Synthesis with silicon derivatives: non symmetrical derivatization of symmetrical diamines

The conversion of symmetrical diamines to monoamides via the use of cyclic silicon-nitrogen compounds as intermediates is described.     

Ionic liquids with symmetrical dialkoxymethyl-substituted imidazolium cations

A new one-step procedure is described for the synthesis of disubstituted imidazolium chlorides. 1,3-Dialkoxymethylimidazolium chlorides thus obtained can be employed as synthetic precursors of symmetrical ILs. The salts have been found to exhibit antimicrobial activity and an antielectrostatic effect. Their densities and viscosities have been determined and are reported herein. It has also been demonstrated that the ILs can be decomposed using an aqueous solution of KMnO(4). For each IL, the permanganate index (I(Mn)) has been estimated, which varies with the structure of cation. The only limitation of I(Mn) is the degree to which the IL dissolves in water.     

The symmetrical porphyrazine with annulated six membered rings

Tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II) with annulated six membered rings has been prepared by two different methods. In Method A: cyclotetramerization of 2,3-dicyano-5,6-cyclohexanopyrazine (1) in the presence of Mg(OPr)₂ in n-propanol afforded the tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II) (2). In Method B: selenodiazole rings on the periphery of tetrakis(selenodiazole)porphyrazinato magnesium(II) were opened by the action of H₂S to yield the vicinal diamino functionalities. The ring closure of the vicinal diamino groups with 1,2-cyclohexanedione afforded the tetrakis(cyclohexylpyrazino) porphyrazinato magnesium(II) (2).     

N-monocarbamoyl derivatives of symmetrical diamines with antiviral activity

Some new N-monocarbamoyl symmetrical diamines have been prepared by the addition of symmetrical amines to isocyanates or isothiocyanates. 2,6-Diaminopyridine (1), (1R,2R)-1,2-diaminocyclohexane [(1R,2R)-2], meso-1,2-diaminocyclohexane (meso-2), or (1R,2R)-1,2-diphenylethylenediamine (3) were used as the starting symmetrical diamine frameworks. All of the newly synthesized compounds were subjected to an evaluation of antiviral activity with herpes simplex virus (HSV)-1. N-Monocarbamoyl 2,6-diaminopyridines (5a, b) showed significant antiviral activity (EC(50)=17.0, 6.2 microg/ml) comparable to that of N-monododecanoyl 2,6-diaminopyridine (A2). As a result, compound 5a showed a better selectivity index (CC(50)/EC(50) = ca. 10.0) than that of A2.     

Monoacylation of unprotected symmetrical diamines with resin-bound benzoic acids

A protocol for monoacylation of unprotected symmetrical diamines with a resin-bound benzoic acid is described. The nature of the resin (gel-based polystyrene vs highly crosslinked macroporous polystyrene) was found to play a minor role in acylation selectivity. Rather, the concentration of the diamine dictates the ratio of mono- and diacylated products. Thus, by employing a high concentration of symmetrical diamine (e.g., 1 M, 20 equiv), monoacylation can be selectively achieved for a variety of unprotected symmetrical alkyl and aryl diamines.     

A new symmetrical micro-thermobalance

A new symmetrical micro-thermogravimetric analyzer has been developed. The symmetrical design of this instrument allows determination of very small mass changes over a wide range of temperatures. The utility of the instrument was demonstrated by studying the decomposition characteristics of CaC₂O₄·H₂O and the curing and decomposition kinetics of a glass filled polymer composite.

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Zusammenfassung Ein neuer symmetrische mikrothermogravimetrischer Analyser wurde entwickelt. Die symmetrische Gestaltung dieses Instruments ermöglicht die Bestimmung sehr geringer, sich über weite Temperaturbereiche hinziehender Massenveränderungen. Die Brauchbarkeit des Instruments wird demonstriert, in dem die Zersetzungscharakteristik von CaC₂O₄.H₂O und die Kinetik der Härtung und Zersetzung von glassverstärkten Polymerverbundstoffen untersucht wird.

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Chemoselective Staudinger-phosphite reaction of symmetrical glycosyl-phosphites with azido-peptides and polygycerols

In this paper we present the synthesis of glyco-phosphoramidate conjugates as easily accessible analogs of glyco-phosphorous esters via the Staudinger-phosphite reaction. This protocol takes advantage of synthetically accessible symmetrical carbohydrate phosphites in good overall yields, in which ethylene or propylene linkers can be introduced between phosphorous and galactose or lactose moieties. The phosphites were finally applied for the chemoselective reaction with azido-peptides and polyazido(poly)glycerols.     

Selective monoacylation of symmetrical diamines via prior complexation with boron

[reaction: see text] Pretreatment of a symmetrical primary or secondary diamine with 9-BBN prior to the addition of an acyl chloride significantly suppressed undesired diacylation, and the product of monoacylation predominated. The reactive preference is interpreted as the result of a selective deactivation of one nitrogen atom of the diamine by 9-BBN.     

Reaction of symmetrical derivatives of B-mercurated carboranes with nucleophilic reagents

Conclusions The B-Hg bond in symmetrical B-mercurated carborane derivatives is resistant to the action of nucleophilic reagents such as LiAlH₄, BuLi, and C₁₀H₆·^–Li⁺.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2594–2596, November, 1981.     

Synthesis of a symmetrical dithiirane

The reaction of p-xylene with epichlorohydrin in the presence of aluminum chloride gave 1,4-dimethyl-2,5-bis(1-chloro-2-hydroxypropyl)benzene, which serves as the starting compound for the synthesis of the corresponding symmetrical dithiirane.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1319–1321, October, 1985.     

Rotational isomers of symmetrical difluoroacetone

Solid-state infrared spectra were obtained for symmetrical difluoroacetone that show different conformations present, depending on whether the solid state was obtained by cooling a liquid film or by deposition of the vapor onto a cooled plate. The spectra were used in conjunction with normal coordinate calculations that utilized a force field transferred from fluoroacetone to show that sym-difluoro-acetone exists in the gauche-gauche and cis-gauche conformations.     

Synthesis of a symmetrical octamethyl-substituted cucurbituril with a dimethyl-substituted glycoluril dimer

A symmetrical octamethyl-substituted cucurbituril has been synthesized in a controlled manner by using a dimer of dimethyl-substituted glycoluril, which was in turn synthesized under formaldehyde-deficient conditions. The dimer of dimethyl-substituted glycoluril and the symmetrical octamethyl-substituted cucurbituril have been characterized by NMR spectrometry, ESI mass spectrometry and single-crystal X-ray diffraction analysis. The structure of the dimer of dimethyl-substituted glycoluril is notable because it constitutes a useful new building block that could permit the formation of such cucurbit[n]urils with substituents in certain positions or with limited numbers of methine groups on their backbones.     

Synthesis of symmetrical 1,5-disubstituted granatanines

A general entry into symmetrical 1,5-disubstituted granatanines that involves an alkylative ring-closure on a 2,6-bis enolate piperidine intermediate is described.     

Dipole moments of symmetrical molecular systems

It is shown that quantization of nuclear motion causes the intrinsic dipole moment of a molecular system to depart from the classical representation, e.g., it is different from zero for symmetrical molecules. A formula is derived for the mean dipole moment ¯p as a function of temperature with allowance for the internal motion of the nuclei, which is functionally related to the dipole moment. Calculations are performed for ammonia with allowance for the inversion splitting, which is due to tunneling between two equivalent equilibrium configurations having their dipole moments in opposite directions. The temperature coefficient of ¯p may be positive or negative, in accordance with the relation between the tunneling frequency and the temperature; the formula usually employed is valid only in the limiting case of low frequencies and high temperatures. A deduction is given for the criterion for instability of the maximally symmetrical configuration with respect to odd nuclear displacements (dipole distortions); this is based on a simple model system having an inversion center, a totally symmetric ground state, and a triply degenerate odd excited state of the T_1u type. The experimental consequences of the results are discussed, as well as the concept of symmetry for a molecular system in which the maximally symmetrical configuration is unstable.