Asymmetric total synthesis of caribenol A via an intramolecular Diels-Alder reaction.

A total synthesis of the caribenol A (1), a novel natural product with an intriguing tetracyclic framework, has been achieved. The synthesis features an intramolecular Diels-Alder (IMDA) reaction for the facile construction of the tricyclic [5-7-6] skeleton of caribenol A (1) and a biomimetic oxidation reaction for the formation of the 2-hydroxyfuran-2(5H)-one motif of caribenol A (1) as key steps. This synthetic approach also reveals that the sp(2) carbon at C(2) in substrate 8 is a critical factor for the formation of the tricyclic [5-7-6] skeleton in 7.