Iminophosphoranylferrocenes as New Nucleophilic Organocatalysts for Regioselective Ring-opening of Epoxides

Sk, Nasiruzzaman; Minhhoang, Vo-Do; Kim, Tae‐Jeong

doi:10.5012/bkcs.2009.30.12.3075

Cited by 7 publications

(1 citation statement)

References 30 publications

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“…It is well known that the ring‐opening reactions of most three‐membered heterocycles (e.g., oxiranes, aziridines, and thiiranes) usually lead to both the more hindered C2 opening ( minor ) and the less hindered C3 opening ( major ). The regioselective C2‐opening reactions have been achieved depending on the following conditions: C2 aromatic activations,9–11 heteroatom activations (e.g., N‐activating groups or aziridinium salts),12–15 catalysts (e.g., Lewis acids, metal–ligand complexes, metal oxides, and organic/inorganic catalysts),16–32 unique nucleophiles,33–38 and C2‐driecting effects of nucleophiles 39–42. Despite previous theoretical studies on the ring‐opening mechanism,43–56 little have been explored in regard to the favored opening at the more‐hindered C2 atom,57–61 especially at the benzylic C2 atom 62, 63.…”

Section: Introductionmentioning

confidence: 99%

Electronic and chelation effects on the unusual C2‐methylation of N‐(para‐substituted)phenylaziridines with lithium organocuprates

et al. 2011

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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∼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.

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