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(–)-Parasantonic acid and its enol lactone, (+)-parasantonide: observation of the rare acid-to-acid catemeric hydrogen-bonding mode in a ,-diketocarboxylic acid

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The title diketo acid, (−)- ,3a,7-tri­methyl-5,8-dioxo-1,4-ethano­per­hydro­pentalene-1-acetic acid, C H O , is shown to aggregate in the solid state as acid-to-acid hydrogen-bonded catemers, whose chains follow 2 screw axes from each carboxyl H atom to the C=O group of a neighboring carboxyl group [O…O = 2.672 (4) Å and O…H—O = 173°]. Two parallel counterdirectional screw-related single-strand hydrogen-bonded chains pass through the cell in the a direction. Two intermolecular C=O…H—C close contacts are present in this compound. Both this diketo acid and its enol lactone, (+)-parasantonide [systematic name: (−)- ,3a,7-tri­methyl-5-oxo-1,4-ethenoper­hydro­pentalene-1,8-carbolactone], C H O , have an R configuration at the methyl­ated chiral center adjacent to the carboxyl group, unlike the precursor from which they are derived, viz. (−)-santonic acid.

Document Type: Research Article

DOI: http://dx.doi.org/10.1107/S010827010400839X

Publication date: June 1, 2004

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