Palladium‐catalyzed dual C–H activation of N‐phenyl‐1H‐indole‐3‐carboxamides for the synthesis of 5,11‐dihydro‐6H‐indolo[3,2‐c]quinolin‐6‐ones

Abstract

AbstractIn this paper, we report a palladium‐catalyzed dual C–H activation of N‐phenyl‐1H‐indole‐3‐carboxamides for the synthesis of 5,11‐dihydro‐6H‐indolo[3,2‐c]quinolin‐6‐ones. The optimal reaction conditions were to use 20 mol % of Pd(TFA)2 as the catalyst, 2.0 equivalents of Cu(OAc)2 as the oxidant, 1.0 equivalent of K3PO4 as the base, and 3.0 equivalents of PivOH as the additive in DMF/dioxane (1: 9). When carried out at 120 °C for 24 h, the reaction could provide nineteen target indoloquinolinones in modest to excellent yields, including the N,N′‐dimethylated and N,N′‐unsubstituted products which are inaccessible by the reported C–H activation methodologies. The dual C–H activation reaction was also applicable to N‐phenyl‐1H‐indole‐2‐carboxamides and formed the corresponding 5,7‐dihydro‐6H‐indolo[2,3‐c]quinolin‐6‐ones. A plausible reaction mechanism based on the data from the control experiments and the literatures was proposed to account for the transformation.