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The preparation of a series of planar chiral, ferrocenyl-substituted hydrosilanes as precursors of ferrocene-stabilized silicon cations is described. These molecules also feature stereogenicity at the silicon atom. The generation and 29Si NMR spectroscopic characterization of the corresponding silicon cations is reported, and problems arising from interactions of the electron-deficient silicon atom and adjacent C(sp3)−H bonds or aromatic π donors are discussed. These issues are overcome by tethering another substituent at the silicon atom to the ferrocene backbone. The resulting annulation also imparts conformational rigidity and steric hindrance in such a way that the central chirality at the silicon atom is set with complete diastereocontrol. These chiral Lewis acid catalysts were then tested in difficult Diels-Alder reactions, but no enantioinduction was seen. [ABSTRACT FROM AUTHOR]

Phenanthroline-based hexadentate ligands L1 and L2 bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as LaIII, EuIII, TbIII, LuIII, and YIII metal ions, were synthesized, and the crystal structures of [ML1Cl3] (M=LaIII, EuIII, TbIII, LuIII, or YIII) complexes were determined. Solvent or water molecules act as coligands for the rare-earth metals in addition to halide anions. The big LnIII ion exhibits a coordination number (CN) of 10, whereas the corresponding EuIII, TbIII, LuIII, and YIII centers with smaller ionic radii show CN=9. Complexes of L2, namely [ML2Cl3] (M=EuIII, TbIII, LuIII, or YIII) ions could also be prepared. Only the complex of EuIII showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine-5′-triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine-5′-diphosphate (ADP) and adenosine-5′-monophosphate (AMP) was found. 31P NMR spectroscopic studies revealed the formation of a [EuL2(ATP)] coordination species. [ABSTRACT FROM AUTHOR]

The rapid and efficient construction of complex chiral bicyclic amines is possible using a novel alkene diamination reaction. Electrophilic iodinating agents promote the intramolecular anti-selective diamination of alkenes and allow the efficient synthesis of chiral amines such as trans-bipyrrolidines. [ABSTRACT FROM AUTHOR]

The development of planar-chiral hydrogen-bond donors based on the [2.2]paracyclophane scaffold is discussed. General strategies to access functionalized enantiopure [2.2]paracyclophane derivatives are briefly reviewed, with the focus on suitable precursors for the synthesis of planar-chiral thiourea derivatives. The synthesis of fourteen hydrogen-bond donors is described. The interaction of four thiourea derivatives with hydrogen-bond acceptors (DMSO and tetramethylammonium chloride) was investigated by 1H NMR spectroscopy and X-ray crystallography. A selection of enantiomerically pure planar-chiral derivatives was applied in asymmetric hydrogen-bond catalysis. [ABSTRACT FROM AUTHOR]

Abstract: The Rh(I)-catalyzed conjugate phosphinyl transfer from an Si–P reagent to an electron-deficient acceptor requires individual protocols for cyclic and acyclic α,β-unsaturated carbonyls and carboxyls. While 1,4-addition to cyclic acceptors is catalyzed by a Rh(I)–phosphine complex, a Rh(I)–carbene complex is needed to promote conjugate phosphination of acyclic acceptors. General procedures for both systems are reported. Aside from monophosphine-derived Si–P reagents as phosphinide sources, dppe- as well as dppp-derived reagent having two Si–P units do also participate in this reaction. The mechanism of this Rh(I)-catalyzed activation of the Si–P reagent is still under debate. Control experiments with enantiopure silicon-stereogenic and racemic phosphorus-stereogenic Si–P reagents support a catalysis commencing with transmetalation rather than oxidative addition. Preparation and full characterization data of the Si–P compounds used in this investigation is included. [Copyright &y& Elsevier]

Efficient selective synthetic pathways to the O-(tert-butyl)diphenylsilyl-protected 2-hydroxyferrocene carbaldehyde enantiomers [(p-S)-12 and (p-R)-12, each >99.5% ee] are described. The general synthesis starts from Kagan's ferrocene carbaldehyde acetal [(S,S)-6], bearing the (2S,4S)-[4-(methoxymethyl)-1, 3-dioxan-2-yl] chiral auxiliary. The synthetic route to (p-S)-12 involves a sequence of directed ortho-lithiation/iodination, followed by acetoxylation (Cu2O/acetic acid), saponification and protection by the TBDPS silyl-protective group. Acid-catalyzed hydrolysis of the chiral acetal then gave the O-TBDPS-protected (p-S)-configurated hydroxyferrocene carbaldehyde enantiomer in an overall yield of 76% over 4 steps. The (p-R)-12 enantiomer was prepared by a similar route starting from (S,S)-6 using the -SiMe3 group as a reversible blocking group to direct the required functionalization to the (p-R)-series. A total of six steps furnished (p-R)-12 in a combined yield of 27%. The aldehyde enantiomers of 12 were used for the synthesis of the corresponding N-2,6-diisopropylphenyl-imines. Subsequent deprotection gave the new "ferrocene-salimine" ligands 2-hydroxy-[N-(2,6-diisopropylphenyl) iminomethyl]-ferrocene (p-S)-2a and (p-R)-2a, respectively. We also synthesized the (p-S)-enantiomers of the corresponding N-mesityl and N-pentafluorophenyl aldimine derivatives [(p-S)-2b, (p-S)-2c]. [ABSTRACT FROM AUTHOR]

Herein, we report on a flexible strategy for the stereoselective construction of highly substituted tetrahydrofurochromene derivatives by Mukaiyama-type cyclizations of enantioenriched enol carbamates with O-protected salicylaldehydes. The chromenes are generated as pure diastereomers and under complete chirality transfer. [ABSTRACT FROM AUTHOR]

A synthetic protocol for optically pure (-)-menthylamine, (-)-8-methylmenthylamine, and the novel (-)-8-phenylmenthylamine is presented including a detailed characterization of these compounds and their isocyanates. Key words: amines; aminations; asymmetric synthesis; chirality; chiral auxiliaries. [ABSTRACT FROM AUTHOR]

Abstract: A five-step synthesis of the chiral building block cis-2 is described. Key steps in the synthesis were a Heck reaction of 1-bromo-2-iodobenzene with allyl alcohol, the introduction of a carboxy group after Br/Li-exchange, and the diastereoselective formation of the tricyclic oxazolidine system cis-2. Activation of cis-2 with TiCl4 led to formation of a carbenium ion, which was attacked by allyltrimethylsilane exclusively from the Re-face leading to the (3S)-configured 2-benzazepinone 8 in 65% yield. The configuration of the new stereogenic center was determined by X-ray crystal structure analysis, which is the basis for the proposed mechanism of this transformation. Enantiomerically pure 3-substituted 2-benzazepines represent interesting drug candidates. [Copyright &y& Elsevier]

Abstract: In a chiral-pool synthesis starting from d-mannono-1,4-lactone 1a, the four diastereomeric C-aryl furanosides (1S,4R)-4a, (1S,4S)-4b, (1R,4R)-4c, and (1R,4S)-4d were obtained in a stereocontrolled manner. The key steps of the synthetic pathway comprise a stereoselective reduction of the diastereomeric hemiketals (4R)-2a and (4S)-2b as well as a stereospecific cycloetherification of the resulting diols (1R,4R)-5a, (1S,4R)-5c, and (1S,4S)-5d. This ring closure which led to the desired C-glycosides was achieved by a Mitsunobu reaction or by preparing the 1-O-benzoyl-4-O-methylsulfonyl derivative 7 which was then treated with sodium methoxide. Final hydrolysis of the 5,6-O-isopropylidene protecting group led to the diastereomeric diols (1S,4R)-4a, (1S,4S)-4b, (1R,4R)-4c, and (1R,4S)-4d, representing versatile building blocks for further synthetic transformations. [Copyright &y& Elsevier]

Abstract: Condensation of the O-protected hydroxyferrocene carbaldehyde (Sp )-1 with suitable diamines, followed by liberation of the hydroxyferrocene moiety leads to a new type of ferrocene-based salen ligands (3). While the use of ethylenediamine in the condensation reaction yields the planar-chiral ethylene-bridged ligand [(Sp ,Sp )-3a], reaction with the enantiomers of trans-1,2-cyclohexylendiamine gives rise to the corresponding diastereomeric cyclohexylene-bridged systems [(S,S,Sp ,Sp )-3b and (R,R,Sp ,Sp )-3c], which feature a combination of a planar-chiral ferrocene unit with a centrochiral diamine backbone. Starting with the ferrocene-aldehyde derivative (Rp )-1, the enantiomeric ligand series (3d/e/f) is accessible via the same synthetic route. The (Sp )-series of these newly developed N2O2-type ligands was used for the construction of the corresponding mononuclear bis(isopropoxy)titanium (4a/b/c), methylaluminum (5a/b/c) and chloroaluminum-complexes (6a/b/c), which were isolated in good yields and identified by X-ray diffraction in several cases. The aluminum complexes (5/6) were successfully used in the Lewis-acid catalyzed addition of trimethylsilylcyanide to benzaldehyde, yielding the corresponding cyanohydrins in 45–62% enantiomeric excess. [Copyright &y& Elsevier]

The rate constant for phosphanylation of an aryl radical with trimethyistannyl diphenyiphosphane (Me3SnPPh2) has been measured as kphos ≈ 9 x 108 M-1 s-1. Aryl radicals derived from several axially chiral o-haloanilides are trapped by Me3SnPPh2 with complete retention of axial chirality as shown by oxidation of the phosphanes to give stable, easily analyzed phosphane oxides or sulfides. Double phosphanylations of o,o'-dihaloanilides followed by treatment with H2O2 or S8 in either order give enantiomers of a mixed diphosphane oxide sulfide. Chemodiver- gent trapping of diastereomers of an N-(cyclohex-2-enyl)anilide anilide is observed. For one isomer, the cyclization precedes the Me3SnPPh2 trapping, while for the other isomer direct trapping with Me3SnPPh2 supersedes the cyclization. The products are chiral triaryl phosphanes, oxides, and sulfides that are potentially interesting ligands in asymmetric catalysis. [ABSTRACT FROM AUTHOR]