Iron‐Catalyzed Intramolecular Aminations of C(sp³)−H Bonds in Alkylaryl Azides

Abstract

The nucleophilic iron complex Bu N[Fe(CO) (NO)] (TBA[Fe]) catalyzes the direct intramolecular amination of unactivated C(sp )-H bonds in alkylaryl azides, which results in the formation of substituted indoline and tetrahydroquinoline derivatives.

Recent Advances in Iron‐Catalyzed C—H Bond Amination via Iron Imido Intermediate

“…Plietker and his coworkers' study showed that this complex can catalyze intramolecular C(sp 2 )-H and C(sp 3 )-H bond amination reactions of ortho-substituted aryl azides. [84,85] Using 2.5 mol% of [Bu n 4 N][Fe-(CO) 3 (NO)] and with the assistance of microwave, aryl azides bearing ortho-aryl or alkenyl group in 1,2-dichloroethane at 100 o C can be converted to carbazoles and indoles, respectively, in moderate to good yields [84] (Table 21). This reaction was also proposed to have iron imido species as key reactive intermediates.…”

“…[86][87][88][89][90] Accordingly, the [Bu the C(sp 2 )-H bond amination reactions. [85] The subtle difference is having higher temperature (120 o C vs. 100 o C), and the use of a mixed solvent of DMF with ClCH 2 CH 2 Cl. Under optimized conditions, the tertiary, secondary, and even primary β-C(sp 3 )-H bonds on ortho-alkyl substituted aryl azides successfully undergo amination reactions, giving indoline and tetrahydroquinoline derivatives in moderate yields (Table 22).…”

“…The study accumulated mechanistic knowledge on the nature of the proposed iron imido species. [85] An intramolecular KIE experiment with o-(PhCHDCHD)C 6 H 4 N 3 showed a KIE value of 6.7 for the iron-catalyzed amination reaction. The large value hints the C-H bond cleavage process to be rate-determing.…”

A Bu4N[Fe(CO)3(NO)]‐Catalyzed Hemetsberger–Knittel Indole Synthesis

“…We initiated this project by employing the reaction conditions that proved successful in the intramolecular C–H‐aminations using aryl azides …”

Synthesis of Annulated Indolines by Reductive Fischer Indolization

“…[7] Furthermore, intramolecular, Pd-catalyzed a-arylations of N-aryl-b-alanine derivatives have been reported. [8] Moreover,p hotocatalytic cyclizations of 3-(iodoethyl)indoles with acrylonitrile, [9] iron-catalyzed CÀH-activation of ortho-alkylarylazides, [10] and samarium-diiodide induced Barbier-type cyclizations of N-(4-oxoalkyl)indole derivatives have been reported. [11] The most prominent reactiont oa ccess indole derivatives is the Fischer indolization of arylhydrazones, [12] that starts from the hydrazone, which is under acidic conditions in equilibrium with enamine 5 (Scheme 1).…”