0-Diketones, condensation with

Although / -diketones condense with DAMN on a 1 1 basis to give diazepines (Section VI,C), -dialdehyde derivatives give [14]annulenes (Scheme 52) (78AGS 18). 

Several complementary reactions, such as the Hantzsch, the Krohnke, and the Chichibabin, lead to tpy in which the central pyridine ring is built up in a condensation process.2 These reactions lend themselves well to the formation of 4 -substituted derivatives. The basic ingredient is acetylpyridine, which provides the two distal rings of tpy, as well as C2, C3, C5, and C6 of the central ring. C4 originates from an aldehyde which is generally aromatic. In the example in Scheme 2, an intermediate 1,5-diketone condenses with a nitrogen source, often ammonium acetate, to provide the final tpy. Table 1 summarizes some tpy derivatives which have been prepared by similar condensation approaches. 

Diketone condensations with primary amines to give tropinones. 

Mesityl oxide (Section 111,79) (I) condenses with ethyl malonate in the presence of sodium ethoxide to give the sodium derivative of (II) this upon hydrolysis with aqueous potassium hydroxide, followed by acidification, gives the cyclic diketone 5 5-dimethyl-l 3-cycfohexanedione (III), of which the enoUc form is 5 5-dimethyldihydroresorcinol (IV) ... 

Cydopentane reagents used in synthesis are usually derived from cyclopentanone (R.A. Ellison, 1973). Classically they are made by base-catalyzed intramolecular aldol or ester condensations (see also p. 55). An important example is 2-methylcydopentane-l,3-dione. It is synthesized by intramolecular acylation of diethyl propionylsucdnate dianion followed by saponification and decarboxylation. This cyclization only worked with potassium t-butoxide in boiling xylene (R. Bucourt, 1965). Faster routes to this diketone start with succinic acid or its anhydride. A Friedel-Crafts acylation with 2-acetoxy-2-butene in nitrobenzene or with pro-pionyl chloride in nitromethane leads to acylated adducts, which are deacylated in aqueous acids (V.J. Grenda, 1967 L.E. Schick, 1969). A new promising route to substituted cyclopent-2-enones makes use of intermediate 5-nitro-l,3-diones (D. Seebach, 1977). 

Reaction of MEK with ammonia and hydrogen produces j i -butylarnine, a fungistat and condensation with aUphatic esters under strongly alkaline conditions produces 1,3-diketones. 

Many pyrazine and quinoxaline syntheses yield mono- or di-N-oxides (76H(4)769). The condensation of a-aminooximes with 1,2-diketones results in the direct formation of pyrazine mono-N-oxides. The a-aminooximes themselves are not easily prepared but 2-amino-2-deoxy sugars readily form the oximes, which have been condensed with glyoxal to yield the pyrazine 4-oxides (Scheme 18) (72JOC2635, 80JOC1693). 

Monooximes of a-diketones have found applicability in the synthesis of 2-aminopyrazine 1-oxides by condensation with a-aminonitriles, and this reaction was used by White and coworkers in an approach to the synthesis of Cypridina etioluciferamine (Scheme 66 R = 3-indoloyl) (73T3761). In this instance, the use of TiCU as a catalyst was essential, since the carbonyl group in 3-acylindoles is normally deactivated and the required amine/carbonyl condensation is impractically slow. Under normal circumstances the carbonyl group in simple alkyl-substituted monoximes of a-diketones is the more reactive site and the reaction is rapid, requiring no catalysis (69LA(726)loo). 

In 1888 Claisen (1888CB1149) first recognized a general synthesis of isoxazoles (283) by the condensation-cyclization of 1,3-diketones (280) with hydroxylamine. It is now generally accepted that the monoxime (281) of the 1,3-diketone and the subsequent 5-hydroxy-isoxazoline (282) are the intermediate products of the reaction. The isolation of the monoxime (281) and 5-hydroxyisoxazoline (282), which were both readily converted into the isoxazole (283) by treatment with acid or base, has been reported (62HC(17)l). 

Trialkylisoxazoles have been prepared by the condensation of primary nitroalkanes under the influence of basic reagents (40JA2604). They can also be obtained from the reaction of a 1,3-diketone RCOCHRCOR with hydroxylamine hydrochloride <62HC(17)l, p. 54). 

Julid investigated the behavior of terfuran 22 and bis(thienyl)furan 23 by cyclic voltammetry as well as the EPR spectra of the radical cations derived from these two compounds. Condensation of the diketone 20 with sulfuric acid furnished furan 22 in 18% yield, while reaction of diketone 21 with hydrochloric acid produced 23 in 84% yield.In a related report, Luo prepared oligomeric bis(thienyl)furans via similar methodology. ... 

The carbanions derived from acylthiophenes have been condensed with aldehydes,and, through the Claisen condensation with esters, thienylsubstituted -diketones have been obtained. 2-Thenoyl trifluoroacetone, first prepared by Reid and Calvin through the Claisen condensation of 2-acetylthiophene with ethyl trifluoracetate, has become an extremely useful chelating agent for the extraction of numerous elements from strongly acidic solutions, The tautomeric form which dominates in aqueous solution is the ketone hy-drate. Other thiophenes have also proved useful for analytical purposes. ... 

Mixed Claisen-like reactions can also be carried out between an ester and a ketone, resulting in the synthesis of a jS-diketone. The reaction works best when the ester component has no a hydrogens and thus can t act as the nucleophilic donor. For example, ethyl formate gives high yields in mixed Claisen condensations with ketones. 

The potential of such reaction sequences for the generation of molecular diversity was also demonstrated by the synthesis of a library of heterocycles. Epoxide ring-opening with hydrazine and subsequent condensation with (3-diketones or other bifunctional electrophiles gave rise to a variety of functionalized heterocyclic structures in high purity [34]. A selection based on the substrate derived from cyclohexene oxide is shown in Scheme 12.12. 

Unactivated aziridines, such as 24, are not as reactive as their N-sulfonyl analogues. Nevertheless, in aqueous conditions they react with different nucleophiles, as Scheme 12.23 illustrates. Treatment with buffered azide at 50 °C gave 25 in 90% yield. Hydrazine proved potent even at room temperature and 26 was fonned in 95 % yield, while phenyltetrazole required heating at reflux in water. The resulting amines participated in dipolar cycloadditions with alkynes and condensations with P-diketones. 

Ozonolysis of condensation products can provide a route to 1,2-difunctionalised compounds. Camphor (13) condenses with many carbonyl compounds (HC02Et is used here) at its only free a-CH2 group to give, e.g. (14). Ozonlysis releases the a-diketone (15). 

Bis(ethylenediamine)gold(III) chloride reacts with /3-diketonates in aqueous base via Schiff base condensation to form complexes of gold(III) with a 14-membered macrocyclic tetraaza ligand such as (292).1711-1713 The X-ray structure showed the cation to be nearly planar. Delocalization of -electrons within the six-membered /3-diketonate rings was indicated by the observed pattern of C—C and C—N distances. Open-chain tetraaza ligand complexes in which condensation of only one /3-diketonate has occurred, can be isolated as intermediates in this reaction. They may be used for further condensation with a different /3-diketonate. Oxidation of this complex with trityl tetrafluoroborate introduces a double bond in position C2C3.1712,1714... 

Earlier work demonstrated that rhena-j8-diketones readily undergo Schiff-base condensation with ammonia or primary amines to give rhena-0-ketoimines 24 and 25 [Eq. (3)] (1). When R is i-Pr, condensation occurs... 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

Aldehydes can be condensed with 1,3-diketones to give vinylic diketones 39 (X = H) and /V-bromsuccinimide converts these into the bromides 39 (X = Br) which supply furans 40 when heated. Yields are poor if the product carries no 5-substituent.101... 

From Table I, it is evident that, generally speaking, the 5-diketones react (with the sugars) like the /3-keto esters. In the condensates of these... 

The reaction sequence outlined in Scheme 20.22 also found application in the synthesis of twisted 4,5-diarylphenanthrenes 256 (Scheme 20.51) [84]. Condensation of the diketone 253 with 2 equiv. of the lithium acetylide of 252 produced the pro-... 

That the two C O-groups of these diketones are adjacent is proved by the fact that they are capable of condensing with o-phenylene-diamine (quinoxalines, Hinsberg). 

Regioselective synthesis of 2-substituted pyrroles using oximinocyanoacetate esters or related compounds in a Knorr-type reductive condensation with diketones was described . Thus, oximinocyanoacetates 63 reacted with pentane-2,4-diones 64 in hot... 

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