Scheme 2. Synthesis of thiodigalactosides 19–20 and 22–23. Reagents and conditions: (a) (i). alkyne (3 equiv.), CuI, DIPEA, DMF, 50 °C; (ii). NaOMe, MeOH, rt; (b) (i). Thiazol-2-ylethynyltrimethylsilane (1.5 equiv.), CuI, DIPEA, DMF, 50 °C; (ii). NaOMe, MeOH, rt; (c) alkyne, CuI, DIPEA, DMF, 50 °C.