One-Pot Gold-Catalyzed Aminofluorination of Unprotected 2-Alkynylanilines

BF3·OEt2-mediated nucleophilic fluorocyclization of sulfonyl 3-methylene-oxabenzocyclooctan-6-ones. Diastereocontrolled synthesis of benzofused fluorooxabicyclo[4.2.1]nonanes

We describe a facile-operational, high-yield method for the diastereocontrolled preparation of novel sulfonyl benzofused fluorooxabicyclo[4.2.1]nonanes by a straightforward synthetic route, including (i) NaBH₄-mediated reduction of sulfonyl 3-methylene-oxabenzocyclooctan-6-ones and (ii) BF₃·OEt₂-mediated intramolecular nucleophilic fluorocyclization. The plausible mechanism for the preparation is proposed and discussed. This protocol can easily install a fluoro-atom on the bridged head position in a short time and under mild conditions, resulting in one carbon-carbon and one carbon-fluorine bond formation.

Divergent synthesis of 4-amino indoles with free amine groups via tandem reaction of 2-alkynylanilines

A dearomatization method for divergent synthesis of 4-amino indoles having N1 or C4 free amine groups from 2-alkynylanilines was reported.

Gold-Catalyzed Reactions Towards Diversity: From Simple Substrates to Functionalized Carbo- and Heterocycles

The field of gold catalysis has been in constant expansion during the last twenty years. Based on the precept of π-activation of unsaturated simple substrates, several new rearrangements have been discovered, implying aryl, alkyne, alkene or keto derivatives as key partners. In this personal account, the main contributions in the field of gold catalysis from our group will be highlighted, emphasizing the recent reports, starting from 1,6- and 1,5-enynes and then moving to keto-ynes derivatives. The gold-catalyzed reactions will be presented starting from classical skeletal rearrangements (cycloisomerization) and then domino processes. In each part, the presentation of asymmetric versions will be highlighted.

The interplay of carbophilic activation and Au(I)/Au(III) catalysis: an emerging technique for 1,2-difunctionalization of C-C multiple bonds

Gold complexes have emerged as the catalysts of choice for various functionalization reactions of C-C multiple bonds due to their inherent carbophilic nature. In a parallel space, efforts to realize less accessible cross-coupling reactivity have led to the development of various strategies that facilitate the arduous Au(i)/Au(iii) redox cycle. The interplay of the two important reactivity modes encountered in gold catalysis, namely carbophilic activation and Au(i)/Au(iii) catalysis, has allowed the development of a novel mechanistic paradigm that sponsors 1,2-difunctionalization reactions of various C-C multiple bonds. Interestingly, the reactivity as well as selectivity obtained through this interplay could be complementary to that obtained by the use of various other transition metals that mainly involved the classical oxidative addition/migratory insertion pathways. The present review shall comprehensively cover all the 1,2-difunctionalization reactions of C-C multiple bonds that have been realized by the interplay of the two important reactivity modes and categorized on the basis of the method that has been employed to foster the Au(i)/Au(iii) redox cycle.

Fluorination and fluoroalkylation of alkenes/alkynes to construct fluoro-containing heterocycles

This review summarize the established strategies through fluorination and fluoroalkylation of alkenes/alkynes for constructing fluoro-containing heterocycles. Reaction scopes, mechanisms and some shortcomings are also discussed.

Experimental and computational evidence on gold-catalyzed regioselective hydration of phthalimido-protected propargylamines: an entry to β-amino ketones

The results of our investigations on the Au-catalyzed regioselective hydration reaction of both alkyl- and aryl-substituted N-propargyl phthalimides directed to the selective formation of the corresponding β-phthalimido ketones are described. Experimental data, in particular the observed regioselectivity, have been qualitatively supported by quantum-chemical calculations carried out on model systems in the framework of Density Functional Theory (DFT) followed by quantum theory of atoms in molecules (QTAIMS). Our results suggest that the electronic features of the initial adduct between the propargyl triple bond and the Au(i) catalyst, in particular the character of the gold-triple bond interaction, are essential for the observed regioselectivity. Other effects, such as the presence of the solvent and the formation of a H-bond between the water molecule and the phthalimido moiety, although apparently irrelevant for the regioselectivity, have proven to be kinetically and catalytically rather important.

Gold-Catalyzed Cycloisomerization of 1,6-Cyclohexenylalkyne: An Efficient Entry to Bicyclo[3.2.1]oct-2-ene and Bicyclo[3.3.1]nonadiene

An efficient and mild synthetic route for the preparation of functionalized bicyclo[3.2.1]oct-2-ene and bicyclo[3.3.1]nonadiene via gold-mediated cycloisomerization of 1,6-enynes has been developed. This atom-economical catalytic process was optimized and relied on the efficiency of IPrAuNTf₂ allowing the formation of functionalized bicyclic adducts in 55-91% isolated yields (18 products). The reliable access to bicyclic derivatives was demonstrated on a 3 g scale with a low catalyst loading. The process occurred on a 5-exo versus 6-endo pathway depending on the substitution of the alkynyl moiety. Density functional theory (DFT) calculations were performed on the stability of intermediates, and this study corroborated the endo/exo ratio and the mechanistic pathway with key intermediates. Reduction of the ester moiety and hydrogenation of the exo-methylene double bond of the bicyclo[3.2.1]oct-2-ene adduct illustrated the potential postfunctionalization of bicyclic derivatives.

Ruthenium Metathesis: A Key Step To Access a New Cyclic Tetrasubstituted Olefin Platform

An rapid and mild synthetic route for the preparation of cyclic tetrasubstituted platforms via ruthenium-catalyzed ring-closing metathesis (RCM) has been developed. This process tolerates a wide range of functionalities such as nitrogen, oxygen, sulfur, silicon, and carbon tethered groups, as well as very challenging fluorine and boron atoms (36 derivatives, up to 96%). This diversity-oriented method was further demonstrated by the postfunctionalization reactions, such as Pd-couplings, N-substitution, and reductive amination introducing a morpholine moiety.

1,4-Fluoroamination of 1,3-Enynes en Route to Fluorinated Allenes

The regioselective synthesis of fluorinated allenes via a metal-free 1,4-fluoroamination of 1,3-enynes is presented. This method employs commercially available N-fluorobenzenesulfonimide serving as both the nitrogen source and the fluorine source, affording access to various tetrasubstituted allenes in a straightforward and atom-economic pathway. Preliminary mechanistic studies and theoretical studies revealed that this reaction might undergo an intimate ion-pair mechanism.

When Gold Meets Perfumes: Synthesis of Olfactive Compounds via Gold-Catalyzed Cycloisomerization Reactions

An efficient, and mild synthetic route for the preparation of functionalized volatile oxa-bicyclo[4.1.0]-hept-4-ene (29 compounds, 44-98% isolated yields) has been developed relying on the association of IPrAuCl with NaBArF. The remarkable selectivity was demonstrated on a 1 g and 25 g scale with low catalyst loadings. The synthetic utility of these low-molecular-weight enols was further demonstrated by the derivatization of some adducts and by the unprecedented olfactory evaluation of all bicyclic derivatives.

Juniperanol: First total synthesis and evaluation in Type 2 Diabetes disease

The first total synthesis of juniperanol, the tricyclic sesquiterpenoid enantiomer of α-cedrol is described. The synthesis relies on stereoselective gold-catalyzed Ohloff-type propargylic ester rearrangement performed on a 10 g scale, and a carbocationic cascade in the presence of acetyl methanesulfonate. The ability of juniperanol to interfere in glucose processes in different cell types is described.

Shielding Effect of Micelle for Highly Effective and Selective Monofluorination of Indoles in Water

Highly selective direct monofluorination of indoles and arenes was developed through an approach that allows site-specific solubility of substrate and fluorine source in the micelle. This approach was highly selective for a broad range of substrates with excellent functional group tolerance. Differences in binding constant and solubility of indoles and arenes in the micelle allowed the fine-tuning of selectivity. Control experiments suggested a radical pathway and provided insight into the role of micelles of the environmentally benign amphiphile PS-750-M. Dynamic light scattering experiments strongly indicated the site-specific solubility of the substrate and fluorine source. The methodology was successfully adapted to gram scale, and the E-factor established from a recycle study indicated that the process is environmentally responsible and sustainable.

Fluorination-triggered tandem cyclization of styrene-type carboxylic acids to access 3-aryl isocoumarin derivatives under microwave irradiation

A practical and straightforward synthetic route through a fluorination-triggered tandem cyclization of styrene-type carboxylic acids was developed to construct a variety of 4-fluoro-3-aryl-3,4-dihydroisocoumarins and 3-arylisocoumarins under microwave irradiation. This novel protocol features mild reaction conditions and operational simplicity, with good yields.

Copper-catalyzed tandem reaction of 2-alkynylanilines with benzoquinones: efficient access to 3-indolylquinones

A simple, mild, catalytic and efficient method for the straightforward synthesis of an interesting class of 2-aryl/alkyl-substituted-3-indolyl quinones in good to high yields is reported for the first time. This atom-efficient method proceeds via copper-catalyzed one-pot sequential intramolecular hydroamination (C-N bond formation) of 2-alkynylanilines followed by oxidative C-C coupling with benzoquinones.

Domino cyclization/trifluoromethylation of 2-alkynylanilines using fluoroform-derived CuCF3: synthesis of 3-(trifluoromethyl)indoles

A domino cyclization/trifluoromethylation strategy for the construction of indole cores with concomitant installation of a CF₃ group is described.

Gold-catalyzed tandem reaction of 2-alkynylanilines followed by 1,6-conjugate addition to p-quinone methides: efficient access to unsymmetrical diarylindolylmethanes

A simple, mild, efficient and chemoselective catalytic method for the straightforward synthesis of an interesting class of 2-aryl/alkyl-substituted-3-diaryl indolyl methanes in high yield is reported.

Hypervalent iodine-triggered transformation of homopropargyl sulfonamides into dihalo-2,3-dihydropyrroles

A novel hypervalent iodine-triggered hydroamination of homopropargyl sulfonamides with copper halides to obtain dihalo-2,3-dihydropyrroles was efficiently developed.

Fluorination methods in drug discovery

Fluorination reactions of medicinal and biologically-active compounds will be discussed. Late stage fluorination strategies of medicinal targets have recently attracted considerable attention on account of the influence that a fluorine atom can impart to targets of medicinal importance, such as modulation of lipophilicity, electronegativity, basicity and bioavailability, the latter as a consequence of membrane permeability. Therefore, the recourse to late-stage fluorine substitution on compounds with already known and relevant biological activity can provide the pharmaceutical industry with new leads with improved medicinal properties. The fluorination strategies will take into account different fluorinating reagents, either of nucleophilic or electrophilic, and of radical nature. Diverse families of organic compounds such as (hetero)aromatic rings, and aliphatic substrates (sp(3), sp(2), and sp carbon atoms) will be studied in late-stage fluorination reaction strategies.

Gold-catalyzed cycloisomerization of trifluoromethylated allenols: sustainability and mechanistic studies

Trifluoromethyl-substituted α-allenols are cyclized to the corresponding 2,5-dihydrofurans in the presence of neutral or cationic gold catalysts.

Silver- versus gold-catalyzed sequential oxidative cyclization of unprotected 2-alkynylanilines with oxone

Divergent catalytic activity of gold and silver complexes towards domino oxidative cyclization reactions of unprotected 2-alkynylanilines.

Silver-catalysed reactions of alkynes: recent advances

Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.