Trifluoromethylation of camphorquinone and its monoimine derivatives

Article abstract of DOI:10.1016/j.tetasy.2008.07.003

Treatment of (1R)-camphorquinone 2 with (trifluoromethyl)trimethylsilane in the presence of catalytic amounts of caesium fluoride in DME at room temperature yields two pairs of exo/endo isomers of trifluoromethylated silylated alcohols 5 and 6. In this case, nucleophilic addition of the CF₃ anion occurs neither regio- nor stereoselectively. On the other hand, the analogous reaction with (1R)-camphorquinone 3-imines 3, followed by hydrolysis with 5 M HCl in ethanol, leads stereoselectively to (1R,2S)-2-hydroxy-2-(trifluoromethyl)bornan-3-one 8. The attempted reductions of the intermediate adducts with NaBH₄ in ethanol gave the corresponding (1R,2S)-3-imino-2-(trifluoromethyl)bornan-2-ols 9 as the sole isomers in high yield. The configuration of C(2), that is, the endo course of the nucleophilic CF₃ addition, was proven by X-ray crystallography. Furthermore, the reduction of the C{double bond, long}N bond in 9 with DIBAL-H leads stereoselectively to the exo amino derivatives 10, which, by treatment with phosgene, smoothly form the fused 1,3-oxazolidin-2-ones 11. In contrast, the reduction of ketone 8 yields a mixture of the exo,exo- and exo,endo-2,3-diols 12.