Indium(I) iodide mediated efficient synthesis of selenoglycosides

A convenient odorless methodology has been developed for the preparation of selenoglycosides through indium(I) iodide mediated cleavage of diselenides and reaction with glycosyl bromides. The yields were excellent in all cases. Retention of the configuration at the anomeric center was observed in each case.     

Glycosylation of organic thio- and selenoacids of phosphorus : The reaction of organic monothio acids of phosphorus with glycosyl bromides. Thiono-thiolo rearrangement of glycosyl phosphorothioates

Ambident anions derived from phosphorus monothio acids have been glycosylated by 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl-, 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl- and 2,3,4-tri-acetyl-α-D-xylopyranosyl bromides, yielding β-S-glycosyl- and /gb-O-glycosylthioates. The S/O ratio of the glycosylated phosphorothioates depends markedly on the salt used. Ammonium salts favour the formation of S-derivatives, whereas silver salts give mainly O-derivatives. O-Glucosyl phosphorothioate undergoes thermal isomerisation to S-glucosyl phosphorothioate, with retention of configuration at the glycosylic centre. The implications of this stereochemical result are briefly discussed.     

Glycosylation of organic phosphorus thio- and selenoacids—II: The reaction of organic phosphorus thioselenoacids with glycosyl bromides under kinetically and thermodynamically controlled conditions

Ambident anions derived from phosphorus thioselcnoacids were glycosylated with 2,3,4,6 - tetra - O - acetyl - α - d - glucopyranosyl bromide, 2,3,4,6 - tetra - O - acetyl - α - d - galactopyranosyl bromide and 2,3,4 - tri- O - acetyl - α - d - xylopyranosyl bromide. The products were β-Se-glucosyl- and β-S-glucosylthioselenoates. The Se/S ratio of the glycosylated phosphorothioselenoates depends on the reaction conditions. At higher temperatures an equilibrium was observed. As a result of this equilibrium the Se/S ratio of the linkages formed in the glycosylated products was different from that observed under kinetic control. The structures of the glycosylated phosphorothioselenoates were confirmed by spectroscopy, independent synthesis and selective oxidation.     

Facile preparation of organozinc bromides using electrogenerated highly reactive zinc and its use in cross-coupling reaction

Highly reactive zinc was readily prepared by electrolysis of a DMF solution containing pyrene as a mediator with a platinum cathode and a zinc anode. Preferential reduction of pyrene occurred to generate the corresponding radical anion, which reduced zinc ions generated from anodic dissolution to give zero valent zinc with high reactivity. The reactive zinc was successfully used for an efficient transformation of bromoalkanes into the corresponding organozinc bromides. Organozinc bromides obtained were further used successfully in Pd-catalyzed cross-coupling reaction with various aryl iodides and bromides.     

Convenient synthesis of glycosyl bromide from 1-O-acetyl sugars by photo-irradiative phase-vanishing reaction of molecular bromine

The synthesis of glycosyl bromides from 1-O-acetyl sugars using a photo-irradiative phase-vanishing method involving molecular bromine was achieved. A bottom phase of molecular bromine was overlaid first with perfluorohexanes (FC-72), followed by overlaying with ethyl acetate containing a 1-O-acetyl sugar. Upon irradiation, the bromine layer gradually disappeared, leaving two phases. Glycosyl bromide was obtained in good yield from the ethyl acetate phase.     

Hammett-type relationship for the cleavage of radical anions of aromatic chlorides and bromides

A Hammett-type correlation pertaining to the cleavage of radical anions of aromatic halides has been formulated. The expression has been verified using the reaction series of aromatic chlorides and bromides. The correlation reveals the sensitive nature of the carbon-chlorine bond to the polar effects of the substituents in comparison to the carbon-bromine bond. The cleavage rate constants of radical anions of some aromatic chlorides and bromides have been deduced using the correlation. The standard potentials for formation of radical anions of aromatic chlorides and bromides have been estimated based on the correlation.     

Condensation of aryl bromides with styrenes,catalyzed by nickel complexes in the presence of zinc

Conclusions Condensation of aryl bromides with styrenes in acetonitrile in the presence of nickel organometallic complex catalysts and metallic zinc occurs regio- and stereoselectively to give E-stilbenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2508–2511, November, 1987.     

Investigation in the coupling of zirconocene complexes and trimethylsilyl(diphenylphosphino)acetylene. P-C bond cleavage chemistry from protonolysis reactions

The regioselectivity of the coupling reactions of the internal acetylenic derivative Ph₂P-CC-SiMe₃ (2) and the benzyne complex [Cp₂Zr(η²-C₆H₄)] (1) resulted preferentially in the formation of the zirconaindene metallacycle with the metal α-carbanions stabilized by the trimethylsilyl group. We have been able to structurally characterize the two regiosomers. The unusual acute Zr-C-P angle and the short Zr-P distance revealed that a significant Lewis-base/Lewis-acid σ-P-Zr interaction occurs in the α-phosphino zirconaindene metallacycle. Addition of HCl · Et₂O on the cyclic α-silyl zirconindene complex led to competition reactions between (i) the nucleophilic attack of the lone pair of the phosphino group followed by P-C cleavage to form Ph₂PH and Ph-CC-SiMe₃ (7) and (ii) protonolysis of the Zr-CSi bond to give the Z-vinyl silyl phosphino product Ph₂PC(Ph)C(H)SiMe₃ (8). When the lone electron pair of the phosphino group is engaged intramolecularly with the metal center to achieve the stable 18-electron configuration protonolysis reaction on the Zr-C bonds to give the Z-vinyl silyl phosphino product Ph₂PC(H)C(Ph)SiMe₃ (9) is the unique process observed. Protonolysis reaction on the complexes prepared in situ from the addition of 2 and zirconocene like reagents “[Cp₂Zr]” gave Ph₂PH, H-CC-SiMe₃, and Ph₂PC(H)C(H)SiMe₃ (18) which resulted from the competitive P-C and Zr-C bond cleavage processes of the transient alkyne complex Cp₂Zr(η²-Ph₂P-CC-SiMe₃)] (14).     

Synthesis of substituted aryltrimethylstannanes by the reaction of trimethylstannylsodium with aryl bromides

The preparation of substituted aryltrimethylstannanes by the reaction of aryl bromides with trimethylstannylsodium in tetraglyme has been studied. Among the substituents present on the aromatic rings were bromine, chlorine, amino, formyl, acetyl and methoxycarbonyl. Factors affecting the success of these and other preparations are discussed in terms of a previously proposed mechanism involving the formation of arylsodium and bromotrimethylstannane as intermediates. These can react with each other in the solvent cage in which they are formed, or after diffusion into the bulk of the solvent. Side reactions can occur by reaction of the arylsodium with functional substituents.     

Reaction of potassium dialkyl thiophosphates with ethynyl bromides in the presence of cupric chloride

Conclusions The reaction of potassium diethyl thiophosphate with phenylbromoacetylene in the presence of equivalent amounts of cupric chloride gives 0,0-diethyl S-phenylethynyl thiophosphate. The cuprous salt of diethylthiophosphate acid is formed as an intermediate which reacts with the ethynyl bromide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 467–469, February, 1986.     

Free-Radical copolymerization of N-vinylsuccinimide with butyl acrylate in the presence of zinc chloride and aluminum chloride

The free-radical copolymerization of N-vinylsuccinimide with butyl acrylate performed in dimethyl sulfoxide and benzyl alcohol in the presence of zinc chloride and aluminum chloride as complexing agents is studied. Under the given conditions, the reactivity ratios are determined. It is shown that zinc chloride influences the electron-density distribution only in butyl acrylate molecules. It is found that benzyl alcohol retards the total rate of polymerization. The character of the monomer-unit distribution in copolymer macromolecules is described.     

Improved synthesis of β,X-unsaturated ketones by the reaction of allylic zinc bromides with nitriles.

The reaction of allylic bromides with nitriles in the presence of ZnAg couple leads, after hydrolysis, to β,X-unsaturated ketones in high yield.     

Copolymerization of vinyl ketones with allylbenzene in the presence of zinc chloride

Copolymerization of 3-buten-2-one (MVK) and 3-methyl-3-buten-2-one (MIPK) with allylbenzene (AB) in the presence of zinc chloride (ZnCl₂) was studied. The apparent monomer reactivity ratio decreased with an increasing concentration of ZnCl₂ added. By assuming a terpolymerization system as free vinyl ketone (M₁), vinyl ketone complexed with ZnCl₂ (M₂), and AB(M₃), the absolute monomer reactivity ratios were determined by using the least squares method: k₁₁/k₁₂ = 0.0038, k₁₁/k₁₃ = 11.77, k₂₂/k₂₁ = 1.37, and k₂₂/k₂₃ = 3.77 for the MVK-AB system, and k₁₁/k₁₂ = 0.0070, k₁₁/k₁₃ = 55.47, k₂₂/k₂₁ = 1.84, and k₂₂/k₂₃ = 11.16 for the MIPK-AB system, respectively. It is seen from these values that the complexed vinyl ketones are more reactive to both polymer radicals which have free and complexed vinyl ketone units at its terminal position than the free vinyl ketones. Q and e values for MVK and MIPK complexed with ZnCl₂ were found to be Q = 850, ^e_(MVK)2ZnCl₂ = 2.97, Q = 2.62, respectively.     

Kinetics and mechanism of benzyl chloride reaction with zinc in dimethylacetamide

Oxidative dissolution of zinc in the system of benzyl chloride-dimethylacetamide was investigated. The reaction stereochemistry as well as intermediates and reaction products formed were studied. The kinetic and thermodynamic parameters of the process were measured. The process was shown to follow the Langmuir-Hinshelwood mechanism with the formation of benzyl radicals and mono-solvated organozinc compound on the zinc surface. The components of mixture are adsorbed at various sites of the zinc surface, while recombination and the isomerization of the benzyl radicals occurs in solution.     

Synthesis of layered zinc hydroxide chlorides in the presence of Al(III)

Zinc hydroxide chloride particles were synthesized by hydrolysis of ZnCl₂ solutions dissolving AlCl₃ at different atomic Al/Zn ratios from 0 to 1.0 and characterized by various techniques. Increasing Al/Zn ratio changed the crystal phases of the products as ZnO→ZnO+ZHC (Zn₅(OH)₈Cl₂·H₂O)→ZHC→LDH (layered double hydroxides, Zn-Al-Cl) and the particle morphology as agglomerates (ZnO)→fine particles (ZnO)→plates (ZHC)+rods (ZnO)→plates (ZHC)→plates (LDH). The atomic Cl/Zn ratios of LDH particles formed at Al/Zn?0.3 were ca. 0.3 despite the increase of Al/Zn ratio, being due to the intercalation of CO₃²⁻ into the LDH crystal. The OH⁻ content of LDH estimated by TG was reduced by the deprotonation of OH⁻ to counteract the excess positive charge produced by replacing Zn(II) with Al(III). ZHC exhibited a high adsorption selectivity of H₂O.     

Spontaneous copolymerization of 1,3-cycloheptadiene with acrylonitrile in the presence of zinc chloride

The reaction of 1,3-cycloheptadiene (1,3-CHpD) with acrylonitrile (AN) in the presence of ZnCl₂ leads spontaneously to the simultaneous formation of an alternating copolymer and a small amount of cycloadduct. The copolymer has a predominantly cis-1,4-structure. The formation of the charge—transfer complex between 1,3-CHpD and (AN)c (AN coordinated to ZnCl₂) in AN was detected by ultraviolet (UV) spectroscopy. The activation energies for the cycloaddition and for the copolymerization under the conditions used were determined to be 17.6 (in the presence of 1,1-diphenyl-2-picrylhydrazyl) and 16.3 kcal/mole, respectively. The rate of copolymerization in AN was found to depend on the 1.5th power of the concentrations of (AN)c and of 1,3-CHpD. Oxygen and UV irradiation causes an acceleration of the copolymerization only. On the basis of these results the mechanism of the spontaneous copolymerization is discussed and its relation to the cycloaddition in systems of 1,3-cyclodienes and AN in the presence of ZnCl₂ is mentioned.