A Curtin-Hammett pentamethylene chain symmetrization process in the Bergman cyclization of an 11-membered ring enediyne

作者：Greer Edyta M^*; Cosgriff Christopher V; Lavinda Olga

来源：Journal of Physical Organic Chemistry, 2012, 25(12): 1293-1298.

DOI：10.1002/poc.3018

• Bergman cyclization
• conformation
• density functional theory
• enediyne symmetry
• symmetrization

Pentamethylene chain conformational effects for the Bergman cyclization of the 11-membered ring enediyne, (3Z)-3-cycloundecene-1,5-diyne, 2, are examined theoretically with unrestricted Becke, three-parameter, LeeYangParr/6-31?G(d,p) calculations. A C1 symmetric enediyne conformation was found to be the global minimum, where its nonsymmetric pentamethylene chain prevented p-orbital alignment of the acetylene groups for CC s bond product formation. The Bergman cyclization of 2 was found to be conformationally dependent. In a CurtinHammett type process, the C1 symmetric 2 inverts to one of the CS or C2 symmetric conformers required for the Bergman cyclization, which produced a CS or C2 symmetric 1,4-diradical intermediate. The activation energy for the cyclization is slightly higher to reach the C2 symmetry diradical compared with the CS symmetry diradical.

• 出版日期2012-12