A Practical and Highly Efficient Hydroacylation Reaction of Azodicarboxylates with Aldehydes in Water

Abstract

The very efficient hydroacylation reaction of azodicarboxylates, with various aldehydes, was carried successfully out at room temperature in water without the use of a catalyst to obtain a variety of hydrazine imide products in high yields. A wide range of aldehydes, including aliphatic and aromatic compounds, was considered, and the reaction is believed to proceed via a radical mechanism, in which water plays an integral role in stabilizing the radical intermediate.

Light-accelerated “on-water” hydroacylation of dialkyl azodicarboxylates

“…28 Thus, we tested water, which is known to have a positive effect in some reactions 29 and as it is mentioned in the literature, it is a quite successful solvent for the specific reaction. 16,17 In particular, following the pioneering contributions by Caddick, Chudasama and coworkers, water is known to accelerate acyl radical formation and facilitates a number of reactions. 30 Thus, in this work, we envisioned a combined activation, derived from the “on-water” effect 29 and the acyl radical formation that is favoured in water.…”

“…Caddick and co-workers reported that the reaction between butanal and 2a in water required 16 h to provide 90% of the hydroacylation product, 16 while Headley, Ni and coworkers reported that the reaction between nonanal and 2a in water required 20 h to provide 92% of the hydroacylation product. 17 Herein, the reaction of heptanal with 2a in water and upon irradiation required 55 min to provide a quantitative yield of 3a (100% conversion, Table 2, entry 11). However, since irradiation at 390 nm was equally effective, we performed the reaction at 390 nm as well, and in this case, the results were even better, since the reaction was completed faster, within just 40 minutes (Table 2, entry 12).…”

“…2 In the literature, air and/or water are well-accepted in being able to generate acyl radical I from aldehydes 1 , a process which is highly dependent on air, but water is known and proposed to accelerate this process (Scheme 6A, Pathway II). 16,17,29 b ,30 a – c ,34 b It is also well accepted that acyl radical I can react with different electrophiles, like DIAD, leading to the desired products (Scheme 6C). 16,17,30 c Moreover, we have more interest in photocatalysis and have been involved in the use of aldehydes as potential photoinitiators (Scheme 6A, up).…”

“…14 In the latter case, pyridine was utilized in catalytic amounts and a short reaction time (10 min) was employed along with the microwave irradiation; however, a high temperature (140 °C) and DMF were utilized. 15 Around the same period, in two different reports, one by Caddick and coworkers 16 and the other by Headley, Ni and coworkers, 17 water was utilized as the solvent (Scheme 1E). In the former case, a slight excess of the aldehyde ( vs. dialkyl azodicarboxylate) was employed, leading to good to high yields with a reaction time that varied from 24–96 h, 16 while in the latter case, a higher reagent ratio (2 : 1) led to similar yields, spanning from 3 to 360 h as the reaction time.…”

“…In the former case, a slight excess of the aldehyde ( vs. dialkyl azodicarboxylate) was employed, leading to good to high yields with a reaction time that varied from 24–96 h, 16 while in the latter case, a higher reagent ratio (2 : 1) led to similar yields, spanning from 3 to 360 h as the reaction time. 17…”