Boryl Radical‐Mediated C−H Activation of Inactivated Alkanes for the Synthesis of Internal Alkynes

Abstract

An intriguing pyridine‐boryl radical‐mediated C−H alkynylation reaction of inactivated alkanes was described. The reaction features mild operation condition and wide substrate scope, and affords the corresponding products in moderate to good yields. Notably, The presence of 4‐cyanopyride N‐oxide was key to the success of the reaction. Cyclohexane are more easily to be functionalized in this reaction than toluene, which could be rationally explained by polarity‐match principle.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

“…Particularly, substrates bearing halogen atoms are compatible in the present case (Scheme C). Recently, a follow-up study of the oxidative C­(sp 3 )–H bond activation of inactivated alkanes 71 - 15 for the synthesis of internal alkynes was developed under the boryl-radical-mediated conditions (Scheme D) …”

“…Recently, a follow-up study of the oxidative C(sp 3 )−H bond activation of inactivated alkanes 71-15 for the synthesis of internal alkynes was developed under the boryl-radical-mediated conditions (Scheme 71D). 240 Based on this strategy, with Cu(OTf) 2 as the catalyst, an approach for the remote C(sp 3 )−H alkynylation of N-fluorosulfonamides was developed by Wu and collaborators. The carbon radical 72-6, which is generated from nitrogen-radicalmediated [1,5]-HAT (via intermediate 72-5), goes through an addition/fragmentation reaction with various acetylene sulfones (Scheme 72).…”

SOMOphilic Alkynylation of Unreactive Alkenes Enabled by Iron-Catalyzed Hydrogen Atom Transfer

“…In 2019, Studer and coworkers utilized alkyl allyl sulfones as alkyl radical precursors to accomplish desulfonylative C ( sp 3 )–C ( sp ) bond coupling initiated by 2, 2′-azobis (2-methylpropionitrile) (AIBN) [ 33 ]. Moreover, some alkanes or functionalized alkanes could be directly converted into internal alkynes with acetylenic sulfones via the diversity of the radical-mediated C–H bond alkynylation process [ 34 , 35 , 36 , 37 , 38 , 39 ]. Although remarkable achievements have been made in this research area, some of the reactions suffer from several limitations, such as the utilization of expensive catalysts or peroxides and the narrow scope of substrates and prolix procedures for the preparation of the radical precursors.…”

B2pin2-Mediated Cascade Cyclization/Aromatization Reaction: Facial Access to Functionalized Indolizines

“…On the basis of literature precedents and the above experiment results, a tentative mechanism was proposed in Scheme . Initially, a direct homolytic cleavage of B 2 pin 2 assisted by 4-cyanopyridine ( 2a ) generated the 4-cyanopyridine-boryl radical A . , This species A would couple with enaminone 12 via reversibly mediating the transfer of the boronyl radical to afford the ketyl radical complex B .…”