Scheme 1.

Reagents and conditions: (a) K₂CO₃, 3-bromoprop-1-yne (for 2a–l) or 4-bromobut-1-yne (for 2m), DMF, 60 °C, 2 h; (b) PPh₃, CBr₄, THF, room temperature, 6 h; (c) NaN₃, CH₃CN, 60 °C, 3 h; (d) 2a–m, copper(I) thiophene-2-carboxylate, CH₂Cl₂, room temperature, 6 h; (e) K₂CO₃, methyl iodide (for 6a) or benzyl bromide (for 6b), DMF, 60 °C, 4 h; (f) acetyl chloride (for 6c) or benzoyl chloride (for 6d), DMAP, DIPEA, CH₂Cl₂, room temperature, 4 h; (g) K₂CO₃, TsCl, CH₃COCH₃, 60 °C, 5 h; (h) 2d, copper(I) thiophene-2-carboxylate, CH₂Cl₂, room temperature, 6 h.