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Construction of 3-Oxazolin-5-one via Visible Light-Induced Nondecarboxylative Coupling and Sequential Reactions

Shanshan Ma, Haoying Cao, Rongwan Gao, Yanhong Feng, Yawen Guo, Wei Guan*, Xinfang Duan* and Peng Jiao*

*Northeast Normal University, Changchun 130024; Beijing Normal University, Beijing 100875, P. R. China, Email: guanw580nenu.edu.cn, xinfangduanvip.163.com, pjiaobnu.edu.cn

S. Ma, H. Cao, R. Gao, Y. Feng, Y. Guo, W. Guan, X. Duan, P. Jiao, Org. Lett., 2023, 25, 2098-2102.

DOI: 10.1021/acs.orglett.3c00469



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Abstract

Photocatalysis enables a straightforward synthesis of 3-oxazolin-5-ones from redox-active esters and secondary nitro compounds. Visible light-induced nondecarboxylative coupling of a redox-active ester, nitro aldol condensation, and subsequent visible light-induced N-oxide deoxygenation were accomplished within 2 h.

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proposed mechanism



Photochemical set-up

A LED tube (inner diameter and height of 10 cm) was used as the lighting device for all photochemical reactions. The length of white, blue or green LED strip is 1.5 meters and the power is 15 W. The reaction temperature is controlled at about 25 C by a small desk fan.

Typical procedure

A dry Schlenk tube charged with a stirring bar was evacuated and backfilled with N2 (three times). 2-Nitropropane (100 μL, 1.12 mmol), TBD (312 mg, 2.24mmol) and anhydrous acetonitrile (10.0 mL) were added via gastight syringe under N2 atmosphere. The mixture was stirred for 30 min at 50 C (oil bath) before fac-Ir(ppy)3 (7 mg, 1 mol %) and 2-phenylacetic acid NHP ester (632 mg, 2.24 mmol) were added. The reaction mixture was degassed by freeze-pump-thaw method and then stirred under irradiation with blue LEDs (460 nm, approximately 3.0 cm distance from the tube). The mixture was maintained at approximately 25 C by a desk fan in air-conditioned room. The reaction was monitored by TLC. Upon completion (2 h), the mixture was concentrated in vacuo. The crude product was purified by flash chromatography on silica gel (50:1 hexanes/AcOEt).


Key Words

N-heterocycles, O-heterocycles, photochemistry


ID: J54-Y2023