Stereospecific Synthesis of Cyclohexenone Acids by [3,3]-Sigmatropic Rearrangement Route

Herein we report a modular synthetic method for the preparation
of diaryl-substituted cyclohexenone acids starting from phenyl pyruvate
and suitable enones. When the reaction is carried out in alkaline tert-butanol or toluene solutions in microwave-assisted
conditions mainly anti configuration products are obtained with up
to 86% isolated yield. However, when the reaction is carried out in
alkaline water, a mixture of products with anti and syn conformations
is obtained with up to 98% overall isolated yield. Mechanistically
the product with anti conformation forms by a hemiketal–oxy-Cope
type [3,3]-sigmatropic rearrangement–intramolecular aldol condensation
route and syn product by an intermolecular aldol condensation-electrocyclization
(disrotatory type) route.