Synthesis of Compounds 21, 22, and 23a
a Reagents and reaction conditions: (a) oxalyl chloride, anhydrous DMF cat., anhydrous THF, 0 °C, 10 min; (b) ethyl 5-chloro-1H-indole-2-carboxylate, AlCl3, 1,2-dichloroethane, closed vessel, 110 °C, 150 W, Pmax = 250 PSI, 2 min, 32%; (c) selenium(IV) oxide, DMSO, closed vessel, 150 °C, 150 W, Pmax = 250 PSI, 2 min, 56%; (d) Et3SiH, CF3COOH, 25 °C, overnight, 40%.