| Abstract
| - The thermal dimerization of 2-boryl-1,3-butadienes and the scope of this reaction to prepare six-membered rings difficult to synthesize by other methodologies have been studied. In addition, thenature of this dimerization has been studied theoretically. It has been found that the reactioncoordinate associated with the formation of the cycloadduct of lowest energy has significant [4+3]character. This behavior is caused by the favorable carbon−carbon overlap and the large values ofthe corresponding resonance integrals. However, beyond the transition structure, the [4+2] pathwaybecomes the preferred one thus leading to the exclusive formation of the [4+2] cycloadduct. Asidefrom this effect, donating groups at the boryl moiety favor the [4+2] mechanism.
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