Persulfate-nitrogen doped graphene mixture as an oxidant for the synthesis of 3-nitro-4-aryl-2H-chromen-2-ones from aryl alkynoate esters and nitrite

Abstract

A series of 3-nitro-4-aryl-2H-chromen-2-ones in good yield have directly been obtained from aryl alkynoate esters and nitrite by employing mixture of K2S2O8-nitrogen doped graphene as an oxidant in watery medium...

2‐Arylbenzyl Methyl Ethers as Precursors for the Tandem Synthesis of Benzo[c]coumarins Over Heterogeneous Visible‐Light Photoredox Catalysis with Graphitic Carbon Nitride (g‐C3N4)

“…It is important to note that bisulfate solutions are acidic in nature and are known to promote ester hydrolysis. [25,26] On the basis of control experiments as well as literature reports, a plausible reaction mechanism is proposed in Scheme 3. The visible-light excitation results in the effective separation of photogenerated electron-hole pairs of g-C 3 N 4 with a band gap of 2.7 eV.…”

“…Later, when 2‐(methoxymethyl)‐1,1′‐biphenyl ( 1 a ) was exposed to radiation in the absence of (NH 4 ) 2 S 2 O 8 under the optimized reaction conditions, a mixture of [1,1′‐biphenyl]‐2‐carboxylic acid, methyl [1,1′‐biphenyl]‐2‐carboxylate, and 6H‐benzo[c]chromen‐6‐one were obtained (Scheme 2), suggesting that the (NH 4 ) 2 S 2 O 8 is necessary for the complete conversion of [1,1′‐biphenyl]‐2‐carboxylic acid into 6H‐benzo[c]chromen‐6‐one as well as hydrolysis of methyl [1,1′‐biphenyl]‐2‐carboxylate. It is important to note that bisulfate solutions are acidic in nature and are known to promote ester hydrolysis [25,26] …”

“…On the other hand, the photogenerated hole (h + ) of g‐C 3 N 4 subjected to single electron transfer (SET) with the 2‐arylbenzyl methyl ethers ( 1 ) and affords the corresponding benzylic radical A [24] . Of course, radical A can also be generated via hydrogen atom abstraction (HAT) with SO 4 − ⋅ [25] . After that, radical A will react with either two moles of SO 4 − ⋅ or one mole of peroxide radical (HOO⋅) to form methyl [1,1′‐biaryl]‐2‐carboxylate ( B ), which will eventually provide [1,1′‐biaryl]‐2‐carboxylic acid ( C ) by hydrolysis [24] .…”

“…When water was replaced with other common organic solvents such as methanol, ethanol, acetonitrile, DMSO, DCE, THF, CH 3 CN-water, DMSO-water and methanol-water, the combination of acetonitrile-water (6 : 4, v/v mL) afforded the desired product 2 a in 38% yield (Table 1, entry 8) may be due to the enhanced solubility of 1 a and Na 2 S 2 O 8 in aqueous acetonitrile solution. [25] The yield of product 2 a was further increased to 66% when O 2 -balloon was employed in place of the open flask air atmosphere (Table 1, entry 11). However, reaction was sluggish under an environment of N 1, entries [14][15][16].…”

“…[7][8][9][10] Furthermore, the combined use of the g-C 3 N 4 photoredox catalyst with 2-arylbenzyl methyl ethers may result in the production of exceptionally valuable benzo[c]coumarins (Scheme 1) under the eco-friendly conditions. As part of our research works on the persulfate activation by carbonaceous materials, [25,26] herein, we disclose three reactions (oxidation, hydrolysis and dehydrogenative lactonization) in one-pot approach for the synthesis of benzo[c]coumarins from 2arylbenzyl methyl ethers using g-C 3 N 4 as a heterogeneous catalyst under blue LEDs irradiation (Scheme 1, right). A feasible reaction mechanism has also been described.…”