α-Sulfonylated ketazine synthesis from vinyl azides and sodium sulfinates using CAN: radical C–S/N–N coupling cascade as a key reaction pathway

Abstract

Synthesis of α-sulfonylated ketazines from vinyl azides and sodium sulfinates proceeding via radical C–S/N–N coupling cascade has been developed. The cascade starts from the generation of sulfonyl radicals through RSO₂Na oxidation by cerium(IV) ammonium nitrate (CAN). Their addition to the double bond of vinyl azides, followed by N₂ elimination, leads to the formation of iminyl radicals, whose N–N coupling provides α-sulfonylated ketazines in yields up to 96%. This process represents one of the rare facets of iminyl radical reactivity, namely, N–N radical coupling while bypassing their reduction, intramolecular cyclization, and 1,n-HAT that are typical for them. The EPR-spectra study and quantum chemical calculations revealed that the selective N–N coupling of iminyl radicals was facilitated by the inertness of Ce(III) towards coordination with iminyl radicals and the inaccessibility of charge transfer. In contrast, Mn(II) coordinates with iminyl radicals and converts them into enamines.