Exploiting the alkylating properties of phosphate esters , we were able to break the O-CH 3 bond in 4 by transalkylation with an excess of pyridine, yielding the pyridinium salt 5. Protonation of the crude salt 5 using the cation exchange resin DOWEX X50 afforded the desired free acid 6 in 81% yield (from 4). However, the acid turned out to be unstable in solution as well. Immediate decomposition to dihydrooxazole 3 was observed.