added to the solution the mixture was stirred at room temperature for 1 hour and then concentrated again in vacuo the residue was dissolved in 400 ml of dioxane and 400 ml of water after triethylamine 108 3 g 1 07 mol was added to the solution di tert butyl dicarbonate 194 2 g 0 89 mol was added to the mixture and then stirred at room temperature overnight the reaction mixture was concentrated after the concentrate was dissolved in diethyl ether the solution was extracted once with water and twice with 90 ml of a 1 m sodium hydroxide aqueous solution under ice cooling 15 ml of concentrated hydrochloric acid was added to the combined aqueous layer after returned to room temperature the liquid mixture was acidified with potassium hydrogen sulfate and then extracted twice with ethyl acetate after the organic layer was dried over anhydrous sodium sulfate the solvent was removed by distillation in vacuo so that 141 0 g 64 of the title compound was obtained 0 99 3h d j 7 hz 1 05 3h d j 7 hz 1 42 9 2h s 1 45 9 2h s 2 01 2 16 1h m 3 55 3 68 1h m 4 39 1 2h d j 2 hz 4 41 1 2h d j 3 hz 4 86 1 2h d j 7 hz 4.