1.2- cyclohexanediones

Conjugation is more important 1 3 Cyclohexanedione exists mainly in its enol form in spite of the fact that intramolecular hydrogen bonding is impossible due to the distance between the carbonyl group and the enohc —OH group... 

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. 

There are several laboratory methods useful for the preparation of suberic acid. One starting material is 1,6-hexanediol which can be converted to the dibromide with HBr. Reaction of the dibromide with NaCN gives the dinitrile which can be hydrolyzed to suberic acid. The overall yield is 76% (42). Another laboratory method is the condensation of 1,3-cyclohexanedione with ethyl bromoacetate foUowed by reductive cleavage to give suberic acid in 50% yield (43). 

The only tetrasubstituted furans that have been prepared using the Feist-Benary reaction are substituted tetrahydrobenzofurans and octahydrodibenzofurans. This strategy was pioneered by Stetter and Chatterjea and applied in a series of total syntheses by Magnus. Stetter demonstrated that 1,3-cyclohexanedione (30) can act as the P-dicarbonyl component and readily combines with either 3-bromo-2-ketobutyric (29) acid or ethyl 2-chloroacetoacetate (32) in the presence of potassium hydroxide to yield tetrahydrobenzofuran derivatives 31 and 33, respectively. ... 

Chatteijea showed that cyclic ot-halocarbonyls are acceptable substrates for the Feist-Benary furan synthesis by combining 1-chlorocyclohexanone (34) with 1,3-cyclohexanedione (30) to yield octahydrodibenzofuran 35. ... 

Magnus prepared tetrahydrobenzofuran 37 using a Feist-Benary reaction of ethyl 2-chloroacetoacetate (32) and functionalized 1,3-cyclohexanedione 36. Compound 37 was a key synthetic intermediate in Magnus s synthesis of linderalactone, isolinderalactone, and niolinderalactone. ... 

A solution of resorcinol (11 g) in sodium hydroxide solution (4.8 g of sodium hydroxide in 20 ml of water) is hydrogenated in the presence of 1.1 g of 5 % rhodium on alumina for 16-18 hours at 50 psi initial pressure in a Parr apparatus. The reduction stops after the absorption of 1 equivalent of hydrogen. The catalyst is removed by filtration through celite, and the aqueous solution is carefully acidified with concentrated hydrochloric acid at 0°. The crude product is collected by filtration, dried in air, and recrystallized from benzene to give 1,3-cyclohexanedione, mp 105-107. ... 

The reaction of 20 g (0.177 mole) of 1,3-cyclohexanedione (Chapter 5, Section II) with 21.8 g (0.22 mole) of maleic anhydride and 0.1 g of/j-toluenesulfonic acid in 150 ml of isopropenyl acetate is conducted as described above to give about 70% of the recrystallized product, mp 156-159°. 

Mesityl oxide (Section 111,79) (I) condenses with ethyl malonate in the presence of sodium ethoxide to give the sodium derivative of (II) this upon hydrolysis with aqueous potassium hydroxide, followed by acidification, gives the cyclic diketone 5 5-dimethyl-1 3-cyclohexanedione (III), of which the enolic form is 5 5-dimethyldihydroresorcinol (IV) ... 

If unreacted DDQ was quenched prior to thermolysis, over-oxidation products could be limited to less than 1%. 1,3-Cyclohexanedione was used to quench unreacted reagent prior to thermolysis. Purity following thermolysis was significantly improved and no problems were found on the laboratory scale. The fully optimized conditions are provided in Scheme 3.16. The reaction was run on pilot scale and performed as expected. 

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,... 

Chiral sulfonium ylides have been known for some 30 years, and their stereochemistry and properties have been studied.15 Optically active selenonium ylides were obtained by reacting selenoxides with 1,3-cyclohexanedione under asymmetric conditions by Sakaki and Oae in 1976 for the first time,16 and also optically resolved by fractional recrystallization of the diastereomeric mixtures in the early 1990s.17 In 1995, optically active selenonium ylides 6 were obtained in over 99% de by nucleophilic substitution of optically active chloroselenurane or selenoxide with active methylene compounds with retention of configuration.18 The absolute configurations were determined by X-ray analysis of one... 

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