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Synthesis of Allylic Amide Functionalized 2H‑Chromenes and Coumarins Using a One-Pot Overman Rearrangement and Gold(I)-Catalyzed Hydroarylation

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journal contribution
posted on 28.09.2016, 00:00 by Salaheddin A. I. Sharif, Ewen D. D. Calder, Alexander H. Harkiss, Marie Maduro, Andrew Sutherland
A four-step synthesis of allylic trichloro­acetimidates bearing a 2-proparyloxyaryl group has been developed from readily available 2-hydroxy­benzaldehydes, and these have been used for the preparation of allylic amide derived 2H-chromenes using an Overman rearrangement and a 6-endo-dig hydroarylation. High yields of the 2H-chromenes were achieved using a stepwise approach involving an Overman rearrangement under thermal conditions followed by a hydroarylation reaction with a gold­(I) triflimide catalyst. An alternative method where both reactions were performed as a one-pot process was also developed and instead used a gold­(I) chloride catalyst activated by silver­(I) hexafluoro­antimonate for the cycloisomerization step. The allylic amide derived 2H-chromenes were converted to the corresponding coumarin analogues by a pyridinium dichromate (PDC)-mediated chemoselective allylic oxidation.