A New Approach to Imidazo[1,5-a]indole Derivatives

Recent development in the synthesis of imidazo[1,5-a]indole derivatives: an in-depth overview

In the realm of nitrogen-fused heterocycles, imidazo[1,5-a]indole and its derivatives are recognized as privileged structural patterns in various pharmaceutical drugs and biologically active natural products, emphasizing their significance. This review comprehensively explores the synthetic strategies for constructing imidazo[1,5-a]indole scaffolds, with a particular focus on transition metal-catalyzed methodologies. The primary highlighted method is [4 + 1] annulation, along with other notable approaches such as C-H activation/cyclization, enantioselective C-H annulation, intramolecular hydroamination, and double cyclization processes.

Design of a new method for the synthesis of novel 2-aryl/alkyl-3H-indol-3-ones

In this research, a mild, efficient, and general method has been developed to synthesize the new derivatives of 2-aryl/alkyl-3H-indol-3-ones in moderate to excellent yields. This method allowed the syntheses of these compounds via the three-component reaction of anhydride compound, sodium cyanide, and aniline derivatives using acetic anhydride as an organic catalyst in one-pot reactions. The advantages of this method include mild reaction conditions, simple procedures, and easy workup.

Easy S-Alkylation of Arylthioureas and 2-Mercaptobenzothiazoles Using Tetraalkylammonium Salts under Transition-Metal-Free Conditions

A highly-efficient and practical method for S-alkylation of arylthioureas was reported. Using tetraalkylammonium salts as alkylation reagents, a series of 68 S-substituted aryl-isothioureas were obtained in good to excellent yields under transition-metal-free conditions. The protocol features simple performance, broad functional group tolerance, good to excellent yields, and easily available starting materials, showing potential synthetic value for the preparation of diverse biologically or pharmaceutically active compounds.

Easy synthesis of imidazo[1,5-a]indol-3-ones through Rh(III)-catalyzed C-H allenylation/annulation

A highly efficient and regioselective synthesis of imidazo[1,5-a]indol-3-ones has been developed via a sequential C-H allenylation/annulation starting from easily available N-methoxycarbamoyl indoles and propargyl alcohols, in which the propargyl alcohols served as a C1 synthon. This strategy displays excellent regioselectivity, high atom economy and tolerates a broad substrate scope.

A route to access imidazol[1,5-a]indole-1,3-diones and pyrrolo[1,2-c]imidazole-1,3-diones

A novel and practical route to synthesize imidazol[1,5-a]indoles and pyrrolo[1,2-c]imidazoles via N-H functionalization has been developed. Indole-2-carboxylic acid or pyrrole-2-carboxylic acid with diverse aniline groups and carbonyldiimidazole (CDI), in the presence of a base under microwave conditions, resulted in imidazol[1,5-a]indoles and pyrrolo[1,2-c]imidazoles, respectively. The present method is free of work-up and no need for column chromatography. Both title scaffolds can serve as useful heterocyclic scaffolds in medicinal chemistry as such, or they can be used as building blocks to construct different classes of useful compounds.

Rapid Syntheses of Heteroaryl-Substituted Imidazo[1,5-a]indole and Pyrrolo[1,2-c]imidazole via Aerobic C2-H Functionalizations

Here we report an aerobic Pd(0) catalyzed C2-H functionalization of indoles and pyrroles with tethered N-methoxylamide as the directing group. A Pd(0)-initiated mechanism overcomes the directing or poisoning effect from a wide range of heterocycles including pyridine, pyrimidine, and thiazole. The imidazo[1,5-a]indole products are transformed to bioactive analogs after one-step manipulations, demonstrating the potential utility of this reaction in drug discovery.

(S)-5-Benzyl- and 5-benzylidene-imidazo-4-one derivatives synthesized and studied for an understanding of their thermal reactivity

Static and flash vacuum pyrolysis were used to get insight into the mechanisms of decomposition of 3-(2-chloroethyl)imidazolidine-2,4-dione and 2,3-dihydroimidazo[2,1-b]thiazol-5(6H)-one derivatives.

Novel Synthesis of Bicycles with Fused Pyrrole, Indole, Oxazole, and Imidazole Rings

Reactions of benzotriazol-1-yl(1H-pyrrol-2-yl)methanone 10 and benzotriazol-1-yl(1H-indol-2-yl)methanone 11 with diverse ketones, isocyanates, and isothiocyanates in the presence of base afforded pyrrolo[1,2-c]oxazol-1-ones 1, oxazolo[3,4-a]indol-1-ones 2, pyrrolo[1,2-c]imidazoles 3, and imidazo[1,5-a]indoles 4 by a simple one-step procedure.