tert butanol 3 5 mmol 0 26 g in dcm 2 ml was added dropwise and the mixture was stirred 20 min at this temperature the mixture was cooled to u2212 10 u00b0 c on an ice ethanol bath and ethyl 4 aminobutyrate hydrochloride 3 9 mmol was added followed by dropwise addition of dipea 3 9 mmol at this temperature and the mixture was stirred overnight slowly warming up to room temperature the solvent was removed by evaporation and the residue was taken up in ethyl acetate 20 ml and washed with 1 m naoh and brine the organic layer was dried na 2 so 4 and evaporated in vacuo the ethyl ester was cleaved by hydrolysis using lioh and the product characterised by 1 h and 13 c nmr and maldi tof ms 3 chlorosulfonyl isocyanate csi 3 5 mmol 0 30 ml was dissolved in dry dichloromethane dcm 20 ml the mixture was cooled to 0 u00b0 c on an ice bath tert butanol 3 5 mmol 0 26 g in dcm 2 ml was added dropwise and the mixture was stirred 20 min at this temperature the mixture was cooled to u2212 10 u00b0 c on an ice ethanol bath and glycine tert butylester hydrochloride 3 9 mmol was added followed by dropwise addition of dipea 3 9 mmol at this temperature and the mixture was stirred overnight slowly warming up to room temperature the solvent was removed by evaporation and the residue.