Facile and Efficient Enantioselective Strecker Reaction of Ketimines by Chiral Sodium Phosphate

Abstract

A facile and efficient enantioselective Strecker reaction of ketimines catalyzed by a chiral alkali-metal salt has been developed. When 10 mol % BNPNa (BNP = 1,1'-binaphthyl-2,2'-diylphosphate) prepared in situ and 10 mol % para-tert-butyl-ortho-adamantylphenol (PBAP) were introduced into the reaction, up to 96% yield and up to 95% ee (ee = enantiomeric excess) were obtained. Both aliphatic and aromatic ketimines, especially sterically bulky cyclic ketimines derived from beta-acetonaphthone, alpha-indanone, and alpha-tetralone were found suitable for this reaction. On the basis of the experimental results and previous reports, trimethylsilyl cyanide (TMSCN) was indicated to be the real reactive nucleophile despite the existence of PBAP, and a possible working model was proposed to explain the origin of the asymmetric induction. The facile availability of 1,1'-binaphthyl-2,2'-diylphosphoric acid (BNPH) and the simplicity of the procedure are beneficial for practical applications.

Highly Enantioselective Catalytic Benzoyloxylation of 3‐Aryloxindoles Using Chiral VAPOL Calcium Phosphate

“…Interestingly, H[ P6 ] washed with 6N HCl exhibited poor catalytic efficiency and enantioselectivity under the same conditions (Table 1, entry 12). Correlation of this result to that of a recent report by Ishihara and co-workers, [10a] showing a high abundance of chiral phosphate salts in the absence of a final HCl wash of the chiral phosphoric acid/salt mixture obtained by silica gel purification, directed us to propose the active catalytic species to be that of a chiral phosphate salt. [15] To identify the metal counterion, several variants of P6 were prepared and evaluated.…”

“…[9] Moreover, the alkali or alkaline earth derived salts of chiral phosphoric acids have proven to be highly effective catalysts in several recent reports. [10] …”

A Protecting‐Group‐Free Route to Chiral BINOL–Phosphoric Acids

“…[9] More recently, asymmetric counteranion-directed catalysis (ACDC) has used chiral BNP in reactions mediated by gold, silver, and manganese complexes to effect enantioselectivity. [10] While the reactions employing BNPH and BNP derivatives have seen an exponential growth, the strategies for their synthesis have remained consistent throughout the years.…”

Eco-friendly synthesis of α-aminonitriles from ketones in PEG-400 medium using potassium Hexacyanoferrate(II) as cyanide source

“…In general, a-aminonitriles are synthesized by the reactions of aldehydes/ketones with amines in the presence of a cyanide source such as HCN [10,11], KCN [12], TMSCN [13,14], (EtO) 2 P(O)CN [15], Et 2 AlCN [16], Bu 3 SnCN [17,18], MeCOCN [19], acetone cyanohydrin [20,21] and ethyl cyanoformate [22,23]. However, these cyanide sources are often hazardous and toxic, and involve harsh reaction conditions.…”