General and Direct Synthesis of 3-Aminoindolizines and Their Analogues via Pd/Cu-Catalyzed Sequential Cross-Coupling/Cycloisomerization Reactions

Diversity-Oriented Metal-Free Synthesis of Nitrogen-Containing Heterocycles Using Atropaldehyde Acetals as a Dual C3/C2-Synthon

A highly efficient and elegant diversity-oriented reaction paradigm employing atropaldehyde acetals as new dual C2/C3 synthons was developed under metal-free conditions using glycine esters as the counterpart reagents, which allowed rapid synthesis of two important nitrogen-containing heterocycles, pyrrolo[1,2-a]quinolines and 3,5-diarylpyridines. The divergent products are subtly controlled by the manipulation of the substitutional groups of glycine esters. When a N-arylglycine ester was used, pyrrolo[1,2-a]quinolines can be formed through cascade oxidative C-C cleavage/multiple cyclization. Instead, N-benzylglycine ester as the counter-reagent led to the synthesis of 3,5-diarylpyridines via two key C-N cleavages. Mild conditions, broad substrate scope, scalability and environmentally acceptable organic solvents rendered this method practical and attractive.

Titanium-Mediated aza-Nazarov Annulation for the Synthesis of N-Fused Tricycles: A General Method to Access Lamellarin Analogues

Fused heterocycles with nitrogen incorporation are of particular bioactive use and high importance in many research fields, especially isoquinoline-based [6/6/5] tricycles. Here, we report a unique strategy to access multifunctional N-fused tricycles from α,β-unsaturated isoquinoline ketone and sulfonamide under mild reaction conditions. The methodology features wide substrate tolerance, and a set of N-fused heteroarenes including quinoline, phthalazine, quinazoline, quinoxaline, and benzothiazole cores are furnished efficiently. Moreover, the protocol is easy to scale up to synthesize lamellarin analogues, and the amide group of the product is also easy to transfer to other functional groups.

Palladium catalyzed synthesis of indolizines via the carbonylative coupling of bromopyridines, imines and alkynes

We report herein the development of a palladium-catalyzed, multicomponent synthesis of indolizines. The reaction proceeds via the carbonylative formation of a high energy, mesoionic pyridine-based 1,3-dipole, which can undergo spontaneous cycloaddition with alkynes. Overall, this provides a route to prepare indolizines in a modular fashion from combinations of commercially available or easily generated reagents: 2-bromopyridines, imines and alkynes.

Transition-metal-free catalyzed [3+2] cycloadditions/oxidative aromatization reactions for the synthesis of annulated indolizines

A transition-metal-free catalyzed [3+2] cycloadditions/oxidative aromatization three-component reactions for direct construction of annulated indolizines was reported.

Synthesis of functionalized indolizines via gold(i)-catalyzed intramolecular hydroarylation/aromatization of pyrrole-ynes

A gold-catalyzed intramolecular hydroarylation/aromatization of pyrrole-ynes has been developed. This method provides a concise and straightforward route to functionalized indolizines through the construction of the pyridine ring of indolizines and also allows elaboration of its pyrrole moiety with or without functional groups. In addition, a wide variety of functional groups, such as aryl, alkenyl, alkynyl, pyridyl or thienyl groups, can be easily incorporated into the pyridine unit of the indolizine products under mild conditions. The utility of the indolizine products was demonstrated by their efficient transformations into various C3-functionalized indolizine derivatives.

Synthesis of indolizine derivatives containing eight-membered rings via a gold-catalyzed two-fold hydroarylation of diynes

A novel strategy for a gold(i)-catalyzed synthesis of indolizine derivatives containing eight-membered rings has been developed, which may have potential usefulness as blue or green OLEDs.

Indium(III)-catalyzed Aza-Conia-Ene Reaction for the Synthesis of Indolizines

A new indium(III)-catalyzed reaction for the synthesis of a series of indolizine scaffolds has been developed. This methodology was highly efficient, allowing a low catalyst loading of 2 mol % (down to 0.5 mol %) and rendering the products in high yields through a 5-exo-dig aza-Conia-ene reaction. Furthermore, the possibility of incorporating an electrophile into the generated pyrrolidone ring in a one-pot synergistic fashion was demonstrated. Finally, based on experimental observations, a mechanism proposal was outlined.

Chloroacetate Promotes and Participates in the Oxidative Annulation of Pyridines/Isoquinoline by Using Oxygen as the Oxidant

The aerobic oxidative annulation of chalcones, pyridines/isoquinoline and ethyl chloroacetate to indolizines was achieved by cascade reaction. Various functional groups on chalcones were tolerated. And different pyridines derivatives could also be suitable substrates. Ethyl chloroacetate is an essential component in participating of the oxidative annulation process. Overall, this protocol is very practical and efficient by using molecular oxygen as oxidant with high selectivity for the annulation product.

Copper NPs supported on hematite as magnetically recoverable nanocatalysts for a one-pot synthesis of aminoindolizines and pyrrolo[1,2-a]quinolines

Copper mixed oxide NPs supported on a hematite surface were achieved using a facile hydrothermal method in a single step. The catalytic potential of the Cu@Fe₂O₃ NPs was explored for the synthesis of aminoindolizines and pyrrolo[1,2-a]quinolines.

Recent advances in the synthesis of indolizines and their π-expanded analogues

Synthesis of indolizines developed during the last decade is reviewed, with special emphasis given to densely functionalized architectures, breakthrough strategies, compounds bearing electron-donating and electron-withdrawing substituents and π-expanded systems.

Multicomponent Strategy to Pyrazolo[3,4-e]indolizine Derivatives under Microwave Irradiation

A simple and efficient one-pot construction of pyrazolo[3,4-e]indolizine derivatives via a diethylamine-catalyzed three-component domino reaction of arylglyoxals, cyclic 1,3-diones, and 5-aminopyrazoles under microwave irradiation is described. In this one-pot transformation, seven bonds and two new rings are efficiently formed. This synthesis was confirmed to follow the group-assisted-purification (GAP) chemistry process, which can avoid traditional recrystallization or chromatography purification methods.

Au-catalyzed ring-opening reactions of 2-(1-alkynyl-cyclopropyl)pyridines with nucleophiles

A novel method for the C-C bond cleavage of cyclopropanes was developed by gold-catalyzed cycloisomerization of 2-(1-alkynyl-cyclopropyl)pyridine with nucleophiles, which provides efficient access to structurally diverse indolizines under mild conditions. A series of N-, C- and O-based nucleophiles were involved in this reaction to afford the corresponding indolizines in modest to excellent yields.

A facile approach for the synthesis of 1,3-di- and 1,2,3-tri-substituted indolizines

A convenient synthesis of 1,3-di- and 1,2,3-tri-substituted indolizines involving the multicomponent reaction of pyridinium salt (or quinolinium salt), olefine acid, and 1,2-dichloroethane has been achieved. The process proceeds smoothly in moderate to high yields.

An I2-catalyzed oxidative cyclization for the synthesis of indolizines from aromatic/aliphatic olefins and α-picoline derivatives

A novel I₂-catalyzed intermolecular oxidative tandem cyclization reaction of aromatic/aliphatic olefins and α-picoline derivatives has been achieved for the synthesis of indolizines under metal-free conditions.

Palladium-catalyzed highly efficient synthesis of functionalized indolizines via cross-coupling/cycloisomerization cascade

Pd-catalyzed cross-coupling/cycloisomerization of 3-(2-pyridyl) propargyl carbonates with organoboronic acids provides a straightforward route for the synthesis of 1,3-disubstituted indolizines.

Indolizine synthesis via Cu-catalyzed cyclization of 2-(2-enynyl)pyridines with nucleophiles

Cu-catalyzed cyclization of 2-(2-enynyl)pyridines with various nucleophiles was developed, providing efficient access to indolizine derivatives.

(11aS)-1,5,11,11a-Tetra-hydro-1-benzo-thieno[3,2-f]indolizin-3(2H)-one

The absolute configuration of the title compound, C₁₄H₁₃NOS, was assigned from the synthesis and confirmed by the structure determination. There are two independent mol­ecules in the asymmetric unit. The central six-membered ring of the indolizine moiety adopts an envelope conformation, with the greatest deviations from the mean planes being 0.569 (3) and 0.561 (3) Å for the indolizine bridgehead C atoms of the two mol­ecules. The benzothieno ring attached to the indolizine ring system is planar to within 0.015 (3) Å in both mol­ecules. In the crystal, weak C—H⋯O and C—H⋯π inter­actions lead to the formation of a three-dimensional framework structure.