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The 5-exo-dig radical cyclisation reaction of the bromoacetals 9, obtained from the enol ethers 8, and treatment of the resulting hemiacetal 10 with Jones' reagent transforms the cyclic ketones 7 and 12 into a-spiro-0-methyleney-butyrolactones 11 and norbakkenolide-A 2.Bakkenolide-A 1, first isolated1 from the bud of Petasites japonicus subsp. giganteus Kitam, is the simplest member of the bakkane class of sesquiterpenes containing a novel a-spirolactone fused hydrindane framework. Interestingly bakkenolide-A, which possesses an unconjugated (3-methyl-ene-y-butyrolactone grouping, shows cytotoxic and antifeedant effects2 normally associated with the conjugated a-methylene-y-butyrolactones. In contrast to the many procedures that exist for obtaining a-methylene-y-butyrolactones,3 there are very few general methods available for the synthesis of

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