Stereocontrolled construction of 1, 7-dimethyl A.B.C.[6.6.6] tricycles. Part II. transannular Diels-Alder reaction of 14-membered macrocycles containing m-dienophiles

Article abstract of DOI:10.1139/v93-153

The synthesis and transannular Diels-Alder reactions of 14-membered macrocyclic trienes containing a methyl-substituted diene and a methyl-substituted cis-dienophile moiety are described. As a result of the dienophile 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 the preceding paper in this series. Thus trans-syn-cis (TSC) tricycle 30 was the sole product obtained from the trans-cis-cis (TCC) macrocycle lb. In a similar fashion TCC macrocycle Id afforded only trans-syn-cis (TSC) tricycle 31. On the contrary, the transannular Diels-Alder reaction in cis-trans-cis (CTC) macrocycle la and trans-trans-cis (TTC) macrocycle lc led to a mixture of the same four tricyclics (30, 32-34) but in different ratio. The above experimental results are rationalized by taking into consideration the interconversion of macrocyclic trienes la, lb, and lc. Pathways for these interconversions are also proposed.