ChemInform Abstract: β-Cleavage of Bis(homoallylic) Potassium Alkoxides. Two-Step Preparation of Propenyl Ketones from Carboxylic Esters. Synthesis of ar-Turmerone, α-Damascone, β-Damascone, and β-Damascenone.
Abstract
The bis(homoallylic) alcohols (III) which are obtained from the corresponding esters (I) and Grignard compounds (II) (generated in situ) are transformed via β-cleavage of their potassium alkoxides in HMPA to the products (IV) + (V) or (VI) + (VII), respectively.
ChemInform Abstract
The bis(homoallylic) alcohols (III) which are obtained from the corresponding esters (I) and Grignard compounds (II) (generated in situ) are transformed via β-cleavage of their potassium alkoxides in HMPA to the products (IV) + (V) or (VI) + (VII), respectively. Using this methodology, an efficient synthesis of ar-turmerone (X) is achieved starting from the ketone (VIII). The β-cleavage of the K salt of the tris(homoallylic) alcohol (XI) affords the products (XII) and (XIII); analogous reactions are carried out with the readily accessible educts (XIV). The relative ease of these cleavage reactions provides synthetic access to α-damascone (XVI) from alcohol (XV). An oxy-Cope rearrangement mainly occurs when the alcohols (XVII) or (XX) are the educts (e.g. → (XVIII) + (XIX)). A further synthetic application of the methodology described is in the preparation of β-damascone (XXIIa) and β-damascenone (XXIIb) starting from the esters (XXI). - The results are partly summarized in several tables.
