Fi-dicarbonyl compound

Second, an enamine from a mowoketone can be used in the Michael addition, whereas enoJate ions only from fi-dicarbonyl compounds can be used. 

To a stirred solution of the aromatic substrate (13.8 mg, 0.1 mmol) and the fi-dicarbonyl compound (6.6 mg, 0.5 mmol) in hexafluoro-2-propanol (0.5 ml) was added BTI (43 mg, 0.1 mmol) at room temperature under nitrogen. The reaction mixture was stirred for 15 min and then concentrated the residue was purified by column chromatography (silica gel, hexane-ethyl acetate) to give 2-(2,5-dimethoxy-phenyl)-2-methyl-l,3-cyclopentanedione (16.5 mg, 66%), m.p. 165-166°C. 

Following the production of 1,2-enol forms of aldose and ketose amines, a series of degradations and condensations results in the formation of melanoidins. The a-fi-dicarbonyl compounds enter into aldol type condensations, which lead to the formation of polymers, initially of small size, highly hydrated, and in colloidal form. These initial products of condensation are fluorescent, and continuation of the reaction results in the formation of the brown melanoidins. These polymers are of nondistinct composition and contain... 

Enols are much more easily oxidized than the corresponding ketone tautomers, however, their tendency to ketonize rapidly has precluded extensive electrochemical and other one-electron oxidation studies so far. Hence, oxidation potentials were only determined of few relatively stable enols of fi-dicarbonyl compounds or a-cyano ketones, where the enol content may be as... 

Similarly, the condensation of fi-dicarbonyl compounds with hydrazines has been used to access pyrazolones [83, 84], which have a long history of application in pharmaceutical chemistry. 

Reaction of j>-Mannose and v-Rhamnose with fi-Dicarbonyl Compounds... 

Arylation of fi-dicarbonyl compounds (5,163-164). Experimental details are available for the preparation of homophthalic acids by arylation of j3-keto esters with 2-bromobenzoic acids with copper catalysts. ... 

Dimerization of fi-dicarbonyl compounds. The dicarbanions of 3-dicarbonyl / compounds are dimerized by treatment with iodine (or bromine) when catalyzed by cuprous chloride or cobaltous chloride. ... 

Thalliutn(I) salts of fi-dicarbonyl compounds. The first step in a recent synthesis nf methyltriacetic lactone (5) involved conversion of r-butyl aceto-acetate (1) into the thallium salt (2). This underwent C-acylation with ethyl... 

Pyrroles.—Formation. A general synthesis of 2-aryl-pyrroles (112) is by cycliz-ation of the esters (111), which are obtained from unsaturated aldehydes and methyl azidoacetate. Thermolysis of the acetylene (113 Ar = p-MeC6H4) gives Al-(p-tolyl)pyrrole with the elimination of p-thiocresol. The pyrrole derivative (115) is the product of the action of benzylamine on tri-(t-butylthio)cyclopropenylium perchlorate (114). Azoalkenes combine with fi-dicarbonyl compounds or with enamines to yield derivatives of Al-aminopyrrole thus the ester (116) and ethyl acetoacetate form (117). The base-catalysed addition of methyl propiolate to toluene-p-sulphonylmethyl isocyanide, T0SCH2NC, gives the ester (118). The dipolar cyclo-adduct (120) of piperidinocyclopentene to the azo-compound (119) forms the A-(tosyl-amino)pyrrole derivative (121) and piperidine on heating. ... 

Principal Synthesis from Fluorinated fi-Dicarbonyl Compounds and Their Analogues... 

Alkyl methyl ketones undergo nitrosation at the reactive methylene group when treated with nitrous acid or an alkyl nitrite [Method (fi)]. The presence of hydrogen on the a-carbon permits tautomeric rearrangement to the oxime of a 1,2-dicarbonyl compound. Acidic hydrolysis of the oxime, which is best carried out in the presence of a hydroxylamine acceptor such as laevulinic acid,143 affords a further useful route to the 1,2-dicarbonyl system. 

Fig. 5.5. Products of the multicomponent domino-Knoevenagel-hetero-Diels-Alder-hydrogenation sequence with a, fi- and y-amino aldehydes with different 1,3-dicarbonyl compounds.

Cyclopentene-l,4-dione is a very reactive dienophile in the Diels-Alder reaction and thus provides access to a variety of compounds containing the reactive fi-dicarbonyl grouping in a five-... 

Acylcuprau renjff nrs. The rcaeiion of cuprates of the type R,(CN)CuLi unth carbon monoxide at IKf results in carbonyiated reagents, possibly with the composition (RCO)R(CN)CuLi . In any case, these cupndes effect 1.4-acylation of a.fi-cnones and -enats to provide 1.4-dicarbonyl compounds. 

Cyclocondensation of fS-disubstituted enone systems with fi-keto esters gives rise to 4H-pyran-3-carboxylates 11 (via primary Michael addition to 1,5-dicarbonyl compounds 10 and their cyclization) ... 

The Hantzsch protocol is of considerable scope and flexibility [121, 122], Thus, fi-enaminones can replace one molecule of fS-dicarbonyl compound (three-component condensation) or can be combined with enones (two-component condensation), as illustrated by syntheses of the l,4-dihydropyridine-3,5-dicarboxylate 172 ... 

Very potent carbon nucleophiles formally equivalent to ester enolates are generated by the interaction of TASF(Me) with unhindered trialkylsilyl ketene acetals. In contrast to lithium enolates, these TAS enolates add 1,4 (nonstereoselectively) to a,fi-unsaturated ketones. These adducts can be alkylated in situ to form two new C-C bonds in one pot, or they can be hydrolyzed to give 1,5-dicarbonyl compounds (eq 5). ... 

Chiral imidazolidinones like 20 serve as chiral organocatalysts for the enantioselective reactions of 2-siloxyfuran with a y9-unsaturated aldehydes through oc,fi-unsaturated iminium species (Scheme 3-83)J The Mukaiyama-Michael reaction with nitroolefines provides an access to 1,3-dicarbonyl compounds... 

A (1/7-imidazol-l-yl) silver species (55) has been postulated as the key intermediate in the 3-l-2-cycloaddition reaction of diazoalkanes (54) with benzynes yielding 2-aryl-2H-indazoles (56) (Scheme 18). The 3-I-2-cycloaddition reaction of 3-trifluoromethyl-4-diazopyrazolinones with dialkyl acetylene dicarboxylates, in refluxing toluene, produced spiro 3/f-pyrazole adducts that rearranged to the trifluoromethyl-substituted pyrazolo[l,5-fi(][l,2,4]triazin-7-ones. ° The 1,3-dipolar cycloaddition reaction of aromatic thioketones (58) with 2-aza-1,3-dicarbonyl compounds (57), at 20-50 C, yielded thiadiazoline adducts (59) that readily eliminate nitrogen to produce oxathioles (60) in moderate yields (up to 70%) (Scheme 19). ... 

The preparation of (83) (Expt 8.29) is an example of the Hantzsch pyridine synthesis. This is a widely used general procedure since considerable structural variation in the aldehydic compound (aliphatic or aromatic) and in the 1,3-dicarbonyl component (fi-keto ester or /J-diketone) is possible, leading to the synthesis of a great range of pyridine derivatives. The precise mechanistic sequence of ring formation may depend on the reaction conditions employed. Thus if, as implied in the retrosynthetic analysis above, ethyl acetoacetate and the aldehyde are first allowed to react in the presence of a base catalyst (as in Expt 8.29), a bis-keto ester [e.g. (88)] is formed by successive Knoevenagel and Michael reactions (Section 5.11.6, p. 681). Cyclisation of this 1,5-dione with ammonia then gives the dihydropyridine derivative. Under different reaction conditions condensation between an aminocrotonic ester and an alkylidene acetoacetate may be involved. 

A Michael reaction involves the conjugate addition of a stable enolate ion donor to an a,/S-unsaturated carbonyl acceptor, yielding a 1,5-dicarbonyl product. Usually, the stable enolate ion is derived from a jS-diketone, )8-keto ester, malonic ester, or similar compound. The C—C bond made in the conjugate addition step is the one bebveen the fi carbon of the acidic donor and the f3 carbon of the unsaturated acceptor. 

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