Scheme 4. Reagents and Conditions.
(a) NaOMe/NaOH, MeOH/H2O, rt, 20 h; (b) 1,2-ethylenediamine, n-BuOH, PhMe, 90 °C, 24 h; (c) Ac2O, Et3N, MeOH, rt; (d) Na/NH3, THF, −78 °C, 11-25% (over 4 steps).
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