Tartaric acid structure

A number of derivatives of the tartaric acid structure have been examined as substitutes for the tartrate ester in the asymmetric epoxidation catalyst. These derivatives have included a variety of tartramides, some of which are effective in catalyzing asymmetric epoxidation (although none display the broad consistency of results typical of the esters). One notable example is the dibenzyltartramide, which in a 1 1 ratio (in reality, a 2 2 complex as shown by an X-ray crystallographic structure determination [138]) with Ti(0-i-Pr)4 catalyzes the epoxidation of allylic alcohols with the same enantiofacial selectivity as does the Ti-tartrate ester complex [18], It is remarkable that, when the ratio of dibenzyltartramide to Ti is changed to 1 2, epoxidation is catalyzed with reversed enantiofacial selectivity. These results are illustrated for the epoxidation of a-phenylcinnamyl alcohol (Eq. 6A.12a). 

Figure 17 The stereoisomers of tartaric acid, (a) Tartaric acid structural isomer with atom labels 1 through 8 (only atoms attached to stereocenters are labeled), (b) Application of the configuration group (1)(2), (12) on the four possible stereoisomers. The second and third stereoisomers are identical, (c) The three resulting stereoisomers, a meso form and a dl pair.

Several structures of the transition state have been proposed (I. D. Williams, 1984 K. A. Jorgensen, 1987 E.J. Corey, 1990 C S. Takano, 1991). They are compatible with most data, such as the observed stereoselectivity, NMR measuiements (M.O. Finn, 1983), and X-ray structures of titanium complexes with tartaric acid derivatives (I.D. Williams, 1984). The models, e. g., Jorgensen s and Corey s, are, however, not compatible with each other. One may predict that there is no single dominant Sharpless transition state (as has been found in the similar case of the Wittig reaction see p. 29f.). 

Although Pasteur was unable to provide a structural explanation—that had to wait for van t Hoff and Le Bel a quarter of a century later—he correctly deduced that the enantiomeric quality of the crystals was the result of enantiomeric molecules The rare form of tartanc acid was optically inactive because it contained equal amounts of (+) tartaric acid and (—) tartaric acid It had earlier been called racemic acid (from Latin racemus meaning a bunch of grapes ) a name that subsequently gave rise to our pres ent term for an equal mixture of enantiomers... 

Multiple Chiral Centers. The number of stereoisomers increases rapidly with an increase in the number of chiral centers in a molecule. A molecule possessing two chiral atoms should have four optical isomers, that is, four structures consisting of two pairs of enantiomers. However, if a compound has two chiral centers but both centers have the same four substituents attached, the total number of isomers is three rather than four. One isomer of such a compound is not chiral because it is identical with its mirror image it has an internal mirror plane. This is an example of a diaster-eomer. The achiral structure is denoted as a meso compound. Diastereomers have different physical and chemical properties from the optically active enantiomers. Recognition of a plane of symmetry is usually the easiest way to detect a meso compound. The stereoisomers of tartaric acid are examples of compounds with multiple chiral centers (see Fig. 1.14), and one of its isomers is a meso compound. 

A large number of chiral crowns have been prepared by numerous groups. The reader is directed to the tables at the end of this chapter to obtain an overview of these structures. It would not be useful to try to recount the synthetic approaches used in the preparation of all of these compounds we have chosen rather to subdivide this mass of compounds into three principal groups. The groups are (1) Cram s chiral binaphthyl systems (2) chiral crowns based on the tartaric acid unit and (3) crowns incorporating sugar subunits. These are discussed in turn, below. 

Table sugar, sec Sucrose Tagatose, structure of, 975 Talose. configuration of, 982 Tamiflu, molecular model of, 130 Tamoxifen, synthesis of, 744 Till] DNA polymerase, PCR and, 1117 Tartaric acid, stereoisomers of, 305-306... 

Reagent 7 is easily prepared from commercially available diacetone-D-glucose and trichloro(cyclopentadienyl)titanium35 (Section 1.3.3.3.8.1.). The monomeric structure of reagent 7 was confirmed by an X-ray crystal structure analysis1 7. Complex 9 is obtained36 analogously from (7 .7 )-tartaric acid derived (R,7 )-2,3-CMsopropylidene-l,l,4,4-tetraphenyl-1,2,3,4-butanetetrol. 

Another group of catalysts consist of cyclic borinates derived from tartaric acid. These compounds give good reactivity and enantioselectivity in Mukaiyama aldol reactions. Several structural variations such as 16 and 17 have been explored.151... 

High stereoselective addition of vinylmagnesium bromide to L-tartaric acid-derived nitrone was used as a key step in the synthesis of (+ )-lentiginosine and its structural analogs (653). 

Figure 14.8 Adsorption models of the bisuccinate and bitartrate phases on Cu(1 1 0). (a) Structural models for the two coexisting chiral domains for bisuccinate on Cu(1 1 0). The (2 2, -9 0) and (9 0, -2 2) unit cells of the overall structure are shown as are the (2 2, -2 0) and (2 0, -2 2) unit cells representing the packing within each chain, (b) Structural models of the bitartrate phases of the two tartaric acid enantiomers on Cu(1 1 0) (S,S)-bitartrate (9 0, -1 2) and (/ ,R)-bitartrate (1 2, -9 0). The (3 1, -2 1) unit cell is also shown for the (/ ,/ )-bitartrate phase showing the packing within the chain [203],...

Glucose on oxidation gives saccharic acid and on the basis of D-glucose structure, XIV would be D and XV, L on the account of the bottom asymmetric carbon atom. But if XV is rotated in the plane of paper through 180° if becomes exactly identical with XIV. Dispute like this and tartaric acid have raised great interest in improving the system of nomenclature. 

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