Studies on the syntheses of heterocyclic compounds—DCXCIII: A total synthesis of atheroline by photolysis

Atheroline (3) an oxoaporphine alkaloid, has been synthesised by photolysis of 8 bromo 1-(3-hydroxy-4-methoxybenzoyl)-6,7-dimethoxyisoquinoline (13) in the presence of sodium hydroxide.     

Determination of dissociation constants of sparingly soluble phenothiazine derivatives by second-derivative spectrophotometry

The dissociation constants (pK_a) for sparingly soluble phenothiazines (promazine, chlorpromazine, trifluoropromazine) in water were measured by second-derivative spectrophotometry. The intense background signals in the absorption spectra due to the turbidity caused by the precipitation of insoluble free base of the phenothiazine derivatives were eliminated in the second-derivative spectra, and the solubilities of the phenothiazine derivatives could be easily determined from the peak-to-trough lengths (D values) of the second-derivative signals. The pK_a values were calculated from the pH dependence of the D values. The pK_a values obtained agreed well with reported values and the standard deviations for 6–10 determinations were ? 0.02. The solubilities of the free bases of the phenothiazines were also determined.     

Syntheses of Polycyclic Natural Products Employing the Intramolecular Double Michael Reaction

The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.     

A new synthetic method for the framework of aspidosperma alkaloids using singlet oxygen chemistry

Abstract1-A singlet oxygen adduct of l-benzyloxycarbonyl-l, 2-dihydro-5-(2-methyl-l,3-dioxolan-2-yl)pyridine 21 was treated with indole in the presence of stannous chloride to yield directly the complex compound 22, which will act as a suitable starting material for the synthesis of various kinds of indole alkaloids. Further transformation from 22, including a new device for construction of the aspidosperma framework, was investigated and pentacyclic compounds 25 (Y = H and OH) were synthesized in moderate yields. The structure of 25 (Y = H) = 38 was confirmed by correlation with l-acetyl-20-deethylaspidospennidine 44. Determination of the structure of a by-product 39 was carried out by single crystal X-ray analysis.     

Stereoselective Construction of Copaborneol and Longiborneol Frameworks by Intramolecular Double Michael Reaction

Stereoselective syntheses of tricyclo[5.3.0.0(3,8)]decane 22 and tricyclo[6.3.0.0(3,9)]undecane 26, the basic skeletons of copaborneol and longiborneol, were achieved by the intramolecular double Michael reactions of 2-cyclopenten-1-ones 15-17. The substrates were prepared starting with tricyclo[5.2.1.0(2,6)]deca-4,8-dien-3-one (6). The intramolecular double Michael reactions were carried out under three different conditions: TMSCl-Et(3)N-ZnCl(2), TMSI-(TMS)(2)NH, and Bu(2)BOTf-(TMS)(2)NH. The framework 26 of longiborneol was constructed in good yields using the latter two reagent systems.     

Intramolecular double Michael reaction. Part II. Synthesis of isoatisirene type compound

Intramolecular double Michael reaction of the α,β-unsaturated enone ester (16), prepared from the dienone (5), stereoselectively gave the tetracyclic product (17), which was converted into the isoatisirene type compound (20).     

Sensitivity enhancement by palladium addition in the electrothermal atomic absorption spectrometry of mercury

In graphite-furnace atomic absorption spectrometry of mercury, addition of 50 μg ml^?1 palladium improves the peak height for 5 μg Hg ml^?1 50 times. Further addition of 20 μg ml^?1 platinum doubles the enhanced peak height. The effect is due to amalgam formation. The best sensitivity is 0.3 ng (1% absorption) and the detection limit is 0.1 ng. The method allows higher ashing temperatures than for solutions without noble metal addition and can be applied to solutions containing substantial amount of organic matter.     

Stereoselective olefinic cyclization assisted by the selenyl group — biogenetic-type synthesis of caparrapi oxide

The acid catalysed cyclization of β-hydroxy selenide ($\text{4}$), which was prepared from nerolidol ($\text{1}$) $\text{via}$ the epoxide ($\text{3}$), was carried out to give bicyclic ether ($\text{5}$) directly which was further transformed into caparrapl oxide ($\text{6}$).     

Non‐Osmotic Hydrogels: A Rational Strategy for Safely Degradable Hydrogels

Hydrogels are promising materials for biomedical applications, where timely degradation is often preferred. In the conventional design, however, the cleavage of polymer networks essentially causes considerable morphological changes (i.e., degradation‐induced swelling), triggering various medical complications. Herein, we report a rational strategy to suppress the degradation‐induced swelling based on the synthetic control of the polymer–solvent interaction parameter (χ) of constituent polymer networks. The resultant hydrogels with an optimal χ parameter (χ_{37 °C}≈0.53; non‐osmostic hydrogels) displayed the capability to retain their original shape and degrade without generating significant swelling pressure under physiological conditions (Π_{37 °C}<1 kPa). This concept of the safely degradable non‐osmotic hydrogel is theoretically universal, and can be exploited for other types of synthetic hydrogels in various settings.     

Microdischarge-Induced Decomposition of Ammonia and Reduction of Silver Ions for Formation of Two-Dimensional Network Structure

Microdischarge-induced reaction processes working at atmospheric pressure create fractal-like network structure of metal nano-particles which shows variable electric and optical properties. Due to their smallness, microdischarges or microplasmas can be installed in a gas-tubing system, and they enable us to create a compact chemical reduction reactor which includes decomposers of molecules, gas flows, and aqueous solutions with metallic ions at atmospheric pressure. Ammonia (NH₃) gas is successfully decomposed in this reactor, and its products which include mainly hydrazine (N₂H₄) and flow in the downstream induce reduction reactions for AgNO₃ solution. Various parameters in the reactor trigger formation of functional patterns of silver nano-particles like partially transparent layers whose conductivity is variable. Optical properties of this equivalent films show some absorption spectra coming from structure resonances, which can be an optical metamaterials in this self-assembly process.