Synthesis of the bifunctional BINOL ligands and their applications in the asymmetric additions to carbonyl compounds
Efficient one-step syntheses of the bifunctional BINOL and H8BINOL ligands (S)-6 and (S)-8 have been developed from the reaction of BINOL and H8BINOL with morpholinomethanol, respectively. The X-ray analyses of these compounds have revealed their structural similarity and difference. The bifunctional H8BINOL (S)-8 is found to be highly enantioselective for the reaction of diphenylzinc with many aliphatic and aromatic aldehydes and especially is the most enantioselective catalyst for linear aliphatic aldehydes. Unlike other catalysts developed for the diphenylzinc addition which often require the addition of a significant amount of diethylzinc with cooling (or heating) the reaction mixture in order to achieve high enantioselectivity, using (S)-8 needs no additive and gives excellent results at room temperature. (S)-8 in combination with diethylzinc and Ti(OiPr)4 can catalyze the highly enantioselective phenylacetylene addition to aromatic aldehydes. It can also promote the phenylacetylene addition to acetophenone at room temperature though the enantioselectivity is not very high yet. Without using Ti(OiPr)4 and a Lewis base additive, (S)-8 in combination with diethylzinc can catalyze the reaction of methyl propiolate with an aldehyde to form the highly functional γ-hydroxy-α,β-acetylenic esters except that the enantioselectivity is low at this stage. The bifunctional BINOL ligand (S)-6 in combination with Me2AlCl is found to be a highly enantioselective catalyst for the addition of TMSCN to both aromatic and aliphatic aldehydes.
Qin, Ying-Chuan,Liu, Lan,Sabat, Michal,Pu, Lin
p. 9335 - 9348
(2007/10/03)
Asymmetric amino acid synthesis: Mitsunobu reaction on chiral cyanohydrins
BOC(SES)NH was reacted with chiral cyanohydrins using the Mitsunobu reaction to give good yields of protected α-aminonitriles, which were converted to chiral amino and imino acids.
Decicco, Carl P.,Grover, Paul
p. 529 - 530
(2007/10/03)
Ueber die erste rekombinante Hydroxynitril-Lyase und ihre Anwendung in der Synthese von (S)-Cyanhydrinen
Enzymatic Resolution of Optically Active Aliphatic Cyanohydrins
Enantioselective acylation of cyanohydrins 1a-9a by PPL catalysis and deacylation of propionates 1b-9b by CCL catalysis in toluene from good (E 15-20) to excellent (E >30) enantioselectivity.A solvent has a clear effect on enzymatic enantioselectivity.
Kanerva, Liisa T.,Kiljunen, Eero,Huuhtanen, Tuomas T.
p. 2355 - 2362
(2007/10/02)
Enzyme-Catalysed Synthesis of Optically Active Aliphatic Cyanohydrins
The enantioselective preparation of aliphatic (R)-cyanohydrins was studied using powdered almond meal, a rich source of mandelonitrile lyase, as a catalyst in organic solvent.The feasibility of powdered almond meal as a catalyst was compared to that of a purified enzyme preparation.
Huuhtanen, Tuomas T.,Kanerva, Liisa T.
p. 1223 - 1226
(2007/10/02)
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