Synthesis of the Cores of Hypocrellin and Shiraiachrome: Diastereoselective 1,8-Diketone Aldol Cyclization

Intramolecular 1,8-diketone aldol reactions were studied as a tool for the construction of the seven-membered rings of hypocrellin and shiraiachrome. Conditions were identified to obtain the relative stereochemistries present in the two natural products with excellent diastereoselectivity. In addition, a nine-membered ring congener, which has yet to be observed in nature, formed with high selectivity when a hindered amine was used in conjunction with silazide bases.