Synthesis of Aromatic Spiroacetals

Abstract

The synthesis of aromatic spiroacetal ring systems related to the papulacandins is reported. ortho-Metalation of diisopropylbenzamide, followed by reaction with the electrophiles δ- valerolactone, γ- butyrolactone and γ-valerolactone, provided the keto alcohol adducts (10),(16) and (21) respectively. Reduction of the ketone followed by treatment with acid afforded phthalides (12),(18) and (23). Finally oxidative cyclization with iodobenzene diacetate provided the spiroacetals (7),(14) and (19).