Reactions of cyclohexadienes. Part V. A new synthesis of 4-substituted cyclohexenones

Abstract

Addition of some 1-methoxycyclohexa-1,3-dienes to but-3-en-2-one or trans-pent-3-en-2-one occurs with the COMe adjacent to the OMe. The adducts are converted by acid initially into diketones with fission of a carbon–carbon bond; aldol ring-closure and dehydration may follow. Other methods of generating a carbonium ion result in similar fissions, and the processes represent new syntheses of 4-substituted cyclohexenones and some derivatives of bicyclo[3,3,1]nonane.