Labeling Stereogenic Centers with R or

Initial studies with taxd were carried out with material isolated from the bark of the Pacific yew tree, but stripping the bark killed these magnificent trees. Taxol can now be synthesized in four steps from a compound isolated from the needles of the common English yew tree. 

Problem 5.10 Locate the stereogenic centers in each compound. A molecule may have zero, one, or more stereogenic centers. 

Problem 5.11 Locate the stereogenic centers in each compound. 

Trade name Zocor (cholesterol-lowering drug) 

Naming enantiomers with the prefixes f or S is called the Cahn-Ingold-Prelog system after the three chemists who devised it. 

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Problem 9.31 Draw the products formed when (2S)-2-butanol 1s treated with TsCI and pyridine, followed by NaOH. Label the stereogenic center in each compound as R or S. What is the stereochemical relationship between the starting alcohol and the final product ... 

The stereogenic center (labeled with ) in both structures can be R or S. 

Analogously, aryl 2-chloro[l- C]ethyl carbinols 49 (Figure 11.19) are accessible by CBS- or IpCaBCl-mediated reduction of aryl (2-chloro)ethyl[carbonyl- C]ketones e.e.s are usually > 90%. Replacement of chlorine with iodine followed by treatment with a primary amine converted haloalcohol 49 (Ar = thien-2-yl) into the 3-aryl-3-hydroxy[3- C]propy-lamine derivative 52, which served as the penultimate intermediate in the preparation of the carbon- 14-labeled CNS-active drug duloxetine" . Furthermore, Mitsunobu reaction (DEAD or ADDP, PhsP or BU3P) on 49 (Ar = phenyl) in the presence of various phenols provided the respective (R)- j8-haloethers with inversion of the configuration at the stereogenic center. This route was followed for the synthesis of [ CJatomoxetine and one of its metabolites. ... 

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