title: Facile synthesis of oxa- and azacyclic dienes via cycloalkenation of alkynyltungsten compounds. Stereoselective construction of tricyclic furan and pyran derivatives via intramolecular diels-alder reaction
abstract: A convenient and short synthesis of functionalized oxacyclic and azacyclic dienes is developed on the basis of organotungsten chemistry. Alkynyltungsten compounds bearing a tethered alcohol and amine are treated with aldehydes and BF(3).Et(2)O in cold diethyl ether to give tungsten-heterocyclic carbenium salts, further leading to tungsten-heterocyclic dienes via deprotonation with Et(3)N. Hydrodemetalation of these tungsten-heterocyclic dienes is performed by the action of anhydrous Me(3)NO in CH(3)CN. This method is applicable to the synthesis of a number of oxa- and azacyclic dienes, including those tethered with an electron-deficient olefin. The oxacyclic 1,3,8-nonatrienes and 1,3,9-decatrienes undergo intramolecular Diels-Alder reactions upon heating in toluene, yielding tricyclic tetrahydropyran and -furan derivatives with excellent diastereoselectivities.
authors.affiliation: Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan, R.O.C.
authors.initials: WT
authors.lastname: Li
authors.initials: MH
authors.lastname: Pan
authors.initials: YR
authors.lastname: Wu
authors.initials: SL
authors.lastname: Wang
authors.initials: FL
authors.lastname: Liao
authors.initials: RS
authors.lastname: Liu