Scheme 1. Synthesis of Core Fragment 2d.
Reagents and conditions: (a) MeNH2 in MeOH, DBU, 125 °C, microwave, 32%; (b) ethyl acrylate, Pd(tert-Bu3P)2, DIPEA, 160 °C, microwave, 64%; (c) Fe, NH4Cl, EtOH, H2O, 75 °C; (d) NaOMe, MeOH, 85 °C, 11% over two steps. See the Supporting Information for other synthetic fragments.