Reaction of Diketene with Grignard Reagents in the Presence of Cobalt Catalyst. A Convenient Method for the Synthesis of 3-Methylenealkanoic Acids Leading to Terpenoids

Article abstract of DOI:10.1246/bcsj.55.3555

Primary alkyl Grignard reagents react regioselectively with diketene in the presence of cobalt(II) iodide to afford 3-methylenealkanoic acids in good yields.The synthetic utility of this reaction is demonstrated in the syntheses of terpenoids by two methods.Utilizing the isomerization of double bond of 3-methylenealkanoic acids, geranic acid and farnesic acid were obtained in two steps.Another method, the tandem <3,3> sigmatropic rearrangement of the corresponding allylic esters was used for the synthesis of C18-Cecropia juvenile hormone.