Glycidic esters, formation

The decomposition of a glycidic ester to an aldehyde and carbon dioxide may involve the formation of a quasi six-membered ring, followed by the shift of three electron pairs ... 

Glycidic esters can easily be converted to aldehydes (2-40). The reaction has been extended to the formation of analogous aziridines by treatment of an imine with an a-halo ester or an a-halo N,N-disubstituted amide and f-BuOK in the solvent 1,2-dimethoxy-ethane.636 However, yields were not high. Acid-catalyzed Darzens reactions have also been reported.637 See also 6-61. 

Isomerization of substituted styrene oxides allows the synthesis of aldehydes in high yields726 [Eq. (5.275)]. Cycloalkene oxides do not react under these conditions, whereas 2,2,3-trimethyloxirane gives isopropyl methyl ketone (85% yield). Isomerization of oxiranes to carbonyl compounds is mechanistically similar to the pinacol rearrangement involving either the formation of an intermediate carbocation or a concerted mechanism may also be operative. Glycidic esters are transformed to a-hydroxy-/3,y-unsaturated esters in the presence of Nafion-H727 [Eq. (5.276)]. 

An illustrative example of oxirane formation by the action of alkali on a / -halohydrin is to be found in the reaction sequence involved in the Darzens glycidic ester synthesis (Section 5.7.6, p. 598). Three target molecules, namely 2-phenylaziridine (4), methyl (S)-thiiranecarboxylate (5) and cyclooctene sulphide (6), are selected here to exemplify this intramolecular cyclisation reaction type. 

The Darzens reaction of isatin with ethyl chloroacetate yields glycidic esters. Alkaline hydrolysis of the glycidic esters yields indole-2,3-dicarboxylic and indole-3-carboxylic acids in a 6 1 proportion. The isolation of two isomeric glycidic esters, and the fact that both produce the indolecarboxylic acids in the same proportion led to a mechanistic proposal for the formation of the later through a common intermediate439 (Scheme 101). 

However, these conditions have not been applied to other epoxides. Catalysis by the boron trifluoride -diethyl ether complex is very useful for the ring opening of cyano-substituted epoxides " and glycidic esters see the formation of and Table 14. This is demonstrated by the regioselective opening of the epoxide ring in 2,3-dimethyloxirane-2-carbonitrile to provide 3-fluoro-2-hydroxy-2.3-dimcthylbutanonitrile... 

Darzens condensation. Formation of a- and (i-epoxy esters (glycidic esters) by the condensation of aldehydes or ketones with esters of a-haloacids the corresponding thermally unstable glycidic acids yield aldehydes or ketones on decarboxylation. 

Isomerization of glycidic esters. BF3 OEt2-induced formation of a-hydroxy-yS.Y-unsaturated esters opens ways to other difunctional compounds such as alkenyl epoxides, which are not directly available from the corresponding dienes. 

Hydracrylic and glycidic esters. Treatment of the methoxymethyl ester (1) with LDA in THF at — 78 20° results in formation of the methyl hydracrylate... 

X-sulfonyloxy-(X,P-unsatuTated ester, and the formation in both cases are kept to a minimum by carrying out the reaction under relatively dilute conditions. Under mild alkaline conditions, the monosulfonates (85) are converted to glycidic esters (86) in high yield. The nosylates, but not the tosylates, undergo displacement by azide ion to give ot-azido-P-hydroxy esters, which are envisioned as precursors to P-hydroxyamino acids [69]. 

The lipase from Serratia marcescens has a high enantioselectivity (E = 135) for the (2R,3S)-(4-methoxyphenyl) glycidic acid methyl ester, which acts as a competitive inhibitor. The formed acid (hydrolyzed (+)-methoxyphenylglycidate) is unstable and decarboxylates to give 4-methoxyphenylacetaldehyde this aldehyde strongly inhibits and deactivates the enzyme. It is removed by transfer to the aqueous phase by formation of a water-soluble adduct with sodium hydrogen sulfite added to the aqueous phase. The bisulfite acts also as a buffer to maintain constant pH during synthesis. 

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