N(OC(C)(C)C)=O.[CH2:8]([O:10][C:11]([C:13]1[NH:14][C:15]2[C:20]([CH:21]=1)=[C:19]([O:22][C:23]1[CH:28]=[C:27]([CH3:29])[CH:26]=[CH:25][C:24]=1N)[CH:18]=[CH:17][CH:16]=2)=[O:12])[CH3:9]>CN(C)C=O.C(OCC)C>[CH2:8]([O:10][C:11]([C:13]1[NH:14][C:15]2[C:20]([CH:21]=1)=[C:19]([O:22][C:23]1[CH:28]=[C:27]([CH3:29])[CH:26]=[CH:25][CH:24]=1)[CH:18]=[CH:17][CH:16]=2)=[O:12])[CH3:9]Tert-butyl nitrite (0.428 ml, 3.609 mmol) is dissolved in 5 ml of dimethylformamide and heated to 65° C. A solution of 135 (1.1 g, 3.609 mmol) in 5 ml of dimethylformamide is added dropwise and the mixture is stirred of additional 10 minutes. The brown solution is cooled to room temperature, diluted with diethyl ether and washed with 2N HCl and brine. The organic layers are dried over sodium sulphate and evaporated. The crude product (930 mg of a brown oil) is further purified by flash-chromatography (hexane/ethyl acetate 7:3).
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