Absolute configuration, acyclic derivatives

Binaphthol-derived titanium complexes [64], prepared from chiral ligands 65 (Figure 3.13), also performed very well in the cycloadditions of conjugated aldehydes with cyclic and acyclic dienes. Judging from the absolute configurations of endo and exo adducts, this catalyst should cover the re-face of carbonyl on its u tz-coordination to s-trans a,/l-unsaturated aldehydes, and hence dienes should approach selectively from the si-face. 

Due to the complexity of conformational equilibria, the application of the dibenzoate chirality rule to determination of the absolute configuration of acyclic diols and polyols requires cautious evaluation of the CD data. For example, (0,0)-dibenzoyl derivatives of diesters and N.N.N ,AT-tetraalkyldiamides of (/t,f )-tartaric acid give exciton Cotton effects of opposite sign due to the preference of diesters for a planar and tetraalkyldiamides for a gauche conformation of the carbon chain176. 

The dibenzoate chirality rule 153,156 (Section 4.4.2.4.1.) allows determination of the absolute configuration of dibenzoylated amino alcohols186 187 198, mercapto alcohols188 and diamines187. For acyclic /1-amino alcohol O.A-dibcnzoate derivatives the dominant rotatory... 

A number of substituted cyclic and acyclic 1,3-dienes have also been reacted, and the absolute configuration of the products assigned129. The enantiomeric excess of the dihydro-1,2-oxazines was determined by H-NMR or GC analysis of the corresponding derivatives prepared with both ( + )-camphor-10-sulfonyl chloride or (S )-3,3,3-trifiuoro-2-methoxy-2-phenylpropanoyl chloride (Table l)96-96. 

The absolute configuration of the benzylic centre in some benzyli-dene derivatives of acyclic polyhydric alcohols and of some carbohydrate benzylidene acetals containing fused-ring systems have been established. The method utilizes the observation that 2-phenyI-... 

Vibrational Raman optical activity of biomolecules, including carbohydrates, has been reviewed (23 refs). l A general procedure for assigning both relative and absolute configuration to multiple stereocentres in acyclic aminopolyols based on application of the exiton chirality method is presented. The method has been applied to the side chain aminopolyol of a natural bacterial-derived terpenoid derivative. ... 

Butane-2,3-diol undergoes a reaction with ketones to form a ketal derivative as shown in Figure 50.12. The absolute configurations of acyclic ketones, cyclopentanones, and cyclohexanones with a preference for the chair conformation can be assigned based on an examination of the NMR spectra of the ketal derivatives. Butane-2,3-thiol can be used in the same manner and gives larger enantio meric discrimination, but it is not commercially available. 

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