Configuration and conformation of (3S,3aR,4R,7S,7aS)-4-methyl-7-(2-propyl)-2-oxo-2,3,3a,4,5,6,7,7a-octahydro-3-benzofurancarboxylic acid

The crystal structure determination of the title compound, C13H2004, together with the knowledge of the configuration of the starting menthyl reagent, define both its absolute configuration and that of the menthyl ester from which it is obtained by hydrolysis. The structure of the title compound in the crystal is compared with that obtained for the isolated molecule by molecularmechanics energy minimization. The largest discrepancies are observed for the carboxyl group which, in the crystal, is involved in hydrogen bonding with the same group of an adjacent molecule packed about a twofold axis of theP21212 space group. The conformation of the molecule is discussed.