Epoxy esters, formation

Other examples of the formation of six-membered rings by means of an intramolecular alkylation of an ester enolate are given in Table 7. Entry 6, i.e., stereoselective transformation of the epoxy ester into the cyclohexane derivative, should be discussed briefly as a representative for the other cases. The probable reason for the unexpectedly high selectivity i.e., the nonappearance of the diastereomer 8, can be demonstrated by the two transition-state-like conformations 9 and 10. 9 displays a very severe 1,3-diaxial interaction in comparison to 10, thus, formation of the diastereomer 7 from conformation 10 is highly favored113. 

In the past, Darzens methodology was primarily used for the synthesis of aldehydes and ketones, as a homologation reaction without any consideration of stereocontrol in the epoxide formation. For this sequence, saponification of the a,P-epoxy ester followed by decarboxylation gives the substituted carbonyl compound ... 

The formation of the six-membered ether ring via epoxy ester-ortho ester cyclic ether rearrangement supports the hypothesis that epoxy ester-ortho ester cyclic ether rearrangement may be involved in the biosynthesis of ladder-type marine polyether toxins. This reaction represents a biomimetic preparation of medium ring cyclic ethers. 

A modification of the asymmetric bromolactonization leads to optically active a,p-epoxy aldehydes (18). Treatment of the bromolactone (14) with Sodium Methoxide results in the formation of the epimeric epoxy ester (17) in a ratio of 2 1 (eq 7). 

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. 

A cationic zirconocene complex formed by treatment of Cp2ZrCl2 with AgC104 has been found to catalyze Diels-Alder reactions [24]. For example, reaction of epoxy ester 55 with isoprene presumably proceeds via the formation of dioxolenium ion 56 then cyclization (Eq. 24). Hydrolysis gave cyclohexenecarboxylic acid 57. 

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. 

Water-Soluble Binders. Water-soluble binders consist of relatively low molecular mass polymers (M < 10000) (e.g., alkyds, polyesters, polyacrylates, epoxides, and epoxy esters) whose individual molecules dissolve in water due to salt formation involving functional anionic or cationic groups. 

Treatment of epoxy ester A with hydrochloric acid in ether gives the products shown. Write a mechanism that would account for the formation of the major products and suggest feasible experiments that could test your mechanism. 

PANI/P-PVA (partially phosphorylated poly(vinyl alcohol)) nanoparticles were successfully dispersed in epoxy resin applied to steel [82]. P-PVA is fundamental to obtain a uniform dispersion of PANI nanoparticles, and this fact is responsible for the uniform formation of Fe Oj passive layer at the interface between coating and substrate and therefore for its effectiveness in corrosion protection. PANI was also used in combination with DBSA to be added to epoxy-ester (EPE) system to form a smart anticorrosion coating [73]. DBSA is used as both surfactant and doping agent. By EIS measurements it is deduced that the better anticorrosion performance of PANI (DBSA)/EPE coatings with respect to simple EPE is due to the formation of a second barrier layer by reaction between released DBSA anions and Fe cations at the defective locations of the coating. 

In recent years, water-dispersed epoxy resins also have gained importance in a variety of applications. Water-soluble epoxy resins are prepared by the esterification of epoxy resin with drying oils/ fatty acids of drying oil, followed by the formation of either half esters of dicarboxylic epoxy esters, or maleinised epoxy esters through reaction with polybasic acid anhydrides. They become water soluble on neutralisation with dimethyl etha-nolamine (Fig. 7.4). The cationic polymerisation of emulsified epoxy resins by 1 % perchloric acid has also been reported. The polyols obtained were cross-linked with MF resin to produce waterborne coatings, which are free from co-solvent and show excellent solvent resistance at low bake temperatures. ... 

Efficient Synthesis of Cardenolides. A general and efficient method has been described for the synthesis of cardenolides, consisting of (1) a-methylsulfenylation of pregnen-20-one, (2) Refor-matsky reaction, and (3) butenolide formation by alumina chromatography of the epoxy ester obtained from the S-methylated Reformatsky product (eq 4). ... 

Silylation Reactions. In the presence of a catalytic amount of tetra-n-butylammonium fluoride (TBAF), ester (1) is a very efficient silylating agent for a wide variety of substrates including carbonyl compounds, alcohols, phenols, carboxylic acids, and alkynes. With unsymmetrical ketones the kinetic enol ether is the preferred product. Indeed, the use of (1) can provide superior selectivity to the use of hindered bases forenolate formation. This is illustrated with a 8,y-epoxy ester which provides an entry to /-keto-a, 8-unsaturated esters (eq 2). These silylation reactions of (1) can also be catalyzed by TBAF supported on silica. ... 

Epoxi ester 1 effeetively rearranges to a 1 1 mixture of acetates 2 and 3 under acidic conditions (0.5 M H2SO4 in THF/H2O 9/1). It is believed that the reaction occurs through the formation of an orthoester intermediate 4 tiiat is subsequently hydrolyzed in the acidic medium (Scheme 25.1). This route provides a convenient method for the synthesis of polyhydroxylated compounds with control of the stereochemistry during the epoxide ring-opening step. 

The acid rearrangement of the epoxy ester moiety of 12 (Fig. 25.1) is the key step in the synthesis of orthoesterol B, a marine natural product with antiviral activity. Based on the meehanism proposed for the formation of 4 formulate the strueture of flie orflioester fliat should be obtained in the rearrangement of 12. Interestingly, when diastereomer 13 was treated under the same eonditions, it remained unaltered for months. Could you explain why ... 

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