Prochiral diols oxidation

Chiral Alcohols and Lactones. HLAT) has been widely used for stereoselective oxidations of a variety of prochiral diols to lactones on a preparative scale. In most cases pro-(3) hydroxyl is oxidized irrespective of the substituents. The method is apphcable among others to tit-1,2-bis(hydroxymethyl) derivatives of cyclopropane, cyclobutane, cyclohexane, and cyclohexene. Resulting y-lactones are isolated in 68—90% yields and of 100% (164,165). 

Oxidation of Meso Diols. Asymmetric induction of meso and prochiral diols by lipases is very successful in the field of organic synthesis. Also it is well known that selective oxidation of prochiral or meso diols by HLADH provides oxidized products with a significant degree of enantioselectivity. However, it has not been reported that alcohol oxidases were applied to such types of oxidation. The microbial oxidation of meso diols by Candida boidinii SA051 was carried out and gave optically active hydroxy ketones (Figure 8). 

Oxidation of Prochiral Diol. The oxidation of prochiral diol 3-methyl-1,5-pentanediol did not give the corresponding -hydroxy aldehyde but gave the corresponding lactol at 22% yield. To determine stereochemistry of the lactol, this was chemically oxidized by Ag20 and afforded 3-(R)-methyl-pentan-l,5-olide at 38% optical purity. (Figure 9). This was determined by comparison of optical rotation with a reference (70). 

Isolated enzymes can also be used to catalyse selective oxidation reactions. For, example, galactose oxidase oxidizes xylitol into (L)-xylose (Scheme 4.15), while HLAD catalyses the stereoselective oxidation of prochiral diols of the type (12) to give, initially, a chiral hydroxyaldehyde... 

S-Lactones are produced by Grignard addition to 8-keto-esters. Chiral 3-substituted S-lactones are obtained by microbiological oxidation of the corresponding prochiral diol. Glycol esters are converted into ap-unsaturated 8-lactones, in good yield, by BFg-catalysed oxidation (Scheme 119). ... 

Chiral N-sulfonyldiamine ligands are used to create effective chiral bifunctional amidoiridium catalysts for the asymmetric aerobic oxidation of meso- and prochiral diols to give up to >99% ee of hydroxyl ketones and 50%ee oflactones. " These catalysts can be also applied for an efficient oxidative kinetic resolution of racemic secondary alcohols affording R enantiomers with >99% ee and with 46—50% yields. 

Enzymatic oxidation of naphthalene by bacteria proceeds by way of the intermediate ciy-diol shown. Which prochiral faces of C-1 and C-2 of naphthalene are hydroxylated in this process ... 

Another method for the asymmetric version of the Baeyer-Villiger reaction was presented by Lopp and coworkers in 1996516. By employing overstoichiometric quantities of Ti(OPr-z)4/DET/TBHP (1.5 eq./1.8 eq./1.5 eq.), racemic and prochiral cyclobutanones were converted to enantiomerically enriched lactones with ee values up to 75% and moderate conversions up to 40% (Scheme 171). Bolm and Beckmann used a combination of axially chiral C2-symmetric diols of the BINOL type as ligands in the zirconium-mediated Baeyer-Villiger reaction of cyclobutanone derivatives in the presence of TBHP (or CHP) as oxidant (Scheme 172)497. With the in situ formed catalysts 233a-d the regioisomeric lactones were produced with moderate asymmetric inductions (6-84%). The main drawback of this method is the need of stoichiometric amounts of zirconium catalyst. 

We (J. Org. Chem. 2004,69, 7234) used the power of the Sharpless oxidations to convert the prochiral 10 into the epoxy diol 11. Base-catalyzed cascade cyclization then converted 11 into crystalline 12, again with high diastereomeric and enantiomeric purity. An advantage of this approach is that by changing the absolute sense of the epoxidation and/or the dihydroxylation, it should be possible to selectively prepare each of the four enantiomerically-pure diastereomers of 12. 

A variation within the osmium-catalysed asymmetric dihydroxylation (AD) of alkenes has been described that yields cyclic boronic esters from alkenes in a straightforward manner. A protocol based on the Sharpless AD conditions (for enantiose-lective oxidation of prochiral olefins) has been developed that gives cyclic boronic esters, rather than free diols, with excellent enantiomeric excesses. Some of the... 

Molinari, F., Gandolfi, R., Villa, R., Urban, E. and Kiener, A. (2003) Enantioselective oxidation of prochiral 2-methyl-l, 3-propan diol by Acetobacter pasteurianus. Tetrahedron Asymmetry,... 

Irwin, A.J. and Jones, J.B. (1977) Asymmetric syntheses via enantiotopicaUy selective horse liver alcohol dehydrogenase catalyzed oxidations of diols containning a prochiral center. Journal of the American Chemical Society, 99, 555-551. 

The use of enzymes for the enantioselective oxidation of prochiral (or racemic) diols has proved to be of significant synthetic interest. A range of simple racemic 1,2-diols proved to be good substrates for a system involving coimmobilized horse liver alcohol dehydrogenase (HLADH) and aldehyde dehydrogenase (AldDH) with NAD cofactor recycling. This produced enantiomerically pure a-hydroxycarbox-ylic acids (Scheme 12). 

Sugimura introduced a diastereotopic differentiating peracid oxidation of ket-als 16 prepared from prochiral ketones 9 with an optically active, C2-symmetri-cal diol (Eq. 7) [31]. 

Efficient synthetic approaches to the optically active spiro-sulfuranes and their oxides have been reported by Martin and Drabowicz [65]. The preparation of optically active spirosulfuranes 45 and 46 was performed by asymmetric dehydration of the corresponding prochiral sulfoxide diols 47, as shown in Scheme 29. The optically active oxides 48 and 49 were prepared by oxidation of 45 and 46 with m-chloroperbenzoic acid (mCPBA). The synthesis of the optically active oxides was conducted by the stereoselective conversion of the chiral sulfuranes using Ru04, according to the procedure reported earlier [66]. 

D-amino acid oxidase will oxidize only serine having R configuration at C(2). Glycolate oxidase will remove only the pro-R hydrogen of glycolic acid. Does the product (0=CHC02H) contain tritium Explain your reasoning, b. Enzymatic oxidation of naphthalene by bacteria proceeds by way of the intermediate aT-diol shown. Which prochiral face of C(l) and C(2) of naphthalene is hydroxylated in this process ... 

Reaction of the aldehyde, Na-methylvellosimine (168), with 37% aqueous formaldehyde (25 equiv.) and 2 N KOH (10 equiv.) in methanol at room temperature for 10 h afforded optimum yields of the desired diol 211. The two prochiral hydroxymethyl functions in 211 were differentiated by the DDQ-mediated oxidative cyclization of the hydroxyl group at the 3-axial position of C-17 with the benzylic position at C-6. This gave the desired cyclic ether 212. Oxidation of the hydroxymethyl functionality was achieved with (PhSe0)20 to provide the aldehyde, which was further oxidized with KOH/R/MeOH to the methyl ester 210. Consequently, the total synthesis of (-l-)-dehydrovoachalotine (210) was achieved in 28% overall yield from D-(- -)-tryptophan. 

As a rule of thumb, oxidation of the (S)- or pro-(S ) hydroxyl group occurs selectively with HLADH (Scheme 2.143). In the case of 1,4- and 1,5-diols, the intermediate y- and 8-hydroxyaldehydes spontaneously cyclize to form the more stable five- and six-membered hemiacetals (lactols). The latter are further oxidized in a subsequent step by HLADH to form y- or 5-lactones following the same (S)-or pro-(5) specificity [1035]. Both steps - desymmetrization of the prochiral or meso-diol and kinetic resolution of the intermediate lactol - are often highly selective. By using this technique, enantiopure lactones were derived from... 

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