LETTER
Microwave-Assisted Synthesis of NHC Precursors
495
Methods and Principles in Medicinal Chemistry, Vol. 25;
Mannhold, R.; Kubinyl, H.; Folkers, G., Eds.; Wiley-VCH:
Weinheim, 2005.
References and Notes
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(16) 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.
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(17) 1H NMR (400 MHz, DMSO-d6): d = 2.35 (s, 6 H, para-
CH3), 4.55 ppm (s, 4 H, CH2), 7.35 (d, J = 4.0 Hz, 2 H,
CHortho), 7.60 (d, J = 4.0 Hz, 2 H, CHmeta), 10.13 (s, 1 H, im-
CH2). 13C NMR (100 MHz, DMSO-d6): d = 20.5 (para-
CH3), 48.3 (CH2), 118.4 (CHortho), 130.0 (CHmeta), 133.8
(Cpara), 136.4 (Cipso), 151.1 (im-CH2).
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manuscript in preparation.
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(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).
Synlett 2006, No. 3, 493–495 © Thieme Stuttgart · New York