Regioselective Nucleophilic 1,4-Trifluoromethylation of 2-Polyfluoroalkylchromones with (Trifluoromethyl)trimethylsilane. Synthesis of Fluorinated Analogs of Natural 2,2-Dimethylchroman-4-ones and 2,2-Dimethylchromenes

Reactions of 2-polyfluoroalkylchromones with (perfluoroalkyl)trimethylsilanes proceed as a 1,4-nucleophilic perfluoroalkylation to give 2,2-bis(polyfluoroalkyl)chroman-4-ones with high regioselectivity and good yields after acid hydrolysis. Oxidation of 6-methyl-2,2-bis(trifluoromethyl)chroman-4-one with a mixture of K2S2O8 and CuSO4 in aqueous acetonitrile leads to fluorinated analogues of natural lactarochromal and the corresponding acid. Reduction of substituted 2,2-bis(trifluoromethyl)chroman-4-one with sodium borohydride in methanol and subsequent dehydration of chromanols in refluxing xylene in the presence of p-toluene sulfonic acid gives 2,2-bis(trifluoromethyl)chromenes, which are fluorinated analogues of natural precocenes.