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Enantioselective reduction of aryl trifluoromethyl ketones ..
G K Surya Prakash, et al. Facile synthesis of TMS-protected trifluoromethylated alcohols using trifluoromethyltrimethylsilane (TMSCF3) and various nucleophilic catalysts in DMF.J Org Chem.2006,71(18), 6806-6813.
The scope of the tandem reaction was examined with various amines and trifluoromethyl ketones outlined in . Several secondary alkylamines, cyclic or linear, were found to be viable amine reagents, providing dienamide products with moderate to good isolated yields (, entries 1–5). More sterically demanding dibutylamine still delivered target, albeit with a diminished yield. -Methyl or Ts aniline, with less nucleophilicity in comparison to aliphatic counterpart, was ineffective under the typical reaction conditions (some intractable polar compounds were observed). In addition, using morpholine or diethylamine, a range of different aryl substituted ketones competently engaged in the one-pot tandem reaction (, entries 6–14). The presence of electron-donating or -withdrawing substituents at different position of phenyl ring in CF3 ketones seemingly had a negligible influence on the chemical yield, and a range of densely functionalized dienamides were obtained in modest yields generally.
A Facile Synthesis of Trifluoromethyl- and 3,3,3 ..
Alternatively, rapid and efficient trifluoromethylation of carbonyl compounds can be carried out at room temperature in DMSO, in the presence of molecular sieves, without fluoride or other basic catayst: Synlett, 112 (2006). The use of as a catalyst has also been advocated: Synlett, 267 (2006). In the presence of CsF and TMS-imidazole, aldimines are converted to ɑ-trifluoromethyl amines: Tetrahedron Lett., 40, 5475 (1999). With a catalytic amount of TBAF, excellent yields of trifluoromethyl ketones can be obtained from methyl esters: Angew. Chem. Int. Ed., 37, 820 (1998). Similarly, alkyl or aryl thiocyanates are converted to the corresponding trifluoromethyl sulfides in generally good yields: Tetrahedron Lett., 38, 65 (1997). Selenocyanates behave similarly. Trifluoromethylation of aromatics bearing electron-withdrawing groups can be effected in the presence of KF, by displacement of nitro-, cyano- or chloro-substituents: J. Chem. Soc., Perkin 1, 3081 (1998). For reviews of this and similar reagents, see: Chem. Rev., 97, 757 (1997); J. Fluorine Chem., 112, 123 (2001).
The reduction of aryl trifluoromethyl ketones by sodium ..
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