Y optically active

Yamamoto, C., Okamoto, Y. Optically active polymers for chiral separation. 

Ogasawara K, Omata K, Kabuto K, Jin H, Sasaki Y. Optically active Ce(IlI)-propylenediaminetetracetate complex a chiral shift reagent for aqueous solution causing less signal broadening. Kidorui 1999 34 152-153. 

Yamamoto, C. and Okamoto, Y, Optically active polymers for chiral separation. Bull. Chem. Soc. Jpn., 77, 227, 2004. 

All the amino-acids of physiological importance are a-amino-acids, e.g. (in addition to the above compounds), alanine or a-amino-propionk acid, CHaCH(NH,)COOH, and leucine or a-amino-Y-dimethyl-rt-butyric acid, (CH,)aCHCH,CH(NHa)COOH, and naturally occurring samples (except glycine) are therefore optically active. 

Terpenes, specifically monoterpenes, are naturally occurring monomers that are usually obtained as by-products of the paper and citms industries. Monoterpenes that are typically employed in hydrocarbon resins are shown in Figure 2. Optically active tf-limonene is obtained from various natural oils, particularly citms oils (81). a and P-pinenes are obtained from sulfate turpentine produced in the kraft (sulfate) pulping process. Southeastern U.S. sulfate turpentine contains approximately 60—70 wt % a-pinene and 20—25 wt % P-pinene (see Terpenoids). Dipentene, which is a complex mixture of if,/-Hmonene, a- and P-pheUandrene, a- and y-terpinene, and terpinolene, is also obtained from the processing of sulfate Hquor (82). 

Chemical Properties. The notation used by Chemical Abstracts to reflect the configuration of tartaric acid is as follows (R-R, R )-tartaric acid [S7-69A-] (4) (S-R, R )-tartaric acid [147-71-7] (5) and y j O-tartaric acid [147-73-9] (6). Racemic acid is an equimolar mixture of the two optically active enantiomers and, hence, like the meso acid, is optically inactive. 

An asymmetric synthesis of estrone begins with an asymmetric Michael addition of lithium enolate (178) to the scalemic sulfoxide (179). Direct treatment of the cmde Michael adduct with y /i7-chloroperbenzoic acid to oxidize the sulfoxide to a sulfone, followed by reductive removal of the bromine affords (180, X = a and PH R = H) in over 90% yield. Similarly to the conversion of (175) to (176), base-catalyzed epimerization of (180) produces an 85% isolated yield of (181, X = /5H R = H). C8 and C14 of (181) have the same relative and absolute stereochemistry as that of the naturally occurring steroids. Methylation of (181) provides (182). A (CH2)2CuLi-induced reductive cleavage of sulfone (182) followed by stereoselective alkylation of the resultant enolate with an allyl bromide yields (183). Ozonolysis of (183) produces (184) (wherein the aldehydric oxygen is by isopropyUdene) in 68% yield. Compound (184) is the optically active form of Ziegler s intermediate (176), and is converted to (+)-estrone in 6.3% overall yield and >95% enantiomeric excess (200). 

Recently, the Michael addition of the optically active Q ,y-disubstituted tetronic acids 146c,e with a variety of Q ,/3-unsaturated aldehydes, ketones, esters, and nitriles was studied (Scheme 53) (99H1321). 

The fragmentation/cyclization ratio is determined by the relative orientation of the respective molecular orbitals, and thus by the conformation of diradical species 2. The quantum yield with respect to formation of the above products is generally low the photochemically initiated 1,5-hydrogen shift from the y-carbon to the carbonyl oxygen is a reversible process, and may as well proceed back to the starting material. This has been shown to be the case with optically active ketones 7, containing a chiral y-carbon center an optically active ketone 7 racemizes upon irradiation to a mixture of 7 and 9 ... 

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

The stereoselectivity of reactions between optically active a-methyl-y-alkoxyallylstannancs and a-alkoxyaldehydes has been investigated with matched or mismatched pairings depending on whether addition to a chelated or nonchelated aldehyde is involved 121. 

The addition of the dianion of /j-sulfmylcarboxylic acids to carbonyl compounds leads to the formation of the corresponding hydroxy derivatives which undergo spontaneous eyclization to give y-lactones. It was found that when optically active ( + )-(/ )-3-(4-methylphenylsulfinyl)pro-panoic acid is used for the reaction, the corresponding diastereomeric /i-sulfinyl-y-lactones are formed in a ratio which is dependent on the substituents of the carbonyl component. However, the diastereoselectivity was always moderate. 

In y-alkoxyfuranones the acetal functionality is ideally suited for the introduction of a chiral auxiliary simultaneously high 71-face selectivity may be obtained due to the relatively rigid structure that is present. With ( + )- or (—(-menthol as auxiliaries it is possible to obtain both (5S)- or (5/ )-y-menthyloxy-2(5//)-furanones in an enantiomerically pure form293. When the auxiliary acts as a bulky substituent, as in the case with the 1-menthyloxy group, the addition of enolates occurs trans to the y-alkoxy substituent. The chiral auxiliary is readily removed by hydrolysis and various optically active lactones, protected amino acids and hydroxy acids are accessible in this way294-29s-400. 

This method is especially useful as part of a three-component condensation of optically active y-alkoxycyclopentenones leading to prostaglandin and compactin precursors268. 

Optically active y-alkoxycyclopentenones have become popular in the diastereoselective synthesis of hms-3,4-disubstituted cyclopentanones. The Michael addition to these cyclic enones catalyzed by sodium ethoxide in ethanol277 or by potassium tm-butoxide278 279 proceeds under kinetic control trans with respect to the y-substituent. 

The stereochemistry of optically active derivatives of Werner s hexol complex. Y. Shimura, Rev. Inorg. Chem., 1984, 6,149 (59). 

Recently, optically active (+)-(R)-methy 1 tolyl sulfoxide 102, R = H was alkylated with a very high diastereoselectivity136. The sulfoxide was treated with either lithium diisopropy-lamide (LDA) or lithium tetramethylpiperidide (LTMP) to form the lithio-derivative, which upon subsequent reaction with lithium a-bromomethyl acrylate gave a mixture of two diastereomers of a-methylene-y-sulfinylcarboxylic acid 103. The use of the sterically highly hindered base, LTMP, gave the product with a higher diastereoselectivity. For example, the Sc4 Rc4 ratio was 95 5 when R was the methyl group. 

Some ten years later, Darwish and Braverman50,51 undertook a more extensive study of this rearrangement, which has revealed some unique features. These investigators examined the behavior of six different esters, namely allyl, crotyl, a-methylallyl, racemic and optically active a, y-dimethylallyl, cinnamyl and a-phenylallyl 2,6-dimethylbenzene-sulfinates under various reaction conditions. 

All the y-sultines were obtained as diastereomeric mixtures (ca 1 1, by NMR), and each one of y-sultines ( + )-49 and ( + )-51 (R = t-Bu) was separated into two diastereomers A and B by column chromatography. The oxidation of y-sultines (— )-49A and (+ )-49B to the corresponding optically active sultones (+ )-52A,B, which lack a chiral sulfur, may be taken as proof that the observed optical activity in the sultines is also due to the y-carbon. This result seems to exclude the intermediacy of vinylsulfene in the reaction mechanism, since its disrotatory closure would lead to racemic y-carbon in the product. 

Hydroperoxides, as optically active oxidizing agents 289-291 Hydrosulphonylation 172 /J-Hydroxyacids 619 a-Hydroxyaldehydes, synthesis of 330 a-Hydroxyalkyl acrylates, chiral 329 j -Hydroxycarboxylic esters, chiral 329 3-Hydroxycycloalkenes, synthesis of 313 Hydroxycyclopentenones, synthesis of 310 -Hydroxyesters 619 synthesis of 616 Hydroxyketones 619, 636 Hydroxymethylation 767 a-Hydroxysulphones, synthesis of 176 / -Hydroxysulphones 638, 639 reactions of 637, 944 electrochemical 1036 synthesis of 636 y-Hydroxysulphones 627 synthesis of 783... 

Nomura T., Hano Y., Ueda S. Studies on the Optically Active Diels-Alder Type Adducts From Mulherry Tree Int. Congr. Ser. 1998 1157 379 390 Keywords mulberry tree, optically active Diels-Alder type adducts from mulberry tree... 

A molecule that contains just one chiral carbon atom (defined as a carbon atom connected to four different groups also called an asymmetric or stereogenic carbon atom) is always chiral, and hence optically active. As seen in Figure 4.1, such a molecule cannot have a plane of symmetry, whatever the identity of W, X, Y, and Z, as long as they are all different. However, the presence of a chiral carbon is neither a necessary nor a sufficient condition for optical activity, since optical activity may be present in molecules with no chiral atom and since some molecules with two or more chiral carbon atoms are superimposable on their mirror images, and hence inactive. Examples of such compounds will be discussed subsequently. 

Compounds With Tervalent Chiral Atoms. Atoms with pyramidal bonding might be expected to give rise to optical activity if the atom is connected to three different groups, since the unshared pair of electrons is analogous to a fourth group, necessarily different from the others. For example, a secondary or tertiary amine where X, Y, and Z are different would be expected to be chiral and thus resolvable. Many attempts have been made to resolve such compounds, but until 1968 all of them failed because of pyramidal inversion, which is a rapid oscillation of the unshared pair from one side of the XYZ... 

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