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.     

TRIS (perfluoroalkylethyl)silyl alkyl amines as calibration standards for electron ionization mass spectrometry in the mass range of 100–3000 Da

A new fluorinated compound mixture has been developed for the calibration of the double focusing mass spectrometer in the mass range of 100–3000 Da in the positive electron ionization (EI) mode. Current calibration standards for EI have either limited mass range [perfluorotributylamine (PFTBA), perfluorokerosene (PFK), s-triazines (TRIS)] or poor peak intensities with significant chemical background in the instrument for several days (perfluoroalkyl phosphazine). The newly synthesized fluorinated silyl alkyl amines mixture is proposed as a reference/calibration standard for EI-MS. This standard produced abundant parent and fragment ions across the entire mass range without any memory effect.     

Radical and palladium-catalyzed cyclizations to cyclobutenes: an entry to the BCD ring system of penitrem D

A novel approach toward the synthesis of the BCD ring system of penitrem D is described. The strategy capitalizes on the fast cyclization rates of aryl radicals into cyclobutenes and allows access to a variety of fused tricyclic structures. Radical/polar crossover reactions of precursors 24-29 promoted by samarium diiodide in the presence of HMPA and acetone allow access to the fully functionalized BCD ring system of penitrem D. The stereochemical implications of these processes are evaluated, and a Pd-mediated cyclization approach toward the penitrems is also introduced.     

B and collider physics: Working group report

This report summarises the work done during WHEPP-6 (Institute of Mathematical Sciences, Chennai, India, Jan 3–15, 2000) in Working group on ‘B and collider physics’.