Dimedone condensation with

Dimedone reacts with carbonyl compounds with the elimination of water yielding the condensation product [1]. The reaction is specific for ketoses aldoses do not react or only weakly [6],... 

Numerous solvent-free Knoevenagel condensations with malononitrile, methylcyanoacetate, dimedone (255), and Meldrum acid proceeded with high to quantitative results with intermediate melt or full melt at higher temperatures but with direct crystallization [107]. 

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. 

Approaches that represent a type (ii) synthesis of 277-pyran-2-ones include the self-condensation of 1,3-dicarbonyl compounds, the reaction of cyclopropanones with pyridinium enolbetaines and the reaction of activated methylene groups with acetylenic esters <1984CHEC, 1996CHEC-II>. 4-Perfluoroalkyl-6-aryl-pyran-2-ones are formed by the reaction of the phosphonium salts 631 with 2-perfluoroalkynoates (Equation 254) <1999JFC(95)135, 1998JFC(91)99>. Dimedone reacts with dimethyl acetylenedicarboxylate to afford the pyran-2-one 632 in excellent yield (Equation 255) <2003PS2627>. 

Condensation of primary dimedone enaminones with formaldehyde according to Greenhill and coworkers26,27 give, in neutral medium, methylenbisenaminones, whereas acidic conditions produce spirocompounds. Structure A is given by Greenhill27 for the spiro-product, but structure B (equation 20) also seems reasonable. Modern spectroscopic methods should be used to solve this problem. Similar products are obtained in the Mannich reaction of enaminones derived from indan-l,3-dione33. 

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... 

Due to the relative rapidity of the reactions and to the protonation of the free amine by the excess scavenger during the deprotection of allyl carbamates, the risk of formation of allylamine seems very limited and has not been reported. In the reactions with dimedone, a possible complication is the formation of substantial amounts of hydrolytically stable oxo-enamine by condensation with the liberated amine. For this reason, the use of N,N-di-methylbarbituric acid is probably a safer solution. 

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). 

The Knoevenagel condensation with 1,3-dicaibonyls followed by a Michael reaction of a second molecule of the methylene compound, with or without addition of an amine or ammonia, may be used for the qualitative and quantitative determination of aldehydes even in the presence of ketones. Thus, cyclic 3-diketones such as dimedone (59) react with aldehydes but not with ketones in the absence of a catalyst. For the characterization the bis(2,6-dioxo-4,4-dimethylcyclohexyl)methanes (67) or the 4,6-dioxo-2,2,8,8-tetramethyl-l,2,3,4,5,6,7,8-octahydro-9F/-xanthene (68) may used. ... 

Formylation of dimedone using ethyl orthoformate in the presence of acetic anhydride gave the 2-formyldimedone whose condensation with two moles of dimedone gave the xanthene 472 (57JCS4798), which can also be obtained directly from reaction of dimedone with triethyl... 

The l,2,4-triazolo[2,3-fl]quinazoline 532 was obtained by reaction of 1 with 3-amino-l,2,4-triazole 531 in DMF (05RJOC114). In the presence of p-substituted benzaldehyde, the condensation with equimolar amounts of 531 and 1 in DMF or methanol gave l,2,4-triazolo[5,l-fr]quinazolin-8-ones 533 (03CHE1213, 07MI11). Also, the reaction can take place under MW irradiation (07MI287227). Alternatively, 533 were obtained from the condensation of 531 with arylidinedimedone 328 or xanthenedione 402 (R = Ar), via a loss of a molecule of dimedone from the latter compound... 

PHA546,04IJC(B)413), via the oxidation of 547 to the disulfides 548 that condensed with 1 to yield the enamino-ketones 549 the phenothiazine that cyclized to 550 (93PHA546). Reaction of 548 with two molar equivalents of dimedone gave 550 in addition to 551 (76JCS(P1) 1146). 

Compound 547 was condensed with 552 and p-nitrobenzaldehyde in DMSO to give the sulfide 553 that underwent oxidative cyclization in DMSO to give 550 (R/R1, R2 = H) without utilizing the p-nitrobenzaldehyde (76JCS(P1)1146). The condensation of dimedone with 2-nitrobenze-nesulfonyl chloride and subsequent reductive cyclization gave 550 (72KGS1901). Synthesis of benzothiazine 554 can be carried out by treatment of 545 with aniline (81KGS563) (Scheme 118). 

Aminoandrostanes (453) open the ring of maleic anhydride to give the N-steroidal maleamic acids (454). which react with acetic anhydride-sodium acetate to give the 17-yl maleimides (456) via the labile isomaleimides (455). Chiroptical properties of steroidal amine-dimedone condensation products are reported on p. 292. 

The stoichiometric reaction of aromatic aldehydes with Meldrum s acid at 50°C gave an intermediate melt from which products 139 crystallized quantitatively at the reaction temperature (Scheme 2.47). These Knoevenagel condensations were termed melt reactions with direct crystallization. Similar condensation with dimedone 140 afforded a cascade reaction starting with Knoevenagel condensation, which was followed by elimination and subsequent Michael addition (Scheme 2.48). Unlike the solution synthesis, yields are superior and no wastes was produced. 

Primary alcohols can be identified by oxidizing them to aldehydes with chromic acid or potassium permanganate in the presence of 2 n sulfuric acid. The aldehyde formed can be isolated by distillation and identified in the form of its dimedone derivative (see p. 230). Primary alcohols can be identified in this manner in the presence of secondary and tertiary alcohols, because dimedone condenses only with aldehydes, i.e., with products of a mild oxidation of primary alcohols. Carbonyl compounds can be isolated from an aqueous distillate by precipitating them with 2,4-dinitrophenyl-hydrazine (see p. 218). If paper chromatography cannot be used for identification (see p. 222), it is advisable to oxidize at least 500 mg of alcohol. 

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). 

Lipson VV, Shirobokova MG, Shishkin OV et al (2006) Synthesis of partially hydrogenated pyrazolo[3, 4-b]quinolinones by condensation of 3-amino-5-methylpyrazole with aromatic aldehydes and dimedone. Russ J Org Chem 42(7) 1015-1021... 

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