An Unusual Cationic [2 + 2] Cycloaddition in a Divergent Total Synthesis of Hongoquercin A and Rhododaurichromanic Acid A

An unusual polyene cyclization pathway that led to a divergent total synthesis of hongoquercin A and rhododaurichromanic acid A is described here. This work uncovered a unique cationic cyclobutane formation that could be relevant to the biosynthetic pathway for the formation of cyclobutane containing terpenoids in addition to rhododaurichromanic acids.