To a cooled (0 °C) solution of 28 (20 mg, 0.03 mmol) in dry DMF (2 mL, 0.01 M) were added propargyl bromide (0.02 mL, 0.03 mmol) and K 2 CO 3 (5.5 mg, 0.04 mmol). After stirring for 1 h at 25 °C, the ...