There have been several successfull attempts to exchange hexamethylphosphoramide against the two urea derivatives 1,3-Dimethyl-2-imidazolidinone (DMEU) and 1,3-Dimethyltetrahydro-2(1H)-pyrimidinon (DMPU). A systematic survey is given by D.Seebach in
Users of the substitutes are found in
Some aspects make the changeover easier. It is quite difficult to purchase hexamethylphosphoramide and if there is a supplier, the price is higher than of the substitutes. Nevertheless is a question of the concrete synthetic problem if a substitute does work.