Carbon–carbon bond formation using hypervalent iodine under Lewis acid conditions: scope of the method for the synthesis of butane-1,4-diones

Abstract

Hypervalent iodine oxidation of the silyl enol ethers of various acetophenones (2a–g), 2-acetylthiophenes (2i–k), 2-acetylfuran (2l) and 2-acetylbenzofuran (2m) with iodosobenzene–boron trifluoride–diethyl ether results in carbon–carbon coupling to yield the corresponding 1,4-disubstituted butane-1,4-dione (3a–m). Cross coupling (dissimilar coupling) between 4-methoxyacetophenone silyl enol ether (2c) and 4-nitroacetophenone silyl enol ether (2e) affords 1-(4-methoxyphenyl)-4-(4-nitrophenyl)butane-1,4-dione (27%); the other minor products (3c)(18%) and (3e)(15%) resulting from similar coupling in this reaction. The sterically hindered aliphatic silyl enol ether (2h) obtained from pinacolone also undergoes smooth coupling whereas other aliphatic ketones do not. This method is likewise unsuccessful in case of nitrogen-containing heterocycles, viz. 2-, 3-, 4-acetylpyridine silyl enol ethers and tropinone silyl enol ether.