1,3-Cyclohexanedione, dimedone

The assay for formaldehyde is today mainly performed by either of two general methods. The one most widely used depends on the reaction of 5,5-dimethyl-1,3-cyclohexanedione (Dimedon) with formaldehyde when applied after the destruction of excess periodate, it proceeds quantitatively,... 

Cycloaddition Reactions with Other Nucleophiles The anodic two-electron oxidation of catechol affords o-quinone that may react with the enolates of 4-hydroxycoumarine or 5,5-dimethyl-1,3-cyclohexanedione (dimedone). The resulting adducts undergo a second anodic oxidation leading to benzofuran derivatives in good yields (90-95%) (Scheme 53) [75, 76]. 

To carry out MCRs of aminoazoles with aldehydes and cyclic CH-acids, the methods of green chemistry were also applied. For example, treatments of 3-methylisoxazol-5-amine and aromatic aldehydes with 1,3-cyclohexanedione, dimedone, 1,3-indanedione, or titronic acid were proceeded in water under micro-wave irradiation at 120°C [100] (Scheme 31). As a result, clean, efficient, and convenient procedures for the generation of polycyclic-fused isoxazolo[5,4-b] pyridines 71 were developed. An interesting fact is that, in the case of 1,3-cyclohexanedione, dihydropyridine s were obtained while in aU other cases only hetero-aromatized derivatives were isolated. No reason for this experimental fact was discussed in the article. 

PROBLEM 19.61 Aldehydes, but not ketones, readily react with 5,5-dimethyl-1,3-cyclohexanedione (dimedone, 1) in the presence of a base (such as piperidine) to give crystalline dime-done derivatives, 2. These compounds can be converted into octahydroxanthenes, 3, upon heating in ethyl alcohol with a trace of acid. Provide arrow formalism mechanisms for the formation of 2 from 1 and an aldehyde (RCHO), as well as for the conversion of 2 into 3. 

When 2-4-0-ethylidene-D-glucofuranurono-6,3-lactone [obtained by the hydrolysis of thioacetal 61 (Ph = Et)] was treated with 5,5-dimethyl-l,3-cyclohexanedione (dimedone), 6-deoxy-6,6-bis(4,4-di-methyl-2,6-dioxocyclohexyl)-3,5-0-ethylidene-L-gulono-1,4-lactone (73) was formed in 71% yield.99... 

Cyclizations involving cyclic 1,3-diones are very effective. Thus 5,5-dimethyl-l,3-cyclohexanedione (dimedone) and 5-phenyl-1,3-cyclohexane-dione react with aldehydes R2CHO to give condensed 4//-pyrans 86a,2,132 86b,63133 86d,63 and 86e.2... 

Dimethyl-l,3-cyclohexanedione (dimedone) and 1,3-cyclohexane-dione (CHD) are highly specific and extremely sensitive reagents which condense with aldehydes to produce fluorescent compounds. The maximum excitation and emission wavelengths are very similar... 

Djmethyl-l, 3-cyclohexanedione Dimedone ot 1,1 -Dime thy l- 3,5-dike tocyclohexane,... 

I, 3-cyclohexanedione (dihydroresorcinol CHD) 5,5-di-methyl-l,3-cyclohexanedione (dimedone)] and ammonia to form fluorescent lutidine derivatives [432]. These reactions of the diketones have been suggested for precolumn derivatization of aldehydes [433-435]. 

In the synthetic research conducted by Kidwai et al. [36], the target compoimds qrrinazoline derivatives were obtained by heating an equimolar amoimt of aldehyde, 5,5-dimethyl-l,3-cyclohexanedione (dimedone), and urea/thiourea tmder micro-wave irradiation in the absence of solvent and catalyst (Scheme 13.3). 

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

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... 

Crystal structures of compounds of the conformation shown in [27] and [28] have been reported 2-phenylmalondialdehyde (Semmingsen, 1977) and 5,5-dimethyl-l,3-cyclohexanedione, i.e. dimedone (Semmingsen, 1974 Singh... 

Cyclic 1,3-diketones can also participate in this MCR. Thus, utilization of two equivalents of 1,3-cyclohexanedione or dimedone instead of (3-ketoesters led to hydrogenated acridine derivatives. However, when only one equivalent of cyclic 1,3-dicarbonyl is used in combination with one equivalent of (3-ketoester, unsym-metric 1,4-DHPs may be obtained (Scheme 3). For example, this reaction was applied to the synthesis of ZD0947, a potassium chaimel opener [20]. 

The only known example of 2-monoalkylaminopyran 123 in the series of tetrahydrochromenes was obtained by the less common three-component reaction of alkylisonitriles 124, acetylenedicarbonic esters 125, and dimedone or 1,3-cyclohexanedione 103 (03M1585) (Scheme 42). This example illustrates how the isonitrile —N =C group can be involved in the formation of a 2-aminopyran ring, similar to the other groups with triple bonds - nitrile C=N and alkynyl C=C. 

Application of 1,3-cyclohexanedione 103a (80CPB648) and dimedone 103b (89CB1323) gives the spiro derivatives of tatrahydrochromenes 217 (Scheme 81). 

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... 

Dimelfiyl-3 5-[Pg.229]

Intermolecular de Mayo reactions are efficient for cyclic 1,3-diketones such as dimedone (5,5-dimethyl-l,3-cyclohexanedione)96,103,104 and acyclic systems such as acetylacetone93-95. Unsymmetrical acyclic /l-diketones, such as 1-phenyl-1,3-butanedione98 can enolize in two directions, however, reaction normally occurs preferentially from a single enol form. Examples of alkene photocycloaddition to trapped ends of /(-dicarbonyl compounds (e.g., 2,2-dimethyl-3(2/f)-furanone and 2,2.6-trimethyl-4/f-l,3-dioxin-4-one) are given in Table 1 (entries 26, 27) and Table 2 (entry 35) 10°. If the enol is stabilized by derivatization (e.g., acetylated dimedone 3-acetoxy-5,5-dimethyl-2-cyclohexenone), the primary cyclobutane photoproducts can be isolated96. 

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