Palladium-Catalyzed α-Arylation of Tetramic Acids

A mild, racemization-free, palladium-catalyzed α-arylation of tetramic acids (2,4-pyrrolidinediones) has been developed. Various amino acid-derived tetramic acids were cleanly arylated by treatment with 2 mol % of Pd(OAc)₂, 4 mol % of a sterically demanding biaryl phosphine, 2.3 equiv of K₂CO₃ or K₃PO₄, and aryl chlorides, bromides, or triflates in THF. With conventional heating, conversions >95% could be attained after 1 h at 80 °C, whereas microwave-induced heating led to much shorter reaction times (5 min at 110 °C). The electron density of the aryl electrophile had no effect on their reactivity: both electron-rich and electron-poor aryl chlorides and bromides or triflates led to good yields. Ortho-substituted aryl halides and heteroaryl halides, however, did not undergo the title reaction.