A Molecular Iodine-Mediated Synthesis of Cyclopenta[]furo[3,2-]furan-5,6-diones: Assembly of an Angular Dioxatriquinane Core.

A molecular iodine-mediated synthesis of angular oxatriqinane core from 3-acetyl-2-chromen-2-ones, β-bromo-β-nitrostyrenes, and pyridine in the presence of EtN in MeCN containing a trace amount of water was developed. The reaction proceeds via intermolecular Michael reaction of 2-oxo-2-(2-oxo-2-chromen-3-yl)-1-(pyridin-1-ium-1-yl)ethan-1-ide with bromonitrostyrene followed by intramolecular Michael reaction and elimination steps. Evidence for the stereochemistry of a typical product is obtained from single-crystal X-ray analyses. The important feature of this strategy is the fact that it forms three stereogenic centers with good selectivity.