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Biradical and zwitterionic cyclizations of oxy-substituted enyne-allenes
C J Cramer1, B L Kormos, M Seierstad
1Department of Chemistry and Supercomputer Institute, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455-0431, USA. cramer@dchem.umn.edu
Organic Letters
|June 19, 2001
Abstract:
[see reaction]. Oxyanion substitution of enyne-allenes causes both Myers-Saito and Schmittel cyclizations to switch their product formation preferences from diradicals to polar, closed-shell singlets. The oxyanion stabilization is larger for the Schmittel products than the Myers-Saito products because the latter must sacrifice aromaticity to maximize interaction. The changing character of the different reaction paths is reflected in their activation energies.