Esters heteroaromatic, reduction

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

Aromatic and heteroaromatic esters can be electrochemically reduced to benzyl alcohols, similar to the carboxylic acids. One example is the cathodic reduction of dimethyl terephthalate531 . 

Bu3SnH cannot generally be used for radical alkylation of heteroaromatics, since it is a reductive radical reagent. However, O-acyl esters (2) are not a reductive reagent. 

Decarboxylation of benzoates in the presence of an aryl halide (20, 33, 211) affords the biphenyl substitution products in yields of up to 50% if the medium is an iV-heteroaromatic solvent. The solvent must be dry to avoid reductive dehalogenation (54). If the solvent is dry diglyme or xylene, an ester can be isolated in high yield (54). 

Carbinols conjugated with aromatic systems, such as benzylic alcohols [59-62], trityl (VIII), tritylone (IX), and benzhydryl alcohols [59,62,63], and 9-hydroxy-9-phenylan-throne, heteroaromatic systems [64], a-hydroxy ketones [65-67], a-hydroxy acids, and their derivatives [68-70] can also be cleaved at potentials less negative than that of the activating group. Thus the radical anion of benzyl benzoate cleaves rapidly to benzoate and benzyl radical, which is reduced to the anion protonation leads to toluene. In the absence of added proton donor, the base generated during the reduction (EGB) may cleave the ester to benzoate and benzyl alcohol [44]. 

Acid-catalyzed addition of aliphatic, aromatic or heteroaromatic cyanohydrins to ethyl vinyl ether, n-butyl vinyl ether or dihydro-4//-pyran provides base stable, protected cyanohydrin derivatives. Phase transfer catalyzed alkylation of aliphatic cyanohydrins with allylic bromides gave a-substituted a-allyl-oxyacetonitrile. Carbonyl compounds react wiA cyanide under phase transfer catalysis to give cyanohydrin anions, which are trapped by an acyl chloride or ethyl chloroformate to give acyl- or alkoxycarbonyl-protected cyanohydrins respectively. The reduction of the carbonyl group of an acyl cyanide by NaBH4 under phase transfer conditions followed by esterification serves as an alternative route to aldehyde-derived cyanohydrin esters. ... 

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