Organic chemistry racemic mixture

Development of new synthetic routes to optically active (3-lactam derivatives is still an attractive problem in organic chemistry. As a synthetic approach to penicillin derivatives, photocyclization of oe-oxoamides 76 to (3-lactams has long been studied 41, 42). This reaction (Scheme 6), however, results in a complex mixture of racemic cis-and trans-isomers of (3-lactams 72 and of oxazolidin-4-ones 73, since the reaction proceeds via a zwitterionic intermediate 7143>. Of these isomers, only the optically... 

As we saw in Chapter 7, one of the goals of synthetic organic chemistry is to develop methods that produce only a single enantiomer of a desired chiral compound rather than the usual racemic mixture that is the result of most reactions. Recently, a method has been developed that employs one enantiomer of a chiral borane to prepare a single enantiomer of a chiral alcohol from an achiral alkene. The chiral borane that is used is /rans-2,5-dimethylborolane. 

The importance of fluorinated organic componnds both in medicinal chemistry and biochemistry has resulted in much recent attention towards efficient carbon fluorine bond formation [30]. The reactions developed include a very successful electrophilic asymmetric mono-fluormation of 1,3-dicarbonyl compounds [31]. A nucleophilic variant was also investigated. In this context, the groups of Togni and Mezzetti have established that ruthenium Lewis acids could efficiently catalyze fluorination reactions [32]. In the presence of [Ru(l,2-bis(diphenylphosphino)ethane)2Cl][PF6] (8) (10 mol%), fert-butyl iodide reacted at room temperature with TIF (1.1 equiv.) to yield fert-butyl fluoride (84% yield). This reaction was extended successfully to a range of organic halides (Entries 1-3, Scheme 10.19). The use of the chiral complex [Ru((lS,2S)-N,N bis[2-diphenylphos-phino)benzylidene]diaminocydohexane))Cl][PF6] (9) showed modest chiral induction at the outset of the reaction (Entry 4, Scheme 10.17). The near-racemic mixture obtained at completion points to an SNl-type process in this nucleophilic halide... 

Asymmetric synthesis of chiral molecules by any type of technology has always been a central theme in organic chemistry and is, furthermore, of vital and fundamental interest for understanding chiral biology in the life sciences. In addition chirality is a key factor in the interaction of man-made new molecules with biopolymers from nature and therefore the mode of action of each enantiomer in a racemic mixture is of enormous practical importance. 

Racemization, epimerization, loss of stereochemical information at C -atom. While the expression racemization is used in organic chemistry for the complete conversion of a single enantiomer into the racemate, it is often used in peptide chemistry for partial or total epimerization at one chiral C , irrespective of whether a mixture of diastereomers or enantiomers is formed. The correct stereochemistry is important for the biological activity of a peptide or protein. Hence, racemization must... 

Chiral Effects Traditional methodology in synthetic organic chemistry led to racemic mixtures of chiral compounds. Recent developments, however, have made it possible to both synthesize the pure enantiomers and resolve them analytically. The fungicide, metalaxyl, contains a chiral carbon and the two enantiomers... 

Both strychnine and brucine (as well as other optically active alkaloids) are used to effect the resolution of racemic mixtures of acids in synthetic organic chemistry. 

Racemic ra- se-mik (1892) adj. Of, relating to, or constituting a compound or mixture that is composed of equal amounts of dextrorotatory (D-) and levorotatory (L-) forms of the same compound and is not optically active. Morrison RT, Boyd RN (1992) Organic chemistry, 6th edn. Prentice-Hall, Englewood Cliffs, NJ. 

Organic chemistry, p. 356 Polarimeter, p. 381 Racemic mixture, p. 383 Radical, p. 363 Saponification, p. 378 Saturated hydrocarbon, p. 356 Structural isomer, p. 357 Unsaturated hydrocarbon, p. 367... 

PROBLEM 21.48 Addition of iodine (I2) to an alkene does not give a diiodide. But the reaction shown below is a standard procedure in organic synthesis. You have sufficient understanding of alkene chemistry to be able to answer several questions about the reaction shown. What would be the stereochemical outcome Is the product optically active, a meso compound, or a racemic mixture Draw the mechanism for this reaction. Your mechanism should explain the stereochemical outcome you have indicated. Why does this reaction make a five-membered ring rather than a six-membered ring ... 

Compounds other than organic bases, acids, or alcohols can also be resolved. Although the particular chemistry may differ from the salt formation just described, the principle remains the same a racemic modification is converted by an optically active reagent into a mixture of diastereomers which can then be separated. 

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