Intramolecular Diels-Alder reactions of tethered homo- and heterotrienes. Synthesis of substituted cyclohexenes and six-membered heterocycles
Intramolecular Diels-Alder reactions of a number of diester-tethered trienes are reported. All-carbon trienes 5, 7 and 13 show little or no selectivity for trans-fused products. Heterotrienes 21 and 25 exhibit good to excellent cis-selectivity, with low to good selectivity for one of the two cis-fused isomers.