Haloethyl ester

Haloethyl esters have been cleaved by a variety of nucleophiles. 

Haloethyl esters have been cleaved under a variety of conditions, many of which proceed by nucleophilic addition. 

Method B (general procedure)7 To an NaHTe solution, prepared from tellurium powder (1.27 g, 10 mmol) and NaBH4 (0.9 g, 24 mmol) in absolute EtOH (25 mL), is added the 2-haloethyl ester (10 mmol) in EtOH (5 mL). (The reaction takes place instantaneously for 2-bromoethyl esters at room temperature.) The mixture is stirred for 1 h, then acidified with dilute HCl, extracted with ether and the organic phase dried and evaporated. The residue is recrystalUzed from appropriate solvents to give pure carboxylic acids. 

Cleavage of 2-haloethyl esters. This reagent, prepared from sodium hydride and ethanedithiol, cleaves 2-haloethyl esters selectively in 80-95% yield (four examples). Compare Sodium trithiocarbonate, this volume. 

Hydrolysis of 2-haloethyl esters. 2,2,2-Trichloroethyl esters have been used for protection of carboxyl groups because they are readily cleaved by zinc-acetic acid at 0° (3, 295-296). Ho has reported that 2-haloethyl esters can be cleaved by sodium trithiocarbonate in refluxing acetonitrUe in 75-85% yield. The suggested mechanism is formulated. ... 

Haller-Bauer reaction, 525 a-Halo acyl chlorides, 75 2-Haloethyl esters, 553 y-Halo ketones, 524 Halomcthyl aryl ketones, 103 Halomethyl aryl sulfones, 41 Halomethylation, 105 tj-Halo-l-phenyl-l-alkynes, 165 Halopropyl isocyanates, 570 2-Halopyridines, 479 Halo-a,p-unsaturated ketones, 647-648 p-Halovinyl ketones, 644 Haworth succinic anhydride synthesis, 474 Hemithioacetal interchange, 381-382... 

The alcohol moieties R of type-1 esters should be as short as possible, preferably methyl or ethyl. If neccessary, the reaction rate of ester hydrolysis may be enhanced by linking electron-withdrawing groups to the alcohol moiety to give methoxymethyl, cyanomethyl, or 2-haloethyl esters. In contrast, carboxy-lates bearing long-chain alcohols are usually hydrolyzed at reduced reaction rates with esterases and proteases. 

Haloethyl ester protecting groups can be efficiently removed using cobalt(i)-phthalocyanin anions. cf. 4, 352 and 353.) The cobalt(l) is oxidized to cobalt(ii) during the reaction and is converted back to cobalt(i) by borohydride hence only catalytic quantities ca. 0.01 eq.) of the phthalocyanin are required. (See also ref. 62.)... 

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