Regioselective C-3-alkylation of quinoxalin-2(1H)-ones via C-N bond cleavage of amine derived Katritzky salts enabled by continuous-flow photoredox catalysis

An efficient, transition metal-free visible-light-driven continuous-flow C-3-alkylation of quinoxalin-2(1H)-ones has been demonstrated by employing Katritzky salts as alkylating agents in the presence of eosin-y as a photoredox catalyst and DIPEA as a base at room temperature. The present protocol was accomplished by utilizing abundant and inexpensive alkyl amine (both primary and secondary alkyl) and as well as this a few amino acid feedstocks were converted into their corresponding redox-active pyridinium salts and subsequently into alkyl radicals. A wide variety of C-3-alkylated quinoxalin-2(1H)-ones were synthesized in moderate to high yields. Further this environmentally benign protocol is carried out in a PFA (Perfluoroalkoxy alkane) capillary based micro reactor under blue LED irradiation, enabling excellent yields (72% to 91%) and shorter reaction times (0.81 min) as compared to a batch system (16 h).

Automated summary

An efficient visible-light driven continuous-flow C-3-alkylation of quinoxalin-2(1H)-ones was achieved using Katritzky salts as alkylating agents. The reaction was catalyzed by eosin-y and base DIPEA at room temperature. The protocol utilized inexpensive alkyl amines and amino acid feedstocks to synthesize a variety of C-3-alkylated quinoxalin-2(1H)-ones. The reaction was carried out in a PFA capillary microreactor under blue LED irradiation, resulting in excellent yields and shorter reaction times compared to a batch system.