Palladium-catalyzed coupling of N-tosylhydrazones with ortho substituted aryl halides: synthesis of 4-arylchromenes and related heterocycles

A convenient and efficient procedure for the synthesis of 4-arylchromenes, thiochromenes, and related heterocycles via a four step-sequence has been developed. The first three steps, which involve hydration of alkynes, hydrazones formation, and their Pd-coupling with ortho substituted aryl halides, furnished stereoselectively Z-trisubstituted olefins without any purification of the intermediates generated in each stage. These latter proved to be suitable precursors, in the last step, for the synthesis of the desired heterocycles of biological interest.