Pd-catalyzed oxidative C–H arylation of heterocycle embedded thiophene/furan with aryl boronic acid/ester

Srinivasan, R.; Kumaran, R. Senthil; Nagarajan, N. S.

doi:10.1039/c4ra06055e

Cited by 12 publications

(4 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, Wu and co‐workers demonstrated a low catalyst loading direct arylation of 2‐(thiophen‐2‐yl)pyridine which resulted in C5‐arylated product excluding the pyridine ring acting as a directing group . A similar behavior was observed by Nagarajan et al in arylation of N‐heterocycle embedded thiophenes and furans with aryl boronic acids under Pd‐catalyzed oxidative reaction conditions which resulted in high C(5)–H arylation selectivity thus enabling an easy access to 2,5‐disubstituted thiophenes …”

Section: Introductionsupporting

confidence: 53%

“…[8] A similar behavior was observed by Nagarajan et al in arylation of Nheterocycle embedded thiophenes and furans with aryl boronic acids under Pd-catalyzed oxidative reaction conditions which resulted in high C(5)-H arylation selectivity thus enabling an easy access to 2,5-disubstituted thiophenes. [9] One of the first examples of exclusive palladium-catalyzed C3-arylation of thiophenes was reported by Miura and co-workers by using a 3-carbamoyl moiety as the directing group. [10] Furthermore, Doucet et al observed that palladium-catalyzed direct arylation of furans and thiophenes containing a secondary carbamoyl group at the C2-position proceeded regioselectively either at C3-or C5-position strongly depending on the reaction conditions used.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Influence of the Quinoline Moiety on Direct Pd‐Catalyzed Arylation of Five‐Membered Heterocycles

et al. 2018

View full text Add to dashboard Cite

Herein we report a study on the reactivity of C2‐quinoline‐substituted furan, thiophene and pyrrole derivatives in palladium‐catalyzed direct C–H arylation. The regioselectivity of the reaction was strongly influenced by site position of the attached five‐membered heterocycle thus giving rise to C3‐ and/or C5‐arylated products. Furthermore, the Hammett correlation performed on 5‐substituted‐8‐(furan‐2‐yl)quinolines indicates that a marginally positive charge is building up in the rate determining transition state and thus pointing towards the electrophilic metalation‐deprotonation reaction mechanism.

show abstract

Section: Introductionsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

The Influence of the Quinoline Moiety on Direct Pd‐Catalyzed Arylation of Five‐Membered Heterocycles

et al. 2018

View full text Add to dashboard Cite

show abstract

“…α-Arylfurans, which have potentially useful bioactivities and physical properties, − are usually prepared by means of Suzuki coupling of 2-furanylboronic acid with aryl halides or by direct arylation of α-furyl C–H bonds with aryl halides. α-Arylfurans can also be prepared by the oxidative coupling of aryl boronic acids with α-furyl C–H bonds in the presence of a strong oxidant such as Mn(OAc) 3 , Ag 2 CO 3 , or TEMPO. − However, oxidative coupling mediated by O 2 , which is an environmentally benign oxidant, has never been reported.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of N,O-Spiroacetals and α-Arylfurans via Pd-Catalyzed Aerobic Oxidative 2,5-Aminoarylation and α-Arylation of N-[3-(2-Furanyl)propyl]-p-toluenesulfonamides with Boronic Acids

et al. 2018

View full text Add to dashboard Cite

Unsaturated N, O-spiroacetals and α-arylfurans were synthesized via palladium-catalyzed aerobic oxidative coupling reactions between N-[3-(2-furanyl)propyl]- p-toluenesulfonamides and boronic acids, with KF and KOAc as the respective additives. These reactions involve an unprecedented dearomatizing 2,5-aminoarylation and a direct α-arylation of furan rings, respectively, with O as the terminal oxidant.

show abstract

“…[96] Moreover, indoles, pyrroles, furans and thiophenes could be arylated in a chemo-and site-selective fashion. [97] Proposed mechanisms include precoordination of the palladium to the heteroatom, as well as an electrophilic mechanism involving ArPd(+II) species. The selectivity of the C-H arylations strongly depends on the electronic properties of the electrophiles and substrates, on the nature of the palladium catalyst, as well as the additives in the reaction.…”

mentioning

confidence: 99%

Iron- and Ruthenium-Catalyzed Site-Selective C–C Forming Direct C–H Functionalizations

Graczyk¹

View full text Add to dashboard Cite

Significant drawbacks of these reactions are the required prefunctionalization of starting materials and potential side reactions, such as ß-hydride elimination and the formation of stoichiometric metal salts as undesired byproducts (Scheme 2a). Therefore, more economically and environmental friendly alternatives are needed to circumvent these disadvantages. To avoid unnecessary and expensive prefunctionalization steps, unfunctionalized (hetero)arenes can be used in transition metal-catalyzed direct C-H bond functionalizations, as shown in Scheme 2b. Another pathway is the cross-dehydrogenative coupling, presented in Scheme 2c. In this context, the use of an external oxidant is required. Scheme 2: Comparison of classical cross-coupling and transition metal-catalyzed C-H transformations.Although a great number of published reactions are described as C-H bond activations, the term "C-H activation" should only be applied to a limited number of reactions. [7,8] True C-H activation involves an elementary C-H metalation step by the active metal species ML n . [9][10][11] First elaborations on the stoichiometric cyclometalations were performed by the groups of Shaw [12] and Reutov, [13] relating to base-promoted metalation reactions. Generally five different main mechanisms are widely accepted up to now (Scheme 3a-e). For example, an oxidative addition can occur if electron-rich, low-valent, late-transition metal complexes of iron, ruthenium, rhenium, osmium, iridium or platinum are employed as the catalysts (Scheme 3a). Electrophilic substitution is more likely occurring when late-or post-transition metals (Pd 2+ , Pt 2+ , Pt 4+ , Hg 2+ ) are used. The reaction starts with an electrophilic attack of the metal complex, acting in this case as a Lewis acid (LA) (Scheme 3b). Early transition metals with d 0 electronic configuration of the groups 3 and 4 as well as the lanthanoids can undergo σ-bond metathesis, highlighting a concerted formation and cleavage of bonds. Herein, usually an alkyl or hydride complex is involved (Scheme 3c). With unsaturated M=X bonds the C-H activation can occur through a 1,2-addition, where a heteroatom-based group bearing a lone electron pair acts as a H-acceptor (Scheme 3d). [9,11] This mechanism is related to the σ-bond metathesis with the constraint that the cleaved proton still remains in the structure of metalated product. This type of reactions can take place with imido and alkylidene complexes of early to middle transition metals. Experimental and theoretical analyses have offered a further type of C-H activation via "base-assisted" metalation (Scheme 3e). [9] The proton is abstracted by a carboxylate or carbonate ligand, which can act as an intramolecular base.Indeed, benzene has a bond dissociation energy of 113 kcal/mol [21] and a pK a value of 43.0-44.7, [21] the C-H bonds are of equal substitution and according to this of equal reactivity. The C-H bonds in heterocycles contain different electronic properties and marginal acidities within the molecule. The resulting pK a values of ...

show abstract

Pd-catalyzed oxidative C–H arylation of heterocycle embedded thiophene/furan with aryl boronic acid/ester

Abstract: Palladium catalyzed oxidative C-H arylation of heterocycle embedded thiophenes with aryl boronic acids is described. This method is found to display high C5-selectivity and thus enabled rapid access to 2,5disubstituted thiophenes. Furan analogs also exhibited a similar selectivity.

Cited by 12 publications

References 57 publications

The Influence of the Quinoline Moiety on Direct Pd‐Catalyzed Arylation of Five‐Membered Heterocycles

The Influence of the Quinoline Moiety on Direct Pd‐Catalyzed Arylation of Five‐Membered Heterocycles

Synthesis of N,O-Spiroacetals and α-Arylfurans via Pd-Catalyzed Aerobic Oxidative 2,5-Aminoarylation and α-Arylation of N-[3-(2-Furanyl)propyl]-p-toluenesulfonamides with Boronic Acids

Iron- and Ruthenium-Catalyzed Site-Selective C–C Forming Direct C–H Functionalizations

Contact Info

Product

Resources

About