Oxazaborolidine catalyzed borane reductions of ketones: a significant effect of temperature on selectivity

Reduction of Carbonyl Compounds with Chiral Oxazaborolidine Catalysts: A New Paradigm for Enantioselective Catalysis and a Powerful New Synthetic Method

“…Since the initial use of BH 3´T HF as the stoichiometric reductant in the CBS reduction, a number of other BH 3 complexes have been employedÐincluding BH 3´M e 2 S, [44b] BH 3´1 ,4-thioxane, [45] and BH 3´d iethylaniline [46] Ðall of which lead to comparable enantioselectivity. An advantage of these reagents over BH 3´T HF is lower sensitivity to moisture and oxygen.…”

Multicomponent domino reactions for the synthesis of biologically active natural products and drugs

“…The enantiomeric excess was determined by NMR-experiments using Eu(hfc) 3 as chiral shift reagent. 31 Although slightly elevated temperatures are most often reported to show the best results, 32 we found the highest ee of 87% and the best yields when the reduction was carried out at À15 C. Thus, reaction at 50 C afforded 90 in only 51% yield without a positive effect on the enantioselectivity. In addition, the ee value could not be improved Scheme 25.…”

Synthesis of a new C2‐symmetric chiral catalyst and its application in the catalytic asymmetric borane reduction of prochiral ketones

“…It was found that the enantiomeric purity of the secondary alcohol product was greatly affected by the reaction temperature. [28][29][30] At low temperature (358C) the reaction gave product with poor ee's of 27.3% and 10.0% in THF and toluene, respectively. When the reaction was carried out at refluxing temperature, 70.3% (in THF) and 40.5% (in toluene) ee values were achieved (Table 1, entries 3 and 8).…”