Effect of BF3 on the enantioselective reduction of trifluoromethyl ketones using a chiral lactam alcohol with borane

Practical Enantioselective Reduction of Ketones Using Oxazaborolidine Catalysts Generated In Situ from Chiral Lactam Alcohols

“…Therefore, we conducted 11 B NMR analysis of the in situ generated oxazaborolidine catalyst as shown in Figure 2 . The 11 B NMR (CDCl 3 ) spectrum indicated the presence of the oxazaborolidine complex with borane (+17.7 ppm and −13.2 ppm) and free oxazaborolidine (+27.2 ppm) [ 14 ]. These chemical shifts were mostly consistent with those of the oxazaborolidine 1a generated in situ from ( S )-diphenylpyrrolidinemethanol and borane [ 10 ] under the same conditions.…”

“…On the other hand, other methods using the catalyst prepared from ( S )-diphenylpyrrolidinemethanol with 9-borabicyclo[3.3.1]nonane (9-BBN) 7 [ 33 ], spiroborate ester 8 [ 34 ], and electronically tuned-CBS catalyst 1f with high Lewis acidity [ 35 ] have been reported with good to high enantioselectivities and, interestingly, stereochemistry opposite to that of 1c ( Scheme 10 ). Therefore, we set out to investigate the catalytic asymmetric reduction of trifluoromethyl ketones using the simple oxazaborolidine 1a generated in situ from the chiral lactam alcohol 2 and borane [ 14 , 36 ] to clarify its scope and enantioselection.…”

Palladium‐Catalyzed Direct Approach to α‐Trifluoromethyl Alcohols by Selective Hydroxylfluorination of gem‐Difluoroalkenes

“…Furthermore, CF 3 COOH, as an additive, involves ligand exchange and affords the C–O bond formation. As far as we know, α‐trifluoromethyl alcohols can only be prepared from trifluoromethylation of aldehyde and carbonyl compounds or reduction of trifluoromethyl ketones , . Compared with existing methods, this new strategy has some significant advantages: (i) easily available fluorine source comes from NFSI, which serves as a good reagent; (ii) only catalytic Pd is needed and no other metal is participated in hydroxylfluorination of gem ‐difluoroalkenes; (iii) based on the investigation of the reaction mechanism, this strategy offers more possibilities for the constructing of other bonds, such as C–C, C–N and C–S.…”

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

“…[1][2][3][4][5][6][7] The ever-increasing demand of enantiomerically enriched trifluoromethylated compounds has dramatically promoted the development of their asymmetric syntheses. 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.…”