General Copper-Catalyzed Coupling of Alkyl-, Aryl-, and Alkynylaluminum Reagents with Organohalides

Abstract

We report the first example of a very general Cu-catalyzed cross-coupling of organoaluminum reagents with organohalides. The reactions proceed for the couplings of alkyl-, aryl-, and alkynylaluminum reagents with aryl and heteroaryl halides and vinyl bromides, affording the cross-coupled products in good to excellent yields. Both primary and secondary alkylaluminum reagents can be utilized as organometallic coupling partners. These reactions are not complicated by β-hydride elimination, and as a result rearranged products are not observed with secondary alkylaluminum reagents even for couplings with heteroaryl halides under "ligand-free" conditions. Radical clock experiment with a radical probe and relative reactivity study of Ph3Al with two haloarenes, 1-bromonaphthalene and 4-chlorobenzonitrile, having two different redox potentials indicates that the reaction does not involve free aryl radicals and radical anions as intermediates. These results combined with the result of the Hammett plot obtained by reacting Ph3Al with iodoarenes containing p-H, p-Me, p-F, and p-CF3 substituents, which shows a linear curve (R(2) = 0.99) with a ρ value of +1.06, suggest that the current transformation follows an oxidative addition-reductive elimination pathway.

Rotation-Triggered Transmetalation on a Heterobimetallic Cu/Al N-Phosphine-Oxide-Substituted Imidazolylidene Complex

“…These results demonstrate the following points: (i) an additional ligand for Cu is essential for the transmetalation between Al­(C 6 F 5 ) 3 under the applied conditions, and NHCs are appropriate in this context. (ii) The addition of phosphine oxide effectively promotes the transmetalation between the Cu–heteroatom and Al–C bonds, while the generation of organoaluminate species upon the addition of Lewis bases such as alkyl amido anions, carbanions, or Cl – has been reported to be critical in the reported examples . (iii) One critical benefit of constructing such intramolecular heterobimetallic systems rather than intermolecular systems is their excellent efficiency to afford the transmetalated products (e.g., Figure A vs eq 3 in Scheme ), as the collision of Cu–O t Bu and Al–C 6 F 5 moieties should be preprogrammed under such intramolecular conditions.…”

Retaining Alkyl Nucleophile Regiofidelity in Transition-Metal-Mediated Cross-Couplings to Aryl Electrophiles

“…One such metal that has been used accordingly is copper. 91 The group of Giri has focused on utilizing copper salts in conjunction with various C-Al reagents, spanning aryl, alkyl, and alkynyl nucleophiles. Interestingly, secondary alkyl nucleophiles are also tolerated without any detectable isomerization (Scheme 40).…”

Emergence of Copper‐Mediated Formation of C–C Bonds

“…Using this catalytic system, they reported coupling between alkyl‐, aryl‐, or alkynylaluminum reagents and aryl or heteroaryl halides or vinyl bromides (Scheme ) . This catalytic system was also employed in the Hiyama reaction for coupling between aryl iodides and aryltriethoxysilanes (Scheme ) . These two reactions were illustrated by various examples, with modest to very good yields.…”