1,3-diketones, reaction with

Reaction of lithiated 3-enaminophosphonj tes of aniline and isocyanates with subsequent cyclization of the resulting amides with triphenylphosphine/triethylamine leads to the 3-phosphonyl-4-aminoquinolines (Equation 92) <1999T5947>. Aniline reaction with /3-diketones < 1999H(51 )2171 > and ethoxymethylenemalonates <1999JFC(94)7> also leads to quinoline formation. The Vilsmeier reaction conditions can also be applied to the synthesis of quinolines with the use of a-oxoketene /V -anilinoacetals (Equation 93) <2003JOC3966>. 

The allylic alcohol products from Morita-Baylis-Hillman reactions were shown to participate in a DMAP-mediated Tsuji-Trost-type reaction with /3-diketones or /3-ketoesters, forming the C-allylation product without requiring the use of palladium. Previously, it was shown that allylic alcohols combined with /8-ketoesters and DMAP afforded the transesterification products, in which the allylic alcohol displaced the ester substituent. The difference between these diverging reaction pathways is likely due to the electron-withdrawing group on the allylic alcohol in the MBH adducts vs. just alkyl substituents in the latter case. 

Mono- and dicyclopalladation of mesogenic pyridazines was achieved and the subsequent reaction with /3-diketones gave metallomesogens 125-128 (Scheme 19). Monometallated derivatives have a flat central core, dimetallated derivatives have a sterically induced twist in the molecule rendering them chiral. Smectic A phases are exhibited, with transition temperatures in the region of 100/300 °G. 

Shaw and McDowell have prepared imidazolone derivatives by cyclization of a-acylamino amides. In a variation of this reaction the azlactone (30) was gradually converted to the hydroxamic acid (31) by methanolic hydroxylamine. Sodium methoxide and hydroxylamine readily gave the acyclic hydroxamic acid (32) which could be cyclized to 31 by dilute acid. Benzyloxynrea has been used in the synthesis of pyrimidine hydroxamic acids (33) by reaction with -diketones followed by catalytic hydrogenation of the benzyl group. Protection... 

The Michael reaction is of central importance here. This reaction is a vinylogous aldol addition, and most facts, which have been discussed in section 1.10, also apply here the reaction is catalyzed by acids and by bases, and it may be made regioselective by the choice of appropriate enol derivatives. Stereoselectivity is also observed in reactions with cyclic educts. An important difference to the aldol addition is, that the Michael addition is usually less prone to sterical hindrance. This is evidenced by the two examples given below, in which cyclic 1,3-diketones add to o, -unsaturated carbonyl compounds (K. Hiroi, 1975 H, Smith, 1964). 

Esters of nonenolizable monocarboxylic acids such as ethyl benzoate give p diketones on reaction with ketone enolates... 

The radicals that are formed from the enolate in this process are rapidly destroyed so that only the stable semidione species remains detectable for EPR study. Semidiones can also be generated oxidatively from ketones by reaction with oxygen in the presence of base. The diketone is presumably generated oxidatively and then reduced to the semidione via reduction by the enolate derived from the original ketone. 

Selectivity in formation of protective groups may also be achieved by a proper choice of reaction conditions and catalyst. Thus formation of the 3-monothioketal from 3,6-diketones is achieved by dilution of the ethane-dithiol-boron trifluoride reaction mixture with acetic acid. 3-Monocyanohydrins are obtained in good yield from 3,20-diketo-(5a)-pregnanes by diluting the exchange reaction with ethanol. Similarly, dilution of the... 

Thioketals are readily formed by acid-catalyzed reaction with ethane-dithiol. Selective thioketal formation is achieved at C-3 in the presence of a 6-ketone by carrying out the boron trifluoride catalyzed reaction in diluted medium. Selective protection of the 3-carbonyl group as a thioketal has been effected in high yield with A" -3,17-diketones, A" -3,20-diketones and A" -3,l 1,17-triones in acetic acid at room temperature in the presence of p-toluenesulfonic acid. In the case of thioketals the double bond remains in the 4,5-position. This result is attributed to the greater nucleophilicity of sulfur as compared to oxygen, which promotes closure of intermediate (66) to the protonated cyclic mercaptal (67) rather than elimination to the 3,5-diene [cf. ketal (70) via intermediates (68) and (69)]." " ... 

Hemithioketals can be prepared from 12,20-diketones [e.g., (81)] by reaction with mercaptoethanol, zinc chloride and sodium sulfate in dioxane. The 12-hemithioketal of triketocholanic acid is prepared by selective cleavage of the 3,7,12-trihemithioketal. " ... 

Terminally unsaturated fluonnated alkenoic acids can be obtained from poly-fluorocycloalkenes by reaction with potassium hydroxide m rert-butyl alcohol [24] (equation 26) The use of a tertiary alcohol is critical because primary and secondar y alcohols lead to ethers of the cycloalkenes The use of a polar aprotic solvent such as diglyme generates enols of diketones [26] (equation 27) The compound where... 

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 -diketones may be modest, but those of p-keto nitnles are excellent (Table 9)... 

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. ... 

A recent paper by Singh et al. summarized the mechanism of the pyrazole formation via the Knorr reaction between diketones and monosubstituted hydrazines. The diketone is in equilibrium with its enolate forms 28a and 28b and NMR studies have shown the carbonyl group to react faster than its enolate forms.Computational studies were done to show that the product distribution ratio depended on the rates of dehydration of the 3,5-dihydroxy pyrazolidine intermediates of the two isomeric pathways for an unsymmetrical diketone 28. The affect of the hydrazine substituent R on the dehydration of the dihydroxy intermediates 19 and 22 was studied using semi-empirical calculations. ... 

In a modified approach, the carbolinyl acetate 393 underwent a Mannich reaction with formaldehyde and acetone to give the keto ester 396 which, with base, cyclized to the diketone 397. This diketone (397) has recently been used to prepare a number of interesting pentacyclic compounds. 

For the mechanistic course of the reaction the diketone 5 is assumed to be an intermediate, since small amounts of 5 can sometimes be isolated as a minor product. It is likely that the sodium initially reacts with the ester 1 to give the radical anion species 3, which can dimerize to the dianion 4. By release of two alkoxides R 0 the diketone 5 is formed. Further reaction with sodium leads to the dianion 6, which yields the a-hydroxy ketone 2 upon aqueous workup ... 

Cyclic 1,3-diacetoxy-l,3-dienes can be generated in situ from cyclic 1,3-diketones under the influence of isopropenyl acetate. The dienes then undergo Diels-Alder reactions with maleic anhydride giving as products 1-acetoxybicycloalkane dicarboxylic anhydride derivatives (10). The procedure is also successful with cyclic 1,2- and 1,4-diketones as well as cyclic a,j3-unsaturated ketones. The products, after hydrolysis to... 

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