Difluorinated Danishefsky's diene:: A versatile C4 building block for the fluorinated six-membered rings

[GRAPHICS] A Mg(0)/Me3SiCl system was found to be effective for the preparation of difluoro Danishefsky's dienes 2, which involves selective C-F bond cleavage of trifluoromethyl ketones 3. Subsequent hetero Diels-Alder reactions of 2 with aldehydes and imines gave a variety of fluorinated six-membered heterocycles.