Synthesis of 2-alkynylquinolines from 2-chloro and 2,4-dichloroquinoline via Pd/C-catalyzed coupling reaction in water

The Pd/C–CuI–PPh3 catalyst system facilitated Sonogashira coupling of 2-chloroquinoline and 2,4-dichloroquinoline with terminal alkynes in water without generating any significant side products. A variety of 2-alkynylquinolines were prepared from 2-chloroquinoline in good to excellent yields and the 2,4-dichloroquinoline afforded monosubstituted product i.e., 2-alkynyl-4-chloro quinoline with high regioselectivity. The methodology was found to be effective for the alkynylation of 1-chloroisoquinoline and 3-methyl-2-chloroquinoline.