1,3,5-Triketonates

The cyclization of 1,3,5-triketones to pyrones will not be discussed here, although this is a related reaction, because pyrones are not true pyrylium salts. Mention will be made, however, of the formation of 2,6-diphenyl-4-pyrone from 1,3-dibenzoylallene this ketone adds secondary amines leading to 3-dialkylamino-l,5-diphenyl-4-penten-l,5-diones, which arc cyclized by hydrogen chloride in acetic acid to 2,6-diphenyl-4-dialkylaminopyrylium chlorides (R = Me and/or Ph) (see Scheme. 5). 

Pyridones from 1,3,5 triketones, 46,60 Pyrolysis, diketene to ketene, 46, SO a-PYRONE, 46,101 in Diels Alder reactions, 46, 104 4-Pyrones, 2,6 disubstituted, from 1,3,5 pentanetnones by acid cycliza tion, 46, 61... 

Pyran-4-ones are formed when acyl ketenes derived from dioxofurans and dioxinones react with vinyl ethers. Intermediate products are 1,3,5-triketones and reduced pyranones <96CPB956,96H(43)2457,96TL6499>. 

Although the most recent modifications of the Prelog condensation of 1,3-dike-tones and 1,3,5-triketones, for example that of acetylacetone with dimethyl 1,3-acetonedicarboxylate in the presence of NaOH in H2O, afford substituted benzenes such as 1486 in up to 94% yield (Scheme 9.22) and coumarins [40], these condensations of highly substituted polyketones with the corresponding aromatic systems might also be effected in the presence of HMDS 2/TCS 14 or TMSOTf... 

As in 0-94, a ketone attacks with its second most acidic position if 2 moles of base are used. Thus, p-diketones have been converted to 1,3,5-triketones. I70 ,... 

Ring closure of 1,3,5-triketones leads to pyran-4-ones. Several routes are based on this reaction, differing in the approach to the carbonyl compound. 

Triketones are homologues of 1,3-diketones and in these, too, keto-enol tautomerism has been probed by H NMR spectroscopy.567,568 Triketones and tetraketones may coordinate to one or more metal ions per molecule. In the latter case the metal centers are held in such close proximity that, in some cases, interesting magnetic effects may be observed. Structural and magnetic properties of polynuclear transition metal jS-polyketonates have been thoroughly reviewed.569,570... 

This procedure appears to be fairly general for the aroylation of /3-diketones to give 1,3,5-triketones. Using this method, the submitters2 have aroylated benzoylacetone with methyl benzoate (87%), methyl />-chlorobenzoate (78%), and ethyl nicotinate (69%). Also, acetylacetone has been monobenzoylated with methyl benzoate to form l-phenyl-l,3,5-hexanetrione in 75% yield or dibenzoylated with the same ester to form 1,7-diphenyl-... 

Triketones are useful intermediates in the preparation of 4-pyrones, 4-pyridones,3,4 and other cyclic products. 

Cyclopenteno-5,6-cycloalkeno-47/-pyran-4-ones 724 are prepared by the reaction of 1-cyclopentenylpiperidine with diacyl chlorides via formation and ring closure of the 1,3,5-triketone intermediate 723 (Scheme 179)... 

Metacyclophanes 740 are synthesized from 4-hydroxy-3-acyl-pyran-2-ones 738 in high yield. The reaction proceeds via hydrolysis of the pyran-2-one ring, followed by decarboxylation to afford the intermediate 1,3,5-triketone 739, which recyclizes to afford 2,6-bridged pyran-4-ones 740 (Scheme 187) <2003T2651>. 

As already indicated, 1,3,5-triketones react anomalously with hydrazines. Interaction of the sodium enolate of a diketone and an a-halogenohydrazone, however, leads to the monohydrazone of a... 

A type of ligand that can hold metals side by side is called compartmental. They can be made by condensing 1,3,5 triketones with a, o> alkanediamines. An example is (9-XXXVa) which can be used to bind two metals as in (9-XXXVb). 

Triketones and similar polyketones exhibit keto-enol tautomerism and have been found to coordinate to one or more metal atoms (24). Such complexes can bring metal atoms in close proximity, resulting in interesting magnetic properties (see Magnetism of Transition Metal Ions). 

The conjugate addition of dithiols to hexa-l,4-diyn-3-ones yields p,P -bis-l,3-dithiane ketones, masked 1,3,5-triketones, which have been converted into dihydro- and tetrahydro-pyrans <03OLl 147>. 

The 1,3,5-triketones are potentially dinegative, tridentate ligands and the well-developed JT-system of the dianion gives to the ligands a preference for a planar configuration, thus precluding tridentate coordination to one metal ion. For example, copper(ll) and heptane-2,4,6-trione give mononuclear (132) and dinuclear complexes (133) ". ... 

Another area where metal /3-diketonates have made a significant impact is in the oxidation of aLkanes , alkenes and alcohols A number of different metal complexes have been used in these reactions, including Pd(acac)2 (29) , Co(acac)3 (30) , Fe(acac)3 (31), a bimetallic Pd(II) complex containing a 1,3,5-triketone ligand, MCI (acac)(PPh3) (32) where M = Ni, Co, Cu, Mn(acac)3 (33) , Mo02(acac)2 (34) , VO (acac)2 (35) and VO(hfac)2 (36) . In the latter study, the oxidation of a-acetylenic... 

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