Optically active diol

The rhodium-catalyzed intramolecular hydrosilylation of allylic alcohol derived silyl ethers has been described. Oxidative cleavage of the resulting cyclized hydrosilylation products affords a route to optically active diols (Scheme 28).129,130... 

Polyurethanes (13) have been prepared with optically active diols and various diisocyanates.69 Chiral recognition depends on the diisocyanate... 

Ligands for catalytic Mukaiyama aldol addition have primarily included bidentate chelates derived from optically active diols,26 diamines,27 amino acid derivatives,28 and tartrates.29 Enantioselective reactions induced by chiral Ti(IY) complex have proved to be one of the most powerful stereoselective transformations for synthetic chemists. The catalytic asymmetric aldol reaction introduced by Mukaiyama is discussed in Section 3.4.1. 

The major breakthrough in the catalytic asymmetric dihydroxylation reactions of olefins was reported by Jacobsen et al.55 in 1988. Combining 9-acetoxy dihydroquinidine as the chiral auxiliary with /V-methylmorphine TV-oxide as the secondary oxidant in aqueous acetone produced optically active diols in excellent yields, along with efficient catalytic turnover. 

Resolution of bicyclic enones. This optically active diol selectively forms a hydrogen-bonded insoluble complex with one enantiomer of the bicyclic enone 2, which when heated liberates ( — )-2 of 100% ee. This resolution is useful for a few... 

Optically active diols are useful building blocks for the synthesis of chiral diphosphite ligands. Chiral diphosphites based on commercially available optically active 1,2 and 1,4-diols, l,2 5,5-diisopropylidene-D-mannitol, L-a,a,a,a-tetramethyl-l,3-dioxalan-4,5-dimethanol and L-diethyl tartrate, were first used in the asymmetric hydroformylation of styrene [75],... 

The configuration of the products was established by periodate oxidation of the D compound, and reduction of the resulting dialdehyde to an optically active diol whose sign and magnitude of optical rotation ([a] ° +2.5° in water) correspond to that of the diol ([a]n° 46.8° in water) obtained by similar treatment of methyl a-L-arabinopyrano-side. The bis(p-nitrobenzoates) of the two diols exhibited similar relationships. Hence, it appears likely that the configuration at C-2 of the anhydride is the same as that at C-l of the L-arabinoside. The cis relationship of the hydroxyl groups was retained from the arabinal started with. 

The unsaturated aldehydes 675 undergo363,364 an enantioface-dif-ferentiating reaction when treated with fermenting bakers yeast, furnishing optically active diols 676. 

Scheme 3 illustrates intriguing enantioselection in organic reactions that proceed in chiral crystalline lattices (5). When inclusion crystals of a ketone and an optically active diol host are treated with BH3-ethyl-enediamine complex, the optically active alcohol is obtained in... 

Optically active diols have been used for several asymmetric syntheses [67] and chiral resolutions [68]. In 1990, Kawashima and co-workers [69] reported the first example of direct optical resolution of racemic 2,2 -dihydroxy-l,l -binaphthyl (34) with (R,R)-29. In this procedure equimolar amounts of racemic 34 and (R,R)-29 were added in benzene and the mixture was heated to a homogeneous solution and then cooled to room temperature. After crystallization of the precipitate and treatment with hydrochloric acid, (R)-(+)-34 was obtained with an optical purity of 94% and in a yield of 86% based on the amount of enantiomer presents in the racemate (Scheme 23). 

Thus, the catalytic addition of ZnEt2 to the aldehyde function was first performed in toluene and then catalytic hydrogenation (150 psi of H2) in isopropanol was carried out using the same bifunctional catalyst. These one-pot catalytic reactions lead to 99% yield of optically active diol with ee = 99% for addition of ZnEt2 and de = 86% for hydrogenation [96]. 

R,R-diphenyl ethylene carbonate CR,R-DPEC)) with a racemic zirconaaziridine. (C2-symmetric, cyclic carbonates are attractive as optically active synthons for C02 because optically active diols are readily available through Sharpless asymmetric dihydroxylations [67].) Reaction through diastereomeric transition states affords the two diastereomers of the spirocyclic insertion product protonolysis and Zr-mediated transesterification in methanol yield a-amino acid esters. As above, the stereochemistry of the new chiral center is determined by the competition between the rate of interconversion of the zirconaaziridine enantiomers and the rate of insertion of the carbonate. As the ratio of zirconaaziridine enantiomers (S)-2/(R)-2 is initially 1 1, a kinetic quench of their equilibrium will result in no selectivity (see Eq. 32). Maximum diastereoselec-tivity (and, therefore, maximum enantioselectivity for the preparation of the... 

With BY, the reduction of a,p-unsaturated aldehydes can act together with a hydration process, affording optically active diols in acceptable yields (eq 18). ... 

Oxiranes cannot be prepared directly from 1,2-diols by dehydration. Formation of the oxirane intermediate has been studied in connection with the mechanism of the pinacolic rearrangement. Oxiranes can be prepared stereoselectively from the acetals and ketals of 1,2-diols. D-(+)-2,3-epoxybutane has been obtained from an optically active diol via conversion of the ketal 64 to a halohydrin ester (Eq. 52). ... 

Curcumin, as well as compounds 40-43 were also isolated from C. xanthorrhiza by Uehara et a/. (29), who obtained from this source also two new compounds, the optically active diol (5,5)-45 and the racemic diketoalcohol 46. While formation of 45 can be envisaged by reduction of hexahydrocurcumin, racemic 46 might have been the result of addition of water onto the double bond of curcumin. Masuda and his coworkers reported in 1992 the isolation of an unsymmetrical curcumin derivative, 5-methoxycurcumin (47) from C. xanthorrhiza (40). 

Figure 2.3.4 Schematic representations of (a) coumarin, thiocoumarin and cyclohex-2-enone molecules (b) optically active diols employed as hosts.

In some cases, a simple tosylation can be equally regioselective, especially when one of the hydroxyl substituents is more sterically hindered then the other. This approach served as a key step in an expeditious approach towards naproxen 217 (Scheme 55). The primary alcohol function of the optically active diol 214, of 98% ee, was selectively activated with tosyl chloride [135]. The resulting to-sylate, upon treatment with NaH, underwent smooth cycHzation to the epoxide 215. Hydrogenolysis proved to be highly facial selective, delivering the primary alcohol 216 in high enantiopuxity. A final Jones oxidation then furnished naproxen of 96% ee. 

Narasaka reported that the titanium compound generated from TiCl2(OiPr)2 and an optically active diol in the presence of 4 A molecular sieve promoted the asymmetric addition of enamine 69 to the activated fumarate 70 [72]. Cyclobutane derivatives were formed when p,p-disubstituted enamines were employed. Titanium oxide derived from (l )-BINOL and (iPr0)2Ti=0 catalyzed the asymmetric addition of silyl thioenol ether 71 to enones [73]. The sulfur derivative ex-... 

An attempt to obtain evidence for this hypothesis was made. Reduction of l-hydroxyl-4-pentanone might proceed via a stereochemically less favorable, seven-membered ring intermediate, and the product (1,4-pentanediol) of much less than 30% optically purity might result. Although optically active diol was obtained, no assignment of optical purity could be made since the diol could not be transformed stereo-specifically, despite several attempts, into 2-methyl-tetrahydrothiophene-1-dioxide, whose maximum rotation is known (18). The validity of the above hypothesis thus remains moot. 

The present approach provides a general method for the preparation of optically active diols. The Table illustrates the preparation of several diols.4 The procedures are simple, and there is no possibility of racemi2ation in any of the steps. This method does not require any difficult-to-handle or disposal of metals, which... 

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