抄録
Dihydrocarvyl acetate [1] and neo-dihydrocarvyl acetate [2] were oxidized with selenium dioxide in aqueous ethanol at refluxing. In each case, 8 (10) -p-menthene-2-acetoxy-9-al, -9-ol, cis- and trans-8-p-menthene-2-acetoxy-4-ols were obtained. The conformations of these compounds were assigned as shown in Fig.-3 and 5 on the basis of the chemical evidence, IR and NMR data. In studies of the mechanism of allylic oxidation of olefins with selenium dioxide, Schaefer, Tracktenberg and Bhalerao have shown that at the first step of the oxidation, protonated selenium dioxide or its hydrate attacks a double bond as forming a allylic selenite ester and the second the solvolysis of this ester is followed. In the oxidation of [1] the allylic selenite ester [A] and [B] were produced and then the solvolysis of these esters gave -9-ol [1d] and -4-ols ([1a], [1c]) respectively. In the solvolysis step of [B] there was no steric hindrance in each case of the cis-attack and trans attack of the water molecule to equatorial acetoxy group, so that it was expected that the formation of [1a] was the same preference to that of [1c]. As shown in Table-1, the ratio of the yields of [1a] and [1c] was about 1 : 1. In the solvolysis step of [C] in Fig.-5, the trans-attack of the water molecule to axial acetoxy group would be preferable to the alternative cis-attack, since the cis-attack produces a 1, 3-diaxial interaction between the acetoxy group and the hydroxy group. In agreement with this, the trans-2, 4-diol monoacetate [2c] was favored over cis-epimer [2a] by fourfold.
