Scheme 1. Reagents and conditions-(i) 2,2-dimethoxypropane, p-toluenesulfonic acid monohydrate, anhydrous acetone, under argon atmosphere 20 h, rt (ii) NaH, propargyl bromide, dry THF, reflux under argon atmosphere, 4 h (iii) benzyl bromide, NaN3, triethylamine, CuSO4·5H2O (10 mol%), ascorbic acid (25 mol%), t-BuOH : H2O (1 : 1), reflux for 6–12 h (iv) THF, 10% conc. sulphuric acid, 70 °C, 6–12 h.
