Sparteine Complex Research Articles

Use of copper(II)/diamine catalysts in the desymmetrisation of meso-diols and asymmetric Henry reactions: comparison of (−)-sparteine and (+)-sparteine surrogates

Four new copper(II)/diamine complexes comprising some (+)-sparteine surrogates and a cyclohexane-derived diamine were prepared and evaluated as chiral catalysts in desymmetrisation of meso-diols and asymmetric Henry reactions. Mono-benzoylation reactions generated two products with high enantioselectivity (90:10 to 97:3 er). Asymmetric Henry reactions gave nitro alcohols in 90:10 to 98:2 er. Notably, the sense of induction with the (+)-sparteine surrogates was opposite to that obtained using the copper(II)/(−)-sparteine complex. One of the nitro alcohol products was utilised in a concise synthesis of a chiral morpholine.

Carbamate-directed benzylic lithiation for the diastereo- and enantioselective synthesis of diaryl ether atropisomers

Diaryl ethers carrying carbamoyloxymethyl groups may be desymmetrised enantio- and diastereoselectively by the use of the sec-BuLi–(−)-sparteine complex in diethyl ether. Enantioselective deprotonation of one of the two benzylic positions leads to atropisomeric products with ca. 80:20 e.r.; an electrophilic quench typically provides functionalised atropisomeric diastereoisomers in up to 97:3 d.r.

Enantioselective synthesis of ( R)-salmeterol employing an asymmetric Henry reaction as the key step

A practical synthesis of ( R)-salmeterol has been accomplished from 3-bromo salicylaldehyde, which involved a Cu(II)–sparteine complex catalyzed asymmetric Henry reaction as the key step. ( R)-Salmeterol can be obtained in 39% overall yield and 95% ee.

Pentacoordinated copper–sparteine complexes with chelating nitrite or nitrate ligand: Synthesis and catalytic aspects

Copper(II)–sparteine complexes, [CuII{(-)Sp}(NO2)Cl] (1) and [CuII{(−)Sp}(NO3)Cl] (2) (Sp=sparteine) with chelating nitrite and nitrate ligands, respectively, have been synthesized and structurally characterized. The penta-coordinated 1 or 2 exhibits distorted square pyramidal geometry and shows characteristic EPR spectra with g||: 2.27 and g⊥: 2.06. 1 and 2 behave similarly towards the catalytic epoxidation of alkenes as well as oxidation of alcohols. Though the epoxidation of cyclohexene using 1 or 2 as a catalyst and tertiarybutyl hydroperoxide (TBHP) as an oxidant at 298K in acetonitrile results in 100% cyclohexene oxide product, under identical reaction conditions styrene selectively transforms to benzaldehyde (∼90%) instead of any styrene oxide. However, at higher temperature (353K) the selectivity of cyclohexene to corresponding epoxide formation decreases appreciably and additional products, cyclohexanol and cyclohexanone are formed. Furthermore, 1 or 2 effectively catalyzes the oxidation of benzyl alcohol to benzoic acid and cyclohexanol to cyclohexanone in presence of molecular oxygen (O2) as an oxidant at 353K in acetonitrile.

ChemInform Abstract: Sparteine Complexes of Lithiated Primary O-2-Alkenyl Carbamates Stereochemistry of the Lithium-Titanium Exchange and Application for the Synthesis of Enantiomerically Enriched γ-Lactones.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Characterization of a rhodium-sparteine complex, [((−)-sparteine)Rh(η4-COD)]+: Crystal structure and DNMR/DFT studies on ligand-rotation dynamics

A cationic rhodium-sparteine complex, [((-)-sparteine)Rh(eta(4)-COD)](+) (1(+); COD = 1,5-cyclooctadiene) was obtained, isolated as its tetrafluoroborate salt (1BF(4)), and characterized using X-ray crystallography and multinuclear ((1)H, (13)C) NMR spectroscopy. This is the first structurally characterized sparteine complex of rhodium. The Rh-N bonds are unusually long (2.214(3) and 2.242(3) A), apparently due to steric repulsion between COD and sparteine. (1)H NMR exchange experiments (EXSY) demonstrate a dynamic process that results in an overall 180 degrees rotation of the COD methine protons in solution (CD(2)Cl(2)) with a first-order rate constant of 460 s(-1) at the coalescence temperature (314 K) and interpolated rate constant of 150 s(-1) at 298 K. Temperature-dependent NMR studies yield DeltaH(++) = 13.0 +/- 0.3 kcal mol(-1), DeltaS(++) = -5 +/- 1 cal mol(-1) K(-1), such that DeltaG(298)(++) = 14.3 +/- 0.3 kcal mol(-1). DFT studies (B3LYP) indicate that the loosely bound (-)-sparteine ligand rotates through a pseudo-tetrahedral transition state where both ligands are rotated approximately 90 degrees relative to each other. While both ligands remain bound (eta(4)-COD, kappa(2)-sparteine), bonding to sparteine is weakened much more than bonding to COD in the transition state. DFT computed DeltaG(298)(++) and DeltaS(++) values (15.55 kcal mol(-1) and -2.67 cal mol(-1) K(-1), respectively) agree very well with the experimental values. Attempts to find alternative mechanisms involving partial dechelation of COD and (-)-sparteine yielded slightly higher barriers along with positive DeltaS values for intermediate formation.

Time-Resolved Chiral Vibrational Spectroscopy

Advances in infrared laser technology and detection sensitivity have made time-resolved chiral vibrational spectroscopy experimentally feasible. Here we describe our recent efforts in detecting, for the first time, transient vibrational circular dichroism (VCD) signals with picosecond time resolution. The absorption changes of the cobalt (?)-sparteine complex Co(sp)Cl2 after visible excitation of a d-d excited state was probed in the CH-stretch region by alternating left- and right-handed circular polarized mid IR laser pulses. VCD spectra can be sensitive reporters of peptide and protein secondary structure or the absolute configuration of chiral organic compounds in solution. Recent developments are presented, which may in the future allow us to access this information in the course of fast chemical reactions.

Variety of polymorphic forms contrasted with uniform crystal packing in sparteine ML 2 complexes: Crystal structure, spectroscopic and magnetic properties of (−)-α-isosparteine and (−)-sparteine complexes with CuBr 2

This paper reports the synthesis, thermogravimetric and magnetic measurements for (−)-α-isosparteine CuBr 2 complex ( 1) and the existence of the fourth polymorph ( 2) of (−)-sparteine CuBr 2 complex. The two CuBr 2 complexes have been structurally characterized by X-ray crystallography. A diverse supramolecular aggregation of (−)-sparteine CuBr 2 complex has been contrasted with strong tendency for isostructuralism observed in a series of ML 2 complexes (M = metal, L = halogen or pseudohalogen) with both sparteine ( 3) and α-isosparteine ( 4). The incidence of polymorphism in a group of compounds which readily form the isomorphic series is quite unusual. Moreover, the reported crystal structure of 2 constitutes the first example showing that the organization of metal complexes of sparteine isomers into similar packing architecture is possible, although in general configurational changes within the sparteine ligand differentiate packing of otherwise similar (−)-sparteine-ML 2 or (−)-α-isosparteine-ML 2 molecules.

Influence of 2-methyl substitution on the geometry and complexing ability of sparteine: Packing of chiral vs. racemic building blocks

2-Methylsparteine ( 1) and its complexes with ZnL 2 of the general formula [(C 16H 28N 2)ZnL 2] [L = CN − ( 2), Br − ( 3), CH 3COO − ( 4), C 4 H 5 O 2 - ( 5)] have been prepared and the 1:1 (metal:alkaloid) stoichiometry was confirmed by elemental analysis. The complexes have been characterised by IR and NMR spectroscopy. Crystal structures are reported for racemic compounds 1, 2 and 3, and compared with the structures of chiral (–)-sparteine analogues. For the sake of comparison, synthesis and crystal structure of 1:1 (–)-sparteine complex with Zn(CN) 2 ( 6) is also reported. The crystal structures of 2, 3 and 6 reveal the zinc center four coordinated by two nitrogen atoms from the alkaloid and two halides or cyanide groups in the form of distorted tetrahedral. Comparison with the crystal structure of 1 reveals that coordination to metal center in 2 and 3 brings about an inversion at the N16 nitrogen and consequent change in configuration at the ring junction from trans to cis, accompanied by a change in the C-ring conformation from boat to chair. The racemic crystals of 2 and 3 display only moderate packing similarity, but 3 exhibits very similar supramolecular architecture to that of the previously reported chiral C 16H 28N 2ZnCl 2, albeit in space groups P 1 ¯ and P2 1, respectively. Packing of 2-methylsparteine ZnL 2 metal complexes in racemic crystals is more efficient and diverse than in chiral crystals of the analogous (–)-sparteine and α-sparteine complexes which, in turn, tend to form an isomorphic series.

Configurationally Labile Lithiated O -Benzyl Carbamates: Application in Asymmetric Synthesis and Quantum Chemical Investigations on the Equilibrium of Diastereomers

The absolute configuration of the lithium atoms in the epimeric (−)-sparteine complexes were assigned incorrectly. The correct absolute configuration of the lithium atoms within the energetically favored pair of complexes is S for both the (−)-sparteine complexes 14⋅11 and 20⋅11. The statements in which the absolute configuration of lithium is explicitly mentioned in the paragraph beginning “At first glance, the quantitative description…︁” on page 82 should read: “In the four diastereomeric complexes of 14⋅11, the pair of diastereomers with an S-configured lithium cation is energetically strongly favored, thus ruling out the pair of RLi-configured complexes. …︁ Again, one pair of diastereomers (SLi-configured) is clearly favored. Here, the SLi,RC-configured complex is favored.” The absolute configurations of the lithium atoms in Figure 2 and in the Supporting Information and the absolute configurations of the benzylic carbon atoms in Figure 2 are wrong. The correct assignments in Figure 2, from top down, are: (SLi,RC) 14⋅11 (SLi,SC), (SLi,RC) 20⋅11 (SLi,SC), (RC) 14⋅12 b (SC), (RC) 20⋅12 b (SC). The conclusions drawn remain valid.

NMR and X-ray characterization of a platinum(II) complex with (−)sparteine

A platinum(II) complex containing the diamine (−)sparteine has been synthesized for the first time and fully characterized by 1H and 13C NMR spectroscopy and X-ray crystallography. (−)Sparteine is an alkaloid containing four fused rings and four asymmetric centers of configurations 6R, 7S, 9S, and 11S at the four tertiary carbon atoms. In the cis conformation it can act as a chelating N-donor ligand toward a metal ion. The steric bulkiness of this ligand is such that the Pt–N bond lengths are greater than normal and the angle between the cis-chlorido ligands is well below the theoretical value of 90°. This sparteine complex of platinum appears to be an ideal substrate for investigating the stereochemistry of adducts with nucleotides and DNA. For instance the orientation of a coordinated nucleobase can be determined with precision by monitoring the strength of NOE cross peaks between the sparteine protons pointing toward the metal center and key protons of the coordinated nucleobase(s) (e.g. H8 protons of guanine or adenine).

Preparation of a Carboxylate-binding Mononuclear Iron(II) (−)-Sparteine Complex with Structural Distortion and Its Reaction with Oxidants

Abstract A novel iron complex with a distorted coordination geometry, [FeII((−)-sp)(OBz)2] (1) ((−)-sp = (−)-sparteine, OBz = benzoate anion), was prepared and structurally characterized by X-ray analysis. The stoichiometric reaction of 1 and mCPBA (m-chloroperbenzoic acid) degraded EtCN to CN− and CH3CHO. In CH2Cl2, a very short-lived intermediate species was generated, exhibiting an intense absorption band at 420 nm (ε ≈ 2000 M−1·cm−1) and a weak absorption band at 870 nm (ε ≈ 100 M−1·cm−1).

Asymmetric Deprotonation with Alkyllithium‐(‐)‐sparteine

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New Chiral Amine Ligands in the Desymmetrization of Prochiral Phosphine Boranes.

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Epoxydisilanes by Direct Double Silylation of Terminal Epoxides.

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New chiral amine ligands in the desymmetrization of prochiral phosphine boranes

P-chirogenic phosphine ligands can be prepared via desymmetrization of prochiral phosphine boranes using s-BuLi·(−)-sparteine complexes. One limitation of this method, however, has been that (+)-sparteine is not easily accessible. Herein, we show that derivatives of another alkaloid, (−)-cytisine, are useful surrogates for (+)-sparteine in the desymmetrization of prochiral phenyl-, cyclohexyl- and tert-butyl dimethyl phosphine boranes, yielding chiral phosphine boranes in up to 92% ee. Other chiral diamines were also tested but did not give as high enantioselectivity as the (−)-cytisine derivatives.

Anionic Polymerization of Novel Styrene Derivatives Bearing Various Amino Groups at ortho-Position

The novel styrene derivatives bearing various amino groups at ortho-position, 2-(1-indolinyl)methylstyrene (2), 2-(9-carbazolyl)methylstyrene (3), 2-(N,N-diphenylamino)methylstyrene (4), 2-(N-3-methoxyphenyl-N-phenylamino)methylstyrene (5), and 2-(N-3-methylphenyl-N-phenylamino)methylstyrene (6), were synthesized and polymerized with radical and anionic initiations. As the bulkiness of the substituents at the ortho-position increased, the polymerizabilities of these monomers during the radical and anionic methods significantly decreased. The anionic polymerization of 4–6 with the n-butyllithium (−)-sparteine complex in toluene at 0 °C afforded the optically active polymers ([α]25365 +48° to +22°), whereas no optical activity was observed for the polymers of 2 and 3 obtained under the same conditions. The optically active polymers likely have a chiral helical conformation which is related to a high stereoregularity.

Epoxydisilanes by Direct Double Silylation of Terminal Epoxides

Terminal epoxides 2 are converted to epoxydisilanes 1 in a one-pot procedure in hexane at low temperatures, by using successive additions of Me3SiCl and s-BuLi-(-)-sparteine complex.

Synthesis, Characterization, and Structure of Metal(II) (-)-Sparteine Complexes Containing Acetate Ligands

The complexes [Co(C15H26N2)(C2H3O2)2] (1), [Ni(C15H26N2)(C2H3O2)2] (2), [Cu(C15H26N2)(C2H3O2)2] (3) and [Zn(C15H26N2)(C2H3O2)2] (4) were prepared from reaction of (−)-sparteine with the corresponding metal(II) acetates in ethanol at stoichiometric ligand to metal ratios. The complexes were characterized by UV-Vis and IR spectroscopies, and magnetic susceptibility measurements. The solid-state structures of 1, 2 and 4 have been determined by X-ray crystallography. The Complexes 1 and 2 display a pseudo-octahedral structure around the metal center, where two acetate ligands coordinate to the metal center in a bidentate fashion, whereas the metal centers in 3 and 4 adopt a pseudo-tetrahedral structure and two acetate ligands in these complexes coordinate to the metal center in a monodentate fashion. The whole set of prepared complexes has been used for comparative structural and spectroscopic studies.

ChemInform Abstract: Synthesis of Enantiomerically Enriched β‐Amino Alcohol Derivatives via Asymmetric Lithiation of O‐Benzyl Carbamates—Imine Addition Using (‐)‐Sparteine Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.