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Reagents and conditions: (a) (1) isobutyl chloroformate or SOCl2, (2) NH4OH for 46, MeNH2 for 51, EtNH2 for 52, Me2NH for 53, NH2CH2CH2OH for 54, NH2CH2CH2NMe2 for 55, or i-PrSO2NH2 for 56; (b) for 15–20, intermediate 36, Cs2CO3, DMF, 50 °C, 2 h,; for 21, intermediate 36, NaOMe, DMF, 60 °C, 16 h.
