Labile coodination dendrimers

Addition of anionic benzylsulfate dendrons to dynamic mixtures of Ag+ and triphosphine ligands results in the assembly of loosely-bonded cage-core dendrimers.     

Mechanisms of sulfanyl (RS) migrations: synthesis of heterocycles

Thiiranium (episulfonium) ions had been acknowledged as reaction intermediates for many years, but it was not until 1977 that Nicolaou demonstrated systematically that these reactive heterocyclic cations could be trapped by carboxylic acids to give lactones. In the years that followed this report, extensive research greatly extended the scope of this reaction, particularly with regard to the methods for generating thiiranium ions, the types of nucleophiles that are compatible with this reaction, and the selectivity involved in the cyclization reactions. For many years we have been using thiiranium ions for the synthesis of saturated heterocycles. Whereas Nicolaou's method relied on electrophilic sulfenylation of alkenes, we have generated thiiranium ions by displacement of a leaving group with neighboring-group participation by a sulfanyl group. Many of the examples we have reported are of cyclizations that are reversible and so where two (and in some cases more) products can result, the outcome of the reactions provides fundamental information about the relative stability of different heterocyclic ring systems. This Review will begin with a brief introduction to sulfanyl participation as a method for generating thiiranium (and thiolanium) ions, and will go on to explore the idea of using sulfanyl migrations in synthesis. Initially, emphasis will be placed on mechanisms of [1,2] sulfanyl migrations: we will look specifically at [1,2] sulfanyl migrations (usually PhS) with elimination, substitution, and cyclization. Emphasis will then shift to the factors that affect the outcome of cyclization reactions. In particular, we will cover cyclizations with hydroxy nucleophiles and examine situations in which there are more than one hydroxy nucleophile present. We will also examine cyclizations with other nucleophiles, namely amines and sulfides. After our discussion of [1,2] sulfanyl migrations, we will look very briefly at the scope of [1,4] sulfanyl participation, before finally drawing up some guidelines that (we hope) will help other organic chemists take advantage of the rearrangement reactions that the sulfanyl group has to offer.     

Real-time phase-resolved functional optical coherence tomography by use of optical Hilbert transformation

We have developed a novel real-time phase-resolved functional optical coherence tomography system that uses optical Hilbert transformation. When we use a resonant scanner in the reference arm of the interferometer, with an axial scanning speed of 4 kHz, the frame rate of both structural and Doppler blood-flow imaging with a size of 100 by 100 pixels is 10 Hz. The system has high sensitivity and a larger dynamic range for measuring the Doppler frequency shift that is due to moving red blood cells. Real-time images of in vivo blood flow in human skin obtained with this interferometer are presented.     

Imaging and quantifying transverse flow velocity with the Doppler bandwidth in a phase-resolved functional optical coherence tomography

The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved functional optical coherence tomography (F-OCT) was used to image the velocity component that is transverse to the optical probing beam. It was found that above a certain threshold level the Doppler bandwidth is a linear function of flow velocity and that the effective numerical aperture of the optical objective in the sample arm determines the slope of this dependence. The Doppler bandwidth permits accurate measurement of flow velocity without the need for precise determination of flow direction when the Doppler flow angle is within +/-15 degrees perpendicular to the probing beam. Such an approach extends the dynamic range of flow velocity measurements obtained with the phase-resolved F-OCT.     

The alkylation of an α,α'-dianion in a β-ketosulphone leading to the preparation of axial 2-substituted thiane-1,1-dioxides

The 1,3-dianion formed across the sulphone of a β- ketosulphone may be selectively dialkylated in a controlled way with an α, ω-difunctional electrophile to give a 2-ketothiane- 1,1-dioxide. Polar groups in the 2-position of thiane-1,1-dioxides preferentially adopt an axial orientation as shown by detailed nmr studies. In cyclic sulphones such conformational preferences, arising from polar rather than steric effects are rare.