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Cyclocondensation reactions of an electron deactivated 2-aminophenyl tethered imidazole with mono/1,2-biselectrophiles: synthesis and DFT studies on the rationalisation of imidazo[1,2-a]quinoxaline versus benzo[f]imidazo[1,5-a][1,3,5]triazepine selectivity switches

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Abstract

Microwave-promoted ring-closure reactions of 5-amino-1-(2-aminophenyl)-1H-imidazole-4-carbonitrile (7) with various mono/1,2-biselectrophiles are presented. The reaction of 7 with aldehydes, ketones and isocyanates produced the corresponding Pictet–Spengler (PS) products i.e. the imidazo[1,2-a]quinoxaline ring system via 6-endo-trig cyclisation. On the other hand, the reaction of 7 with CH(OEt)3, and CDI resulted in the formation of benzo[f]imidazo[1,5-a][1,3,5]triazepine scaffolds via a 7-exo-trig cyclisation process. The mechanistic aspects of these ring cyclisation processes have been analysed and studied to rationalise 6- versus 7-membered ring formation using density functional theory (DFT). DFT calculations revealed the involvement of N-Heterocyclic Carbene (NHC) in the PS reaction mechanism.

Graphical abstract: Cyclocondensation reactions of an electron deactivated 2-aminophenyl tethered imidazole with mono/1,2-biselectrophiles: synthesis and DFT studies on the rationalisation of imidazo[1,2-a]quinoxaline versus benzo[f]imidazo[1,5-a][1,3,5]triazepine selectivity switches

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Publication details

The article was received on 11 Jul 2018, accepted on 25 Oct 2018 and first published on 26 Oct 2018


Article type: Research Article
DOI: 10.1039/C8QO00706C
Citation: Org. Chem. Front., 2018, Advance Article
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    Cyclocondensation reactions of an electron deactivated 2-aminophenyl tethered imidazole with mono/1,2-biselectrophiles: synthesis and DFT studies on the rationalisation of imidazo[1,2-a]quinoxaline versus benzo[f]imidazo[1,5-a][1,3,5]triazepine selectivity switches

    G. Joshi, M. Chauhan, R. Kumar, A. Thakur, S. Sharma, R. Singh, A. A. Wani, A. Sharon, P. V. Bharatam and R. Kumar, Org. Chem. Front., 2018, Advance Article , DOI: 10.1039/C8QO00706C

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