Electrochemical Reduction and Oxidation of 3,4-Disubstituted 1,2,5-Thiadiazoles

The electron-acceptor nitrogen and sulfur atoms in 3,4-disubstituted 1,2,5-thiadiazoles are responsible for much decreased reduction potentials and much increased oxidation potentials of these compounds compared with the corresponding carbocyclic derivatives. The thiadiazole ring is resistant to oxidation, and the reversible electron transfer gives rise to fairly stable radical cations. Reductive stability of the heterocycle depends on the nature of its substituents and on the medium: When nucleofuge substituents are present, two-electron transfer in aprotic media results in heteroring opening with iminonitrile formation, whereas in the presence of two readily leaving groups, the electron transfer induces cleavage of the complete heteroring into inorganic anions.     

Kinetics of the mediatory reduction ofgem-dichlorocyclopropanes

The effect of the nature of organic electron transfer agents and of Pt^II, Pd^II, Rh^II, Co^II, Ni^II, Cu^II, Cr^III, Mn^II, Ti^III, V^III, Zn^II, and Ag^I metal ions on the kinetics of the homogeneous reduction ofgem-dichlorocyclopropanes has been studied. Pt^II, Pd^II, Rh^III, Co^II, and Ni^II ions accelerate this process, V^III and Ag^I ions exert practically no effect on the reduction rate, and the rest of the metal ions exhibit inhibitor properties.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1407–1410, August, 1993.     

New reaction of glycidols with oxalyl chloride and phosgene—an approach to cyclic esters

2,3-Epoxy alcohols (glycidols) react with carboxylic acid dichlorides to form cyclic esters of 3-chloro-1,2-diols. The reaction proceeds with complete retention of the configuration of the C(2) atom of the initial glycidol and with predominant (but not complete) inversion of the configuration of the C(3) atom in the final heterocycle. Translated fromIzvestiya Akademii Nuak. Seriya Khimicheskaya, No. 11, pp. 2110–2114, November, 1999.     

(4R,5R)-Bis(N,N-dimethylaminocarbonyl)-2-chloro-1,3,2-dioxaphospholane: A convenient reagent for control of enantiomeric composition of chiral alcohols by31P NMR spectroscopy

The use of enantiomerically pure cyclic chlorophosphite obtained by the reaction of PCl₃ withN,N,N′,N′-tetramethyldiamide of naturall-(+)-tartaric acid for analysis of the enantiomeric composition of chiral primary and secondary alcohols by³¹P NMR spectroscopy is considered. Translated fromIzvestiya Akademii Nauk., Seriya Khimicheskaya, No. 1, pp. 172–175, January, 1998.     

Kinetics of electrochemical reduction of 2-carbomethoxy-1,1-dichloro-2-methylcyclopropane by the double mediator system anthracene-PtII,PdII, and NiII complexes of cyclic aminomethylphosphines

Effective rate constants of homogeneous reduction of 2-carbomethoxy-1,1-dichloro-2-methylcyclopropane have been calculated by the polarographic method of determining the catalytic increase in the limiting current of the reduction wave of mediators,i.e., individual complexes of platinum, palladium or nickel with cyclic aminomethylphosphines and their combination with anthracene radical anions. Platinum compounds show higher catalytic activity than palladium and nickel complexes in direct reduction with metallocomplexes. The catalytic activity of a double mediator system for the majority of metallocomplexes is higher than the total catalytic activity of the individual metallocomplex and organic carrier.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No.3, pp. 414–416, March, 1994.The authors are grateful to G. N. Nikonov for the aminomethylphosphine complexes.     

Metal complex electrocatalytic reduction of 1,1-dihalocyclopropanes

Catalytic electroreduction of several substituted gem-dihalocyclopropanes was studied in the presence of metal salen-complexes by polarography, cyclic voltammetry, and preparative electrolysis. Monohalocyclopropanes (54—59%) and the corresponding allene (5—9%) were the main reduction products. The reaction rate constants were determined. The inner-sphere electron transfer was shown to occur under these conditions.     

Jacobsen-type enantioselective hydrolysis of aryl glycidyl ethers. 31P NMR analysis of the enantiomeric composition of oxiranes

The enantioselective partial hydrolysis of a number of racemic aryl glycidyl ethers in the presence of chiral Co(salen)-catalyst was studied. The enantiomeric composition of the isolated (R)-aryl glycidyl ethers was analyzed by ³¹P NMR using optically active substituted 2-chloro-1,3,2-dioxaphospholanes. A synthesis of -adrenoblocking agents (S)-toliprolol and (S)-moprolol based on the simultaneously obtained (S)-3-aryloxypropane-1,2-diols was proposed.     

Electroreduction of Phthalazines and 1,2,5-Thiadiazoles: Structural Factors Determining the Opening of Heterocycle

Electrochemical reduction of phthalazines and 1,2,5-thiadiazoles containing nucleofugaceous groups at the carbon -atoms are studied in aprotic and proton-donating media. Heteroatoms, substituents, and media are found to affect potentials and reaction path for the electroreduction. The factors determining the reductive opening of heterocycles are revealed. In diazines the heterocycle opening in annelated systems is induced by the electron transfer, provided there exist (a) a heteroatom–heteroatom bond and (b) an easily splitting-off group at the carbon -atom, whose nucleofugacity is comparable with or exceeds that of the chloride ion. Stability of the 1,2,5-thiadiazole cycle toward its reduction is determined by the substituent and the medium nature. On adding a nucleofugaceous group to the molecule, the transfer of two electrons in an aprotic medium results in the heterocycle opening with the formation of iminonitrile; when two easily splitting-off groups are present, the electron transfer makes the cycle decompose into inorganic anions.     

Cyclic phosphorochloridites (chloridates) based on chiral butane-2,3-diol and dihydrobenzoin as reagents for the analysis of enantiomeric compositions of alcohols by31P NMR spectroscopy

The use of cyclic phosphorochloridites which were prepared based on PCl₃ and chiral butane-2,3-diol or hydrobenzoin as possible reagents for the analysis of the enantiomeric composition of chiral alcohols by³¹P NMR spectroscopy is considered. The diastereomeric dispersion of chemical shifts of the resulting phosphites as well as of derived phosphates and thiophosphates is compared with that of structurally similar reagents. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 308–311, February, 2000.     

A Comparative Study of the Cyclic Chlorophosphites with C2-Symmetrical Organic Fragments as the Reagents for Enantiomeric Composition Control of the Chiral Alcohols

Abstract

The ³¹P NMR method is intensively used for enantiomeric composition control during the last years [I]. Among all other derivatizing agents the C2-symmetrical ones have some advantages.