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Enantioselective Deprotonation/Electrophile Addition Reactions of Tricarbonyl(phenyl carbamate)chromium Complexes

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Published in Helvetica Chimica Acta. 1999, vol. 82, no. 1, p. 90-104
Abstract Sequential reaction of the tricarbonyl[(?6-phenyl) carbamate]chromium complex 3 with chiral amide bases (see 4 and 5) and electrophiles yielded planar chiral ortho-substituted complexes 6 with up to 70% enantiomeric excess (ee) (Scheme 2, Table 1 and 2). The enantiomer purity could be increased to >90% ee by fractional crystallization. In all but one case the racemate crystallized selectively, leaving the enantiomerically enriched complex in solution. X-Ray crystal-structure analyses of rac-6a and (1R)-6a suggest that this can be ascribed to a more favorable packing of enantiomers of opposite configuration in the solid state than that of the enantiomerically pure solid. Increasing the temperature of the intermediate ortho-lithiated aryl carbamate complex induced an anionic ortho-Fries rearrangement: The 1,3-transposition of the carbamoyl group yielded the ortho-substituted (?6-benzamide)tricarbonylchromium complexes 10 in 65% yield, after exposure to the electrophile (Scheme 6), and the use of a chiral amide base 5 in the deprotonation step afforded the product with an ee of 54%.
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QUATTROPANI, Anna, BERNARDINELLI, Gérald Hugues, KUNDIG, Ernst Peter. Enantioselective Deprotonation/Electrophile Addition Reactions of Tricarbonyl(phenyl carbamate)chromium Complexes. In: Helvetica Chimica Acta, 1999, vol. 82, n° 1, p. 90-104. https://archive-ouverte.unige.ch/unige:7826

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