Ozonolysis of tetrahydropyranyl ethers

The relationship between the conformation of the acetal function and its reactivity towards ozone has been described in detail (cf p. 41 ). It was shown that the insertion of ozone into the C-H bond of the acetal function to form the corresponding hydrotrioxide tetrahedral intermediate is subject to stereoelectronic control. This section deals with the next step of this reaction, i,e., the decomposition of the hydrotrioxide tetrahedral intermediate to yield the ester product. Experimental results will be presented to show that this step is also controlled by stereoelectronic effects. These results can therefore be used as evidence for the principle of stereoelectronic control in ester formation. 

These results demonstrate that the hydrotrioxide intermediate 118 which is formed from a cyclic acetal such as V[7 is cleaved in a completely specific manner, yielding the hydroxy-ester 119 in preference to the lactone 

Ozone oxidation of the trans-decal in diol benzylidene 133 has been carried out (71). Under kinetically controlled conditions, it produces the axial benzoate 134 in preference to the more stable equatorial benzoate 135. Similar results were obtained with an analogous case derived from cholestane-2s,36-dio1. These results are essentially identical to those obtained by King and Allbutt (60. 62) in their study on the hydrolysis of dioxolane orthoesters and dioxolenium salts (cf. p. 82), and can therefore be explained in the same manner. These results further confirm that the oxidation of acetals by ozone produces an intermediate which behaves like the hemiortho-ester tetrahedral intermediate which is formed in the hydrolysis of orthoesters. 

It is appropriate to point out here that the development of the theory of stereoelectronic control has had its origin in the study of the ozonolysis of the acetal function (67, 58). It was first demonstrated that there 

The study of the cleavage of the axial and the equatorial vinyl bicyclic orthoesters 140 and 141 (Fig. 10) with potassium permanganate was reported recently (1. 3). Permanganate reacts with the vinyl orthoester double-bond yielding first 142 and then the tetrahedral intermediate 143. On that basis, 

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Hydrolysis of cyclic orthoesters Ozonolysis of tetrahydropyranyl ethers Cleavage of vinyl orthoesters... 

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