Absolute configuration correlations

Olovsson, G., Scheffer, J. R., and Trotter, J. (1997) Determination of the Absolute Steric Course of an Enantioselective Single Crystal-to-Single Crystal Photorearrangement, J. Am. Chem. Soc., 119, 1462-1463,. (e) Leibovitch, M., Olovsson, G., Scheffer, J. R., and Trotter, J. (1997) Absolute configuration correlation studies in solid state organic photochemistry, PureAppl. Chem., 69, 815-823. 

Highly sensitive chiral discrimination of amino acids with low ee was described. Amino acids with low ee act as a chiral initiator of asymmetric autocatalysis. In the presence of amino acids with low ee, pyrimidine-5-carbaldehyde was treated with z-P Zn to produce chiral pyrimidyl alkanol with the absolute configuration correlated with that of the amino acid by the consecutive asymmetric autocatalysis with amplification of ee. In addition, direct examination of extraterrestrial chirality was performed using meteorites by applying the asymmetric autocatalysis as the chiral sensor. The results indicated the presence of some chiral factor in the meteorites other than known organic compounds such as amino acids. 

For four of the reactions shown in Table 4 (entries 1,5,11, and 12), absolute configuration correlations were established between the reactant and its solid-state photoproduct. Such correlations represent one of the most powerful methods available to the organic chemist for elucidating reaction mechanisms. In the Norrish/Yang type II reaction (entries 1 and 5), for example, it allows an unequivocal determination of which y-hydrogen is abstracted, and for the di-7r-methane rearrangement of dibenzobarrelene derivatives (entries 11 and 12), it tells us precisely which atoms are involved in the formation of the initial cyclopropyldi-carbinyl diradical. 

For the di-7t-methane reactions of the (S)-(-)-proline tert-butyl ester salt and the (S,S)-(+)-pseudoephedrine salt in Scheme 36, absolute configuration correlations between reactant and photoproduct could be elucidated by X-ray crystallography. The correct absolute configurations of the reactants and the products are as shown in the scheme. The observed selective benzo-vinyl bridging to one direction is ascribed both to reduced steric repulsion between the vinyl substituents and to better orbital overlap in the transition state [65]. It is concluded for the 11,12-dicarboxydibenzobarrelene derivatives that initial benzo-vinyl bridging is favored at the carboxylate salt-bearing vinyl carbon atom both in the solid state and in solution [66]. 

Among the questions which arise when considering absolute configuration of coumarins in relation to biosynthesis are Do the changes in absolute configuration correlate with the nature of the chemical transformations in the various steps of coumarin biosynthesis Does the absolute configuration of oxidized isopentenyl substituted coumarins correlate with their botanical distribution Is there a simple biosynthetic model which can accommodate the occurrence of the different coumarin enantiomers as well as racemates ... 

Gudmundsdottir, A. D., Scheffer, J. R., and Trotter, J., Ionic chiral handle-induced solid state asymmetric synthesis origin of the asymmetric induction elucidated through absolute configuration correlation studies. Tetrahedron Lett., 35, 1397,1994. 

ORD and CD also provide a basis by which the absolute configuration of a compound may be correlated with that of a known compound of similar stmcture by observing changes in degree of rotation with wavelength (87). 

The absolute configuration of koumine has also been confirmed by a biomimetic synthesis of koumine from vobasine (50) (43). The configuration was correlated with L(—)-tryptophan, since vobasine was reduced to drega-mine (51) and the latter had been synthesized from L(—)-tryptophan with conservation of the (S) configuration of the amino acid, which corresponds to C-5 of koumine (44). 

As mentioned in the introduction, the first empirical correlation between the absolute configuration of dopants and the handedness of induced cholesterics was proposed in 1975.20 The first attempt to find a general correlation was a few years later Krabbe et al.58 related the sense of the cholesteric to a stereochemical descriptor of the dopant based on the effective volume of the substituents and listed many compounds following this rule. However, exceptions were described at that time,59 and, furthermore, this approach neglects the role of the structure of the nematic solvent in determining the sense of the cholesteric. It is well known that chiral compounds may induce cholesterics of opposite handedness in different nematics.60,61... 

Alkylation of the configurationally unknown compound (+)-39 followed by chlorination in Scheme 1-12 afforded product )-41 with retained configurations. This was then converted to S)-(—)-42 with an inversion of configuration.62 In this manner, the correlation between compounds (+)-39 and 42 in the sense of absolute configuration has been established, and the starting (+)-39 is determined to have an absolute configuration of (R) (Scheme 1-12). 

The absolute configuration of dichomine was determined by chemical correlation. Reduction with LiAlH4 in THF gave a product identical to (145, 20/ )-velbanamine (160) through sequential carbinolamine C—O reductive cleavage... 

Dehydrodarlingianine (69) and dehydrodarlinine (72) were synthetized by base-catalyzed reaction of hygrine with cinnamaldehyde and benzaldehyde, respectively. The relative stereochemistry of darlingianine (65) was established by X-ray diffraction (111). The structure of the other bases was established by chemical correlations as well as by spectroscopic methods. The absolute configurations of these bases remain to be determined. 

The absolute configuration was determined by chemical correlation with the known (2R)-2-allyl-2-hydroxycyclohexanone. 

The method, also called heavy atom method, consists in introducing a heavy atom in the molecule. Then X-rays with a wave length close to the X-ray absorption of the heavy atom is introduced. As a result a phase shift is superimposed on the ordinary diffraction pattern and configuration is then deduced. The method was first employed in 1951 by Bijvoet et al. to examine sodium rubidium tartrate who concluded that it is possible to differentiate between the two optically active forms. In other words it was possible to determine the absolute configuration of the enantiomers. Since then the absolute configurations of about two hundred optically active compounds have been elucidated by their correlation with other substances of known configuration. 

The benzene sector rule105 may be used to correlate the absolute configuration of a contiguous chiral center of a monosubstituted benzene compound with the sign of the CE... 

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