Non-Decarboxylative Ruthenium-Catalyzed Rearrangement of 4-Alkylidene-isoxazol-5-ones to Pyrazole- and Isoxazole-4-carboxylic Acids.

Treatment of 4-(2-hydroaminoalkylidenyl)- and 4-(2-hydroxyalkylidenyl)-substituted isoxazol-5(4H)-ones with catalytic amounts of [RuCl2(p-cymene)]2, without any additive, afforded pyrazole- and isoxazole-4-carboxylic acids, respectively. The presence of an intramolecular H-bond in these substrates was the key to divert the classical mechanism toward a ring-opening non-decarboxylative path that is expected to generate a vinyl Ru-nitrenoid intermediate, the cyclization of which affords the rearranged products. A gram scale protocol demonstrated the synthetic applicability of this transformation.

Direct Synthesis of Fluorescent Oxazolo-phenoxazines by Copper-Catalyzed/Hypervalent Iodine(III)-Mediated Dimerization/Cyclization of 2-Benzylamino-phenols.

A dimerization/cyclization reaction of 2-benzylamino-phenols for the direct synthesis of the oxazolo-phenoxazine skeleton is reported. The reaction occurs under copper catalysis in the presence of hypervalent iodine(III), giving selectively the 5H-oxazolo[4,5-b]phenoxazine compounds. The cascade process, which allows the conversion of the substrates into the tetracyclic products, involves three C-H functionalization steps. Initial oxidation of electron-rich arenes by the hypervalent iodine is essential for the dimerization of substrates, whereas the formation of the five-membered rings is promoted by the copper species. 1-Benzyl-2-phenyl-6-(aryl-benzyl)amino-benzimidazoles are regioselectively obtained using N,N'-dibenzyl-phenylenediamines as starting substrates. The fluorescence emission properties of these classes of products have been evaluated.

Switchable Oxidative Reactions of N-allyl-2-Aminophenols: Palladium-Catalyzed Alkoxyacyloxylation vs an Intramolecular Diels-Alder Reaction.

The Pd(II)-catalyzed reaction of N-allyl-2-aminophenols in the presence of PhI(OCOR)2 as the oxidant resulted in an alkoxyacyloxylation process, with the formation of functionalized dihydro-1,4-benzoxazines. The reaction performed in the absence of palladium catalyst switched to an intramolecular Diels-Alder reaction (IMDA) pathway, which was the result of an oxidative dearomatization of the 2-aminophenol, nucleophilic addition, and Diels-Alder reaction cascade, highlighting the role of the oxidant as both a nucleophilic donor and an oxidizing agent.

Divergent Conversion of 4-Naphthoquinone-substituted 4H-Isoxazolones to Different Benzo-fused Indole Derivatives.

4,4-Disubstituted 4H-isoxazol-5-ones bearing a 1,4-naphthoquinone moiety undergo transformation into different types of benzoindolyl products depending on the different reaction conditions. A decarboxylative ring opening/ring closure promoted by catalytic [Ru(p-cymene)2Cl2]2 yields benzo[f]indole-4,9-diones. Alternatively, hydrogenation reactions provide the conversion of 4-(1,4-naphthoquinone)-substituted isoxazol-5-ones to benzo[g]indole compounds, with the level of reduction depending on the substituents present on the ring. Starting materials have been easily prepared by the functionalization of isoxazolinones with naphthoquinone under mild conditions.

Intramolecular Aminoazidation of Unactivated Terminal Alkenes by Palladium-Catalyzed Reactions with Hydrogen Peroxide as the Oxidant.

The palladium-catalyzed aminoazidation of aminoalkenes yielding azidomethyl-substituted nitrogen-containing heterocycles was developed. The procedure requires oxidative conditions and occurs at room temperature in the presence of hydrogen peroxide and NaN3 as the azide source. These conditions provide selective exo-cyclization/azidation of the carbon-carbon double bond, furnishing a versatile approach toward five-, six-, and seven-membered heterocyclic rings.

Novel 3,3-disubstituted oxindole derivatives. Synthesis and evaluation of the anti-proliferative activity.

3,3-Disubstituted oxindole derivatives bearing a nitrogen atom at the C-3 position have been synthesized starting from 3-alkyl oxindole through a metal free pathway. These derivatives have been tested in five human tumor cell lines (PC3, MCF7, SW620, MiaPaca2 and A375) and on primary cells (PBMCs) from healthy donors providing compound 6d showing a strong anticancer effect in all cancer lines on the low micromolar range.

Imidazo[2,1-b]benzothiazol Derivatives as Potential Allosteric Inhibitors of the Glucocorticoid Receptor.

Glucocorticoid receptor (GCR) transactivation reporter gene assays were used as an initial high-throughput screening on a diversified library of 1200 compounds for their evaluation as GCR antagonists. A class of imidazo[2,1-b]benzothiazole and imidazo[2,1-b]benzoimidazole derivatives were identified for their ability to modulate GCR transactivation and anti-inflammatory transrepression effects utilizing GCR and NF-κB specific reporter gene assays. Modeling studies on the crystallographic structure of the GCR ligand binding domain provided three new analogues bearing the tetrahydroimidazo[2,1-b]benzothiazole scaffold able to antagonize the GCR in the presence of dexamethasone (DEX) and also defined their putative binding into the GCR structure. Both mRNA level measures of GCR itself and its target gene GILZ, on cells treated with the new analogues, showed a GCR transactivation inhibition, thus suggesting a potential allosteric inhibition of the GCR.

A new scaffold of topoisomerase I inhibitors: Design, synthesis and biological evaluation.

The synthesis of a new hexacyclic system was realized starting from tryptamines and exploiting as a key step a sequential Pd-catalyzed N-arylation/acylation reaction. Having topoisomerases as biological target and the campthotecins class as benchmark, the new scaffold was decorated with substituents having different polarity and tested as Topoisomerase I inhibitors.

Copper(II)-Catalyzed Alkoxyhalogenation of Alkynyl Ureas and Amides as a Route to Haloalkylidene-Substituted Heterocycles.

A highly effective synthesis of haloalkylidene-substituted heterocycles by copper(II)-catalyzed cyclization of alkynyl ureas and secondary amides has been developed. The reaction, which involves a catalytic amount of CuCl2 and a stoichiometric amount of N-halosuccinimide, occurs selectively through an alkoxyhalogenation process. Alternatively, alkoxychlorination and alkoxybromination reactions can be performed working solely with stoichiometric CuCl2 and CuBr2, respectively.

Recent advances in heterobimetallic palladium(II)/copper(II) catalyzed domino difunctionalization of carbon-carbon multiple bonds.

The double functionalization of carbon-carbon multiple bonds in one-pot processes has emerged in recent years as a fruitful tool for the rapid synthesis of complex molecular scaffolds. This review covers the advances in domino reactions promoted by the couple palladium(ii)/copper(ii), which was proven to be an excellent catalytic system for the functionalization of substrates.

Palladium-catalyzed dual C-H or N-H functionalization of unfunctionalized indole derivatives with alkenes and arenes.

This review highlights the development of palladium-catalyzed C-H and N-H functionalization reactions involving indole derivatives. These procedures require unactivated starting materials and are respectful of the basic principle of sustainable chemistry tied to atom economy.

Solvent-free, microwave-assisted N-arylation of indolines by using low palladium catalyst loadings.

Indoline-based compounds are abundant in nature, and the indoline skeleton is an often-encountered scaffold in a range of biologically active alkaloids, pharmaceutically active compounds, and functional molecules (e.g., sensitizers for solar cells). The wide range of uses warrants further interest in the structural modification of this class of compounds. A series of substituted N-aryl indolines is prepared by a solvent-free, palladium-catalyzed procedure. The procedure requires only low loadings of catalyst, uses microwave irradiation, and starts from commercially available substrates. The method proceeds in good yields and in short reaction times with aryl bromides, chlorides, and iodides, also on 2-substituted indolines. The combination of solvent-free methods with microwave heating will further increase in importance in the search for more environmentally acceptable synthesis methods.

Tunable Pd-catalyzed cyclization of indole-2-carboxylic acid allenamides: carboamination vs microwave-assisted hydroamination.

A variety of 3-vinyl-substituted imidazo[1,5-a]indole derivatives were synthesized by intramolecular Pd-catalyzed cyclization of the title allenamides through either a domino carbopalladation/exo-cyclization process or a novel hydroamination reaction that proceeds smoothly under microwave irradiation. Both the observed pathways involve a π-allyl-palladium(II) complex arising from insertion of the allene group into a palladium(II) species, the latter being formed in situ by the intervention of an aryl iodide or of the N-H group. In both cases, the role of nucleophile is covered by the indole nitrogen.

Sigma-alkylpalladium intermediates in intramolecular Heck reactions:isolation and catalytic activity.

The isolation of sigma-alkylpalladium Heck intermediates, possible when beta-hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N-allyl-2-halobenzylamines in the presence of [Pd(PPh(3))(4)], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X-ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five-membered palladacycle with the metal center bearing a PPh(3) ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the sigma-alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for beta-hydride elimination. Subsequently, the thus obtained bridged five-membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross-coupling processes such as Suzuki and Stille reactions.

Palladium-catalyzed domino carbopalladation/5-exo-allylic amination of alpha-amino allenamides: an efficient entry to enantiopure imidazolidinones.

Allenamides of alpha-amino acids were converted into enantiopure 2-vinylimidazolidin-4-ones by a carbopalladation/exo-cyclization process. The products were obtained in 2.5:1-5.5:1 dr, with 94-99% ee. The palladium-catalyzed carbonylative cyclization of the same substrates afforded enone structures. Starting from properly substituted allenamides, an intramolecular carbopalladation followed by intramolecular amination gave rise to tricyclic fused-ring imidazolidinones.

Intramolecular Pd(II)-catalyzed cyclization of propargylamides: straightforward synthesis of 5-oxazolecarbaldehydes.

Direct synthesis of 2-substituted 5-oxazolecarbaldehydes was performed by intramolecular reaction of propargylamides through treatment with a catalytic amount of Pd(II) salts in the presence of a stoichiometric amount of reoxidant agent. The heterocyclization process was well-tolerated by a wide range of aryl, heteroaryl, and alkyl propargylamides. This protocol constitutes a valuable synthetic pathway to 5-oxazolecarbaldehydes, alternative to the formylation on oxazole rings, often unsatisfactory in term of regioselectivity and yields.

New 4-spiroannulated tetrahydroisoquinolines by a one-pot sequential procedure. isolation and characterization of sigma-alkylpalladium heck intermediates.

A simple and efficient entry to new tetrahydroisoquinolines 4-spiroannulated to a five-membered heterocyclic ring has been achieved starting from secondary N-allylamines and involving sequential 2-iodobenzylation/intramolecular Heck reaction/1,3-dipolar cycloaddition. A variety of Heck cyclization conditions were surveyed. When using Pd(PPh(3))(4) as catalyst, stable sigma-alkylpalladium iodide complexes were isolated and characterizated.

Regioselective formation of six- and seven-membered ring by intramolecular Pd-catalyzed amination of N-allyl-anthranilamides.

A divergent synthesis of quinazolin-4-ones and 1,4-benzodiazepin-5-ones by Pd(II)-catalyzed intramolecular amination of tosylated N-allyl-anthranilamides is described. Both kinds of products were available in high yields depending on the different reaction conditions.

Regioselectivity on the palladium-catalyzed intramolecular cyclization of indole derivatives.

Indole 2-carboxamide derivatives 4 underwent palladium-catalyzed intramolecular cyclization reactions to afford beta-carbolinones or pyrazino[1,2-a]indoles according to different reaction pathways. The complete regioselectivity of the reactions was obtained in different reaction conditions.