Menthol absolute configuration

By this method, for example, the absolute configurations of the following compounds were established (-)-2-phenylbutyric acid,[48] (-)-hydratropic acid,[48] (+)-0-acetyl-mandelic acid,t48] (-)-2-(7/-carbazolyl)propionic acid,t48] (+)-1 -phenylethanol,[48] (-)-menthol,t48] (+)-1 -phenylethylamine,[48] and 1-alanine ethylester.[48] The determination of the absolute configuration of bacteriochlorophylles c, d and e was made possible by the esterification of the phaeophorbides by CDI to imidazolides.[49]... 

Determine the absolute configurations of the chiral centres in menthol and phenbutrazate. List the configurations of the pairs of enantiomeric diastereoisomers of menthol (Fig. 2.24). 

As a first step towards the measurement of single molecule effects, Schrader and Korte (1972) reported the measurement of the infrared rotatory dispersion of carvone in liquid crystalline solution. They used a modified commercial spectrometer. They observed a huge effect which is not the result of the carvone itself but of the liquid crystal in which a helical arrangement (cholesteric state) is induced by the chiral solute (Sec. 4.6.4). In this case the liquid crystal acts as a kind of molecular amplifier which allows the absolute configuration of tiny amounts of solutes to be determined reliably. At about the same time Dudley et al., (1972) measured the infrared circular dichroism of (-)-menthol in a liquid crystal. Their equipment consisted of a normal infrared spectrometer supplemented by a Fresnel rhomb made from sodium chloride. 

We became interested in synthesizing both the enantiomers of differolide to clarify whether one or both of them are bioactive. Our synthesis is summarized in Figure 5.14 and 5.15.23 Because both the enantiomers 135 and 135 were necessary for bioassay, we adopted enantiomer separation (optical resolution) of an intermediate as our key step (Figure 5.14). A crystalline acetal (-)-B was obtained from ( )-A and (—)-menthol, and analysed by X-ray to reveal its structure as (—)-B, basing on the known absolute configuration of (-)-menthol. When (+)-menthol was used for acetal formation, crystalline (+)-B was obtained in a similar manner. We thus secured both (-)-B and (-t-)-B as pure crystals. 

Cationic rhodium(I) complexes catalyze the isomerization of tertiary ally-lamines E-11.17 and Z-11.17 to enamines 11.18. In THF at 80°C, these enamines are readily hydrolyzed to provide aldehydes. When the rhodium ligand is a chiral diphosphine such as (R)- or (6)-binap 3.43 (Ar = Ph), or better yet, (R)- or (S)-tolbinap 3.43 (Ar = 4-MeC6H4), (R) or (5)-enamines 11.18 are obtained with an excellent enantiomeric excess. This method is used in industry for the synthesis of optically active dtronellol and menthol [811, 812, 853, 889], Biphemp 3.45 is also a highly potent ligand for the isomerization of Z-11.17, and ee s as high as 99.5% are observed [905]. The absolute configuration of the enatnine product... 

Treatment of racemic methoxysilane 30 with (-)-menthol afforded a mixture of diastereomeric menthoxysilanes 31. Fractional crystallization from pentane gave the less soluble diastereomer ([a]D -53.9°) in 46% yield. Lithium aluminum hydride reduction led to (+)-l-naphthylphenylmethylsilane (4, [a]D +33.4°). The more soluble diastereomer similarly gave rise to (-)-l-NpPhMeSiH ([a]D -32.8°). The absolute configuration of (+)-l-NpPhMeSiH was shown to be R by X-ray diffraction studies (45). 

S) enantiomers of the complex [Mn(C5H5)(NO)COP(C6H5)3]X (2.12)-X was achieved by using natural menthol as the chiral auxiliary. The covalent bond so formed could be readily broken without effecting the absolute configuration of the manganese complex. 

The ring H- and C-chemical shifts of 8 aldofuranoses have been recorded in DMSO-de and those of 14 aldopyranoses in DMSO-de as well as D2O, to assess the solvent dependencies and the accuracy in calculated predictions of chemical shifts. A new method for determining the absolute configuration of optically active secondary alcohols (menthol, cholesterol, etc.) involves measurement of the differences in the pyridine-induced chemical shifts of their P-d- and P-l-fucofuranosyl derivatives. ... 

S, R configuration of chiral silicon center Is determined by the absolute configurations of chiral centers of menthol and 1R S,5R]... 

The enantioselective approach to (—)-menthol is outlined in Scheme 9.2 [11]. It is a real challenge to our understanding of synthetic chemistry that such a simple short synthetic route, which starts from the achiral natural hydrocarbon isoprene, well known for its huge consumption by the mbber industry, can afford a chiral, cyclic alcohol with three stereogenic centres in defined absolute configurations and with high enantiopurity ... 

OA alcohols of rigid structure like (-)-menthol, (-)-isoborneol, (+)-neomenthol, (+)-isopinocampheol, (+)-borneol are effective co-initiators for asymmetric selection polymerization [145] as well as D(-)-l-methoxypropane-2-ol or poly(D-PO) of low molecular weight with hydroxy end groups. No simple correlation was found between the sign of selected antipodes and the absolute configuration of the alcohol [146]. Other co-initiators have been used as in binary systems consisting of equimolar amount of diethylzinc with amines [147] or various /-a-amino acids [148] which were found to be effective initiators for the asymmetric selection polymerization of PO. The increasing order of efficiency... 

---