N-Bromosuccinimide-Induced C-H Bond Functionalization: An Intramolecular Cycloaromatization of Electron Withdrawing Group Substituted 1-Biphenyl-2-ylethanone for the Synthesis of 10-Phenanthrenol

TEMPO-Mediated Interrupted 6π-Photocyclization of ortho-Biaryl-Appended 1,3-Dicarbonyl Compounds toward 10-Phenanthrenols

In this paper, we present an example of a photoinduced catalyst, halogen-, and base-free TEMPO-mediated interrupted 6π-photocyclization/dehydrogenative aromatization of ortho-biaryl-appended 1,3-dicarbonyl compounds for the preparation of 10-phenanthrenols. The reaction involves rapid photocycloaddition via a 1,2-biradical of 1,3-dicarbonyl compounds, followed by subsequent dehydrogenative aromatization of 1,4-biradical intermediates using TEMPO as the commercially available oxidant rather than trapped by TEMPO to form an alkoxyamine product.

Synthesis of 10-Phenanthrenols via Photosensitized Triplet Energy Transfer, Photoinduced Electron Transfer, and Cobalt Catalysis

Due to the inert redox activity and high triplet energy, radical chemistry of 1,3-dicarbonyl compounds usually requires prefunctionalization substrates, external oxidant, and high-energy UV light. Here, we report a visible-light-driven photocatalyst/cobaloxime system composed of a photosensitized energy transfer reaction (PEnT) and photoinduced electron transfer reaction (PET) and with an interrupted 6π-photocyclization/dehydrogenative aromatization in one pot to synthesize 10-phenanthrenols. Preliminary mechanistic studies revealed that fac-Ir(ppy)₃ plays the dual roles of energy transfer catalysis for photocycloaddition via 1,2-biradical intermediates of 1,3-dicarbonyl compounds and photoredox/cobaloxime catalysis dehydrogenative aromatization of 1,4-biradical rather than the intermediates via 6π photocyclization in the tandem reaction. In contrast to previous well-established radical chemistry of 1,3-dicarbonyl compounds, we provide a new strategy for the activation of 1,3-dicarbonyl compounds under visible light catalysis, affording a novel cyclization strategy with extremely high atom economy for the synthesis of 10-phenanthrenols.

Photocatalytic synthesis of 10-phenanthrenols via intramolecular cycloaromatization under oxidant-free conditions

A novel tandem photocycloaddition/dehydrogenative aromatization with hydrogen evolution of ortho biaryl-appended 1,3-dicarbonyl compounds for the synthesis of 10-phenanthrenol via cobaloxime catalysis is disclosed.

Removal and modification of directing groups used in metal-catalyzed C–H functionalization: the magical step of conversion into ‘conventional’ functional groups

This feature review is focused on recent approaches for removing versatile directing groups.

Palladium-Catalyzed Q-Tube-Assisted Protocol for Synthesizing Diaza-dibenzo[a,e]azulene and Diaza-benzo[a]fluorene Derivatives via O2 Acid-Promoted Cross-Dehydrogenative Coupling

An appropriate and efficient Q-tube-assisted palladium-catalyzed strategy for the synthesis of novel, unparalleled diaza-dibenzo[a,e]azulene and diaza-benzo[a]fluorene derivatives has been sophisticated, which includes oxygen and AcOH-induced oxidative C(sp³)-C(sp²) cross-dehydrogenative coupling reactions of 1-amino-2-imino-4-arylpyridine-3-carbonitriles with benzocyclic ketones such as benzosuberone, tetralone, thiochromone, and chromone, respectively. This Q-tube gas purging kit assisted-protocol features safe due to easy pressing and sealing, a wide substrate scope, easy workup and purifying phases, and the use of O₂ as a benign oxidant, in addition to being scalable and having a high atom economy. The suggested mechanistic pathway includes a formal dehydrative step followed by palladium AcOH-induced CH(sp³)-CH(sp²) oxidative cross-coupling. In this study, X-ray crystallographic analysis has been used to authenticate the targeted products.

PIFA-Mediated Dearomatizative Spirocyclization of Phenolic Biarylic Ketones via Oxidation and C-C Bond Cleavage

The dearomatizing spirocyclization of phenolic biarylic ketones using PhI(OCOCF₃)₂ as oxidant is presented. The reaction affords various cyclohexadienones through C-C bond cleavage under mild conditions. Mechanistic investigations reveal that an exocyclic enol ether acts as the key intermediate in the transformation.

Synthetic Strategy for Pyrazolo[1,5-a]pyridine and Pyrido[1,2-b]indazole Derivatives through AcOH and O2-Promoted Cross-dehydrogenative Coupling Reactions between 1,3-Dicarbonyl Compounds and N-Amino-2-iminopyridines

An efficient method has been developed for the synthesis of uniquely substituted pyrazolo[1,5-a]pyridine and pyrido[1,2-b]indazole derivatives, which involves acetic acid and molecular oxygen promoted cross-dehydrogenative coupling reactions of respective β-ketoesters and β-diketones (like ethyl acetoacetate, ethyl benzoylacetate, methyl propionylacetate, acetylacetone, dimedone, 1,3-cyclohexanedione, and 1,3-cyclopentanedione) with N-amino-2-iminopyridines. The proposed tentative mechanism involves formal acetic acid-promoted oxidative C(sp3)-C(sp2) dehydrogenative coupling followed by dehydrative cyclization under a catalyst-free condition within high atom economy processes.

Sustainable Synthetic Approach for (Pyrazol-4-ylidene)pyridines By Metal Catalyst-Free Aerobic C(sp2)-C(sp3) Coupling Reactions between 1-Amino-2-imino-pyridines and 1-Aryl-5-pyrazolones

A novel, metal catalyst-free, and efficient method has been developed for the synthesis of (pyrazol-4-ylidene)pyridine derivatives. The process involves dehydrogenative coupling of 1-amino-2-imino-pyridines with 1-aryl-5-pyrazolone derivatives utilizing O2 as the sole oxidant. The new method benefits from a high atom economy, efficiency, and substrate scope, as well as the simplicity of reaction and product purification procedures.

Theoretical investigation on the mechanism of Cu(ii)-catalyzed synthesis of 4-quinolones: effects of additives HOTf vs. HOTs

Hydrogen-bond donor/proton-donor ability is revealed to be the primary factor that controls the catalytic capability of additives (HOTf vs. HOTs).