Na₂S₂O₈‐Mediated Tandem One‐Pot Construction of 3,3‐Disubsituted 3,4‐Dihydroquinoxalin‐2(1H)‐ones with 4‐Alkyl‐1,4‐dihydropyridines as Alkyl Radical Sources

Abstract

Tandem one-pot synthesis of 3,3-disubstituted 3,4dihydroquinoxalin-2(1H)-ones bearing a quaternary carbon center from readily available 1,2-diaminobenzenes, α-ketoesters and 4-alkyl-1,4-dihydropyridines mediated by cheap and stable Na 2 S 2 O 8 has been achieved. This transition-metal-free protocol operates under mild thermal conditions, delivers high product yields for a wide variety of substrates and displays good compatibility with diverse functional groups and facile scalability. Choosing a suitable oxidant and an acid additive is very crucial for the success of this transformation. Mechanistic investigations provide evidence for the involvement of a radical chain mechanism.

Metal-Free Addition of Alkyl Bromides to Access 3,3-Disubstituted Quinoxalinones Enabled by Visible-Light Photoredox Catalysis

“…This reaction likely proceeds via a mechanism involving radical intermediates. Based on previous reports in the literature, ,,, we proposed the mechanism shown in Scheme . Supersilanol is first oxidized by the excited state photocatalyst.…”

“…Traditionally, this can be achieved via nucleophilic addition of an organometallic reagent (Scheme A, Path C) . Recently, Xu and co-workers have reported the use of 4-substituted Hantzsch esters as radical precursors to access these compounds under both thermal and photoredox conditions (Scheme A, Path D) . Notably, however, there were limited examples of primary alkyl groups, all of which were benzyl or α-heteroatom stabilized.…”