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Photodecarboxylative C-H Alkylation of Azauracils with N-(Acyloxy)phthalimides

Satya Prakash Panda, Sudhir Kumar Hota, Rupashri Dash, Lisa Roy and Sandip Murarka*

*Department of Chemistry, Indian Institute of Technology Jodhpur, Karwar, Rajasthan 342037, India, Email: sandipmurarkaiitj.ac.in

S. P. Panda, S. K. Hota, R. Dash, L. Roy, S. Murarka, Org. Lett., 2023, 25, 3739-3744.

DOI: 10.1021/acs.orglett.3c01210



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Abstract

The combination of NaI/PPh3/TMEDA mediates a direct C-H alkylation of azauracils using N-(acyloxy)pthalimides (NHPIs) as readily available alkyl surrogates under visible light irradiation. This transition-metal-free reaction offers a broad scope, scalability, and appreciable functional group tolerance.

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proposed mechanism



General Procedure for the Preparation of NHPI Esters

The corresponding alkyl carboxylic acid (10 mmol, 1.0 eq.), N-hydroxyphthalimide (11 mmol, 1.1 eq.), and 4-dimethylaminopyridine (1.0 mmol, 10 mol%) were mixed in a flask with a magnetic stirring bar. Dry DCM (40 mL) was added. Then a solution of N,N'-dicyclohexylcarbodiimide (11.0 mmol, 1.1 eq.) in DCM (15 mL) was added slowly at room temperature. The reaction mixture was monitored by TLC at room temperature. After completed, the white precipitate was filtered off and the solution was concentrated under vacuum. Corresponding redox active esters were purified by column chromatography on silica gel (DCM or petroleum ether/ethyl acetate as eluent).

Representative General Procedure for the visible light-mediated photoredox-catalyzed Reaction

Azauracil derivative (0.25 mmol, 1 equiv), alkyl NHPI ester (0.3 mmol, 1.2 equiv), NaI (0.25 mmol, 1 equiv), PPh3 (0.05 mmol, 0.2 equiv), and TMEDA (0.375 mmol, 1.5 equiv) were added in a pre-dried 10 ml Schlenk tube under N2 atmosphere. The tube was degassed and purged with N2 three times. Then dry acetonitrile (2.5 mL) was added under the N2 atmosphere. The resulting reaction mixture was allowed to stir for 5 h at room temperature under the irradiation of 40 W Kessil blue LED (427 nm) lamp. After completion (5 h), the reaction mixture was concentrated under vacuum and purified by silica gel column chromatography using 10-20% ethyl acetate in hexane to afford the desired product


Key Words

N-heterocycles, photochemistry


ID: J54-Y2023