Steric and electronic effects on the Weiss reaction. Isolation of 1∶1 adducts

Abstract

The mechanism of the Weiss reaction has been studied with respect to the intermediacy of 4-hydroxycyclopent-2-en-1-ones (1∶1 adducts) in this process. Analysis of these experiments provides additional evidence that 4-hydroxycyclopentenones are indeed key intermediates in the Weiss reaction. Based on the reaction of dimethyl 3-oxoglutarate with benzil, pyridil, thenil, furil and phenanthrenequinone, steric effects play the major role in the overall success of this condensation to provide substituted cis-bicyclo[3.3.0]octane-3,7-diones. Moreover a trihydroxyindene [5.6] system (see 26) has been isolated for the first time under the Weiss conditions which provides additional support for the existence of cyclopentenone intermediates in this process.