The synthesis of the four acyclic trienes 11 a, b and 20 a, b is reported. The tandem macrocyclization and stereoselective transannular Diels-Alder reaction of acyclic trienes 11 b (trans-trans-cis) and 20 b (trans-trans-trans) were observed in the presence of Cs2CO3 at 85° C to give tricycles 30 (TST) and 32 (CAT) respectively. However, treatment of acyclic trienes 11 a (cis-trans-cis) and 20 a (cis-trans-trans) under the same conditions yielded ...