Glyceraldehyde, chiral forms

Fischer projection A method of representing three-dimensional structures in two-dimensional drawings in which the chiral atom(s) lies in the plane of the paper. The two enantiomeric forms of glyceraldehyde are represented as... 

Glyceraldehyde can be considered to be the simplest chiral carbohydrate It is an aldotriose and because it contains one chirality center exists in two stereoisomeric forms the D and l enantiomers Moving up the scale m complexity next come the aldotetroses Examining their structures illustrates the application of the Fischer system to compounds that contain more than one chirality center... 

Stork and Takahashi took -glyceraldehyde synthon from the chiral pool and condensed it with methyl oleate, using lithium diisopropyl amide as catalyst for the mixed aldol reaction, leading to The olefinic linkage is a latent form... 

Reactions of nitro compounds with chiral imines have only recently been described. Either chiral 1-phenylethylamine (auxiliary) or the glyceraldehyde acetonide aldehyde was used as the chiral precursors of the imines 66 and 68, which reacted with 3-mesyloxynitropropane to give the 3-nitropyrrolidines dl)-67 and 69, respectively, with good diastereoselectivity. In fact, both products were obtained (almost) exclusively as trans diastereomers with high level of asymmetric induction, but the configurations of the newly formed stereocenters were not determined [44] (Scheme 13). N-Boc imines can be formed... 

Various kinds of chiral acyclic nitrones have been devised, and they have been used extensively in 1,3-dipolar cycloaddition reactions, which are documented in recent reviews.63 Typical chiral acyclic nitrones that have been used in asymmetric cycloadditions are illustrated in Scheme 8.15. Several recent applications of these chiral nitrones to organic synthesis are presented here. For example, the addition of the sodium enolate of methyl acetate to IV-benzyl nitrone derived from D-glyceraldehyde affords the 3-substituted isoxazolin-5-one with a high syn selectivity. Further elaboration leads to the preparation of the isoxazolidine nucleoside analog in enantiomerically pure form (Eq. 8.52).78... 

The substrate-controlled diastereoselective addition of lithiated alkoxyallenes to chiral nitrones such as 123, 125 and 126 (Scheme 8.32) furnish allenylhydroxyl-amines as unstable products, which immediately cydize to give enantiopure mono-orbicyclic 1,2-oxazines (Eqs 8.25 and 8.26) [72, 76]. Starting with (R)-glyceraldehyde-derived nitrone 123, cydization products 124 were formed with excellent syn selectivity in tetrahydrofuran as solvent, whereas precomplexation of nitrone 123 with... 

All the monosaccharides except dihydroxyacetone contain one or more asymmetric (chiral) carbon atoms and thus occur in optically active isomeric forms (pp. 17-19). The simplest aldose, glyceraldehyde, contains one chiral center (the middle carbon atom) and therefore has two different optical isomers, or enantiomers (Fig. 7-2). 

When there are several chiral carbons in a molecule, the configuration at one center usually is related directly or indirectly to glyceraldehyde, and the configurations at the other centers are determined relative to the first. Thus in the aldehyde form of the important sugar, (+)-glucose, there are four chiral centers, and so there are 24 = 16 possible stereoisomers. The projection formula of the isomer that corresponds to the aldehyde form of natural glucose... 

Since the middle carbon of glyceraldehyde is connected to four different substituents, it is a chiral center leading to two possible forms of glyceraldehyde. D-Glycer-aldehyde is illustrated in figure 12.2 in the Fischer projec-... 

Glyceraldehyde has only one chiral carbon atom and can exist as two enantiomers, but other sugars have two, three, four, or even more chiral carbons. In general, a compound with n chiral carbon atoms has a maximum of 2n possible isomeric forms. Glucose, for example, has four chiral carbon atoms, so a total of 24 = 16 isomers are possible, differing in the spatial arrangements of the substituents around the chiral carbon atoms. 

C is correct. A pair of enantiomers would be formed bv the addition of one chiral carbon. Only one configuration of glyceraldehyde is used, so that chiral carbon does not increase the number of enantiomers. 

Glyceraldehyde contains a single chiral carbon, located in position 2. All carbohydrates contain chiral carbons. The number of possible isomers is given by 2 . For glyceraldehyde, only two isomers are possible, d and l. For a hexose, on the other hand, which in its open form (Figure 9.2) contains four chiral atoms, the number of isomers is 24 = 16, half of them in the d and half in the l series. The first and last carbons in a carbohydrate molecule, if the open structure (e.g., Figure 9.2) is viewed, are nonchiral. 

Stable and easily handled, protected forms of l- and D-glyceraldehyde were obtained by the Sharpless asymmetric dihydroxylation [56] of the benzene-1,2-dimethanol acetal of acrolein (Scheme 13.23). The method produces either diol (7 )-32 or (S)-32 with 97% ee after recrystallization from benzene. These diols can be converted into useful C-3 chiral building blocks such as epoxides (7 )-33 and (5)-33, respectively [28,57]. 

---