Asymmetric palladium-assisted alkylation of olefins

Palladium-promoted alkylation of some alkenes using chiral sulfoxide-containing carbanion as nucleophiles or using optically N,N-dimethyl-α-phenylethylamine as ligand together with a non-chiral stabilized carbanion as nucleophile results in an asymetric induction of 10–40%.     

Asymmetric epoxidation of conjugated olefins with dioxygen

A complex situation: Asymmetric epoxidation of conjugated olefins was achieved at room temperature using ruthenium complex 1 as the catalyst and air as the oxidant to give epoxides in up to 95?%?ee. When the product was acid sensitive, the reaction was carried out at 0?°C under oxygen.     

Asymmetric Simmons-Smith cyclopropanation of unfunctionalized olefins

This paper describes a promising asymmetric cyclopropanation system for unfunctionalized olefins using readily available dipeptide N-Boc-l-Val-l-Pro-OMe as ligand.     

Asymmetric reductive ring-opening of bicyclic olefins catalyzed by palladium and nickel complexes

[reaction: see text] Asymmetric reductive ring opening of oxa- and azabenzonorbornadienes with organic acids and zinc powder under mild conditions catalyzed by Ni(binap)Cl(2) or Pd(binap)I(2) produces the corresponding 1,2-dihydronaphth-1-ols in good to excellent yields with high enantioselectivity.     

Asymmetric intramolecular arylcyanation of unactivated olefins via C-CN bond activation

The enantioselective, intramolecular arylcyanation of unactivated olefins via C-CN bond activation has been accomplished using a Ni(0) catalyst and BPh3 co-catalyst. High enantioselectivities are achieved using TangPHOS as a chiral ligand. This method allows the generation of two new C-C bonds and one new quaternary carbon stereogenic center in a single synthetic step, converting readily available benzonitrile substrates into 1,1-disubstituted indanes in 49-85% yield and 92-97% ee.     

Asymmetric hydrogenation of imines and olefins using phosphine-oxazoline iridium complexes as catalysts

Herein we describe the synthesis of a new class of chiral phosphine-oxazolines and their application as ligands in iridium-catalyzed hydrogenations. Mechanistic aspects of olefin hydrogenation with this class of iridium catalysts are discussed and a selectivity model to help rationalize the results obtained is also presented.     

Asymmetric N1 unit transfer to olefins with a chiral nitridomanganese complex: novel stereoselective pathways to aziridines or oxazolines

Chiral nitridomanganese complex 1 was found to be a highly potential N1 unit source for the asymmetric synthesis of aziridines and 2-oxazolines from olefins such as styrene and its derivatives. When sulfonyl chlorides were employed as activators of the complex in the presence of pyridine, pyridine N-oxide, and a silver salt, the reaction of olefins with complex 1 proceeded smoothly to afford the N-sulfonylated aziridines. The aziridination of styrene derivatives with complex 1 using 2-trimethylsilylethanesulfonyl chloride (SESCl) gave the N-SES-aziridines, which were easily converted into chiral N-unsubstituted aziridines. It was found that the reaction was applicable to the asymmetric synthesis of 2-oxazolines from olefins when acyl chlorides were employed as activators. Complex 1 provided an effective asymmetric environment for trans-disubstituted styrenes in the reaction (up to 92% ee). This is the first example of a direct asymmetric synthesis of 2-oxazolines from olefins. Additional experiments, conducted during the course of this investigation, suggest that the isomerization of the N-acylaziridine intermediate is involved in this reaction.     

Asymmetric [3 + 2] photocycloadditions of cyclopropylamines with electron-rich and electron-neutral olefins

Radical addition to olefins is a common and useful chemical transformation. In the context of offering enantioenriched three-dimensional molecules via such a highly reactive process, chiral hydrogen-bonding (H-bonding) catalysis has been widely used to provide enantiocontrol. The current strategies for operating H-bonding induction are confined to following that are prevalent in ionic-type manifolds. Here, we report a novel protocol towards electron-rich olefins based on converting these species from acting as H-bonding donors to acceptors. It facilitates the first development of asymmetric [3 + 2] photocycloadditions with cyclopropylamines. The method is also effective for electron-neutral olefins, in which the successful construction of all-carbon quaternary stereocentres from 1,1-diaryl ethylenes that feature two structurally similar aryl substituents demonstrates the versatility of this new chiral H-bonding catalytic strategy. Furthermore, the importance of the obtained six kinds of products in pharmaceuticals and asymmetric catalysis underscores the practicability of this work.

Radical addition to olefins is a common and useful chemical transformation.     

Asymmetric hydrogenation of aromatic olefins catalyzed by iridium complexes of proline derived phosphine-oxazoline ligands

The synthesis of a series of phosphine-oxazoline ligands is reported. This ligands are synthesized by reaction of a phosphine chloride with the secondary nitrogen of proline. Upon coordination to iridium the resulting complexes can be used in the asymmetric hydrogenation of simple olefins. The effect of different counter ions and substitution at the oxazoline and the phosphine is reported.     

Asymmetric intramolecular [3 + 2] cycloaddition reactions of acylhydrazones/olefins using a chiral zirconium catalyst

Catalytic asymmetric intramolecular [3 + 2] cycloaddition of hydrazone/olefins has been attained. In the presence of a chiral zirconium catalyst prepared from zirconium alkoxide and a BINOL derivative, the desired pyrazolidine derivatives were obtained in high yields with high selectivities. The products were easily converted to 1,3-diamine or beta-aminonitrile derivatives by N-N bond cleavage.     

Asymmetric hydrogenation of prochiral olefins catalysed by furanoside thioether-phosphinite Rh(I) and Ir(I) complexes

Thioether-phosphinite ligands (P-SR, R = Ph, Pr(I) and Me) bearing substituents with different steric demands on the sulfur centre were tested in the rhodium- and iridium-catalysed asymmetric hydrogenation of prochiral olefins. High enantiomeric excesses (up to 96%) and good activities (TOF up to 860 mol product x (mol catalyst precursor x h)(-1)) were obtained for alpha-acylaminoacrylates derivatives. Our results show that enantiomeric excesses depended strongly on the steric properties of the substituent in the thioether moiety, the metal source and the substrate structure. A bulky group in the thioether moiety along with the metal Rh had a positive effect on enantioselectivity. Reaction of these chiral ligands with [M(cod)2]BF4(M = Ir, Rh; cod = 1,5-cyclooctadiene) yielded complexes [M(cod)(P-SR)]BF4, which were present in only one diastereomeric form having the sulfur substituent in a pseudoaxial disposition. The addition of H2 to iridium complexes gave the cis-dihydridoiridium(iii) complexes [IrH2(cod)(P-SR)]BF4. For complexes [IrH2(cod)(P-SPh)]BF4 and [IrH2(cod)(P-SMe)] only one isomer was present in solution. However, for the complex [IrH2(cod)(P-Si-Pr)]BF4, which contained the more hindered substituent on sulfur, two isomers were detected. In all cases there was a pseudoaxial disposition of the sulfur substituents.     

Designing new chiral ketone catalysts. Asymmetric epoxidation of cis-olefins and terminal olefins

This paper describes a new class of chiral oxazolidinone ketone catalyst for asymmetric epoxidation. High ee values have been obtained for a number of cyclic and acyclic cis-olefins. The epoxidation was stereospecific with no isomerization observed in the epoxidation of acyclic systems. Encouragingly high ee values have also been obtained for a number of terminal olefins. Mechanistic studies show that electronic interactions play an important role in stereodifferentiation.     

Multipolymers with Fischer-Tropsch olefins

Multipolymers consisting of ethylene, 1-heptene, 3-methylpentene and 4-methylpentene were prepared with a heterogeneous Ziegler-Natta catalyst. The polymers were prepared in such a way that the molar fraction of the comonomers remained the same. Copolymers of ethylene/1-heptene and ethylene/4-methylpentene were prepared in order to study the changes in polymer characteristics as one moves from an ethylene/linear alpha olefin copolymer through ethylene multipolymers to an ethylene/4-methylpentene copolymer. The mechanical, rheological and application properties showed expected trends.     

Ethylene copolymers with Fischer-Tropsch olefins

The properties of ethylene copolymers, terpolymers and multipolymers prepared with even and uneven carbon number linear and branched α-olefins were compared. The most likely microstructures of ethylene/linear α-olefin copolymers was assigned by considering co-unit bulkiness, average crystallizable sequence lengths and thermal properties. The higher α-olefins were found to be more effective at decreasing density, but peak melting temperatures were higher. In terpolymers where lower α-olefins such as 1-butene and 1-pentene were used as comonomers, density was decreased more than the mathematical average expected from the ratio of comonomers in the terpolymers. Peak melting temperatures were also lower. Based on NMR evidence and the microstructures of the different copolymers the rationale for this occurrence could be ascribed to decreased clustering for these terpolymers. Branched α-olefins produced ethylene co- and terpolymers with significantly decreased densities as compared to the linear α-olefins. Impact strength of these polymers was also substantially higher, even at low comonomer content. Thermal evidence indicates that the microstructure of the co- and terpolymers containing branched α-olefins are very similar to that of the copolymers prepared with linear α-olefins of the same carbon number.     

Ruthenium-catalyzed oxidative cleavage of olefins to aldehydes.

Three oxidation protocols have been developed to cleave olefins to carbonyl compounds with ruthenium trichloride as catalyst (3.5 mol %). These methods convert olefins that are not fully substituted to aldehydes rather than carboxylic acids. While aryl olefins were cleaved to aromatic aldehydes in excellent yields by using the system of RuCl3-Oxone-NaHCO3 in CH3CN-H2O (1.5:1), aliphatic olefins were converted into alkyl aldehydes with RuCl3-NaIO4 in 1,2-dichloroethane-H2O (1:1) in good to excellent yields. It is noteworthy that terminal aliphatic olefins were cleaved to the corresponding aldehydes in excellent yields by using RuCl3-NaIO4 in CH3CN-H2O (6:1).     

Asymmetric epoxidation of 1,1-disubstituted terminal olefins by chiral dioxirane via a planar-like transition state

Various 1,1-disubstituted terminal olefins have been investigated for asymmetric epoxidation using chiral ketone catalysts. Up to 88% ee has been achieved with a lactam ketone, and a planar transition state is likely to be a major reaction pathway.     

Ring-opening polymerizations of cyclic olefins

A ziegler-type catalyst system consisting of tungsten hexachloride and alkyl or aryl tin compounds was found to polymerize cyclopentene and other cyclic olefins through a ring-opening mechanism. This catalyst system also polymerized α-olefins such as ethylene and 1-octene. An attempt was made to copolymerize cyclopentene and ethylene. Other catalyst systems were also employed for ring-opening polymerizations with limited success.     

Selectfluor-promoted fluorination of piperidinyl olefins

A simple and straightforward synthesis of 1-substituted-4-aryl-5-fluoro-1,2,3,6-tetrahydropyridine (3) or 1-substituted 4-diarylmethanoyl-4-fluoropiperidine (6) by the treatment of piperidinyl exo- or endo-olefin with 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate (Selectfluor) is reported. Two transformations from endo-olefin 1 to allylic fluoride 3 and from exo-olefin 2 to fluorohydrin 6 proceed via allylic fluorination and fluorohydroxylation in moderate yields. It presents two novel reactions promoted by Selectfluor and broadens the scope of application.