Collect. Czech. Chem. Commun. 1991, 56, 1052-1063

11,13-Methylenation of sesquiterpene exomethylene-γ-lactones: Synthesis of sesquiterpene cyclopropyl-γ-lactones

Giovanni Appendinoa,*, Elisabetta Ghilardia, Giancarlo Cravottoa and Pierluigi Gariboldib

a Dipartimento di Scienza e Tecnologia del Farmaco, C. so Raffaello 31, 10125 Torino, Italy
b Dipartimento di Scienze Chimiche, Via S. Agostino 1, 62032 Camerino (MC), Italy


11,13-Methylene derivatives of sesquiterpene exomethylene-γ-lactones were prepared by reaction of diazomethane and photolysis of the resulting pyrazoline adduct(s). Variable amounts of exomethylene- and ethylidene-γ-lactones were also formed in the photolysis reaction. These compounds could bee removed after reaction with diethylamine and chromatography on a bilayer (basic alumina/silica gel) column. Also 11,13-methylene derivatives of acid-and thermolabile germacranolides could be prepared in good yield with this procedure. Results obtained using alternative methods of methylenation are reported. A comparative study of the reactivity towards nucleophiles of exomethylene- and cyclopropyl sesquiterpene-γ-lactones provided little support for the involvement of compounds of the latter class in in vivo alkylation reactions.