A Synthesis of Fused Butenoudes

It has been shown that tert-butyldimethylsilylated (Z) 2-carboethoxymethylene cycloalkanols are readily desilylated with concomitant cyclization to give the corresponding butenolides. The (E) isomers are desilylated, but not cyclized under these conditions.     

Preparation of Trans-β-Acyl Cyclopentanols and Cyclohexanols

The utility of organoboranes in the synthesis of a wide variety of functional groups is now well established.¹ There have been, however, only a limited number of reports where an organoborane containing a β-functionalized carbon was utilized in organic synthesis. Part of the reason for this is the difficulty in preparing β-functional organoboranes and their tendency to undergo elimination under a variety of reaction conditions.² Those β-functionalized organoboranes utilized synthetically, which we could find in the literature are the β-ethoxy³, 1, and β-carboethoxyvinyl-boranes⁴, 2, of Zweifel and coworkers and the trans-β-tert-butyldimethylsilyloxy organoborane, 3, of Corey and Ravindranathan,⁵ who proposed this system as a potential precursor to prostanoids.     

Phase Transfer Promoted Ruthenium Oxide Oxidations of Carbohydrates II

ABSTRACT

The use of a phase transfer catalyst, benzyltriethylammonium chloride (BTEAC), is described in conjunction with the ruthenium dioxide/periodate : water/chloroform system for the oxidation of carbohydrate alcohols to the corresponding ketone, aldehyde, or carboxylic acid. The method was found to be applicable to carbohydrates appropriately protected as acetals, ethers, or containing a benzoyloxy group not positioned to readily undergo β-elimination. While the method was very suitable for the oxidation of carbohydrate secondary alcohols to ketones, it was found to be less suitable for the oxidation of a carbohydrate primary alcohol to the corresponding aldehyde or carboxylic acid. Evidence presented suggests that under the mildly basic conditions of the reaction, ruthenium tetraoxide is converted to ruthenate and perruthenate ions in the aqueous solution and then the perruthenate ion is carried by the phase transfer catalyst into the organic layer where oxidation of the substrate occurs. A number of examples illustrating the scope of the method are presented.     

Optical spectroscopic methods for intraoperative diagnosis

Molecular analytical methods are increasingly needed for a quick and reliable analysis of tissue in an operating room to provide more information during operations. In this Trends article, we highlight the current state and the developments of optical spectroscopic methods as intra operative tools. The clinical problem and challenges are illustrated on the example of brain tumor surgery. While fluorescence microscopy is already used, vibrational spectroscopy techniques will complement the standard method for brain tissue diagnostics. New portable instruments are currently available and can be stationed in the operating room for quick evaluation of tissue. The promise and limitations of fluorescence and vibrational spectroscopy as intraoperative tools are surveyed in this report.     

Subcentimeter depth resolution using a single-photon counting time-of-flight laser ranging system at 1550 nm wavelength

We demonstrate subcentimeter depth profiling at a stand off distance of 330 m using a time-of-flight approach based on time-correlated single-photon counting. For the first time to our knowledge, the photon-counting time-of-flight technique was demonstrated at a wavelength of 1550 nm using a superconducting nanowire single-photon detector. The performance achieved suggests that a system using superconducting detectors has the potential for low-light-level and eye-safe operation. The system's instrumental response was 70 ps full width at half-maximum, which meant that 1 cm surface-to-surface resolution could be achieved by locating the centroids of each return signal. A depth resolution of 4 mm was achieved by employing an optimized signal-processing algorithm based on a reversible jump Markov chain Monte Carlo method.     

Photochemical Transformations with Iodine Azide after Release from an Ion‐Exchange Resin

This report discloses the photochemical homolytic cleavage of iodine azide after its formation following release from polymer‐bound bisazido iodate(I) anions. A series of radical reactions are reported including the 1,2‐functionlization of alkenes and the unprecedented chemoselective oxidation of secondary alcohols in the presence of primary alcohols.     

Defect Structure in Te-doped GaAs Single Crystals after Plastic Deformation (II). Dislocation Slip and Cell Formation

At temperatures above the brittle-to-ductile transition (490 °C) in Te-doped GaAs three types of predominant defect configurations have been observed after uniaxial compression along a [001] direction: (i) twins and stacking faults (500 … 520 °C), (ii) slip zones of dislocations (≈550 °C) and (iii) dislocation cells (580 … 590 °C). In Part II quantitative details of the appearance of slip and cell formation are given. Leading segments of gliding half loops are mainly of 60° type. Cell walls were formed by multiple slip of perfect dislocations.     

Linear infrared dichroism by a double modulation technique

In the first part of this paper an experimental setup using Fourier-transform infrared spectroscopy (FTIR) in combination with a photoelastic modulator (PEM) for linear dichroism measurements is described. The second part shows the influence of PEM-amplitude and scan-velocity on the sensitivity of the instrument. The third part deals with the fringe-problem in the baselines of absorbance spectra and its influence on the determination of the linear dichroic ratio.     

Swelling and fractal heterogeneities in networks

In this paper we revisit old swelling data on polymer networks that have not been interpreted theoretically on a closed molecular basis. If the osmotic pressure of the swollen network is compared to the osmotic pressure of the corresponding uncrosslinked solution unsolved problems appear, when the relative osmotic pressure is plotted against the degree of swelling, i.e. the deformation due to swelling. A significant maximum appears which cannot be explained by any of the recently derived elastic models, such as junction constraint or other entanglement models. It is suggested in this paper that the maximum is a consequence of structural heterogeneities of fractal nature. If such fractal heterogeneities are assumed a strong maximum in the relative osmotic pressure can be reproduced. The physical reason is the different thermodynamic behavior of uncrosslinked linear chains and crosslinked self-similar (non-linear) polymers. The conclusion is supported by numerical (Monte Carlo) simulations.