Epoxy /3-keto esters

Vitamin B12 derivatives are also effective catalysts for the electroreductive cyclization of bromoalkenes in conductive microemulsions,299 300 or for ring-expansion reactions in cyclic a-(bromomethyl)-(3-keto esters in DMF.301 Vitamin Bi2 attached to an epoxy-polymer has been used in electrosynthesis of valeronitrile by reductive coupling of iodoethane and acrylonitrile.302... 

Despite the lack of diastereoselectivity and the moderate yields, the present procedure complements other syntheses of 1,3-diols such as hydride reductions of p-diketones,9 p-hydroxy ketones10 and p-keto esters,11 or the opening of 2,3-epoxy alcohols12 and 3,4-epoxy alcohols13 with Lipshutz cuprates. 

Cyclization epoxy -fceto esters. Treatment of I with BF3 etherate effects cyclization to the S,8-dioxabicyclo[3.2.1]octane 2 in higli yield. This basic skeleton had been encountered in several sex pheromones of bawk beetles such as frontalin (3), which can be synthesized readily by the -keto ester cyclization, since the carboxylic acid corresponding to 2 is readily decarboxylated when heated at 220°. ... 

Functional groups include allene, acetylene, hydroxy, methoxy, epoxy, keto, aldehyde, carboxylate, lactone, acyl ester, glycoside, glycosyl ester and sulphate. Carotenoids with elements other than oxygen directly attached to the carbon skeleton have not been found in Nature. 

The formation of epoxy products from the reaction of diazomethane with a-keto esters and oxomalonates could also involve soft attack at carbonyl oxygen initially. 

Nemoto T, Ohshima T, Shibasaki M. Catalytic asymmetric synthesis of a,p-epoxy esters, aldehydes, amides, and -y,8-epoxy p-keto esters unique reactivity of a,p-unsaturated carboxylic acid imidazolides. J. Am. Chem. Soc. 2001 123 (38) 9474-9475. 

Substituted phenethyl isocyanates undergo cyclization to lactams when treated with BF3-OEt2. Vinyl ether epoxides (eq 12), vinyl aldehydes, and epoxy p-keto esters all undergo cyclization with BF3 -OEt2. 

In the event, iodolactonization of the carboxylate salt derived from the ester 458 afforded 459, and subsequent warming of the iodo lactone 459 with aqueous alkali generated an intermediate epoxy acid salt, which suffered sequential nucleophilic opening of the epoxide moiety followed by relactonization on treatment with methanol and boron trifluoride to deliver the methoxy lactone 460. Saponification of the lactone function in 460 followed by esterification of the resulting carboxylate salt with p-bromophenacylbromide in DMF and subsequent mesylation with methanesulfonyl chloride in pyridine provided 461. The diazoketone 462 was prepared from 461 by careful saponification of the ester moiety using powdered potassium hydroxide in THF followed by reaction with thionyl chloride and then excess diazomethane. Completion of the D ring by cyclization of 462 to the keto lactam 463 occurred spontaneously on treatment of 462 with dry hydrogen chloride. 

The phorphorus betaine method is recommended for inversion of the stereochemistry of acyclic di- and Irisubstituted alkencs. Highly hindered epoxides react very slowly with LDP and alkenes arc not obtained in good yield. Keto groups interfere with the sequence owing to enolate formation unless 2 eq. of reagent is used. Epoxy esters cannot be dcoxygenated in practical yield. 

Structural information obtained from these modem methods is complemented by fast atom bombardment (FAB) mass spectra [22] of both free and functionalized monosaccharides with a variety of functional groups such as thiols, nitro, keto, benzyl, azido, epoxy, esters, etc. FAB mass spectrometry is one of the most reliable and sophisticated techniques developed thus far. Moreover, one can predict the specific fragmentation pattern for the selected class of functionalized monosaccharides through the FAB method as well as the matrix assisted laser desorption ionization (MALDI) mass spectrometry method. 

Carbonyl reduction. Many substrates have been reduced enantioselectively to give alcohols trifluoromethyl ketones, a-acetoxyketones, pyridinophenones, ethyl a-methylacetoacetate, a-keto acid derivatives," and 3-chloro-2-oxoaIkanoic esters a,/3-Epoxy ketones undergo reduction and hydrolytic ring opening/... 

Oxidation causes the formation of hydroperoxides and conjugated compounds, which by cleavage give aldehydes, alcohols, ketones, lactones, acids, esters, and hydrocarbons. Radical mechanisms lead to the formation of dimers, other oligomers, and oxidized TAG. The latter have one or more acyl group with an extra oxygen (hydroxy, keto, epoxy derivatives). Other oxidation products are TAG with short-chain fatty acyl and n-oxo fatty acyl groups. 

Methyl oleate produces small amounts of allylic keto-oleates (with CO on carbons 8-, 9-, 10- and 11), epoxy-stearate or epoxy-oleates (8,9-, 9,10- and 10,11-epoxy), dihydroxy-oleates (8,9-, 9,10-, and 10,11-diOH) and dihydroxy-stearates (between carbon-9 and carbon-11). The allyhc keto-oleates may be derived by dehydration of the corresponding hydroperoxides. 9,10-Epoxystearate may be produced by the reaction of oleate and the hydroperoxides. The other epoxy products can be formed by cychzation of an alkoxy radical formed from the corresponding hydroperoxides of oleate (Figure 4.1). Accordingly, the 11-hydroperoxide forms the 10,11-epoxy ester, the 8-hydroperoxide forms the 8,9-epoxy ester, and the 9- and 10-hydroperoxides form the 9,10-epoxy ester. The 1,2- and 1,4-dihydroxy esters may be formed from a similar alkoxyl radical that undergoes hydroxyl and hydrogen radical substitution via an allylic hydroxy ester radical (Figure 4.1). 

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