Oxidative amidation of benzaldehyde using a quinone/DMSO system as the oxidizing agent

Abstract

An efficient transition-metal-based heterogeneous catalyst free procedure for obtaining the oxidative amidation of benzaldehyde using quinones as oxidizing agents in low molar proportions is described here.

Contemporary Approaches for Amide Bond Formation

“…The use of chemical oxidants is often discouraged due to the need of stoichiometric amounts, leading to compatibility issues with other functional groups. Nevertheless, catalytic oxidants paired with oxygen or solvents for regeneration continue to find mention in literature [142] . A more pragmatic approach involves recyclable oxidants, as exemplified by Leadbeater and co‐workers [143] with oxoammonium salts.…”

A Two-Step Synthesis of a Novel 7,8-Dihydro-5,8-ethanoindolizine-6,9(5H)-dione

“…Our group reported a novel pyrrolyl quinone system obtained from the natural product perezone or from 2,5-dimethyl-1,4-benzoquinone (Scheme 1), which showed an ability to carry out aldehyde oxidative amidation reactions, as well as being efficiently recognized by the fluoride ion when treated with tetrabutylammonium fluoride (TBAF) solution. [11][12][13] The synthesis of the pyrrolyl quinone 8 (R 1 = H; R 2 = Me), when obtained from dimethylbenzoquinone 7 (R 1 = H; R 2 = Me) and pyrrole, gave a 4% yield of the secondary product 9 through addition of pyrrole to the most-substituted position of the quinone (Scheme 1). In an attempt to evaluate the fluoride-recognition capacity of compound 9 toward TBAF, we carried out trials by following its titration course using 1 H NMR spectroscopy in CD 3 CN, as shown in Figure 2.…”

“…Compound 9 was initially obtained by the addition of pyrrole to position 2 of the 2,5-dimethyl-1,4-benzoquinone under the same reaction conditions reported by us previously for the synthesis of the optical sensor pyrrolyl quinone 8. 12 However, under these reaction conditions, which included catalysis by SiO 2 , the yield of compound 9 was limited to trace amounts. Considering that compound 9 was synthesized by the addition of pyrrole to a sterically hindered position in 4% yield, the first challenge was then to increase the yield of 9 (Table 1, entry 1) Our first attempt to invert the ratio of the products 9 and 8 by modifying the reaction time resulted an increase in the yield of 9 to 17%, (Table 1, entry 2) which represented progress, although this yield was still low.…”

Cooperative Recognition of Ni2+ Triggered by Fluoride Ions in Naturally Occurring α-Hydroxyquinone Derivatives

“…Modifications to pyrrolyl quinones, as well as to quinones, alter their electrochemical properties; the latter phenomenon was recently used for oxidative amidation of aromatic aldehydes. 34 …”

“…This receptor presumably recognizes fluoride, both by an anion−π interaction with quinone and by hydrogen bonding with pyrrole. Modifications to pyrrolyl quinones, as well as to quinones, alter their electrochemical properties; the latter phenomenon was recently used for oxidative amidation of aromatic aldehydes …”