Scheme 1.

Reagents and conditions: (i) Pd(PPh3)2Cl2, CuI, Et3N, THF, rt, 12 h; (ii) (a) Zn, HCOONH4, MeOH, rt, 4 h, (b) Lindlar cat., H2, quinoline, 1 atm, MeOH, 4 h; (iii) 1,3-bis(methoxycarbonyl)-2-methyl-2-thiopseudourea, MeOH, PTSA, reflux, 10 h.