A, 3-Epoxy esters

Shibasaki et al. have reported a new approach to a,/3-epoxy esters the epoxidation of cv. j-unsaturated carboxylic acid imidazolides with a La(OPr )3, BINOL, Ph3As=0, and TBHP system provides epoxy-peroxy-esters (41), which are generated in situ from the intermediary epoxy acid imidazolide and converted to the corresponding methyl ester (42) upon treatment with methanol (Scheme 27).134... 

Aldehydes and ketones condense with a-halo esters in the presence of bases to give a, 3-epoxy esters, called glycidic esters. This is called the Darzens condensation.623 The reaction consists of an initial Knoevenagel-type reaction (6-41), followed by an internal Sn2 reaction (0-13) 624... 

Mai and co-workers have reported that the deoxygenation of cyclic a,/3-epoxy ketones (and acyclic a,/3-epoxy esters) is accomplished in high yields under mild and neutral conditions by the use of Mo(CO)6 (Table 14) <2003TL2355>. 

The condensation of aldehydes and ketones with ethyl chloroacetate in the presence of sodium ethoxide or sodium amide produces a,/3-epoxy esters (Darzens). The scope, limitations, typical experimental procedures, and examples have been given. Briefly, aliphatic and aromatic ketones, and aromatic aldehydes react satisfactorily, whereas aliphatic aldehydes give poor yields. a-Halopropionic and a-halobutyric... 

The Darzens glycidic ester condensation involves the condensation of an aldehyde or ketone with an a-halo ester, in the presence of a base, to afford an a,3 epoxy ester (a glycidic ester ). The first synthesis of a glycidic ester was reported by Erlenmeyer in 1892 and is illustrative of the general reaction, as shown in equation (1). The reaction was subsequently developed and generalized by Darzens. Glycidic esters, in addition to undergoing transformations normally associated with epoxides, afford upon hydro-... 

Inanaga et al. have developed the use of HMPA for the highly regioselective reduction of a,(3-epoxy esters and 5,y-epoxy a, 3-unsaturated esters [40] (Scheme 10). 

Epoxycycloliexane, 126 a,/3-Epoxy esters, 258 Epoxy ketones, 166, 245, 343 a,i3-Epoxy ketoximes, 505 Epoxy mesylates, 15-16 a,/3-Epoxysilanes, 277-278 a,/3-Epoxy sulfones, 340 a-Epoxy sulfoxides, 95 Ergosterol, 435, 436 Ergosterol B, 435,436 Ergosterol Bj, 435,436 Erythronolide B, 84 Ester cleavage, 304, 447 Ester hydrolysis, 262 Esterification, 95, 163, 186, 230, 500 Esters, 444... 

The electroreductive ring-opening of a,/3-epoxy esters (475) and nitriles (478) proceeds stepwise as shown in Schemes (164 and 165). In both cases, the intermediates (476) and (479) can be isolated when the mediator-assisted reductions are carried out at room temperature. The whole reduction can be completed at 50 °C. For example, the electrolysis of a phenylglycidic ester (475) (r1 = Ph, r2 = H) in an MeOH-NaCl04-(Pt) system in the presence of PhSeSePh at room temperature gives... 

When an aldehyde or a ketone is condensed with ethyl a-chloroacetate in the presence of sodinm ethoxide, the product is an a,/3-epoxy ester called a glycidic ester. The synthesis is called the Darzens condensation. 

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