Of dimedone

B) A solution of 1 g. of dimedone (preparation, p. 277) in 10 ml, of ethanol. This solution will be required only for the glycerol oxidation experiment. 

Filter the mixed product at the pump, and wash it well with ethanol to remove excess of dimedone, and then with water and again with ethanol. The dried white residual methylene-dimedone , m.p. 186-188°, weighs o 55-o-65 g. It may be recrystallised from ethanol containing about 10% of water, and then has m.p. 189°. 

Add 0 1 g. of the aldehyde in 5 ml. of 50 per cent, ethanol to 2 ml. of a 10 per cent, or saturated alcoholic solution of dimedone. If a precipitate does not form immediately, warm for 5 mintues if the solution is still clear at the end of this period, add hot water until the mixture is just cloudy and cool to about 6°. Collect the crystalline derivative and recrystallise it from methanol - water or ethanol - water. 

Dimedone " Anhydride of Dimedone 2 4-Dlnltro-phenyl-hydrazone Semi- carbazone Ozime Phenyl- hydrazone />-Nltro. phenyl- hydrazone... 

ALKYLATION OF DIMEDONE WITH A TRICARBONYL(DIENE)IRON COMPLEX TRlCARBONYL[2-[(2,3,4,5-t))-4-METHOXY 2,4 CYCLOHEXADUEN-l-YLJ-5,5-DIMETHYL-l,3-CYCLOHEXANEDIONE]IRON... 

Acylation of the vinylogous pyrrolidine amide of dimedone with acetic anhydride or acetyl chloride led (possibly indirectly) to the carbon acylation product, whereas trichloroacetyl chloride gave rise to products derived from attack of chloride at the oxygenated double bond position in an initial 0-acylation product (401-404). 

In a 500-ml round-bottom flask is placed a mixture of 25 g (0.178 mole) of dimedone, 21.8 g (0,22 mole, 25 % excess) of pulverized maleic anhydride, 0.1 g of /7-toluenesulfuric acid, and 150 ml of isopropenyl acetate. The mixture is refluxed for 72 hours, then cooled, and the acetone is removed at room temperature on a rotary evaporator. The resulting solution is cooled to —20° in a Dry Ice bath, whereupon the product crystallizes. It is collected by filtration to yield the crude product in about 80% yield. Recrystallization from hexane-ethyl acetate and decolorization by Norit gives colorless crystals, mp 164-166°. 

Silyl-derived linker 36 was prepared in three steps from a silyl ether of serine and incorporated for Fmoc/tBu-based assembly of protected gly-copeptide blocks (Scheme 11) [42]. The a-carboxylic acid function of serine was protected as an allyl ester. Deprotection by a Pd(0) catalyst in the presence of dimedone liberated the carboxylic acid in order for subsequent... 

A new domino lithium acetylide addition/rearrangement procedure on trans-1,2-dibenzoyl-3,5-cyclohexadiene furnished 3-alkylidene-2,3-dihydrofurans via an intriguing mechanism involving three bond formations and two bond cleavages in one single operation <06SL1230>. The reaction of dimedone with meso-diacetoxycyclohexene in the presence of a palladium catalyst led to the formation of the tricyclic product as depicted below <06S865>. 

The hypothesis of Kellogg 38> described above, that autoxidation reactions display low quantum yields in spite of high yields of excited products, due to oxygen quenching in the solvent cage, is criticized by J. Beutel 13) who very thoroughly investigated the chemiluminescent autoxidation of dimedone (1.1. dimethyl 3.5 cyclohexandione). Here the recombination of dimedone peroxy radicals should be the excitation step ... 

A detailed mechanism is proposed for this recombination process. On the basis of the experimental results obtained, Beutel (for details see 13>) comes to the conclusion that in the case of dimedone autoxidation the triplet triketone D = O cannot be efficiently quenched by ground-state triplet oxygen formed in the decomposition of a Russell tetroxide which in this case should have the formula. 

The fact that the kinetic chain length of dimedone autoxidation is very low appears to indicate structural effects in autoxidation reactions. These may account for some of the discrepancies found in autoxidation chemiluminescence studies of different types of compounds. 

The early addition of Dimedon is reported234 to depress the formation of hexamethylenetetramine from formaldehyde in the presence of ammonia. O Dea282 found that the activated methylene center, sometimes formed in periodate oxidations of carbohydrates, reacts appreciably with the formaldehyde formed, thus giving low yields of apparent formaldehyde. He was able to depress this side reaction by the use of lowered temperatures and by the addition of benzaldehyde or of p-hydroxybenzaldehyde. The analyses for formaldehyde have often been more successful at a pH of 7.5 than at lower pH values.57, 68 59a 60 264... 

The reaction of dimedone with 3-alkyl-5-ercapto-1,2,4-triazoles 315 in the presence of NBS gives intermediates, which after reaction with a solution of aqueous sodium carbonate afford 2-alkyl-5a-hydroxy-6,6-dimethyl-8-oxo-5a, 6,7,8,8a-hexahydro[l,2,4]triazolo[3,2-3]benzothiazoles 49. Finally, reaction with PPA provides the dehydrated heterocyclic derivatives 316 (Scheme 30) <1999IJH127>. 

By using this approach, Morken found a variety of interesting results, one of which is that [ RhCl(cod) 2] with dppe [bis(l,2-diphenylphosphino)ethane], PBu3, or P(OEt)3 as ligands acts as an active catalysts for this reaction. Another interesting finding is that [ IrCl(cod) 2] with i-Pr-pybox is an active catalyst for the addition of dimedone to the allyl carbonate (Scheme 27). 

JOC4885). For example, decomposition of dimedone iodonium ylide (42) in the presence of acetonitrile and phenyl isocyanate provides 4,5,6,7-tetrahydrobenzoxazoles 155 (87TL4449) and 156 (75JOC1166), respectively (Scheme 43). 

Lipson et al. in several publications [91-93] in the reactions of dimedone and aromatic aldehydes with 2-aminobenzimidazole, 3,5-diamino-l,2,4-triazole, and 3-amino-5-methyltio-l,2,4-triazole described a formation of angular tri- and four-cyclic heterocycles as minor reaction products. However, aldehydes did not participate in these MCRs and the solvent (DMF) acted as a carbonyl component... 

Tetrahydrochromenes 107, containing perfluoroalkyl and phosphonic groups in the same molecule, have been obtained via the interaction of dimedone 103b with nitriles 108 at room temperature in chloroform (04JFC1853) (Scheme 36). 

The different selectivity between Sc -mont and Sc(OTf)3 has been rationahzed by the mechanism of the transformation. While the Sc(OTf)3 catalyzed reaction in water afforded 17 through the classical mechanism, when Sc -mont is used the compounds are reacting when coordinated to the Sc center in the silicate layer of Sc -mont, giving rise to the addition of two molecules of dimedone... 

The efficient formation of diaryliodo-nium salts during the electrolysis of arylio-dides has been reported by Peacock and Fletcher [166]. The electroiodination of a 3D-aromatic molecule, dodecahydro-7,8-dicarba-nido-undecaborate has also been reported [167]. The iodination (and bromi-nation) of dimedone has been reported to yield 2-iododimedone, which formally is an electrophilic substitution reaction [123]. In a similar process, the indirect electrochemical oxidation of aliphatic ketones in an alkaline Nal/NaOH solution environment has been shown to yield a,a-diiodoketones, which rapidly rearrange to give unsaturated conjugated esters [168]. Dibenzoylmethane has been converted into dibenzoyliodomethane [169]. Terminal acetylenes have been iodinated in the presence of Nal. However, this process was proposed to proceed via oxidation of the acetylene [170]. 

ALKYLATION OF DIMEDONE WITH A TRICAEBONYL(DIENE)IEON COMPLEX TRICAEB0NYL[2-[(2,8,4,5-7,)-4-METH0XY-2,4-CYCL0HEXADIEN-1-YLJ-5,5-DIMETHYL-I,3-CYCLOHEXANEDIONE]IEON... 

The Niki reaction474 (alkylation of dimedone by l,4-dibromo-2-methyl-2-butene, with formation of compound 218), applied to phloro-acetophenone and to 3-isopentyl-2,4,6-trihydroxyisobutyrophenone, leads respectively to 2,3-dihydrobenzofurans 219a and 219b. Furan 219b with toluene- >-sulfonic acid rearranges to the benzofuran 220b.475... 

A more general method for carbohydrates that can be used equally well on handsections and on sections of plastic embedded materials uses the Periodic acid SchifFs (PAS) reaction or one of its variants [29] for vicinal hydroxyl groups [22,23]. Sections are treated with 1%W/V Periodic acid at room temperature for 10 minutes and rinsed. The aldehydes created by this treatment are detected with SchifFs reagent (decolorized para-rosaniline) by immersion for 30 minutes. A red color (or fluorescence with excitation at 540 nm) indicates vicinal hydroxyl groups in starch and many other carbohydrates. If the specimen has been fixed with aldehydes then an aldehyde-blocking step must precede this reaction [22]. The best treatment is immersion for 24 hr in a saturated solution of dimedone. 

Frequently the basic conditions used cause the initial Michael adduct to undergo intramolecular transformations, as for example in the synthesis of dimedone (Expt 7.11). This involves a Michael reaction between mesityl oxide and diethyl malonate followed by an internal Claisen ester condensation. 

Benzaldehyde (4f) can be condensed with 2equiv. of dimedone (90) and a substoichiometric amount of FeCl3-6H20 to give xanthenedione derivative 91 in good yield (Scheme 8.37) [107]. The reaction is carried out in an ionic liquid as solvent. Only minor amounts of EtOH and H20 are required for workup and purification of the product. 

These masked enolate complexes also react smoothly with carbonyl compounds, in reactions surprisingly reminiscent of the reaction of dimedone with formaldehyde (Fig. 5-13). The dinuclear products are of some interest as models for the dinuclear sites of some metalloproteins. 

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