Inhaltszusammenfassung

(Schiff base)vanadium(v) complexes 5 with tridentate imine auxiliaries served as catalysts for the oxidation of Br- with tert-butyl hydroperoxide (TBHP) in nonaqueous solvents. This reaction has been applied for the conversion of substituted 4-penten-1-ols into 5-exo-bromo-cyclized products, including a diastereomerically pure heterocyclic precursor used in a synthesis of the all-trans-configured 2,3,4,5-substituted tetrahydrofuran 2-epi-magnosalicin. Treatment of omega-substituted bis(homoal...(Schiff base)vanadium(v) complexes 5 with tridentate imine auxiliaries served as catalysts for the oxidation of Br- with tert-butyl hydroperoxide (TBHP) in nonaqueous solvents. This reaction has been applied for the conversion of substituted 4-penten-1-ols into 5-exo-bromo-cyclized products, including a diastereomerically pure heterocyclic precursor used in a synthesis of the all-trans-configured 2,3,4,5-substituted tetrahydrofuran 2-epi-magnosalicin. Treatment of omega-substituted bis(homoallylic) alcohols with the reagent combination of pyHBr, TBHP, and a vanadium(v) catalyst 5 afforded 6-endo-cyclized products, i.e. brominated tetrahydropyrans, as major compounds. The results from V-51 NMR, ESI-MS, and supporting reactivity-selectivity studies indicated that the mechanism of the new bromination reaction consists of vanadium-dependent and vanadium-independent steps. A (Schiff base)vanadium(v) compound 5 is required for activation of TBHP via in situ formation of the corresponding tert-butylperoxy complex. This reagent oxidizes Br-, which under the reaction conditions provides Br-2 as the active brominating reagent. The molecular bromine generated thus is released into the solution at a steady rate and serves as a reagent for the synthesis of beta-brominated cyclic ethers from bis(homoallylic) alcohols in a second, vanadium-independent step. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004). » weiterlesen» einklappen

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