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. Author manuscript; available in PMC: 2014 Jun 1.
Published in final edited form as: Bioorg Med Chem Lett. 2013 Mar 29;23(11):3385–3388. doi: 10.1016/j.bmcl.2013.03.077

Scheme 3.

Scheme 3

Reagents and conditions: (a) Carbon disulfide, NaOH, MeOH, 160-180 °C, 3 h, 15a: 100%; 15b: 100%; (b) 1N HCl, 16a: 62%; 16b: 51%; (c) NH4OH, rt; (d) H2O2, 0 °C;(e) NH3(l), 0 °C, then 120 °C, 3 h, over three steps, 19a: 40%; 19b: 35%.