CC BY 4.0 · SynOpen 2019; 03(01): 46-48
DOI: 10.1055/s-0037-1611772
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Flow Electrochemical Cyclizations via Amidyl Radicals: Easy Access to Cyclic Ureas

a  School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT, UK   Email: AhmedN14@cardiff.ac.uk
b  School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
,
Aggeliki Vgenopoulou
a  School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT, UK   Email: AhmedN14@cardiff.ac.uk
› Author Affiliations
Support from the EU Horizon 2020 project (Grant No 663830) and the School of Chemistry, Cardiff University, UK, is gratefully acknowledged.
Further Information

Publication History

Received: 11 January 2019

Accepted after revision: 03 March 2019

Publication Date:
27 March 2019 (online)

  

Abstract

Flow chemistry has advantages over batch processes and can achieve the synthesis of substances in high yield under safe working conditions. The combination of electrochemistry and flow microreactor technology has made chemical transformations possible without the use of oxidants or catalysts. Herein, we report flow electrosynthesis of cyclic ureas via oxyamination of N-allylic ureas. We have found that continuous flow is able to outperform its batch counterpart, producing cyclic ureas in excellent yields.

Supporting Information

 
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  • 14 General Procedure for Flow ElectrolysisThe N-allylic urea (0.20 mmol) was dissolved in a mixture of acetonitrile/water (19:1, 8.30 mL), then TEMPO (0.30 mmol, 1.5 equiv) and benzyltrimethylammonium hydroxide solution (Triton B, 40% solution in water, 0.21 mmol, 1.1 equiv) were added to the solution, and the mixture was electrolyzed in the electrochemical reactor, fitted with a graphite anode and a platinum cathode and separated by a FEP (fluorinated ethylene propylene) film spacer of 500 (m (0.40 mL inner volume; 3 F, 1–3 V), by using a syringe pump (0.1 mL min–1). After attaining steady flow, the solution (8.0 mL) was collected in a vial after 100 min. The resulting reaction mixture was quenched with saturated aqueous NH4Cl (5 mL), concentrated in vacuo, diluted with water (25 mL), and extracted with ethyl acetate (25 mL). The aqueous phase was extracted with ethyl acetate (3 ( 20 mL), and the extracts were washed with brine. The combined organic layers were dried over anhydrous MgSO4, filtered, and the filtrate concentrated in vacuo. The residue was purified by column chromatography, eluting with hexane/ethyl acetate, 9:1, giving the pure cyclic urea. Spectroscopic data (NMR, MASS) were in agreement with reported data given in reference 8.