Derivatives of 1,3-Diketones

Many compounds of metal ions with 1,3-diketones, RCOCH2COR, are known. Because of their characteristic and somewhat unusual properties, the metallic derivatives of the 1,3-diketones have been found useful not only in laboratory operations but also in the development of chemical theory. The properties and behavior of these diketone derivatives are visualized most clearly in terms of the coordination theory of Werner. 

Structure of 1,3-Diketones. The 1,3-diketones exist in two tautomeric forms, keto and enol  

For example, chemical analyses and measurements of the absorption spectra of 2,4-pentanedione, CH3COCH2COCH8 (acetylacetone), by Grossman and by Acly and French, indicate that the enol form is present in water at 25° to the extent of 15 to 20 per cent and in 95 per cent alcohol to the extent of 55.7 per cent. The tautomerism has also been studied by means of the Raman effect, by exchange reactions with deuterium, and by polarographic oxidation-reduction measurements. Insofar as 2,4-pentanedione and other 1,3-diketones exist in the enol form, they probably 

Formation of Chelate Compounds. The hydrogen of the hydroxyl group of the enol form of a 1,3-diketone may be replaced by metals. In general, the resulting compounds in the case of the alkali metals behave like ordinary salts. For example, the anhydrous sodium salt of l-phenyl-1,3-butanedione chars on heating without melting, dissolves readily in water, and is insoluble in toluene and benzene, properties that are considered to be saltUke. However, the 2-hydrate of this compound 

The metallic derivatives of the aromatic o-hydroxyalde-l .ydes and the o-hydroxyphenones fall into the group of 

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A total synthesis of functionalized 8,14-seco steroids with five- and six-membered D rings has been developed (467). The synthesis is based on the transformation of (S)-carvone into a steroidal AB ring moiety with a side chain at C(9), which allows the creation of a nitrile oxide at this position. The nitrile oxides are coupled with cyclic enones or enol derivatives of 1,3-diketones, and reductive cleavage of the obtained cycloadducts give the desired products. The formation of a twelve-membered ring compound has been reported in the cycloaddition of one of the nitrile oxides with cyclopentenone and as the result of an intramolecular ene reaction, followed by retro-aldol reaction. 

Aryldiazonium salts react at once with dihydrodiazepinium salts and provide a further example of a reaction between two cations, but the coupling products are hydrolyzed very readily and the products isolated were a-arylazo derivatives of 1,3-diketones (70CC1320). 6-Arylazo-A,A -disubstituted dihydrodiazepinium salts have, however, been obtained by condensation of 2-arylazo derivatives of oxomalonaldehyde with ethylene-diamine (75HCA2283) or N,N -disubstituted ethylenediamines (71LA207) or of ethylenediamine with 2-arylazo derivatives of 2-oxo-1,3-diketones (78JIC577). 

The methods of preparation and purification of metal derivatives of 1,3-diketones have been described in a previous volume. Because of the interest in the structure " and reactions of metal derivatives of /3-keto imines, RC0CH2C(=NR )R", it is desirable to consider the methods of preparation of these compounds. Inasmuch as /3-keto imines are closely related to 1,3-diketones and to salicylaldimines, o-HOC6H4CH==NR, the methods of preparation show similarities. Although this review is concerned principally with /3-keto imines, some comparisons with 1,3-diketones and salicylaldimines are made. 

Interaction of a Soluble -Keto Imine Salt and a Soluble Metal Salt. The syntheses of a number of metal derivatives of 1,3-diketones are representative of this method, but the extension to metal jS-keto imines has been limited to the synthesis of chromium (III) derivatives. These have been prepared by the interaction of trichlorotris-(tetrahydrofuran)chromium(III) and the potassium salt of a /3-keto imine. (See synthesis 38.)... 

De Mayo reaction. Synthesis of 1,5-diketones by photoaddition of enol derivatives of 1,3-diketones to olefins, followed by a retro-aldol reaction. 

See also Preparation of metal derivatives of 1,3-diketones, synthesis 29 Dichloro(di-2-pyridylamine)cobalt(II), synthesis 50... 

The structures, types, properties, uses, nomenclature, and general methods of preparation of metal derivatives of 1,3-diketones have been discussed in a previous volume.1 It now seems desirable to consider in somewhat more detail the various factors involved in the preparation and purification of these substances. 

Preparation of Metal Derivatives of 1,3-Diketones. Methods of preparation may be grouped into several general classes. 

Purification of Metal Derivatives of 1,3-Diketones. Despite all care in the preparation of metal derivatives, it may still be necessary to purify such compounds after they are formed. Distillation, sublimation, and crystallization (particularly the last) are the methods generally available... 

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