Intramolecular C(sp³)–H Imination towards Benzimidazoles Using Tetrabutylammonium Iodide and tBuOOH

Abstract

Development of sustainable and economically viable methods is challenging but desired in organic synthesis. Herein, intramolecular C(sp3)–H imination between a free amine group and N‐methylene group is established using TBAI (20 mol %)‐TBHP (3.0 equiv.) in DMSO which is found to be an inexpensive replacement of PhI‐mCPBA in HFIP.

Synthesis of imidazolocoumarins by the amide-directed oxidative cyclisation of enol-Ugi derivatives

“…28,29 Scheme 1 Examples of C-H functionalisation via iminium intermediates. [12][13][14][15][16] Scheme 3 Proposed synthesis of imidazolocoumarins.…”

“…Noteworthy, in contrast to previous results, C-H activation is not limited to benzylic positions. 15,16 Moreover, the use of formaldehyde provides a novel method for the preparation of 2-carboxamide imidazolocoumarins.…”

“…12 In the last few years, oxidative α-amination of tertiary amines has received great attention as an effective methodology for the synthesis of N-heterocyclic compounds. [13][14][15][16] Thus, Fu's group developed a visible light-mediated intramolecular α-amination of tertiary aliphatic amines containing β-O-aryl oximes, leading to imidazoles (Scheme 1b). 13 Using an alternative activation method, Kapdi and co-workers synthesised quinazolinones by coppercatalysed C-H oxidative functionalisation of 2-amino-N,N-dialkylbenzamides involving elimination of four hydrogen atoms (Scheme 1c).…”

“…14 Similarly, Mal and co-workers developed a synthesis of benzoimidazoles prompted by different oxidating conditions (Scheme 1d). 15,16 Selectivity is still an issue when there are different C-H positions adjacent to N, so these transformations are limited to relatively simple aliphatic and aromatic starting amines. Therefore, it would be desirable to have a general method to obtain substrate amines that could easily undergo selective α-C-H activation/cyclisation leading to more complex heterocyclic compounds.…”

Hypervalent iodine-mediated synthesis and late-stage functionalization of heterocycles

“…Later, the same group developed another catalytic route employing precatalyst tetrabutylammonium iodide 222 in combination with t-BuOOH in DMSO as relatively inexpensive replacement for the previously designed PhI-mCPBA-HFIP system. 90 Symmetrical dibenzylamines 220 gave single isomer of benzimidazoles while unsymmetrical ones yielded mixture of isomers of imination product under both catalytic conditions. Scheme 58.…”