Synthesis of the ABCD Trioxadispiroketal Subunit of Azaspiracid-1:  An Iodoetherification−Dehydroiodination Strategy for Complex Spiroketals

2007-10-11T00:00:00Z (GMT) by Xiaohua Li Jialiang Li David R. Mootoo
An unusual spiroketalization strategy in which a hydroxyalkene serves as a precursor to a cyclic enol ether was applied to the synthesis of the ABCD trioxadispiroketal subunit of azaspiracid-1. The trioxadispiroketal product, which represents a double anomeric effect, was obtained as a single trioxadispiroketal diastereomer. A key ploy in the synthesis of the CD segment was the use of a cyclopropane as a synthon for the C-14 methyl group.