Catalytic Asymmetric Synthesis of O‐Acetylcyanohydrins from Potassium Cyanide,Acetic Anhydride,and Aldehydes,Promoted by Chiral Salen Complexes of Titanium(IV) and Vanadium(V) |
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Authors: | YuriN Belokon Paola Carta AndreyV Gutnov Viktor Maleev MargaritaA Moskalenko LidiaV Yashkina NicolaiS Ikonnikov NikolaiV Voskoboev ViktorN Khrustalev Michael North |
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Abstract: | The utility of the chiral Ti(μ‐O)(salen)]2 complexes (R)‐ and (S)‐ 1 (H2salen was prepared from (R,R)‐ or (S,S)‐cyclohexane‐1,2‐diamine and 3,5‐di(tert‐butyl)‐2‐hydroxybenzaldehyde) as catalysts for the asymmetric addition of KCN and Ac2O to aldehydes to produce O‐acetylcyanohydrins was investigated. It was shown that the complexes were active at a substrate/catalyst ratio of 100 : 1 and produced the O‐protected cyanohydrins with ee in the range of 60–92% at ?40°. Other complexes, Ti2(AcO)2(μ‐O)(salen)2] ((R)‐ 4 ) and Ti(CF3COO)2(salen)] ((R)‐ 5 ), were prepared from (R)‐ 1 by treatment with different amounts of Ac2O and (CF3CO)2O, and their catalytic activities were tested under the same conditions. The efficiency of (R)‐ 4 was found to be even greater than that of (R)‐ 1 , whereas (R)‐ 5 was inactive. The synthesis of the corresponding salen complexes of VIV and VV, V(O)(salen)] ((R)‐ 2 ) and V(O)(salen)(H2O)] S(O)3OEt] ((R)‐ 3 ), was elaborated, and their X‐ray crystal structures were determined. The efficiency of (R)‐ 3 was sufficient to produce O‐acetyl derivatives of aromatic cyanohydrins with ee in the range of 80–91% at ?40°. |
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