A Novel Oxidative Intramolecular (4+2)Cycloaddition of Silylene-Protected Dihydroxystyrene Derivatives Leading to peri-Hydroxy Polycyclic Aromatic Compounds: A Synthesis of the ABCD Ring.

Heating of the silylene protected dihydroxystyrene generated from the O-hydroxyacetophenone (3a) at 130-150°C for 15-48h in a sealed tube gave intramolecular [4+2]cycloaddition products (5 and 6). The addition of chloranil to the reaction mixture brought about an oxidative intramolecular [4+2]cycloaddition to give the linearly condensed peri-hydroxy aromatic compound(7a) in excellent yield. The generality of this cycloaddition and application to a short and efficient synthesis of the ABCD ring system of fredericamycin A are described.