Nanocrystalline MgO for asymmetric Henry and Michael reactions

Nanomaterials with their three-dimensional structure and defined size and shape are considered to be suitable candidates for proper alignment with prochiral substrates for unidirectional introduction of reacting species to induce an asymmetric center. We herein report the design and development of a truly recyclable heterogeneous catalyst, nanocrystalline magnesium oxide, for the asymmetric Henry reaction (AH) to afford chiral nitro alcohols with excellent yields and good to excellent enantioselectivities (ee's) for the first time. Bronsted hydroxyls are the sole contributors for the ee, while they add on to the activity in AH. It is demonstrated that the hydrogen bond interactions between the -OH groups of (S)-(-)-binol and the -OH groups of MgO are essential for the induction of enantioselectivity. Further, to prove the above hypothesis, we have successfully carried out another reaction, asymmetric Michael reaction (AM) with nanocrystalline MgO. The reusable and suitably aligned nanocrystalline MgO-catalyzed AH and AM reactions afforded chiral products with comparable ee's to that of the homogeneous system.     

Catalytic asymmetric Michael reactions using a chiral rhodium complex

Catalytic asymmetric Michael reaction of β-keto esters and methyl vinyl ketone was achieved using a chiral diamine-based Rh complex to give the Michael adducts in up to 75% e.e.     

催化不对称反应新发展: 不对称活化

介绍了催化不对称催化反应中的一个新概念－不对称活化(asymmetricactivation)及其研究的最新发展。运用不对称活化策略,一个光学活性的整或者甚至外消旋的催化剂可以被另一种手性活化剂(chiralactivator)选择性的活化,从而催化反应生成非外消旋产物。该方法较不对称活化(asymmetricactivation)方法的优点是被活化的催化剂能够产生较使用光学纯催化剂更高对映体过量的产物。     

Pseudoephedrine as a chiral auxiliary for asymmetric Michael reactions: synthesis of 3-aryl-delta-lactones

[reaction: see text] The asymmetric Michael reaction of pseudoephedrine amides is reported. The 1,5-dicarbonyl products are converted to 3-aryl-delta-lactones in a two-step reduction/lactonization sequence. This method provides access to enantiomerically enriched trans-3,4-disubstituted delta-lactones.     

Asymmetric induction in domino Heck-aza-Michael reactions

Domino Heck-aza-Michael reactions are an efficient method for the rapid synthesis of functionalised N-heterocycles. An asymmetric version of this domino process has been developed to access chiral 1,3-disubstituted N-heterocycles from amino acid precursors in excellent yields (68–81%) with moderate to high diastereoselectivity (up to 92% de).     

Direct catalytic asymmetric Michael reaction of hydroxyketones: asymmetric Zn catalysis with a Et2Zn/linked-BINOL complex

Full details of our direct Michael addition of unmodified ketones using new asymmetric zinc catalysis are described. Et(2)Zn/(S,S)-linked-BINOL complexes were successfully applied to direct 1,4-addition reactions of hydroxyketones. The first generation Et(2)Zn/(S,S)-linked-BINOL 1 = 2/1 system was effective for 1,4-addition of 2-hydroxy-2'-methoxyacetophenone (3). Using 1 mol % of (S,S)-linked-BINOL 1 and 2 mol % of Et(2)Zn, we found that a 1,4-addition reaction of beta-unsubstituted enone proceeded smoothly at 4 degrees C to afford products in high yield (up to 90%) and enantiomeric excess (up to 95%). In the case of beta-substituted enones, however, the first generation Et(2)Zn/(S,S)-linked-BINOL 1 = 2/1 system was not at all effective. The second generation Et(2)Zn/(S,S)-linked-BINOL 1 = 4/1 with MS 3A system was developed and was effective for various beta-substituted enones to afford products in good dr, yield (up to 99%), and high enantiomeric excess (up to 99% ee). With the Et(2)Zn/1 = 4/1 systems, catalyst loading for beta-unsubstituted enone was reduced to as little as 0.01 mol % (substrate/chiral ligand = 10 000). The new system was also effective for 1,4-addition reactions of 2-hydroxy-2'-methoxypropiophenone (9) to afford chiral tert-alcohol in high enantiomeric excess (up to 96% ee). Mechanistic investigations as well as transformations of the Michael adducts into synthetically versatile intermediates are also described.     

Asymmetric induction in Diels-Alder reactions of o-quinodimethanes

Asymmetric inductive effects have been measured on the Diels-Alder reaction of dimethyl fumarate with o-quinodimethane bearing a chiral α-alkoxy group. The chiral substituents used were 1-phenylethoxy, 2-(1-phenyl)propoxy, 1-(2-phenyl)propoxy, 2-(4-phenyl)-butoxy and 1-cyclohexylethoxy. The greatest asymmetric induction was found with the first of these chiral substituents (47% ee). A π-stacking effect, previously suggested as the rationale for asymmetric induction in a similar system, is shown to be inconsistent with the results from this study.     

Asymmetric exchange of cyclopalladated ligands with a high level of asymmetric induction: a new route to optically active phosphapalladacycles

The first example of an asymmetric CH bond activation with chirality transfer (up to 91% ee) from an enantiopure CN-palladacycle is described. This asymmetric version of cyclopalladated ligand exchange was elaborated in an aprotic medium using prochiral phosphines as substrates and an enantiopure benzylaminate palladacycle bearing a primary amino group and a bulky tert-Bu substituent on the side chain as the palladation agent.     

Asymmetric induction in the reactions of azinones with C-nucleophiles

Effect of acylating agents on the course of addition of C-nucleophiles to 1,2,4- and 1,3,5-triazinones, as well as to quinoxalin-2(1H)-one, was studied. A series of new azinone derivatives was obtained. A method for the preparation of diastereomerically pure addition products of indoles to 1,2,4-triazinones and quinoxalin-2(1H)-one in the presence of N-Ts-L-amino acid acyl chlorides was suggested.     

外表面钝化SBA-15固载奎宁催化不对称Michael加成反应

以聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物(P123)为模板剂制备SBA-15分子筛,将未除模板剂的SBA-15用三甲基氯硅烷钝化后固载奎宁制得外表面钝化CH_3-SBA-15-QN非均相催化剂.对非均相催化剂进行XRD、FT-IR、N_2吸附-脱附表征.并以查尔酮类化合物与丙二腈的不对称Michael加成反应为模型来考察非均相催化剂CH_3-SBA-15-QN的催化活性,实验结果表明,非均相催化剂CH_3-SBA-15-QN比SBA-15-QN催化剂对产物表现出较高的对映选择性.4-甲氧基查耳酮为底物时,CH_3-SBA-15-QN为催化剂时,产物对映选择性能够达到77%,甚至比均相催化剂高6%,充分发挥了载体孔道效应和手性催化剂的不对称诱导能力.     

Chiral aldehyde catalysis: a highly promising concept in asymmetric catalysis

<正>Asymmetric organocatalysis has been a robust tool for manufacturing optically active molecules, in addition to asymmetric metal and biocatalysis [1]. The development of new concepts and catalysts to enable the creation of efficient synthetic methods has been a longstanding activity in this field. During the last decades, a diverse spectrum of chiral organocatalysts, including ketones, amine, Br?nsted acids     

Asymmetric induction in thia-Diels-Alder reactions of chiral polyfluoroalkylthionocarboxylates

A series of chiral S- or O-alkyl thionoesters have been synthesized by treatment of trifluorothioacetyl- or 2,2,3,3-tetrafluorothiopropionyl chloride with corresponding thiols or alcohols. The thia-Diels-Alder reaction of the thionoesters with symmetrical 1,3-dienes proceeds with diastereoselectivity up to 60%. Structures of cycloaddition products and corresponding transition states have been studied at the DFT level of approximation. The experimentally observed diastereomeric excess has been referred to differences in activation energies of transition states, preceding formation of the diastereomeric cycloaducts.     

MOP-phosphonites: a novel ligand class for asymmetric catalysis

Chiral phosphonite ligands (S,R(b))-5a, (S,S(b))-5b, (R,R(b))-6a and (R,S(b))-6b are introduced, comprising a MOP-type backbone with a binol-based binaphthyl group bound to the phosphorus. Their reaction with [Pd(η(3)-C(4)H(7))Cl](2) affords η(3)-methallylpalladium chloride complexes 7a/b and 8a/b which have been isolated and structurally characterised. Solid-state and solution studies indicate subtle differences in their coordination behaviour, which ultimately affects their efficacy in the asymmetric hydrosilylation of styrene.     

Asymmetric epoxidation using aqueous hydrogen peroxide as oxidant: bio-inspired construction of pentacoordinated Mn-salen complexes and their catalysis

Pentacoordinated Mn-salen complexes 1 and 5 possessing an internal pyridine or N-methylimidazole ligand, respectively, were found to be efficient catalysts for asymmetric epoxidation of conjugated Z-olefins using aqueous hydrogen peroxide. In particular, the epoxidation of chromene derivatives proceeded with high enantioselectivity greater than or equal to 97% ee.     

Asymmetric induction—V : Effect of R on asymmetric induction in additions to abcC-COR compounds

The diastereomeric product ratios from reactions involving the addition of various reagents to the carbonyl of φCH₃HC-COR compounds varies over a wide range. This variation is interpreted as due partly to changes in the structure of the diastereomeric transition states with changes in the size of R. For example, when R is smaller than the φCH₃HC group the diastereomeric product ratios are close to those predicted on the assumption that 1 and 2 are the minimum energy diastereomeric transition states; and when R is larger than the φCH₃HC group, the diastereomeric product ratios are large and closer to those that one might expect if 5 and 6 were the minimum energy transition states.