ANNULATED PYRANOSIDES-V. AN ENANTIOSPECIFIC ROUTE TO (+) AND (-) CHRYSANTHENUM DICARBOXYLIC ACIDS.

Article abstract of DOI:10.1016/S0040-4020(01)82414-5

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.