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

Abstract

Rather u(Ni)que: Two new C-H alkenylation reactions, that is C-H/C-O alkenylation and decarbonylative C-H alkenylation, of azoles are uniquely catalyzed by Ni/dcype. These azole alkenylation reactions are successfully applied to the convergent formal synthesis of siphonazole B.

High-Valent Co(III)- and Ni(II)-Catalyzed C–H Activation

“…During their studies into C-H/C-O couplings, Itami and coworkers found that, under identical reaction conditions, when an aryl or alkenyl ester is used, rather than pivaloyl esters, a decarbonylative coupling was observed (Chart 8) [81,82]. The authors propose this reaction proceeds via oxidative addition into the C (acyl) -O bond, followed by decarbonylation and C-H activation to generate the bisarylated nickel(II) species.…”

Toward an Ideal Synthesis of (Bio)molecules through Direct Arene Assembling Reactions

“…For example, we demonstrated the coupling of benzoxazole (80) with styryl pivalate (102), carbamate (102¤), and phenyl cinnamate (103) as alkenylating agents (Scheme 29). 40 Thus, 80 was coupled with 102 (1.5 equiv) in the presence of Ni(cod) 2 (10 mol %), dcype (20 mol %), and K 3 PO 4 (2.0 equiv) in 1,4-dioxane at 130°C to produce 104 in 47% yield (CH/CO alkenylation). When styryl carbamate (102¤) was used instead of pivalate 102, 104 was obtained in 77% yield.…”

“…Thiazole (42) was coupled with iodobenzene under Pd(OAc) 2 /CuI catalysis 22 to give 2-phenylthiazole (40) in 72% yield. Thereafter, palladium-catalyzed C4-selective CH arylation of 40 with p-tolylboronic acid (14b) was conducted under the influence of Pd(OAc) 2 /phen/ TEMPO/LiBF 4 to furnish the corresponding 2,4-diarylthiazole 41b in 75% yield with >95% regioselectivity.…”

Synthesis of Natural Products and Pharmaceuticals via Catalytic CH Functionalization

“…Meanwhile, in 2013, Yamaguchi, Itami, and coworkers reported a C-H alkenylation of 1,3-azoles with enol derivatives (C-H/C-O type alkenylation) or alkenyl esters (decarbonylative C-H alkenylation) as electrophiles and applied this strategy to the formal synthesis of siphonazole B (Scheme 16.29b) [63]. Oxazole 137 was coupled with enol derivative 144 under their nickel catalytic system using the dcype ligand to form alkenyl oxazole 145 in 72% yield by C-H alkenylation at the C2 position of oxazoles.…”