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The transannular Diels-Alder reaction of trans-trans-trans macrocyclic trie
ne A, bearing two cis substiuents in C-12 and C-13 as well as a gem-dimethy
l in C-4, was studied. Under thermal conditions, only the desired trans-ant
i cis tricycle B was obtained. This tricycle represents an advanced interme
diate toward the total synthesis of cassaine C.