Enantioselective para-Claisen Rearrangement for the Synthesis of Illicium-Derived Prenylated Phenylpropanoids.

The development of the first enantioselective para-Claisen rearrangement has been achieved. Using a chiral aluminum Lewis acid, illicinole is rearranged to give (-)-illicinone A (er 87:13), which can then be converted into more complex Illicium-derived prenylated phenylpropanoids. The absolute configurations of the natural products (+)-cycloillicinone and (-)-illicarborene A have been determined, and our results cast doubt on the enantiopurity of the natural samples.