Expansion of the ring of cyclododecanone by two and four carbon atoms

Abstract

Condensation of 1-methoxycyclododec-1-ene (II) with 2-methylbut-3-yn-2-ol forms, through Cope rearrangement of the intermediate enol ether, the α-3,3-dimethylallenyl-cyclododecanone (III). On u.v. irradiation (II) isomerises with 1,3-acyl migration to 2-isopropylidenecyclotetradec-3-trans-enone (V). The alcohol (VII) from addition of vinylmagnesium bromide to the allenic ketone (III) undergoes thermal Cope rearrangement to 4-isopropylidenecyclohexadec-5-trans-enone (VIII).