Partial reductions of carboxylic acids and their derivatives to aldehydes

Abstract

The reductive synthesis of aldehydes from carboxylic acids and their derivatives without the formation of alkanol intermediates, in a redox-economic fashion, is synthetically very intriguing yet practically very challenging. Recent...

Catalytic One‐Pot Reductive Amination of Carboxylic Acids

“…(2) The formation of amides from carboxylic acids and amines is severely interfered with by their acid-base interactions, and consequently harsh conditions or mandatory promoters are required to ensure the amide formation. (3) The low electrophilicity of the amide carbonyl group requires strong reducing agents, (4) which, however, are more susceptible to deactivation by the carboxylic acids. These problems make it quite challenging to realize the desired chemoselectivity control in the reductive amination of carboxylic acids.…”

“…However, it is not the case in the reductive amination of carboxylic acids, in which several intermediates (for example, aldehydes 2 , their equivalents 6 , or amides 7) might be involved (Scheme 1B). Meanwhile, there are several challenges associated with this process: (1) The partial reduction of carboxylic acids to aldehydes is very difficult to control, [3] as the generated aldehydes are much more prone to hydride reduction compared to carboxylic acids. (2) The formation of amides from carboxylic acids and amines is severely interfered with by their acid‐base interactions, and consequently harsh conditions or mandatory promoters are required to ensure the amide formation.…”

Recent advances in the photocatalytic synthesis of aldehydes

“…Traditionally, aldehydes could be synthesized through the oxidation of the parent primary alcohols (Scheme 1a), 1 or the reduction of the corresponding carboxylic acids (or their derivatives) or nitriles (i.e., Stephen reduction) (Scheme 1b). 2 Moreover, formylation reactions such as the Gattermann formylation, Gattermann-Koch reaction, Duff aldehyde synthesis (hexamine aromatic formylation), palladium-catalyzed formylation of aryl halides with CO/H 2 , etc. are indispensable for the construction of aldehydes.…”

“…, Stephen reduction) (Scheme 1b). 2 Moreover, formylation reactions such as the Gattermann formylation, Gattermann–Koch reaction, Duff aldehyde synthesis (hexamine aromatic formylation), palladium-catalyzed formylation of aryl halides with CO/H 2 , etc . are indispensable for the construction of aldehydes.…”