Synthesis of the Inhibitors 6, 8, 11 and 16a
aReagents and conditions : (i) CH3COCH2CO2C2H5, AcOH, reflux, 3.5–25 h, yield 70–85 %; (ii) POCl3, reflux, 40 min-2 h, yield 60–65 %; (iii) RNH2, EtOH, 12–18 h, room temp., yield 65–80 % (compounds 6,8 and 16); Pd(OAc)2, BINAP, NaOt-Bu, anhydrous toluene, 24 h reflux, yield 45 % (compound 11)