Flow Electrochemical Cyclizations via Amidyl Radicals: Easy Access to Cyclic Ureas

Aggeliki Vgenopoulou,Nisar Ahmed

doi:10.1055/s-0037-1611772

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.

Highlights

We have investigated urea derivatives that allow the generation of N-centered radicals under electrochemical reaction conditions in an undivided cell
Flow electrosynthesis performed in microreactors offers a number of benefits, allowing reactions to be performed in a more convenient and safer manner,[2] and even allow electrochemical reactions to take place without a supporting electrolyte due to a very short interelectrode distance[3] that results in the two diffusion layers of the electrodes becoming ‘coupled’, allowing ions to be electrogenerated and play the role of the electrolyte
Continuous-flow electrochemistry has the potential to act as a new enabling technology to replace some aspects of conventional batch electrochemical processes.[4]

Summary

Ph N N Ar

We have investigated urea derivatives that allow the generation of N-centered radicals under electrochemical reaction conditions in an undivided cell These nitrogen radicals react with alkenes and the resulting carbon radicals can be trapped with 2,2,6,6-tetramethylpiperidine1-oxyl (TEMPO) resulting in the addition of a nitrogen and an oxygen atom to the double bond. In this way, we have synthesized various cyclic ureas derivatives in a batch electrochemical process (Scheme 1, Eq (2)).[8] to facilitate access to these cyclic ureas, we decided to apply flow conditions, by replacing the inorganic base Na2CO3 with the organic base Triton B. We have contributed to this development by reporting an electrochemi-

Ar N

NN O