[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.
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Cramer et al. (2001) studied this question.
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