| Autor: |
Fung AKK; Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory2601, Australia., Sowden MJ; Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory2601, Australia., Coote ML; Institute for Nanoscale Science & Technology, College of Science & Engineering, Flinders University, Sturt Road, Bedford Park, South Australia5042, Australia., Sherburn MS; Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory2601, Australia. |
| Abstrakt: |
Cadiot-Chodkiewicz cross-couplings generate an unsymmetric buta-1,3-diyne by way of a Cu(I)-catalyzed coupling between a terminal alkyne and a 1-haloalkyne. Despite their widespread use, Cadiot-Chodkiewicz reactions are plagued by the generation of symmetric buta-1,3-diyne side products, formed through competing: (a) formal reductive homo-coupling of the 1-haloalkyne and (b) oxidative (Glaser-Hay/Eglinton) homo-coupling of the terminal alkyne. To overcome this issue, a large excess of one of the two reacting alkynes is commonly deployed, and difficult separations of cross- and homo-coupled products are often encountered. Here, we demonstrate that the use of ascorbate as a reductant leads to a suppression of these unwanted side reactions, hence permitting excellent yields with a roughly stoichiometric ratio of reactants. The procedure also avoids an inert gas atmosphere and uses a sustainable solvent. A similar approach is effective for cross-couplings involving a Pd(0)/Pd(II) catalytic cycle, with air tolerant Sonogashira couplings also established. |
