Gold(I)-Catalyzed [2+2+2] Cyclotrimerization of 1,3-Diarylpropargyl Acetals

A gold-nitrone catalyzed [2 + + 2] cydotrimerization of 1,3-diarylpropargyl acetals into cyclohexylidene products (up to 74% yield) is reported. The trimerization is proposed to proceed through allenic intermediates via gold catalyzed 1,3-alkoxy rearrangement. The presence of catalytic amounts of different nitrones, tuning of the Au(I) catalyst activity, was essential for controlled regio-/chemoselective cydotrimerization. A linear nitrone-O-Au(I)-P coordination mode was shown (X-ray analysis) for a catalytic active phosphane-gold-nitrone catalysts with specific properties.