CH Alkenylation of Azoles with Enols and Esters by Nickel Catalysis

Abstract

Transition metal catalyzed alkenylation is one of the most reliable methods for making alkenyl-substituted arenes as exemplified by the Mizoroki-Heck reaction. [1] Recently, direct CÀH alkenylation [2] has received growing interest as an emerging tool for constructing alkenylated arenes and particularly alkenylated heteroarenes, since they are predominant motifs in biologically active natural products, pharmaceuticals and organic materials (Scheme 1 a). [3] Representative reaction types of CÀH alkenylation include (Scheme 1 b): 1) CÀH/CÀX alkenylation (X = halogens including triflates) of heteroarenes with alkenyl halides by using palladium and copper catalysts, [4] 2) CÀH/CÀH alkenylation (oxidative Mizoroki-Heck reaction) of heteroarenes with simple alkenes by using palladium and rhodium catalysts, [5] and 3) C À H addition of heteroarenes to alkynes by transitionmetal catalysts. [6] There also exist other CÀH couplings which are outside the realm of the above-mentioned category. [7] Meanwhile, our group has developed a number of unique C À H arylation reactions of heteroarenes catalyzed by transition-metal complexes. [8][9][10] For example, we recently discovered the first nickel-catalyzed C À H/C À O coupling of heteroarenes and phenol derivatives [10a] as well as a decarbonylative CÀH coupling between heteroarenes and aryl esters. [10b] These catalytic processes are unique among other CÀH arylation methods not only because they allow incorporation of unconventional aryl electrophiles in C À H arylation (phenol derivatives and arenecarboxylates), but also because these reactions are uniquely promoted by an enabling supporting ligand, 1,2-bis(dicyclohexylphosphino)ethane (dcype), on a nickel(0) catalyst (other closely related ligands display extremely low or no promoting effect in these catalyses).Based on these auspicious discoveries, we questioned whether unprecedented C À H alkenylations of heteroarenes would become possible with a Ni/dcype catalyst by using enol derivatives [Scheme 1 b, 4)] and a,b-unsaturated esters [Scheme 1 b, 5)] as alkenylation agents. The CÀH/CÀO alkenylation of heteroarenes is rare, [11] and the decarbonylative CÀH alkenylation is thus far unknown. Herein, we report the CÀH Scheme 1. a) Useful alkenyl-substituted heteroarenes. b) A classification of the type of direct CÀH alkenylation of heteroarenes.

Nickel-catalysed retro-hydroamidocarbonylation of aliphatic amides to olefins

“…Initial studies involved the evaluation of decarbonylative elimination of substrate 1 by acyl C–N bond activation ( Table 1 ). This compound was chosen as the model substrate because of its structure, containing both ester 32 33 34 35 36 37 38 39 and amide group, and selective activation of amide C–N bond was very meaningful. In the presence of 10 mol% Ni(COD) 2 , 20 mol% ICy·HCl, 20 mol% NaO t Bu and 3.0 equiv K 3 PO 4 , at 130 °C under an argon atmosphere in toluene, we indeed observed the desired product 2 in 33% yield after 36 h in GC-MS ( Table 1 , entry 1).…”

Recent advances in the functionalization of azulene through Rh‐, Ir‐, Ru‐, Au‐, Fe‐, Ni‐, and Cu‐catalyzed reactions

“…The potential of iridium catalysts was first demonstrated in the asymmetric hydrogenation of unsaturated organic bonds, including imines and nonfunctionalized alkene bonds, and was later extended to other reactions that have proven to be important in organic synthesis. [18] Iridium catalysts have been tested in this regard for a variety of reactions including isomerization, [19] hydrogenation, [20,21] hydrazine decomposition, hydroarylation reactions via CH activation, and hydrogenolysis reactions. [22][23][24] Because of its ability to produce highly versatile aryl organoboronate ester intermediates from arenes without the use of reactive groups such as halides or sulfonates, iridium-catalyzed CH borylation of arenes has also proven to be a method for the functionalization of arenes.…”

Nickel-Catalyzed C−H Functionalization Using A Non-directed Strategy

“…Itami reported the alkenylation of benzoxazole and oxazoles with enol ethers and a,b-unsaturated esters as coupling partners (Scheme 7D). 95 This coupling was achieved by using a Ni(cod) 2 /dcype catalytic system without the need of a Lewis acid.…”