Straightforward synthesis of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivatives containing P–N bonds

The H-phosphinate 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a commercial compound of interest for its flame retardant properties, was successfully converted to related phosphonamidates following a recently patented one-pot method based on the oxidation of the species in the presence of a suitable aliphatic or aromatic amine under mild conditions. In this way, the compounds 6-morpholinodibenzo[c,e][1,2]oxaphosphinine 6-oxide, 6-(4-acetylpiperazino)dibenzo[c,e][1,2]oxaphosphinine 6-oxide, 6-p-tolylaminodibenzo[c,e][1,2]oxaphosphinine 6-oxide and 6-(methyl(phenyl)amino)dibenzo[c,e][1,2]oxaphosphinine 6-oxide, where the P–H bond is formally replaced by P–N bonds, were isolated in good yields and with high purities. The characterization data were supported by the single-crystal X-ray structure determination of 6-morpholinodibenzo[c,e][1,2]oxaphosphinine 6-oxide and 6-(methyl(phenyl)amino)dibenzo[c,e][1,2]oxaphosphinine 6-oxide.