Scheme 3.

Reagents and conditions: (i) (a) SOCl2, reflux, 12 h, (b) 3-methoxythiophene, AlCl3, dry DCM, reflux, 12 h; (ii) (a) H2, Pd/C, 60 psi, 12 h, (b) 1,3-bis(methoxycarbonyl)-2-methyl-2-thiopseudourea, MeOH, PTSA, reflux,10 h.

Reagents and conditions: (i) (a) SOCl2, reflux, 12 h, (b) 3-methoxythiophene, AlCl3, dry DCM, reflux, 12 h; (ii) (a) H2, Pd/C, 60 psi, 12 h, (b) 1,3-bis(methoxycarbonyl)-2-methyl-2-thiopseudourea, MeOH, PTSA, reflux,10 h.