Synthesis of Selectively Functionalized Carbosilane Dendrimers with a Carbohydrate Core

Organic Letters

Volumn 1, Issue 12, 1999, Pages 1925-1927

  Boysen, Mike M K ^a   Lindhorst, Thisbe K ^a  

^a UNIVERSITY OF HAMBURG   (Germany)

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Indexed keywords

EID: 0000828433     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol9910619     Document Type: Article

References (26)

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25. General Procedure for the Preparation of Carbosilan Dendrimers from Tetraallylated Glucosides. For both reactions in this two-step protocol, except for the final workup, the Schlenk technique is required. Hydrosilylation. The tetraallylated compound (3 or 7) was dissolved in dry THF (0.11-0.37 mol/L). After addition of dichloromethylsilane (6 equiv) and 1-4 drops of Speier's catalyst, the mixture was stirred at rt for l h and then under reflux for another 10 h. After cooling to rt, the solvent and excess dichloromethylsilane were removed under vacuum as completely as possible. The resulting oily crude product (chlorosilane 8 or 9) which still contained residual solvent and silane reagent was used in the next synthetic step without any further purification. Grignard Addition of Allylmagnesiumbromide to Si-Cl Bonds. The crude chlorosilane (8 or 9) was dissolved in dry diethyl ether under an atmosphere of nitrogen (0.11-0.22 mol/L). To this solution was added dropwise allylmagnesiumbromide in diethyl ether (1 mol/L, 1.5 equiv per Si-Cl bond; a larger excess of Grignard reagent should be used because of residual dichloromethylsilane in the crude product). Precipitation of magnesium salts resulted instantly. After the addition was finished, the mixture was stirred under reflux for 12 h and then cooled to rt and poured onto an ice-cold saturated ammonium chloride solution. The aqueous phase was extracted three times with diethyl ether, and the combined organic phases were then twice washed with water and finally once with brine. Drying over magnesium sulfate, filtration, and evaporation of the solvent yielded the crude product which was purified by flash chromatography on silica gel.
26. +, calcd 876.1).