Figure 4

Synthesis of 2–5. Reagents and conditions: (a) LiOH, Me₂SO₄, acetone, reflux, quantitative; (b) N-phenyl-bis(trifluoromethanesulfonimide), K₂CO₃, THF, 22 h, rt, 86%; (c) ZnCN₂,Pd(PPh₃)₄, DMF, 16 h, 100 °C, 86%; (d) LiOH, THF, 1 h, rt, quantitative; (e) BOP, Et₃N, THF, 19 h, rt, 74%; (f) Raney Ni, 4.8 atm H₂(g), NH₃/MeOH, 21 h, rt, 99%; (g) HCl/dioxane, MeOH, 2–6 h, rt, 40%-quantitative; (h) 1,3-bis (tert-butoxycarbonyl)-2-methyl-2-thiopseudourea, HgCl₂, Et₃N, THF, 2.5 h, rt, 36%, (i) Cl-SO₂CH₃, pyridine, CH₂Cl₂, 16 h, rt, 50%.