Diels-alder reactions of a cyclopentadienone derivative

An ester derivative of cyclopentadienone, a very reactive species, was generated from methyl-2-bromo-3-oxocyclopent-1-enecarboxylate (96) which dimerized instantaneously and decarbonylated to generate an indanone (97). Diels-Alder reactions were performed by trapping this fleeting cyclopentadienone derivative with electron rich dienes to generate [4+2] Diels-Alder adducts. The cycloadducts were diastereoand regioselective. The yields of these reactions were moderate to high. A wide range of dienes were used to show the versatility and scope of these reactions. Using the developed methodology, at attempt was taken to synthesize steroidal drug desogestrel (218).