Compound 15 (200 mg, 0.4 mmol) was dissolved in tetrahydrofuran (10 ml). A tea-spoon of sodium hydrogencarbonate was added, followed by phosgene (1.8 μl, 1.9 M in toluene). The reaction mixture was stirred for 30 min and filtrated. The solvent was evaporated and the crude chloride was re-dissolved in dichloromethane (10 ml). Sodium hydrogencarbonate (1 tea-spoon) and N′-hept-6-enyl-hydrazinecarboxylic acid tert-butyl ester (182 mg, 0.8 mmol). The reaction mixture was stirred at room temp. for 40 h. and then filtrated and purified by silica chromatography (1%→2% methanol in ether) to give pure title product (240 mg, 79%).
