Spectroscopic Feature and Stereochemistry of 1,2-Dioxan-3-ols

The cyclic peroxides and hydroperoxides obtained by the manganese(III)-based aerobic oxidation was characterized by 1H NMR, 13 C NMR, and IR spectroscopies, FAB MS spectrometry, and combustion analysis. The absolute structure of the crystalline peroxides was determined by X-ray crystallography. The spectroscopic feature of the cyclic peroxides is that two quaternary carbons attached to the oxygen atom appear at 110-80 ppm in the 13C NMR spectrum. On the other hand, in the case of the hydroperoxides, only one quaternary carbon attached to the oxygen atom appears at 88-85 ppm. The chemical shifts of the characteristic peaks in the 13C NMR spectrum are summarized in Figs. 7 and 8.

The absolute structure of some cyclic peroxides and hydroperoxides were established by the X-ray crystallographic measurement. The O - O bond lengths of the cyclic peroxides and hydroperoxides were 1.43-1.47 A, which were similar to those of the reported crystalline 1,2-dioxanes [3,163-165]. Some O - O bond lengths are shown in Figs. 7 and 8.

The stereochemistry of the hydroxyl group in the synthesized cyclic peroxides is also characteristic. In the solid state, the hydroxyl group was arranged in an axial-like orientation due to the anomeric effect [166] based on the X-ray crystallographic analysis (Fig. 4) [77,128,133,143].

Since the 1,2-dioxan-3-ol is a hemiketal structure, it is considered that it exists as an equilibrium mixture of an OH-axzal and an OH-equatorial diox-ane in solution (Scheme 28). In fact, the phenomenon was observed in the case of the 4-carbamoyl-1,2-dioxan-3-ols (Schemes 11 and 12) [83]. It seems that the equilibrium depends on the balance of the anomeric effect and the strength of the hydrogen bonding between the hydroxyl group and the car-bonyl function.

Methylation of the 1,2-dioxan-3-ol in the presence of p-toluenesulfonic acid gave two stereoisomers in 95% yield, and the isomer ratio was 42 : 58

Ph COMe -H

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