Scheme 1. Synthesis of Azido-Ketolide Intermediates 7a,b.

Reagents and conditions: (a) EtOH, 1M HCl, room temperature, 10–24 h, yield = 67%; (b) acetone, Ac₂O, 40°C, 24–48 h, yield = quantitative; (c) dichloromethane (CH₂Cl₂), N-chlorosuccinimide (NCS), Me₂S, Et₃N, −20 °C, 3 h, yield = 81%; (d) THF/DMF, CDI, NaHMDS, room temperature, 24 h, yield = 59%; (e) (i) CH₃CN/H₂O, 6a or 6b, 50°C, 24 h; (ii) MeOH, room temperature, 24 h, yield = 60–90%.