Absolute configuration alcohol determination

Other examples of absolute configuration determination by the exciton coupling between a chromophore and a benzoate derived from the alcohol include ... 

Thus, the enantiomeric contents in a pair of sulphoxides can be determined by the H NMR chemical shifts in the methine or methylene protons in the two diastereomeric complexes which are stabilized by the hydrogen bond between the hydroxyl and the sulphinyl groups (Scheme 13). Similarly, the enantiomeric purity and absolute configurations of chiral sulphinate ester can be determined by measuring the NMR shifts in the presence of the optically active alcohols. ... 

Considering an olefinic functionality as a chromophore, the absolute configuration of cyclic allylic alcohols can be determined using a method that involves the conversion of the alcohol to the corresponding benzoate.60 This can also be extended to acyclic alcohols where the conformations are dynamic (see Fig. 117). Interested readers may consult the literature for details.61... 

It is always advisable to examine the complete molecular topology in the neighborhood of the chiral carbon atom and to confirm the results by employing another analytical method before the final assignment. In conclusion, Prelog s rule does predict the steric course of an asymmetric synthesis carried out with a chiral a-keto ester, and the predictions have been found to be correct in most cases. Indeed, this method has been widely used for determining the absolute configuration of secondary alcohols. 

Another method for determining the absolute configurations of secondary alcohols is Horeau s method, which is based on kinetic resolution. As shown in Scheme 1-14, an optically active alcohol reacts with racemic 2-phenylbutanoic anhydride (54), and an optically active 2-phenylbutanoic acid (52) is obtained after hydrolysis of the half-reacted anhydride. 

Procedures for using this method to determine the absolute configuration of secondary alcohols can be outlined as follows (Fig. 1-2IB) ... 

Figure 1-21. Model to determine the absolute configurations of secondary alcohols. Reprinted with permission by Am. Chem. Soc., Ref. 75.

The absolute configuration of a secondary alcohol can also be determined through the NMR spectra of a single methoxyphenylacetic ester derivative... 

For the absolute configuration of the acid moieties, that of chrysanthemic acid was elucidated by Crombie et al. [13] in 1954 and that of chrysanthemum acid was determined by Inoue et al. [14] in 1955, respectively. The absolute configuration of the alcohol moiety was found by Katsuda et al. [15] in 1958. The complete elucidation of the absolute configuration of natural pyrethrins (Fig. 6) has led to the development of new useful synthetic products based on this model. 

NMR spectroscopy was found to be a valuable technique for differentiation between the enantiomers of optically active compounds. The principles of the methods used to distinguish between enantiomers by means of NMR have been developed and reviewed by Mis-low and Raban (217). The best results from the point of view of the determination of optical purity and absolute configuration of chiral sulfur compounds, especially of sulfinyl compounds, have been obtained with the help of chiral solvents (218). Pirkle (86) was the first to demonstrate that enantiomeric sulfoxides have nonidentical NMR spectra when dissolved in chiral alcohols having the following general formula ... 

Upon hydrogenation of 24 a 1,2-rearrangement of the epoxide occurred generating aldehyde 25 as a mixture of diastereoisomers. After reaction with methyl lithium, the diastereomeric alcohols 26 and 27 were separated and isolated in yields of 23% and 71%. While alcohol 26 as the minor diastereo-isomer could be oxidized with pyridinium dichromate (PDC) and methyle-nated to give the enantiomer of kelsoene (cnM), its diastereoisomer 27 with the inverse configuration at C-7 required a supplementary epimerization step with sodium methanolate. The enantiomerically pure ent- allowed for the determination of the absolute configuration of natural kelsoene (1) [9, 10]. The previously reported assignment based on NMR-correlation experiments [5] was corrected. 

Extracts of the male oil palm bunch moths, Tirathaba mundella Walker (Lepidoptera Pyralidae), were shown to contain four compounds namely, 5S, 65)-2,2,6-trimethyl-6-vinyl-tetrahydro-pyran-3-ol, 4-hydroxy-3-methoxy benzaldehyde (vanillin), 6,10,l4-trimethyl-2-pentadecanone, and the corresponding alcohol 6,10,l4-trimethyl-2-pentadecanol, which elicited responses from the females. However, when synthetic compounds were used in lures, the ketone and alcohol by themselves did not attract females, suggesting that they might not be an essential part of the blend. This can only be confirmed once their absolute configuration has been determined and the proper stereoisomers tested in the... 

---