Chiral biarylamido/anisole complexes of yttrium in enantioselective aminoalkene hydaroamination/cyclisation

A group of chiral, dibasic, biaryl-bridged amido proligands containing peripheral methoxyphenyl (anisole) ligation are developed for the synthesis of new amide complexes of yttrium and lanthanum. A potentially tetradentate bis(amidoanisole) system gives, on reaction with [Y[N(SiMe(2)H)(2)](3)(THF)] a crystallographically-characterised bis complex [Y(H)] presumably as a result of low steric demand, since a more bulky version gives the target [Y[N(SiMe(2)H)(2)](THF)]. The molecular structure of the latter reveals a similar cis-alpha structure to our recently reported Schiff-base analogue. Variable-temperature NMR studies are consistent with low rigidity in the molecular structure. A potentially tridentate, amidoanisolyl/amido proligand gives complexes [M[N(SiMe(2)H)(2)](THF)(n)](M = Y, n= 1; M = La, n= 2). Chiral non-racemic versions of the above complexes were tested in the hydroamination/cyclisation of 2,2'-dimethylaminopentane to the corresponding pyrrolidine. Activities were relatively low compared to recently reported examples, and ee values were in the range 20-40% despite the well-expressed chirality of the catalysts.     

Assessing the quality of absolute hydration free energies among CHARMM‐compatible ligand parameterization schemes

Multipurpose atom‐typer for CHARMM (MATCH), an atom‐typing toolset for molecular mechanics force fields, was recently developed in our laboratory. Here, we assess the ability of MATCH‐generated parameters and partial atomic charges to reproduce experimental absolute hydration free energies for a series of 457 small neutral molecules in GBMV2, Generalized Born with a smooth SWitching (GBSW), and fast analytical continuum treatment of solvation (FACTS) implicit solvent models. The quality of hydration free energies associated with small molecule parameters obtained from ParamChem, SwissParam, and Antechamber are compared. Given optimized surface tension coefficients for scaling the surface area term in the nonpolar contribution, these automated parameterization schemes with GBMV2 and GBSW demonstrate reasonable agreement with experimental hydration free energies (average unsigned errors of 0.9–1.5 kcal/mol and R² of 0.63–0.87). GBMV2 and GBSW consistently provide slightly more accurate estimates than FACTS, whereas Antechamber parameters yield marginally more accurate estimates than the current generation of MATCH, ParamChem, and SwissParam parameterization strategies. Modeling with MATCH libraries that are derived from different CHARMM topology and parameter files highlights the importance of having sufficient coverage of chemical space within the underlying databases of these automated schemes and the benefit of targeting specific functional groups for parameterization efforts to maximize both the breadth and the depth of the parameterized space. © 2013 Wiley Periodicals, Inc.     

Heterogeneously catalyzed oxidation of butanediols in base free aqueous media

The oxidation of four butanediols under base-free conditions has been investigated using a set of Au, Pd and Pt catalysts prepared using sol-immobilization. The supported nanoparticles are found to be active with bimetallic alloys having much higher activity when compared with the monometallic counterparts. In general the AuPt catalysts are the most active and in all cases the corresponding C4 oxidation products were observed with high selectivity; sequential reaction of these products leads to the formation of acetic acid as an undesired by-product.     

Conformational Dependence of Through‐Space Tellurium–Tellurium Spin–Spin Coupling in Peri‐Substituted Bis(Tellurides)

Three related series of peri‐substituted bis(tellurides) bearing naphthalene, acenaphthene and acenaphthylene backbones (Nap/Acenap/Aceyl(TeY)₂ (Nap=naphthalene‐1,8‐diyl N ; Acenap=acenaphthene‐5,6‐diyl A ; Aceyl=acenaphthylene‐5,6‐diyl Ay ; Y=Ph 1 ; Fp 2 ; Tol 3 ; An‐p­ 4 ; An‐o­ 5 ; Tp 6 ; Mes 7 ; Tip 8 ) have been synthesised and their solid‐state structures determined by X‐ray crystallography. Molecular conformations were classified as a function of the two C9‐C‐Te‐C(Y) dihedral angles (θ); in the solid all members adopt AB or CCt configurations, with larger Te(aryl) moieties exclusively imposing the CCt variant. Exceptionally large J(¹²⁵Te,¹²⁵Te) spin–spin coupling constants between 3289–3848 Hz were obtained for compounds substituted by bulky Te(aryl) groups, implying these species are locked in a CCt‐type conformation. In contrast, compounds incorporating smaller Te(aryl) moieties are predicted to be rather dynamic in solution and afford much smaller J values (2050–2676 Hz), characteristic of greater populations of AB conformers with lower couplings. This conformational dependence of through‐space coupling is supported by DFT calculations.     

Stereospecific synthesis of cis-2-alkenylcyclopropane carboxylic acids; A total synthesis of (±)-cis-chrysanthemic acid

A stereospecific route to $\text{cis}$-2,2-dimethyl-3-alkenyl-cyclopropanecarboxylic Acids is illustrated by a total synthesis of (±)-$\text{cis}$-Chrysanthemic Acid (11). The key step consists of an alicyclic Claisen rearrangement of $\text{O}$-silyl enolates derived from appropriately substituted ($\text{Z}$)-4-hexen-6-olides [e.g.(9)].     

X-ray studies on phospholipid bilayers. VI. Comparative hydration effects on oriented films

Oriented films of three diacylphosphatidylethanolamines containing 12, 14 and 16 methylene groups in their hydrocarbon chains and one 14 carbon chain lecithin were studied by X-ray fiber diffraction. Their molecular conformations, packing arrangement, crystallographic and physico-chemical parameters as a function of hydration were determined. Basically the four phospholipids exhibit a common bilayer structure. However, they also present some interesting differences which might be relevant to their biological functions.