Scheme 1. Synthetic pathway to target compounds 5 and 6. Reagents and conditions: (a) acetic anhydride, pyridine, 8 h, r.t, (b) acetic acid, K2CrO7, 70 °C, 5 h, r.t, (c) sodium hydride, THF, propargyl amine, Et3N, 8 h, r.t, (d) NaNO2, 10% HCl, 3 h, r.t, (e) sodium azide, DMF, r.t, (f) CuSO4, sodium-l-ascorbate, t-BuOH : H2O (1 : 1), 48 h, r.t, (g) NaOH, 2 h, r.t.
