4 6 R eferences
5.1 G eneral procedures
Proton (XH) and carbon (13C) nuclear magnetic resonance (NMR) spectra were recorded on a Varian Mercury 300 ( XH at 300 MHz, 13C at 75 MHz), Varian Inova 500 ( 3H at 500 MHz, 13C at 125 MHz) or Varian Inova 600 ( XH at 600 MHz, 13C at 150 MHz) spectrometer. Signals arising from the residual protio-forms of the solvent were used as the internal standards. Chemical shifts are recorded as 8 values in parts per million (ppm). The residual CHCI3 peak (8 7.26), the residual benzene peak (5 7.15) and the central residual acetone pentet peak (8 2.05) were used as references. *H NMR data are recorded as follows: chemical shift (8) (multiplicity, coupling constant(s) J (Hz), relative integral) where multiplicity is defined as: s=singlet, d=doublet, t=triplet, q=quartet, m=multiplet or combinations of the above. The central peak of the CDCI3 "triplet" (8 77.0), the central peak of the benzene-d6 "triplet" (8 128.0) and the central peak of the acetone-d6 "septet" (8 30.60) were used as references for proton-decoupled 13C NMR spectra. The data are given as: chemical shift (8) (protonicity), where protonicity is defined as: C=quaternary; CH = methine; CH2=methylene; CH3=methyl. The assignment of signals observed in various NMR spectra were often assisted by conducting an attached proton test (APT), gradient homonuclear (1H/1H) correlation spectroscopy (gCOSY), gradient heteronuclear ^H /^C ) correlation spectroscopy (gHSQC and gHMBC) or nuclear Overhauser effect (NOE) experiments.
Infrared (IR) spectra were measured on a Perkin-Elmer 1800 Series or Spectrum One FT-IR Spectrometer. A sample of the compound to be analysed was dissolved
86 C h a pte r 5
in CDCI3. In some cases a different solvent was used and this is indicated in brackets. A drop of the resulting solution was placed on a KBr disk and the solvent evaporated.
A VG Fisons AutoSpec three sector (E/B/E) double focussing mass spectrometer was used to obtain low and high-resolution electron impact (El) mass spectra. Low and high-resolution electrospray impact (ESI) mass spectra were obtained on a VG Quattro II triple quadrupole MS instrument operating in either positive or negative ionisation modes. Gas chromatography mass spectra (GC-MS) were obtained on an Agilent 5973N instrument. Low resolution mass spectral data are recorded as follows: m/z value (relative intensity as a percentage of the base peak).
Optical rotations were measured with a Perkin-Elmer 241 or 343 polarimeter at the sodium-D line (589 nm), and at the concentrations (c) (g/100 ml) and temperatures (T, °C) indicated. The measurements were carried out in a cell with a path length (I) 1 dm, using spectroscopic grade CHCI3 as solvent. Specific rotations [a]J were calculated using the equation [a]o = (100-a)/(c-l) and are given in 1 0 '1 deg cm2g '1.
Melting points (m.p.) were measured on a Reichert hot-stage microscope apparatus or a Stanford Research Systems Optimelt-Automated Melting Point System and are uncorrected.
Elemental analyses were performed by the Australian National University's Microanalytical Unit at the Research School of Chemistry, in Canberra.
High-pressure promoted reactions were carried out using a PSIKA Pressure Systems Ltd. 20 kbar Pressure Reaction System apparatus. A solution of the starting materials in dichloromethane was subjected to pressure contained in a Teflon® compressible reaction vessel.
Photochemical reactions were performed using a Philips 125 W HPL-N Hg arc lamp or an Ace Glass 450 W immersion lamp housed in a quartz water-cooled jacket. Analytical thin layer chromatography (TLC) was performed on glass backed silica gel 60 F254 plates as supplied by Merck. Eluted plates were visualised using a 254 nm UV lamp and/or by treatment with a phosphomolybdic acid dip made up of 37.5 g phosphomolybdic acid, 7.5 g ceric sulfate, 37.5 g cone, sulphuric acid and 720 ml water, followed by heating. Flash chromatography was conducted using the analytical grade solvents indicated and silica gel 60 (40-63 pm) as supplied by Carlo Erba Reagents.
Experimental Procedures 87
High-pressure liquid chromatography (HPLC) was carried out using a system that consists of a Waters 600 E quaternary solvent delivery system with inline degasser, a Rheodyne 7725i ejection valve (5-20 jil loops) and a Waters 2996 Photodiode Array Detector device. Peaks were detected using a UV lamp or a 2414 differential refractive index detector.
Starting materials and reagents were generally available from the Sigma-Aldrich, Merck, Alfa Aesar or Acros Chemical Companies and were used as supplied. Occasionally some liquids were distilled and solids recrystallised prior to use. C/s-1,2- dihydrocatechol 59 was provided by Questor, Queens University of Belfast, Northern Ireland (http://questor.qub.ac.uk/newsite/contact.htm). Similarly, 4-AcNH-TEMPO was supplied Professor T. Bobbitt, University of Connecticut, USA. The latter two reagents were used as supplied.
Drying agents and other inorganic salts were purchased from the AJAX, BDH or Unilab Chemical Companies. Solvents were either distilled in a still or obtained from a Glass Contour solvent purification system that is based upon a technology originally described by Grubbs e ta /.1 Spectroscopic grade solvents were used for all analyses.
In the cases were distilled solvents were used, THF and diethyl ether were distilled from sodium benzophenone ketyl. Methanol was distilled from its magnesium alkoxide salts. Benzene and toluene were distilled from sodium wire. Dichloromethane was distilled from calcium hydride.
Glassware was soaked and washed in a solution of Pyroneg® and water before being rinsed with water then acetone and oven-dried at 120°C. All moisture-sensitive reactions were conducted in a system that was evacuated and flushed three times with dry nitrogen or argon prior to use. Manipulations under protective gas occurred using standard Schlenk techniques. Reaction temperatures above 18°C refer to the external oil bath temperatures.
88 C h a p te r 5