Interception of Radicals by Molecular Oxygen and Diazo Compounds: Direct Synthesis of Oxalate Esters Using Visible-Light Catalysis

Abstract

The synthesis of oxalate esters through a radical process, rather than the traditional ionic reaction, has been well developed in which the radicals induced by visible light are trapped by molecular oxygen and diazo compounds under room temperature. This reaction is operationally simple, mild, and shows broad substrate scopes in α-bromo ketones and diazo compounds.

Lightening Diazo Compounds?

“…In the presence of oxygen, it transforms into oxyradical B, which then in a key step reacts with diazo ester 27 with the release of nitrogen. The resulting radical C attaches another oxygen molecule, and expected oxalate 178 is formed after rearrangement and oxidation of oxy radical D. 115 Remarks. The vast majority of the above-mentioned transformations represent new reactivity modes of diazo compounds.…”

Efficient and practical synthesis of monoalkyl oxalates under green conditions

“…The 1 H NMR and 13 C NMR spectra were recorded in CDCl 3 with the use of a JEOL JNM-ECA500 spectrometer operated at 500 MHz for 1 H NMR and 125 MHz for 13 C NMR with tetramethylsilane (TMS) as an internal standard. The IR spectra were recorded on a JASCO 4100 FT-IR spectrometer.…”

“…9 a , c ,12 As for derivatives of oxalate half-esters, the synthesis of various non-symmetric dialkyl oxalates were reported from α-bromoketones and diazoacetates mediated by molecular oxygen and visible light in 50–90% yields. 13 However, these reactions must be carried out in organic solvents, which can be of environmental concern. Some of them utilize toxic reagents such as oxalyl chloride, which generates corrosive HCl gas upon reaction with water.…”

“…1 H NMR (500 MHz, CDCl 3 ) d ¼ 1.42 (t, 3H, CH 3 , J ¼ 7.2 Hz), 4.42 (q, 2H, OCH 2 , J ¼ 7.2 Hz), 10.09 (b.s, 1H, OH) 13. C NMR (125 MHz, CDCl 3 ) d ¼ 13.79, 64.24, 158.19, 159.27.…”

Visible Light‐Induced [3+2] Cyclization Reactions of Hydrazones with Hypervalent Iodine Diazo Reagents for the Synthesis of 1‐Amino‐1,2,3‐Triazoles

“…Recently, with the growth of modern photochemistry, photocatalyzed reactions of diazo compounds have attracted considerable attention. In general, diazo compounds can act as radical acceptors, [14a] carbene [14b–g] and radical precursors, [7a,14h] and nucleophiles [15a] in photocatalytic systems to develop new and valuable chemical transformations. In such transformations, diazo compounds often require N 2 extrusion as a driving force under light irradiation conditions, [16] with few reported examples showing retention of the diazo functionality [7,15] .…”