New formal (3+3) cycloaddition of enaminones for forming tetracyclic indolo[2,3-b]quinolines under microwave irradiation

Concise and efficient base-promoted domino formal (3+3) cycloaddition has been established for the formation of tetracyclic indolo[2,3-b]quinoline derivatives under microwave heating. The present methodology shows attractive properties, such as the maximum efficiency of a process, short reaction periods, and operational simplicity, and it can avoid time-consuming and costly syntheses, tedious work-up and isolation of intermediate. This chemistry provides a facile and promising synthetic strategy to construction of tetracyclic indolo[2,3-b]quinoline skeleton.