Bicyclopentanoid sesquiterpenes. the synthesis of cedranoid sesquiterpenes via the photo-rearrangement of bicyclo[2.2.2]octenones

(±) - exo - 2,6,6 - Trimethyltricyclo[5.3.1.01,5]undecane - 8,10 - dione (11) has been synthesized from dimethyl 6,6 - dimethyl - 5 - oxobicyclo[2.2.2]oct - 7 - ene dicarboxylate (17). This constitutes a new synthesis of cedrol (3) since 11 has previously been converted to this compound.