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

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.