Alkene Difunctionalization Triggered by a Stabilized Allenyl Radical: Concomitant Installation of Two Unsaturated C−C Bonds

Abstract

Radical‐mediated difunctionalization of alkenes provides a promising approach to introduce one alkenyl or alkynyl group to target compounds. However, simultaneous installation of two unsaturated C−C bonds via alkene difunctionalization remains elusive, attributable to the high instability and transient lifetimes of alkenyl and alkynyl radicals. Herein, we report the photocatalytic 1,2‐alkynylalkenylation and 1,2‐enynylalkenylation of alkenes for the first time, triggered by the intermolecular addition of a stabilized allenyl radical to an alkene. A portfolio of strategically designed, easily accessible dual‐function reagents are applied to a radical docking‐migration cascade. The protocol has broad substrate scope and efficiently increases the degree of unsaturation.

Synthesis of Tetrasubstituted Allenes via Visible-Light-Promoted Radical 1,3-Difunctionalization of Alkynyl Diazo Compounds

“…The high reactivity of short-lived allenyl radicals and the lack of convenient methods for their generation might be the underlying obstacles for such neglect. Because allenylic precursors for producing allenyl radicals are usually difficult to prepare, current methods critically depend on the tautomerization of propargyl radicals, which can be generated from their propargylic derivatives or via radical addition to 1,3-enynes (Scheme a) . However, the EPR spectral studies indicate that the unpaired electron prefers to populate the propargyl rather than the allenic structures .…”

Allenyl Radicals in Organic Synthesis: Challenges and Recent Advances

“…In 2021, Zhu's group developed the first photocatalytic 1,2‐alkynylalkenylation and 1,2‐enynylalkenylation of alkenes, triggered by the addition of a stabilized allenyl radical to an alkene (Scheme 20). [36] This reaction featured a decent scope of alkenes, in which both activated and unactivated alkenes were readily tolerated. The obtained allenes complemented the library of complex unsaturated molecules with high unsaturation degree, which are otherwise difficult to access.…”

A regiodivergent Truce–Smiles rearrangement: a strategy for the synthesis of arylated indoles promoted by KN(SiMe3)2

“…To our knowledge, there are only a few examples of T-S rearrangements wherein a vinyl group undergoes the migration. [80][81][82] To exam the ability of the styrenyl group to participate in this process, we prepared the β-styrenyl sulfenyl-containing substrate. When exposed to reaction conditions with KN(SiMe 3 ) 2 and diamine ligand, indole formation was followed by T-S β-styrenyl group transfer producing the vinyl-containing product 3aE in 59% yield.…”