(–)-Parasantonic acid and its enol lactone, (+)-parasantonide: observation of the rare acid-to-acid catemeric hydrogen-bonding mode in a ,-diketocarboxylic acid
Abstract: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
Publication date: 2004-06-01