A Short-step Synthesis of Theaspirane

Theaspirane has been found as a naturally occurring substance in raspberry, yellow passion fruit and tea.1) The synthesis of theaspirane has been reported by some investigators.2) We now report a new synthesis of theaspirane from β-ionone through dihydro-β-ionol.When two equivalents of aluminium chloride hexahyd-rate (A1C13-6H20) is present in sodium-ammonia reduction, β-ionone (1) can be efficiently reduced to dihydro-β-iaonol (2). The bromination of 2 using cupric bromide, followed by dehydrobromination in the presence of calcium carbonate, affords a mixture of (E)-theaspirane and (Z)-theaspirane. The process of synthesis is outlined in Scheme 1.