Of p-diketones

Deprotonation of enols of P-diketones, not considered unusual at moderate pH because of their acidity, is faciUtated at lower pH by chelate formation. Chelation can lead to the dissociation of a proton from as weak an acid as an aUphatic amino alcohol in aqueous alkaU. Coordination of the O atom of triethanolamine to Fe(III) is an example of this effect and results in the sequestration of iron in 1 to 18% sodium hydroxide solution (Fig. 7). Even more striking is the loss of a proton from the amino group of a gold chelate of ethylenediamine in aqueous solution (17). 

AEyl chloride reacts with sodamide in Hquid ammonia to produce benzene when sodamide is in excess, hexadiene dimer is the principal product, with some trimer and tetramer (C24, six double bonds). AEylation at carbon atoms alpha to polar groups is used in the preparation of a-aEyl-substituted ketones and nittiles. Preparation of P-diketone derivatives, methionic acid derivatives, and malonic ester, cyanoacetic ester, and P-keto-ester derivatives, etc, involving substitution on an alpha carbon between two polar carbonyl groups, is particularly facEe. 

The fluorination of P-diketones and p-ketoesters with N-/luorobis(trifluo-romethanesulfonyl)imide (Table 3a, B) can be controlled to give either mono-fluorination or difluorination. Monofluorination occurs when the strong acid, bis(trifluoromethanesulfonyl)imide, a reaction product, is removed by addition of water, which prevents further enolization and fluormation of the monofluoro adduct [83] (equation 38)... 

The enone system itself is usually part of a five- or six membered ring, although acyclic a,(3-unsaturated ketones and enols of P-diketones are also found to undergo cycloadditions under certain conditions. For seven- and higher membered rings the primary photochemical event is Z—E isomerization around the C—C double bond, the E-isomer then eventually undergoing further thermal reactions. 

Despite the lack of diastereoselectivity and the moderate yields, the present procedure complements other syntheses of 1,3-diols such as hydride reductions of p-diketones,9 p-hydroxy ketones10 and p-keto esters,11 or the opening of 2,3-epoxy alcohols12 and 3,4-epoxy alcohols13 with Lipshutz cuprates. 

However, when the Q-value of P-diketones is plotted against Rq-. -o little correlation (Emsley et al., 1990a). 

The vibrational assignments for a selection of P-diketones are given in Table 10, which includes those p-diketones for which complete structural and nmr data are available. 

Table 11 p-Substituent factors, A, for calculating H- and C-nmr spectra of p-diketones. 

When a metal atom donates electron density to a bound ligand, usually by means of Ji-back bonding, electrophilic substitution reactions may be promoted. This is observed then usually with metals in low oxidation states and is therefore prevalent with organometallic complexes - and less with those of the Werner-type, where the metals are usually in higher oxidation states. Nevertheless there have been detailed studies of electrophilic substitution in metal complexes of P-diketones, 8-hydroxyquinolines and porphyrins. Usually the detailed course of the reaction is unaffected. It is often slower in the metal complexes than in the free ligand but more rapid than in the protonated form. 

Cleavage of P-diketones, the products of a mixed Claisen reaction between an ester electrophile and a ketone nucleophile (see Box 10.13), behave similarly towards base, and a reverse Claisen reac-... 

The double bonds of the oxadiazole ring activate certain functional groups in the 5-position. For instance, when a keto group is in /S position, alkaline hydrolysis is facilitated as in the case of p diketones [50, 83, 95, 107,117), e.g. ... 

Cyanogen Iodide (ICN) has been used extensively for the cyanation of alkenes and aromatic compounds [12], iodination of aromatic compounds [13], formation of disulfide bonds in peptides [14], conversion of dithioacetals to cyanothioacetals [15], formation of trans-olefins from dialkylvinylboranes [16], lactonization of alkene esters [17], formation of guanidines [18], lactamization [19], formation of a-thioethter nitriles [20], iodocyanation of alkenes [21], conversion of alkynes to alkyl-iodo alkenes [22], cyanation/iodination of P-diketones [23], and formation of alkynyl iodides [24]. The products obtained from the reaction of ICN with MFA in refluxing chloroform were rrans-16-iodo-17-cyanomarcfortine A (14)... 

Monocyanohydrins of P-diketones.3 In the presence of TiCl4, acetyl cyanide reacts with enol silyl ethers of ketones at - 78° to afford monocyanohydrins of diketoncs in excellent yield. The corresponding reaction with enol silyl ethers aldehydes proceeds in only about 35% yield. A low temperature is essential for this reaction. A similar reaction is possible with allyltrimethylsilane. 

The electrophilic substitution of P-diketonate complexes appears to occur as for arenes, and a process involving initial coordination of the electrophile, followed by an intramolecular group transfer, has not been observed, although it has been postulated for the reaction of copper(II) acetylacetonate with thioacetals (equation 14).31... 

Initial C-perfluoroalkylation of p diketones occurs during their UV irradiation in the presence of perfluoroalkyl iodides in liquid ammonia Fluorinated enami-noketones are obtained by subsequent ammonolysis of a difluoromethylene group and removal of the acetyl group [131] C-alkylation of dimethyl malonate takes... 

Fluorinated esters may also act as electrophiles in reactions with nonfluori-nated ketones [28] (equation 23) or malononitrile [29] (equation 24). Unfortunately, the yields of p-diketones may be modest, but those of p-keto nitriles are excellent (Table 9)... 

Scheme 8.14 Michael reaction of p-diketones (X = alkyl) and p-oxo esters (X = alkoxy) with methyl vinyl ketone (41a, MVK).

Batzar, K. Goldberg, D.E. Newman, L.J. Effect of P-diketone structure on the synergistic extraction of uranyl ion by tributylphosphate, J. Inorg. Nucl. Chem. 29 (1967) 1511-1518. 

A recent review [440], published 100 years after Werner s coordination theory was first presented, was dedicated to the complex compounds obtained on the basis of polypyrazolyl-borates or scorpionates. Complexes of this kind, an example of which is presented by structure 234, have been obtained with practically all p, /-elements and they can be examined as N-containing analogoues (MN4 coordination unit) of p-diketonates 2 (M04 coordination unit) ... 

Using small metal particles of Cr, Fe, Co, Ni, Ti, Zr, Hf (instead of metal atoms) carried by inert gas in a reactor, reported in Ref. 202, it is possible to increase yields of metal P-diketonates to 90-100% [540]. If the metal particles are in the 0.1-0.3 mm size range and their specific surface is between 50 and 100m2/g, the time for full reaction is reduced to a fraction of a second. The product output increases sharply (up to 10-60g of P-diketonate/min) when the P-diketone is introduced to the reactor as an aerosol. 

The electrolysis of P-diketone solutions in ethanol (0.4-0.6 M) was carried out using a uranium anode and nickel cathode for 3-5 hr at 45-60 mA in an inert atmosphere (Ar, He) as in an oxidative one (02, dry air) with agitation. LiCl was used as supporting electrolyte (O.lmol/L). P-Diketones [acetylacetone (Hacac) and benzoylacetone (Hba)] were distilled before use. 

N-Donors. NNN N -Tetramethylethylenediamine and a range of P-diketones (e.g. acacH, hfacH, dipivaloylmethane) form [Cu(tetren)(P-diket)]X,nH20 (X = C104 or N03), which have been examined spectroscopically to establish the effect of the various substituents upon the observed spectra.674... 

Rh complexes of ferrotanes (12) show good performance for amido itaconates (Table 15.4, Entry 1), and Ru-ferrotane catalyzes the hydrogenation of P-diketones with high stereoselectivity... 

---