805230-21-1Relevant articles and documents
Application of the lewis acid-lewis base bifunctional asymmetric catalysts to pharmaceutical syntheses: Stereoselective chiral building block syntheses of human immunodeficiency virus (HIV) protease inhibitor and β3- adenergic receptor agonist
Nogami, Hiroyuki,Kanai, Motomu,Shibasaki, Masakatsu
, p. 702 - 709 (2003)
Chiral building block syntheses of promising drugs were achieved using two types of catalytic stereoselective cyanosilylations of aldehydes promoted by Lewis acid-Lewis base bifunctional catalysts 1 and 2 as the key steps (diastereoselective cyanosilylation of amino aldehyde and enantioselective cyanosilylation). In the first part of this article, syntheses of chiral building blocks (6) of Atazanavir (3: human immunodeficiency virus (HIV) protease inhibitor) using the bifunctional catalyst 2 are discussed. The reaction of Boc-protected phenylalaninal 21 in the presence of 1 mol% catalyst 2 selectively afforded the anti isomer 22 as the major product (diastereomeric ratio=97:3), which was successively converted to the corresponding epoxide 6 in six steps. In the second part, we describe a chiral building block synthesis of β3-adrenergic receptor agonists. The enantioselective cyanosilylation of 3-chlorobenzaldehyde (38) with 9 mol% catalyst 1 gave the chiral cyanohydrin 39, which was converted to β-hydroxyethylamine 40 by reduction. Moreover, the chiral ligand of catalyst 1 could be recovered without column chromatography and reused without decreasing its activity.
Enantioselective cyanosilylation of aldehydes catalyzed by novel camphor derived Schiff bases-titanium(IV) complexes
B?ocka, Ewelina,Bosiak, Mariusz J.,We?niak, Miros?aw,Ludwiczak, Agnieszka,Wojtczak, Andrzej
, p. 554 - 562 (2014/05/06)
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
Investigation of lewis acid versus lewis base catalysis in asymmetric cyanohydrin synthesis
North, Michael,Omedes-Pujol, Marta,Williamson, Courtney
experimental part, p. 11367 - 11375 (2010/11/17)
The asymmetric addition of trimethylsilyl cyanide to aldehydes can be catalysed by Lewis acids and/or Lewis bases, which activate the aldehyde and trimethylsilyl cyanide, respectively. It is not always apparent from the structure of the catalyst whether Lewis acid or Lewis base catalysis predominates. To investigate this in the context of using salen complexes of titanium, vanadium and aluminium as catalysts, a Hammett analysis of asymmetric cyanohydrin synthesis was undertaken. When Lewis acid catalysis is dominant, a significantly positive reaction constant is observed, whereas reactions dominated by Lewis base catalysis give much smaller reaction constants. [{Ti(salen)O}2] was found to show the highest degree of Lewis acid catalysis, whereas two [VO(salen)X] (X = EtOSO3 or NCS) complexes both displayed lower degrees of Lewis acid catalysis. In the case of reactions catalysed by [{Al(salen)}2O] and triphenyl- phosphine oxide, a non-linear Ham- mett plot was observed, which is indicative of a change in mechanism with increasing Lewis base catalysis as the carbonyl compound becomes more electron-deficient. These results suggested that the aluminium complex/tri- phenylphosphine oxide catalyst system should also catalyse the asymmetric addition of trimethylsilyl cyanide to ke- tones and this was found to be the case.
Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate
North, Michael,Omedes-Pujol, Marta
experimental part, p. 1043 - 1055 (2011/03/22)
Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding re
An efficient titanium catalyst for enantioselective cyanation of aldehydes: Cooperative catalysis
Zhang, Zhipeng,Wang, Zheng,Zhang, Ruzhou,Ding, Kuiling
supporting information; experimental part, p. 6746 - 6750 (2010/12/24)
(Figure Presented) Two-in-one: The integration of two salen/ Ti=O units into one molecule allows the enantioselective cyanation of aldehydes to afford the enantioenriched natural or nonnatural cyanohydrin derivatives with turnover numbers of 1960-172000 a
A bimetallic aluminium(salen) complex for asymmetric cyanohydrin synthesis
North, Michael,Williamson, Courtney
experimental part, p. 3249 - 3252 (2009/08/17)
In the presence of a phosphine oxide cocatalyst, a bimetallic aluminium(salen) complex was found to catalyse the asymmetric addition of trimethylsilyl cyanide to aldehydes. Under optimised conditions, enantioselectivities of 53-96% were obtained using 2 m
Catalytic, asymmetric cyanohydrin synthesis in propylene carbonate
North, Michael,Omedes-Pujol, Marta
experimental part, p. 4452 - 4454 (2009/12/01)
Propylene carbonate can be used as a green solvent for asymmetric cyanohydrin synthesis catalyzed by VO(salen)NCS. A range of 10 aromatic and aliphatic aldehydes gave high enantioselectivities (up to 93%) and conversions (up to 100%) in reactions carried
Synthesis of the bifunctional BINOL ligands and their applications in the asymmetric additions to carbonyl compounds
Qin, Ying-Chuan,Liu, Lan,Sabat, Michal,Pu, Lin
, p. 9335 - 9348 (2007/10/03)
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.
Asymmetric cyanosilylation of aldehydes catalyzed by novel chiral tetraaza-titanium complexes
Liu, Yanling,Liu, Xiaohua,Xin, Junguo,Feng, Xiaoming
, p. 1085 - 1089 (2007/10/03)
The asymmetric addition of trimethylsilyl cyanide (TMSCN) to a range of aldehydes was efficiently catalyzed by a novel, easily prepared C 2-symmetric chiral tetraaza-Ti(IV) complex in high yields with up to 92% ee under mild conditions. A negative nonlinear effect between the ee of the ligand and the ee of the product was observed. Georg Thieme Verlag Stuttgart.
Enantioselective homoallyl-cyclopropanation of dibenzylideneacetone by modified allylindium halide reagents-rapid access to enantioenriched 1-styryl-norcarene
Lloyd-Jones, Guy C.,Wall, Philip D.,Slaughter, Jennifer L.,Parker, Alexandra J.,Laffan, David P.
, p. 11402 - 11412 (2007/10/03)
Dibenzylideneacetone (8) reacts with in situ-generated allylindium halide reagents to yield the product of a homoallyl-cyclopropanation reaction: 2-(3″-butenyl)-1,1-bis[(E)-2′-phenylethenyl]cyclopropane (9), which proceeds via step-wise cleavage of the C{double bond, long}O bond and delivery of two allyl fragments from the reagent. A range of enantiomerically enriched ligands have been tested as stoichiometric asymmetric modifiers for this process. Enantiopure compounds such as cinchona alkaloids, ephedra, aminoalcohols and tartaric acid derivatives, which have proven of utility as asymmetric modifiers for the indium-mediated allylation of aldehydes and ketones, were very inefficient in the process 8→9. However, mandelic acid derivatives, in particular mandelates, were found to be of significant potential. The absolute stereochemistry of the cyclopropane 9 has been determined by degradation to 1,1-dicarboxymethyl-2-butylcyclopropane, converging with an independent enantioselective synthesis starting from hexene. Under optimised conditions, viz. using allylindium iodide reagents and working-up with aqueous Na2SO3 to avoid iodine-mediated polymerisation, (S)-9 can be generated in 86% yield and with (S)-methyl mandelate as modifier useful enantiopurity (94/6 er) was observed. The cyclopropane product ((S)-9) undergoes RCM using standard conditions to afford a norcarene unit ((1S,6S)-1-(E)-2′-(phenylethenyl)-bicyclo[4.1.0]hept-2-ene) without loss of enantiopurity.
