3-Methylcyclohex-2-enone derivatives as initiators of cyclisation. Part 3. Cyclisation to form five-membered rings

2-Substituted 3-methylcyclohex-2-enones and the derived epoxides have been cyclised to a variety of hydrindanone derivatives. When the 2-substituents are pent-3-ynyl or 4-chloropent-3-enyl the cyclisations take a predictable course; however, with 4-methylpent-3-enyl in the enone, the initial cyclisation product undergoes hydride and methyl migration. In the related eposide an unexpected ‘ene’ reaction occurs.