Hydrogen-Bond-Assisted Epoxidation of Homoallylic and Allylic Alcohols with Hydrogen Peroxide Catalyzed by Selenium-Containing Dinuclear Peroxotungstate.
英文:
Hydrogen-Bond-Assisted Epoxidation of Homoallylic and Allylic Alcohols with Hydrogen Peroxide Catalyzed by Selenium-Containing Dinuclear Peroxotungstate.
The reaction of peroxotungstates (H2WO4 + H2O2) with H2SeO4 gave the novel selenium-contg. dinuclear tungsten species, (TBA)2[SeO4{WO(O2)2}2] (I, TBA = [(n-C4H9)4N]+), which was characterized by elemental anal., IR, Raman, UV-vis, 77Se NMR, 183W NMR, and CSI-MS. Various kinds of homoallylic and allylic alcs. were efficiently epoxidized to the corresponding epoxy alcs. in high yields with 1 equiv. H2O2 with respect to the substrates. Compd. I showed the highest catalytic activity for H2O2-based epoxidn. of homoallylic and allylic alcs. among selenium and tungsten complexes. The turnover frequency reached up to 150 h-1 in a 10 mmol-scale epoxidn. of cis-3-hexen-1-ol and this value was the highest among those reported for the transition-metal catalyzed epoxidn. of homoallylic alcs. with H2O2. The kinetic, mechanistic, computational studies showed that the stabilization of the transition-state by the hydrogen bonding between I and the substrates results in the high reactivity for the I-catalyzed epoxidn. of homoallylic and allylic alcs. The nature of the hetero atoms in the di- and tetranuclear peroxotungstates with XO4n- ligands (X = As(V), P(V), S(VI), Si(IV), etc.) was crucial in controlling the Lewis acidity of the peroxotungstates, which significantly affects their electrophilic oxygen transfer reactivity. All the data of the structural, kinetic, spectroscopic, and computational comparison show that the dimeric peroxotungstate unit, {WO(O2)2}2, in I is activated by the SeO42- ligand. [on SciFinder(R)]
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