Catalyzed asymmetric Diels-Alder reaction of benzoquinone. Total synthesis of (-)-ibogamine

[GRAPHICS] The Diets-Alder addition of diene 2 with benzoquinone catalyzed by (S)-BINOL-TiCl2 produced cycloadduct 5 in >65% yield and 87% ee. The cycloadduct was transformed into (-)-ibogamine in nine steps (10% overall yield from benzoquinone). A model for the transition state leading to 5 is proposed.