<scp>Palladium‐catalyzed</scp> Aerobic Benzannulation of Pyrazoles with Alkynes

Song, Jae Yeong; Jang, Jin Ho; Chuang, Shih‐Ching; Joo, Jung Min

doi:10.1002/bkcs.12175

Cited by 10 publications

(2 citation statements)

References 27 publications

(18 reference statements)

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“…Unless an aryl group is installed at the nitrogen atom of pyrazole, we found that Pd-catalyzed, Cumediated benzannulation of pyrazoles occurred to afford indazole compounds (Scheme 11D). 60,61 In addition to a commonly employed stoichiometric metal oxidant, Cu(OAc) 2 • H 2 O, for benzannulation reactions, oxygen can be used as a green oxidant in the presence of sodium acetate and acetic acid. This aerobic method is extended to the benzannulation of functionalized furans and pyrroles with internal alkynes.…”

Section: Pyrazolementioning

confidence: 99%

Transition-Metal-Catalyzed Divergent C–H Functionalization of Five-Membered Heteroarenes

Jeong

Joo

2021

Acc. Chem. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS: Conversion of common reactants to diverse products is a key objective of organic syntheses. Recent developments in transition-metal-catalyzed C−H functionalization have increased the interest in such conversions. Both the position of functionalization and the type of the substituent can be varied, allowing systematic diversification of common structural cores. Because five-membered heteroarenes (pyrazole, imidazole, thiazole, pyrrole, and thiophene) are ubiquitous in pharmaceuticals and organic functional materials, the selective C−H functionalization of these heterocyclic cores facilitates both the optimization of their physicochemical properties and streamlining of their preparation. In addition, the parent forms of these heterocycles are more readily available and inexpensive than any other derivatives of their families. Hence, their nondirected C−H functionalization is highly desirable. Although various regioselective reactions have been developed, many of them target the most reactive site; hence, except for some extensively studied arylation reactions, regiodivergent functionalization of two or more sites has been limited. This Account summarizes our work on the regiodivergent, nondirected C−H functionalization of five-membered heteroarenes with alkenes and alkynes. These unsaturated hydrocarbons are readily available, and all the composing atoms can be incorporated into products with high atom efficiency. Furthermore, the installed alkenyl groups can be transformed to other useful functional groups.To achieve comparable selectivity to that observed in the traditional reactions of these heteroarenes with highly electrophilic reagents and strong bases, a transition metal catalytic system was carefully devised with a more streamlined synthesis. A judicious choice of metals, ligands, acid and base additives, and solvents orchestrates divergent transformations using electronic and steric effects of the heteroarenes. Although C−H cleavage is a rate-and site-selectivity-determining step in most cases, the subsequent steps involving the formation of C−C bonds are often more critical than the other steps. For the C−H cleavage step, modulating the electronic properties of catalysts to make them electrophilic allows preferential alkenylation at the nucleophilic position. In addition, the presence of an internal base that can be exploited for concerted metalation−deprotonation of the acidic C−H bond offers alternative regioselectivity. Furthermore, we developed our own ligand system based on a conformationally rigid pyrazolonaphthyridine scaffold that enables aerobic C−H alkenylation reactions with steric control. We showed that the electronic and steric effects of heteroarenes can be further extended to chemodivergent reactions with norbornene derivatives. Depending on whether the palladacycle is formed, heteroarenes selectively undergo 1:2 annulation with norbornene derivatives and threecomponent reactions with other azoles through the Pd−norbornene adducts or Catell...

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Section: Pyrazolementioning

confidence: 99%

Transition-Metal-Catalyzed Divergent C–H Functionalization of Five-Membered Heteroarenes

Jeong

Joo

2021

Acc. Chem. Res.

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“…β-Ketonitriles are highly valuable motifs in organic synthesis because they can be readily converted to a variety of heterocyclic compounds, such as azoles, 1 pyrroles, 2 furans, 3 dihydropyridazines, 2 thiophenes, 4 imidazo[1,2- a ]pyridines, 5 2-pyridones, 6 and dioxapropellanes 7 as shown in Fig. 1.…”

Section: Introductionmentioning

confidence: 99%