Stereoselective Double Spirocyclization of 2-Benzyl-3-alkynyl Chromone with Nitrone via Gold-Catalyzed Cascade
Amit Vijay Sasane1, Chun-Tang Chiou1, Ming-Yiang Chang1
1National Research Institute of Chinese Medicine, Ministry of Health and Welfare, Taipei 112304, Taiwan, R.O.C.
Abstract:
A novel, highly stereoselective gold-catalyzed spirocyclization of 2-benzyl-3-alkynyl chromone with nitrone is described. This cascade reaction involves gold-catalyzed cycloisomerization, nitrone-olefin [3 + 2]-annulation, alkene oxidation, and rearrangement for the formation of spirocyclic products. Interestingly, the isoxazolidine ring generated from [3 + 2]-annulation donates oxygen to alkene to generate a new pyran-3(4H)-one and azetidine ring for dispiro-benzofuran formation upon heating. This work demonstrates the one-pot, gold-catalyzed, multiple-step reaction, and the reaction temperature directly affects the formation of spirocyclic products.
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