The oxidation of vinyl and silyl enol ethers with aqueous hydrogen peroxide was first achieved by the use of peroxotungstophosphate (PCWP) as the catalyst. For example, the oxidation of 1-ethoxy-1-octene with a stoichiometric amount of 35% H(2)O(2) in the presence of PCWP (0.5 mol %) in a mixed solvent of methanol and dichloromethane at room temperature gave 1-ethoxy-1-methoxy-2-hydroxyoctane, a synthetic equivalent of 2-hydroxyoctanal, in 70% yield. The oxidation of acyclic silyl enol ethers such as 1-[(trimethylsilyl)oxy]-1-octene under these conditions gave 1-hydroxy-2-octanone in 72% yield, while the same oxidation in dichloromethane alone resulted in cleavage of the enol double bond to form heptanal in 71% yield. Cyclic silyl enol ethers were converted into the corresponding alpha-hydroxy ketones in 48-71% yields under similar reaction conditions.
Dehomologation of aldehydes has been first successfully achieved via oxidative cleavage of silyl
enol ethers, derived from aldehydes and trimethylchlorosilane, using aqueous hydrogen peroxide
in the presence of a catalytic amount of peroxotungstophophate (PCWP) under phase-transfer
conditions. For instance, the oxidation of 1-[(trimethylsilyl)oxy]-1-octene resulting from octanal
and Me3SiCl with 35% H2O2 catalyzed by PCWP in dichloromethane at room temperature afforded
the one-carbon shorter aldehyde, heptanal, in 79% yield. A variety of silyl enol ethers were also
converted into one-carbon shorter aldehydes in good yields. The oxidation under homogeneous
conditions using tert-butyl alcohol gave hydrolysis products such as 2-oxooctanol and octanal. It is
of interest that [1-(trimethylsilyl)oxy]-1,10-undecadiene involving an enol moiety and a terminal
double bond afforded exclusively 9-decenal, in which the enol moiety was selectively oxidized. A
plausible reaction path for the oxidative cleavage of silyl enol ethers by the present system has
been suggested from the oxidation results of α-[(trimethylsilyl)oxy]styrene.
Die Cyclisierung des cis‐disubstituierten Cyclohexens (I) mit Diethyl‐Al‐(4‐methyl‐2,6‐di‐tert.‐butyl‐phenolat) unter milden Bedingungen liefert ein Gemisch der isomeren Dekalone (II) und (III); aus dem trans‐disubstituierten Cyclohexen (IV) erhält man unter gleichen Bedingungen stereospezifisch das cis‐Dekalon (II) (Ausb. 89%).
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Intermolecular Radical Addition of 1-Alkoxyalkyl Radicals to VinylDerivatives.-1-Alkoxyalkyl radicals, generated from 1-alkoxy-1-(phenylseleno) alkanes such as (I) and tri-n-butylstannane/AIBN, react with the activated alkenes (II), forming the adducts (III). -(NISHIYAMA, Y.; YAMAMOTO, H.; NAKATA, S.; ISHII, Y.; Chem. Lett. (1993) 5, 841-844; Dep. Appl. Chem., Fac. Eng., Kansai Univ.,
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