Journal
ADVANCED SYNTHESIS & CATALYSIS
Volume 358, Issue 10, Pages 1654-1663Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adsc.201501123
Keywords
flavin; green chemistry; light-emitting diodes (LED); photocatalysis; photooxidation; sulfoxides
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Funding
- Czech Science Foundation [14-09190S]
- German National Science Foundation [GRK 1626]
- National Science Centre of Poland (NCN) [DEC-2012/05/B/ST4/01207]
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We have developed a metal-free process for the aerobic photooxygenation of sulfides to sulfoxides mediated by riboflavin tetraacetate or riboflavin (vitamin B-2) photocatalysts and visible light (450 nm) in an acetonitrile-water (85:15 v/v) mixture. The optimised solvent system leads to both singlet-oxygen and electron-transfer pathways in photooxygenation, thus allowing oxidation of electron-poor and electron-rich thioanisoles, dialkyl sulfides and sterically hindered sulfides. Besides having a broad substrate scope, the method has very short reaction times and requires low catalyst loading (down to 0.1 mol%). These properties are due to the high photocatalyst stability and the extremely high quantum yields (1.3 for thioanisole oxygenation). Moreover, the method is chemoselective, producing only sulfoxides without overoxidation to sulfones. Taking into account the broad substrate scope, high selectivity and high efficiency, this method distinguishes itself from those previously reported. Other advantages include easy work-up of the reaction mixture, the availability and biodegradability of the photocatalysts and mild reaction conditions. We demonstrated, on a preparative scale, its practical application in the synthesis of the psychostimulant modafinil, in the selective oxidation of methionine derivatives, and in the detoxification of mustard gas.
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