1.3- diketo compound

The pyrazolone ring system is accessible through ring closure by the condensation of 1,3-diketo compounds with hydrazine derivatives. 

The combination of his-electrophilic and his-nucleophilic components is the basis of general pyrimidine synthesis. A reaction between an amidine (urea or thiourea or guanidine) and a 1,3-diketo compound produces corresponding pyrimidine systems. These reactions are usually facilitated by acid or base catalysis. 

The only moderate selectivity is irrelevant because in the following step, 28 is oxidized to the 1,3-diketo compound 17 using pyridinium-chlorochromate (PCC). PCC has been developed particularly for the selective oxidation of primary alcohols to aldehydes, but it also works well for the oxidation of secondary alcohols. 

Figure 2.67 The reaction with 1,3-diketo compounds in the presence of copper or manganese ions also follows a radical mechanism.

Reaction with diketene affords the corresponding /3-diketo compound 124. 

Alternatively, Cushman has devised a facile route to pyrroles by the reaction of Boc-a-amino aldehydes or ketones 14 with the lithium enolates of ketones 15 to afford aldol intermediates 16 which cyclize to pyrroles 17 under mild acidic conditions <96JOC4999>. This method offers several advantages over the Knorr since it employs readily available Boc-a-amino aldehydes or ketones and utilizes simple ketones instead of the p-diketo compounds or p-keto esters normally used in the Knorr. 

Typically, 40 gl of 5.0 M alkyne compoimd and 40 gl of 5.0 M alkyne of the diketo compound were placed in the corresponding reservoirs (Figure 4.70) [8]. The same holds for diisopropylethylamine (40 gl 5.0 M). The electrical fields applied were ... 

Ketoaldehydes and 1,4-diketones are reduced to cA-cyclopentanediols 258 1,5-Diketo compounds can be cyclized to cyclopentanediols, again with a preference for cis-diols.259 These reactions are believed to occur through successive one-electron transfer, radical cyclization, and a second electron transfer with Sm2+ ether serving as a tether and Lewis acid, as well as being the reductant. 

Towards the end of this section it may be worthwhile to point out some new reactions with high-valent metals and TBHP. The first is a pyridinium dichromate PDC-TBHP system134. Nonsubstituted or alkyl-substituted conjugated dienes, such as 1,3-cyclooctadiene (87) and others (also linear dienes), yield keto allyl peroxides 88 (equation 18), whereas phenyl-substituted dienes such as 1,4-diphenylbutadiene (89) gave diketo compounds, 90 (equation 19). In further research into a GIF-type system135 with iron and TBHP, limonene gave a mixture of products with carvone as the major product. The mechanism is thought to proceed initially by formation of a Fe(V)-carbon... 

Figure 11.11 Library of amines and diketo compounds, which was employed in a polymerization catalyst study described in Section 11.7 [87], For simplicity, amines have a number and diketones a letter as library name.

Mechanistic aspects of the intermolecular cyclization reaction in the anodic oxidation of catechol in the presence of 4-hydroxycoumarin were discussed in Sect. 2.2. This reaction is a synthetically simple and versatile method for the preparation of formally [3 + 2] cycloadducts between a -diketo compound and catechol [44,45]. Anodic oxidation of catechol using controlled potential electrolysis (E = 0.9-1.1 V vs SCE) or constant current electrolysis (i = 5 mA/cm ) was performed in water solution containing sodium acetate (0.15 mol/1) in the presence of various nucleophiles such as 4-hydroxycoumarin,... 

There are a few published reports on the use of HOSA 3p for enolate amination. Some /3-diketo compounds were reacted with HOSA in 10% aqueous K2CO3 solution at room temperature to give substituted pyrroles (equation 21) ° °. ... 

Included in this section are oxidations of benzene and phenyl rings, and in general the oxidation of aromatic and polycyclic aromatic compounds. The main catalyst for this type of reaction is RuO. The earliest example was the use of stoich. RuOy CCI4 for phenanthrene oxidation [239], while the first catalytic reagent was RuO / aq. Na(I04)/acetone for oxidation of pyrene [240]. Another early example was the conversion of diketo compounds to the nor-diketo acids, with concomitant destruction of the two phenyl rings by RuO /aq. NallO l/acetone (Fig. 3.18, 3.2.2.1) [206]. 

Oxidation of 2,3-epoxynorbomane to diol, ketohydroxy, and diketone derivatives was studied with RuCyaq. oxidant/CCl -CHjCN (co-oxidant=(I04) , H O, Oxone , (CIO)", (S Og) " (BrO )" was ineffectual) [73]. The system RuClj/aq. Na(10 )/CCl4-CH3CN oxidised substituted epoxides containing bicyclic [2.2.1] heptane skeletons, e.g. exo-2,3-epoxynorbomanes to the corresponding diketo compounds [74]. Stoicheiometric RuOyCCl converted 20,21-dihydroxy-lip,... 

Oxidation Oxidation of naphthalene by oxygen in the presence of vanadium pentoxide (V2O5) destroys one ring and yields phthalic anhydride (an important industrial process). However, oxidation in the presence of CrOs and acetic acid (AcOH) destroys the aromatic character of one ring and yields naphthoquinone (a diketo compound). 

A general way of synthesizing heterocyclic compounds is by cyclization of a dicarbonyl or diketo compound using a nucleophilic reagent that introduces the desired hetero-atom. 

Addition of a-diketo compounds to three-coordinate phosphorus compounds 533... 

Selected arylation of diketo compounds by iodonium suits... 

The roles of vanadium and copper are complex and not fully understood. A large number of intermediates, including the nitroso and the diketo compound as shown by reaction 8.21 are formed. The ion V02 stoichiometrically oxidizes the diketo compound to adipic acid. This is shown by reaction 8.22. 

The auration of acetylacetone and other jS-diketo compounds affords complexes of the type [RC(0)]2CHAuL and [RC(0)]2C(AuL)2, with the gold atoms exclusively C-bonded." The former are useful aurating reagents." ... 

Diketones have been prepared by the Friedel-Crafts method. Both acyl chloride groups in adipyl chloride react with benzene in the presence of aluminum chloride to form the diketo compound, 1,4-dibenzoylbutane (81%). When diketene is treated with benzene under the conditions of the Friedel-Crafts reaction, benzoylacetone, COCHjCOCH, is formed... 

Except for hydroxymethylation (Scheme 26) and self-condensation (Scheme 6), 1,2,4-triazoles do not give definable products on reactions with aldehydes but the resins formed are worth closer investigation. Reactions of aminotriazoles with jS-diketo compounds are used to prepare some fused triazoles (see Chapter 4.15). 

Proceeding to two rings going-on one class, neutral derivatives of bicyclobutane with the two non-bridgehead carbons replaced by sp hybridized or trigonally coordinated atoms show self-destructive behavior for related reasons (see Chapter 19 by Hoz for a review of bicyclobutanes). Our suicidal species include the hypothetical bicyclobutane-2,4-dione (51) and its 1,3-disubstituted derivatives, recognized as squaraines (52) . The theoretical analysis of the parent diketo compound suggests the non-planar form also lacks the C-C bond. The 2,4-dibora compounds are experimentally known to be... 

The evidence for the other forms of DHA shown in Scheme 1 is based on theory of reaction mechanisms. The fact that DHA reacts with DNPH to form a hydrazone is supportive evidence for the existence of a 2- or 3-monoketo compound. A 3-monoketo compound is required by any reasonable mechanism for the formation of the hydrated hemiketal form. The 2,3-diketo compound would be very unstable due to the high positive charge associated with the carbonyl carbons. These carbons would be very susceptible to nucleophilic attack. However, a small concentration of the 2,3-diketo form should exist in equilibrium mixtures. Direct oxidation of AA should give the 2,3-diketo form. 

---