Two‐in‐one: The integration of two salen/TiO units into one molecule allows the enantioselectivecyanation of aldehydes to afford the enantioenriched natural or nonnatural cyanohydrin derivatives with turnover numbers of 1960–172 000 and ee values up to 97 % (see scheme). Some of the cyanohydrin derivatives are key intermediates for the synthesis of chiral pharmaceuticals or agrochemicals.
Enantioselective cyanosilylation of aldehydes catalyzed by novel camphor derived Schiff bases-titanium(IV) complexes
作者:Ewelina Błocka、Mariusz J. Bosiak、Mirosław Wełniak、Agnieszka Ludwiczak、Andrzej Wojtczak
DOI:10.1016/j.tetasy.2014.03.001
日期:2014.4
Five tridentate Schiff bases have been prepared from (1R,2S,3R,4S)-3-amino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol and salicylaldehydes. X-ray structure investigation revealed differences in their molecular conformation, and their titanium(IV) complexes have been studied with NMR techniques. Among them the complex with the Schiffbase obtained from 2-hydroxy-3-isopropylbenzaldehyde, is the most selective
The enantioselective addition of trimethylsilyl cyanide to a variety of aldehydes proceeded by the aid of a catalyst prepared in situ from titanium tetraisopropoxide [Ti(O-i-Pr)4] and chiral Schiff bases and gave the corresponding cyanohydrins in high optical yield (up to 96% e.e.). A remarkable rate enhancement was brought about by the addition of the Schiffbase to the titanium alkoxide mediated
The β-amino alcohol 1b−Ti(Oi-Pr)4 complex has been shown to catalyze the enantioselective cyanosilylation of aldehydes efficiently. In the presence of 5 mol % of 1b−Ti(Oi-Pr)4 complex catalyst, the aromatic, conjugated, heteroaromatic, and aliphatic aldehydes were converted to their corresponding trimethylsilyl ethers of cyanohydrins in 90−99% yields with up to 94% ee under mild conditions.
β-氨基醇1b -Ti(O i -Pr)4配合物已显示出可有效催化醛的对映选择性氰基硅烷化反应。在5摩尔%的1b -Ti(O i -Pr)4络合催化剂存在下,芳族,共轭,杂芳族和脂族醛以90-99%的产率转化为相应的氰醇三甲基甲硅烷基醚,产率最高为94 %ee在温和条件下。
Asymmetric Cyanohydrin Synthesis Catalyzed by Al(salen)/Triphenylphosphane Oxide
作者:Sung Soo Kim、Dae Ho Song
DOI:10.1002/ejoc.200400721
日期:2005.5
Various aldehydes undergo asymmetric trimethylsilylcyanation with (CH3)3SiCN (TMSCN) in the presence of a chiral Al(salen) complex and Ph3PO as the catalyst. This is a double activation where Al(salen) plays the role of Lewis acd and POPh3 acts as a Lewis base. Various kind of aldehydes were subjected to the enantioselective addition of (CH3)3SiCN at temperatures between –40 °C and –50 °C. Hydrolysis