[CH2:1]([O:8][CH:9]1[CH2:12][CH:11](C(O)=O)[CH2:10]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([N:18]([CH2:21]C)CC)C.[N-]=[N+]=[N-].C1([O:32]P(=O)(O)OC2C=CC=CC=2)C=CC=CC=1.[C:43]([OH:47])([CH3:46])([CH3:45])[CH3:44]>ClCCl>[CH2:1]([O:8][CH:9]1[CH2:10][CH:11]([NH:18][C:21](=[O:32])[O:47][C:43]([CH3:46])([CH3:45])[CH3:44])[CH2:12]1)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=19.28 g (45 mmol) 3-benzyloxy-cyclobutancarboxylic acid (Org. Lett. 6(11), 1853-1856, 2004) are suspended in 80 ml dry tert-butanol and combined with 5.1 g (50 mmol) triethylamine and 13.8 g (50 mmol) phosphoric acid diphenylester azide. The reaction mixture is stirred for 20 h under reflux conditions. The solvent is eliminated in vacuo and the residue is taken up in dichloromethane. The organic phase is washed three times with 2 N sodium hydroxide solution, dried with sodium sulphate and the dichloromethane is eliminated in vacuo. The crude product is recrystallised from acetonitrile (1 g crude product: 5 ml acetonitrile).
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