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Reagents and conditions: (i) K2CO3, 18-crown-6, DMF, r.t. 72 h for synthesis of 4, 94%, 16 h for synthesis of 5, 81% (ii) (a) 2 M aqueous HCl, 90 °C, 3 h (b) 10% aqueous NaOH, 4 °C 24 h, 77% (iii) (a) 2 M aqueous HCl, THF, 75 °C overnight (b) 10% aqueous NaOH, 4 °C 24 h, 81% (iv) NaH, DMF, r.t. 6 h, 38–79%.
