Studies toward the synthesis of arteminolide: [5+2] cycloaddition reaction of allenes with oxidopyrylium ions

The oxidopyrylium cycloaddition reaction of allenes was investigated. Contrary to other cycloaddition reactions, electron deficient allenes were not reactive at all and electron rich allenes were slightly more reactive than neutral allenes. The intermolecular cycloaddition reaction occurred at the terminal position regardless of substitution patterns. For the intramolecular reaction only the perhydroazulene structure was obtained over other possible products.