In a 3 l three necked flask fitted with mechanical stirrer and reflux condenser, under inert atmosphere, 89.7 g (322 mmoles, 1 eq) of {1-[(1S)-1-(aminocarbonyl)propyl]-5-oxo-3-pyrrolidinyl}methyl methanesulfonate 37 are dissolved in 300 ml of acetonitrile. 27.3 g (419 mmoles, 1.3 eq) of sodium azide are added in one portion, with 150 ml of acetonitrile. The mixture is brought to reflux in 20 min, and stirred overnight. 3.1 g (48 mmoles, 0.2 eq) of sodium azide are added and reflux continued for a total of 44 hours. After cooling down to 10° C., the mixture is filtered, the precipitate washed with 3×50 ml of acetonitrile and the combined organic fractions concentrated to dryness to give 77.3 g of crude 32. It is crystallised from 150 ml of ethyl acetate at 10° C. to give 60 g of pure 32, 82%. Alternatively, (2S)-2-[4-(fluoromethyl)-2-oxo-1-pyrrolidinyl]butanamide 44, (2S)-2-[2-oxo-4-(1H-tetrazol-1-ylmethyl)-1-pyrrolidinyl]butanamide 39, (2S)-2-[2-oxo-4-(1H-tetrazol-1-ylmethyl)-1-pyrrolidinyl]butanamide 40, (2S)-2-[2-oxo-4-(1H-1,2,4-triazol-1-ylmethyl)-1-pyrrolidinyl]butanamide 55, 2-[2-oxo-4-(1H-1,2,3-triazol-1-ylmethyl)-1-pyrrolidinyl]butanamide 56, (2S)-2-{4-[(isopropylsulfanyl)methyl]-2-oxo-1-pyrrolidinyl}butanamide 24, (2S)-2-[2-oxo-4-pyrrolidinylmethyl)-1-pyrrolidinyl]butanamide 15, (2S)-2-[2-oxo-4-(4-thiomorpholinylmethyl)-1-pyrrolidinyl]butanamide 17, are prepared in similar ways, from activated alcohol derivatives, such as mesylates, tosylates or halides.
