- Chiral C2-symmetric ligands with 1,4-dioxane backbone derived from tartrates: Syntheses and applications in asymmetric hydrogenation
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Chiral 1,4-diphenylphosphines 5-7 as well as thioether 8 were synthesized from tartrates employing Ley's "BDA" and "Dispoke" methodologies as the key step. Rhodium(I) complexes with 5-7 are efficient catalysts for the asymmetric hydrogenation of β-substituted enamides and MOM-protected β-hydroxyl enamides, which furnished chiral amines or β-amino alcohols with 94-99% ee. These results indicated that the 1,4-dioxane backbone in the ligands having the general structure 2 played an important role in stabilizing metal-ligand chelate conformation. Higher enantioselectivities with ligand 2 were achieved compared with the analogous ligands having the general structure 1.
- Li, Wenge,Waldkirch, Jason P.,Zhang, Xumu
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- Synthesis of C2-symmetric bisphosphine ligands from tartaric acid, and their performance in the Pd-Catalyzed asymmetric o-allylation of a phenol
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Starting from tartaric acid derived chiral diols or dicarboxylic acid dichlorides with either a 2,2-dimethyl-1,3-dioxolane (Taddol) or a 2,3-dimethoxy-2,3-dimethyl-1,4-dioxane (Tatrol) core structure, and BH 3-protected ortho-phosphanyl phenols, a set of fourteen new C 2-symmetric diphosphine ligands was synthesized. In addition, three related ligands were obtained from ortho-diphenylphosphino-anilines. The fully characterized ligands were then tested in the Pd-catalyzed enantioselective O-allylation of 4-methoxyphenol using crotyl methyl carbonate as a reagent. In addition, a pseudo-intramolecular variant of the reaction, using crotyl 4-methoxyphenyl carbonate as a substrate, was studied. The so-called Trost ligand was used as a reference. Although the Trost ligand (3 mol-%) gave up to 84% ee, one of the new ligands showed higher activity (50% ee with 0.075 mol-%). Copyright
- Dindaroglu, Mehmet,Akyol Dincer, Sema,Schmalz, Hans-Guenther
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supporting information
p. 4315 - 4326
(2014/07/21)
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- New organocatalysts derived from tartaric and glyceric acids for direct aldol reactions
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The synthesis of several new pyrrolidine based asymmetric organocatalysts derived from tartaric, glyceric acids and a pyrrolidine moiety is described with a study of their application in the development of an enantioselective aldol protocol. The influence
- Maycock, Christopher D.,Rita Ventura
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p. 1262 - 1271
(2012/11/07)
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- CATALYSTS
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Catalysts suitable for asymmetric hydrogenation reactions is described comprising the reaction product of a group (8) transition metal compound a chiral phosphine and a chiral diamine of formula (1) in which R1, R 2 R 3 or R 4 are independently hydrogen, a saturated or unsaturated alkyl, or cycloalkyl group, an aryl group, a urethane or sulphonyl group and R 5 , R 6 , R 7 or R8 are independently hydrogen, a saturated or unsaturated alkyl or cycloalkyl group, or an aryl group, at least one of R1, R 2 , R3 or R 4 is hydrogen and A is a linking group comprising one or two substituted or unsubstituted carbon atoms.
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Page/Page column 13-14
(2008/06/13)
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- New building blocks for efficient and highly diastereoselective polyol production-synthesis and utility of (R',R',S,S) and (S",S",R,R)-2,3-butane diacetal protected butane tetrol derivatives
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The efficient synthesis of aldehydes derived from 2,3butane diacetal protected butane tetrols (S1,S',R,R)-5 and (R',R',S,S)-6 and their utility in the controlled synthesis of polyhydroxylated materials through highly diastereoselective Lewis acid mediated addition reactions of allyltributylstannane and silyl enol ether nucleophiles is described.
- Barlow, Jaqueline S.,Dixon, Darren J.,Foster, Alison C.,Ley, Steven V.,Reynolds, Dominic J.
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p. 1627 - 1629
(2007/10/03)
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- Investigations of the asymmetric intramolecular [2 + 2] photocycloaddition and its application as a simple access to novel C2-symmetric chelating bisphosphanes bearing a cyclobutane backbone
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The asymmetric intramolecular [2 + 2] photocycloaddition of αβ-enoates was evaluated as a simple access to the novel C2-symmetric bisphosphanes 22 and 27 possessing a cyclobutane backbone. A source of different chiral auxiliaries for investigations of the photochemical key step was provided by the transacetalization of dialkyl tartrates 3 with the corresponding 3,3-dialkoxybutan-2-ones 4. An insight into the selection mechanism was gained by temperature dependent measurements on the irradiation of the dicinnamates 10a-d, since the corresponding Eyring diagram discloses strictly linear functions as well as an isoselective relationship. Diol 8a turned out to be a structurally optimized auxiliary in terms of chiral induction and product crystallization and was also successfully applied in the first asymmetric photodimerization of 2-indenecarboxylic acid esters. Indeed, in this case excellent diastereoselectivities were achieved, too, but head-to-tail dimers 16a and 16b were formed predominantly. Diesters 11a and 16a were converted by standard procedures into the desired enantiopure 1,4-diphosphane 22 and 1,5-diphosphane 27. Furthermore, the hitherto unknown absolute configuration of δ-truxinic acid was elucidated from a single crystal X-ray structure analysis of 11a.
- Haag, Dieter,Scharf, Hans-Dieter
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p. 6127 - 6135
(2007/10/03)
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- Transacetalization of Diethyl Tartrate with Acetals of α-Dicarbonyl Compounds: A Simple Access to a New Class of C2-Symmetric Auxiliaries and Ligands
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A simple access to a new class of C2-symmetric auxiliaries and ligands is based on the transacetalization of diethyl tartrate (1) with monoacetals of butane-2,3-dione in the key step.Acid-catalyzed reaction of 1 with 2 equiv of 3,3-diethoxybutan-2-one (2) gives the C2-symmetric 1,4-dioxane 7 in 88percent yield.Reduction of 7 with LiAlH4 affords the crystalline diol 9.The structure of 7 was established from the X-ray structure of 9.Dioxane 7 was converted by standard methodology into the diphosphine 24 and the TARTROL 22.Reaction of 1 with 3,3-dimethoxybutan-2-one (3) in the presence of BF3-etherate gives in analogy to the formation of 7 the 1,4-dioxane 8.This compound was transformed into the diphosphine 25 and the TARTROL 23.The trans-diaxial relationship of the methoxy groups present in 8 could be deduced without X-ray analysis from the 1H-NMR spectrum of 23.
- Berens, Ulrich,Leckel, Dieter,Oepen, Susanne C.
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p. 8204 - 8208
(2007/10/02)
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