1-O,1-O'-ditert-butyl 2-O-ethyl cyclopropane-1,1,2-tricarboxylate

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: TFA (4.5 g, 39.7 mmol) was added into a solution of 1,1-di-tert-butyl 2-ethyl cyclopropane-1,1,2-tricarboxylate (4.9 g, 13.2 mmol) in dichloromethane (20 mL) and the mixture was stirred at room temperature for 48 h. The solvent was evaporated in vacuo and the excess TFA was lyophilized to afford 2-(ethoxycarbonyl)cyclopropane-1,1-dicarboxylic acid (3.3 g, 100%). 1H NMR (300 MHz, CD3OD): δ 1.23-1.29 (t, J=6.9 Hz, 3H), 1.60-1.64 (m, 1H), 1.85-1.88 (m, 1H), 2.48-2.53 (m, 1H), 4.10-4.18 (m, 1H). The solvent was evaporated in vacuo

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a THF (200 mL) solution of t-BuOK (11.4 g, 102 mmol) at −30° C. was added slowly di-tert-butyl malonate (20 g, 92.6 mmol). The internal temperature was maintained between −30° C. and −10° C. After 30 min, ethyl 2,3-dibromopropanoate (29 g, 111.1 mmol) was added. The cooling bath was removed. After 1.5 h, the reaction mixture was cooled to −10° C. for addition of t-BuOK (11.4 g, 102 mmol). The cooling mixture was removed and the mixture was stirred overnight. The solution was evaporated and the residue was extracted with ethyl acetate (600 mL), dried and purified by CombiFlash (PE:EA=15:1) to afford 1,1-di-tert-butyl 2-ethyl cyclopropane-1,1,2-tricarboxylate (18 g, 62%). 1H NMR (300 MHz, CDCl3): δ 1.34-1.51 (t, J=7.2 Hz, 3H), 1.54-1.56 (d, J=4.4 Hz, 18H), 1.58-1.60 (m, 1H), 1.90-1.94 (m, 1H), 2.52-2.57 (m, 1H), 4.21-4.31 (m, 2H). The internal temperature was maintained between −30° C. and −10° C The cooling bath was removed After 1.5 h The cooling mixture was removed The solution was evaporated the residue was extracted with ethyl acetate (600 mL) dried purified by CombiFlash (PE:EA=15:1)