Vinyl orthoesters cleavage

The study of the cleavage of the axial and the equatorial vinyl bicyclic orthoesters HO and H (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,... 

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

In previous studies, i,e. concurrent carbonyl-oxygen exchange in the hydrolysis of esters, acid hydrolysis of orthoesters and oxidation of acetals by ozone, the configuration of the tetrahedral intermediate was determined by the application of the principle of stereoelectronic control. There could be some ambiguity in these experiments as the theory of stereoelectronic control is used to predict both the stereochemistry of the tetrahedral intermediate as well as its breakdown. The oxidation cleavage of vinyl orthoesters can therefore be considered a more powerful experimental technique in that respect because the configuration of the hemi-orthoester... 

At this stage in the project, we decided to use a model system to try and learn more about the potential of future steps in the synthetic route. As such, the orthoester of acid 35 was formed (36 Scheme 5). Ozonolysis and addition of a vinyl Grignard reagent were not successful however, the failure of this process was possibly due to cleavage and decomposition of the orthoester. To further simplify the process, the acid was protected by reduction to the alcohol (38) and formation of the sUyl ether 39. While this was not ideal for an eventual synthetic route for reasons of step/atom/redox economy, a silyl ether would be more stable to future conditions and help determine... 

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