Transition Metal-Catalyzed Activation of Aliphatic C−X Bonds in Carbon−Carbon Bond Formation

Aus der Sicht des Synthetikers: Palladiumkomplexe N‐heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

“…Methode A: 1 oder Chloralkanen; [133,134] 2) wegen des Platzbedarfs der NHCs ist ebenso wie bei sperrigen Phosphanen die reduktive Eliminierung erleichtert; [135,136] 3) wegen der starken Pd-NHC-Bindung und den wenigen möglichen Zerfallswegen bleibt das Metall, selbst wenn nur ein einziger NHC-Ligand koordiniert ist, sicher in einem löslichen, katalytisch aktiven Zustand. Durch die besonderen Komplexierungseigenschaften von NHCs an Pd sind also definierte Komplexe synthetisierbar, die leicht aktiviert werden können und gegenüber in situ hergestellten Komplexen viele Vorteile bieten.…”

Highly Selective Palladium‐Catalyzed Oxidative Csp2Csp3 Cross‐Coupling of Arylzinc and Alkylindium Reagents through Double Transmetallation

“…When R alkyl X was the electrophile, the success was more limited due to the difficult oxidative addition of R alkyl X towards metal catalysts, and the fast but deleterious b-H elimination. [6][7][8][9] Recently, pioneered by Fu, Organ and Nolan etc., cross-coupling reactions involving R alkyl X were revolutionized by employing electronrich and sterically hindered phosphine ligands or carbene ligands, and showed good potential in organic synthesis. [7,[10][11][12][13][14][15][16][17][18][19][20] With our strong interest in Csp 3 -related coupling reactions, we recently developed an oxidative crosscoupling reaction (shown in Scheme 1 B), in which two nucleophiles, prepared readily from inexpensive and abundant organic chlorides, could be coupled together in the presence of an oxidant, A À B.…”

An Electron‐Deficient Diene as Ligand for Palladium‐Catalyzed Cross‐Coupling Reactions: An Efficient Alkylation of Aryl Iodides by Primary and Secondary Alkylzinc Reagents

“…[8][9][10][11][12][13][14][15][16][17][18][19][20] However, Csp 3 -related bond formations are still immature due to sluggish reductive elimination and competitive fast b-hydride elimination, although the methodologies, especially those invovling Csp 3 À Ar bond formations, are of great importance both in laboratory synthesis and industrial application. 10,21,22 Two options are viable for construction of the Csp 3 À Ar bond utilizing cross-coupling methods. One is to use Csp 3 À X as electrophile and ArM as nucleophile, which would involve oxidative addition of Csp 3 À X to Pd(0).…”

“…Recent applications of electron-rich and sterically hindered phosphine and carbene ligands have enabled the difficult oxidative addition of Csp 3 À X, [23] but the formed Csp 3 À Pd species is exposed to the risk of b-H elimination at the initial step and the electronic properties of the ligands are disadvantageous to the reductive elimination step. [22] The other option is to use ArX as the electrophile and Csp 3 M as the nucleophile, in which the oxidative addition of ArX to Pd(0) to form II is facile, but after transmetallation with a secondary alkylzinc reagent, the resultant complex III might undergo reductive elimination to afford the desired product IV (path a), or b-H elimination to form V (path b). Since the alkyl group is a good sigma donor ligand, the reductive elimination path is not easy.…”