Divergent Synthesis of 3-Hydroxyfluorene and 4-Azafluorene Derivatives from ortho-Alkynylarylketones

Silver-Catalyzed and Base-Mediated Double Cyclization for the Streamlined Synthesis of Benzo[4,5]imidazo[2,1-b]naphtho[2,3-d]oxazole from ortho-Alkynylarylketones

We report a novel silver-catalyzed and base-mediated double cyclization strategy for the streamlined synthesis of benzo[4,5]imidazo[2,1-b]naphtho[2,3-d]oxazoles from ortho-alkynylarylketones. The transformation proceeds through an initial ketonization step catalyzed by silver trifluoroacetate (AgTFA), generating a reactive 1,5-diketone intermediate, followed by a sequential double cyclization under basic conditions. This method affords a broad range of benzo[4,5]imidazo[2,1-b]naphtho[2,3-d]oxazoles with good functional group tolerance in moderate-to-good yields. Moreover, this methodology also enhances the synthetic utility of ortho-alkynylarylketones, expanding their applicability in constructing diverse fused heterocycles.

Synthesis of CF3-Azafluorenes through the Cascade Reaction of 2H-Imidazoles with CF3-Ynones

A concise synthesis of trifluoromethyl (CF3)-substituted azafluorenes based on the reaction of 5-aryl-2H-imidazoles with CF3-ynones is reported. The reaction proceeds through C-H activation-initiated formal [3+2] cycloaddition to give spiro[imidazole-4,1'-indene] as a key intermediate, followed by its retro [3+2] cycloaddition, isomerization, and enamine nucleophilic addition. This synthesis of CF3-azafluorene derivatives via simultaneous formation of both the indene and the pyridine scaffolds through cascade C-H/C-C/C-N bond cleavage and C≡C bond formation has not been disclosed before. Moreover, the products thus obtained showed antiproliferative activity against cancer cell lines.

Manganese Complex Catalyzed Sequential Multi-component Reaction: Enroute to a Quinoline-Derived Azafluorenes

The development of innovative synthetic strategies for constructing complex molecular structures is the heart of organic chemistry. This significance of novel reactions or reaction sequences would further enhance if they permitted the synthesis of new classes of structural motifs, which have not been previously created. The research on the synthesis of heterocyclic compounds is one of the most active topics in organic chemistry due to the widespread application of N-heterocycles in life and material science. The development of a new catalytic process that employs first-row transition metals to produce a range of heterocycles from renewable raw materials is considered highly sustainable approach. This would be more advantageous if done in an eco-friendly and atom-efficient manner. Herein we introduce, the synthesis of various new quinoline based azafluorenes via sequential dehydrogenative multicomponent reaction (MCR) followed by C(sp3)-H hydroxylation and annulation. Our newly developed, Mn-complexes have the ability to direct the reaction in order to achieve a high amount of desired functionalized heterocycles while minimizing the possibility of multiple side reactions. We also performed a series of control experiments, hydride trapping experiments, reaction kinetics, catalytic intermediate and DFT studies to comprehend the detailed reaction route and the catalyst's function in the MCR sequence.

Synthesis of Naphtho[2,3-d]oxazoles via Ag(I) Acid-Mediated Oxazole-Benzannulation of ortho-Alkynylamidoarylketones

A cascade oxazole-benzannulation for the synthesis of naphtho[2,3-d]oxazoles has been developed employing ortho-alkynylamidoarylketones as substrates. This procedure provides the advantage of preparing a wide variety of substituents on naphtho[2,3-d]oxazole structures. In addition, o-alkynylamidoarylketones could be prepared from easily accessible and a wide variety of commercially available starting materials. Therefore, this method is a judicious choice of strategy to synthesize naphtho[2,3-d]oxazoles with a great variety of substituents. In this work, 27 examples were demonstrated to provide the desired products in moderate to good yields.

Ag(I)-Catalyzed/Acid-Mediated Cascade Cyclization of ortho-Alkynylaryl-1,3-dicarbonyls to Access Arylnaphthalenelactones and Furanonaphthol Libraries via Aryl-Disengagement

ortho-Alkynylarylketone derivatives were employed as key precursors for a one-pot synthesis of arylnaphthalenelactone and furanonaphthol libraries. In this work, we discovered a cost-effective protocol to prepare arylnaphthalenelactones in one-pot using inexpensive starting material, malonate ester, which was conveniently functionalized leading to a variety of structures. Moreover, we also found an unexpected oxy-dearylation reaction which could be used to synthesize furanonaphthol analogs. These novel methods could be applied to a broad range of substrates to give the corresponding products in up to 83% yield. Notably, these classes of compounds exhibited more significant inhibition against protein-tyrosine phosphatase 1B (PTP1B) enzyme than a standard compound, ursolic acid.

Utilization of ortho-alkynylarylcarbonyl derivatives for creating structurally diverse chemical compounds

ortho-Alkynylarylcarbonyl compounds, including ketones, aldehydes, carboxylic acids, carboxylate esters and amides, have served as useful building blocks for synthetic chemists to prepare numerous classes of important molecules. Various synthetic conversions starting from ortho-alkynylarylcarbonyl precursors are made possible by their unique and enabling structures embedded with reactive carbonyl and alkyne functional groups. These functional groups can be converted directly and independently to other compounds by several reactions. This review highlights the use of these compounds as common precursors for the divergent synthesis of valuable molecules. Moreover, these ortho-alkynylarylcarbonyl compounds can be decorated with other functional group tethers which can lead to an even greater diversity of molecular scaffolds.

Rh(iii)-Catalyzed [3 + 2]/[4 + 2] annulation of acetophenone oxime ethers with 3-acetoxy-1,4-enynes involving C–H activation

A novel, synthetically simple, selective rhodium(iii)-catalyzed [3 + 2]/[4 + 2] annulation cascade reaction to construct complex azafluorenone frameworks has been developed.