Figure 1

Reaction and reagents for the synthesis of the tosylate precursor 5: (a) Pyridine, 0–5 °C, stirring, 3 h (b) acetone, Cs2CO3, stirring at room temperature followed by heating and stirring at 50 °C for 6 h.

Reaction and reagents for the synthesis of the tosylate precursor 5: (a) Pyridine, 0–5 °C, stirring, 3 h (b) acetone, Cs2CO3, stirring at room temperature followed by heating and stirring at 50 °C for 6 h.