New Synthesis of 2,4,6,8-Tetramethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione Using Etidronic Acid as a “Green” Catalyst

A new method has been developed for the synthesis of 2,4,6,8-tetramethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione in 62% yield using etidronic acid [1-hydroxyethane-1,1-diylbis(phosphonic acid), HEDP] as a “green” catalyst. A plausible stepwise mechanism of the reaction has been proposed and partially confirmed by NMR data and studying model processes. The effects of the reaction medium and HEDP on particular species involved in the reaction, namely N , N ′-dimethylurea, 4,5-dihydroxy-1,3-dimethylimidazolidin-2-one, and 2,4,6,8-tetramethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione, have been studied by 1 H and 13 C NMR spectroscopy in D 2 O, neutral and acidified solutions (acetic acid- d 4 ), and solutions containing 1 equiv of HEDP.