Catalytic phosphorylation of polyfluoroalkanols. 17. Synthesis and the stereochemistry of tris(α-trifluoromethylbenzyl) phosphates

Catalytic phosphorylation of -trifluoromethylbenzyl alcohols with POCl₃ taken in a ratio of 3 : 1 under particular temperature conditions afforded predominantly symmetrical tris(-trifluoromethylbenzyl) phosphates. The latter were obtained as mixtures of two diastereomers with a statistical ratio of the components.     

Total synthesis of the ionophore antibiotic X-206. Studies relevant to the stereoselective synthesis of the C(17)–C(26) synthon.

A stereoselective synthesis of the keto-aidehyde 4, which embodies the structural features of the C(17)–C(26) section of the polyether X-206, is described.     

Transformed steroids. 185. Use of the Nicholas reaction for regio- and stereo-selective transformation of 16α,17a-epoxy-17Β-ethynyl-androstanes into 16α,17α-cis-disubstituted steroids

The HBF₄·Et₂O-catalyzed methanolysis reactions of the 16, 17-oxides of 17-ethy-nylandrost-4-en-3-one and its dicobalt hexacarbonyl complex were studied. It was shown that these reactions proceed with the same regiodirectivity of the oxide ring opening at the tertiary center but with a different mode of stabilization of the intermediates formed. The reaction of the free oxide proceeds without the inclusion of the external nucleophile and is concluded by the Wagner-Meerwein rearrangement; the C¹⁷-carbocation formed in the Co-coordinated oxide is stabilized by the addition of the methoxide ion and the elimination of a proton or of water. The opening of the oxide ring of dicobalt tetracarbonyl 16, 17-epoxy-17-ethynylandrost-4-en-3-one can be realized with decomplexation accompanied by carbonylation and heterocyclization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp.1180–1184, May, 1991.     

Alkaloids of Nitraria komarovii. XI. Structure of komavicine and the products of the dehydrogenation of the nitrarine method of dehydrogenation in the quinolinyl-β-carboline series

The new alkaloid komavicine has been isolated from the epigeal part ofNitraria komarovii, and its structure has been established on the basis of spectral characteristics and chemical transformations. The products of the dehydrogenation of nitrarine with selenium and sulfur have been studied. A method has been developed for the dehydrogenation of dihydro and tetrahydro derivatives in the quinolinyl--carboline series.Institute of Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 33–39, January–February, 1993.     

Anionic Polymerization of α-Methylstyrene. IX. Nature of the Propagating Species

Abstract

The nature of the initiating and propagating species involved in the anionic polymerization of α-methylstyrene has been explored. The earlier hypothesis that multimodal GPC molecular weight distributions in polymers arise solely out of different reaction steps or different ion-pair mechanisms being involved has been modified for poly-α-methylstyrene. Multimodal GPC molecular weight distributions in poly-α-methylstyrene initiated with potassium at 25°C and polymerized at 25°C or higher in THF, p-dioxane, or cyclohexane as solvents have been ascribed to the presence of two different types of tetramers which grow simultaneously but at different rates, each responding to its own well-defined thermodynamic equilibrium and yielding dormant and living polymers. Reaction schemes describing the initiation (at 25°C) and propagation reactions (between -25 and 60°C) in the polymerization (in solution of THF as well as in bulk) of α-methylstyrene initiated with potassium-naphthalene, butyl-lithium, and butyllithium-tetramethylethylenediamine (TMEDA) have been presented. The role of coordinating agents naphthalene and TMEDA in changing irreversible propagations into reversible ones has been emphasized.     

Assessing the activity concentration of β-emitters by means of the end-window g.m. tube

The activity concentrations of β-emitters including ³⁵S (0.15 MeV) and presumably also ¹⁴C (0.14 MeV) may be determined with satisfactory accuracy using an end-window G.M. counter. For single preparations (if weighed), the described procedure warrants that the standard error will not exceed 0.8%, if the amount of substrate is kept below 0.2 mg/cm², and if carrier-free solutions are avoided. With a minimum of 4 preparations per sample solution, the error of the mean should not exceed 0.4%,     

Polymorphism of Inclusion Complexes and Unsolvated Hosts. I. Trimorphism of the Host-Guest Complex of Gossypol with Dichloromethane. The Structure of the β-Phase

The formation of host-guest complexes of gossypol at different temperatures has been investigated for the same pressure and concentration. Gossypol forms three different clathrates with dichloromethane within the temperature interval of 22-36 °C. Single crystals of these three modifications (phases) were obtained and their crystallographic parameters measured. The structure of the -phase has been determined previously and the -phase is isostructural to the inclusion complex of gossypol with benzene, while the structure of the -phase has been solved during the present research. Crystals of C30H30O8·CH2Cl2 are triclinic, space group P1, a = 8.604(1), b = 11.858(2), c = 14.405(2) (Å), = 84.60(1), = 89.14(1), = 89.73(1)°, V = 1463(1) Å3, Z = 2, R = 0.089 for 2419 observed reflections.Under ambient conditions gossypol forms unstable tubulates of the -phase; the -phase is a stable cage-type clathrate (cryptate) and the host-guest complex of the -phase is a clathrate of intermediate tubulato-cryptate type.     

Polymorphism of Inclusion Complexes and Unsolvated Hosts. II. Structure of the β-Dimorph of the Host-Guest Complex of Dianilinegossypol with Ethylacetate

Depending on crystallization conditions, dianilinegossypol and ethylacetate form low (ambient temperature, -phase) and high temperature (t = 35°C, -phase) clathrate modifications. The structure of the -phase has been discussed earlier [1]. Crystals of the 1 : 1 -phase complex, C42H40O6N2·C4O2H8, are monoclinic, space group P21/c, a = 11.362(6), b = 19.479(9), c = 19.085(9) Å, = 103.21(4)°, V = 4112(3)Å3, Z = 4, R = 0.084 for 3210 observed reflections.In these complexes centrosymmetric dimers of dianilinegossypol molecules formed via O(5)—H···O(3) hydrogen bonds are associated into columns by a weak O(8)—H···O(7) H-bond. A difference in the structure of these two phases is in the packing mode of the columns. The angle formed by intersecting host columns is about 126° for the -phase and 104° for the -modification. Guest molecules are hydrogen bonded to the host molecules via an O(1)—H···O(10) bond and are accommodated in channels in -phase complex and in cavities in -phase complex.     

Esters ofβ -ketophosphonic acids. VII. The products of the reaction ofα-chlorocyclohexanone with the diethyl ester of ethylphosphonous acid and the sodium salt of the monoethyl ester of ethylphosphonous acid

Summary The action of diethyl ethylphosphonite on-chlorocyclohexanone gives cyclohexen-1-yl-1 -ethyl ethylphosphonate, Cyclohenen-1-yl-1-ethyl ethylphosphonate is also obtained by the action of sodium monoethyl ethylphosphonite on a-chlorocyclohexanone.     

Dipole-stabilized carbanions in the series of cyclic aldonitrones. 3. The influence of the configuration of the nitrone group on H—D exchange of the methine hydrogen atom and metallation of aldonitrones

The spin-spin coupling constants ³ J _C,H between the hydrogen atom of the aldonitrone group and the carbon atom bound to the nitrogen atom of the N-oxide fragment were determined for a wide range of cyclic and acyclic aldonitrones. Based on comparison of these constants (trans-³ J _C,H (E isomer) > cis-³ J _C,H (Z isomer)), the Z configuration was assigned to acyclic nitrones. Coordination of organolithium compounds to the oxygen atom of the NO group was revealed by ¹³C NMR spectroscopy. This coordination is the necessary condition for the metallation of aldonitrones. The configuration of the nitrone group is responsible for the ability of the E form of acyclic aldonitrones to undergo CD₃ONa-catalyzed isotope exchange of the methine proton in CD₃OD and metallation with Bu^sLi.     

Regiochemical control in the hemiacetalization of a dihydroxydialdehyde. An application of the use of homochiral 3-methyl-δ-butyrolactones to the construction of homochiral tripropionate units.

A method for the inversion of lactone homochirality and subsequent chain extension of dipropionate to tripropionate units is discussed. The synthetic sequence leads to (+)-methyl Prelog-Djerassi lactonic acid.     

Unleashing the Potential of 17O NMR Spectroscopy Using Mechanochemistry

¹⁷O NMR spectroscopy has been the subject of vivid interest in recent years, because there is increasing evidence that it can provide unique insight into the structure and reactivity of many molecules and materials. However, due to the very poor natural abundance of oxygen-17, ¹⁷O labeling is generally a prerequisite. This is a real obstacle for most research groups, because of the high costs and/or strong experimental constraints of the most frequently used ¹⁷O-labeling schemes. Here, we show for the first time that mechanosynthesis offers unique opportunities for enriching in ¹⁷O a variety of organic and inorganic precursors of synthetic interest. The protocols are fast, user-friendly, and low-cost, which makes them highly attractive for a broad research community, and their suitability for ¹⁷O solid-state NMR applications is demonstrated.     

M. S. Tswett and the discovery of chromatography II: Completion of the development of chromatography (1903–1910)

Summary In this, the second part of our review we continue the discussion of the activities of M. S. Tswett related to the development of chromatography. We shall deal here with his activities in Warsaw from 1903 onwards, resulting in his fundamental twin papers of 1906 and his book of 1910, summarizing all his activities related to the investigation of plant pigments and to the development of chromatography. Finally, a few special questions related to Tswett's work shall be discussed.For Part I, seeChromatographia 35, 223 (1993). References are numbered through.     

Polymorphism of Inclusion Complexes and Unsolvated Hosts. IV. Dimorphism of the Acetone Host–Guest Complex of Dianilinegossypol. Structures of the α- and β-Phase Complexes

Crystal structures of the - and -phase inclusion complexes of dianilinegossypol with acetone obtained at 20° and 30 °C, respectively, have been determined by X-ray structure analysis. Crystal data of the -phase complex are: C₄₂H₄₀O₆N₂2C₃H₆O, orthorhombic, space group Pccn, a = 29.501(9), b = 10.866(2), c = 13.756(3) Å, V = 4409(1) ų, Z = 4, D _x = 1.18 g cm^-3. The structure has been refined to a final R value of 0.117 for 1401 observed reflections. The host–guest ratio for the -phase complex is the same (1 : 2) and the crystals are monoclinic, space group C2/c, a = 28.352(6), b = 11.836(2), c = 13.196(1) Å, = 93.05(1)°, V = 4422(2) Å3, Z = 4, D _x =1.18 g cm^-3. The structure has been refined to a final R value of 0.077 for 1414 observed reflections.In both phases molecules of dianilinegossypol form hydrogen-bondedribbons by O(4)–-HO(3) H-bonds. Phases are determined by the same structural motif. In the -phase complex the cages are in the form of prisms but in the -phase clathrate they undergo a modification by shrinking in two directions and widening in one. Molecules of acetone are hydrogen bonded to the host molecules via aO(1)–-HO(G) bond and are accommodated in cavities for both complexes, i.e. both phases are cryptate-type inclusion complexes.Supplementary data relevant to this publicationhave been deposited with the British Library,No. SUP 82227 (24 pages).     

Extraction and Structure Investigation of the Poly-saccharides from the Pollen of Typha Angustifolia L.

Three polysaccharides, TAA, TAB, TAC have been isolated from the pollen of Typha angustifolia L. , and purified by hot water extraction, alcohol precipitation, Sevage method, gel filtration (Sephadex G50) and ion-exchange chromatography on DEAE Sephadex A25 and DEAE-cellulose. Their purities were tested by gel filtration and electrophoresis. Their structures were characterized by paper chromatography of the hydrolysis products, GLC analysis of the alditol acetates, alkylation analysis, 1H NMR and 13C NMR spectra. TAA is mainly composed of a-L-arabinofuanose, β-D-galactose and α-D-galacturonic acid, while the backbones of TAB and TAC are composed of (1→5)-linked α- L-arabinofuranosyl residues.     

On the study by D.S.C. of the unexpected ice melting at 0°C of emulsified aqueous saline solutions

Firstly, the behavior of droplets (Φ ≈ 1μm) of aqueous saline solutions dispersed within an emulsifying medium and subjected to steady cooling and heating is described. Droplets undergo freezing around a temperature T¹(x) and partial ice melting and total salt melting at the eutectic temperature T_E. This melting is followed by progressive melting of the remaining ice which ceases when the equilibrium temperature (T_e(x)) ice ⇆ solution is reached. Between T_e and T¹ the droplets are undercooled. Secondly, the results obtained when water crystallization occurs versus time at a fixed temperature _C, such as T¹(x) < > _C < T_e(x) are reported. During heating following crystallization at Θ_C, an unusual ice melting at 0° and/or ice melting ending at T & >; T_e(x) is noticed on the thermogram obtained by differential scanning calorimetry of the emulsion. This shows that pure ice or at all events less concentrated solutions must be present within the emulsion. A possible mechanism of crystallization at Θ_C is proposed.     

Investigation of the regio-and stereoselectivity of the annelation reaction of cyclic schiff base with structurally asymmetrical β,β′-triketones. Synthesis and properties of 17-acetoxy-8-aza-D-homogona-12,17a-diones

Annelation ([2+4]-cyclocondensation) of 3,4-dihydroisoquinolines and 2-acetyl-4-acetoxycyclohexane-1,3-dione gives 17-acetoxy-8-aza-D-homogona-12,17a-diones as a mixture of the C(9),C(17)-stereoisomers with the (9R,17S: 9S,17R) racemic pair predominating.Institute of Bioorganic Chemistry, National Academy of Sciences of the Belorussian Republic, Minsk 220141; e-mail: prostan@ns.iboch.ac.by. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1092–1099, August, 2000.     

Anomalies of the partition coefficient and properties of crystals in the region of low concentrations of an isomorphous admixture. 1. Unusual decomposition of solid solutions of the NaCl—CdCl2 system

Solid solutions NaCl—CdCl₂ were studied in an interval of CdCl₂ concentrations of 0.05—3 mol.% by Raman spectroscopy. The molecular form Na₂CdCl₄ decomposes: Na₂CdCl₄ 2Na⁺ + Cd²⁺ + 2Cl₂ ^– + 2e^–; 2Na + 2e^– 2Na⁰. Free sodium atoms form color centers of crystal (F centers) in the region of jumpwise changing the partition coefficient of CdCl₂ in NaCl (K jump).