A Total Synthesis of (+/-)-Rhododaurichromanic Acid A via an Oxa-[3+3] Annulation of Resorcinols

摘要

Development of an oxa-[3+3] annulation of vinyliminium salts with resorcinols as a 1,3-diketo equivalent is described. This annulation constitutes a cascade of Knoevenagel condensation-oxa-electrocyclization leading to a direct access to chromenes. A series of attempts was made to demonstrate its synthetic utility in natural product synthesis, culminating in a total synthesis of (+/-)-rhododaurichromanic acid A that also featured an intramolecular Gassman-type cationic [2+2] cycloaddition.