Novel Trichloroacetimidates and their Reactions

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ALI, Ibrahim Ahmed Ibrahim, 2003. Novel Trichloroacetimidates and their Reactions. Göttingen : Cuvillier-Verl.. ISBN 3-86537-025-X

@phdthesis{Ali2003Novel-9822, title={Novel Trichloroacetimidates and their Reactions}, year={2003}, author={Ali, Ibrahim Ahmed Ibrahim}, address={Konstanz}, school={Universität Konstanz} }

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:bibo="http://purl.org/ontology/bibo/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:dcterms="http://purl.org/dc/terms/" xmlns:xsd="http://www.w3.org/2001/XMLSchema#" > <rdf:Description rdf:about="https://kops.uni-konstanz.de/rdf/resource/123456789/9822"> <dc:publisher>Göttingen : Cuvillier-Verl.</dc:publisher> <dcterms:available rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">2011-03-24T18:14:39Z</dcterms:available> <bibo:issn>3-86537-025-X</bibo:issn> <dc:rights>deposit-license</dc:rights> <dcterms:title>Novel Trichloroacetimidates and their Reactions</dcterms:title> <dc:creator>Ali, Ibrahim Ahmed Ibrahim</dc:creator> <dcterms:issued>2003</dcterms:issued> <dcterms:rights rdf:resource="http://nbn-resolving.org/urn:nbn:de:bsz:352-20140905103416863-3868037-7"/> <dcterms:alternative>Neuartige Trichloracetimidate und ihre Reaktionen</dcterms:alternative> <bibo:uri rdf:resource="http://kops.uni-konstanz.de/handle/123456789/9822"/> <dc:date rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">2011-03-24T18:14:39Z</dc:date> <dc:format>application/pdf</dc:format> <dc:contributor>Ali, Ibrahim Ahmed Ibrahim</dc:contributor> <dcterms:abstract xml:lang="eng">A successful multi-step synthesis of complex oligosaccharide structures requires an appropriate protecting group strategy. Generally, the presence of three or more hydroxy groups in each sugar residue necessitates the protection of those hxdroxy groups which are not involved in the glycosylation step. In our study, the phthalimidomethyl protecting group has been used for the protection of hydroxy groups. The trichloroacetimidate 2 was prepared by the reaction of N-ydroxymethyl phthalimide (1) with trichloroacetonitrile in dichloromethane as solvent and in the presence of DBU in 87 % yield. The trichloroacetimidate 2 was reacted with primary and secondary hydroxy groups in various types of organic compounds. The deallylation of O-1 in 22 which possesses a phthalimidomethyl group on O-2 and reaction with trichloroacetonitrile in the presence of DBU as a base led to trichloroacetimidate 24. Glycosylation of methanol, n-octanol and 6-O-unprotected glucopyranoside 15 with 24 as glycosyl donor in the presence of TMSOTf as a catalyst afforded glucosides 25-27 in high yields. Thus, it was demonstrated that the Pim group on O-2 controls the anomeric selectivity essentially based on steric hindrance. The required trichloroacetimidates 41 and 42 of the DPM 128 and Fl, respectively, were prepared by the reaction of diphenylmethanol (39) and 9-fluorenol (40), with trichloroacetonitrile in the presence of 1,8-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalyst. Also, trichloroacetimidates 41 and 42 were reacted with different hydroxy groups in alcohols and carbohydrates. It became interesting to study the effect of the DPM and Fl group of glycosyl donors 67 and 68 on the stereoselectivity during the glycosylation reaction as shown for the reactions leading to compounds 69-74. Also, the stereoselectivity in mannosylation reactions was studied. The coupling of the trichloroacetimidate donor 78 with n-octanol, glucose derivatives 15, 84 and 4-OH free glucose derivative 17 as acceptor was carried in dry dichloromethane at room temperature and at -40oC in the presence of TMSOTf as catalyst to afford the desired mannopyranosides 81, 82, 85 and 86. Thus, it became obvious, that compared with the benzyl group the DPM group supports in most cases β-mannopyranoside formation. This part describes the reaction of cyclopropylmethyl and cyclobutyl trichloroacetimidates, respectively, with hydroxy groups of varied nucleophilicities in order to investigate its use as alkylating agent under mildly acidic condition and to throw some light on the mechanism of the trichloroacetimidate procedure in forming glycosyl bonds. The cyclopropylmethyl cation has been found to be formed readily from the trichloroacetimidate 101 in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) as catalyst. Dibenzyl phosphate 120, as weak acid, gave only cyclopropylmethyl derivative 121 without any catalyst and the reaction proceeded without rearrangement. When the acceptor has a slightly more acidic character such as diphenyl phosphate 122 reaction with trichloroacetimidate 101 gave, in addition to 123, rearrangement products 124 and 125. When the acceptor has a slightly more acidic character such as diphenyl phosphate 122 reaction with trichloroacetimidate 101 gave, in addition to 123, rearrangement products 124 and 125. In the case of 4-toluenesulfonic acid, the cyclobutyl 127 and homoallyl derivatives 128 were formed. The required cyclobutyl trichloroacetimidate 102 was prepared in 87% yield by the reaction of cyclobutanol 99 with trichloroacetonitrile in the presence of DBU as catalyst. The cyclobutyl trichloroacetimidate 102 was reacted with acceptors such as benzyl alcohol (5), dinitrobenzyl alcohol (11) and the O-6-unprotected hydroxy group in glucose derivative 15; it gave the same reaction products as cyclopropylmethyl trichloroacetimidate 101 and also in about the same ratio. The double bond rearrangement of many unsaturated compounds can take place on treatment with acids. Thus, rearrangement of allyl compounds carrying a leaving group of the type shown in the following scheme may take place in presence of acids via carbonium ions, which in presence of alcohol may give two products. It has been found that the phthalimidomethyl group (Pim) can be used as an aminomethylating agent for C-nucleophiles.</dcterms:abstract> <dc:language>eng</dc:language> </rdf:Description> </rdf:RDF>

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

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