Regioselective electrophilic trifluoromethylation of indolines, oxindoles and indoles in superacid

Treatment of indolines and N-acylindoles with HF/SbF₅/CCl₄ yields 6-trifluoro derivatives (indole numbering) whereas indoles and oxindoles give the 5-trifluoro derivatives in good yield.     

Regioselective Synthesis of Polyheterocycles From 4-Cyclohex-2-ENYL-3-Hydroxy-1-Methylquinolin-2(1H)-One

4-Cyclohex-2-enyl-3-hydroxy-1-methylquinolin-2(1H)-one (4) was prepared in 90% yield by the thermal [3,3]sigmatropic rearrangement of 3-cyclohex-2-enyloxy-1-methylquinolin-2(1H)-one (3) in refluxing chloroben-zene for 10 h. Compound (4) was cyclised through a sequence of reactions viz. i) acetylation ii) addition of bromine and iii) treatment of the acetyl dibromo compound (6) with base to give a bicyclic product (7) in 90% yield. Treatment of compound 4 with pyridine hydro-bromide perbromide in dichloromethane at 0–5° C afforded a cyclic product 8 in excellent yield. Compound 4 when treated with cold conc. sulphuric acid at 0–5° C furnished the bicyclic product 12 in 89% yield.     

Regioselective C5 nitration of N-protected indolines using ferric nitrate under mild conditions

An efficient and facile process has been developed for the regioselective C5 nitration of the N-protected indolines using ferric nitrate as the nitrating reagents. The reaction proceeded smoothly in moderate to excellent yields with high efficiency and broad substrate scope under mild conditions. In addition, the synthesized nitration products can be further transformed to 5-nitroindolines and C5-nitroindole derivatives. The method is operationally simple, efficient, and might have potential application in industry production.     

Synthesis of cyanoalkyl indolines through cyanoalkylarylation of N-allyl anilines with alkyl nitriles under metal-free and neutral conditions

An α-C(sp³)−H functionalization of alkyl nitriles under metal-free and neutral conditions is presented. In the presence of di-tert-butyl peroxide (DTBP), N-allyl anilines underwent exo-selective cyanoalkylation/cyclization cascade, providing a direct access to 3-cyanoalkyl indolines. Previously, a transition-metal catalyst and/or a strong base were generally required to activate nitrilic α-C−H bonds. This reaction features a broad substrate scope and low cost, and primary, secondary and tertiary indolin-3-yl nitriles could all be assembled.     

Rhodium(III)-catalyzed direct C-7 sulfonamidation and amination of indolines with arylsulfonamides and trifluoroacetamide

A rhodium-catalyzed direct C–H sulfonamidation and amidation of C-7 position of indolines by simple and commercially available arylsulfonamides and trifluoroacetamide has been developed, affording a series of N-arylsulfonamides and N-aryltrifluoroacetamides in moderate to excellent yields, respectively. Notably, this catalytic system is highly convenient on mmol scale.     

Synthesis and tautomerism of spiro-pyrazolines

An experimental study on the synthesis, tautomerism, and acid promoted structural changes of spiro-pyrazolines is described. The target was achieved through a [3+2]-dipolar cycloaddition of an alkene with nitrile imines generated in situ and was isolated in high yield. The synthesized cycloadduct displayed a tendency to exhibit an imine–enamine type of tautomerism as evidenced by X-ray crystal and NMR studies. Furthermore, addition of an acid resulted in the transformation of an imine tautomer to an enamine. The current report constitutes a first formal observation of this kind of tautomerism observed in spiro-indoline pyrazolines.     

One-pot synthesis of substituted indolines via a copper-catalyzed sequential multicomponent/C-N coupling reaction

One-pot synthesis of 2-(N-sulfonylimino)indolines has been developed. The procedure combines the copper-catalyzed three-component reaction of sulfonyl azides, o-bromophenylacetylenes, and amines and the copper-catalyzed intramolecular C-N coupling in one sequence, which afforded the products in moderate to good yields. The resulting 2-(N-sulfonylimino)indolines could be easily transformed to pharmaceutically valuable oxindoles (indolin-2-ones).     

Ru(II)-catalyzed regioselective C-7 hydroxymethylation of indolines with formaldehyde

A regioselective addition of C7H bonds of indolines to formaldehyde is reported to synthesize a variety of C-7 hydroxymethylated indolines via a Ru(II)-catalyzed CH activation. More importantly, a one-pot CH formylation procedure is also developed to synthesize valuable C7-formyl indoles.     

Brønsted acid-catalyzed radical CH functionalization of acetone with N-allyl anilines to give 3-(3-oxobutyl)indolines

K₂S₂O₈ was unprecedentedly used instead of tert-butyl hydroperoxide (TBHP) in Brønsted acid-assisted catalytic strategy for ketonic radical generation, and the first Brønsted acid-catalyzed radical CH functionalization of acetone across unactivated alkenes is presented. In the presence of TsOH and K₂S₂O₈, N-allyl anilines underwent addition/cyclization cascade with acetone to afford 3-(3-oxobutyl)indolines with exo-selectivity and broad substrate scope at a relatively low temperature.     

A new approach for the ortho-substitution of anilines and for the synthesis of indolines

Intermolecular radical addition of a xanthate to a vinyl sulfanilide is followed by ring closure to the aromatic ring to give a dihydrobenzoisothiazole dioxide structure, which upon heating loses sulfur dioxide to give a 2-substituted aniline; in some examples, the presence of DBU during heating induces the formation of an indoline.