Synlett 2006(17): 2833-2835  
DOI: 10.1055/s-2006-950269
LETTER
© Georg Thieme Verlag Stuttgart · New York

1,5-Diketone Synthesis Promoted by Barium Hydride or Barium Alkoxides

Hiroshi Takahashia, Takayoshi Araib, Akira Yanagisawa*b
a Graduate School of Science and Technology, Chiba University, Inage, Chiba 263-8522, Japan
b Department of Chemistry, Faculty of Science, Chiba University, Inage, Chiba 263-8522, Japan
Fax: +81(43)2902789; e-Mail: ayanagi@scichem.s.chiba-u.ac.jp;
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Publikationsverlauf

Received 7 August 2006
Publikationsdatum:
09. Oktober 2006 (online)

Abstract

A tandem cross-coupling reaction of ketones with aldehydes has been achieved using barium hydride or isopropoxide as a promoter, in which barium enolates are generated in situ and then three successive reactions (aldol reaction-β-elimination-Michael addition) follow; this one-pot process is effective for obtaining ­symmetrical 1,5-diketones in good yields.

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We examined catalytic activity of NaOi-Pr, KOi-Pr, and Mg(Oi-Pr)2 in the present reaction, however, these metal isopropoxides were found to be less effective, [M(Oi-Pr)n, equiv, time, yield]: NaOi-Pr, 0.4 equiv, 4 h, 40%; KOi-Pr, 0.4 equiv, 4 h, 35%; Mg(Oi-Pr)2, 0.2 equiv, 18 h, <1%.

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Typical Procedure for Tandem Cross-Coupling Reaction of Ketones with Aldehydes Catalyzed by Barium Isopropoxide: Synthesis of 1,3,5-Triphenylpentane-1,5-dione (Entry 2 in Table 3).
An oven-dried, 30 mL two-necked round-bottomed flask equipped with a Teflon®-coated magnetic stirring bar was flushed with argon. Then, Ba(Oi-Pr)2 (26 mg, 0.10 mmol) was put into the apparatus and covered with dry DMF (5 mL) and i-PrOH (1.5 mL, 20 mmol), and the mixture was stirred for 10 min at r.t. To the resulting solution were added acetophenone (0.35 mL, 3.0 mmol) and benzaldehyde (0.10 mL, 1.0 mmol). After being stirred for 7 h at r.t., the mixture was treated with a sat. aq NH4Cl solution (10 mL) at this temperature and the aqueous layer was extracted with Et2O (20 mL). The combined organic extracts were dried over anhyd Na2SO4 and concentrated in vacuo after filtration. The residual crude product was purified by column chromato­g­-raphy on silica gel to give the 1,5-diketone (0.25 g, 76% yield) as colorless crystals.
Spectral Data of the Product.
TLC: R f = 0.52 (hexane-EtOAc, 3:1). IR (KBr): 3062, 3025, 2960, 2888, 1686, 1668, 1597, 1580, 1496, 1449, 1422, 1408, 1352, 1268, 1207 cm-1. 1H NMR (400 MHz, CDCl3): δ = 3.36 (dd, 2 H, J = 16.4 Hz, 7.0 H, CH2), 3.50 (dd, 2 H, J = 16.7 Hz, 7.0 H, CH2), 4.04-4.11 (m, 1 H, CH), 7.15-7.21 (m, 1 H, arom.), 7.24-7.29 (m, 4 H, arom.), 7.43-7.46 (m, 4 H, arom.), 7.53-7.57 (m, 2 H, arom.), 7.94-7.96 (m, 4 H, arom.). 13C NMR (100 MHz, CDCl3): δ = 36.5, 44.4, 126.2, 127.1, 127.3, 127.7, 128.1, 132.6, 136.4, 143.5, 198.0. The above-mentioned spectral data (IR, 1H NMR, and 13C NMR) of the product indicated good agreement with reported data. [9]