| Abstract: | A new route to the direct preparation of H‐phosphinate esters has been explored. The ring‐opening reaction of cyclic ether (tetrahydrofuran or tetrahydropyrane) was carried out with magnesium halide in the presence of phosphine halide (PRCl2 or PCl3). The process is straightforward and all the reagents are relatively cheap and readily available. Magnesium halide‐mediated THF ring‐opening (SN2@C) and the subsequent SN2@P elementary reactions that giving rise to the intermediate of haloalkyl phosphinates have been discussed based on our experimental findings ( Path I : SN2@C−+SN2@P). Another possible route, the direct SN2 between THF (nucleophile) and phosphine halide (electrophile) that followed by THF ring opening by halide dissociated from phosphine halide ( Path II: SN2@P−+SN2@C), was also proposed. However, path II is the least likely reaction path because neutral THF is not a good nucleophile. H‐phosphinate esters could be readily available in the subsequent hydrolysis process. Considering the ionic bond strength in magnesium halides and the nucleophilicity of halides dissociated from MgX2 in protic solvents like water, MgBr2 is recommended for ring‐opening reactions of cyclic ethers. |
