Synthesis of limonoid CDE fragments related to limonin and nimbinim

A practical, brief and selective synthesis of limonoid CDE fragments from a readily available starting diketone is described. The key step is a cationic electrocyclization promoted by strong acids. In general the methodology has been demonstrated for compounds with sensitive furane and thiophene substituents to obtain diverse substituted indenones. Several of the compounds obtained show significant antifeedant activity against Spodoptera littoralis.