3,4-bis- methylenecyclopentadienone ethylene ketal: a useful diene for [6.5] ring systems. Application to a formal synthesis of gibberellic acid

A convenient prepn. of 3,4-bismethylenecyclopentanone ethylene ketal (I), a new valuable diene for Diels-Alder reaction, designed to produce functionalized [6.5] ring systems, is described. A formal synthesis of gibberellic acid GA3 (II) using as starting materials two cycloadducts derived from the title compd. demonstrates the value and the applicability of this methodol. for the construction of functionalized hydrindane systems