The bergman cyclizations of the enediyne and its N-substituted analogs using multiconfigurational second-order perturbation theory

• The Bergman cyclizations of the enediyne and its four N-substituted analogs [(Z)-pent-2-en-4-ynenitrile, 3-azahex-3-en-1,5-diyne, malenotrile, and 3,4-azahex-3-en-1,5-diyne] have been studied using the complete active space self-consistent field and multiconfigurational second-order perturbation theory methods in conjunction with the atomic natural orbital basis sets. The geometries and energies of the reactants, transition states, and products along both the S0 (the ground state) and T1 (the lowest-lying triplet state) potential energy surfaces (PESs) were calculated. The calculated geometries are in good agreement with the available experimental data. The distance between two terminal carbons in enediyne, which was considered as an important parameter governing the Bergman cyclization, was predicted to be 4.319 angstrom, in agreement with the experimental value of 4.321 angstrom. Our calculations indicate that the replacements of the terminal C atom(s) or the middle C atom(s) in the C-C bond by the N atom(s) increase or decrease the energy barrier values, respectively. There exist stable ring biradical products on the T1 PESs for the five reactions. However, on the S0 PESs the ring biradical products exist only for the reactions of enediyne, (Z)-pent-2-en-4-ynenitrile, and 3-azahex-3-en-1,5-diyne.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

Bergman cyclizations

enediyne

multiconfigurational second-order perturbation theory

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