Tandem imination/annulation of γ- and δ-ketoalkynes in the presence of ammonia/amines

Synthesis of Nitrogen-Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls

Sequential reactions of aminoalkynes represent a powerful tool to easily assembly biologically important polyfunctionalized nitrogen heterocyclic scaffolds. Metal catalysis often plays a key role in terms of selectivity, efficiency, atom economy, and green chemistry of these sequential approaches. This review examines the existing literature on the applications of reactions of aminoalkynes with carbonyls, which are emerging for their synthetic potential. Aspects concerning the features of the starting reagents, the catalytic systems, alternative reaction conditions, pathways and possible intermediates are provided.

Synthesis and photophysical evaluation of polarity sensitive push-pull isoquinolines and their alkynyl precursors

Two sets of unprecedented push-pull isoquinolines, characterized by an opposite "dipolar moment" with respect to the longitudinal axis of the molecule, have been prepared. The key step of the approach is the microwave-promoted domino imination/cycloisomerization of 2-alkynyl benzaldehydes in the presence of methanolic ammonia. Absorption spectra and emission spectra of the D-π-A isoquinolines and their alkynyl precursors in nine different solvents have been recorded. The absolute QYs of all compounds have been recorded in three solvents with different polarities, i.e. toluene, DMSO and ethanol. Among the D-π-A isoquinolines prepared - nicknamed QuinaChroms - two compounds characterized by opposite dipolar moments, i.e. 3-(4-methoxyphenyl)-7-nitroisoquinoline 1a and N,N-diethyl-3-(4-(methylsulfonyl)phenyl)isoquinolin-7-amine 2b displayed more interesting photophysical profiles, whereas 5-(diethylamino)-2-(A)arylethynylbenzaldehydes precursors 8a-c - having a free aldehyde group that is suitable for possible conjugation - exhibited strong fluorescence and wide Stokes shifts. These products are interesting for potential use as polarity-sensitive fluorescent probes or advanced functional materials.

Cycloisomerization of π-Coupled Heteroatom Nucleophiles by Gold Catalysis: En Route to Regiochemically Defined Heterocycles

Since the dawn of millennium, catalytic gold chemistry is at the forefront to set off diverse organic reactions via unique activation of π-bonded molecules. Within this purview, cycloisomerization of heteroatom nucleophiles linked to a π-system is one of the well recognized chemistry for the construction of numerous heterocyclic cores. Though the rudimentary aspects of this transformation are reviewed by several groups in different timeline, a holistic view on regiochemistry of such reactions went largely overlooked. Hence, this account emphasizes the gold catalyzed regioselective cycloisomerization of structurally distinctive π-connected hetero-nucleophiles leading to different heterocycles documented in the last two decades. From an application perspective, this account also highlights those methodologies which find a role in the total synthesis of natural products. Wherever appropriate, mechanistic details and contributing factors for selectivity are also discussed.

Silver comes into play: Henry reaction and domino cycloisomerisation sequence catalysed by [Ag(i)(Pc-L)] complexes

The Ag(i) complexes of pyridine-containing ligands with an active pendant arm are new catalysts for an old reaction: the nitroaldol condensation. When the substrates are 2-alkynylarylaldehydes, a smart cascade cycloisomerisation process can occur.

Silver and gold-catalyzed multicomponent reactions

Silver and gold salts and complexes mainly act as soft and carbophilic Lewis acids even if their use as σ-activators has been rarely reported. Recently, transformations involving Au(I)/Au(III)-redox catalytic systems have been reported in the literature. In this review we highlight all these aspects of silver and gold-mediated processes and their application in multicomponent reactions.

Gold versus silver catalyzed intramolecular hydroarylation reactions of [(3-arylprop-2-ynyl)oxy]benzene derivatives

The scope and the generality of gold versus silver catalyzed intramolecular hydroarylation reactions of 3-[(3-arylprop-2-ynyl)oxy]benzene derivatives in terms of rings substitution were investigated. Only products deriving from 6-endo cyclization were exclusively formed. The features of substituents had a considerable effect on the reaction outcome in the presence of silver catalysis, whereas gold catalysis revealed a unique blend of reactivity and selectivity and represented the only choice for the intramolecular hydroarylation reaction of the starting substrates bearing electron deficient arenes.

Synthesis of two unnatural oxygenated aaptaminoids

Two unprecedented oxygenated aaptaminoids have been synthesized starting from cheap and easily available 2,3-dihydroxybenzoic acid with the satisfactory overall yields of 31% and 34%. The key step of the procedure is the divergent thermic 5-exodig vs base-promoted 6-endodig cyclization of a 5-alkynylquinolinone derivative.

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold-triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

The gold-catalyzed, seven-membered ring forming, intramolecular hydroamination of alkynic sulfonamides has been investigated. The protocol, with a semihollow-shaped triethynylphosphine as a ligand for gold, allowed the synthesis of a variety of azepine derivatives, which are difficult to access by other methods. Both alkynic sulfoamides with a flexible linear chain and the benzene-fused substrates underwent 7-exo-dig cyclization to afford the nitrogen-containing heterocyclic seven-membered rings, such as tetrahydroazepine and dihydrobenzazepine, in good yields.