Asymmetric synthesis. Part 5. Asymmetric reduction of phenyl trifluoromethyl ketone with chiral alkoxy-aluminium and -magnesium halides

Two Classes of Enzymes of Opposite Stereochemistry in an Organism: One for Fluorinated and Another for Nonfluorinated Substrates

“…The inversion in stereochemistry is also observed for the reduction of 1Ha and 1Fa by (−)-DIP-chloride and CBS/catecholborane but not by ( R) -BINAL-H, LAH-sulfamide, NB-enantride and K-glucoride. The mechanism of the inversion for the biocatalytic reactions has not been thoroughly investigated, whereas that for the organometallic reaction has been explained by structural and mechanistic analyses. 5a-f…”

Synthesis of Axially Dissymmetric Ligands with Two Chiral Centers of Perfluoroalkyl Carbinol Moiety, and Their Application to Asymmetric Syntheses

“…First, we used lithium menthoxide for the attempted chiral reduction of 2,2,2-trifluoroacetophenone (7), since Nasipuri and his co-worker had reported that dichloroaluminum menthoxide showed the moderate asymmetric induction on the reduction of 7 while the yield was low [14]. However, lithium menthoxide gave a very low yield of the reduction product at room temperature.…”

“…The nitro alcohol (16) from 15 was hydrogenated in the presence of Pd-C to the ortho amino compound (17), which was converted to a diazonium salt. The diazonium salt was heated with HBr−CuBr to give 3c or heated with H 3 PO 2 to yield the unsubstituted phenyl derivative (14). So we could determine the absolute configurations of 14, 3c, and 16 to be (R), as shown in Scheme 5.…”

Catalytic asymmetric β-hydrogen transfer reduction of α-trifluoromethyl aromatic ketones with diethylzinc

“…3,[8][9][10][11][12][13] Among the developed methodologies, the enantioselective reduction of trifluoromethyl ketones is of great value and many types of approaches have been reported, such as asymmetric transition metal-catalyzed hydrogenations, [14][15][16][17][18][19] biocatalyzed reductions, 20-24 chiral organometallic reagents reductions, 25-28 asymmetric borane reductions, [29][30][31][32][33] and asymmetric b-hydrogen transfer reductions. [34][35][36] Compared with other asymmetric reduction transformations, asymmetric b-hydrogen transfer reduction of trifluoromethyl ketones is underdeveloped with few examples. [34][35][36] In 2002, Yong and Chong introduced a chiral organomagnesium amide as a hydrogen source in the asymmetric b-hydrogen transfer reduction of a-trifluoromethyl ketones, affording the corresponding a-trifluoromethyl secondary alcohol products with up to 96% ee and up to 95% yield.…”

“…[34][35][36] Compared with other asymmetric reduction transformations, asymmetric b-hydrogen transfer reduction of trifluoromethyl ketones is underdeveloped with few examples. [34][35][36] In 2002, Yong and Chong introduced a chiral organomagnesium amide as a hydrogen source in the asymmetric b-hydrogen transfer reduction of a-trifluoromethyl ketones, affording the corresponding a-trifluoromethyl secondary alcohol products with up to 96% ee and up to 95% yield. 36 However, due to the high reactivity of the diorganomagnesium reagent, a stoichiometric amount of chiral amide ligand and a low temperature (À78°C) were required to achieve high enantioselectivity.…”