E -Olefins through intramolecular radical relocation

Abstract

Full control over the selectivity of carbon–carbon double-bond migrations would enable access to stereochemically defined olefins that are central to the pharmaceutical, food, fragrance, materials, and petrochemical arenas. The vast majority of double-bond migrations investigated over the past 60 years capitalize on precious-metal hydrides that are frequently associated with reversible equilibria, hydrogen scrambling, incompleteE/Zstereoselection, and/or high cost. Here, we report a fundamentally different, radical-based approach. We showcase a nonprecious, reductant-free, and atom-economical nickel (Ni)(I)-catalyzed intramolecular 1,3-hydrogen atom relocation to yieldE-olefins within 3 hours at room temperature. Remote installations ofE-olefins over extended distances are also demonstrated.

Visible‐Light Controlled Divergent Catalysis Using a Bench‐Stable Cobalt(I) Hydride Complex

“…No conversion was observed in the dark without pinacolborane. Although alkene isomerisation has been reported with a wide array of metal catalysts including non‐noble metal examples with nickel or cobalt, we believed that this method compares well, requiring no additional co‐catalysts, ligands or bases . It is noteworthy that few existing alkene isomerisation methods are reported to isomerise this particular electron‐deficient substrate …”

Positional and Geometrical Isomerisation of Alkenes: The Pinnacle of Atom Economy

“…Anon-precious nickel(I) dimer catalyst has been developed by Schoenebeck and co-workers to enable the positional isomerisation of allyl benzenes to generate E-configured styrenes (Scheme 8). [46] Predicated on am etalloradical induced intramolecular 1,3-H atom relocation, the formation of simple styrenes was achieved with high E-stereoselectivity in the presence of ab road range of functionalities.T his mechanistic paradigm was extended to long-chain isomerisation with predominant formation of the styrenyl product observed over ac hain distance of up to 9 carbons.C omplete geometrical selectivity was observed in most substrates highlighting the importance of this scientific advance. Overcoming the thermodynamic driving forces that dictate positional selectivity in the aforementioned reactions renders controlled monoisomerisation extremely challenging.…”

Tackling Remote sp3 C−H Functionalization via Ni‐Catalyzed “chain‐walking” Reactions

“…[47] Recently, Schoenebeck and co-workers have disclosed the olefin isomerization of industrially relevant olefins catalyzed by a chlorobridged dimeric nickel complex supported by electron-rich NHC ligand L2 (Scheme 20). [48] Control experiments and DFT calculations ruled out the intervention of either (L2) 2 Ni(0) or (L2)Ni(II)(H)Cl and suggested a pathway consisting of a radical-based [1,n]À H shift via open shell, monomeric (L2)Ni (I)Cl species instead. Unfortunately, the non-negligible effect exerted by the ligand on both reactivity and selectivity remains to be elucidated.…”