aReagents and conditions: (i) ethylene glycol, p-TsOH, benzene, reflux (98 %); (ii) triethylene glycol, Cs2CO3, DMF, microwave, 150 °C, 50 min (61 %); (iii) p-TsCl, Et3N, DMAP, CH2Cl2 (82 %); (iv) TBAF·H2O, THF, reflux (57 %); (v) PPTS, acetone, H2O, 70 °C (89 %); (vi) p-TsCl, pyridine, CH2Cl2, 0 °C to rt (84 %); (vii) TBAF·H2O, THF, reflux (40 %).