General Information: All reactions were performed under a nitrogen atmosphere in oven-dried round-bottomed flasks fitted with rubber septa or yellow polyethylene stoppers. Liquid reagents were transferred with stainless steel syringes. Flash Chromatography was performed with EM Science silica gel 60 (230-400 mesh).
Materials:Dichloromethane was distilled from CaH 2 at 760 Torr. Commercially available aldehydes were purified by distillation from anhydrous calcium sulfate and/or column chromatography prior to use. Commercially available nitroalkenes were used as received.trans -β-nitrostyrene, trans-4-methoxy-β-nitrostyrene, trans-2-(2-nitrovinyl)thiophene, trans-2-(2-nitrovinyl)furan, trans-4-bromo-β-nitrostyrene, trans-β-nitro-2-(trifluoromethyl)styrene, 2-phenylpropionaldehyde, 2-methylpentanal, 2,6-dimethyl-5-heptenal, 2-methyl-3-(3,4-methylenedioxyphenyl)propanal were purchased from Aldrich. 3-(2-nitroethenyl)pyridine was purchased from TCI America. 4-fluoro-β-nitrostyrene was purchased from Fluka. (R)-3,3-dimethyl-2-butylamine was purchased from Lancaster. (E)-1-nitroprop-1-ene, [1] (E)-1-nitrohex-1-ene, [1] (E)-3-(benzyloxy)-1-nitroprop-1-ene, [1] trans -3,3,3-trifluoro-1-nitroprop-1-ene, [2] 3-(tertbutyldimethylsilyloxy)-2-methylpropanal, [3] 2-(4-methoxybenzyloxy)propanal, [4] thiourea catalysts [5] 1-2 were prepared according to previously published procedures.Instrumentation: Proton nuclear magnetic resonance ( 1 H NMR) spectra and carbon nuclear magnetic resonance ( 13 C NMR) spectra were recorded on a Varian Mercury-400 (400 MHz) NMR spectrometer. Chemical shifts for protons are reported in parts per million downfield from tetramethylsilane and are referenced to the solvent residual peak (CHCl 3 : δ 7.26). Chemical shifts for carbon are reported in parts per million downfield from tetramethylsilane and are referenced to the carbon resonances of the solvent (CDCl 3 : δ 77.0). Data are represented as follows: chemical shift, integration, multiplicity (br = broad, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), and coupling constants in Hertz (Hz). Infrared (IR) spectra were obtained using a Mattson Galaxy Series FTIR 3000 spectrophotometer referenced to a polystyrene standard. Data are represented as follows: frequency of absorption (cm -1 ), intensity of absorption (s = strong, m = medium, w = weak). Optical rotations were measured using a 2.0 mL cell (2S,3R)-2,3-dimethyl-4-nitro-2-phenylbutanal (6): Under a positive pressure of nitrogen at room temperature, thiourea catalyst 1 (75.3 mg, 0.20 mmol, 20 mol%) was loaded into an oven-dried 25 mL round-bottomed flask, equipped with a magnetic stir bar, rubber septum, and nitrogen inlet. The catalyst was dissolved in dichloromethane (6.7 mL). Water (90.1 µL, 5.0 mmol, 5.0 equiv.) and 2-phenylpropionaldehyde (265.4 µL, 2.0 mmol, 2.0 equiv.) were subsequently added via syringe. The resulting clear colorless solution was stirred for approximately two minutes. 1-nitropropene (87.1 mg, 1.0 mmol, 1.0 equiv.) was added via syringe re...
