Diallyllactones (obtained from cyclic anhydrides via a double allylation reactionpromoted by titaniumtetrachloride) were cycloisomerised using 5 mol% of cyclooctadienyl ruthenium dichloride in ethanol providing the corresponding exomethylene spirolactones in good yields, with moderated to good diastereomeric excess.
Starting from cyclic anhydrides the diallyl or dibutenyl lactones were obtained. The ring closing metathesis reaction of these using the Grubbs catalyst provided the corresponding spirolactones in good yields. With diallyl delta-lactone 2h, RCM occurred only in the presence of titanium tetraisopropoxide. (C) 2000 Elsevier Science S.A. All rights reserved.