Synthesis of new dibenzo[c.e][1,2]oxaphosphorine 2‐oxide containing diols based on diethanolamine

Different approaches were applied to obtain new diol compounds based on dibenzo[c.e][1,2]oxaphosphorine 2‐oxide (DOPO, 1) and diethanolamine (DEolA). Of four processes investigated, a four‐step synthesis of 1 containing propionic acid amide of DEolA proved to be the most efficient one. In addition, the intramolecular amine salt of the DOPO derivative with a ring‐opened structure was obtained by reinvestigation of the reaction of DOPO with DEolA and paraformaldehyde. The Atherton–Todd reaction of 1 and DEolA was investigated as well.