Two-stage sonogashira coupling method in the synthesis of auxin active acetylenes

- A sequential Sonogashira coupling of a protected acetylene precursor with aryl halides (5) followed by pyrazolyl iodides (14) allows efficient access to the unsymmetrical aryl-heteroarylacetylene (8). Subsequent regioselective lithiation exchange followed by dimethyl oxalate quench produced readily vicinal ketoesters (9) which show auxin effects in a wide variety of plant species. Dedicated to Professor Kevin M. Smith, vice-chancellor of Louisiana State University and recipient of the Robert Burns Woodward Award on Lifetime Achievement at the International Conference on Porphyrins and Pthalocyanines (ICPP- 4) held in Rome 2006.