- Use of Radical Ring-Opening for Introduction of Alkyl and Substituted Alkyl Groups with Stereochemical Control: A Synthetic Application of Cyclopropylcarbinyl Radicals
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Cyclopropylcarbinols 2a and 2b (see Scheme I), which are accessible by a number of routes, can be converted into the corresponding radicals 3a and 3b, respectively.These radicals undergo peripheral ring-opening of the cyclopropyl substructure to afford su
- Clive, Derrick L. J.,Daigneault, Sylvain
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p. 3801 - 3814
(2007/10/02)
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- ANNULATED PYRANOSIDES-V. AN ENANTIOSPECIFIC ROUTE TO (+) AND (-) CHRYSANTHENUM DICARBOXYLIC ACIDS.
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Methyl 2,3-anhydro-4,6-O-benzylidene-α-D-allopyranoside undergoes the Wadsworth-Emmons cyclopropanation with phosphonopropionate to give a cyclopropyl carboxylate which is processed to give the gem-dimethylcyclopropano pyranoside.The glycosylic acetal of this substance is readily hydrolyzed by boiling water, and the resulting cis-cyclopropane carboxaldehyde may epimerized quantitatively to the trans-analog by treatment with sodium methoxide.These are now converted into the (+)- and (-)-chrysanthenum dicarboxylic acids, respectively, by the same sequence of reactions involving (a) olefination with methyl 2-(triphenylphosphoranylidene)propionate, (b) hydrolysis of the benzylidene ring and cleavage of the resulting triol with sodium metaperiodate, and (c) oxidation of the resulting aldehyde with silver I oxide.In the case of the (+)-enantiomer the last reaction is preceeded by epimerization.The overall yields from the D-allopyranoside are respectively 27percent, in 10 steps for the (+)-enantiomer, and 24percent, in 10 steps for the (-)-enantiomer, from the known epoxide 7.
- Fitzsimmons, Brian J.,Fraser-Reid, Bert
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p. 1279 - 1288
(2007/10/02)
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