Patent US5847166 - Synthesis of aryl ethers - Google Patents
In particular, attention has been focussed on the coupling of different arylboronicacids to chloroarylphosphine oxides, which are, in general, considered challenging couplingpartners for this type of reaction.
A user-friendly synthesis of aryl arsines and phosphines.
Once the appropriate reaction conditions and catalystwere identified, the reaction was run on other substrates to verify that this could be a generalmethodology for the synthesis of phosphines.
The conversion–time data for 168 different Pd/Cu-catalyzed Sonogashira cross-coupling reactions of five arylacetylenes (phenylacetylene; 1-ethynyl-2-ethylbenzene; 1-ethynyl-2,4,6-R3-benzene (R = Me, Et, -Pr)) and Me3SiCCH with seven aryl bromides (three 2-R-bromobenzenes (R = Me, Et, -Pr); 2,6-Me2-bromobenzene and three 2,4,6-R3-bromobenzenes (R = Me, Et, -Pr)) with four different phosphines (P--Bu3, -Bu2PCy, -BuPCy2, PCy3) were determined using quantitative gas chromatography. The stereoelectronic properties of the substituents in the aryl bromides, acetylenes, and phosphines were correlated with the performance in Sonogashira reactions. It was found that the nature of the most active Pd/PR3 complex for a Sonogashira transformation is primarily determined by the steric bulk of the acetylene; ideal catalysts are: Pd/P--Bu3 or Pd/-Bu2PCy for sterically undemanding phenylacetylene, Pd/-BuPCy2 for 2- and 2,6-substituted arylacetylenes or Me3SiCCH and Pd/PCy3 for extremely bulky acetylenes and aryl bromides. Electron-rich and sterically demanding aryl bromides with substituents in the 2- or the 2,6-position require larger amounts of catalyst than 4-substituted aryl bromides. The synthesis of tolanes with bulky groups at one of the two aryl rings is best done by placing the steric bulk at the arylacetylene, which is also the best place for electron-withdrawing substituents.