Metal-Free Domino One-Pot Decarboxylative Cyclization of Cinnamic Acid Esters: Synthesis of Functionalized Indanes

Acid-Mediated Domino Cyclization of ortho-Formyl Cinnamate Esters: Synthesis of Substituted Indene/Indane Esters and Indeno[a]indenones

A Bro̷nsted acid-driven protocol to access substituted monoarylindene esters, biarylindane esters, and indeno[a]indenones from simple ortho-formylcinnamate esters and external arenes has been revealed. Remarkably, this single-pot process enabled the construction of two, three, and four new C-C bonds in building monoarylindene esters, biarylindane esters, and indeno[a]indenones, respectively, under metal-free and mild reaction parameters via triggering the inactive cinnamate ester moiety. In addition, the present strategy is investigated with widespread substrate scope.

Acid-Promoted Domino Access to Substituted Benzo[b]carbazoles

Herein, a straightforward Bro̷nsted acids-promoted domino pathway to build substituted benzo[b]carbazoles has been described from easily accessible ortho-formyl (or ortho-acyl) cinnamate esters and indoles. Noticeably, the protocol was amenable to protecting group-free indoles. Notably, this methodology is based on a single-pot regioselective construction of two new C-C bonds and aromatization sequences under mild and metal-free reaction conditions. The mechanistic studies suggested the initial formation of bis-indole substituted intermediate via a dual aromatic substitution with two indole molecules at the carbonyl carbon of ortho-formyl (or ortho-acyl) cinnamate ester followed by intramolecular cyclization and aromatization with exclusion of a second indole molecule. Besides, the efficacy of this approach was also illustrated by scale-up and derivatization reactions, including the photophysical properties study.

Total Synthesis of Alanense A through an Intramolecular Friedel-Crafts Alkylation

The first total synthesis of cadinane sesquiterpenoid alanense A, in which an intramolecular dehydrative Friedel-Crafts alkylation of 2,5-diaryl-2-pentanol is incorporated as a key step, has been achieved. The combinatorial use of p-TsOH·H2O as a catalyst and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a solvent provides 1,1-disubstituted tetrahydronaphthalene in 97% yield. It was also found that the combination of p-TsOH and HFIP is effective for the removal of phenolic MOM ether.

Regioselective Coupling of Different Conjugate Esters by Magnesium Metal Reduction: A Route to Unsymmetrical Adipic Acid Esters

A novel tactic to synthesize unsymmetrical 3-aryladipic acid esters has been developed via magnesium-promoted reductive coupling of ethyl cinnamates with methyl acrylate. In the present methodology, 3-aryladipic acid derivatives were prepared with good functional group tolerance and a wide substrate scope under very mild reaction conditions in good yields. The application of this reaction to dienic acid esters led to the successful control of the reaction to give 5-aryl-oct-3-enedioic acid esters with high regioselectivity.

Acid-Mediated Cascade Cyclization Pathway to Indeno[2,1-c]chromen-6(7H)-ones

Developing mild and effective synthetic strategies for producing significant molecules starting from readily available starting materials is indispensable in organic synthesis. Herein, we present a triflic acid-driven dual cyclization pathway to produce functionalized indeno[2,1-c]chromen-6(7H)-ones from simple 2-formyl (or 2-acyl) cinnamate esters and phenols. Notably, this protocol enabled the construction of two C-C bonds and one C-O bond under metal-free reaction conditions via the activation of the unreactive ester moiety in a single pot. The isolation of intermediate indenol-ester might suggest self-intramolecular cycloaddition by the proximate double bond of the enoate ester with the o-carbonyl moiety, followed by an electrophilic attack with phenol and a subsequent cyclocondensation pathway. In addition, the photophysical properties have also been examined.

A two-step access to fused-/spiro-polycyclic frameworks via double Heck cascade and acid-driven processes

This report illustrates the rapid construction of two divergent classes of polycyclic frameworks, benzo[a]fluorenones and spiro-chromenone indenes, via a double Heck cascade and an acid-driven cyclization from easily accessible precursors, alkyl 2-bromocinnamate esters and diphenylacetylenes. The present strategy has surveyed a broad substrate scope and delivered an array of products with interesting structural features. Besides, fluorescence studies were performed for the synthesized benzo[a]fluorenones.

Cationic and Neutral PdII and PtII Pincer Complexes of Phosphinamino-Triazolyl-Pyridine [PN(H)N]: Pincer Ligand-Stabilized Palladium Nanoparticles and Their Catalytic Annulation of Internal Alkynes to Indenones

We describe the synthesis of a triazolyl-pyridine-based aminophosphine, N-(diphenylphosphaneyl)-6-(1-phenyl)-1H-(1,2,3-triazol-4-yl)pyridine-2-amine [2,6-{(PPh₂)-N(H)(C₅H₃N)(C₂HN₃C₆H₅)}] [1, PN(H)N hereafter], and its palladium and platinum complexes and their catalytic application. The reaction of 1 with [M(COD)Cl₂] (M = Pd or Pt) afforded the cationic complex [(MCl){PN(H)N}-κ³-P,N,N]Cl [M = Pd (2) or Pt (3)]. Alternatively, compounds 2 and 3 were also synthesized by treating [2,6-{H₂N(C₅H₃N)(C₂HN₃C₆H₅)}] (A) with [M(COD)Cl₂] (M = Pd or Pt), followed by the addition of stoichiometric amounts of PPh₂Cl and Et₃N. The neutral, dearomatized complexes [(MCl){PNN}-κ³-P,N,N] [M = Pd (4) or Pt (5)] were prepared by the deprotonation of the NH of 2 and 3 with 1 equiv of ^tBuOK. Compounds 4 and 5 were also synthesized stepwise by treating [2,6-{H₂N(C₅H₃N)(C₂HN₃C₆H₅)}] (A) with [M(COD)Cl₂] (M = Pd or Pt) to give intermediate complexes [{MCl₂}2,6-{NH₂(C₅H₃N)(C₂HN₃C₆H₅)-κ²-N,N}] [M = Pd (B) or Pt (C)], which were subsequently phosphinated. The in situ-generated PNN ligand-stabilized Pd nanoparticles from compound 2 catalyzed the annulation of o-bromobenzaldehyde with alkynes to yield indenone derivatives. Mechanistic investigations suggested that the reaction was catalyzed by Pd nanoparticles (Pd@2) generated from compound 2 and proceeded through sequential oxidative addition, alkyne insertion, and reductive elimination steps to produce indanone products.

Electrophotocatalytic diamination of vicinal C-H bonds

The conversion of unactivated carbon-hydrogen (C-H) bonds to carbon-nitrogen (C-N) bonds is a highly valued transformation. Existing strategies typically accomplish such reactions at only a single C-H site because the first derivatization diminishes the reactivity of surrounding C-H bonds. Here, we show that alkylated arenes can undergo vicinal C-H diamination reactions to form 1,2-diamine derivatives through an electrophotocatalytic strategy, using acetonitrile as both solvent and nitrogen source. The reaction is catalyzed by a trisaminocyclopropenium (TAC) ion, which undergoes anodic oxidation to furnish a stable radical dication while the cathodic reaction reduces protons to molecular hydrogen. Irradiation of the TAC radical dication (wavelength of maximum absorption of 450 to 550 nanometers) with a white-light compact fluorescent light generates a strongly oxidizing photoexcited intermediate. Depending on the electrolyte used, either 3,4-dihydroimidazole or aziridine products are obtained.

Palladium mediated domino reaction: synthesis of isochromenes under aqueous medium

Isochromenes have been synthesized using palladium-catalyzed C–C and C–O bond forming reactions starting from ortho-bromo tertiary benzylic alcohols and internal acetylenes. Notably, this domino process is feasible by using the green solvent, water. The protocol exhibited a broad substrate scope and afforded various isochromenes.

Isochromenes have been synthesized using palladium-catalyzed C–C and C–O bond forming reactions starting from ortho-bromo tertiary benzylic alcohols and internal acetylenes.

Selective Formation of Internal Olefinic Trimer of α-Methylstyrenes with HI Gas and Ketones

Reaction of α-methylstyrene in the presence of HI gas and methyl p-tolyl ketone selectively resulted in an internal olefinic trimer. We revealed that the ketones with the stabilization of the protonated state were efficient to give the corresponding trimers, whereas the other ketones gave the usual indane compound. From the investigation for the mechanistic path, we found that the trimer is a kinetic product and that indane is a thermodynamic product.

Synthesis and antimetastatic activity evaluation of cinnamic acid derivatives containing 1,2,3-triazolic portions

It is herein described the preparation and evaluation of antimetastatic activity of twenty-six cinnamic acid derivatives containing 1,2,3-triazolic portions. The compounds were prepared using as the key step the Copper(I)-catalyzed azide (A)-alkyne (A) cycloaddition (C) (CuAAC reaction), also known as click reaction, between alkynylated cinnamic acid derivatives and different benzyl azides. The reactions were carried in CH₂Cl₂/H₂O (1:1 v/v) at room temperature, and the triazole derivatives were obtained in yields ranging from 73%99%. Reaction times varied from 5 to 40 min. The identity of the synthesized compounds was confirmed by IR and NMR (¹H and ¹³C) spectroscopic techniques. They were then submitted to in vitro bioassays to investigate how they act over metastatic behavior of murine melanoma. The most potent compound, namely 3-(1-benzyl-1H-1,2,3-triazol-4-yl)propyl cinnamate (9a), showed significant antimetastatic and antiproliferative activities against B16-F10 cells. In addition, gelatin zymography and molecular docking analyses pointed to the fact that this compound has potential to interact with matrix metalloproteinase 9 (MMP-9) and MMP-2, which are directly involved in melanoma progression. Therefore, these findings suggest that cinnamic acid derivatives containing 1,2,3-triazolic portions may have potential for development of novel candidates for controlling malignant metastatic melanoma.

Brønsted Acid-Mediated Domino One-Pot Dual C-C Bond Formation: Chemoselective Synthesis of Fused Tricyclic Ketones

A chemoselective synthesis of fused novel tricyclic motifs via a facile domino intramolecular cyclization is presented. The strategy enables the formation of dual C-C bond via intramolecular Friedel-Crafts alkylation followed by acylation to accomplish fused tricyclic ketones. Significantly, these fused tricyclic compounds are ubiquitous and constitute major structural cores of natural products.