title: Electronic and chelation effects on the unusual C2-methylation of N-(para-substituted)phenylaziridines with lithium organocuprates.
abstract: 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∼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∼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 3δ- 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.
authors: Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea.
authors: Jongtaek
authors: J
authors: Kim
authors: Eunjung
authors: E
authors: Yoo
authors: Sukbok
authors: S
authors: Chang
authors: Yoon Sup
authors: YS
authors: Lee
mesh_terms: D001388:Aziridines / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry*; D004583:Electrons; D008094:Lithium / Q000737:chemistry*; D008745:Methylation; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*
chemical_list: D001388:Aziridines; D002614:Chelating Agents; D009942:Organometallic Compounds; D008094:Lithium