The hydrolysis of cis and trans methoxy bicyclic and tricyclic orthoesters. Evidence for a chair–boat inversion prior to breakdown in some hemiorthoester tetrahedral intermediates

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Abstract
The acid hydrolysis of cis and trans methoxy bicyclic and tricyclic orthoesters 1–4 was studied. The trans isomers gave only the corresponding hydroxy-lactones (2 → 14 and 4 → 16 + 10) whereas the cis isomers gave mixtures of dihydroxy-esters and hydroxy-lactones (1 → 13 + 14) and 3 → 15 + 16 + 10). These results are rationalized on the basis of the stereoelectronic theory for hydrolytic processes. The fact that hydroxy-lactone 16 is produced to a larger extent than the isomeric hydroxy-lactone 10 is taken as evidence that when a tetrahedral intermediate is not allowed (stereoelectronically) to break down in a chair conformation, it will take a boat form prior to cleavage.

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