Photoredox-Catalyzed Hydrodifluoroalkylation of Alkenes Using Difluorohaloalkyl Compounds and a Hantzsch Ester

Abstract

Photoredox-catalyzed hydrodifluoroalkylation of alkenes proceeded smoothly in the presence of a Hantzsch ester as a hydrogen source under visible light irradiation. The reaction was also applicable to the hydrodifluoroalkylation of alkynes, and a continuous photo flow reaction was also successful.

Visible‐Light‐Driven Intermolecular Reductive Ene–Yne Coupling by Iridium/Cobalt Dual Catalysis for C(sp3)−C(sp2) Bond Formation

“…Then, the Co II salt may be reduced in situ to Co I species by the photocatalyst . Next, considering that the HE can contribute in both SET and HAT processes, a hydrogen atom transfer from the radical cation A to Co I could afford the Co II −H complex . Here, it is assumed that DMAP would facilitate the deprotonation of A to give B .…”

“…Next, considering that the HE can contribute in both SET and HAT processes, a hydrogen atom transfer from the radical cation A to Co I could afford the Co II −H complex . Here, it is assumed that DMAP would facilitate the deprotonation of A to give B . The acrylate could undergo migratory insertion in to Co−H giving the five‐membered metallacycle C .…”

“…Then, we turnedo ur attentiont oe asily accessible and bench-stable Hantzsch esters (HEs), [13] which over the last decadeh ave emerged as key electron [14] and proton [15] donors in av ariety of challenging photoredoxr eactions. HEs can be readily converted in to the corresponding pyridines by means of as tepwise pathway by either single electron transfer (SET) followed by hydrogen atom transfer (HAT) or vice versa.…”

Alkene Carboarylation through Catalyst‐Free, Visible Light‐Mediated Smiles Rearrangement

“…We envisaged ar eaction wherebyaphotocatalyst could undergo oxidative quenching by ethyl bromodifluoroacetate 6 (E red = À0.57 Vv s. SCE) [10] to yield an electrophilic radical speciest hat could undergo addition to an unactivated alkenes uch as 7 bearing as ulfonamide residue. The bromodifluoroacetate moiety providesastable radical that has been widelye xploited in photoredox catalysis, [11] and introducesavaluable gem-difluoro groupi nto the reactionp roducts. The resulting secondarya lkyl radical 8 is then in a1 ,5-relationship to the ipso position on the aryl ring, allowing Truce-Smiles rearrangement to take place.…”

“…[15] Ethyl difluorobromoacetate 6 has been widely employed in intermolecular difluoroalkylation reactionsu sing ruthenium and iridium photoredox catalysis (usually in the presence of an inorganic base). [11] Likewise, its facility as af luoroalkyl radical precursor in S RN 1p rocesses is well-known, [16] but with the usual requirement for metal salts to promote the initial electron-transfer event.H owever,anumber of visible light photochemicalm etal-free systemsh ave recently being reported [17] for 6 and relatedh aloalkanes that use tertiary amine donors as reductants. To elucidateh ow the ethyl bromodifluoroacetate startingm aterialc ould be reduced in our process, we studied its interaction with TMEDA by 19 FNMR (Table 2).…”