Nickel-catalyzed substitution reactions of propargyl halides with organotitanium reagents

Abstract

A simple and mild catalytic coupling reaction of propargyl halides with organotitanium reagents is reported. The reaction of propargyl bromide with organo-titanium reagents mediated by NiCl2 (2 mol%) and PCy3 (4 mol%) in CH2Cl2 afforded coupling product allenes in good to excellent yields (up to 95%) at room temperature. However, NiCl2(PPh3)2 was the best catalyst for substituted propargyl halides to yield allenes or alkynes preferentially. On the basis of the experimental results, a possible catalytic cycle has been proposed.

NiI Catalyzes the Regioselective Cross‐Coupling of Alkylzinc Halides and Propargyl Bromides to Allenes

“…[1] Pd, [2] Cu, [3] Rh, [4] Fe, [5] and Ni [6] derivativesh ave been used as catalysts in these reactions for the activation of propargylh alides, esters, carbonates,a nd phosphonates. [1] Pd, [2] Cu, [3] Rh, [4] Fe, [5] and Ni [6] derivativesh ave been used as catalysts in these reactions for the activation of propargylh alides, esters, carbonates,a nd phosphonates.…”

Iron‐Catalyzed Coupling of Propargyl Bromides and Alkyl Grignard Reagents

“…This approach constitutes a convenient method since formation of the allene occurs along with C–C bond formation. Pd, Cu, Rh, Fe, and Ni derivatives have been used as catalysts in these reactions for the activation of propargyl halides, esters, carbonates and phosphonates. We recently reported the formation of allenes by Ni‐catalyzed coupling of propargyl bromides and alkylzinc regents .…”

Cooperative Ni/Cu‐Catalyzed Asymmetric Propargylic Alkylation of Aldimine Esters

“…The catalytic cycles begin with the Ni-mediated decarboxylation of the propargylic carbonate 1 to afford the electrophilic allenylnickel complex I (top cycle). [15,16] Simultaneously, the coordination of the copper catalyst to aldimine ester 2 gives rise to the nucleophilic metalated azomethine ylide II (below cycle). [17] At this point, the Cu-coordinated azomethine ylide II can undergo nucleophilic substitution of the in situ formed allenylnickel complex I, followed by acid hydrolysis to furnish the final propargylated product 3.…”

“…[12] In particular, bimetallic catalysis could give rise to fundamentally new reactivity capable of providing access to currently inaccessible reaction pathways. [13,14] Our reaction design involves a cooperative strategy involving nickel catalysis [15,16] and copper catalysis [17] to provide a powerful route to access enantioenriched aquaternary amino acids. [18] To date, the asymmetric apropargylation of amino esters with propargylic alcohol derivatives bearing internal alkyne groups poses a significant challenge, [19] while the resulting a-quaternary propargylated amino acids and their derivatives are the common motifs in a range of biologically active natural products and pharmaceuticals (Scheme 1).…”

“…However, no improvement in yield and enantioselectivity was observed for the reaction by screening different chiral PHOX ligands (entries 11-13), which implies that the ferrocene subunit of ligand 5 plays an important role in the catalytic system. We next investigated the influence of achiral ligands on the outcome and in particular the enantioselectivity of the reaction (entries [14][15][16][17]. The use of achiral ligand 5 g or rac-5 c resulted in a marked decrease in the enantioselectivity (entries 14 and 15), while the achiral bidentate phosphine ligand 4 d or rac-4 a exhibited similar catalytic activity, albeit with slightly reduced enantioselectivity (entries 16 and 17).…”