Use of X-ray diffraction data in stereochemical studies of (−)-menthone reactions with aromatic aldehydes

Conformational analysis of some 1R,4S‐2‐arylidene‐p‐menthan‐3‐ones by 1H NMR spectroscopy and molecular simulation

“…Moreover, the calculated endocyclic torsion angles for the chair conformer A of 1a agree entirely with experimental x-ray data. 19 Analogously, the experimental geometry of the cyclohexanone ring on x-ray data for compound 1b in the twist-boat conformation 18 is very close to that calculated for conformers D-F. Therefore, the 3 J chair and 3 J twist values calculated from the torsion angles between the protons obtained by molecular simulation are convincing.…”

“…18,19 The assignment of the 1R,4S-configuration to a product of Claisen-Schmidt condensation of ( )-menthone with 3-methoxybenzaldehyde given 20 by analogy with the starting ketone is erroneous because the inversion of the C-4 chiral centre always occurs under conditions of this reaction. 9,12,16 The authors 20 were also mistaken in analysing x-ray experimental data for one of the transformation products of the compound mentioned above. According to our examination of these data, 20,21 this product possesses a 1R,4R-configuration in accordance with expectations based on our previous findings.…”

“…According to our examination of these data, 20,21 this product possesses a 1R,4R-configuration in accordance with expectations based on our previous findings. 9,12,16 Note that compounds 1a and 1b have different molecular conformations in the crystals. Carbomethoxy-substituted compound 1a has been found 19 to form crystals with a chair conformation of the cyclohexanone ring (both alkyl groups are axial), but a twist-boat conformation has been established 18 for phenyl substituted analogue 1b.…”

“…9,12,16 Note that compounds 1a and 1b have different molecular conformations in the crystals. Carbomethoxy-substituted compound 1a has been found 19 to form crystals with a chair conformation of the cyclohexanone ring (both alkyl groups are axial), but a twist-boat conformation has been established 18 for phenyl substituted analogue 1b. In this connection, it is especially important to ascertain the conformational states of compounds 1a and 1b in solution.…”

“…As for the molecular structures of 1R,4S-diastereomeric compounds, no data on their conformational states in solutions have been obtained up to now. X-ray results concerning the configurations of two synthesized 16,17 derivatives of 1R,4S-diastereomeric series, viz. 1R,4S-2-(4-carbomethoxybenzylidene)-p-menthan-3-one (1a) and 1R,4S-2-(4-phenylbenzylidene)-p-menthan-3-one (1b) were presented in previous papers.…”