Aromatische Aldehyde aus Kohlenwasserstoffen über die Carbonsäure-N-methylanilide. Aldehyde aus Carbonsäuren, VI. Mitteil

Counterintuitive chemoselectivity in the reduction of carbonyl compounds

The reactivity of carbonyl functional groups largely depends on the substituents on the carbon atom. Reversal of the commonly accepted order of reactivity of different carbonyl compounds requires novel synthetic approaches. Achieving selective reduction will enable the transformation of carbon resources such as plastic waste, carbon dioxide and biomass into valuable chemicals. In this Review, we explore the reduction of less reactive carbonyl groups in the presence of those typically considered more reactive. We discuss reductions, including the controlled reduction of ureas, amides and esters to aldehydes, as well as chemoselective reductions of carbonyl groups, including the reduction of ureas over carbamates, amides and esters; the reduction of amides over esters, ketones and aldehydes; and the reduction of ketones over aldehydes.

Zur Formylierung von Hydroxy- und Alkoxyaromaten mit Ameisensäure

By treatment of ethers of phenol, resorcinol, 2-napththol, alkylanisoles 10, 13, 15, 17, 20, 22, 24, 28 with formic acid/borontrichloride the aromatic aldehydes 11, 14, 16, 18, 21, 23, 25, 26, 29 can generally be prepared in low yields. The formylation reactions proceed between −20 and −10°C within 20 min in 1,2-dichloroethane, chlorobenzene, or methylene chloride as solvents when formic acid and borontrichloride are used in excess [molar ratio of aromatic compound to HCOOH to BCl3 = 1:1.2–1.7:1.6–1.8]. The more strongly activated 3,5-dimethoxyphenol (33) is formylated by formic acid/borontrichloride to give the aldehyde 34 with an acceptable yield. The reactions of resorcinol dimethylether with formic acid in the presence of super acids (mainly trifluormethansulfonic acid) in chlorobenzene or nitromethane deliver the aldehyde 21 only in small amounts.