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We described a copper(II)‐catalyzed [3+2] cycloaddition of N‐aryl‐α,β‐unsaturated nitrones with disubstituted allenoates bifurcated to prepare various [1,3]oxazino[3,2‐a]indolines and dihydropyrido[1,2‐a]indolines in moderate to excellent yields. Mechanistic studies revealed that [1,3]oxazino[3,2‐a]indoline was a kinetically favored product and dihydropyrido[1,2‐a]indoline was thermodynamically favored product. Moreover, the reaction was easily performed at gram scales and chiral dihydropyrido[1,2‐a]indoline could be obtained by using chiral auxiliary. The present method highlights broad substrate scope, good functional group tolerance, and diversity of indoline scaffolds with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

A variety of functionalized 3‐(2‐hydroxyaryl)indazoles and N‐(tetrahydrofuran‐2‐yl)‐3‐(2‐hydroxyaryl)indazoles were prepared in moderate to good yields through a transition metal‐free radical O‐arylation and sequential [3,3]‐rearrangement cascade strategy from N‐hydroxyindazoles and diaryliodonium salts. The equivalents of diaryliodonium salts controlled the formation of the product structures. Mechanistic studies revealed that the O‐arylation and N−O bond cleavage via [3,3]‐rearrangement involved an intermolecular radical process. The reaction tolerated various sensitive functional groups, such as halides, ester, and aldehyde groups. [ABSTRACT FROM AUTHOR]

Various spirooxindole‐benzo[d]oxazoles and dihydrobenzofurans were prepared in good to excellent yields by [3+2] cycloaddition and selective rearrangement of N‐vinyl oxindole nitrones and arynes under transition metal‐free conditions. Experimental results showed that the substituent on the nitrone N‐vinyl group controlled the [1,3]‐ or [3,3]‐rearrangement of their cycloadduct owing to its steric effect. The present method features broad substrate scope, good functional group tolerance, controllable [1,3]‐ or [3,3]‐rearrangement, and diverse oxindole scaffolds. [ABSTRACT FROM AUTHOR]

A variety of pseudorutaecarpine derivatives were prepared in good to excellent yields through a gold(I)‐catalyzed selective cyclization and 1,2‐shift of N‐alkynyl quinazolinone‐tethered indoles. Mechanistic study revealed that spiroindolenines generated in situ by cyclization at the the indole C3 position underwent an alkenyl 1,2‐shift to generate pseudorutaecarpine. The reaction proceeds under mild reaction conditions, has a broad substrate scope, good functional group tolerance, and gram‐scalable application. Furthermore, biological evaluation showed that most of the pseudorutaecarpine scaffolds prepared exhibit anti‐inflammatory activity. [ABSTRACT FROM AUTHOR]

We report a green cascade approach to prepare a variety of 3-aminoindole derivatives in good to excellent yields through an iron(III)-catalyzed dehydrogenative cross-coupling reaction of 2-arylindoles and primary benzylamines under mild reaction conditions. Mechanistic studies show that a cascade reaction involves a tert-butyl nitrite (TBN)-mediated nitrosation of 2-substituted indoles and a 1,5-hydrogen shift to afford indolenine oximes, sequential iron(III)-catalyzed condensation and a 1,5-hydrogen shift over four steps in a one-pot reaction. The reaction shows a broad substrate scope of indoles and benzylamines and tolerates a wide range of functional groups. Moreover, the reaction is easily performed at the gram scale without producing waste after the reaction is completed. The 3-aminoindole product is purified by simple extraction, washing, and recrystallization without flash column chromatography. A double imine ligand containing the 3-aminoindole unit is facile to obtain in a 52% yield in one step. The present method highlights readily available starting materials, a simple purification procedure, and the usage of cheap, nontoxic, and environmentally benign iron(III) catalysts. [ABSTRACT FROM AUTHOR]

We describe a cascade strategy for tri- or tetrafunctionalization of alkenylboronic acids to prepare diverse tetrahydrocarbazol-1-ones and indolo[2,3-a]carbazoles in good yields with N-hydroxybenzotriazin-4-one (HOOBT) and arylhydrazines as oxygen and nitrogen sources, respectively. Mechanistic studies reveal that the domino reaction undergoes the copper-catalyzed Chan–Lam reaction, [2,3]-rearrangement, nucleophilic substitution, oxidation and sequential [3,3]-rearrangement over five steps in a one-pot reaction. The reaction shows a broad substrate scope and tolerates a wide range of functional groups. More importantly, the reaction is easily performed at gram scales and the product is purified by simple extraction, washing, and recrystallization without flash column chromatography. The present protocol features easily available starting materials, high site-marked functionalization, five-step cascade in one pot, multiple C–C/C–O/C–N bond formation, and diversity of indole motifs. [ABSTRACT FROM AUTHOR]

An efficient and metal‐free double C−H bond amination of N‐aryl enamines using isobutyl nitrite (IBN) has been developed. This method enables the preparation of functionalized quinoxalines in good to excellent yields and tolerates a variety of N‐aryl enamines with diverse functional substituents. Mechanistic studies revealed the presence of a key β‐imino oxime ester intermediate. A quinoxaline derivative could be prepared from β‐carbonyl ester in one‐pot sequence on a gram scale. Finally, two important quinoxaline scaffolds were easily prepared in moderate yields over two steps. [ABSTRACT FROM AUTHOR]

An efficient synthesis of 1-vinyl/arylbenzotriazole 3-oxides via the copper-promoted coupling of N-hydroxybenzotriazoles with alkenyl- or arylboronic acids is reported. This strategy features mild reaction conditions, good functional group tolerance, broad substrate scope and rapid introduction of benzotriazole N-oxide moieties into molecules. Density functional theory calculations revealed that the formation of the favored N-coupling product depends on the kinetically more favorable C-N bond formation pathway. [ABSTRACT FROM AUTHOR]