Myanmar opposition’s bond proceeds will not go far

Headline MYANMAR: Opposition’s bond proceeds will not go far

SYNTHESIS OF GLYCIDYL AND THIOGLYCIDYL ETHERS OF DIACETYLENE SERIES AND THEIR USE AS A MODIFIER OF PHENOL-FORMALDEHYDE OLIGOMERS

It has been shown that the chlorine-containing unconjugated enyne alcohols react with epichlorohydrin in the presence of boron trifluoride etherate with formation of chlorohydrines, which further without their isolation, under the action of potassium hydrochloride are dehydrochlorinated with formation of the corresponding glycidyl ethers. Under the action of an alcoholic solution of potassium hydroxide at temperature of 75-80 °С on synthesized chlorine-containing ethers the dehydrochlorination reaction on double С=С bond proceeds and glycidyl ethers of 1,4-diine series are formed. It has been revealed that the synthesized glycidyl ethers are the very reactive compounds. In patricular, it has been shown that the ethers of 1,4-diine series with the participation of oxirane ring undergo the reaction with thiurea medium of methanol at 30-35 °С, forming the corresponding tyrants. The data of IR- and NMR-spectra of the prepared compounds have been presented and their modifying properties in relation to phenol-formaldehyde oligomers in acidic and alkaline media have been revealed. The prepared modified oligomers are the products of liquid-viscous consistency, soluble in acetone, tetrahydrofuran, dimethyl formamide and dioxane. It has been proved by the carried out analyses that the prepared PhFOs, modified by glycidyl and thiglycidyl ethers of diacetylene series are not mechanical mixtures of phenol, formaldehyde and modifier. On the basis of obtained results the formation mechanism of modified resol and novolac PhFO has been also revealed. It has been established that the physical-chemical and physical-mechanical parameters of the prepared phenol-formaldehyde oligomers modified by modifiers proposed by us, in comparison with unmodified ones, are improved. From the proposed diglycidyl and thiodiglycidyl ethers for the modification of PhFO the best results on all parameters are achieved at modification with thioglycidyl ether of diacetylene series.

Stereoselective syntheses of functionalized cyclic ethers via (Schiff-base)vanadium(V)-catalyzed oxidations

(Schiff-base)vanadium(V) complexes catalyze the oxidation of Br- (formation of Br2) and the stereoselective synthesis of functionalized tetrahydrofurans from substituted bishomoallylic alcohols. In both instances, tert-butyl hydroperoxide (TBHP) serves as primary oxidant. The oxidation of Br- was applied as the key step for stereo- and 6-endo-selectively constructing the 2,2,3,5,6,6-substituted tetrahydropyran nucleus of the marine natural product aplysiapyranoid A starting from an adequately substituted bishomoallylic alcohol. In the absence of Br-, 1-alkyl-, 1-vinyl-, and 1-phenyl-5,5-dimethyl-substituted bishomoallylic alcohols are selectively oxygenated to furnish 2,5-cis-configured tetrahydrofurans as major products. 2- Or 3-substituted ω,ω-dimethyl-substituted bishomoallylic alcohols afford trans-disubstituted tetrahydrofurans under these conditions. Oxidation of substituted 4-penten-1-ols, i.e., substrates with a terminal π-bond, proceeds with a preference for formation of trans-disubstituted tetrahydrofurans. According to data from (i) 51V NMR spectroscopy, (ii) mass spectrometry, (iii) a structure-selectivity survey, (iv) competition kinetics, and (v) a stereochemical analysis, the oxygen atom transfer onto a bishomoallylic alcohol occurs in a peroxide- and alkenol-loaded (Schiff-base)vanadium(V) complex.

Femtosecond Transient Absorption Studies of Simple Polyenes in Solution

We have conducted femtosecond transient absorption experiments on the excited-state dynamics of trans- and cis-hexatriene (HT) in solution. The transient absorption in the visible region decays with the time constant of about 500 fs, indicating that the internal conversion (IC) to the ground state occurs quite efficiently. The bleach recovery signal contains several time constants. The vibrational relaxation in the ground state occurs in 10–20ps and the slow relaxation process, which may be due to the conformational change around C—C single bond, proceeds in a subnanosecond time scale.

S-Sulphinates of cobalt(III) planar chelates and sulphur dioxide insertion into a cobalt(III)-carbon bond

The reactivity of the cobalt-carbon bond towards sulphur dioxide has been investigated in the compounds Rco111(L)B where L = N,N'-ethylenebis(salicyl-aldiminato), N,N'-phenylenebis(salicylaldiminato), or bis(dimethylg1yoximato);B = water or pyridine. In the Schiff base complexes, for R = alkyl, insertion into the cobalt-carbon bond proceeds smoothly to give the corresponding sulphinato derivatives. Reaction also occurs with methylcobaloxime and a pentafluorobenzene- cobalt-Schiff base compound, but the products are not so well defined. There is no reaction with cobalt-aryl bonds for any of the chelates. The alkane- and arene- sulphinato complexes can be synthesized by an alternative oxidative-addition reaction NaCOL+RSO2Cl or a replacement reaction XCoL+AgSO2R or NaSO2R (X = Cl,I). The infrared spectra of the complexes show that the sulphinato group is bonded in the manner shown: (See diagram in article) The p.m.r. spectra of the complexes are discussed in some detail. Reactions of the sulphinato derivatives with donor molecules and the halogens are briefly described.