2,3-Dihydroxy acids from aldehydes

In plants a-dioxygenases (Chapter 18) convert free fatty acids into 2(R)-hydroperoxy derivatives (Eq. 7-3, step d).32a These may be decarboxylated to fatty aldehydes (step e, see also Eq. 15-36) but may also give rise to a variety of other products. Compounds arising from linoleic and linolenic acids are numerous and include epoxides, epoxy alcohols, dihydroxy acids, short-chain aldehydes, divinyl ethers, and jasmonic acid (Eq. 21-18).32a... 

Recent developments tend to focus on the asymmetric aspects of stereoselective aldols but the diastereoselectivity is just as important. The cyclic ester 56 must of course form an E enolate and when the boron enolate -57 reacts with aldehydes the an//-aldol products 58 are formed with good stereoselectivity ranging from 4 1 to >20 1. The predominate isomer is that expected from the Zimmerman-Traxler transition state. The two benzylic-0 bonds can be cleaved by hydrogenation and the 2,3-dihydroxy acids anti-59 released in good yield.17... 

A sigruficant use is as a catalyst in a multitude of reactions, such as the formation of acrjdic and methacrjdic acid amides from fatty acid amides (81) of cychc ketones such as 4-phen5icyclopentane-l,2-dione and 2,5-dihydroxy-/)-benzoquinone from benzaldehyde diethji acetal and 2,4-dioxo-5,5-dimethoxy-hexanoic acid methyl ester (82) of dimer aldehydes from propane (83) and for the polymerization of epoxy compounds (84). Mag nesium Kthylate. Magnesium ethoxide [2414-98-4]y Mg(OC2H 2 niol wt 114.4, is an almost white hygroscopic powder density,... 

Reactions of Carboxylic Acids and their Derivatives.—A novel series of /8-lactones has been obtained from 17,20-dihydroxypregnan-21-oic acids (406) and (407). The reaction occurs, along with formation of the 17,20-diacetate, in acetic anhydride-pyridine. Lactonization is most efficient with the 20a-isomer (406) which affords the less-hindered rrans-20-acetoxy-lactone (408). The crystalline lactones (408) and (409) are stable at - 20 °C but suffer slow decarboxylation at room temperature or in refluxing benzene to give the trans- (410) and cis-enol acetate (411), respectively, of the 17-aldehyde (412). In a similar way the dihydroxy-acids (406) and (407) react with ethyl chlorocarbonate-pyridine to give 20-cathyl-21, 17a-lactones several novel transformations of these products are described. 

A number of heterocyclic acid amides in dilute hydrochloric acid are reduced to the aldehyde level where this is protected from further reaction as the dihydroxy... 

Optically active 1,2-diol units are often observed in nature as carbohydrates, macrolides or polyethers, etc. Several excellent asymmetric dihydroxylation reactions of olefins using osmium tetroxide with chiral ligands have been developed to give the optically active 1,2-diol units with high enantioselectivities. However, there still remain some problems, for example, preparation of the optically active anti-1,2-diols and so on. The asymmetric aldol reaction of an enol silyl ether derived from a-benzyloxy thioester with aldehydes was developed in order to introduce two hydroxyl groups simultaneously with stereoselective carbon-carbon bond formation by using the chiral tin(II) Lewis acid. For example, various optically active anti-a,p-dihydroxy thioester derivatives are obtained in good yields with excellent diastereo-... 

He and his students then tried to s oithesize simple analogs of the above monomeric unit, an endeavor which proved fruitless, but, in the course of their studies, they accumulated a large amount of knowledge regarding the preparation and properties of cyclic acetals. Thus, they found that a trace of acid catalyzes the formation of a polymer from 5,6-dihydroxy-2-hexanone, and that aliphatic aldehydes (RCHO) readily combine with chloral to give polymers of the general formula (2 RCHO -j- CUCCHO). ... 

A facile synthesis of (3R,5R)-dihydroxy-L-homoproline, an idulonic acid mimic, was realized using L-threonine aldolase-catalyzed reaction of glycine with an aldehyde derived from L-malic acid [96]. 

For the synthesis of (69), the enol ether (71) from the indanone (70) was carboxylated with COa-n-butyl-Iithium in THF at —70 C to yield (72). The methyl ester (73) was converted into (75) via the maleic anhydride adduct (74), essentially as described in earlier work. Lithium aluminium hydride reduction followed by oxidation with dicyclohexylcarbodi-imide afforded the aldehyde (76). This was condensed with excess (77) to yield a mixture of the diastereomers (78). Oxidation with chromium trioxide-pyridine in methylene dichloride gave (79), which could be converted into the diketone (80) by treatment with excess benzenesulphonylazide. The diketo-lactam (81) was prepared from (80) as described for the synthesis of the analogous intermediate used in the synthesis of napelline. Reduction of (81) with lithium tri-t butoxyaluminohydride gave the desired dihydroxy-lactam (82). Methylation of (82) with methyl iodide-sodium hydride gave (83). Reduction of this lactam to the amine (84) with lithium aluminium hydride, followed by oxidation with potassium permanganate in acetic acid, gave (69). 

The next step consisted of the condensation of the aldehyde with the dlol, 1,4-ditosylthreitol. This compound was previously prepared by refluxing one gram of L-(+)-0-isopropylidene-2,3-dihydroxy-l,4-bis(jv-tosyl)butane In 20 ml of absolute ethanol In the presence of 5.5 mg of -toluenesulfonic acid. The solution was allowed to reflux for 24 hr, after which the solvent was removed on a rotary evaporator. The oily residue which remained was redissolved In chloroform, and evaporation of this solvent then produced a grayish solid. The solid was recrystallized from 1 1 chloroform hexane to yield white needles of 1,4-ditosyl-threitol (0.86 g, 98Z yield). 

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