5-Mercaptotetrazoles as Synthetic Equivalents of Nitrogen-Contaning Functional Groups. The Case of the Organocatalytic Enantioselective aza-Michael Reaction (original) (raw)

signal; dd, doublet of doublets. 13 C NMR spectra were acquired on a broad band decoupled mode. IR spectra were measured in a Perkin-Elmer 1600 apparatus and only characteristic bands are given. Mass spectra were recorded on a Waters micromass GCT spectrometer using electronic impact (EI) or chemical ionization (CI) techniques (70 eV). Analytical thin layer chromatography (TLC) was performed using pre-coated aluminumbacked plates (Merck Kieselgel 60 F254) and visualized by ultraviolet irradiation or KMnO 4 dip. Melting points were measured in a Büchi B-540 apparatus. Optical rotations were measured on a Perkin-Elmer 241 polarimeter. The enantiomeric excess (ee) of the products were determined by chiral stationary phase HPLC in a Waters 2695 with a Waters 2998 photodiode array detector and using Daicel Chiralpak IA and Daicel Chiralcel OD or OJH columns. Materials. Analytical grade solvents and commercially available reagents were used without further purification. Silica gel (Silica gel 60, 230-400 mesh, Fluka) or basic Al 2 O 3 (0.05-0.2 mm, pH 8.8-10.2, 90-170 m 2 /g) were employed for flash column chromatography (FC). 1 SGIker technical support (MEC, GV/EJ and European Social Fund) is gratefully acknowledged (NMR, HRMS and X-ray analysis). S3 Experimental Procedures and Characterizations. General Procedure for the Preparation of aza-Michael adducts 4. An ordinary vial equipped with a magnetic stirring bar was charged with catalyst 3d (10 mol%, 0.05 mmol), mercaptotetrazole 2 (1.00 mmol), toluene (3.0 mL), and benzoic acid (0.20 mmol). The mixture was stirred for 30 min at-30 °C and then α,βunsaturated aldehyde 1 (0.50 mmol) was added at once. After the reaction was completed (TLC monitoring,

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