Cu-Catalyzed Ullmann-Type Double C-N Coupling Approach to 5-Aryl-5H-indolizino[3,2-b]indoles

Synthesis of two nitrogen-containing polyaromatic compounds through gold catalysis/DBU-promoted cyclizations

This work reports an efficient synthesis of novel benzo[7,8]indolizino[2,3,4,5-ija]quinazoline derivatives between 2-(2-ethynylaryl)acetonitriles 1 and anthranils 2. The synthetic approach involves the initial formation of 7-formylindole intermediates that can be implemented by DBU to activate a novel indole-nitrile-aldehyde cyclization.

Switchable Synthesis of Spirodihydroindolizines and Indolizines from Aurones and Pyridin-2-yl Active Methylene Compounds

A novel and flexible domino reaction of aurones with pyridin-2-yl active methylene compounds promoted by I2/BF3 has been developed to afford spirodihydroindolizines and indolizines in a controllable manner. When the reaction was performed in 1,2-dichloroethane at 80 °C, a variety of spirodihydroindolizines were obtained, whereas it almost exclusively provided a series of indolizines when the reaction was performed in a mixed solvent of 1,2-dichloroethane and N,N-dimethylformamide at a relatively higher temperature of 100 °C. Being metal-free, excellent product selectivity, high atom economy, good functional group tolerance, and feasibility for large-scale synthesis are the salient features of the developed methodology.

One-Step Synthesis of 7-Bromobenzo[c]chromeno[4,3,2-gh]phenanthridines through a Sequential Bromination/Cyclization/Aromatization Reaction Using N-Bromosuccinimide (NBS)

Herein, metal- and oxidant-free synthesis of 7-bromobenzo[c]chromeno[4,3,2-gh]phenanthridines is reported using N-bromosuccinimide. Sequential regioselective bromination, intramolecular ring cyclization, and aromatization reactions occur in a single step through a successive radical-catalyzed pathway. The mechanistic pathway for the cyclization is supported by a DFT study. Selective bromination in the fully aromatic skeleton is accomplished without involving additional aromatic electrophilic ring bromination. As a synthetic application, the Suzuki coupling reaction of compound 5a with boronic acid is reported to get compound 8a. Aggregation-induced emission of one of the synthesized compounds (5h) is also investigated in THF/hexane solvent along with concentration-dependent emission spectroscopy.

Regioselective Access to 1,2,4-Triazole-Fused N-Heterocycle, Pyrrolo[1,2-a][1,2,4]triazolo[5,1-c]pyrazine, via Double Dehydrative Cyclizations

A highly efficient and regioselective approach to a novel 1,2,4-triazole-fused N-heterocyclic scaffold, pyrrolo[1,2-a][1,2,4]triazolo[3,4-c]pyrazine, was established by base-promoted reaction of pyrrole-2-carbonitrile-derived substrate with acyl hydrazide where domino double ring closures comprised of enamine formation, attack on nitrile, and cyclodehydration enabled sequential construction of pyrazine and 1,2,4-triazole ring systems with formation of three C-N bonds.

Divergent synthesis of two types of indolizines from pyridine-2-acetonitrile, (hetero)arylglyoxal, and TMSCN

Herein we describe the divergent synthesis of two types of indolizines via construction of the pyrrole moiety from pyridine-2-acetonitriles, arylglyoxals, and TMSCN. While one-pot three-component coupling provided 2-aryl-3-aminoindolizines via an unusual fragmentation process, a sequential two-step assembly protocol with these starting materials allowed efficient access to a wide range of new 2-acyl-3-aminoindolizines through an aldol condensation-Michael addition-cycloisomerization process. The subsequent manipulation of 2-acyl-3-aminoindolizines enabled direct access to novel polycyclic N-fused heteroaromatic skeletons.