or oxepine derivative 9.     

Gold-catalyzed cyclization in the synthesis of antimitotic 2,3-dihydrobenzo[b]oxepine derivatives of colchicine

Russian Chemical Bulletin - New allocolchicine derivatives bearing 2,3-dihydrobenzo[b]oxepine moiety were synthesized via gold-catalyzed cyclization as a key synthetic step. The obtained...     

Synthesis and reactions of the thioamide derivatives of methyl vinyl ketone

The reaction of isothiocyanates with in situ generated carbanions of α,β‐unsaturated ketones yielded α,β‐unsaturated keto thioamides which in the reaction with acids or bases cyclized to give 2,6‐disubstituted thiopyran‐4‐ones and in the reaction with α‐bromoesters gave thiazolidin‐4‐one derivatives. The thiopyran‐4‐ones reacted with α,β‐unsaturated aldehydes to yield tetrahydrothiopyran[2,3‐b]pyridin‐4‐ones, while thioanilides were formed in the reaction with phenyl isothiocyanate.     

Volumetric properties of methyl,tert-butyl, and alkoxy derivatives of tetraphenylporphyrin in benzene solution

Densities, apparent molar volumes, and partial molar volumes of benzene solutions ofmeso-tetradimethylphenyl porphyrin derivatives H₂T(i,j-CH₃)PP (where i,j = 2,3-; 2,4-; 3,4-; 2,5-; 3,5-);meso-tetra-4-alkoxyphenyl porphyrin derivatives H₂T(4-OC_nH_2n+1)PP (wheren = 2–4,6–8,10,12,16);meso-tetra-3-butoxyphenyl porphyrin H₂T(3-OC₄H₉)PP;meso-tetra-4-tert-butylphenyl porphyrin H₂T(4tBu)PP;meso-tetra-3,5-ditert-butylphenyl porphyrin H₂T(3,5-tBu)PP at 25°C and tetraphenylporphyrin, H₂TPP,H₂T(4-OC₁₀H₂₁)PP;H₂T(4-OC₁₂H₂₅)PP and H₂T(4tBu)PP at 20°C; 30°C; 40°C; 50°C were determined. The solubilities of the compounds in benzene at 25°C were measured. The solvent excluded volumes for different conformational states and the topology of dimethyl derivatives of tetraphenylporphyrin were calculated and compared with partial molar volume data. The correlation between the partial molar volumes and van der Waals volumes for the derivatives H₂TPP,n-alkanes,n-alkanols, fatty acids, cyclic compounds, and crown ethers using the equation of Terasawa was elaborated. The average increment of the methylene group for alkoxy-substituted H₂TPP was calculated as δV ₂ ^o (CH₂) = 16.6±0.4cm³-mol^-1. The volumetric expansion coefficients of benzene solutions of H₂TPP; H₂T(4-OC₁₀,H₂₁)PP; H₂T(4-OC₁₂H₂₅)PP and H₂T(4-tBu)PP were determined and discussed. The importance of packing efficiencies around the solute molecules were examined.     

Regio- and stereo-selectivities of the ortho and meta photocycloaddition reactions of ethylenes to benzene and its simple derivatives

The photoreactions of benzene, toluene, anisole, and benzonitrile with acrylonitrile, methacrylonitrile, and vinyl acetate, and of toluene and o- and p-xylene with maleic anhydride are described. The acrylonitriles do not react with benzonitrile but yield mixtures of ortho photocycloadducts with the other arenes. Contrary to previous findings both exo and endo stereoisomers of the ortho cycloadducts of benzene and acryloitrile are formed: the reaction is selective towards the exo isomer but the stereoisomers from methacrylonitrite and benzene are formed with approximately equal efficiencies. Complex mixtures of regio- and stereoisomers of the ortho cycloadducts are formed between toluene and the acrylonitriles but their addition to anisole is more selective and in acetonitrile essentially only 1,2-attack of the ethylene on the arene is observed. The 2:1 photoadducts of maleic anhydride with toluene and o- and p-xylene reflect formation of two regio ortho photocycloadducts in each case. The variation in the ratios of these isomers with temperature and light intensity is interpreted in terms of the differing photolabilities of the 1:1 adducts and their reactivities towards the thermal addition of the second molecule of maleic anhydride. Vinyl acetate undergoes 1,2-cycloaddition to benzonitrile but with the other arenes, meta cycloadducts are favoured. These latter additions are specifically 2,6- with respect to toluene and anisole but there is little regioselectivity with respect to the ethylene although the 7-endo acetate of the meta cycloadduct with benzene does constitute 60% of the reaction mixture.     

Isocyanide-based multicomponent reactions: synthesis of 3,3-dicyano-N-alkyl-2-arylpropanamide derivatives

A new isocyanide-based multicomponent reaction between an aromatic aldehyde, malononitrile, an isocyanide, and acetic acid efficiently provides 3,3-dicyano-N-alkyl-2-arylpropanamide derivatives in excellent yields in ethanol at 70 °C. This reaction led to the construction of two carbon-carbon bonds and one amide group in a single synthetic step.     

Facile selective aminolysis of phenolic benzoates with 1-butanamine in benzene

1-Butanamine in benzene at room temperature effects selective aminolysis of phenolic benzoates without affecting aliphatic benzoates     

Zr-promoted ‘pair’-selective and regioselective synthesis of penta-substituted benzene derivatives

Tetra-substituted zirconacyclopentadiene derivatives, obtainable via in situ generation of zirconacyclopropenes and their cyclic carbozirconation with alkynes, can be treated with alkynyllithiums to induce 1,2-migration accompanied by aromatization and protonolysis, leading to the formation of penta-substituted benzene derivatives, in which all five substituted may be different.     

Indirect electrochemical side-chain oxidation of alkyl aromatic compounds - selective synthesis of methyl benzoates or ortho-benzoic acid trimethylesters

The technically important side-chain oxidation of alkyl aromatic compounds to from either methyl benzoates or orthobenzoic acid trimethylesters can be performed electrochemically at low potentials in methanol solution using an undivided cell and tris(2,4-dibromopheny1)amine as redox catalyst. Under neutral or slightly acidic conditions methyl benzoates are selectively formed while under basic conditions the ortho-esters are predominating. In a similar way ortho benzoic acid trimethylesters are formed selectively starting from benzaldehyde dimethylacetals. The redox catalyst is stable under the reaction conditions so that several thousand cycles can be performed without noticeable loss.     

The synthesis of several para-substituted tropanyl benzoates

The synthesis of the p-methyl-, p-methoxy-, p-t-butyl-, p-phenyl-, p-cyano-, p-bromo-, p-chloro-and p-nitrobenzoate esters of tropine are reported. These compounds were characterized by their hmr, ir, mass spectra and analytical data.     

Vanadium oxide anion cluster reactions with methyl isobutyrate and methyl methacrylate monomer and dimer: a study by FT/ICR mass spectrometry

Laser ablation of vanadium pentoxide (V₂O₅) powder produces VO₃⁻, V₂O₅⁻, V₃O₇⁻, V₃O₈⁻, and V₄O₁₀⁻ cluster ions which have subsequently been reacted with methyl isobutyrate, methyl methacrylate monomer and its dimer in the ion cell region of a Fourier transform ion cyclotron resonance mass spectrometer. Gas phase ion/molecule chemistry has revealed that reactivity decreases with increased mass of the vanadium oxide cluster anions. VO₃⁻, V₂O₅⁻, and V₃O₇⁻ ions react with the three reagents, methyl isobutyrate, methyl methacrylate and its dimer, respectively, either by addition of a whole reagent molecule or an associated fragment. All products formed are a result of parallel processes. V₄O₁₀⁻ undergoes no reaction for reaction times of up to 500 s, while V₃O₈⁻ adds a water molecule. Although the ions possess a net negative charge, the reactive site toward electron rich reagents such as methyl isobutyrate, methyl methacrylate and its dimer is the under-coordinated vanadium atom. This observation is supported by the lack of reactivity toward the studied reagents by those anions (V₃O₈⁻ and V₄O₁₀⁻) whose most likely stable structures contain fully coordinated vanadium atoms.     

Improved synthesis of phenylethylamine derivatives by Negishi cross-coupling reactions

Trifluoroacetamido-protected β-aminoalkylzinc iodides undergo Negishi cross-coupling reaction with aryl iodides in moderate to excellent yields (42-84%) based on the corresponding trifluoroacetamido-protected β-aminoalkyl iodides, employing a catalyst prepared in situ from Pd₂(dba)₃ and SPhos (1:2 M ratio). In general, meta- and para-substituted aryl iodides give good results using relatively low levels of catalyst [0.25 mol % Pd₂(dba)₃], but more hindered ortho-substituted examples require higher catalyst loadings. The preparation of trifluoroacetamido-protected β-aminoalkyl iodides is straightforward, and the intermediates are significantly more stable than the corresponding Boc-protected derivatives.     

A versatile synthesis of fused triazolo derivatives by sequential Ugi/alkyne-azide cycloaddition reactions

We report a facile synthesis of fused dihydrotriazolo[1,5-a]pyrazinones and triazolobenzodiazepines by an Ugi/alkyne-azide cycloaddition synthetic sequence. The coupling of the Ugi multi-component reaction with the intramolecular alkyne-azide cycloaddition provides access to highly functionalized heterocyclic ring systems in two steps from easily available starting materials in excellent overall yields.