The cyclisation of geraniol in superacids

Abstract

The cyclisation of geraniol (1)[(E)-3,7-dimethylocta-2,6-dien-1-ol] in FSO₃H–SO₂at –78°C to yield the iridoid ether 3β,4α,6aα-trimethyl-cis-perhydrocyclopenta[b]furan was investigated. Decomposition of the ether in FSO₃H at room temperature gave the 2-isopropyl-1,3-dimethylcyclopentenium ion, whose structure was confirmed independently. Synthesis of geraniol labelled with deuterium on the gem-dimethyl group and on the single methyl group established the positions of these methyls in the iridoid ether. Synthesis of 2-(1-hydroxy-2,2-dimethylcyclopentyl)propan-1-ol established that the ion derived from it did not lie on the reaction pathway.