Carbonyl compounds heteroaromatic, reduction

The electrochemical behavior of azomethine derivatives, e.g., oximes, of heteroaromatic carbonyl compounds is much like that of the corresponding benzene derivatives.91 Pyridine aldoximes271-274 and ketoximes275 are reduced in acid solution by a four-electron reaction to the amine. The reaction mechanism is probably, as in other oximes,01 a reduction of the protonated compound with cleavage of the N-0 bond, followed by saturation of the C=N double bond. The amine is often further reducible at a more negative potential (Section VI, E). 

The anion BH, formed in Eq. (3), is thermodynamically a stronger base than B and will react with another molecule of substrate, as in Eq. (4). Each PB will therefore consume a total of two protons (and two electrons). An exception to the fast removal of BH by further reduction is sometimes found for radical anion oxygen bases derived from carbonyl compounds, as discussed in Sec. III.B.2. Radical anion EGBs are usually derived from aromatic systems such as aromatic hydrocarbons, A-heteroaromatic systems or azo-arenes. An example was given in Scheme 3 [3]. Radical anion EGBs are normally pro-... 

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. ... 

Carbonyl compounds, especially aldehydes and ketones, regardless of whether they are aliphatic, aromatic, heteroaromatic, or a,g-unsaturated have been investigated mostly at mercury electrodes as regards their reduction mechanism. It follows from literature, however, that they can be reduced at copper, silver, platinum, tin, nickel, aluminium, zinc or carbon cathodes. The mechanisms differ strongly being a function of the electrode material, of the solution composition and of the reducible carbonyl compound ... 

Shortly after Sadighi and Buchwald s 2003 report, Nolan reported that [(IPr)CuCl] could be used in the hydrosilylation of simple ketones, leading to the silylated alcohols in high yields. Subsequent work permitted the development of fine-tuned catalytic systems for different classes of carbonyl compounds. Hence, while [(IPr)CuCl] was found optimal for the 1,4-reduction of conjugated carbonyls and 1,2-reduction of simple ketones, [(ICy)CuCl] proved more efficient for hindered carbonyl substrates and [(SIMes)CuCl] turned out to be the best choice for heteroaromatic ketones (Scheme 11.1). Other NHC architectures e.g. six-membered diamino carbenes) and alternative... 

One of the most common uses of [ C]acetyl chloride is its Lewis acid- (AICI3, SnCLi) catalyzed Friedel-Crafts reaction with aromatic or heteroaromatic substrates to produce labeled aryl/heteroaryl methyl ketones. As these intermediates are subject to several types of transformations, they have been used as key intermediates for the synthesis of a wide variety of a,)8-functionalized aryl/heteroaryl alkyl target compounds. For example, aryl/ heteroaryl methyl ketones can be (a) halogenated in the methyl group to provide substrates for reaction with carbon or nitrogen nucleophiles, (b) deprotonated so as to react with appropriate electrophilic partners, (c) subjected to stereoselective carbonyl group reduction to alcohols, or (d) reduced to aryl/heteroaryl alkyls. Such transformations can be conducted sequentially in many combinations. 

---