Scheme 2.
Synthesis of compounds 22–25 (Procedure B). Reagents and conditions: (i) (COCl)2, DMF, carboxylic acids 10–13, CH2Cl2, 0 °C→r.t., 1 h; (ii) Et3N, CH2Cl2, 0 °C→r.t., 1 h, 81–91%.
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