Electron-withdrawing group effect in aryl group of allyl bromides for the successful synthesis of indolizines via a novel [3+3] annulation approach

Pyrrole-Based Enaminones as Building Blocks for the Synthesis of Indolizines and Pyrrolo[1,2-a]pyrazines Showing Potent Antifungal Activity

As a new approach, pyrrolo[1,2-a]pyrazines were synthesized through the cyclization of 2-formylpyrrole-based enaminones in the presence of ammonium acetate. The enaminones were prepared with a straightforward method, reacting the corresponding alkyl 2-(2-formyl-1H-pyrrol-1-yl)acetates, 2-(2-formyl-1H-pyrrol-1-yl)acetonitrile, and 2-(2-formyl-1H-pyrrol-1-yl)acetophenones with DMFDMA. Analogous enaminones elaborated from alkyl (E)-3-(1H-pyrrol-2-yl)acrylates were treated with a Lewis acid to afford indolizines. The antifungal activity of the series of substituted pyrroles, pyrrole-based enaminones, pyrrolo[1,2-a]pyrazines, and indolizines was evaluated on six Candida spp., including two multidrug-resistant ones. Compared to the reference drugs, most test compounds produced a more robust antifungal effect. Docking analysis suggests that the inhibition of yeast growth was probably mediated by the interaction of the compounds with the catalytic site of HMGR of the Candida species.

Base-promoted [4 + 2] annulation of pyrrole-2-carbaldehyde derivatives with β,γ-unsaturated α-ketoesters: syntheses of 5,6-dihydroindolizines

A base-promoted [4 + 2] annulation of pyrrole-2-carbaldehyde derivatives with β,γ-unsaturated α-ketoesters for the syntheses of multisubstituted 5,6-dihydroindolizines was developed.

The Kröhnke synthesis of benzo[a]indolizines revisited: towards small, red light emitters

Benzo[a]indolizines with an ordered arrangement of various electron-withdrawing substituents (NO2, CF3, CN, CO2R and COPh) were prepared directly from pyridinium salts and chloronitroarenes, allowing for refined control of the photophysical...

A domino annulation approach to 3,4-diacylpyrrolo[1,2-a]pyrazines: decoration of pyrazine units

A new one-pot, sequential three-component access to 3,4-diacylpyrrolo[1,2-a]pyrazine was achieved from the reaction of an α-haloketone, azide, and N-substituted pyrrole-2-carboxaldehyde under mild reaction conditions, through which a polysubstitution pattern on the pyrazine moiety of the scaffold was realized. The formation of multiple bonds (one C-C and two C-N) was enabled by this domino process involving the in situ generation of α-iminoketones, intermolecular Mannich reaction, intramolecular imine formation, and aromatization. Construction of the relevant 3,4-diacylpyrazino[1,2-a]indole and further expansion of this chemical space via synthetic elaboration of the resulting products were demonstrated as well. Preliminary biological screening of the synthesized derivatives against oral adenosquamous carcinoma cells (CAL-27) and triple negative human breast cancer cells (MDA-MB-231) led us to identify a potent hit compound (7o) having ∼3 times stronger in vitro anticancer activity than that of the anticancer agent, capecitabine.

Recent advances in the synthesis of pyrido[1,2-a]indoles

This review deals with the different accesses leading to the pyrido[1,2-a]indole nucleus in the last 20 years.

Synthesis of a crystallochromic indolizine dye by a base- and catalyst-free photochemical route

Irradiation of 2-benzoyl-N-benzylpyridinium derivatives and dimethyl acetylene dicarboxylate resulted in the formation of inolizine derivatives, one which was found to be the first example of a crystallochromic indolizine.

Metal-Free Cascade Approach toward Polysubstituted Indolizines from Chromone-Based Michael Acceptors

An efficient cascade transformation toward indolizine-based molecules has been developed. This process leads to the rapid construction of two C-N bonds and one C-C bond without the need of any metal catalysis. The approach involves easily accessible chromone-based Michael acceptors and propargylamine derivatives as starting materials. This cascade constitutes a novel and very competitive alternative to the well reported strategies using pyridine or pyrrole derivatives for accessing the indolizine ring with substituents at uncommon C-positions.

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.

Construction of benzo-fused indolizines, pyrrolo[1,2-a]quinolines via alkyne–carbonyl metathesis

The strategic use of a sequential Sonogashira coupling/intramolecular alkyne–carbonyl metathesis process for the synthesis of a pyridine ring from 1-(2-haloaryl)-1H-pyrrole-2-carbaldehydes allowed ready access to diverse novel benzo-fused indolizines, pyrrolo[1,2-a]quinolines, in good to excellent yields.

C3 functionalization of indolizines via In(iii)-catalyzed three-component reaction

Post-functionalization at the C3 position of indolizines via In(iii)-catalyzed three-component coupling reaction with amines and aldehydes allowed rapid access to a new class of indolizines with diverse functional groups at the C3 position in good to excellent yields.