Benzyl 2-((E)-Tosyliminomethyl)phenylcarbamate

Abstract

Benzyl 2-((E)-tosyliminomethyl)penylcarbamate was prepared in good yield and characterized by the condensation reaction of benzyl 2-formylphenylcarbamate with p-toluenesulfonyl amine. The structure of the newly synthesized compound was determined using ¹H, ¹³C-NMR, IR and mass spectral data.

1. Introduction

The Schiff base, structurally known as imine or azomethine, is a nitrogen analog of aldehyde or ketone in which the C=O group is replaced by C=N-R group after water molecular elimination [1]. Schiff bases are some of the most widely used organic compounds which used as pigments and dyes, catalysts and intermediates in organic synthesis [2]. Schiff bases have also been shown to exhibit a broad range of biological activities, including antibacterial, antimalarial, anti-inflammatory, antiviral, and anticancer properties [3,4,5]. In continuation of our research intefrest in 2-aminobenzaldehyde for the synthesis of highly functionalized chiral heterocylcles [6,7,8,9], we report here the preparation of a novel benzyl 2-((E)-tosyliminomethyl)phenylcarbamate.

The synthesis of the title compound 3 was achieved in one step, as presented in Scheme 1, which was performed by the condensation reaction of benzyl 2-formylphenylcarbamate (1) [10] with p-toluenesulfonyl amine (2). The reaction was carried out in toluene in the presence of 2 mol% of boron trifluoride diethyl etherate as a catalyst and provided the desired product in good yield. The structure of compound 3 was confirmed by ¹H- and ¹³C-NMR, IR, mass spectral data, and all data are in accordance with the assumed structure.

2. Experimental Section

2.1. General Information

All reagents were used as received without further purification. Organic solutions were concentrated under reduced pressure using a Büchi rotary evaporator. Chromatographic purification of the title compound 3 was accomplished using forced-flow chromatography on ICN 60 32–64 mesh silica gel 63. Thin-layer chromatography (TLC) was performed on EM Reagents 0.25 mm silica gel 60-F plates. Developed chromatograms were visualized by fluorescence quenching and anisaldehyde stain. ¹H and ¹³C-NMR spectra were recorded on a 400 MHz instrument as noted, and were internally referenced to residual protio solvent signals. Data for ¹H-NMR were reported as follows: chemical shift (δ ppm), multiplicity (s = singlet, d = doublet, t = triplet, m = multiplet), integration, coupling constant (Hz) and assignment. Data for ¹³C-NMR were reported in terms of chemical shift. IR spectra were recorded on Perkin-Elmer 1600 FT-IR spectrometer (Waltham, MA, USA), and reported in terms of frequency of absorption (cm⁻¹). High-resolution mass spectrometry data was recorded on a JEOL JMS-700 MStation mass spectrometer (JEOL, Tokyo, Japan).

2.2. Syntheis of Benzyl 2-((E)-Tosyliminomethyl)penylcarbamate (3)

p-Toluenesulfonyl amine (2, 94 mg, 0.55 mmol) was added to a solution of BF₃·Et₂O (1 μL, 0.01 mmol) and benzyl 2-formylphenylcarbamate (1, 128 mg, 0.50 mmol) in toluene (2 mL) at room temperature. The resulting mixture was refluxed for 60 h until complete consumption of benzyl 2-formylphenylcarbamate 1 was observed as determined by TLC. After being cooled to room temperature, water (2 mL) was added and the products were extracted with dichloromethane (3 × 5 mL). The organic phase was washed with aqueous saturated NaCl solution (2 × 5 mL), dried with anhydrous MgSO₄, and concentrated in vacuo. The crude residue was purified by flash silica gel column chromatography using EtOAc/hexane (1/10) as eluent to afford the desired title compound 3 (64%, 154 mg).

White solid; m.p. 158–160 °C; ¹H-NMR (400 MHz, CDCl₃) δ 10.83 (s, 1H), 9.02 (s, 1H), 8.46 (d, J = 8.4 Hz, 1H), 7.89–7.77 (m, 2H), 7.64–7.52 (m, 2H), 7.47–7.33 (m, 5H), 7.14 (ddd, J = 8.4, 6.9, 3.0 Hz, 3H), 5.20 (s, 2H), 2.39 (s, 3H); ¹³C-NMR (100 MHz, CDCl₃) δ 170.38, 153.17, 144.79, 142.28, 137.27, 136.43, 135.96, 135.33, 129.87, 128.61, 128.35, 128.21, 127.78, 122.37, 118.76, 117.46, 67.11, 21.67; IR (film) 3248, 2923, 2855, 1735, 1597, 1562, 1537, 1447, 1376, 1317, 1222, 1162, 1088, 1067, 1067 cm⁻¹; HRMS (EI) m/z calcd for [M]⁺ C₂₂H₂₀N₂O₄S: 408.1144 Found: 408.1158.