STEREOCONTROLLED CONSTRUCTION OF 1,7-DIMETHYL A.B.C.[6.6.6] TRICYCLES.2. TRANSANNULAR DIELS-ALDER REACTION OF 14-MEMBERED MACROCYCLES CONTAINING CIS-DIENOPHILES

The synthesis and transannular Diels-Alder reactions of 14-membered ma crocyclic trienes containing a methyl-substituted diene and a methyl-s ubstituted cis-dienophile moiety are described. As a result of the die nophile cis geometry the 1,7-dimethyl A.B.C.[6.6.6] tricycles obtained from the Diels-Alder reaction have a different stereochemistry at the four chiral centers than similar tricycles that were the subject of t he preceding paper in this series. Thus trans-syn-cis (TSC) tricycle 3 0 was the sole product obtained from the trans-cis-cis (TCC) macrocycl e 1b. In a similar fashion TCC macrocycle 1d afforded only trans-syn-c is (TSC) tricycle 31. On the contrary, the transannular Diels-Alder re action in cis-trans-cis (CTC) macrocycle 1a and trans-trans-cis (TTC) macrocycle 1c led to a mixture of the same four tricyclics (30, 32-34) but in different ratio. The above experimental results are rationaliz ed by taking into consideration the interconversion of macrocyclic tri enes 1a, 1b, and 1c. Pathways for these interconversions are also prop osed.