Menthofuran

Menthofuran is an organic compound found in a variety of essential oils including that of pennyroyal ("Mentha pulegium"). It is highly toxic and believed to be the primary toxin in pennyroyal responsible for its potentially fatal effects. After ingestion of menthofuran, it is metabolically activated to chemically reactive intermediates that are hepatotoxic.
Biosynthesis.
Menthofuran is produced biosynthetically from pulegone by the enzyme menthofuran synthase.
Synthesis.
Menthofuran can be synthesized from 5-methylcyclohexane-1,3-dione and allenyldimethylsulfonium bromide in two steps via a furannulation strategy consisting of enolate addition and rearrangement.