Scheme 4.
Synthesis of intermediate 9: i) BF3•Et2O, TMSN3, CH2Cl2; ii) NaOMe, MeOH; iii) TBDMSCl, pyridine; iv) DMTCl, pyridine; v) Pd/CaCO3, H2, EtOH; vi) DIPEA, 5, EtOH; vii) Phenoxyacetic acid, PyBOP, DIPEA, CH2Cl2; viii) Et3N•3HF, THF.
Synthesis of intermediate 9: i) BF3•Et2O, TMSN3, CH2Cl2; ii) NaOMe, MeOH; iii) TBDMSCl, pyridine; iv) DMTCl, pyridine; v) Pd/CaCO3, H2, EtOH; vi) DIPEA, 5, EtOH; vii) Phenoxyacetic acid, PyBOP, DIPEA, CH2Cl2; viii) Et3N•3HF, THF.