Unusual selectivity of unprotected aziridines in palladium-catalyzed allylic amination enables facile preparation of branched aziridines

Functionalized branched aziridines can be prepared in high yields and with high levels of regioselectivity using unprotected aziridines as nitrogen sources in palladium-catalyzed allylic amination. High levels of enantioselectivity can be achieved with BINAP on palladium. This methodology allows for strategic placement of an aziridine-containing fragment within a complex molecule environment for further elaboration.     

Versatile solid-phase synthesis of secondary amines from alcohols. Development of an N-Boc-(o-nitrobenzene)sulfonamide linker

The development of a versatile amine releasing linker based on the modified o-nitrobenzene sulfonamide protective group is described. This new N-Boc-o-nitrobenzenesulfonamide (Boc-ONBS) linker enables the elaboration on resin of primary and secondary amines by sequential substitution of the sulfonamide moiety using the Mitsunobu reaction. A 16-member array of secondary and Boc protected primary amines was then prepared using this linker.     

Reactions of N-silylphosphoranimines with alcohols: synthesis and structure of cyclotriphosphazenes with nongeminal methyl and phenyl substituents

The reactions of Me(3)SiN=P(OR")RR'(R" = Ph, CH(2)CF(3); R, R' = Me, Ph) with alcohols were investigated. With nonequivalent amounts of CF(3)CH(2)OH, the reactions produced high yields of the cyclic phosphazene (Me(2)PN)(3) and both the cis and trans isomers of nongeminally substituted [(Ph)(Me)PN](3). The isomers of this new cyclic phosphazene were separated by column chromatography and characterized by NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. Crystals of the cis isomer 6a have a monoclinic crystal system, while the trans isomer 6b has a triclinic crystal system with two different molecules in an asymmetric unit. The bond lengths and bond angles are very similar to those of the simpler cyclic trimers (Me(2)PN)(3) and (Ph(2)PN)(3.) A likely pathway for the formation of these compounds is discussed.     

Sequencing and four-state minisatellite variant repeat mapping of the D1S7 locus (MS1) by fluorescence detection

Minisatellite variant repeat mapping by polymerase chain reaction (MVR-PCR) reveals an enormous degree of variation in the human minisatellite regions. The original approach involved the use of 32P-labelled probes to detect the MVR-PCR products generated. To date, the loci mapped include D1S8, D7S21 and D16S309. However, the most polymorphic locus, D1S7 (MS1), which has been used in forensic analysis, has presented technical difficulties, initially due to its short 9 bp repeats that are much shorter than any conventional primer sequences. This was overcome by using the method of "wrapping around" primers employing inosine at the redundancy position. The difficulty of cloning highly repetitive DNA was overcome by utilising specialised competent SURE cells. We report the cloning and sequencing of selected short MS1 alleles to determine the variety of repeat types. This survey revealed nine types, four of which represented greater than 80% of the sequenced repeats. The reported MVR-PCR system maps the MS1 locus for these four common repeat types by fluorescence detection.     

Capillary liquid chromatography with MS3 for the determination of enkephalins in microdialysis samples from the striatum of anesthetized and freely-moving rats

In vivo microdialysis sampling was coupled to capillary liquid chromatography (LC)/electrospray ionization quadrupole ion trap mass spectrometry (MS) to monitor [Met]enkephalin and [Leu]enkephalin in the striatum of anesthetized and freely-moving rats. The LC system utilized a high-pressure pump to load 2.5 microl samples and desalt the 25 microm i.d. by 2 cm long column in 12 min. Samples were eluted with a separate pump at approximately 100 nl min(-1). A rapid gradient effectively separated the endogenous neuropeptides in 4 min. A comparison was made for operating the mass spectrometer in the MS2 and MS3 modes for detection of the peptides. In standard solutions, the detection limits were similar at 1-2 pM (2-4 amol injected); however, the reproducibility was improved with MS3 as the relative standard deviation was <5% compared with 20% for MS2 for 60 pM samples. For dialysate solutions, reconstructed ion chromatograms and tandem mass spectra had much higher signal-to-noise ratios in the MS3 mode, resulting in more confident detection at in vivo concentrations. The method was successfully used to monitor the peptides under basal conditions and with stimulation of peptide secretion by infusion of elevated K+ concentration.     

Density-functional generalized-gradient and hybrid calculations of electromagnetic properties using Slater basis sets

In this paper we extend our density-functional theory calculations, with generalized gradient approximation and hybrid functionals, using Slater-type orbitals (STOs), to the determination of second-order molecular properties. The key to the entire methodology involves the fitting of all STO basis function products to an auxiliary STO basis, through the minimization of electron-repulsion integrals. The selected properties are (i) dipole polarizabilities, (ii) nuclear magnetic shielding constants, and (iii) nuclear spin-spin coupling constants. In all cases the one-electron integrals involving STOs were evaluated by quadrature. The implementation for (ii) involved some complexity because we used gauge-including atomic orbitals. The presence of two-electron integrals on the right-hand side of the coupled equations meant that the fitting procedure had to be implemented. For (iii) in the hybrid case, fitting procedures were again required for the exchange contributions. For each property we studied a number of small molecules. We first obtained an estimate of the basis set limit using Gaussian-type orbitals (GTOs). We then showed how it is possible to reproduce these values using a STO basis set. For (ii) a regular TZ2P quality STO basis was adequate; for (i) the addition of one set of diffuse functions (determined by Slater's rules) gave the required accuracy; for (iii) it was necessary to add a set of 1s functions, including one very tight function, to give the desired result. In summary, we show that it is possible to predict second-order molecular properties using STO basis sets with an accuracy comparable with large GTO basis sets. We did not encounter any major difficulties with either the selection of the bases or the implementation of the procedures. Although the energy code (especially in the hybrid case) may not be competitive with a regular GTO code, for properties we find that STOs are more attractive.     

Unexpected conversion of a polycyclic thiophene to a macrocyclic anhydride

Oxygenation of 2,5,9,12-tetra(tert-butyl)diacenaphtho[1,2-b:1′,2′-d]-thiophene (1, C₄₀H₄₄S) by peracids gave the cyclic sulfonic ester 4 (2,7,10,13-tetra(tert-butyl)diacenaphtho[1,2-c:1′,2′-e]oxathiin 5,5-dioxide, C₄₀H₄₄O₃S) which, when heated in nitrobenzene, is converted into a complex, macrocyclic anhydride 3 (C₈₀H₈₈O₃), which is derived from two molecules of 4. Further investigation found a likely intermediate in this reaction, 4,4′,7,7′-tetra(tert-butyl)-1,1′-biacenaphthylenylidene-2,2′-dione (5, C₄₀H₄₄O₂), apparently formed from 4 by additional oxidation. Anhydride 3 plausibly arises by Diels-Alder reaction of 4 and 5 followed by several ring fragmentations. The structures of 3, 4, and 5 were unambiguously established by X-ray crystallography.     

ETC and Thermal Ligand Substitution in PhCCo3(CO)9 with 2,3-Bis(diphenylphosphino)-N-phenylmaleimide(bppm). X-Ray Diffraction Structure of Co3(CO)6[μ2,η2, η1-C(Ph)(O)](μ2-PPh2)

The reactivity of the bidentate ligand 2,3-bis(diphenylphosphino)-N-phenylmaleimide (bppm) with the tetrahedrane cluster PhCCo₃(CO)₉ under thermolysis and ETC conditions has been studied and found to ultimately give Co₃(CO)₆[μ₂,η²,η¹-C(Ph) ${\text{C}}{\text{ = }}{\text{ = }}{\text{C(PPh}}_{\text{2}} {\text{)C(O)NPhC}}$ (O)](μ₂-PPh₂) as the final product. The intermediate cluster compound PhCCo₃(CO)₇(bppm), which was observed by IR and ³¹P NMR spectroscopies, readily and rapidly transforms into the product cluster under the reactions conditions. The solid-state structure of Co₃(CO)₆[μ₂,η²,η¹-C(Ph)fptt(O)](μ₂-PPh$_{2})$ was unequivocally determined by X-ray crystallography. Co₃(CO)₆[μ₂, η², η¹-C(Ph)Õ(O)](μ₂-PPh₂) crystallizes in the monoclinic space group P2(1)/n, a = 11.825(5) Å, b = 31.20(1) Å, c = 11.831(5) Å, β = 108.720(7)°, V = 4134(7) ų, Z = 4, d _calc = 1.567 Mg/m³; R = 0.0350, R _w = 0.0817 for 4747 observed reflections with I > 2σ(I). The X-ray structure confirms the coupling of the benzylidyne ligand with the bppm ligand in Co₃(CO)₆[μ₂,η²,η¹-C(Ph)Õ(O)](μ₂-PPh₂). The course of the thermolysis reaction is identical to those reactions carried out with the related diphosphine ligands bma and bpcd. The utility of electron-transfer catalysis (ETC) in the preparation of PhCCo₃(CO)₇(bppm) is discussed relative to the reduction potential of the bppm ligand and the tricobalt cluster PhCCo₃(CO)₉.     

Self-assembly of electron donor-acceptor dyads into ordered architectures in two and three dimensions: surface patterning and columnar "double cables"

We report the synthesis and characterization of covalent dyads and multiads of electron acceptors (A) and donors (D), with the purpose of exploiting their nanophase separation behavior toward (a) two-dimensional (2D) surface patterning with well-defined integrated arrays of dissimilar molecular electronic features and (b) bulk self-assembly to noncovalent columnar versions of the so-called "double cable" systems, the likes of which could eventually provide side-by-side percolation pathways for electrons and holes in solar cells. Soluble, alkylated hexa-peri-hexabenzocoronenes (HBCs) bearing tethered anthraquinones (AQs) are shown by scanning tunneling microscopy (STM) to self-assemble at the solution-graphite interface into either defect-rich polycrystalline monolayers or extended 2D crystalline domains, depending on the number of tethered AQs. In the bulk, the thermal stability of the room-temperature HBC columnar phase is increased, which is attributed to the desired nanotriphase separation of HBC columns, insulating alkyl sheaths, and AQ units. Homeotropic alignment (columns normal to surfaces), predicted to be ideal for potential exploitation of such "double cables" in photovoltaic devices, is demonstrated.     

Metallocene ethylene-1-octene copolymers: Influence of comonomer content on thermo-mechanical, rheological, and thermo-oxidative behaviours before and after melt processing in an internal mixer

The influence of the comonomer content in a series of metallocene-based ethylene-1-octene copolymers (m-LLDPE) on thermo-mechanical, rheological, and thermo-oxidative behaviours during melt processing were examined using a range of characterisation techniques. The amount of branching was calculated from ¹³C NMR and studies using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were employed to determine the effect of short chain branching (SCB, comonomer content) on thermal and mechanical characteristics of the polymer. The effect of melt processing at different temperatures on the thermo-oxidative behaviour of the polymers was investigated by examining the changes in rheological properties, using both melt flow and capillary rheometry, and the evolution of oxidation products during processing using infrared spectroscopy.The results show that the comonomer content and catalyst type greatly affect thermal, mechanical and oxidative behaviour of the polymers. For the metallocene polymer series, it was shown from both DSC and DMA that (i) crystallinity and melting temperatures decreased linearly with comonomer content, (ii) the intensity of the β-transition increased, and (iii) the position of the tan δ_max peak corresponding to the α-transition shifted to lower temperatures, with higher comonomer content. In contrast, a corresponding Ziegler polymer containing the same level of SCB as in one of the m-LLDPE polymers, showed different characteristics due to its more heterogeneous nature: higher elongational viscosity, and a double melting peak with broader intensity that occurred at higher temperature (from DSC endotherm) indicating a much broader short chain branch distribution.The thermo-oxidative behaviour of the polymers after melt processing was similarly influenced by the comonomer content. Rheological characteristics and changes in concentrations of carbonyl and the different unsaturated groups, particularly vinyl, vinylidene and trans-vinylene, during processing of m-LLDPE polymers, showed that polymers with lower levels of SCB gave rise to predominantly crosslinking reactions at all processing temperatures. By contrast, chain scission reactions at higher processing temperatures became more favoured in the higher comonomer-containing polymers. Compared to its metallocene analogue, the Ziegler polymer showed a much higher degree of crosslinking at all temperatures because of the high levels of vinyl unsaturation initially present.