Allene-Based Gold-Catalyzed Stereodivergent Synthesis of Azapolycyclic Derivatives of Unusual Structure

Gold catalysis in quinoline synthesis

Quinolines are biologically and pharmaceutically important N-heterocyclic aromatic compounds, which have broad applications in medicinal chemistry. Thus, their efficient synthesis has attracted extensive attention, and a broad range of synthetic strategies have been established. Of note, gold-catalyzed methodologies for the synthesis of quinolines have greatly advanced this field. Various gold-catalyzed intermolecular annulation reactions, such as annulations of aniline derivatives with carbonyl compounds or alkynes, annulations of anthranils with alkynes, and annulations based on A3-coupling reactions, as well as intramolecular cyclization reactions of azide-tethered alkynes, 1,2-diphenylethynes, and 2-ethynyl N-aryl indoles, have been developed. This review provides an overview of this exciting research area. Typical achievements in reaction methodologies and plausible reaction mechanisms are summarized.

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.

Gold-Catalyzed Divergent Ring-Closing Modes of Indole-Tethered Amino Allenynes

Indole-tethered amino allenynes were chemodivergently cyclized for the controlled preparation of fused polycyclic indoles using gold catalysis. Double cyclization of terminal allenynes afforded hexacyclic 15 H-indolo[1,2,3-de]quinolino[3,2,1-ij]quinoxalines, in which allenynes bearing a substituted alkyne at the terminal end generated 12,13-dihydro-7 H-indolo[3,2-c]acridines, which are 5-membered cyclized adducts. Density functional theory calculations were performed to shed light on this difference in reactivity.