Scheme 2.

Synthesis of 10a

^aReagents and conditions: (a) K₂CO₃ (2 equiv), CH₃CN, 68%; (b) m-CPBA, CH₂Cl₂; (c) Ac₂O, reflux; (d) NaOH (aq), EtOH, reflux, 4h, 87%; (e) SO₃˙pyridine, NEt₃, DMSO, CHCl₃, 16 h, 83%; (f) H₂NOH˙HCl, NaOAc, CH₃OH, reflux, 2 h, 90%; (g) Ac₂O, reflux, 94%; (h) H₂, 10% Pd-C, CH₃OH, 85%; (i) CH₃OH, 0.1 M pH 6 buffer, NaHCO₃, 75 °C, 48 h, 95%.