Cl[C:2]([O:4][CH2:5][CH:6]=[CH2:7])=[O:3].C([N:15]1[CH2:19][CH2:18][C@H:17]([O:20][S:21]([CH3:24])(=[O:23])=[O:22])[CH2:16]1)C1C=CC=CC=1.CO.O>CCCCCCC>[CH2:5]([O:4][C:2]([N:15]1[CH2:19][CH2:18][CH:17]([O:20][S:21]([CH3:24])(=[O:23])=[O:22])[CH2:16]1)=[O:3])[CH:6]=[CH2:7]6.4 ml of allyl chloroformate were added dropwise to 10.2 g of methanesulphonic acid (S)-1-benzyl-pyrrolidin-3-yl ester in 880 ml of n-heptane at room temperature within 10 minutes under argon and with slight cooling. The two-phase mixture was stirred vigorously for 2 hours 45 minutes and subsequently treated with 40 ml of methanol/water (1:1). The aqueous methanolic phase was separated, extracted with 40 ml of heptane and thereafter the methanol was distilled off on a rotary evaporator. The aqueous phase was extracted twice with 30 ml of ethyl acetate. The organic phases were combined, dried over Na2SO4, filtered and the filtrate was concentrated. 8.23 g of beige oil were obtained.
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