The extraordinary reactions of phenyldimethylsilyllithium with N,N-disubstituted amides

Phenyldimethylsilyllithium reacts with N,N-dimethylamides in a variety of ways, depending upon the stoichiometry, the temperature and, most subtly, on the structure of the amide, with quite small-seeming changes in structure leading to profound changes in the nature of the products. When equimolar amounts of the silyllithium reagent and N,N-dimethylamides 6 are combined in THF at -78 degrees C, and the mixture quenched at -78 degrees C, the product is the corresponding acylsilane . If the same mixture is warmed to -20 degrees C before quenching, the product is a cis enediamine 11. The enediamines are easily isomerised from cis to trans, easily oxidised to dienediamines , and, with more difficulty, hydrolysed to alpha-aminoketones 13. If two equivalents of the silyllithium reagent are used, the product is an alpha-silylamine 20. The mechanism of formation of the enediamines appears to be by way of a Brook rearrangement of the tetrahedral intermediate 17 followed by loss of a silanoxide ion to give a carbene or carbene-like species. The 'carbene' combines with the Brook-rearranging nucleophile to give an intermediate 28, which loses another silanoxide ion to give the enediamine. The same carbene can be attacked by a second equivalent of the silyllithium reagent to give the alpha-silylamine 20. Other nucleophiles, like alkyllithiums, phenyllithium, and tributylstannyllithium also trap the carbene to give products 48-52. The intermediate anions in these reactions, when benzylic, can be further trapped with alkylating agents to give the products 33, 34 and 53-55. In special cases, the anion formed by attack on the carbene can be trapped by intramolecular reactions displacing internal leaving groups, as in the formation of the enamine 37 and the cyclopentane 41, or attacking a carbonyl group, as in the formation of the indanone 61, or attacking a double or triple bond, as in the formation of the cyclopentanes 71 and 75. In another special case, the carbene reacts with vinyllithium to give an allyllithium intermediate 56, which selectively attacks another molecule of carbene to give eventually the gamma-aminoketone 58. Small changes in the structure of the amide lead to a variety of other pathways each of which is discussed in the text. Notably, each member of the homologous series of amides Ph(CH2)nCONMe2 gives rise to a substantially different product: when n= 0, the reaction is normal, and the yield of the alph]-silylamine 20e is high; when n=1, proton transfer in the intermediate anion 64 and displacement of the phenyl group leads to the silaindane 66; when n=2, fragmentation of the intermediate anion 80, and capture of the carbene by benzyllithium leads to the 1,4-diphenylbut-2-ylamine 83; and when n=3, proton transfer in the intermediate anion 67 and displacement of the phenyl group leads to the silacyclopentane 69.     

Biochemical data-processing with microcomputers : Part 3. On-line data acquisition from a continuous flow analyzer

A program, written in BASIC, is described which allows data acquisition from a continuous flow analyzer. The program was developed for a readily available microcomputer, but should be easily modified for use on similar machines. Once the peak height has been measured, the concentration of the analyte is calculated by reference to a previously defined calibration. The program is designed to handle data from more than one channel, although there is a practical limit of 3–4 simultaneously active channels. The results of the separate assays are collated and printed as a group for each specimen, even when the analytical methods require different times for completion.     

Supramolecular recognition forces: an examination of weak metal-metal interactions in host-guest formation

Molecular receptors consisting of two parallel-disposed terpy-M-Cl units (M = Pd2+, Pt2+) are used to form host-guest adducts with aromatic molecules and with neutral square-planar Pt2+ complexes. Host-guest formation is controlled by several factors including pi-pi interactions and, in some cases, weak Pt-Pt interactions between the host and the guest. This latter interaction was examined by comparing the host-guest stability of adducts formed by isoelectronic Pt2+ and Au3+ complexes with the Pt2+ receptor. Consistently, the former is more stable.     

Typing dinucleotide repeat loci using microplate array diagonal gel electrophoresis: proof of principle

Polymorphic dinucleotide repeat loci ('microsatellite markers') are found in varying abundance throughout the genomes of most organisms. They have been extensively used for genetic studies, but conventional techniques used for their genotyping require sophisticated equipment. Microplate array diagonal gel electrophoresis (MADGE) has previously been extended to economical high-throughput genotyping of trinucleotide and tetranucleotide microsatellite amplicons. However, the capability of this technique to resolve the alleles of dinucleotide repeat loci has not been explored previously. Here we show that a modified microsatellite-MADGE approach can provide sufficient resolution for dinucleotide repeat typing. This enables economical and convenient set up for analysis of single markers in many samples in parallel, suitable, for example, for population association studies.     

The formation of thioamide complexes of manganese,molybdenum and rhodium from organosilicon and organotin intermediates

The interaction of N-trimethylsilylthioacetanilide and N-phenyl-S-trimethyl- tinthioacetimidate, with carbonyl halides of molybdenum, manganese and rhodium afforded a range of N-phenylthioacetamido metal carbonyl complexes in which the group behaves as a chelating ligand, and also in two different ways as a bridging group in binuclear products.     

Preparation and structure of mixed tungsten bronzes containing tin and europium

An isothermal section has been established for the system Eu_xWO₃Sn_yWO₃ at 1000°C from X-ray powder and single-crystal data and Mössbauer spectroscopy and chemical analyses. A single-phase region with the (12 × 3) tetragonal structure has been established. Single-crystal X-ray analysis shows that the Sn and Eu occupy pentagonal tunnel sites. Mössbauer spectroscopy shows that both Sn(II) and Eu(II) are present. The extent of the single-phase field is controlled by two factors: First, the ratio $\text{Eu}\text{Sn}$ must be <1, and second, the supernumerary electron concentration per WO₃ must be <0.6.     

On partitioning the overlap charge density in self-consistent charge molecular-orbital calculations

Alternatives to the Mulliken method of partitioning the overlap charge density in self-consistent charge molecular-orbital calculations are examined. It is found that more realistic methods may lead to significantly different self-consistent charges, and different ordering of the electronic energy levels.     

Polymer science with transition metals and main group elements: Towards functional,supramolecular inorganic polymeric materials

Inorganic polymers are relatively unexplored because the efficient formation of macromolecular chains from atoms of transition metals and main group elements has presented a synthetic challenge. Nevertheless, these materials offer exciting opportunities for accessing properties that are significantly different from and which therefore complement those available with the well‐established organic systems. Inorganic block copolymers are of particular interest for the generation of functional, nanoscale supramolecular architectures and hierarchical assemblies using self‐assembly processes. This article focuses on research in my group over the past decade, which has targeted the development of new and controlled routes to inorganic polymers and their subsequent use in forming supramolecular materials as well as studies of their properties and applications. The use of ring‐opening polymerization (ROP) and transition‐metal‐catalyzed polycondensation approaches are illustrated. Controlled ROP procedures have been developed that allow access to polyferrocene block copolymers that self‐assemble into interesting nanoscopic architectures such as cylinders and superstructures such as flowers. The future prospects for inorganic polymer science are discussed, and a growing emphasis on the study of supramolecular inorganic polymeric materials is predicted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 179–191, 2002     

Cerebrosides from the Rhizomes of Gynura Japonica

Four new cerebrosides, gynuramides I?IV ( 1 ‐ 4 ), together with 37 known compounds were isolated from the rhizome of Gynura japonica. The structures of cerebrosides 1 ‐ 4 were determined by chemical and spectroscopic examination to be: (2S,3S,4R,8E)‐2‐[(R)‐2‐hydroxypentacosanoylamino]‐8‐en‐1,3,4‐octadecanetriol, (2S,3S,4R,8E)‐2‐[(R)‐2‐hydroxytetracosanoylamino]‐8‐en‐1,3,4‐octadecanetriol, (2S,3S,4R,8E)‐2‐[(R)‐2‐hydroxytricosanoylamino]‐8‐en‐1,3,4‐octadecanetriol, and (2S,3S,4R,8E)‐2‐[(R)‐2‐hydroxydocosanoylamino]‐8‐en‐1,3,4‐octadecanetriol.     

Incorporation of oxygen atoms into As+ implanted silicon during cw CO2 laser annealing in O2

By annealing Si layers amorphised by ion-implantation with a cw CO₂ laser beam in oxygen rich environments, it has been possible to incorporate O atoms into the recrystallized lattice. Absorption measurements on such regrown layers by infrared spectrometry have shown that the impurities are preferentially bonded into substitutional lattice sites, rather than existing interstitially. Supplementary RHEED studies have indicated thatβ-cristobalite, a crystalline form of SiO₂, has been formed. These investigations highlight the importance of the ambient during cw laser annealing.