Rhodium enalcarbenoids: direct synthesis of indoles by rhodium(II)-catalyzed [4+2] benzannulation of pyrroles

One-pot construction of sterically challenging and diverse polyarylphenols via transition-metal-free benzannulation and their potent in vitro antioxidant activity

One pot novel synthesis of highly functionalized polyarylphenols via benzannulation under transition-metal-free conditions and their antioxidant activities are described.

Catalytic, Cascade Ring-Opening Benzannulations of 2,3-Dihydrofuran O,O- and N,O-Acetals

An Al(OTf)3 -catalyzed intramolecular cascade ring-opening benzannulation of 2,3-dihydrofuran O,O- and N,O-acetals is described. The cascade sequence involves the dihydrofuran ring-opening by acetal hydrolysis, an intramolecular Prins-type cyclization, and aromatization to generate an array of benzo-fused (hetero)aromatic systems in up to 95 % yield. This method represents the first example of dihydrofuran acetal usage in benzannulation reactions. The approach provides excellent regiocontrol based on the choice of alkenes used to form the requisite dihydrofuran acetals.

Rhodium(I)-Catalyzed Benzannulation of Heteroaryl Propargylic Esters: Synthesis of Indoles and Related Heterocycles

A de novo synthesis of a benzene ring allows for the preparation of a diverse range of heterocycles including indoles, benzofurans, benzothiophenes, carbazoles, and dibenzofurans from simple heteroaryl propargylic esters using a unified carbonylative benzannulation strategy. Multiple substituents can be easily introduced to the C4-C7 positions of indoles and related heterocycles.

Rhodium-catalyzed pyridannulation of indoles with diazoenals: a direct approach to pyrido[1,2-a]indoles

A new rhodium-catalyzed [4 + 2]-pyridannulation of 3-substituted indoles with diazoenals resulted in the biologically important pyrido[1,2-a]indoles.

An unprecedented benzannulation of oxindoles with enalcarbenoids: a regioselective approach to functionalized carbazoles

An unusual rhodium-catalyzed tandem reaction of oxindoles with diazoenals involving the cleavage of sp² C–O and sp² C–C bonds resulted in the formation of 1-hydroxy-2-acylcarbazoles.

Lewis Acid Mediated Vinylogous Additions of Enol Nucleophiles into an α,β-Unsaturated Platinum Carbene

A variety of substituted indoles and benzofurans are accessed via a platinum catalyzed annulation and vinylogous addition of enol nucleophiles. Several β-dicarbonyl compounds participate in the reaction, as do α-nitro and α-cyano carbonyl species. Subjecting the indole products to acidic conditions results in the formation of fused heterocycles.

Palladium-catalyzed oxidative annulation of in situ generated enones to pyrroles: a concise route to functionalized indoles

Pd(ii)-catalyzed, Cu(ii)-mediated indole synthesis from pyrroles and 3-chloropropiophenones has been efficiently achieved. In-situ generated enones were employed for the establishment of a benzene ring onto a pyrrole backbone via dehydrochlorination/C–H olefination/cycloaddition/dehydrogenative aromatization.

Copper-Catalyzed Synthesis of N-Aryl and N-Sulfonyl Indoles from 2-Vinylanilines with O2 as Terminal Oxidant and TEMPO as Co-Catalyst

A copper-catalyzed intramolecular alkene oxidative amination that utilizes TEMPO as co-catalyst and O₂ as the terminal oxidant has been developed. The method furnishes N-aryl and N-sulfonyl indoles from N-aryl and N-sulfonyl 2-vinylanilines, respectively. Additionally, sequential copper-catalyzed reactions where initial Chan-Lam coupling of 2-vinylanilines with arylboronic acids is followed by oxidative amination of the alkene can generate N-aryl indoles in one pot.

Novel [4 + 2]-benzannulation to access substituted benzenes and polycyclic aromatic and benzene-fused heteroaromatic compounds

A common [4 + 2]-benzannulation of Morita-Baylis-Hillman acetates of acetylenic aldehydes with boronic acids has been developed for the synthesis of aromatic and heteroaromatic compounds through tandem allylic substitution/hydroarylative cycloisomerization process. This method provides a facile and general route to substituted benzenes, naphthalenes, other polycyclic aromatics, and various benzene-fused heteroaromatic compounds such as benzofuran, benzothiophene, indole, and carbazoles.