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DOI: 10.1055/s-2006-932455
Microwave-Assisted Synthesis of N-Heterocyclic Carbene Precursors
Publikationsverlauf
Publikationsdatum:
06. Februar 2006 (online)
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Abstract
A very simple and efficient procedure is reported for the synthesis of 1,3-diarylimidazolinium chlorides by cyclization of N,N′-diarylethylenediamines dihydrochlorides with triethyl orthoformate under microwave irradiation.
Key words
amines - cyclizations - heterocycles - imidazolinium salts - ligands
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References and Notes
General Procedure for the Microwave-Assisted Synthesis of 1,3-Diarylimidazolinium Chlorides. A 10-mL glass vial equipped with a stirring bar was charged with a N,N′-diarylethylenediamine dihydrochloride (1 mmol) and triethyl orthoformate (1-2 mL). The vial was capped and irradiated 5 min at 145 °C (monitored by IR sensor) in a CEM Discover instrument with a 50-W microwave power. No ramp and no simultaneous cooling were applied. After rapid air cooling by the unit, the reaction mixture was diluted with Et2O (3 mL) and filtered under vacuum. The precipitate was rinsed with a few milliliters of Et2O and dried under vacuum to afford pure 1,3-diaryl-imidazolinium chloride.
171H NMR (400 MHz, DMSO-d 6): δ = 2.35 (s, 6 H, para-CH3), 4.55 ppm (s, 4 H, CH2), 7.35 (d, J = 4.0 Hz, 2 H, CH ortho ), 7.60 (d, J = 4.0 Hz, 2 H, CH meta ), 10.13 (s, 1 H, im-CH2). 13C NMR (100 MHz, DMSO-d 6): δ = 20.5 (para-CH3), 48.3 (CH2), 118.4 (CH ortho ), 130.0 (CH meta ), 133.8 (C para ), 136.4 (C ipso ), 151.1 (im-CH2).
18Maj, A.; Delaude, L.; Demonceau, A.; Noels, A. F. manuscript in preparation.
20
Scaled-up Preparation of 1,3-Dimesitylimidazolinium Chloride.
A 20-mL glass vial equipped with a stirring bar was charged with N,N′-dimesitylethylenediamine dihydrochloride (7.39 g, 20 mmol) and triethyl orthoformate (15 mL). The vial was capped and irradiated 5 min at 145 °C (monitored by IR sensor) in a Biotage Emrys Optimizer instrument with a 75-W microwave power. No ramp was applied. After rapid cooling in an ice bath, the reaction mixture was diluted with Et2O (20 mL) and filtered under vacuum. The precipitate was rinsed with Et2O (2 × 10 mL) and dried under vacuum to afford pure 1,3-dimesitylimidazolinium chloride (6.57 g, 97% yield).