Copper-free palladium-catalyzed Sonogashira coupling-annulation: efficient one-pot synthesis of functionalized pyrano[4,3-b]quinolines from 2-chloro-3-formylquinolines.

A convenient, one-pot, copper-free, Pd-catalyzed methodology has been described for the synthesis of 1,3-disubstituted pyrano[4,3-b]quinolines from 2-chloro-3-formylquinolines. Formation of annulated products 3 is attributed to the presence of Pd(OAc)2 and PPh3. Further, PPh3 in the reaction mixture promotes the cyclization by reducing the reaction time and increasing the yield of cyclized product.