Scheme 1. Synthesis of 2–5. Reagents and conditions: (a) Boc₂O, DMAP, MeCN, 80 °C; (b) n-BuLi, THF, –78 °C; (c) diethyl chlorophosphate, THF, –78 °C to rt; (d) DMF, THF, –78 °C to rt; (e) neat, 150 °C for 2; 170 °C for 3; (f) LDA, 1,2-dibromotetrachloroethane, THF, –78 °C to rt; (g) NaOMe, THF/MeOH, 80 °C; (h) 4-Mes₂B-3,5-Me₂C₆H₂B(pin), Pd(PPh₃)₄, K₂CO₃, THF/H₂O, 80 °C; (i) trimethylsilylacetylene, Pd(PPh₃)₄, CuI, i-Pr₂NH, 70 °C; (j) HBMes₂, THF, rt.