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Synlett 2009(18): 2943-2944  
DOI: 10.1055/s-0029-1218269
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

2-Azido-1,3-dimethylimidazolinium Chloride: An Efficient Diazo Transfer Reagent for 1,3-Dicarbonyl Compounds

Mitsuru Kitamura*, Norifumi Tashiro, Tatsuo Okauchi
Department of Applied Chemistry, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu-shi, Fukuoka, 804-8550, Japan
Fax: +81(93)8843304; e-Mail: kita@che.kyutech.ac.jp;
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Publication History

Received 22 July 2009
Publication Date:
08 October 2009 (online)

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Abstract

Diazo transfer from 2-azido-1,3-dimethylimidazolinium chloride to 1,3-dicarbonyl compounds has been developed. The ­reaction proceeds under mild conditions to give 2-diazo-1,3-dicarbonyl compounds in high yields, which are easily isolated because the by-products are highly soluble in water.

Key words

azides - diazo compounds - diazonium salt - diazo-transfer - heterocycles

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6

The formation of salt 2 was confirmed by mass spectral analysis. The FAB(positive) mass spectrum of the mixture of the chloroimidazorium salt 3 and sodium azide showed a peak at m/z = 140, which corresponds to the calculated mass of [2 - Cl-]+.

7

Typical procedure: [Caution: Although we have never had any trouble with azidoimidazolinium salt 2 , it is potentially explosive.] To a solution of 2-chloro-1,3-dimethyl-imidazolinium chloride (3; 1.2 mmol) in acetonitrile (2 mL), sodium azide (1.2 mmol) was added at 0 ˚C and the mixture was stirred for 30 min. 1,3-Dicarbonyl compound (1.0 mmol) and triethylamine (2.0 mmol) in THF (4 mL) was added to the mixture, which was stirred until the 1,3-dicarbonyl compound was consumed (reaction monitored by TLC). The reaction was quenched with water, and organic materials were extracted three times with CH2Cl2. The combined extracts were washed with water and brine, and then dried over anhydrous sodium sulfate. The solvent was removed in vacuo to afford the crude compound, which was almost pure. The crude materials were purified by flash column chromatography (silica gel: hexane-ethyl acetate) to give pure 2-diazo-1,3-dicarbonyl compound.