A four step, efficient and general methodology for the conversion of a
cyclic ketone into the corresponding alpha-spiro-beta-methylene-gamma
-butyrolactone, the key structural feature present in tricyclic sesqui
terpenes bakkanes, has been developed employing a regiospecific 5-exo
dig radical cyclisation reaction as the key step. The methodology has
been extended to the total synthesis of bakkanes including homogynolid
e-B and chiral homogynolide-A.