Acylperrhenate-Induced Tandem syn-Oxidative Cyclizations of Hydroxydienes

摘要

Tandem syn-oxidative polycyclizations of acyclic hydroxypolyenes represent efficient and possibly biomimetic strategies for the chemical synthesis of polyether natural products. Hydroxyl-directed syn-oxidative cyclizations of bishornoallylic alcoholsprovide access to trans-tetrahydrofurans, whereas hydroxyl-directed epoxidation strategies generally produce cis-tetrahydrofurans upon acid-catalyzed anti-cyclization. Although chromium(VI)-induced syn-oxidative cyclizations are limited to tertiary alcohols, Kennedy has developed a dirhenium heptoxide-mediated syn-oxidative cyclization method which produces predominantly trans-tetrahydrofuranyl alcohols and is compatible with primary and secondary hydroxyalkenes. More recently, Sinha et al. have reported that mixtures of Re_2O_7 and periodic acid promote tandem syn-oxidative bicyclization of a vic-disubstituted diene to give synthetically useful yields of a trans,trans-bis-tetrahydrofuran product. However, we found that application of these published rhenium oxide methodologies to trisubstituted diene substrates 6 and 10 (vide infra) gave complex reaction mixtures including oxidative cyclization and acid-catalyzed (nonoxidative) eyclohydration byproducts, even in the presence of an amine base.