Quantum chemical study of the transformation of 2-(N-alkylamino)-3-(indol-1-yl)-and 2-(N-alkylamino)-3-(indol-3-yl)maleimides by protic acids: Tandem hydride transfer/cyclization mechanism |
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Authors: | E E Bykov S A Lakatosh M N Preobrazhenskaya |
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Institution: | (1) G. F. Gause Institute of New Antibiotics, Russian Academy of Medical Sciences, 11 ul. B. Pirogovskaya, 119021 Moscow, Russian Federation |
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Abstract: | The geometric parameters, the charge distribution, and the energetics of N-methyl-2-(N-ethylanilino)-3-(indol-1-yl)-and N-methyl-2-(N-ethylanilino)-3-(indol-3-yl)maleimides and their conjugated acids were studied by density functional theory calculations
at the B3LYP/6-31G(d) level. The mechanism of the tandem hydride transfer/cyclization sequence, which occurs after protonation
of N-methyl-2-(N-ethylanilino)-3-(indol-1-yl)-and N-methyl-2-(N-ethylanilino)-3-(indol-3-yl)maleimides, was analyzed. The investigation of the potential energy surface for the tandem hydride
transfer/cyclization of the iminium cation that formed upon protonation revealed that the hydride transfer followed by intramolecular
cyclization at position 7 of the indole fragment in N-methyl-2-(N-ethylanilino)-3-(indol-1-yl)maleimide is the preferable process, unlike alternative intramolecular cyclization involving
the cationic center at the C(2) atom of the indole fragment and the benzene ring of the N-ethylaniline fragment of the indoleninium cation in N-methyl-2-(N-ethylanilino)-3-(indol-3-yl)maleimide. A study of the key intermediates of the assumed reaction mechanism demonstrated that
these intermediates are actually stationary points on the potential energy surface (minima and transition states).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2069–2073, December, 2006. |
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Keywords: | quantum chemical calculations N-methyl-2-(N-ethylanilino)-3-(indol-1-yl)maleimide N-methyl-2-(N-ethylanilino)-3-(indol-3-yl)maleimide protonation cyclization potential energy surface hydride transfer activated complex indoleninium iminium intermediate annulation |
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