Synthesis of Indeno[1′,2′:4,5]imidazo[1,2‑<i>a</i>]pyridin-11-ones and Chromeno[4′,3′:4,5]imidazo[1,2‑<i>a</i>]pyridin-6-ones through Palladium-Catalyzed Cascade Reactions of 2‑(2-Bromophenyl)imidazo[1,2‑<i>a</i>]pyridines

A novel and efficient synthesis of 11<i>H</i>-indeno­[1′,2′:4,5]­imidazo­[1,2-<i>a</i>]­pyridin-11-one, a hybrid structure of indenone with imidazo­[1,2-<i>a</i>]­pyridine, from the reaction of 2-(2-bromophenyl)­imidazo­[1,2-<i>a</i>]­pyridine with carbon monoxide through palladium-catalyzed CO insertion and C–H bond activation, has been developed. Intriguingly, under similar conditions but in the presence of Cu­(OAc)₂, the reaction selectively afforded 6<i>H</i>-chromeno­[4′,3′:4,5]­imidazo­[1,2-<i>a</i>]­pyridin-6-one, a hybrid structure of chromenone with imidazo­[1,2-<i>a</i>]­pyridine, via a more sophisticated cascade process including acetoxylation, deacetylation, CO insertion, and C–H bond activation

Synthesis of Indeno[1′,2′:4,5]imidazo[1,2‑<i>a</i>]pyridin-11-ones and Chromeno[4′,3′:4,5]imidazo[1,2‑<i>a</i>]pyridin-6-ones through Palladium-Catalyzed Cascade Reactions of 2‑(2-Bromophenyl)imidazo[1,2‑<i>a</i>]pyridines

A novel and efficient synthesis of 11H-indeno­[1′,2′:4,5]­imidazo­[1,2-a]­pyridin-11-one, a hybrid structure of indenone with imidazo­[1,2-a]­pyridine, from the reaction of 2-(2-bromophenyl)­imidazo­[1,2-a]­pyridine with carbon monoxide through palladium-catalyzed CO insertion and C–H bond activation, has been developed. Intriguingly, under similar conditions but in the presence of Cu­(OAc)2, the reaction selectively afforded 6H-chromeno­[4′,3′:4,5]­imidazo­[1,2-a]­pyridin-6-one, a hybrid structure of chromenone with imidazo­[1,2-a]­pyridine, via a more sophisticated cascade process including acetoxylation, deacetylation, CO insertion, and C–H bond activation

Synthesis of Naphtho[1′,2′:4,5]imidazo[1,2‑<i>a</i>]pyridines and Imidazo[5,1,2-<i>cd</i>]indolizines Through Pd-Catalyzed Cycloaromatization of 2‑Phenylimidazo[1,2‑<i>a</i>]pyridines with Alkynes

In this paper, palladium-catalyzed oxidative cycloaromatization of 2-phenylimidazo­[1,2-<i>a</i>]­pyridine (PIP) with internal alkyne is studied. From this reaction, two classes of fused <i>N</i>-heterocycle, naphtho­[1′,2′:4,5]­imidazo­[1,2-<i>a</i>]­pyridine (NIP) and imidazo­[5,1,2-<i>cd</i>]­indolizine (IID), were formed through dehydrogenative coupling featured with cleavage of the C–H bonds located on different moiety of the PIP substrates. Moreover, when 5-methyl-2-phenylimidazo [1,2-<i>a</i>]­pyridine or 2-mesitylimidazo­[1,2-<i>a</i>]­pyridine was used, either NIP or IID could be obtained as an exclusive product with good efficiency. Intriguingly, Pd­(II) showed different action mode in promoting this reaction compared with Rh­(III) and led to the formation of NIP with reversed regio-selectivity for the reaction of asymmetrical alkyne

Zinc-Mediated One-Pot Tandem Reaction of Nitriles with Propargyl Bromides: An Access to 3‑Alkynylpyridines

A one-pot procedure for the synthesis of 3-alkynylpyridines via a zinc-mediated tandem reaction of nitriles with propargyl bromides under extremely mild reaction conditions has been developed. This reaction exhibits high efficiency, broad substrate scope, and good functional group tolerance. In addition, the 3-alkynyl­pyridines obtained herein were found to be versatile and convenient intermediates for the preparation of fused-heterocyclic compounds with potential biological and material interests

Condition-Dependent Selective Synthesis of Indolo[1,2‑<i>c</i>]quinazolines and Indolo[3,2‑<i>c</i>]quinolines from 2‑(1<i>H</i>‑Indol-2-yl)anilines and Sulfoxonium Ylides

In this paper, a selective synthesis of indolo­[1,2-c]­quinazolines and indolo­[3,2-c]­quinolines through the cascade reactions of 2-(1H-indol-2-yl)­anilines with sulfoxonium ylides is presented. The formation of products involves the generation of a carbene species from sulfoxonium ylide and its N–H bond insertion reaction with 2-(1H-indol-2-yl)­aniline followed by deoxygenative imine formation, intramolecular N– or C– nucleophilic addition and deoxygenative aromatization. This switchable synthesis was condition-dependent. In the presence of K2CO3 in CH3CN, the reaction mainly furnished indolo­[1,2-c]­quinazolines. In the presence of HOAc in dioxane, it selectively afforded indolo­[3,2-c]­quinolines. In addition, direct C–H/N–H functionalization of the products obtained provides a convenient and direct access to polycyclic heteroaromatic compounds. These novel protocols have advantages such as readily accessible substrates, easily tunable selectivity, good compatibility with diverse functional groups, and the use of air as a cost-free and sustainable oxidant

Synthesis of Naphtho[1′,2′:4,5]furo[3,2‑<i>b</i>]pyridinones via Ir(III)-Catalyzed C6/C5 Dual C–H Functionalization of <i>N</i>‑Pyridyl-2-pyridones with Diazonaphthalen-2(1<i>H</i>)‑ones

Presented herein is an unprecedented synthesis of naphtho[1′,2′:4,5]furo[3,2-b]pyridinones via Ir(III)-catalyzed C6/C5 dual C–H functionalization of N-pyridyl-2-pyridones with diazonaphthalen-2(1H)-ones. This protocol forms C–C and C–O bonds in one pot in which diazonaphthalen-2(1H)-ones serve as bifunctional reagents, providing both alkyl and aryloxy sources. To the best of our knowledge, this is the first example of an Ir(III)-catalyzed synthesis of the title compounds by using diazonaphthalen-2(1H)-ones as bifunctional substrates. Notably, this method features operational simplicity, good functional group tolerance, high efficiency, and high atom economy

Synthesis of β‑Dicarbonylated Tetrahydropiperidines via Direct Oxidative Cross-Coupling between Different C(sp³)–H Bonds

A novel and convenient synthesis of β-dicarbonylated tetrahydropiperidines from the cascade reactions of piperidine derivatives with methyl ketones is presented. Mechanistically, the formation of the title compounds involves a hitherto unreported oxidative cross-coupling between different C­(sp3)–H bonds through the in situ generation of a cyclic enamine and an α-keto radical as the key intermediates followed by their radical addition and further oxidation of the addition adduct. To our knowledge, this is the first example in which β-dicarbonyl-substituted tetrahydropiperidines were prepared using readily available saturated cyclic amines as substrates and inexpensive and ubiquitous methyl ketones as dicarbonylation reagents. In addition, the product thus obtained could be easily transformed into structurally and pharmaceutically interesting polycyclic compounds in good efficiency

Selective Construction of Spiro or Fused Heterocyclic Scaffolds via One-pot Cascade Reactions of 1‑Arylpyrazolidinones with Maleimides

Presented herein is a controllable selective construction of spiro or fused heterocyclic scaffolds through the one-pot cascade reactions of 1-phenylpyrazolidinones with maleimides. To be specific, succinimide spiro pyrazolo[1,2-a]pyrazolones were effectively formed via [4 + 1] spiroannulation of 1-phenylpyrazolidinones with maleimides through simultaneous C(sp2)-H bond activation/functionalization and intramolecular cyclization along with the traceless fusion of the pyrazolidinonyl unit into the final product. In this reaction, air acts as a cost-effective and environmentally sustainable oxidant to assist the regeneration of the Rh(III) catalyst. Alternatively, succinimide-fused pyrazolidinonylcinnolines were formed from the same starting materials through an initial [4 + 1] spiroannulation followed by base-promoted skeleton rearrangement of the in situ formed spiro product without isolation. Notable features of these protocols include easily tunable selectivity, broad substrate scope, cost-effective and sustainable oxidant, excellent atom economy, and facile scalability

Synthesis of β‑Dicarbonylated Tetrahydropiperidines via Direct Oxidative Cross-Coupling between Different C(sp³)–H Bonds

A novel and convenient synthesis of β-dicarbonylated tetrahydropiperidines from the cascade reactions of piperidine derivatives with methyl ketones is presented. Mechanistically, the formation of the title compounds involves a hitherto unreported oxidative cross-coupling between different C­(sp3)–H bonds through the in situ generation of a cyclic enamine and an α-keto radical as the key intermediates followed by their radical addition and further oxidation of the addition adduct. To our knowledge, this is the first example in which β-dicarbonyl-substituted tetrahydropiperidines were prepared using readily available saturated cyclic amines as substrates and inexpensive and ubiquitous methyl ketones as dicarbonylation reagents. In addition, the product thus obtained could be easily transformed into structurally and pharmaceutically interesting polycyclic compounds in good efficiency