Molecular and crystal structures of stereoisomeric2R,3R,6S-2-(1′S-hydroxy-1′-biphenylyl)- and2R,3R,6S-2-(1′R-hydroxy-1′-biphenylyl)methyl-3-methyl-6-isopropylcyclohexanones

Abstract

It was established by X-ray diffraction analysis that 2-(1′-hydroxy-1′-biphenylyl)methyl-3-methyl-6-isopropylcyclohexanone, one of the minor products of the directed aldol reaction of (−)-menthone bromomagnesium enolate with 4-phenylbenzaldehyde, has the2R,3R,6S, 1′R configuration. The characteristic features of the spatial structure of this β-hydroxyketone were compared with those of the major stereoisomeric product of the above-mentioned reaction. The latter has the2R,3R,6S,1′S configuration. In the crystals, both stereoisomers have the cyclohexanone ring in a chair-like conformation with the three substituents in equatorial positions and are characterized by the presence of the annelated (cis-fused) pseudoring with an −OH…O=C< intramolecular hydrogen bond. The structures of the stereoisomers differ in the orientation of the aryl group and the hydrogen atom at the C(1′) chiral center with respect to the cyclohexanone ring. The results of X-ray diffraction analysis were compared with the data of molecular mechanics calculation for the energetically most favorable conformations of the isolated molecules of β-hydroxyketones under study.