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Unexpected Imidazoquinoxalinone Annulation Products in the Photoinitiated Reaction of Substituted‐3‐Methyl‐Quinoxalin‐2‐Ones with N ‐Phenylglycine
Author(s) -
Fuente Julio R.,
Cañete Álvaro,
Jullian Carolina,
Saitz Claudio,
Aliaga Christian
Publication year - 2013
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12162
Subject(s) - chemistry , annulation , radical , photodissociation , substituent , electron transfer , photochemistry , decarboxylation , photoinduced electron transfer , medicinal chemistry , methyl radical , stereochemistry , organic chemistry , catalysis
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, PhNHCH 2 •, 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(5 H )‐ones, annulation products, 3a–f, were generated; likely by the addition of two PhNHCH 2 • 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.