Diastereoselective synthesis of propargylamines catalyzed by Cu-MCM-41

In this work, a rapid, efficient and protecting group free diastereoselective synthesis of propargylamines through a multicomponent coupling reaction between (S)-prolinol, phenylacetylene and commercially available aldehydes catalyzed by Cu-MCM-41 in heterogeneous phase is reported. The reactions were carried out under solvent free conditions with good yields and moderate reaction times. In all the cases, catalyst was recovered and reused up to five cycles. Recyclability of the catalyst, low catalyst loading, solvent and protecting group free conditions, and the use of inexpensive catalyst are the key features that provide green aspects to this synthetic protocol.     

Catalytic enantioselective fluorination of α-cyano acetates catalyzed by chiral palladium complexes

The catalytic enantioselective electrophilic fluorination promoted chiral palladium complexes is described. Treatment of α-cyano acetates with N-fluorobenzenesulfonimide as the fluorine source under mild reaction conditions afforded the corresponding α-cyano α-fluoro acetates in high yields with excellent enantiomeric excesses (85-99% ee).     

Catalytic enantioselective electrophilic α-amination of β-ketoesters catalyzed by chiral palladium complexes

The catalytic enantioselective electrophilic α-amination promoted chiral palladium complexes is described. Treatment of β-ketoesters with azodicarboxylates as electrophilic amination reagents under mild reaction conditions afforded the corresponding α-amino β-ketoesters with excellent enantiomeric excesses (91-99% ee). Palladium complexes were immobilized in [bmim]PF₆, and their applications to catalytic α-amination of β-ketoesters were successfully demonstrated.     

Enantioselective addition of phenyl and alkyl acetylenes to imines catalyzed by chiral Cu(I) complexes

The stereoselective addition of phenyl acetylene and alkyl acetylenes to imines, catalyzed by chiral bis-imines-Cu(I) complexes was studied. A very simple experimental procedure allowed to obtain at room temperature optically active propargyl amines in very good yields and enantioselectivity up to 81%.     

Asymmetric hydroamination/cyclization catalyzed by group 4 metal complexes with chiral biaryl-based ligands

Group 4 metal complexes based on chiral biaryl ligands are readily prepared by a convenient amine elimination procedure, and they are efficient catalysts for the asymmetric hydroamination/cyclization of aminoalkenes. The biaryl-based ligands are highly modular enabling facile tuning of the catalyst reactivity and selectivity. The corresponding heterocyclic products have been obtained in excellent enantiomeric excesses (up to 93%) using sterically hindered C₂-symmetric titanium and zirconium mesitoylamidate complexes such as [1,1′-(C₁₀H₁₀)₂-2,2′-{NCO(2,4,6-Me₃C₆H₂)}₂]M(NMe₂)₂ (M = Ti, Zr). These results are presented in this short review.     

Asymmetric hydrophosphonylation of aldehydes catalyzed by bifunctional chiral Al(III) complexes

A new bifunctional chiral Al(III) complex of BINOL derivative, which contained tert-amine at 3,3′-position of the BINOL, has been developed for the effective enantioselective hydrophosphonylation of aldehydes. A variety of aromatic, heteroaromatic, condensed-ring, α,β-unsaturated, and aliphatic aldehydes were found to be suitable substrates for the reaction, and the desired α-hydroxy phosphonate were obtained in good to excellent yields (up to 99%) with moderate to good enantioselectivities (up to 87% ee) under mild conditions (at 0 °C). A possible catalytic cycle based on the experimental results was proposed.     

Rhodium-catalyzed multicomponent synthesis of chiral oxazolopiperidines

A multicomponent reaction that employs an unsaturated carboxylic acid, a 1,2 or 1,3 amino alcohol and gaseous CO and H₂ has been discovered. Thus, hydrocarbonylation of the carboxylic acid double bond generates a linear aldehyde, that is, immediately transformed into an oxazolidine. Further microwave assisted intramolecular lactamization delivers oxazolopiperidines with the generation of six new bonds in a one-pot single step. Bicylic, tricyclic, tetracyclic, and spirocyclic oxazolopiperidines can be prepared in good yields and acceptable stereoselection. The reaction did not occur under conventional heating even at higher temperature and pressure and for longer time, showing that microwave heating is indispensable to the process.     

Recent advances in asymmetric reactions catalyzed by chiral phosphoric acids

The very recent advances in chiral phosphoric acids (CPAs) catalyzed asymmetric reactions are discussed.     

Asymmetric addition of diethylzinc to aromatic aldehydes by chiral ferrocene-based catalysts

A series of chiral C₁- and C₂-symmetric ferrocenyl Schiff bases (1a-c), ferrocenyl aminoalcohols (2a), ferrocenylphosphinamides (2b-c), 1,1′-ferrocenyl-diol (3), and 1,1′-ferrocenyl-disulfonamide (4) were prepared and employed as base catalysts or as ligand for titanium(IV) complexes in the asymmetric addition of diethylzinc to aromatic aldehydes. High enantioselectivity up to almost 100% ee was achieved for the alkylation of benzaldehyde and p-methoxybenzaldehyde with 1 or 3. In contrast, however, the β-aminoalcohol (2a) and phosphinamides (2b and c) that are ubiquitous classes of base catalysts for this reaction proved inefficient in our hands, regardless of the types of substrates or reaction conditions. Comparative studies show that there exist various reaction parameters governing not only chemical yields but also optical yields. These include steric and electronic environment of the substrate, the solvent, the reaction temperature, and the nature of the ferrocene moieties.     

手性金属络合物催化不对称Baeyer-Villiger反应

Baeyer-Villiger反应是有机化学基本反应之一,但是催化不对称Baeyer-Villiger反应的研究尚处于起步阶段。本文按手性配体的不同,评述了手性金属络合物催化不对称Baeyer-Villiger反应的研究,特别是由外消旋或前手性酮制备光学活性内酯的研究进展。     

Homogeneous and heterogeneous asymmetric reactions. Part IX. Asymmetric transfer hydrogenation of 16-methyl-substituted steroid 17-ketones in the presence of rhodium(I) complexes

Chiral transfer hydrogenation of 16 methyl-substituted steroid 17-ketones in the presence of rhodium(I) complexes by hydrosilylation is described. During the preparation of the complex catalysts a wide variety of bidentate phosphines were used including chiral ligands, as well. The diastereoselectivity of the reduction depends strongly on the structure of the ligands. The method applied produces the hydroxy steroid products with excellent yield under very mild reaction conditions. Additionally, the procedure makes possible the preparation of 17α-OH isomers beside the easily synthesizable 17β-OH products. Part. VIII: B. T?r?k, K. Felf?ldi, G. Szakonyi, K. Balázsik and M. Bartók: Enantiodifferentiation in Asymmetric Sonochemical Hydrogenations, Catal. Letters (in press)     

Asymmetric hydroazidation of α-substituted vinyl ketones catalyzed by chiral primary amine

We report herein the first example of asymmetric hydroazidation of α-substituted vinyl ketones by using chiral primary amines as the catalysts.A simple chiral primary-tertiary diamine catalyst derived from lphenylalanine was found to readily promote this aza-Michael addition reaction with enamine protonation as the key stereogenic step,thus enabling the effective synthesis of α-chiral β-azido ketones with good yields and moderate enantioselectivities.     

A new dinuclear chiral salen complexes for asymmetric ring opening and closing reactions: Synthesis of valuable chiral intermediates

A new dinuclear chiral Co(salen) complexes bearing group 13 metals have been synthesized and characterized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides with H₂O, chloride ions and carboxylic acids and consequently provide enantiomerically enriched terminal epoxides (>99% ee). It also catalyzes the asymmetric cyclization of ring opened product, to prepare optically pure terminal epoxides in one step. The homogeneous dinuclear chiral Co(salen) have been covalently immobilized on MCM-41. The potential benefits of heterogenization include facilitation of catalyst separation and recyclability requiring very simple techniques. The system described is very efficient.     

Enantioselective synthesis of nitrocyclopropanes via conjugate addition of bromomalonate to nitroalkenes catalyzed by Ni(II) complexes

A novel one-pot methodology for the catalytic enantioselective synthesis of highly functionalized nitrocyclopropanes promoted by chiral nickel complexes is developed. The treatment of bromomalonates with nitroalkenes under the mild reaction conditions afforded the corresponding Michael adducts which cyclizes to controlled reaction conditions with excellent diasteroselectivities (>99 de) and enantioselectivities (up to 99% ee).     

Asymmetric cyclopropanation reactions catalyzed by carbohydrate-based crown ethers

Optically active cyclopropane derivatives were prepared by a novel, simple and green approach in high enantioselectivities using monosaccharide-based chiral crown ethers as phase transfer catalysts. The crown ethers having d-glucopyranoside, d-mannopyranoside and d-altropyranoside units proved to be efficient catalyst in a few asymmetric phase transfer cyclopropanation reactions. The Michael-initiated ring closure (MIRC) reactions of diethyl bromomalonate with chalcones took place with complete diastereoselectivity and up to 99% ee. Using benzylidenemalononitrile, 2-arylidenemalononitriles, 2-benzylidene-1,3-indandione, substituted 2-benzylidene-1,3-indandiones, 2-arylidene-1,3-indandiones and 2-benzylidene-1,3-diphenyl-1,3-propanediones enantioselectivities up to 92%, 99%, 54% 93%, 89% and 72%, respectively, were achieved, in the presence of chiral lariat ethers derived from different monosaccharides. The absolute configuration of a cyclopropane diester product was determined by a combined CD spectroscopic and theoretical study.     

Asymmetric transfer hydrogenation of ketones catalyzed by ruthenium(II) complexes bearing a chiral phosphinoferrocenyloxazoline ligand

The catalytic activity in asymmetric transfer hydrogenation of ketones using octahedral and half-sandwich (η⁵-indenyl and η⁶-arene) ruthenium(II) complexes containing the chiral ligand (4S)-2-[(S_p)-2-(diphenylphosphino)ferrocenyl]-4-(isopropyl)oxazoline (FcPN) has been explored. Catalytic studies with complex fac-[RuCl₂{η²(P,N)-FcPN}(PMe₃)₂] (1) show excellent TOF values (9600 h⁻¹). Experiments in the presence of free FcPN, which lead to an increase in conversion rates and ee values when the catalyst is complex [Ru(η⁵-C₉H₇){κ²(P,N)-FcPN}(PPh₃)][PF₆] (4) have been carried out. The characterization of the new complexes mer-trans-[RuCl₂{P(OMe)₃}₂{κ²(P,N)-FcPN}] and of the water-soluble complexes fac- and mer-trans-[RuCl₂(PTA)₂{κ²(P,N)-FcPN}] is also reported.     

Asymmetric synthesis of novel spirocycles via a chiral phosphoric acid catalyzed desymmetrization

A straightforward method for the asymmetric preparation of novel lactone and lactam spirocycles is described. An initial desymmetrization via a chiral Brønsted acid yields enantioenriched lactones which readily undergo a second cyclization to give the desired spirocycle.     

Asymmetric cyanohydrin synthesis using heterobimetallic catalysts obtained from titanium and vanadium complexes of chiral and achiral salen ligands

Titanium(IV)(salen) and vanadium(V)(salen) complexes are both known to form catalysts for asymmetric cyanohydrin synthesis. When a mixture of titanium and vanadium complexes derived from the same or different salen ligands is used for the asymmetric addition of trimethylsilyl cyanide to benzaldehyde, the absolute configuration of the product and level of asymmetric induction can only be explained by in situ formation of a catalytically active heterobimetallic complex, and is not consistent with two monometallic species acting cooperatively. Combined use of complexes containing chiral and achiral salen ligands demonstrates that during the asymmetry inducing step of the mechanism, the aldehyde is coordinated to the vanadium rather than the titanium ion. The titanium complexes also catalyse the asymmetric addition of ethyl cyanoformate to aldehydes, a reaction in which vanadium(V)(salen) complexes are not active. For this reaction, use of a mixture of titanium and vanadium(salen) complexes results in a complete loss of catalytic activity, a result which again can only be explained by in situ formation of a heterometallic complex. Both the titanium and vanadium based catalysts also induce the asymmetric addition of potassium cyanide/acetic anhydride to aldehydes. For this reaction, combined use of chiral and achiral complexes indicates that during the asymmetry inducing step of the mechanism, the aldehyde is coordinated to titanium rather than vanadium, a result which contrasts with the observed results when trimethylsilyl cyanide is used as the cyanide source.