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Visible-Light 2,4-Dinitrophenol-Mediated Photoannulation of α-Azidochalcones into 2,5-Diaryloxazoles

Uma Devi Newar, Satheesh Borra and Ram Awatar Maurya*

*Applied Organic Chemistry Group, Chemical Sciences & Technology Division, CSIR-North East Institute of Science & Technology (NEIST), Jorhat 785006, India, Email: ram.cdrigmail.com

U. D. Newar, S. Borra, R. A. Maura, Org. Lett., 2022, 24, 4454-4458.

DOI: 10.1021/acs.orglett.2c01691


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Abstract

2,4-dinitrophenol (2,4-DNP) mediates an efficient photoannulation of α-azidochalcones into 2,5-diaryloxazoles under visible-light irradiation. The scope of the reaction was studied by synthesizing a series of 2,5-diaryloxazoles including two naturally occurring oxazoles (Texamine and Balsoxin) in excellent yields.

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proposed mechanism



General procedure for the synthesis of 2,5-diaryloxazoles via photoannulation of α-azidochalcones in presence of 2, 4-dinitrophenol:

In a 50 mL round bottom flask, α-azidochalcone (0.5 mmol) and 2,4-dinitrophenol (0.1 mmol) were dissolved in DCE (6 mL). The reaction mixture was stirred and irradiated with 7 W blue LEDs until the completion of reaction (24 h). Next, the reaction mixture was concentrated to obtain a crude product which was purified by silica gel (100-200 mesh) column chromatography using ethyl acetate / n-hexane in increasing polarity to yield the desired compounds.


Key Words

oxazoles, organocatalysis, photochemistry


ID: J54-Y2022