Synthesis of Analogs of Optically Active α-Ionylideneacetic Acid

Abstract

The Wittig reaction of (-)-α-ionone (VIa) with carbethoxymethylenetriphenylphosphorane afforded (-)-ethyl α-ionylideneacetate (VIIa). tert-Butyl chromate oxidation of the above ester (VIla) gave (-)-ethyl 4'-keto-α-ionylideneacetate (VIIIa). Selenium dioxide oxidation of (-)-α-ionone (IVa) in ethanol afforded (-)-1'-hydroxy-α-ionone (X), which reacted with carbethoxymethylenetriphenylphosphorane to give (-)-ethyl 1'-hydroxy-α-ionylideneacetate (XI). tert-Butyl chromate oxidation of the hydroxy-ester (XI) gave (-)-ethyl abscisate (XII) and ethyl 3'-keto-β-ionylideneacetate (XIII). The sensitized photooxidation of ethyl dehydro-β-ionylideneacetate (XVI) using chlorophyll was attempted.