Electronic and Chelation Effects on the Unusual C2-Methylation of N-(para-Substituted)Phenylaziridines with Lithium Organocuprates

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Density functional theory calculations with the B3LYP functional were performed for the title ring-opening reaction to understand the intrinsic activating and directing effects of the N-substituents, as well as the electron donating effect of the para-substituted (Y = Cl, H, Me) phenyl group at the more hindered benzylic C2 atom. The N-tosyl group (i.e., N-Tos) or the N-(2-pyridyl)sulfonyl group (i.e., N-Py) was introduced to activate the ring nitrogen atom (N1) and the para-substituted (Y = Cl, H, Me) phenyl group for the activation of the C2 atom. Conformational searches and geometry optimizations were performed for the N-(para-substituted)phenylaziridines (1 similar to 6). Calculations indicate that the aziridine 6 (i.e., Py/Me) has the most elongated C2-N1 bond intrinsically due to the electronic activating effects, implying the aziridine 6 to be the most potent candidate for the more-hindered C2 opening. Transition states (TSs) were investigated for the prospective ring-opening paths (I similar to IV), considering the types of intermolecular push-pull interactions between the N-activated phenylaziridines and the cuprate. The N-Py group provides an unique C2-favored TS along the path IV, which the N-Tos group cannot afford, due to the less charge transfer from the nucleophilic CH(3)(delta-) of the cuprate into the electrophilic C2 atom. Furthermore, the e-donating effect of the para-substituents (Y = Cl, H, Me) enhances the C2 opening for the path IV. This study enables us to understand the unusual ring-opening phenomena in terms of electronic and directing effects and hence may serve as a tool to design substrates for highly regioselective ring openings. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 32: 1859-1868, 2011
Publisher
WILEY-BLACKWELL
Issue Date
2011-07
Language
English
Article Type
Article
Keywords

RING-OPENING REACTIONS; NUCLEOPHILIC-SUBSTITUTION REACTIONS; CYSTEINE PROTEASE INHIBITORS; SOLUBLE EPOXIDE HYDROLASE; BETA-ALKOXY ALCOHOLS; REACTION-MECHANISM; AMINO-ACIDS; 3-MEMBERED HETEROCYCLES; THEORETICAL APPROACH; CARBON NUCLEOPHILES

Citation

JOURNAL OF COMPUTATIONAL CHEMISTRY, v.32, no.9, pp.1859 - 1868

ISSN
0192-8651
URI
http://hdl.handle.net/10203/98239
Appears in Collection
CH-Journal Papers(저널논문)
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