Cyclooctatrienes from pyran-2-ones via a tandem [4 + 4]-photocycloaddition/decarboxylation process
Electronic Supporting Information General information. Reactions were carried out in oven-dried (110 °C ) or flame-dried glassware under argon atmosphere unless otherwise noted. Transfer of anhydrous solvents and reagents was accomplished with oven-dried syringes or cannulae. Solvents were distilled before use: methylene chloride from calcium hydride, tetrahydrofuran, diethylether and benzene from sodium/benzophenone ketyl, toluene from sodium metal. The 4-hydroxypyran-2-one starting materials
... ere prepared using literature procedures. 1 Irradiations were carried out using an Ace-Hanovia 450W medium pressure, quartz, mercury-vapor lamp in a quartz water cooled jacket. Reactions were carried out in a pyrex round bottom flask under argon after deoxygenation with a slow stream of argon for 10 min. The solution of the pyran-2-one substrate in a Pyrex vessel was clamped at a distance of 10 cm from the lamp, inside a light-proof enclosure. Thin layer chromatography (TLC) was performed on glass plates precoated with 0.25 mm Kieselgel 60 F 254 (Merck). Flash chromatography columns were packed with 230-400 mesh silica gel (Silicycle, Pharma grade). Proton nuclear magnetic resonance spectra ( 1 H NMR) were recorded at 400 MHz or 500 MHz and are reported (ppm) relative to the centerline of the triplet from chloroform-d (7.26 ppm). Coupling constants (J) are reported in Hertz (Hz). Carbon nuclear magnetic resonance spectra ( 13 C NMR) were recorded at 100 MHz or 125 MHz and are reported (ppm) relative to the centerline of the triplet from chloroform-d (77.23 ppm). Infrared (IR) spectra were measured with a Mattson Galaxy Series FT-IR 3000 spectrophotometer. Mass spectra were determined on a PerSeptive Biosystems Mariner high-resolution electrospray positive ion mode spectrometer or a Kratos Analytical MS-50G spectrometer.