Modified BINAP: The How and the Why

Asymmetric Hydrogenations One by One: Differentiation of up to Three β-Ketocarboxylic Acid Derivatives Based on Ruthenium(II)–Binap Catalysis

Noyori-type reductions of pairs of beta-ketoamides and beta-ketoesters with elemental hydrogen (4 bar) proceeded substrate by substrate. When Et(2)NH(2) (+)[{RuCl(S)-binap}(2)](mu-Cl)(3)(-) was employed as a catalyst in a methanol or ethanol solution, the substrates were reduced at room temperature in the order beta-ketopyrrolidide > or = beta-ketopiperidide > or = beta-keto(N,N-diethylamide) > beta-keto(alkyl esters) > beta-keto(oligofluoroalkyl esters). This is the first time that beta-ketoamides have been reduced asymmetrically (91 to >98 % ee) under such mild conditions. Monitoring the concentrations of these beta-ketocarboxyl acid derivatives and their respective hydrogenation products over the course of time showed that the most electron-rich substrate is captured by the catalyst preferentially and exothermically; whether this occurs reversibly or irreversibly remains to be determined. The hydrogenation product is subsequently formed. The last transformation includes the rate-determining step. The combination of these events explains why starting from appropriate mixtures of substrates a "first-choice substrate" reacted from early on while the "second-choice substrate" stayed virtually untouched over an extended period of time and reacted no earlier than after the "first-choice substrate" had disappeared. From then onward, however, the "second-choice substrate" also reacted relatively rapidly.

The enantioselective Morita-Baylis-Hillman reaction and its aza counterpart

The development of asymmetric Morita-Baylis-Hillman (MBH) reactions has evolved dramatically over the past few years, parallel to the emerging concept of bifunctional organocatalysis. Whereas organocatalysis is starting to compete with metal-based catalysis in several important organic transformations, the MBH reaction belongs to a group of prototypical reactions in which organocatalysts already display superiority over their metal-based counterparts. This Minireview summarizes recent mechanistic insights and advances in the design and synthesis of small organic molecules for enantioselective MBH and aza-MBH reactions.

Synthesis and Determination of the Absolute Configuration of Chiral Tetracosanaphthalenes

Tetracosanaphthalenes with diethylaminocarbonylmethoxy side chains were constructed by bottom-up synthesis, and their absolute configurations were determined by an exciton chirality method.

Syntheses and applications of 2-phosphino-2'-alkoxy-1,1'-binaphthyl ligands. Development of a working model for asymmetric induction in hydrovinylation reactions

Among the handful of monophosphine ligands that effect asymmetric hydrovinylation of vinylarenes, 2-diphenylphosphino-2'-methoxy-1,1'-binaphthyl (MOP) is among the most accessible. Addition of a methyl group at the 3'-position of this ligand significantly improves the enantioselectivity of hydrovinylation of prototypical alkenes. Introduction of a chiral phospholane at the C2 position of this scaffolding has no effect on the enantioselectivity. These results are consistent with a model proposed for the asymmetric induction for this exacting reaction.

Easily Accessible Benzamide-Derived P,O Ligands (Bphos) for Palladium-Catalyzed Carbon–Nitrogen Bond-Forming Reactions

Easily accessible benzamide-derived hemilabile phosphine ligands were efficiently prepared through ortho-directed lithiation of the corresponding N,N-diethylbenzamide followed by quenching with chlorodialkylphosphines. These structurally simple hemilabile ligands were found to be highly effective in palladium-catalyzed amination of aryl and heteroaryl chlorides. Various sterically congested and functionalized aryl halide substrates were compatible in these reaction conditions. By using optimized reaction conditions, remarkable catalyst productivity (total turnover number up to 8400) was obtained.

Sulfonated N-heterocyclic carbenes for Suzuki coupling in water

Sulfonated, water-soluble imidazolium and imidazolinium salts were synthesized and the respective Pd-complexes with N,N'-bis(2,6-dialkyl-4-SO(3)(-)-phenyl)imidazol-2-ylidene and N,N'-bis(2,6-dialkyl-4-SO(3)(-)-phenyl)-4,5-dihydroimidazol-2-ylidene ligands were applied in aqueous Suzuki coupling reactions of aryl chlorides.

Configurationally stable propeller-like triarylphosphine and triarylphosphine oxide

Configurationally stable, propeller-like triarylphosphine and triarylphosphine oxide can be synthesized; a chiral scaffold based on Lissoclinum-cyclopeptides linked via three peptide bonds with a triphenylphosphine and triphenylphosphine oxide moiety, respectively, prevents effectively epimerization at the chiral phosphorus atom.

Synthesis and properties of the chiral oligonaphthalenes

Helical oligonaphthalenes were constructed by bottom-up synthesis (repeating dimerization reactions), their absolute configurations were determined by an exciton chirality method and their functions, such as energy transfer, are also reported.

An unusual norcaradiene/tropylium rearrangement from a persistent amino-phosphonio-carbene

An amino-phosphonio-carbene featuring a bromobiphenyl backbone was prepared and spectroscopically characterized at low temperature. This carbene was found to readily rearrange upon warm up, affording an original tricyclic phospholium derivative, presumably via a norcaradiene/tropylium isomerization.

Diastereospecific intramolecular Ullmann couplings: unique chiral auxiliary for the preparation of 3,3'-disubstituted MeO-BIPHEP derivatives

[reaction: see text] A chiral auxiliary is described that provides only one diastereomer during intramolecular Ullmann couplings. Treatment of five Ullmann coupling precursors with Cu powder in DMF at 115 degrees C provides 2,2',3,3',6,6'-hexasubstituted 1,1'-biphenyls as single diastereomers in yields ranging from 66% to 91%.

Cyclic C-amino phosphorus ylides as a source of bidentate heteroditopic ligands (phosphine/aminocarbene) for transition metals

In contrast with most of their congeners, acyclic and cyclic C-amino phosphorus ylides behave as genuine carbene and phosphine transfer agents for transition metal centers. They allow the facile synthesis of a variety of metal complexes that feature heteroditopic ligands, such as 1,6-(phosphine)(aminocarbene) systems with a biphenyl backbone.

New Ru Complexes Containing the N-Tridentate bpea and Phosphine Ligands: Consequences of Meridional vs Facial Geometry

The synthesis and isolation of the complex cis,fac-[RuIICl2(bpea)(PPh3)][3; bpea = N,N-bis(2-pyridylmethyl)ethylamine] and three geometrical isomers of the complex [RuIICl(bpea)(dppe)](BF4) [4; dppe = (1,2-diphenylphosphino)ethane], trans,fac (4a), cis,fac (4b), and mer(down) (4c), have been described (see Chart 1 for a drawing of their structures). These complexes have been characterized through analytical, spectroscopic (IR, UV/vis, and 1D and 2D NMR), and electrochemical (cyclic voltammetry) techniques. In addition, complexes 3, 4a, and 4b have been further characterized in the solid state through monocrystal X-ray diffraction analysis. The molecular and electronic structures of isomers 4a, 4b, 4c, and 4d (the mer(up) isomer) have also been studied by means of density functional theory (DFT) calculations. Furthermore, their low-energy electronic transitions have been simulated using time-dependent DFT approaches, which have allowed unraveling of their metal-to-ligand charge-transfer nature. Complexes 3 and 4a-c are capable of catalyzing H-transfer types of reactions between alcohols and aromatic ketones such as acetophenone and 2,2-dimethylpropiophenone (DP). A strong influence of the facial versus meridional geometry in the bpea ligand coordination mode is observed for these catalytic reactions, with the meridional isomer being much more active than the facial one. The meridional isomer is even capable of carrying out the H-transfer reaction of bulky substrates such as DP at room temperature.

Non-Biaryl Atropisomers in Organocatalysis

A new class of 6'-hydroxy cinchona alkaloids, with a non-biaryl atropisomeric functionalisation at position 5' of the quinoline core can be prepared by an easy amination procedure. These are the first derivatives for which the principle of atropisomerism is engrafted in the classical core of the cinchona alkaloids. The aminated cinchona alkaloids are effective organocatalysts for the Michael addition of beta-keto esters to acrolein and methyl vinyl ketone, in up to 93 % ee (ee=enantiomeric excess), as well as for the asymmetric Friedel-Crafts amination of a variety of 2-naphthols, permitting the preparation of the latter in up to 98 % ee. The aminated 8-amino-2-naphthol itself is the first chiral organocatalyst based on non-biaryl atropisomerism. The two enantiomers of this chiral primary amine can be used for the direct alpha-fluorination of alpha-branched aldehydes. The fluorinated compounds can thereby be accessed in up to 90 % ee.

2,2′-Disubstituted F12binaphthyl derivatives: stannanes, boranes, and (R)-F12BINOL

2,2'-Distannyl derivatives of dodecafluorobinaphthalene are converted to a novel D2 symmetric borane dimer, which can be oxidized to (+)-F12BINOL; resolution using (S)-acetoxypropanoyl chloride affords enantiopure material.

Highly Efficient Chromatographic Resolution of α,α‘-Dihydroxybiaryls

[graph: see text] Separation factors as high as 115 were observed for the chromatographic resolution of many alpha,alpha'-dihydroxybiaryls with a single chiral stationary phase made from readily available amino acid derivatives. The stationary phase works well for biphenyl-type compounds. It works extremely well for larger bis-aromatic compounds, such as binaphthyl-type compounds.

Facile Preparation of a New BINAP-Based Building Block, 5,5‘-DiiodoBINAP, and Its Synthetic Application

[reaction: see text] Bis(pyridine)iodonium tetrafluoroborate was successfully used for regioselective iodination of BINAP dioxide to give 5,5'-diiodoBINAP dioxide in an excellent yield of 92%, with no observed formation of 4,4'-diiodoBINAP dioxide. A Sonogashira cross-coupling reaction with 5,5'-diiodoBINAP dioxide gave the desired bis(trimethylsilylethynyl) product in 86% yield. The resulting 5,5'-disubstituted BINAP dioxides were reduced to the corresponding phosphines, which were used as chiral ligands for rhodium-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone to give 3-phenylcyclohexanone in excellent yield with high enantioselectivity.

3,3‘-Disubstituted BINAP Ligands: Synthesis, Resolution, and Applications in Asymmetric Hydrogenation

A novel family of BINAP ligands were prepared with alkoxy- and acetoxy-derived substituents in the 3,3'-positions. They were prepared through a convergent synthesis starting from readily available 4-bromo-2-naphthol. These ligands afforded excellent enantioselectivities in the asymmetric hydrogenation of substituted olefins. The presence of the 3,3'-substituents was shown to be beneficial by a direct comparison with the parent unsubstituted BINAP. [reaction: see text]