N-Acylsulfonamide safety-catch linkers are versatile tools in solid-phase organic synthesis because of their stability. This stability necessitates linker activation prior to compound cleavage. Here, we demonstrate that the N-acylsulfonamide group can react with a pi-allyl palladium complex and that these mild and neutral conditions can be exploited for linker activation. The advantages of this process are illustrated by its use in the efficient synthesis of thioesters. We anticipate that this activation method will extend the utility of the N-acylsulfonamide group. [reaction: see text]
ence of time on the solubility of silver selenide and telluride is illustrated by Table I.After boiling for 5 minutes, the ammonia content had decreased to 8.4% by weight with the concentrated solution, and 3% by weight with the 1:1 solution. Determinations of silver, selenium, and tellurium were made on the filtrate of the filtered samples. Silver was determined gravimetrically as chloride; selenium and tellurium were determined gravimetrically in the elemental state after precipitation by means of sulfur dioxide in accordance with the following procedures.
General methodsAll moisture-and oxygen-sensitive reactions were carried out in flame-dried glassware under nitrogen atmosphere, unless otherwise specified. All purchased materials were used without further purification, unless otherwise noted. Methylene chloride was distilled from calcium hydride, methanol was distilled from magnesium, and pyridine was distilled from sodium and anthracene. Tetrahydrofuran and toluene were distilled over sodium and benzophenone. All protected amino acids and 4-sulfamylbenzoyl NovaGel 3 (loading 0.62 mmol/g) were purchased from NovaBiochem.Analytical thin layer chromatography (TLC) was carried out on E. Merck (Darmstadt) TLC plates pre-coated with silica gel 60 F 254 (250 Å layer thickness). Analyte visualization was accomplished using an UV lamp and/or by charring with at least one of the following solutions: a p-anisaldehyde stain (18 mL p-anisaldehyde, 7.5 mL glacial acetic acid, 25 mL concentrated H 2 SO 4 , 675 mL absolute EtOH), ninhydrin stain (200 mg ninhydrin, 95 mL n-butanol, 5 mL 10% AcOH), or potassium permanganate stain (3 g KMnO 4 , 20 g K 2 CO 3 , 5 mL 5% aqueous NaOH, 300 mL H 2 O). Flash chromatography was performed on Scientific Adsorbents Incorporated silica gel (32-63 µM, 60 Å pore size) using distilled reagent grade hexanes and ACS grade ethyl acetate or methanol and chloroform. The term, "concentrated under reduced pressure" refers to the removal of solvents and other volatile materials using a rotary evaporator at water aspirator pressure (< 20 torr) while maintaining the water bath temperature below 40 °C. Residual solvent from such sample was removed at high vacuum (< 0.1 torr). The term, "high vacuum," refers to vacuum achieved by a mechanical belt-drive oil pump.1 H, 13 C, and 31 P nuclear magnetic resonance (NMR) spectra were recorded on Bruker AC-300 spectrometers, and chemical shifts are reported in parts per million relative to tetramethylsilane or a residual solvent peak (CHCl 3 : 1 H: δ 7.26, 13 C: δ 77.0). 1 H NMR data are assumed to be first order. Peak multiplicity is reported as: singlet (s), doublet (d), triplet (t), quartet (q), pentet (p), sixtet (s), multiplet (m), and broad (br). Mass spectrometry was performed on a Micromass LCT instrument.LC-MS (ESI) spectra were obtained using a Shimadzu LCMS-2010 (Columbia, MD) equipped with two pumps (LC-10Advp), controller (SCL-10Avp), autoinjector (SIL-10Advp), UV diode array detector (SPD-M10Avp), and single quadrupole analyzer (by electrospray
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