Stannyl Group Research Articles

ChemInform Abstract: APPLICATIONS OF CONSECUTIVE RADICAL ADDITION‐ELIMINATION REACTIONS IN SYNTHESIS

Abstract(VIIIa) erzeugten Radikale reagieren mit Alkenen (II) und (IV) unter Eliminierung von Stannylradikalen zu den Verbindungen (III) und (V) sowie (VIb) und (VIc) bis (VIIIb) und (VIIIc).

A new method for the deoxygenation of tertiary and secondary alcohols

The derivatisation of alcohols as their methyl oxalyl esters is shown to be a convenient and selective method for deoxygenation by stannyl radicals.

The cobalt way to vitamin B 6: Regioselective construction of the tetrasubstituted pyridine nucleus by cobalt-catalyzed alkyne-nitrile cooligomerizations

Cocyclization of bis(trimethylsilyl)- and bis(trimethylstannyl)di-2-propynyl ether with acetonitrile provides a synthetic entry into 1,3-dihydro-6-methyl-4,7-bis(trimethylsilyl)- and bis(trimethylstannyl)-furo[3,4- c]pyridines. Regioselective electrophilic substitution of the respective silyl or stannyl groups allows for a regiocontrolled construction of tetrasubstituted pyridines. This method has been applied to a total synthesis of vitamin B 6.

Applications of consecutive radical addition–elimination reactions in synthesis

Alkyl radicals add to the tri-n-butylstannyl substituted terminus of several alkenes; elimination of the stannyl radical results in a preparatively useful, carbon–carbon bond forming reaction, under mild and neutral conditions.

On the mechanism of reduction of dithiocarbonates (xanthates) with tributylstannane

Competition experiments with various dithiocarbonates show that the deoxygenation occurs by addition of stannyl radicals to give (2) followed by fragmentation rather than by direct SH2 attack on sulphide sulphur.

The stereochemistry of attack by a carbon electrophile on a tin-carbon bond

In the cyclisation of the 5-stannyl aldehyde ( 3), the cyclopentanol ring ( 4) is formed with retention of configuration at the carbon bearing the stannyl group.

Über sterisch gehinderte freie radikale X. Zur darstellung von gemischt alkylierten zinnverbindungen Me 2RSnX und MeR 2SnX, R  neopentyl, 1-methyl-cyclohexyl, X  Me, Cl, H

A number of the compounds Me 2RSnX (R  neopentyl, 1-methylcyclohexyl; X  Me, Cl, H) has been prepared for the first time. Generally, replacement of Me in a higher methylated precursor against Cl in polar medium by HgCl 2 has been shown to be the best way to obtain the halides mentioned. The hydrides are used for ESR measurements of the corresponding stannyl radicals.

The configuration of the tin-centered radical R 3Sn (R = 2,4,6-tri- i-propyphenyl) as studied by ESR

ESR data of the stannyl radical ( i-Pr 3Ph) 3Sn at temperatures between −140 and +200°C are presented. In solution, the isotropic 119Sn hyperfine coupling decreases with increasing temperature (20°C < T < 200°C) dicating that the radical is non-planar and configurationally stable. At −140°C in a toluene matrix, anisotropic features have been observed ( A |( A |( 119Sn) = 211 mT, A ⊥( 119Sn) = 139 mT; g | = 1.995, g ⊥ = 2.016) leading to an out-of-plane angle of 12.7°.

Direkte Lithiierung von BicycIo[3,2,1]octa-2.6-dien / Direct Lithiation of Bicyclo[3,2,1]octa-2,6-diene

Abstract Bicyclo[3,2,1]octa-2,6-diene (1) has been lithiated directly with t-butyllithium/TMEDA at low temperature. After quenching with tri-methyltin chloride essentially two stannyl derivatives of 1 were obtained. The stannyl group did not bind to the allylic carbon of 1 as expected but to C-6 and C-7. This has been shown by means of elemental analysis, mass spectroscopy as well as 1H, 13C and 119 Sn NMR spectroscopy.

Free radicals derived from 1,4-diaza-1,3-butadienes: I. Esr of adducts with silyl, germyl and stannyl radicals and of the diprotonated radical cation

Silyl, germyl and stannyl radicals add to N, N′-di-t-butyl-1,4-diaza-1,3-butadiene (t-Bu-DAB) to give cis and trans isomers of 1-azaallylic radicals. Similar isomers have also been observed in the ESR spectrum of the diprotonated t-Bu-DAB radical cation.

Trimethylsilylverbindungen der Vb-Elemente, HI [1]. Tris(trimethylsilyl)- und Tris(trimethylstannyl)bismutan sowie Tetrakis(trimethylsilyl)dibismutan / Trimethylsilyl Derivatives of Vb-Elements, III [1]. Tris(trimethylsilyl)- and Tris(trimethylstannyl)bismuthine as well as Tetrakis(trimethylsilyl)dibismuthine

Abstract Chlorotrimethylsilane and sodium/potassium bismuthide, easily prepared from finely powdered bismuth and sodium potassium alloy in 1,2-dimethoxyethane (DME), react to give tris(trimethylsilyl)bismuthine (1) in 48% yield. When compound 1 is treated with chlorotrimethylstannane all trimethylsilyl substituents are successively replaced by stannyl groups, and tris(trimethylstannyl)bismuthine (4) is obtained. As in analogous reactions of other tris(trimethylsilyl) derivatives of Vb-elements with methyl lithium in diethylether/tetrahydrofuran (THF), one trimethylsilyl group of tris (trimethylsilyl)-bismuthine (1) can also be removed, and lithium bis(trimethylsilyl)bismuthide · 2 THF (5) is formed. With 1,2-dibromoethane bismuthide 6 reacts with metal halogen exchange to give green lustrous needles of tetrakis(trimethylsilyl)dibismuthine (6). In contrast to other dibismuthines described in the literature, this compound is thermally rather stable and can be isolated in preparative amounts. Similar to several distibines a colour change from green to red, resp. orange-red occurs on melting or dissolving dibismuthine 6 in organic solvents.

Electron spin resonance spectra of transient tin-centered radicals in solution

ESR data for short-living stannyl radicals in solution are presented. The radicals are generated in the cavity of the ESR spectrometer by UV irradiation of di-t-butyl peroxide with the appropriate tin hydride. The radicals R 3Sn . (R = Me, n-Pr, n-Bu) show multiplets caused by interaction with the β-protons ( a H = 0.30–0.31 mT, g = 2.0160–2.0163) and line broadenings depending on [R 3SnH]. The radicals Ph n Me 3− n Sn . ( n = 1, 2) exhibit only splittings due to the methyl protons ( a H = 0.30 mT). The observed linewidths show that a o,p ≲ 0.05 mT, a m ≲ 0.03 mT. The radicals Ph n Et 3− n Sn . ( n = 0–2) show no splittings caused by the methylene protons because of exchange narrowing effects. The g values decrease with increasing n from 2.0163 and 2.015 ( n = 0) to 2.0023 ( n = 3) because of increasing deviations from the planar conformation at the radical center. The line broadening and exchange narrowing effects are caused by rapid hydrogen exchange between the radicals and hydride molecules ( k ≳ 10 6 M −1 s −1); in Zavitsas' model, the relatively high k values are the consequence of the large SnH bond lengths which diminish the repulsive forces between the terminal Sn atoms in the transition state [R 3Sn--H--SnR 3] .. The observation of line broadenings in the NMR spectrum of Me 3SnH during irradiation with di-t-butyl peroxide confirms the ESR results.

Substitutionen und insertionen an stannylierten inethern

Stannylethynyl ethers 1 react with acyl halides or some elemental halides under substitution of the stannyl group; the carbonyl group of ketenes insert into the single bond between the acetylenic carbon atom and the stannyl group.

Triaryl-silyl, -germyl, and -stannyl radicals .MAr 3 (M = Si, Ge, or Sn and Ar = 2,4,6-Me 3C 6H 2) and .Ge(2,6-Me 2C 6H 3) 3: Synthesis and ESR studies

The triarylmetal-centred radicals .MAr 3 (M = Si, Ge, or Sn; Ar = 2,6-Me 2C 6H 3 or 2,4,6-Me 3C 6H 2) have been prepared from the appropriate triarylmetal chloride, MAr 3Cl, and an electron-rich olefin [R NCH 2CH 2NRC ] 2 (R = Me or Et) under UV irradiation in toluene at low temperature. The triarylgermyl radicals are persistent ( t 1 2 > 24 h, 20°C) whilst the analogous tin and silicon radicals are only stable under constant irradiation at temperatures below −20°C; the ESR spectra of the germanium radicals and of .Si(2,4,6-Me 3C 6H 2) 3 (which is the first triarylsilyl radical to be spectroscopically identified) show coincidental equivalence of all the proton couplings due to twisting of thearomatic rings into a “propeller” arrangement about the metal. The synthesis and characterisation of precursors to these radicals are also reported.

Vier-und fünfgliedrige Phosphorheterocyclen, L [1] Tautomeric und Substitution am 5 -Dimethylamino -1.2.4.3λ3-triazaphosphol [2] / Four- and Fivemembered Phosphorus Heterocycles, L [1] Tautomerism and Substitution at 5-Dimethylamino-l,2,4,3λ3 -triazaphosphole [2

Abstract 1,2,4,3 λ3 -Triazaphospholes unsubstituted at the heteroatoms can be synthesized only if they carry an amino group in 5-position. The title compound, being the first representative, was prepared from N,N-dimethyl-N′-aminoguanidinium iodide and P(NMe2)3. Its single proton is not bonded to phosphorus but to nitrogen and causes association by NH···N bridges. The proton was substituted for silyl, stannyl, phosphino and thiophosphinyl groups assumedly in 2-position. The phosphino derivatives react with sulfur only at the exocyclic phosphorus. Loss of N2 from the triazaphosphole ring was observed in one case.

Molecular orbital correlation of arylmethyl chloride atom abstraction by stannyl radicals

A series of monochloromethylated polycyclic benzenoid hydrocarbons have been treated with triphenyltin hydride and AIBN initiator at 70°C. Under these conditions the only observable reaction is reduction of the starting materials to methylarenes. A significant range of relative rates (factor of 40) has been found among the compounds studied. All relative rates yielded an excellent correlation when plotted against PPP-SCF calculated energy differences. The present works shows the ability of such calculations to treat processes involving nucleophilic radicals.

Alkyl and stannyl radical generation by CSn and SnSn bond dissociation in photolytically excited peralkylated tristannanes as studied by ESR and 119Sn-CIDNP

Tristannanes used as photochemical precursors for the synthesis of organic compounds react via triplet states followed by homolytic CSn and SnSn bond scission.

Electron spin resonance and kinetic studies on tin centered radicals r3sn. with bulky substituents

AbstractESR data of stannyl radicals R3Sn. with residues R of considerable bulkiness in solution are presented. With R = neophyl (PhMe2C‐CH2), (g = 2.0150) an alternating linewidth effect indicating hindered rotation around the Sn‐C bonds is found. The radical is non‐planar by 14.0° and configurationally stable. The radicals (2, 4, 6‐alkyl3Ph) Sn., alkyl = H, Me, Et, i‐Pr show singlets (g = 2.0023 ‐ 2.0078) broadened by unresolved hyperfine interactions with ring and alkyl protons, aH ≤ 0.05 mT. They are non‐planar by 15.1 – 16.1°, (i‐Pr3Ph)3Sn. being less pyramidal than Ph3Sn because of steric repulsions between the substituents, and are in recombination‐dissociation equilibria with the corresponding distannanes. The Sn‐Sn bond energies drop from 205 kj (alkyl = Me) to 36 kJ (alkyl = i‐Pr). For (Et3Ph)3Sn., the activation energy of recombination is 38 kJ/mol.

(Aminoethinyl)metallierungen : VII. Synthese und reaktivität von (3-stannyloxy-3-alken-1-inyl)aminen

The CO double bond of diphenylketene inserts into the tin-acetylenic carbon single bond of β-stannylated ynamines. The formation of 4,4-diphenyl-3-stannyloxy-3-buten-1-ynyl amines is proved partly by spectroscopic data, partly by isolation. Under detachment of the stannyl group they hydrolyze relatively easily to the corresponding acyl ynamines and react with acyl chlorides to give the corresponding 3-acyloxyenynamines. N-Methyl- N-(4,4-diphenyl-3-triphenyl-stannyloxy-3-buten-1-ynyl)aniline yields under the conditions of chromatography on silica gel a destannylated β-naphthol derivative; the same enynamine isomerizes in CDCl 3 solution spontaneously to 4-( N-methylanilino)-1-phenyl-3-triphenylstannyl-2-naphthol, the structure of which is established by an X-ray analysis. The reaction of the β-stannylated ynamines with ketene or dimethylketene directly gives the corresponding acyl ynamines, which are characterized by the reaction with tosylazide as crystalline diazo compounds. By addition of an excess of ketene the 2-acetyl-3-amino-2-cyclobuten-1-ones are formed as 1:2 adducts.

Adducts of silyl, germyl and stannyl radicals with heterocyclic α-diketones: an electron spin resonance investigation

Hyperfine coupling constants are reported for adducts of silyl, germyl and stannyl radicals with a series of substituted benzo [ b]thiophen-2,3-diones (Ia—Ip), benzo [ b] furan-2,3-dione (II), ninhydrin (III), and thieno [ 3,2- b] thiophen-2,3-dione (IV). The conformational and electronic properties of these radicals are compared with those of similar adducts formed by diaryl ketones.