Pd catalyzed facile synthesis of cyclopenta[b]quinolin-1-one via sequential Sonogashira coupling and annulation. An unusual mode of ring closure, using sulphur as a soft nucleophile

Abstract

Pd mediated one pot sequential Sonogashira coupling followed by annulation using o-alkynyl aldehyde is reported. Contrary to the established modes of ring closures, an unusual mode of the initial attack of sulphur across the triple bond occurs leading to a cascade of reactions. The protocol requires just single column chromatography, delivering cyclopenta[b]quinolin-1-one in high yields. Furthermore chemoselective transformations were carried out across annulated precursors.