Facile Borylation of Alkenes,Alkynes, Imines,Arenes and Heteroarenes with N-Heterocyclic Carbene-Boranes and a Heterogeneous Semiconductor Photocatalyst

Although the development of radical chain and photocatalytic borylation reactions using N-heterocyclic carbene (NHC)-borane as boron source is remarkable, the persistent problems, including the use of hazardous and high-energy radical initiators or the recyclability and photostability issues of soluble homogeneous photocatalysts, still leave great room for further development in a sustainable manner. Herein, we report a conceptually different approach toward highly functionalized organoborane synthesis by using recoverable ultrathin cadmium sulfide (CdS) nanosheets as a heterogeneous photocatalyst, and a general and mild borylation platform that enables regioselective borylation of a wide variety of alkenes (arylethenes, trifluoromethylalkenes, α,β-unsaturated carbonyl compounds and nitriles), alkynes, imines and electron-poor aromatic rings with NHC-borane as boryl radical precursor. Mechanistic studies and density functional theory (DFT) calculations reveal that both photogenerated electrons and holes on the CdS fully perform their own roles, thereby resulting in enhancement of photocatalytic activity and stability of CdS.     

Quantum invariant families of matrices in free probability

We consider (self-adjoint) families of infinite matrices of noncommutative random variables such that the joint distribution of their entries is invariant under conjugation by a free quantum group. For the free orthogonal and hyperoctahedral groups, we obtain complete characterizations of the invariant families in terms of an operator-valued R-cyclicity condition. This is a surprising contrast with the Aldous-Hoover characterization of jointly exchangeable arrays.     

A short synthesis of bicyclic dipeptides corresponding to Xxx-L-Pro Xxx-D-Pro having constrained trans-proline amides

[formula: see text] A short synthesis that generates two isomeric bicyclic dipeptides having constrained, trans-proline amide bonds has been developed. One of these bicyclic dipeptides corresponds to an Xxx-L-Pro dipeptide (4), while the other isomer corresponds to an Xxx-D-Pro dipeptide (5). The two isomers are readily distinguished by their 1H NMR spectra.     

Coulometric titration of some phenolic steroids with bromine based on thin-layer hydrodynamic biamperometric end-point detection

Four phenolic steroids were titrated coulometrically with bromine in a methanol—water solvent containing hydrochloric acid and sodium bromide. End-point detection was achieved with a twin electrode thin-layer cell placed in a flow loop connected to the titration vessel. Linear-segmented biamperometric titration curves were recorded. Concentrations of 17-β-estradiol were determined in the range from 442 ppb to 8.84 ppm with relative inaccuracies of -1.3% and +2.2%, respectively. Part-per-million solutions of estrone and estriol were titrated with good accuracy and precision. Somewhat poorer precision and accuracy was found for the determination of 17-α-ethynyl estradiol.     

Resolution of 1-(2-naphthyl)ethanol by a combination of an enzyme-catalyzed kinetic resolution with a fluorous triphasic separative reaction

[reaction: see text] Kinetic resolution of a fluorous ester rac-1 with Candida antarctica B lipase provided a mixture of enantioenriched alcohol (R)-2 and fluorous ester (S)-1. The mixture was subjected to a fluorous triphasic reaction to give both enantiomers of 1-(2-naphthyl)ethanol 2 in high ee without chromatographic separation or fluorous-organic liquid-liquid extractive purification.     

Second generation fluorous DEAD reagents have expanded scope in the Mitsunobu reaction and retain convenient separation features

First generation fluorous DEAD reagent bis(perfluorohexylethyl)azo dicarboxylate (C(6)F(13)(CH(2))(2)O(2)CN=NCO(2)(CH(2))(2)C(6)F(13), F-DEAD-1) has been shown to underperform relative to diisopropylazodicarboxylate in difficult Mitsunobu reactions involving hindered alcohols or less acidic pronucleophiles (phenols). Two new second generation fluorous reagents bearing propylene spacers instead of the ethylene spacers show expanded reaction scope while retaining the easy fluorous separation features. Byproducts from "half fluorous" reagent perfluorooctylpropyl tert-butyl azo dicarboxylate (C(8)F(17)(CH(2))(3)O(2)CN=NCO2(t)Bu, F-DEAD-2) can be removed by fluorous flash chromatography, and byproducts from bis(perfluorohexylpropyl)azo dicarboxylate (C(6)F(13)(CH(2))(3)O(2)CN=NCO(2)(CH(2))(3)C(6)F(13), F-DEAD-3) can be removed by fluorous solid-phase extraction. The new reagents promise to provide general and complementary solutions for separation problems in Mitsunobu reactions without restricting reaction scope.     

Single-walled carbon nanotube purification, pelletization, and surfactant-assisted dispersion: a combined TEM and resonant micro-raman spectroscopy study

Resonant Raman spectroscopy and transmission electron microscopy were used to characterize the structural changes of three single-walled carbon nanotube samples processed with purification, pelletization, and surfactant-assisted dispersion. A two-stage purification process selectively removes metallic tubes as well as small-diameter ones, enriching large-diameter semiconducting tubes. Pelletizing reduces the intertube distance but greatly increases the intensity ratio of the D band to the G band. Single-walled nanotube (SWNT) bundle size decreases during ultrasonication dispersion aided by a surfactant. SWNT bundles composed of large-diameter tubes are prone to debundling.     

Bridged ring systems—XIII The synthesis of cycloheptene carboxylic acids

β-(2-Oxocyclopentyl)ethylaryl ketones are transformed under acid conditions via a 2-aryl-bicyclo[3.2.1]oct-2-en-8-one intermediate into a mixture of arylcycloheptene carboxylic acids. The scope and the mechanism of the reaction are both discussed.