Radical Chain Isomerization of N-Sulfonyl Ynamides to Ketenimines and Its Application to Furan Dearomatization

Abstract

A radical chain isomerization of N-sulfonyl ynamides to isolable ketenimines is developed, featuring mild reaction conditions, a high efficiency, ∼100% atom economy, a broad substrate scope, and column chromatography-free workup in most cases. Meanwhile, an unprecedented dearomatization of furans is achieved by the radical chain isomerization-triggered aza-Claisen rearrangement, providing highly chemo-, regio-, stereo-, and diastereoselective access to functionalized quaternary nitriles.

Leveraging Propargyl Sulfides as Radical Trappers for the Synthesis of Sulfonyl Allenes

“…[7] In 2021, Zhu and coworkers disclosed the radical chain isomerization of N-sulfonylynamides to ketenimines via the addition of sulfonyl radicals to ynamides. [8] As a result, radical synthesis of allenes from propargylic compounds via CÀ C bond formation has been extensively explored. However, to the best of our knowledge, radical synthesis of allenes from propargylic compounds via Cheteroatom bond formation has been scarcely documented.…”

“…Studer and colleagues reported a example of radical allylation employing a homoallylic alcohol, albeit yielding modestly [7] . In 2021, Zhu and coworkers disclosed the radical chain isomerization of N ‐sulfonylynamides to ketenimines via the addition of sulfonyl radicals to ynamides [8] . As a result, radical synthesis of allenes from propargylic compounds via C−C bond formation has been extensively explored.…”

Investigation of UV Light-Promoted Synthesis of α-Sulfonyl Amides from N-Sulfonyl Ynamides

“…Wudl described in 2006 that ynamide A can undergo upon heating the N-to-C thermal migration of the tosyl group leading to a ketenimine intermediate that can be hydrated to give the α-tosylated amide A′ (Scheme a). More recently, Yuan and Zhu have reported a radical chain isomerization of N -sulfonyl ynamides in the presence of catalytic tosyl chloride and an iridium-based photocatalyst to give stable ketenimines. They showed that this process can be combined with an aza-Claisen rearrangement.…”