1.3- Dibenzoylpropane

For further contributions on the dia-stereoselectivity in electropinacolizations, see Ref. [286-295]. Reduction in DMF at a Fig cathode can lead to improved yield and selectivity upon addition of catalytic amounts of tetraalkylammonium salts to the electrolyte. On the basis of preparative scale electrolyses and cyclic voltammetry for that behavior, a mechanism is proposed that involves an initial reduction of the tetraalkylammonium cation with the participation of the electrode material to form a catalyst that favors le reduction routes [296, 297]. Stoichiometric amounts of ytterbium(II), generated by reduction of Yb(III), support the stereospecific coupling of 1,3-dibenzoylpropane to cis-cyclopentane-l,2-diol. However, Yb(III) remains bounded to the pinacol and cannot be released to act as a catalyst. This leads to a loss of stereoselectivity in the course of the reaction [298]. Also, with the addition of a Ce( IV)-complex the stereochemical course of the reduction can be altered [299]. In a weakly acidic solution, the meso/rac ratio in the EHD (electrohy-drodimerization) of acetophenone could be influenced by ultrasonication [300]. Besides phenyl ketone compounds, examples with other aromatic groups have also been published [294, 295, 301, 302]. 

Dibenzoylpropane was prepared by the method described for 1,4-dibenzoylbutane in Organic Syntheses. ... 

To a 1-1. three-necked, round-bottomed flask equipped with a magnetic stirrer and a dropping funnel are added 35 g. (0.14 mole) of 1,3-dibenzoylpropane (Note 1) and a solution of 11.2 g. (0.28 mole) of sodium hydroxide in 400 ml. of methanol. The mixture is warmed to 45° with stirring to dissolve the diketone. It is allowed to cool to 40°, and a solution of 35 g. (0.14 mole) of iodine in 200 ml. of methanol is then slowly added to the stirred solution from the dropping funnel (Note 2). After the addition of iodine is completed, the resulting clear solution is stirred at room temperature for 1.5 hours. During this period, a white solid precipitates (Note 3). The mixture is filtered and the filtrate is placed in a round-bottomed flask. The white... 

Dibenzoylcyclopropane has been prepared by the method described here4 and previously by Conant and Lutz.2 Both procedures use 1,3-dibenzoylpropane as tho reactant. The present procedure is accomplished in one step under very mild conditions and in nearly quantitative yield. The method of... 

Exploration of the reduction of dicarbonyl compounds has centered on attempts to achieve intramolecular coupling of radical intermediates to give a cyclic 1,2-diol. A mechanistic study of the production of cyclopropanediols, during the reduction of 1,3-dibenzoylpropane in acetonitrile, has been made [110]. It is suggested that the ratedetermining cyclization step is the addition of the radical anion from one ketone function onto the second carbonyl group in the same molecule. 

In preparative-scale reduction of 108a in MeCN, bipyrilene (110) has been observed as a side product in addition to the bi-4/f-furan, 109 [311]. Clean 1-F reduction was found ( = 0.8—1.0) in all cases, and at low substrate concentrations (5 mM) 109 was the only product. However, at substrate concentrations in the range 30-100 mM up to 48% of the product was 110 together with 15% 1,3-dibenzoylpropane. 

Oxidation (1, 497-498 2, 220-221). Iodine in methanolic sodium hydroxide oxidizes 1,3-dibenzoylpropane to trans-1,2-dibenzoylcyclopropane, probably by the mechanism formulated ... 

Zinc in a protic solvent has also been applied to the reductive ring opening of activated cyclopropane derivatives. Usually the most activated cyclopropyl bond was cleaved. Treatment of arylcyclopropyl aryl ketones 7 with zinc in ethanol alforded aryl propyl ketones in excellent yields. The reduction of 1,2-dibenzoylcyclopropane (7f) with zinc/zinc(II) chloride produced 1,3-dibenzoylpropane (81) in quantitative yield. Dimethyl 2-benzoyl-3-phenylcyclop-ropane-l,l-dicarboxylate (7e) was converted to the corresponding (2-benzoyl-1-phenylethyl)malonate (8e) when heated with zinc in methanol. ... 

Iodination of ketones (1, 499). The cyclization of 1,3-dibenzoylpropane by reaction with iodine and sodium hydroxide in methanol involves iodination at the position a to one carbonyl group and elimination of the acidic hydrogen adjacent to the second carbonyl group.1 A mixture of 35 g. (0.14 m.) of 1,3-dibenzoylpropane and a solution of 11.2 g. (0.28 m.) of sodium hydroxide in 0.4 1. of... 

The conversion was not initiated by base or by the presence of oxygen, and the mechanistic explanation includes (Scheme 27) slow hydride transfer from the initially formed 109 to the substrate cation, followed by elimination of a proton and formation of 110. The 4i/-pyran formed by hydride transfer reacts with water during workup to give the dibenzoylpropane, and the apparent 1-F coulometry may be due to reduction of the liberated proton, since the reduction was carried out using a Pt cathode [311]. Similar results were obtained in the reduction of 108h and 108c. 

Dibenzoylpropane (71) was inactive as an inducer probably due to its lack of an enone moiety. Dibenzoylmethane (69) was quite active with a CD value of 0.8 [iM the keto-enol tautomerization of the /3-diketone can provide the Michael reaction acceptor feature. The three natural curcuminoids showed similar CD values therefore, the methoxy group in the phenyl ring does not greatly affect the potency. However, the CD... 

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