Selective Reactions of the Silicon-Hydrogen Group with Grignard Reagents. The Preparation of Some Unsymmetrical Silane Derivatives

Gilman, Henry; Zuech, Ernest A.

doi:10.1021/ja01531a021

Cited by 38 publications

(7 citation statements)

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“…In 1959, Gilman et al. reported that triphenylsilane and benzyl Grignard reagent in boiling THF gave triphenyl(benzyl)silane ( 1 ) in 53 % yield after 4 days 3a. This is consistent with our observation that a similar reaction for a shortened period of 8 hours yielded only a small amount of 1 [Eq.…”

Section: The Licl Acceleration Of the Allylation Of Silanessupporting

confidence: 90%

Do Photolyases Need To Provide Considerable Activation Energy for the Splitting of Cyclobutane Pyrimidine Dimer Radical Anions?

Song

Tang

et al. 2007

Chemistry A European J

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cis-syn Cyclobutane pyrimidine dimers, major UV-induced DNA lesions, are efficiently repaired by DNA photolyases. The key step of the repair reaction is a light-driven electron transfer from the FADH(-) cofactor to the dimer; the resulting radical anion splits spontaneously. Whether the splitting reaction requires considerable activation energy is still under dispute. Recent reports show that the splitting reaction of a dimer radical anion has a significant activation barrier (0.45 eV), and so photolyases have to provide considerable energy. However, these results contradict observations that cis-syn dimer radical anions split into monomers at -196 degrees C, and that the full process of DNA photoreactivation was fast (1.5-2 ns). To investigate the activation energies of dimer radical anions, three model compounds 1-3 were prepared. These include a covalently linked cyclobutane thymine dimer and a tryptophan residue (1) or a flavin unit (3), and the covalently linked uracil dimer and tryptophan (2). Their properties of photosensitised splitting of the dimer units by tryptophan or flavin unit were investigated over a large temperature range, -196 to 70 degrees C. The activation energies were obtained from the temperature dependency of splitting reactions for 1 and 2, 1.9 kJ mol(-1) and 0.9 kJ mol(-1) for the thymine and uracil dimer radical anions, respectively. These values are much lower than that obtained for E. coli photolyase (0.45 eV), and are surmountable at -196 degrees C. The activation energies provide support for previous observations that repair efficiencies for uracil dimers are higher than thymine dimers, both in enzymatic and model systems. The mechanisms of highly efficient enzymatic DNA repair are discussed.

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Section: The Licl Acceleration Of the Allylation Of Silanessupporting

confidence: 90%

Do Photolyases Need To Provide Considerable Activation Energy for the Splitting of Cyclobutane Pyrimidine Dimer Radical Anions?

Song

Tang

et al. 2007

Chemistry A European J

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“…Analyses of the cleavage reaction mixtures have been slightly complicated by the presence in these mixtures of various but substantial amounts of silanols arising from silanes 5f − h . Indeed, hydrosilanes are known to undergo nucleophilic substitution reactions by strong nucleophiles leading to displacement of hydride ions …”

Section: Resultsmentioning

confidence: 99%

Kinetic Control in the Cleavage of Unsymmetrical Disilanes

et al. 1997

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A series of 12 phenyl-substituted arylpentamethyldisilanes 1a-l have been synthesized in order to examine the regioselectivity of their nucleophilic Si,Si bond cleavage reactions under Still's conditions (MeLi/HMPA/0 degrees C). It has been found that the sensitivity of these reactions to the electronic effects of the substituents in the phenyl ring could be described by the Hammett-type equation log(k(A)/k(B)) = 0.4334 + 2.421(Sigmasigma); (correlation coefficient R = 0.983). The k(A)/k(B) ratio represents the relative rate of attack at silicon atom A (linked to the aryl ring) or at silicon atom B (away from the aryl ring) of the unsymmetrical disilanes. Thus, the present investigation shows that the earlier belief according to which the nucleophilic cleavage of unsymmetrical disilanes always produces the more stable silyl anionic species (thermodynamic control) should be abandoned, or at least seriously amended: kinetic factors appear to exert a primary influence on the regioselectivity of such reactions. Since the two major kinetic factors (i.e., electrophilic character of and steric hindrance at a given silicon atom) have opposite effects on the orientation of the reaction, it may happen that kinetic and thermodynamic control lead to the same result. For some of the unsymmetrical disilanes studied, the major reaction path was not the Si,Si bond cleavage; instead, Si-aryl bond breaking occurred, producing the corresponding aryl anions.

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“…: 23 g (0,174 Mol) = 52% 1,3-Dihydrodisilmethylen4). (Formel (3) (2) (Forrnel (3), n = 2 4 ) Zu einer Losung von 7,45 Mol Dimethylsilylrnethylrnagnesiurnchlorid in THF, die in der iiblichen Weise aus 216 g ( 9 Mol) Magnesium, 872 g (8 Mol) Chlorrnethyldirnethylsilan und 3 1 trockenern THF hergestellt worden war, wurden 481 g (3,73 Mol) Dimethyldichlorsilan irn Laufe von 30 Min. zugetropft.…”

Section: Herstellung Von 13-dihydrodisilmethylenunclassified

“…C 49,68 H 11,81 3 . Herstellung der Monochlormonohydropolysilmethylene (Formel (5), n = 1-4) a) 1,634 Mol Dimethylsilylmethylmagnesiumchlorid wurden zu 451 g (3,5 Mol) Dimethyldichlorsilan, die mit 300 ml absol. THF verdiinnt waren, innerhalb 2 Stdn.…”

Section: Herstellung Der Ow'-dihydropolysilmethyleneunclassified

Über oligomere siliciumverbindungen mit funktionellen gruppen. 8. Mitt.: Über die herstellung von hydropolysilmethylenen und deren addition an ungesättigte verbindungen

Greber

Degler

1962

Makromol. Chem.

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ZUSAMMENFASSUNG: Die homologen w,w'-Dihydropolysilmethylene (Formel (I), R und R' = H ) CH, CH, CH, LH, wurden auf zwei verschiedenen Wegen hergestellt : a ) durch Reduktion der entsprechenden w,w'-Dichlorpolysilmethylenhomologen (Formel (I), R und R' = Cl) mit Lithiumaluminiumhydrid und b) durch Umsetzung der w,w'-Dichlorpolysilmethylenhomologen und Dimethyldichlorsilan mit dem bisher nicht beschriebenen Dimethylsilylmethylmagnesiumchlorid. Mit Hilfe dieser GRIGNARD-Verbindung waren auch die interessanten Monochlormonohydropolysilmethylene (Formel (I), R = C1 und R' = H ) einfach zuganglich, die mit den Allyl-und Vinylmagnesiumhalogeniden in die entsprechenden Monoallylmonohydro-und Monovinylmonohydropolysilmethylene (Formel (I), R = H und R' = Allyl-bzw. Vinyl) iibergefuhrt wurden. Mit den hergestellten Hydropolysilrnethylenderivaten wurden Additions-und Polyadditionsreaktionen an ungesattigte Verbindungen durchgefiihrt. n = 1 -4 I (1) R--$-( CH,--Si),-R SUMMARY: o,w'-Dichloropolysilrnethylenes (formula (I), R and R' = Cl)

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Selective Reactions of the Silicon-Hydrogen Group with Grignard Reagents. The Preparation of Some Unsymmetrical Silane Derivatives

Cited by 38 publications

References 0 publications

Do Photolyases Need To Provide Considerable Activation Energy for the Splitting of Cyclobutane Pyrimidine Dimer Radical Anions?

Do Photolyases Need To Provide Considerable Activation Energy for the Splitting of Cyclobutane Pyrimidine Dimer Radical Anions?

Kinetic Control in the Cleavage of Unsymmetrical Disilanes

Über oligomere siliciumverbindungen mit funktionellen gruppen. 8. Mitt.: Über die herstellung von hydropolysilmethylenen und deren addition an ungesättigte verbindungen

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