Pd-Catalyzed Triple-Fold C(sp²)-H Activation with Enaminones and Alkenes for Pyrrole Synthesis via Hydrogen Evolution

Leiqing Fu, Yunyun Liu* and Jie-Ping Wan*

*College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022, P. R. China, Email: chemliuyunyunjxnu.edu.cn, wanjiepingjxnu.educn

L. Fu, Y. Liu, J.-P. Wan, Org. Lett., 2021, 23, 4250-4255.

DOI: 10.1021/acs.orglett.1c01301

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Abstract

A Pd-catalyzed annulation of enaminones and alkenes provides various NH-free pyrroles via activation of multiple C(sp²)-H bonds. The evolution of hydrogen has been confirmed by a hydrogen detector.

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proposed mechanism

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General procedure for the pyrrole synthesis with enaminones and alkenes

To a 25 mL round-bottom flask were added enaminone 1 (0.2 mmol), acrylate 2 (0.7 mmol), PdCl₂ (0.02 mmol), CuBr₂ (0.2 mmol), AgOAc (0.03 mmol) and DMF (0.5 mL). Then, the mixture was stirred at 60 °C with oil bath heating for 12 h. Upon completion, the vessel was allowed to cool down to room temperature. After 5 mL of saturated brine was added, the resulting mixture was extracted with ethyl acetate (3 × 8 mL). The organic phases were combined and washed with small amount of water for three times. After drying with anhydrous Na₂SO₂, the solid was filtered and the solvent in the acquired solution was removed under reduced pressure. The resulting residue was subjected to flash silica gel column chromatography to provide pure products with the elution of mixed petroleum ether/ethyl acetate (v /v = 5:1-3:1).

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Key Words

Pyrroles, Copper(II) Compounds

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ID: J54-Y2021