Photochemical Activation of Aromatic Aldehydes: Synthesis of Amides, Hydroxamic Acids and Esters

Abstract

A cheap, facile and metal-free photochemical protocol for the activation of aromatic aldehydes has been developed. Utilizing thioxanthen-9-one as the photocatalyst and cheap household lamps as the light source, a variety of aromatic aldehydes have been activated and subsequently converted in a one-pot reaction into amides, hydroxamic acids and esters in good to high yields. The applicability of this method was highlighted in the synthesis of Moclobemide, a drug against depression and social anxiety. Extended and detailed mechanistic studies have been conducted, in order to determine a plausible mechanism for the reaction.

Impact of Fluoroalkyl Substituents on the Physicochemical Properties of Saturated Heterocyclic Amines

“…Phenyl(pyrrolidin‐1‐yl)methanone (5 b) : [49] Yield 600 mg (96 %) from 5 a (253 mg, 3.56 mmol). Colorless liquid.…”

“…19 13 C NMR (126 MHz, CDCl 3 ): δ = 170.7, 132.4, 131.6, 128.7, 127.9, 126.2 (q, J = 275.5 Hz), 52.5, 48.4, 32.6 ppm (q, J = 32.3 Hz). 19 [49] Yield 600 mg (96 %) from 5 a (253 mg, 3.56 mmol). Colorless liquid.…”

Synthesis and characterization of rare earth/lithium complexes stabilized by ethylenediamine-bridged bis(phenolate) ligands and their activity in catalyzing amidation reactions

“…A diversity of various secondary cyclic amines, including pyrrolidine, piperidine, azepane, morpholine, thiomorpholine and piperazine, were also explored, generating amides 8ag–8ak in 83–96% yields. Amidation of pyrrolidine gave the amide 8ag in a much higher yield of 90% than the reported yields of 33% and 38% obtained with the thioxanthen-9-one photocatalyst 20 and monometallic Ln[N(SiMe 3 ) 2 ] 3 complexes. 10 a The bis-amidation of piperazine resulted in 94% yield under the optimal conditions (Table 3, 8al ).…”

Thioxanthone: a powerful photocatalyst for organic reactions

“…During the preparation of this review, Kokotos and coworkers reported the use of thioxanthone as the photocatalyst for the generation of acyl radicals from aromatic aldehydes. 101 This acyl radical was trapped by N-chlorosuccinimide, leading to the corresponding acyl chloride, which is subsequently reacted with amine, a hydroxyamine or an alcohol leading to an amide, a hydroxamic acid or an ester, respectively. Aliphatic aldehydes could not be employed.…”