- Catalytic asymmetric synthesis of O-acetyl cyanohydrins from KCN, Ac2O and aldehydes
-
A (salen)titanium catalyst has been found to induce the asymmetric addition of potassium cyanide and acetic anhydride to aldehydes, giving enantiomerically enriched cyanohydrin esters with up to 92% enantiomeric excess using just 1 mol% of the catalyst. T
- Belokon, Yuri N.,Gutnov, Andrey V.,Moskalenko, Margarita A.,Yashkina, Lidia V.,Lesovoy, Denis E.,Ikonnikov, Nicolai S.,Larichev, Vladimir S.,Michael North
-
-
Read Online
- Asymmetric addition of KCN and Ac2O to aldehydes catalyzed by recyclable polymeric salen-Ti(IV) complexes
-
Polymeric salen-Ti(IV) complexes were employed in the enantioselective O-acetyl cyanation of aldehydes with KCN and Ac2O. The polymeric catalysts with appropriate crosslinking degree exhibited good activities and enantioselectivities, up to 94%
- Huang, Wei,Song, Yuming,Bai, Changmin,Cao, Guoying,Zheng, Zhuo
-
-
Read Online
- Fast microwave-assisted resolution of (±)-cyanohydrins promoted by lipase from Candida antarctica
-
Enzymatic kinetic resolution (EKR) of (±)-cyanohydrins was performed by using immobilized lipase from Candida antarctica (CALB) under conventional ordinary conditions (orbital shaking) and under microwave radiation (MW). The use of microwave radiation contributed very expressively on the reduction of the reaction time from 24 to 2 h. Most importantly, high selectivity (up to 92percent eep) as well as conversion was achieved under MW radiation (50-56percent).
- Ribeiro, Sandra S.,Ferreira, Irlon M.,Lima, Jo?o P. F.,De Sousa, Bruno A.,Carmona, Rafaela C.,Santos, Alcindo A. Dos,Porto, André L. M.
-
p. 1344 - 1350
(2015/07/15)
-
- Lewis acid-lewis base-catalysed enantioselective addition of α-ketonitriles to aldehydes
-
Additions of structurally diverse α-ketonitriles to aromatic and aliphatic prochiral aldehydes yielding highly enantioenriched acylated cyanohydrins were achieved using a combination of a titanium salen dimer and an achiral or chiral Lewis base. In most cases high yields and high enantioselectivities were observed. The ee was moderate in the initial part of the reaction but increased over time. This could be avoided, and higher ees obtained, by keeping the titanium complex, in the presence or absence of aldehyde and ketonitrile, at -40°C prior to the addition of the Lewis base. A mechanism initiated by nucleophilic attack of the tertiary amine at the carbonyl carbon atom of the ketonitile is supported by 13C labelling experiments.
- Lundgren, Stina,Wingstrand, Erica,Moberg, Christina
-
p. 364 - 372
(2008/02/07)
-
- Asymmetric cyanosilylation of aldehydes catalyzed by novel organocatalysts
-
A novel proline-based N,N′-dioxide, which is easily prepared from inexpensive chemicals, serves as an effective catalyst for enantioselective cyanosilylation of aldehydes in up to 73% ee. Georg Thieme Verlag Stuttgart.
- Wen, Yuehong,Huang, Xiao,Huang, Jinglun,Xiong, Yan,Qin, Bo,Feng, Xiaoming
-
p. 2445 - 2448
(2007/10/03)
-
- Development of β-hydroxyamide/titanium complexes for catalytic enantioselective silylcyanation of aldehydes
-
A highly enantioselective addition of trimethylsilylcyanide to aldehydes catalyzed by chiral titanium complexes is described. The chiral titanium complexes were prepared in situ from Ti(OiPr)4 and β-hydroxyamide ligands, that could easily be synthesized from ketopinic acid and C2 symmetrical chiral diamines in a small number of steps. Graphical Abstract.
- Uang, Biing-Jiun,Fu, I-Pin,Hwang, Chyuan-Der,Chang, Chun-Wei,Yang, Chun-Tzu,Hwang, Der-Ren
-
p. 10479 - 10486
(2007/10/03)
-
- Polymeric salen-Ti(IV) or V(V) complex catalyzed asymmetric synthesis of O-acetylcyanohydrins from KCN, Ac2O and aldehydes
-
Polymeric salen-Ti(IV) and V(V) complexes were employed in the enantioselective O-acetyl cyanation of aldehydes with potassium cyanide and acetic anhydride. The crosslinked polymeric salen-Ti(IV) catalyst exhibited good activities and enantioselectivities, up to 91% ee with 99% conversion was obtained at -20°C with 1 mol% of catalyst (based on bimetallic catalytic unit). Moreover, six consecutive recyclings with the easily recovered crosslinked polymeric catalyst showed no obvious decrease in either activity or enantioselectivity. Linear polymeric salen-V(V) catalyst showed good catalytic efficiency too, up to 94% ee with 99% conversion was obtained at -42°C with 5 mol% of catalyst. Graphical Abstract.
- Huang, Wei,Song, Yuming,Wang, Jing,Cao, Guoying,Zheng, Zhuo
-
p. 10469 - 10477
(2007/10/03)
-
- Process for the cyanation of aldehydes
-
A process for cyanating an aldehyde is provided. The process comprises reacting the aldehyde with: i) a cyanide source which does not comprise a Si—CN bond or a C—(C=O)—CN moiety; and ii) a substrate susceptible to nucleophilic attack not comprising a hal
- -
-
Page/Page column 8
(2008/06/13)
-
- 1,2-Diphenylethylenediamine linked chiral Ti(IV) complex - A new entry to the highly enantioselective silylcyanation of aliphatic and aromatic aldehydes
-
Highly enantioselective silylcyanation of aliphatic and aromatic aldehydes was achieved by using a 1,2-diphenylethylenediamine linked chiral Ti(IV) complex as the catalyst.
- Chang, Chun-Wei,Yang, Chun-Tzu,Hwang, Chyuan-Der,Uang, Biing-Jiun
-
-
- Enantioselective synthesis of protected cyanohydrins
-
A straightforward process for the preparation of optically active protected cyanohydrins, important building blocks for the synthesis of drugs and agrochemicals, has been established. Lipase B from Candida Antarctica (CAL-B) catalysed the kinetic resoluti
- Veum, Lars,Kuster, Marina,Telalovic, Selvedin,Hanefeld, Ulf,Maschmeyer, Thomas
-
p. 1516 - 1522
(2007/10/03)
-
- Catalytic asymmetric synthesis of O-acetylcyanohydrins from potassium cyanide, acetic anhydride, and aldehydes, promoted by chiral salen complexes of titanium(IV) and vanadium(V)
-
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°.
- Belokon, Yuri N.,Carta, Paola,Gutnov, Andrey V.,Maleev, Viktor,Moskalenko, Margarita A.,Yashkina, Lidia V.,Ikonnikov, Nicolai S.,Voskoboev, Nikolai V.,Khrustalev, Viktor N.,North, Michael
-
p. 3301 - 3312
(2007/10/03)
-
- Preparation of optically active cyanohydrins using the (S)-hydroxynitrile lyase from Hevea brasiliensis
-
Several aliphatic, aromatic and heteroaromatic aldehydes have been converted into the chiral cyanohydrins using the (S) hydroxynitrile lyase from Hevea brasiliensis. The corresponding cyanohydrins were obtained in moderate to good yield and high enantiomeric excess with the exeption of phenyloxyacetaldehyde, benzyloxyacetaldehyde and the pyrrole-, pyridine- and indolealdehydes investigated. In contrast to previously reported results, cinnamaldehyde could be converted into (S)-(-)-2-hydroxy-4-phenyl-(E)-but-3- enenitrile with good selectivity by means of optimized reaction conditions.
- Schmidt, Michael,Herve, Stephanie,Klempier, Norbert,Griengl, Herfried
-
p. 7833 - 7840
(2007/10/03)
-
- Attempted Enantioselective Synthesis of Terbutaline. Unexpected Partial Racemization During Lithium Aluminium Hydride Reduction of a Secondary Amide
-
Syntheses leading to compounds related to the brobchodilator (-)-terbutaline via optically active cyanohydrins suffered unexpected partial racemization during lithium aluminium hydride reduction of key amide intermediates.
- Donohue, Andrew C.,Jackson, W. Roy
-
p. 1741 - 1746
(2007/10/03)
-
- One-Pot Synthesis of Optically Active Cyanohydrin Acetates from Aldehydes via Lipase-Catalyzed Kinetic Resolution Coupled with in Situ Formation and Racemization of Cyanohydrins
-
A novel one-pot synthesis of optically active cyanohydrin acetates from aldehydes has been accomplished by lipase-catalyzed kinetic resolution coupled with in situ formation and racemization of cyanohydrins in an organic solvent.Racemic cyanohydrins 2, generated from aldehydes 1 and acetone cyanohydrin in diisopropyl ether under the catalysis of basic anion-exchange resin (OH- form), were acetylated stereoselectively by a lipase from Pseudomonas cepacia (Amano) with isopropenyl acetate as an acylating reagent.The (S)-isomer of 2 was preferentially acetylated by the lipase, while the unreacted (R)-isomer was continuously racemized through reversible transhydrocyanation catalyzed by the resin.These processes thus enabled one stage conversion of various aldehydes 1a-n into the corresponding (S)-cyanohydrin acetates 3a-n with up to 94 percent ee in 63-100 percent conversion yields.The racemization of the optically active cyanohydrin 2e by Amberlite IRA-904 (OH- form) was found to be much faster then the enzymatic acetylation, confirming the effective second-order asymmetric transformation.Enzymatic deacetylation of (S)-cyanohydrin acetates in an organic solvent and the synthesis of optically active pyrethroids are also described.
- Inagaki, Minoru,Hiratake, Jun,Nishioka, Takaaki,Oda, Jun'ichi
-
p. 5643 - 5649
(2007/10/02)
-
- One-Pot Synthesis of Optically Active Cyanohydrin Acetates from Aldehydes via Quinidine-Catalyzed Transhydrocyanation Coupled with Lipase-Catalyzed Kinetic Resolution in Organic Solvent
-
A novel one-pot synthetic method was developed for the preparation of optically active cyanohydrin acetates.Racemic cyanohydrins were generated from aldehydes and acetone cyanohydrin by quinidine-catalyzed transhydrocyanation, and the resulting cyanohydrins 2a-j were then acetylated by lipase in a stereoselective manner using isopropenyl acetate as an acylating reagent.A variety of aldehydes 1a-j were successfully transformed into the corresponding cyanohydrin acetates 3a-j having 47-95percent e.e. without isolating the unstable cyanohydrins 2.Moreover, the reversible nature of base-catalyzed transhydrocyanation allows for in situ racemization of the unreacted cyanohydrins and concurrent kinetic resolution by lipase enabled the preparation of (S)-3b-d with 40-82percent e.e. in more than 50percent yield.Polymer-supported cinchona alkaloid was also used as a catalyst for this one-pot reaction and showed the comparable chemical and optical yield to that for the soluble monomeric alkaloid.The insoluble polymer and lipase were recovered by filtration and found to have almost the same catalytic activity even after four times of reuse.
- Inagaki, Minoru,Hatanaka, Akihiko,Mimura, Mitsuo,Hiratake, Jun,Nishioka, Takaaki,Oda, Jun'ichi
-
p. 111 - 120
(2007/10/02)
-
- LIPASE-CATALYZED IRREVERSIBLE TRANSESTERIFICATION USING ENOL ESTERS: XAD-8 IMMOBILIZED LIPOPROTEIN LIPASE-CATALYZED RESOLUTION OF SECONDARY ALCOHOLS
-
Procedures for preparation of XAD-8 immobilized lipoprotein lipase and the resolution of secondary alcohols of synthetic value in organic solvents using this immobilized enzyme have been developed.
- Hsu, Shu-Hui,Wu, Shihn-Sheng,Wang, Yi-Fong,Wong, Chi-Huey
-
p. 6403 - 6406
(2007/10/02)
-