Copper‐ and Ligand‐free Heteroannulation of <i>o</i>‐Halohydroxypyridine with Terminal Alkynes Using Pd/C Catalyst: One‐Pot Synthesis of 2‐Substituted Furopyridines and their Functionalization

Furoquinoline scaffolds are one of the important heterocycles and their analogues are found not only in nature 1 but also in pharmacological and biological materials, whose properties include anti-inflammatory, 2 TLR8 (Toll-like receptor-8) agonistic, 3 anti-cancerous, 4 a protein inhibitory, 5 and antimicrobial activity. 6 Owing to their diverse biological activities, there have been great efforts to extract 7 or synthesize furoquinolines, i.e., [3 + 2] cyclization reaction for furo [2,3-b]quinolines, 8 [4 + 2] cycloaddition of imines with enol ethers, 9 and a three component reaction of 4-hydroxyquinolin-2(1H)-one, aromatic aldehyde and isonitrile, and so on. 10 Recently we have paid much attentions to develop green and practical synthetic methods for synthesizing various furoheterocycles 1-6 as shown in Scheme 1. 11 The isomeric 2-substituted furopyridines such as furo[3,2b]-, furo[2,3-b]-, and furo[3,2-c]pyridine were synthesized starting from o-halohydroxypyridines and terminal alkynes catalyzed by commercial Pd/C under copper-and ligandfree conditions. Also we were able to show diversification of our protocol to make 2,3-disubstituted furoquinolines, 5 and 6, by Suzuki and Heck reactions, respectively. 11a As a part of our continuing organometallic studies on diversification of nitrogen-containing biologically active heterocycles, we attempted to synthesize furo[2,3-b]-and furo[3,2-c]quinolines starting from o-halohydroxyquinolines and terminal alkynes with heterogeneous Pd(OAc) 2 catalyst, which was supported by nanosized pore carbon ball. The best reaction condition was obtained under CNB-Pd(OAc) 2

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Synthesis of 2‐Substituted Furo[2,3‐b]‐ and Furo[3,2‐c]quinolines via Heterogeneous Palladium‐catalyzed Heteroannulation

Park

Yang

Park

et al. 2016

Bulletin Korean Chem Soc

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ChemInform Abstract: Copper‐ and Ligand‐Free Heteroannulation of o‐Halohydroxypyridine with Terminal Alkynes Using Pd/C Catalyst: One‐Pot Synthesis of 2‐Substituted Furopyridines and Their Functionalization.

et al. 2015

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Synthesis of 2-Substituted Furopyridines and Their Functionalization. -The double functionalization can be achieved through heteroannulation followed by bromination and Suzuki/Heck reactions (X), (XII). The introduced catalyst can be reused more than five times during the same heteroannulation process while still affording acceptable yields. -(PARK, H. J.; KIM, J.-E.; YUM*, E. K.; KIM, Y. H.; HAN, C.-W.; Bull. Korean Chem. Soc. 36 (2015) 1, 211-218, http://dx.

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Synthesis of New Multivalent Furo[3,2-c]pyridine and Bifuro[3,2-c]pyridine Derivatives

Reißig¹,

Taszarek²

2022

HETEROCYCLES

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A series of furo[3,2-c]pyridine derivatives was prepared by an efficient cascade process involving Sonogashira reactions of 4-hydroxy-3-iodopyridine with suitable terminal alkynes followed by an immediate 5-endo-dig cyclization to generate the furan ring. Several multivalent furo[3,2-c]pyridines were prepared by employing dialkynes or trialkynes. Two bifuro[3,2-c]pyridine derivatives were prepared by alternative coupling methods. The photophysical properties of several of these compounds are compared.During the last decade our group studied syntheses and properties of a series of multivalent heterocycles, 1 in particular of oxazole 2 and of pyridine derivatives. 3 The 2D self-assembly at a solution-graphite interface 2,3a,c,e,g and the photophysical properties 3d,j of these multivalent compounds were thereby of special interest. During these investigations efficient routes to furo[2,3-c]-and furo[3,2-c]pyridines were developed employing a very flexible building block system. 4 Since furopyridines are a very interesting class of heterocycles [5][6][7] we extended our synthetic efforts to the preparation of a series of new multivalent furo[3,2-c]pyridine derivatives (Scheme 1). Simple furo[3,2-c]pyridines A, spacer-connected divalent or trivalent compounds B, and directly connected bifuropyridine derivatives of type C should be synthesized.

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Copper‐ and Ligand‐free Heteroannulation of o‐Halohydroxypyridine with Terminal Alkynes Using Pd/C Catalyst: One‐Pot Synthesis of 2‐Substituted Furopyridines and their Functionalization

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References 43 publications

Synthesis of 2‐Substituted Furo[2,3‐b]‐ and Furo[3,2‐c]quinolines via Heterogeneous Palladium‐catalyzed Heteroannulation

Synthesis of 2‐Substituted Furo[2,3‐b]‐ and Furo[3,2‐c]quinolines via Heterogeneous Palladium‐catalyzed Heteroannulation

ChemInform Abstract: Copper‐ and Ligand‐Free Heteroannulation of o‐Halohydroxypyridine with Terminal Alkynes Using Pd/C Catalyst: One‐Pot Synthesis of 2‐Substituted Furopyridines and Their Functionalization.

Synthesis of New Multivalent Furo[3,2-c]pyridine and Bifuro[3,2-c]pyridine Derivatives

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