Synthesis of fluoren-9-ones by the palladium-catalyzed cyclocarbonylation of o-halobiaryls

Synthesis of Fluoren-9-ones via Pd-Catalyzed Annulation of 2-Iodobiphenyls with Vinylene Carbonate

A palladium-catalyzed reaction for intermolecular selective C-H cyclocarbonylation of 2-iodobiphenyls is described. Intriguingly, the vinylene carbonate acts as a carbon monoxide transfer agent to enable the annulation reaction. Moreover, as a versatile synthon, fluoren-9-one can be transformed into a variety of functionalized organic molecules, such as [1,1'-biphenyl]-2-carboxylic acid, 1'H,3'H-spiro[fluorene-9,2'-perimidine] and N-tosylhydrazones.

Rhodium(III)-Catalyzed C-H Cascade Annulation of Arylhydrazines with 2-Diazo-1,3-indandiones for the Synthesis of Tetracyclic Indeno[1,2-b]indoles

An efficient approach for the preparation of tetracyclic indeno[1,2-b]indoles via Rh(III)-catalyzed C-H cascade annulation between arylhydrazines and diazo indan-1,3-diones has been established. In addition, a series of indeno[1,2-b]indoles were obtained in up to 96% yield with a wide range of substrates and high functional group tolerance. Finally, the diverse transformations of the desired products demonstrate the synthetic utility and utilization of this protocol.

Carbonylative Transformations Using a DMAP-Based Pd-Catalyst through Ex Situ CO Generation

A phosphine-free, efficient protocol for aminocarbonylation and carbonylative Suzuki-Miyaura coupling has been developed using a novel palladium complex, [PdII(DMAP)2(OAc)2]. The complex was successfully synthesized using a stoichiometric reaction between PdII(OAc)2 and DMAP in acetone at room temperature and characterized using single-crystal X-ray analysis. Only 5 mol % catalyst loading was sufficient for effective carbonylative transformations. "Chloroform-COware" chemistry was utilized for safe and facile insertion of the carbonyl unit using chloroform as an inexpensive CO source in a two-chamber setup. Various value-added pharmaceutically relevant compounds such as CX-516, CX-546, and farampator were synthesized using the technique. Furthermore, the commercially designed COware was engineered to COware-RB setup for sequential one-pot synthesis of indenoisoquinolines (topoisomerase I inhibitors).

Copper-Catalyzed Synthesis of 3-Aryl-9H-imidazo[1,5-a]indol-9-ones Using Oxygen as the Sole Oxidant

A three-component strategy was developed for 3-phenyl-9H-imidazo[1,5-a]indol-9-one preparation from indole-2-carboxaldehydes, aromatic aldehydes, and ammonium acetate under copper catalysis conditions. In this process, a new five-membered ring was formed and the C3 position in the indole substrate was selectively oxidized into a ketone skeleton using oxygen as the sole oxidant and ammonium acetate as the nitrogen source. Furthermore, same products also could be achieved from indole-2-carboxaldehydes and benzyl amines under similar reaction conditions.

Direct Dehydrogenative Access to Unsymmetrical Phenones

The first non‐directed dehydrogenative phenone coupling method of methylarenes with aromatic C−H bonds, displaying a large substrate scope, is herein reported. This reaction represents a far more direct atom‐ and step‐efficient alternative to the classical Friedel–Crafts or Suzuki–Miyaura derived acylation reactions. The method can be carried out on a gram scale and was successfully applied to the synthesis of several Ketoprofen drug analogues.

Microwave-assisted palladium catalysed C-H acylation with aldehydes: synthesis and diversification of 3-acylthiophenes

The use of MW allows the efficient palladium(II)-catalysed C-3 acylation of thiophenes with aldehydes via C(sp²)-H activation for the synthesis of (cyclo)alkyl/aryl thienyl ketones (43 examples). Compared to standard thermal conditions, the use of MW reduces the reaction time (15 to 30 min vs. 1 to 3 hours), leading to improved yields of the ketones (up to 92%). The control of positional selectivity is achieved by 2-pyridinyl and 2-pyrimidyl ortho-directing groups at C-2 of the thiophene scaffold. To show the synthetic applicability, selected ketones were subjected to further transformations, including intramolecular reactions to directly embed the directing group in the core structure of the new molecule.

La(OTf)3 facilitated self-condensation of 2-indolylmethanol: construction of highly substituted indeno[1,2-b]indoles

The Lewis acid-promoted self-condensation of 2-indolylmethanols has been revealed. On treatment with La(OTf)₃, highly substituted indeno[1,2-b]indole derivatives have been synthesized by using easily accessible 2-indolylmethanols with up to 94% yields. The utility of this method is further highlighted by evaluating the initial photophysical properties of some prepared products, indicating that the protocol may have potential applications in the construction of novel fluorescent materials.

Rhodium-Catalyzed Reductive trans-Alkylacylation of Internal Alkynes via a Formal Carborhodation/C-H Carbonylation Cascade

A rhodium-catalyzed reductive annulation cascade reaction that consists of a formal anti-carborhodation of a C≡C bond and an aromatic C-H carbonylation cascade for producing cyclopenta[de]quinoline-2,5(1H,3H)-diones is described. This method uses the Mn reductant to reductively regenerate the active rhodium species, hence obviating the need for prefunctionalization, and represents a new route to the carbonylation of aromatic C-H bonds with alkynes leading to aryl vinyl ketone frameworks.

Palladium catalyzed annulation of 2-iodobiphenyl with a non-terminal alkene enabled by neighboring group assistance

In this work, an efficient palladium catalyzed annulation of 2-iodobiphenyl with a non-terminal alkene was developed. The key factor in this transformation was the formation of a highly reactive oxo-palladacycle intermediate, which was enabled by a neighboring hydroxyl group, and remarkably restrained the β-H elimination process. Mechanistically, control experiments demonstrated that the hydroxyl group may act as an anionic ligand, which was irreplaceable in this reaction. This transformation presented good reactivity and selectivity, and no simple Heck coupling products were detected for all of the explored substrates.

A transition-metal-free, base-promoted annulation/ring-cleavage/ring-reconstruction cascade reaction: a facile access to N-protection free indole-indenones

An unprecedented base-promoted reaction of 2-halogenated arylglyoxals with 2-oxindoles is accomplished under metal-free conditions, furnishing a wide range of biologically important (NH)-indeno[2,1-b]indol-6(5H)-ones in useful to good yields.

Palladium catalyzed carbonylative generation of potent, pyridine-based acylating electrophiles for the functionalization of arenes to ketones

We describe here the design of a palladium catalyzed route to generate aryl ketones via the carbonylative coupling of (hetero)arenes and aryl- or vinyl-triflates. In this, the use of the large bite angle Xantphos ligand on palladium provides a unique avenue to balance the activation of the relatively strong C(sp²)–OTf bond with the ultimate elimination of a new class of potent Friedel–Crafts acylating agent: N-acyl pyridinium salts. The latter can be exploited to modulate reactivity and selectivity in carbonylative arene functionalization chemistry, and allow the efficient synthesis of ketones with a diverse array of (hetero)arenes.

A palladium catalyzed approach to the overall carbonylative functionalization of arenes to form ketones with aryl- and vinyl-triflates is described.

Synthesis of benzofurans from the cyclodehydration of α-phenoxy ketones mediated by Eaton’s reagent

Cyclodehydration of α-phenoxy ketones promoted by Eaton’s reagent (phosphorus pentoxide–methanesulfonic acid) is used to prepare 3-substituted or 2,3-disubstituted benzofurans with moderate to excellent yields under mild conditions. The method provides a facile access to benzofurans from readily available starting materials such as phenols and α-bromo ketones. The reaction is highly efficient, which is attributed to the good reactivity and fluidity of Eaton’s reagent. The reaction can be applied to prepare naphthofurans, furanocoumarins, benzothiophenes, and benzopyrans.

A palladium-catalyzed C-H functionalization route to ketones via the oxidative coupling of arenes with carbon monoxide

We describe the development of a new palladium-catalyzed method to generate ketones via the oxidative coupling of two arenes and CO. This transformation is catalyzed by simple palladium salts, and is postulated to proceed via the conversion of arenes into high energy aroyl triflate electrophiles. Exploiting the latter can also allow the synthesis of unsymmetrical ketones from two different arenes.

A palladium catalyzed route to prepare aryl ketones from their two fundamental building blocks, two arenes and carbon monoxide, is described.

Preparation of Polyfunctional Biaryl Derivatives by Cyclolanthanation of 2-Bromobiaryls and Heterocyclic Analogues Using nBu2 LaCl⋅4 LiCl

Various aryl- and heteroaryl-substituted 2-bromobiaryls are converted to cyclometalated lanthanum intermediates by reaction with nBu2 LaCl⋅4 LiCl. These resulting lanthanum heterocycles are key intermediates for the facile preparation of functionalized 2,2'-diiodobiaryls, silafluorenes, fluoren-9-ones, phenanthrenes, and their related heterocyclic analogues. X-ray absorption fine structure (XAFS) spectroscopy was used to rationalize the proposed structures of the involved organolanthanum species.

i-Pr2NMgCl·LiCl Enables the Synthesis of Ketones by Direct Addition of Grignard Reagents to Carboxylate Anions

The direct preparation of ketones from carboxylate anions is greatly limited by the required use of organolithium reagents or activated acyl sources that need to be independently prepared. Herein, a specific magnesium amide additive is used to activate and control the addition of more tolerant Grignard reagents to carboxylate anions. This strategy enables the modular synthesis of ketones from CO₂ and the preparation of isotopically labeled pharmaceutical building blocks in a single operation.

Metastable 9-Fluorenone: Blueshifted Fluorescence, Single-Crystal-to-Single-Crystal Reactivity, and Evaluation as a Multimodal Fingermark Visualization Treatment

A metastable form of 9-fluorenone (MS9F) has been characterized using Raman spectroscopy, fluorimetry, and X-ray diffraction techniques. MS9F emits blue fluorescence (λ_max =495 nm) upon 365 nm irradiation and undergoes a single-crystal-to-single-crystal (SCSC) transformation to reach the ground state form (GS9F) over approximately 30 minutes, whereupon it emits the expected green fluorescence. A structure-property relationship for this fluorescent behavior has been posited. MS9F and GS9F were applied as a means of visualizing latent fingermarks on a nonporous surface. This approach identified three different modes of fluorescent fingermark visualization using 9-fluorenone.

Aerobic oxidation of fluorene to fluorenone over Co–Cu bimetal oxides

Aerobic oxidation of fluorene to fluorenone was achieved over Co–Cu bimetal oxides using O₂ as an oxidant in the absence of a radical initiator. Co–Cu bimetal oxides showed better catalytic performance than CuO and Co₃O₄.

Benziodoxole Triflate as a Versatile Reagent for Iodo(III)cyclization of Alkynes

The utility of benziodoxole triflate, derived from α,α-bis(trifluoromethyl)-2-iodobenzyl alcohol, as a versatile reagent for iodo(III)cyclization via electrophilic activation of alkyne, is reported herein. The reagent promotes cyclization of alkynes tethered to a variety of nucleophilic moieties, affording benziodoxole-appended (hetero)arenes such as benzofurans, benzothiophenes, isocoumarins, indoles, and polyaromatics under mild conditions. This unprecedented class of (hetero)aryl-I^III compounds proved easy to purify, stable, and amenable to various synthetic transformations.

Pd/Cu-catalyzed dual C–H bond carbonylation towards the synthesis of fluorazones

Pd catalyzed oxidative dual C–H bond activation/carbonylation still remains a great challenge due to the generation of by-products via C–C bond formation. Herein, we developed a straightforward Pd/Cu-catalyzed oxidative dual C–H bond carbonylation process to access biologically and pharmaceutically important fluorazones from easily available N-aryl pyrroles and CO utilizing O₂ as the terminal oxidant.