Photooxygenation of Heterocycles

Structural analysis of photo-degradation in thiazole-containing compounds by LC–MS/MS and NMR

“…It is proposed that the solid thiazole I underwent photooxygenation by reacting with singlet oxygen ( 1 g ) upon photo-irradiation as in solution, leading to unstable endoperoxides [16]. However, it is known that in solution, the final characteristic rearranged degradation products depend on the heteroatoms, substitution patterns and experimental conditions.…”

“…In addition, the thiazole ring has also been widely used in the synthesis of natural products [12], polymers [13], fluorescent dyes [14], and insecticides [15]. Like other conjugated fivemembered heterocycles (such as furans, thiophenes, pyrroles, indoles, oxazoles, and imidazoles), thiazoles can undergo photo-oxygenation involving singlet oxygen ( 1 g ) under photoirradiation in solution [16] and in the solid state [17]. Although several modes for singlet oxygen reactions have been proposed [18][19][20], the singlet oxygenation of these systems occurs mainly via [4 + 2] Diels-Alder cycloaddition, leading to unstable endoperoxides which, in addition to the classical transformations of peroxides (reduction, hydrolysis, and deoxygenation), afford characteristic rearranged products depending on the heteroatoms, substitution patterns and experimental conditions.…”

Synthesis of Antiviral Tetrahydrocarbazole Derivatives by Photochemical and Acid-catalyzed C-H Functionalization via Intermediate Peroxides (CHIPS)

“…Nevertheless inspired by this discovery, we developed a related oxidative coupling method that utilizes the principle of C-H functionalization via Intermediate PeroxideS (CHIPS) to synthesize pharmaceutically active indole derivatives 16 . Indoles, especially tetrahydrocarbazoles 1, can be easily oxidized to hydroperoxides 2 in the presence of singlet oxygen [17][18][19] , which can be generated using a sensitizer and visible light . Hydroperoxides are also known to undergo acid catalyzed rearrangement reactions as utilized in the industrial synthesis of phenol from cumene, the Hock process 23 .…”

Oxidation of Free L-histidine by tert-Butylhydroperoxide

“…The byproduct(s) responsible for producing the yellow color have not been elucidated in any publications, although its presence has been noted in publications describing protein formulations (1). L-histidine is susceptible to singlet molecular oxygen-mediated photooxidation, which is also known as the "photodynamic effect" (2)(3)(4)(5). The attack by singlet oxygen on Lhistidine occurs at the imidazole ring via unstable endoperoxide intermediates (6,7), resulting in a large variety of products, most of which are unstable and occur as intermediates for the overall reaction.…”