Unexpected Imidazoquinoxalinone Annulation Products in the Photoinitiated Reaction of Substituted‐3‐Methyl‐Quinoxalin‐2‐Ones with N‐Phenylglycine

Abstract

Photoinduced electron transfer between N-phenylglycine (NPG) and electronically excited triplets of 7-substituted-3-methyl-quinoxalin-2-ones in acetonitrile generate the respective ion radical pair, where by decarboxylation the phenyl-amino-alkyl radical, PhNHCH2•, is generated. This radical reacts with the 3-methyl-quinoxalin-2-ones ground states, leading to the product 2. Other, unexpected, 7-substituted-1,2,3,3a-tetrahydro-3a-methyl-2-phenylimidazo[1,5-a]quinoxalin-4(5H)-ones, annulation products, 3a-f, were generated; likely by the addition of two PhNHCH2• radicals, to positions 3 and 4 of the quinoxalin-2-ones. The reaction mechanism includes a photoinduced one electron transfer initiation step, propagation steps involving radical intermediates and NPG with radical chain termination steps that lead to the respective products 2a-f and 3a-f and NPG by-products. The proposed mechanism accounts for the strong dependency found for the initial photoconsumption quantum yields on the electron-withdrawing power of the substituent. Therefore, photolysis of common reactants widely used such as NPG and substituted quinoxalin-2-ones may provide a simple synthetic way to the unusual, unreported tetrahydro-imidazoquinoxalinones 3a-f.

Supramolecular Reversible On–Off Switch for Singlet Oxygen Using Cucurbit[n]uril Inclusion Complexes

“…Experiments were performed on our modernized instrument described previously. , The flash photolysis setup is provided with a Continuum Surelite I 10 Hz Q-switched Nd:YAG laser with the second harmonic generators to excite the samples at 532 nm with pulses of 15 mJ. The signals are captured by a Hamamatsu 928 photomultiplier into a WaveSurfer 600 MHz LeCroy oscilloscope.…”

Spectral and Kinetic Properties of Radicals Derived from Oxidation of Quinoxalin-2-One and Its Methyl Derivative

“…3-Methylquinoxalin-2(1 H )-one (3-methyl-2-quinoxalinol, 3-MeQ) was prepared by the classical reaction of the corresponding o -phenyldiamine (1 mmol) by adding dropwise methyl pyruvate (1.2 mmol) and triethylamine (3 mmol) in ethanol. A detailed description of the synthesis, purification and spectral characterization has been given elsewhere [34]. All solutions were made with water triply distilled provided by a Millipore Direct-Q 3-UV system.…”

“…Recently, the stable products resulting from the photoreduction of six 7-substituted- 3-methyl-quinoxalin-2(1 H )-one derivatives (substituents: H 3 CO-, H 3 C-, F-, H-, CF 3 -, CN-) by α-amino-type radicals derived from N -phenylglycine (PhNHCH 2 • ) in acetonitrile solutions have been identified. Moreover, spectral and kinetic characteristics of the intermediate species: triplets ( 3 Q), radical anion (Q •− ) and hydrogenated neutral radicals (QH • ) have been obtained by laser flash photolysis in the presence of DABCO and N -phenylglycine (NPG) [34].…”

Radiation-induced reduction of quinoxalin-2-one derivatives in aqueous solutions

“…The stable product resulting from the recombination of the former radical with the phenyl-aminoalkyl radical (PhNHCH 2  ) was unambiguously identified (De la Fuente et al, 2013). What is more, protonation of the nitrogen atom N4 was postulated during a pH dependent two-electron reduction process of quinoxalin-2-ones (Zimpl et al, 2012).…”