Nickel-catalyzed asymmetric reductive cross-coupling of α-chloroesters with (hetero)aryl iodides

An asymmetric reductive cross-coupling of α-chloroesters and (hetero)aryl iodides is reported. This nickel-catalyzed reaction proceeds with a chiral BiOX ligand under mild conditions, affording α-arylesters in good yields and enantioselectivities. The reaction is tolerant of a variety of functional groups, and the resulting products can be converted to pharmaceutically-relevant chiral building blocks. A multivariate linear regression model was developed to quantitatively relate the influence of the α-chloroester substrate and ligand on enantioselectivity.

A Ni-catalyzed enantioselective reductive cross-coupling of α-chloroesters and (hetero)aryl iodides is reported. A MLR model was developed to quantitatively relate the influence of the α-chloroester substrate and ligand on enantioselectivity.     

Structural, spectroscopic, and electrochemical studies of the complexes [Ni2(mu-CNR)(CNR)2(mu-dppm)2](n+) (n = 0, 1, 2): unusual examples of nickel(0)-nickel(I) and nickel(0)-nickel(II) mixed valency

Reaction of Ni(COD)(2) (COD = cyclooctadiene) with dppm (dppm = bis(diphenylphosphino) methane) followed by addition of alkyl or aryl isocyanides yields the class of nickel(0) dimers Ni(2)(mu-CNR)(CNR)(2)(mu-dppm)(2) (R = CH(3) (1), n-C(4)H(9) (2), CH(2)C(6)H(5) (3), i-C(3)H(7) (4), C(6)H(11) (5), t-C(4)H(9) (6), p-IC(6)H(4) (7), 2,6-(CH(3))(2)C(6)H(3) (8)). The cyclic voltammograms of the dimers exhibit two sequential single electron oxidations to the +1 and +2 forms. Specular reflectance infrared spectroelectrochemical (IRSEC) measurements demonstrate reversible interconversions between the neutral Ni(0) dimers and their +1 and +2 forms. Bulk samples of the +2 forms are prepared by chemical oxidation using [FeCp(2)][PF(6)], while the +1 forms are prepared by the comproportionation of neutral and +2 forms. The neutral complexes 6 and 8 were characterized by X-ray diffraction as symmetric, locally tetrahedral binuclear Ni(0) complexes. The +2 forms of these complexes, 6(2+) and 8(2+), have asymmetric structures with one locally square planar and one locally tetrahedral metal center, evidence for a Ni(II)-Ni(0) mixed valence state. The X-ray structural characterization of 6(+) is symmetrical and qualitatively similar to that of the neutral complex 6. The +1 forms all exhibit intense near IR electronic absorptions that are assigned as intervalence charge transfer (IVCT) bands. On the basis of structural, spectroscopic, and electrochemical data, the +1 forms of the complexes, 1(+)-8(+), are assigned as Robin-Day class III, fully delocalized Ni(+0.5)-Ni(+0.5) mixed valence complexes.     

Chiral Recognition of Amino Acid Esters in Organic Solvents Using a Glucose-Based Receptor

Due to the chemical and biological relevance of amino acids, efficient methods for the recognition and separation of their enantiomers are highly sought after. Chiral receptors based on extended molecular scaffolds are typically employed for this purpose. These receptors are often effective only in specific environments and towards a narrow scope of amino acid guests. Recently we reported a simple, glucose-based macrocycle capable of enantioselective binding of a broad range of amino acid methyl esters in water. Herein we demonstrate that the same receptor can be used for chiral recognition of amino acid esters in organic solvents. We show that the binding affinity and selectivity of the receptor are highly dependent on the coordinating strength of the solvent. An in-depth analysis of the receptor’s conformation and its interactions with amino acid methyl esters allowed us to propose a binding mode of amino acids to the receptor in CDCl₃. The binding modes in CDCl₃ and D₂O were then compared, highlighting the main interactions responsible for binding affinity and selectivity in each solvent. We envision that the insight provided by this study will facilitate the development of further amino acid receptors based on monosaccharides with improved binding affinities and both enantio- as well as chemoselectivities.     

Structure of the amodiaquine-FPIX mu oxo dimer solution complex at atomic resolution

Using NMR inversion recovery experiments and XPLOR distance restraint calculations, we recently deduced the structure of ferriprotoporphyrin IX (FPIX) heme mu oxo dimer-antimalarial drug complexes for chloroquine (CQ), quinine (QN), and quinidine (QD) at atomic resolution [A. Leed et al., Biochemistry 2002, 41, 10245-55]. Using similar methods, we now report an unexpected structure for the complex formed between FPIX and the related drug amodiaquine (AQ). The deduced structure is further supported by comparing AQ chemical-shift data to restricted Hartree-Fock calculations. The structure further highlights the critical nature of quinoline drug side-chain composition in stabilizing noncovalent association to FPIX. Heme Fe-AQ proton distances are longer, relative to those of the CQ complex, and the AQ aromatic side chain seems to have a significant role in stabilizing the complex. Relative to the FPIX-CQ complex, a similar 2:1 stoichiometry was determined for the AQ complex, in contrast to a 4:1 stoichiometry previously suggested from calorimetry data. These solution structures add to our rapidly growing understanding of the mechanism of quinoline antimalarial drug action and will help elucidate the mechanism(s) of quinoline antimalarial drug resistance phenomena.     

Lariat ether alcohols based on dibenzo‐16‐crown‐5

Synthetic routes to forty‐four dibenzocrown ether alcohols are reported. The new crown ether com pounds are based on a sym‐dibenzo‐16‐crown‐5 platform. Most have a hydroxy group and an alkyl, aryl, aralkyl, alkenyl, alkynyl, or perfluoroalkyl group on the central carbon of the three‐carbon bridge. Others have substituted benzene rings and either a hydroxy or ‐O(CH₂)_nOH group attached to the central carbon of the three‐carbon bridge.     

Local dynamics of intersections: V. I. Arnold’s theorem revisited

V. I. Arnold proved in 1993 that the intersection multiplicity between two germs of analytic subvarieties at a fixed point of a holomorphic invertible self-map remains bounded when one of the germs is dragged by iterations of the self-map. The proof is based on the Skolem-Mahler-Lech theorem on zeros in recurrent sequences. We give a different proof, based on the Noetherianity of certain algebras, which allows one to generalize Arnold’s theorem for local actions of arbitrary finitely generated commutative groups, with both discrete and infinitesimal generators. Simple examples show that for non-commutative groups the analogous assertion fails.     

Intracavity laser absorption spectroscopy of platinum fluoride, PtF

Two vibrational bands of an electronic transition of PtF occurring at 11 940 cm⁻¹ and 12 496 cm⁻¹ were recorded and analyzed. These transitions are identified as the (0,0) and (1,0) bands of an [11.9] Ω = 3/2 − XΩ = 3/2 electronic transition. Gas phase PtF was produced in a copper hollow cathode lined with platinum foil using a trace amount of SF₆, and the spectrum was recorded at Doppler resolution by intracavity laser absorption spectroscopy. This work represents the first published spectroscopic data on PtF. Molecular constants for the ground and excited electronic states are presented.