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Synlett 2005(9): 1453-1455  
DOI: 10.1055/s-2005-868492
LETTER
© Georg Thieme Verlag Stuttgart · New York

Iridium-Catalyzed Oxidative Dimerization of Primary Alcohols to Esters Using 2-Butanone as an Oxidant

Takeyuki Suzuki*, Tomohito Matsuo, Kazuhiro Watanabe, Tadashi Katoh*
Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-Ku, Sendai, Miyagi 981-8558, Japan
Fax: +81(22)2752013; e-Mail: suzuki-t@tohoku-pharm.ac.jp; e-Mail: katoh@tohoku-pharm.ac.jp;
Further Information

Publication History

Received 28 February 2005
Publication Date:
25 April 2005 (online)

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Abstract

Oxidative dimerization of primary alcohols with 2-butanone in the presence of an amino alcohol-based Ir bifunctional catalyst was accomplished for the first time. The reaction proceeds with 1-2 mol% of the catalyst and 0.3 mol equivalents of K2CO3 in 2-butanone at room temperature to give the corresponding dimeric esters in 30-93% yield.

Key words

alcohols - esters - hydrogen transfer - iridium catalyst - oxidative dimerization

19

Related oxidative lactonization of diols in the presence of acetone was reported by Murahashi et al., see ref. 13a.

21

General Procedure for the Oxidative Dimerization of 1.
A 10 mL test tube equipped with a magnetic stirring bar was charged with 42 mg (0.3 mmol) of K2CO3 and 1.0 mmol of alcohol under Ar. Then a solution of 11 mg (0.02 mmol, 2 mol%) of Ir complex 3 in butanone (0.24 mL, 2.7 mmol) was added to the above mixture and stirred at r.t. The mixture was passed through a short silica gel column (12 g, EtOAc) to remove the catalyst. The yields for the products of 2c and 2d were determined by gas chromatography using authentic samples and appropriate correction factors. The products of 2a, 2b, and 2d-m were purified by silica gel column chromatography (hexane-EtOAc).

22

Although TONs were not optimized at the moment, they were roughly calculated to be in range between 17 and 23 for most substrates [with single entry as high as 40 (entry 7)].

23

The mechanism of saturation is not clear at present. Partially saturated products were observed even without K2CO3 under a high-concentration condition (4.2 M). However, such saturated products were not observed with K2CO3 under a diluted condition (0.08 M). See also ref. 17c.