Various approaches to the total synthesis of the unusual diterpenoid tropon
e (2), discovered in the yew species Cephalotaxus harringtonia and C. haina
nensis, are described. The rhodium-catalysed intramolecular cyclopropanatio
n reaction of an aryl ring by means of the transition metal catalysed react
ion of a diazoacetyl function was used to assemble the 5/7 ring system and
to provide a cycloheptatrienyl precursor to the tropone moiety, e.g. (28) -
-> (29) and (38) --> (39). In the most promising approach, the carbocyclic
system was assembled by means of the aldol reaction (42) --> (43) with the
newly formed a-hydroxyl being employed subsequently in the formation of the
delta-lactone function of (44). The tropone ring may be formed from the me
thoxycycloheptatriene moiety simply by treatment with mercuric nitrate. Tro
pone (45) was formed from (44) in this way, but attempts to convert it into
harringtonolide by means of transannular oxidation based on the 4-hypoiodi
te failed. The crystal structure of an intermediate is reported.