Remote Chiral Induction in the Organocatalytic Hydrosilylation of Aromatic Ketones and Ketimines

Abstract

Lewis basic, metal‐free pyridyloxazolines catalyze the reduction of prochiral aromatic ketones and ketimines with Cl3SiH in good enantioselectivity (up to 94 % ee). Arene–arene interactions between the substrate and the catalyst are likely to play a role in the enantiodifferentiation process.

l-Valine derived chiral N-sulfinamides as effective organocatalysts for the asymmetric hydrosilylation of N-alkyl and N-aryl protected ketimines

“…The reaction mixture was stirred at room temperature for 12 h, and then concentrated under vacuum. The residue was diluted with EtOAc (200 mL), washed with 1 N aqueous HCl, saturated aqueous NaHCO 3 (15 mL) and brine, and then dried over anhydrous MgSO 4 . Solvents were evaporated under vacuum.…”

Synthesis of (R)- and (S)-2-N-methylamino-2,3-dimethylbutanamides and (R)- and (S)-(5-isopropyl-1,5-dimethyl-4,5-dihydro-1H-imidazol-4-on-2-yl)pyridines

“…5 In order to verify this possibility in the case of our ligands, the aim of the this work was to prepare enantiomerically pure (5-isopropyl-1,5-dimethyl-4,5-dihydro-1H-imidazol-4-on-2-yl)pyridine ligands 7. These ligands differ from our earlier derivatives in having their stereogenic centre at the 5-position of the 4,5-dihydro-1H-imidazole cycle, that is, at a position more remote from the chelate-forming centre than that present in our earlier ligands.…”

Chiral N-formyl amino alcohol as Lewis basic organocatalyst for enantioselective hydrosilylation of ketimines

“…Thus, we prepared a series of N-formamides (8−14, Figure 2) on the basis of the three stereoisomers of 2-amino-1,2-diphenylethanol and tested their catalytic efficacies in the hydrosilylation of ketimine 18a. Compounds 15−17 were also synthesized and tested for comparison.Under an argon atmosphere, trichlorosilane (0.4 mmol) was added dropwise to a stirred solution of imine 18 [5][6][7][8][9][10][11][12][13] (0.20 mmol) and catalyst [16] (0.02 mmol) in anhydrous CH 2 Cl 2 at 0°C. The mixture was stirred at the same temperature for 16 h. The reaction was quenched with a saturated aqueous solution of NaHCO 3 (5 mL) and was extracted with EtOAc.…”

“…So far a number of highly effective Lewis base organocatalysts have been developed for the enantioselective hydrosilylation of imines, including 1 [5] and 2 [6] developed by Malkov, Kocovsky and co-workers and 3 [7,8], 4 [9,10], 5 [11], 6 [12], 7 [13] by us ( Figure 1). Although excellent results have been obtained with these catalysts, there are still some limitations regarding the catalytic efficiency and the substrate spectrum.…”

“…Recently, we have demonstrated the usefulness of this compound in the design and implementation of the N-formamide Lewis basic catalyst 3 [6,7]. Although this compound only played a supporting role in the case of 3, we speculated that such chiral amino alcohol itself, upon N-formylation and modification if necessary, could behave as effective Lewis basic catalysts for the asymmetric hydrosilylation of imines [15].…”