IMIDAZOLE-PROMOTED HYDROLYSIS OF OXAPHOSPHOLENE ESTERS. NUCLEOPHILIC VS. GENERAL BASE CATALYSIS.

Article abstract of DOI:10.1021/ja00351a043

A 2. 4-fold excess of imidazole (Im) accelerated the hydrolysis of 5,5-dimethyl-2-methoxy-1,2-oxaphosphol-3-ene 2-oxide (2a) in 50% aqueous methanol by a rate factor greater than 50. The reaction was first order in Im and led to the imidazolium salt (3-Im) of 5,5-dimethyl-2-hydroxy-1,2-oxaphosphol-3-ene 2-oxide and methanol via two independent routes. One route involved direct nucleophilic attack at the methoxy carbon; the other route was a multistep process with nucleophilic attack at phosphorus to give a ring-opened intermediate which was observed by **1H NMR. Possible intermediate 5,5-dimethyl-2-imidazoyl-1,2-oxaphosphol-3-ene 2-oxide was prepared and demonstrated to be highly reactive toward solvolysis in methanol and aqueous methanol. The Im-promoted hydrolysis was interpreted as involving general base catalysis.