2,3‐Diazabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxylic Acid, 2,3‐Diethyl Ester

[14011-60-0] C11H16N2O4 (MW 240.26) InChI = 1S/C11H16N2O4/c1-3-16-10(14)12-8-5-6-9(7-8)13(12)11(15)17-4-2/h5-6,8-9H,3-4,7H2,1-2H3 InChIKey = XMAKWQGDHULQOS-UHFFFAOYSA-N (building block for numerous stereoselective transformations) Alternate Names: 2,3-Diazabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diethyl ester(6CI,7CI,8CI,9CI); diethyl 2,3-diazabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate;Diethyl 1,2,3,6-tetrahydro-3,6-methano-1,2-pyridazinedicarboxylate; NSC 44163. Physical Data: mp 38–39 °C; bp 131 °C (1 mm); d 1.272 ± 0.06 g cm−3. Solubility: alcohol, ether, and most organic solvents. Form Supplied in: clear fluid oil, solidifies on long standing, rare chemical. Analysis of Reagent Purity: 1H NMR. Preparative Method: To a freshly distilled cyclopentadiene (1.5–2 equiv) solution in diethyl ether at 0 °C was added the diethyl azodicarboxylate (1 equiv)2. The reaction was allowed to stir for 6–12 h at room temperature until full consumption of the diethyl azodicarboxylate. The solvent was evaporated under reduced pressure and the crude clear oil was purified by silica-gel flash column chromatography with EtOAc/hexanes as eluent (20–40% gradient) to afford the 2,3-diazabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, 2,3-diethyl ester as a clear viscous liquid in 95% yield (eq 1). (1) The corresponding dibenzyl ester or ditertbutyl ester can be prepared in almost quantitative yield in a similar manner.3 Handling, Storage, and Precautions: Very stable. Can be stored in the refrigerator for several months. Stable at room temperature, turns into pale yellow viscous oil on long standing.