5.5- Dimethylcyclohexane-1,3-dione dimedone

Amines, thiols, eOH (p. 226), etc., will also add to the 0-carbon atom of 0-unsaturated carbonyl compounds and esters, but the most important reactions of C=C—C=0 systems are in Michael reactions with carbanions reactions in which carbon-carbon bonds are formed. A good example is the synthesis of l,l-dimethylcyclohexan-3,5-dione (dimedone, 100) starting from 2-methylpent-2-ene-4-one (mesityl oxide, 101) and the carbanion 0CH(CO2Et)2 ... 

Reaction of 31d-f or 154 with a cyclic active methylene compound such as 5,5-dimethylcyclohexane-l,3-dione (dimedone) gave 299a-d (47-85%), which by subsequent cyclization led to the substituted 1,2,3,4,5,6,7,8-octahy-droxanthenes 300a-d (72-90%) <1999CCC1135>. 

Dimethylcyclohexane-l,3-dione (dimedone) and Ai,Ai-dimethylbarbituric acid are relatively acidic (3-dicarbonyl compounds 5.3 and 4.7, respectively). The deprotection reaction involves (Scheme 16) a prototropic equihbrium between the P-dicarbonyl compounds and the deprotected carbamate species (shifted further to right by the formation of carbon dioxide and the respective amine). 

F. Hansske and F. Cramer, Reaction of the ribose moiety of adenosine and AMP with periodate and 5,5-dimethylcyclohexane-l,3-dione (dimedone), Carbohydr. Res., 41 (1975) 366-369. P. N. Lowe and B. R. Beechey, Preparation, structure, and properties of periodate-oxidised ATP, a potential affinity-labelling reagent, Bioorg. Chem., 11 (1982) 55-71. 

Unusual and novel spiro dihydrofuran structure 148 was obtained in condensation reaction of 5,5-dimethylcyclohexane-l,3-dione (dimedone), aldehyde, dimethylami-nopyridine (DMAP), and molecular iodine (Scheme 2.51 Table 2.45) [44]. Wang has found that other bases (DABCO, DBU, Na2C03, CS2CO3, and K2CO3) and different promoters (MBS, NCS, CBr4, Oxone/NaBr, and Oxone/ZnCl2) were less successful. 

Dimethylcyclohexane-l,3-dione (dimedone) (55) reacts with amines to form enamine derivatives which are stable toward adds and bases. Those derivatives are set apart from the enamines which are obtained by the reaction between amines and other /3-dicarbonyl compounds since deavage takes place only after bromination or... 

In the following examples, pinacol is oxidised to acetone, which is identified as its semicarba2one and its 2,4 dinitrophenylhydra2one, and glycerol is oxidised to formaldehyde and formic acid. The formaldehy de is readily detected by the condensation product which it gives with dimedone, 5,5-dimethylcyclohexan-i,3-dione (p, 277). 

Dipping solution Dissolve 0.3 g dimedone (S,S-dimethylcyclohexane-1.3-dione) in... 

Dimedone (5,5-dimethylcyclohexane-l,3-dione) in saturated aqueous solution or in 10 per cent alcohol solution gives crystalline derivatives (2) with aldehydes, but not with ketones. The reaction is ... 

You can buy dimedone (5,5-dimethylcyclohexane-l,3-dione) from chemical suppliers. If, as is wise when you buy any compound, you run an NMR spectrum of the compound to check on its purity, you might be inclined to send the compound back. In CDCI3 solution it is clearly a mixture of two compounds. Overleaf you can see lH and l3C NMR spectra of the mixture with the peaks of the dione in red. 

The Dde-protected amino acids are readily synthesized by acylation of dimedone (5,5-dimethylcyclohexane-l,3-dione) with acetic acid (DCCyDMAP activation), followed by condensation with the primary amine, e.g. Fmoc-Lys-OH, in refluxing ethanol for 60 hours, affording the orthogonally protected amino acid 24 (Scheme 9). 

Dimedon, 5,5-dimethylcyclohexane-l,3-dione, is prepared by an interesting process discovered by Vorlander. The reaction of 1 mole each of diethyl malonate, mesityl oxide, and sodium ethoxide in absolute ethanol probably involves a Michael addition followed by an intramolecular ester condensation to close the ring to give the diketo ester formulated (procedure of Shriner and Todd. Aqueous potassium... 

When 144 was reacted with phenyl isothiocyanate in dichloro-methane at room temperature, 4-oxo-6,6-dimethyl-tetrahydro-l,3-benzoxathiole-2,2-dimethylcyclohexane-2, 6 -dione 213 was obtained together with phenyl-2-iododimedonyl ether 214 and 2-(2-benzothiazo-lyl)dimedone 215 (76JOC125). Both 213 and 214 were obtained when 144 was treated with methyl isothiocyanate. Both reactions may proceed through common intermediate 216. An attempt to synthesize 216 by treatment with hydrogen sulfide was unsuccessful, but compound 213 was isolated in higher yield (40%) (76JOC125) (Scheme 39). 

Dimedone was treated with two equivalents of bromine in glacial acetic acid to yield 2,2-dibromo-5,5-dimethylcyclohexane-l,3-dione. The dibromo compound was subjected to reaction with substituted 2-aminothiophenols, 2-aminophenol, thiocarbohydrazones, and triazoles to furnish spiro-(2, 6 -dioxo-4, 4 -dimethylcyclohexane)-6-substituted-l,... 

The cyclic ketone dimedone, 5,5-dimethylcyclohexane-l,3-dione, gives derivatives which are much more stable towards acids than those from acyclic diketones [215, 216]. When these derivatives are used removal of the protective group is brought about either by bromination [215, 217] or by nitrosation [217, 218] which converts the derivatives into unconjugated, easily hydrolyzable azomethines. 

Zare et al. [210] reported the use of a Bronsted acidic reusable IL 1,3-disulfonic acid imidazolium hydrogen sulfate [DS1M][HS04] in the synthesis of hexahydroquinolines 124 via one-pot multicomponent condensation of aryl aldehydes, dimedone (5,5-dimethylcyclohexane-l,3-dione), p-ketoesters, and ammonium acetate under solvent-free... 

If we now consider the NMR spectrum of the keto and enol tautomers of dimedone (5,5-dimethylcyclohexane-l,3-dione), another puzzle emerges (Figure 17.8). Despite the fact that there can be no intramolecular hydrogen bond, the enol form still appears to be symmetrical— only one type of CHj. At equilibrium, about 40 % of the material is enolized. It is suggested that under these conditions, the material is part of a dimeric structure, 17.17, in which rapid proton transfers are possible. However, in very dry dimethylsulfoxide, NMR spectroscopy suggests that dimedone is completely enolized, and monomeric, with distinct CHj carbon atoms. 

Methones or substituted methylene-bis(5,5 -dimethylcyclohexane-l,3-diones) (products of aldehydes with dimedone, dimethyldihydroresorcinol or 5,5 -dimethylcyclohexane-l,3-diones) have been widely used as specific derivatives to characterize and quantify aldehydes (Vorlander, 1899 Homing and Homing, 1946), including glyoxylic acid (Vorlander, 1929 Klein and Linser, 1929). They were not suitable, however, for gas-chromatographic studies, even when trimethylsilylated, because of their intractable involatility (Chalmers and Watts, 1972c). 

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