PROCESS FOR THE PREPARATION OF [2-((8,9)- DIOXO-2,6-DIAZABICYCLO [5.2.0]-NON-1(7)-EN-2-YL)-ETHYL] PHOSPHONIC ACID

This invention relates to a process for the preparation of formula (I) compound [2-((8,9)-dioxo-2,6-diazabicyclo[5.2.0]-non-1(7)-en-2-yl)ethyl]phosphonic acid, an NMDA antagonist useful as an anticonvulsant and neuroprotectant in situations involving excess release of excitatory amino acids. In the process of the present invention, 3-aminopropyl carbamic acid 1,1-dimethyl-ethyl ester is reacted with a dialkyl vinylphosphonate to obtain N-[3-(t-butyloxycarbonyl-amino)propyl]-2-aminoethylphosphonic acid dialkyl ester (d) in 80 % yield. Reaction of (d) with a 3,4-dialkoxycyclobut-3-en-1,2-dione gives [3-[[2-(dialkoxyphosphoryl)ethyl]-(2-alkoxy-3,4-dioxo-1,2-cyclobuten-1-yl)amino]propyl] carbamic acid 1,1-dimethylethyl ester (e) in 96 % yield. Deprotection and cyclization of (e) in trifluoroacetic acid gives [2-((8,9)-dioxo-2,6-diazabicyclo[5.2.0]-non-1(7)-en-2-yl)ethyl]phosphonic acid dialkyl ester (c) in 58 % yield. The phosphonic acid diethyl ester (c) was treated with bromotrimethylsilane to give compound (I).