Sonogashira/hydroarylation sequential reactions: catalyzed by NHC–Pd complexes

It was found that an air-stable NHC–palladium complex of Pd[(s)-3-C3H5-4-(C5H5CH2)-1-(2,6-iPr2C6H3)-C3H3N2](C5H5N)Br2 derived from l-phenylalanine is an effective pre-catalyst for copper-free and phosphine-free Sonogashira reaction of alkynes under aerobic conditions in short reaction time. Moreover, the palladium compound would be reused to catalyze the hydroarylation of alkyne prepared from Sonogashira reaction, which makes firstly Sonogashira/Hydroarylation sequential reactions successful. The arylation of alkynes underwent with a high regio- and stereoselectivity and only trans-arylation of alkyne was observed. No Z/E isomerization of the olefin was observed in the system.

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