[CH2:1]([O:8][C:9]([NH:11][C@@H:12]([CH2:17][CH2:18][C:19]#[N:20])[C:13]([O:15][CH3:16])=[O:14])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([Sn]([N:34]=[N+:35]=[N-:36])(CCCC)CCCC)CCC>C1COCC1>[CH2:1]([O:8][C:9]([NH:11][C@@H:12]([CH2:17][CH2:18][C:19]1[NH:36][N:35]=[N:34][N:20]=1)[C:13]([O:15][CH3:16])=[O:14])=[O:10])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A mixture of methyl (2S)-2-benzyloxycarbonylamino-4-cyanobutyrate (10 g), tri-n-butyltin azide [prepared according to the method in Rec. Trav. Chim. Pavs-Bas, 1963, 81, 286; 12 g] and THF (60 ml) was stirred and heated to reflux for 40 hours. The mixture was evaporated. The resultant brown oil was triturated in diethyl ether which had been saturated with hydrogen chloride gas. The precipitate was isolated and washed with diethyl ether. There was thus obtained methyl (2S)-2-benzyloxycarbonyl-amino-4-(tetrazol-5-yl)butyrate (2.23 g, 32%);
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