2-(4-Pyridyl)-1,3-di(4-picolyl)imidazolidine

Abstract

The title compound was prepared by treatment of N,N’-di(4-picolyl­amino)ethane with N,N-dimethylformamide dimethylacetal in toluene and it was characterized by elemental analysis, ¹H NMR and ¹³C NMR.

Introduction

Olefins with four electron-donating substituents react as nucleophiles and are referred to as electron-rich olefins [1,2]. These compounds have been used as strong reducing agents, precursors to carbene complexes, effective formylating agents for proton-active compounds, catalysts for benzoin-type C-C coupling reactions and chemoluminescent materials [3,4,5,6,7]. Carbene complexes, formed by treatment of an electron-rich olefin with metal, are air-stable and have been used for several catalytic applications including olefin metathesis, hydrogenation and hydrosilylation reactions [8,9,10]. Symmetric electron-rich olefins are generally prepared from an N,N’-disubstituted 1,2-diaminoethane with N,N-dimethylformamide dimethylacetal in an inert atmosphere [11]. Unsymmetric and bridged electron-rich olefins are prepared by a convenient salt elimination procedure [12]. The compound 1 was not obtained using the acetal procedure, and if formed, it would spontaneously rearrange to the compound 2. This thermal amino-Claisen rearrangement was believed to be [3,3]-sigmatropic [13,14]. We report here on the synthesis and characterization of 2-(4-pyridyl)-1,3-di(4-picolyl)imidazolidine.

Experimental

Reaction for the preparation of 2-(4-pyridyl)-1,3-di(4-picolyl)imidazolidine was carried out under argon using standard Schlenk-type flasks. Solvents were dried using standard procedures and were distilled prior to use. ¹H and ¹³C NMR spectra were recorded in DMSO-d₆ using a Bruker AC300P FT spectrometer operating at 300.13 MHz (¹H) and 75.47 MHz (¹³C). Chemical shifts (δ) are given in ppm relative to TMS and coupling constants (J) in Hertz. The melting point was measured in open capillary tubes with an Electrothermal-9200 melting point apparatus and it is uncorrected. Elemental analyses was performed at TUBITAK Microlab (Ankara, Turkey).

Synthesis of 2-(4-pyridyl)-1,3-di(4-picolyl)imidazolidine (2)

A solution of N,N’-di(4-picolylamino)ethane (1.87 g; 8.5 mmol) and N,N-dimethylformamide dimethyl acetal (1.10 g; 9.27 mmol) in toluene (15 mL) was heated under reflux for 4 h at 90 °C. The reaction mixture was then heated at 110 °C under distillation conditions, allowing the produced dimethylamine and methanol to escape. Hexane (10 mL) was added and a white solid precipitaded. The crude product was filtered off and washed with hexane (2 × 10 mL). The precipitate was then crystallized from toluene/hexane (10:10 mL). Yield: 0.93 g, 73%, m.p.: 125 ^oC.

¹H NMR (CDCl₃) δ: 3.3 (s, 1H, 2-CH), 1.71 and 2.52 (m, 4H, NCH₂CH₂N), 2.53 and 3.03 (m, 4H, CH₂C₅H₄N), 6.55 and 8.26 (d, 4H, J = 5.6 Hz, CH₂C₅H₄N and m, 4H, CH₂C₅H₄N), 6.88 and 8.25 (m, 4H, C₅H₄N).

¹³C NMR(CDCI₃) δ: 87.3 (2-CH), 50.8 (NCH₂CH₂N), 55.7 (CH₂C₅H₄N), 123.2, 147.2 and 150.2 (CH₂C₅H₄N), 124.1, 148.9 and 150.5 (C₅H₄N).

Anal. Calcd. for C₂₀H₂₁N₅: C, 72.50; H, 6.34; N, 21.14. Found C, 72.87; H, 6.12; N, 21.38.