All reactions requiring anhydrous conditions were carried out under an atmosphere of argon in flame-dried glassware. Syringes, needles and cannula were oven-dried. Materials: CH 2 Cl 2 , Et 2 O and toluene were distilled from CaH 2 under argon and stored over 3 Å MS. THF was distilled over sodium and benzophenone under an atmosphere of nitrogen. Petrol refers to the fraction that boils at 30-40 o C. PhLi (2.0 M in Bu 2 O) was obtained from Acros Organics ® . Chloromethyl pivalate was purchased

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... rom Sigma-Aldrich ® . Other starting materials were obtained commercially and used without further purification, unless stated otherwise. Chromatography: Thin layer chromatography (TLC) was performed on aluminium-backed plates pre-coated with silica (Merck 60 F 254 ). The plates were visualised by irradiation with UV light (254 nm) and by immersion in phosphomolybdic acid or KMnO 4 solutions, followed by heating. Purification of reaction products was carried out by flash chromatography using silica gel (35-70 µM) or neutral alumina. Chiral HPLC was performed using Dionex ASI-100 plus auto sampler. Optical rotations were recorded on a Perkin-Elmer 241 Polarimeter, with a path length of 10 cm in CHCl 3 . [α] D values are given in 10 -1 deg cm 2 g -1 . Concentrations (c) are given in grams per 100 cm 3 . IR spectra were recorded as thin films on NaCl plates using a Perkin-Elmer Paragon Fourier Transform spectrometer; abbreviations br, s, m, and w refer to broad, strong, medium and weak, respectively. NMR : 1 H NMR and 13 C NMR spectra were recorded in CDCl 3 using Brücker AVC500 spectrometer. Chemical shifts are reported in ppm and referenced to the residual CHCl 3 at  δ 7.27 for 1 H NMR spectra, and to the central line of CDCl 3 triplet at 77.0 for 13 C NMR spectra. Coupling constants (J) are given in Hz. The 13 C NMR peaks were assigned by standard methods using HSQC or DEPT experiments. E/Z Assignments were based on NOE studies. Mass Spectra: Low and high resolution mass spectra [MS(TOF Cl + )] were recorded on a Micromass GCT equipped with a reflectron TOF mass spectrometer operating at 60 eV (Flow rate (He) = 1 mL/min) and Brücker MicrOTOF II. Gas Chromatography: The reported E/Z ratios were determined by GC/MS analysis of crude reaction mixtures, using an Agilent HP-5 column (dimethylsilicone capillary column, 30 m x 0.32 mm x 0.25 µm), He, 1 mL/min (initial temperature = 80 o C, max. temperature = 280 o C; rate = 20 o C/min unless otherwise stated).