TRANSITION-METAL-CATALYZED OXIDATIONS .7. ZIRCONIUM-CATALYZED OXIDATION OF PRIMARY AND SECONDARY ALCOHOLS WITH HYDROPEROXIDES

A new procedure for the oxidation (dehydrogenation) of primary and sec ondary alcohols employing Zr(O-t-Bu)(4) or Zr(O-n-Pr)(4)/tert-butyl hy droperoxide/3 Angstrom molecular sieves is presented. Secondary alcoho ls-if not severely sterically hindered-are usually converted quantitat ively to the corresponding ketones. Esters or acids can be byproducts in the reaction of primary alcohols. However, the aldehydes are obtain ed in good yield by lowering the reaction temperature, decreasing the amount of TBHP or replacing TBHP by cumene hydroperoxide (CHP), and/or exchanging the catalyst Zr(O-t-Bu)(4) by Zr(O-n-Pr)(4) or silica gel- supported Zr(OR)(x). A remarkable selectivity of equatorial alcohol gr oups (e.g., 11 and 13) is observed in contrast to chromium(VI)-based o xidations. Strongly chelating substrates such as furfuryl alcohol (18) or 1,2-diol 25 that prevent hydride transfer in the six-membered tran sition state A are not converted.