ISOMERIZATION OF 4-ARYL-4-METHYLHEX-5-EN-2-ONES TO 5-ARYL-4-METHYLHEX-5-EN-2-ONES BY AN INTRAMOLECULAR ENE-RETRO ENE REACTION SEQUENCE

Acid-catalysed thermal rearrangement of 4-aryl-4-methylhex-5-en-2-ones (products of the Claisen rearrangement of beta-methylcinnamyl alcohol s and 2-methoxypropene) to isomeric 5-aryl-4-methylhex-5-en-2-ones via an intramolecular ene reaction of the enol tautomer followed by a ret ro ene reaction of the resultant acetylcyclopropane is described. Form ation of the known diketone 13 via the ozonolysis of the rearrangement product 10, confirmed the structures of the rearranged enones, wherea s formation of the enone 15 containing an extra methyl group on the st yrene double bond confirmed the proposed mechanism. Finally, the rearr angement has been extended to the formal synthesis of beta-cuparenone 20 via the enones 22 and 23.