- Synthesis and applications of tert-alkoxysiloxane linkers in solid-phase chemistry
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Straightforward syntheses of two tert-alkoxysilyl chloride functionalised resins 3 and 31 that allow facile attachment of 1°, 2°, 3° alcohols and phenols to the solid-phase have been achieved. Resin 3 displayed useful loading levels (0.7 mmol/g), and it was stable to storage in activated form. Siloxanes from reaction of 3 with alcohols and phenols were compatible with a variety of reaction conditions commonly used in solid-phase synthesis.
- Meloni, Marco M.,White, Peter D.,Armour, Duncan,Brown, Richard C.D.
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p. 299 - 311
(2007/10/03)
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- Design and evaluation of inclusion resolutions, based on readily available host compounds
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Resolution of enantiomers through selective crystallisation of diastereomeric inclusion compounds can extend the scope of traditional racemate resolution beyond salt forming compounds. To assess the practical value of this approach the literature was carefully screened and promising results were checked. Also an extensive range of new inclusion hosts suitable for resolution processes, derived from simple hydroxy- and amino acids were prepared and tested. Several techniques, including the Dutch Resolution approach utilizing mixtures of resolving agents, were applied. Over 70 potential resolving agents were tested in combinations with 34 racemates (over 100 racemates if literature results are included). Reproducibility of literature results was found to be problematic. Also the number of successful new resolutions found was very limited: only two efficient resolutions out of 1200 combinations of racemate and resolving agent tested in over 10.000 experiments! Crystal studies of representative combinations of resolving agents and inclusion compounds revealed some of the causes for the low rate of success in inclusion resolution. Compared to diastereomeric salts, the absence of strong electrostatic interactions substantially reduces the probability of forming crystals including both components. Molecular structure features allowing formation of intricate intramolecular and intermolecular H-bond networks were found to be responsible for inclusion crystal formation, and for the quality of the ensuing resolution through selective diastereomer crystallisation, in the successful cases. Whereas diastereomeric salt resolution continues to be of scientific and industrial interest, inclusion resolution should be viewed as of very limited scope; useful in specific instances, but lacking the wide applicability of classical resolution. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Mueller, Simona,Afraz, Marcel Cyrus,De Gelder, Rene,Ariaans, Gerry J. A.,Kaptein, Bernard,Broxterman, Quirinus B.,Bruggink, Alle
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p. 1082 - 1096
(2007/10/03)
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- A PROCESS FOR THE STEREOSELECTIVE SYNTHESIS OF LACTONES
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A process is described for the stereoselective synthesis of a chiral lactone which can be used as an intermediate in the synthesis of biotin. The process includes a reaction sequence in which a cyclic meso-carboxylic acid anhydride is converted with the aid of a chiral alcohol with ring opening into a dicarboxylic acid monoester. With respect to the dicarboxylic acid monoester obtained from the cyclic meso-carboxylic acid anhydride and the chiral alcohol, the reaction proceeds diastereoselectively. The reaction is performed in the presence of a specific catalyst improving the diastereomeric purity of the dicarboxylic acid monoester.
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- Facile one-pot procedure for Et3Al-promoted asymmetric pinacol-type rearrangement
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A facile procedure for the synthesis of enantiomerically pure α-substituted ketones is described. The pinacol-type 1,2-shift of sec-tert 1,2-diols could be effected by performing the following two processes in a one pot procedure, (1) regioselective methanesulfonylation, and (2) direct treatment of the resulting mesylate with Et3Al. This procedure allowed 1,2-shift reactions of various groups, including vinyl, aryl, and heteroaromatic groups, giving enantiomerically pure ketones in high yields.
- Shionhara, Tomoichi,Suzuki, Keisuke
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p. 141 - 146
(2007/10/03)
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- Novel silyl linkers for solid-phase synthesis
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The syntheses of two silyl chloride resins, 2 and 10 are described starting from Merrifield resin, 3-methyl-1,3-butanediol and diphenyldichlorosilane or dimethyldichlorosilane, respectively. The silyl chloride resin 2 was used for the attachment of 1° alcohols, 2° alcohols and phenols to the solid phase. A preliminary study of the stability of the diphenylsiloxane linker towards certain reaction conditions was also carried out. A more reactive silyl chloride resin 10 was found to be suitable for the attachment of 3° alcohols to the solid phase.
- Meloni, Marco M.,Brown,White, Peter D.,Armour, Duncan
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p. 6023 - 6026
(2007/10/03)
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- Catalytic asymmetric glyoxylate-ene reaction: A practical access to α-hydroxy esters in high enantiomeric purities
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An efficient asymmetric catalysis is developed for the glyoxylate-ene reaction to afford the α-hydroxy esters of biological and synthetic importance. The key to the success is the use of the chiral titanium complex prepared in situ from (i-PrO)2TiX2 (X = Cl or Br) and the (R)- or (S)-binaphthol in the presence of molecular sieves (MS 4A). The presence of the molecular sieves (zeolite) is clarified to facilitate the alkoxy-ligand exchange reaction. Thus, the use of MS is shown to be essential for the in situ preparation step of the chiral catalyst and not for the ene reaction step. The present catalytic process is applicable to various 1,1-disubstituted olefins by the judicious choice of the dichloro or dibromo catalyst.
- Mikami, Koichi,Terada, Masahiro,Nakai, Takeshi
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p. 3949 - 3954
(2007/10/02)
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- Preparing method of optically active ketones
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A preparing method of optically active ketones given by a general formula STR1 (wherein R represents a hydrocarbon group having 2 to 20 carbon atoms and R' represents a hydrocarbon group having 1 to 20 carbon atoms. The hydrocarbon groups of R and R' may
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