- Efficient and practical protocol for silylation of hydroxyl groups using reusable lithium perchlorate dispread in silica gel under neutral condition
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A very efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols with hexamethyldisilazane on the surface of silica gel dispersed with LiClO4 in room temperature at few minutes in excellent yields under neutral conditions is reported. This procedure also allows the excellent selectivity under LP-SiO2 system for silylation of alcohols in the presence of amine and phenolic hydroxy groups.
- Azizi, Najmedin,Yousefi, Rozbeh,Saidi, Mohammad R.
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p. 817 - 820
(2007/10/03)
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- Chemoselective protection of hydroxyl groups and deprotection of silyl ethers
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Trimethylsilylation of alcohols and phenols is carried out using hexamethyldisilazane and LiClO4 under microwave irradiation and neutral conditions. The deprotection of silyl ethers is carried out similarly using natural kaolinitic clay and a few drops of water.
- Bandgar,Kasture
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p. 1101 - 1104
(2007/10/03)
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- Silicon-29 NMR spectra of tert-butyldimethylsilyl and trimethylsilyl derivatives of some non-rigid diols
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29Si NMR spectra of trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBDMS) derivatives of selected diols were measured under standardized conditions (i.e., in diluted CDCl3 solutions). Application of the recently reported correlation between the chemical shifts in TMS and TBDMS derivatives revealed considerable and systematic deviations which exceeded experimental errors and error estimates from the correlation. Two possible explanations of the deviations are considered: interaction between the two bulky substituent groups and invalidity of the reported correlation for simple hydroxy derivatives. An independent study of analogous derivatives of monohydroxy compounds has shown that the linear correlation holds but the slope and intercept are significantly different from those reported previously on the basis of a study of amino acid derivatives. The data obtained for the diol derivatives fit the new correlation very well and no indication of an interaction between the bulky TBDMS groups was noticed. However, deviations do occur in branched diol derivatives in which branching reduces accessibility of the oxygen atoms surface to associate with proton donors. The largest deviation was found when intramolecular hydrogen bond was formed.
- Kvicalova, Magdalena,Blechta, Vratislav,Kobylczyk, Krzysztof,Piekos, Ryszard,Schraml, Jan
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p. 761 - 768
(2007/10/03)
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- Fluorophosphoranes as Lewis acids. The conditions of access to hexacoordinated neutral adducts via the intramolecular addition of an electrondonor
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The possibility of obtaining bicyclic neutral hexacoordinated fluorophosphorus adduct of type 2 was investigated for R=F, Me, Ph and X=O, S, NH, NMe, NtBu NPh.Adduct 2g was formed predominantly only in the case where R=F and X=S.In all the othe
- Robert, Dominique,Gawad, Hoda Abdel,Riess, Jean G.
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p. 511 - 516
(2007/10/02)
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