Dimedone, oxidation

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. 

Unique methods based on new principles have been developed within the past 10 years. Threonine (27,28,249) is oxidized by lead tetraacetate or periodic acid to acetaldehyde, which is determined by photometric analysis of its p-hydroxydiphenyl complex or iodometric titration of its combined bisulfite. Serine is oxidized similarly to formaldehyde, which is determined gravimetrically (207) as its dimedon (5,5-dimethyldihydro-resorcinol) derivative or photometric analysis (31) of the complex formed with Eegriwe s reagent (l,8-dihydroxynaphthalene-3,5-disulfonic acid). It appears that the data obtained for threonine and serine in various proteins by these oxidation procedures are reasonably accurate. [Block and Bolling (26) have given data on the threonine and serine content of various proteins. ]... 

Allyl carbonate esters are also useful hydroxy-protecting groups and are introduced using allyl chloroformate. A number of Pd-based catalysts for allylic deprotection have been developed.209 They are based on a catalytic cycle in which Pd° reacts by oxidative addition and activates the allylic bond to nucleophilic substitution. Various nucleophiles are effective, including dimedone,210 pentane-2,4-dione,211 and amines.212... 

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 ... 

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... 

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]. 

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]. 

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. 

The photochemical addition of cyclic 1,3-diones such as dimedone, 1,3-cylohexandione 62, or their respective silyl enol ethers leads to the formation of two fused furanylfullerenes, (1) achiral 63 and (2) chiral 64 [244], The latter having an unusual bis-[6,5] closed structure. In the initial step of this reaction, [2 + 2] photocycloaddition across a [6,6] bond to form cyclobutanols or the corresponding TMS ethers is involved (Scheme 26). Oxidation with 02 yields in the formation of the radical 65a. Cleavage to 66a followed by cyclization gives furanyl radical 67a. H abstraction by 102 or a peroxy radical finally leads to product 63. In competition, formation of fullerene triplets by absorption of a... 

The standard assay for haloperoxidase activity is the halogenation of monochloro-dimedone (mcd) (2-chloro-5,5-dimethyl-l,3-dimedone) using dihydrogen peroxide as the oxidant of the halide (Figure 4) [48],... 

Dimedone monoimide (91) reacts with p-chlorophenyl isothia-cyanate to give an adduct (92) which may be oxidized to a 4-keto-... 

The last-mentioned authors22 have described also the oxidation of D-xylo-benzimidazole (XVII) with sodium periodate in 35% ethanol solution. Three molar equivalents of oxidant produced two molar equivalents of formic acid and one of formaldehyde 60% of the latter was isolated as the dimedon derivative. The remainder of the original mole-(31) A. Bistrzycki and G. Przeworski, Ber., 46, 3483 (1912). 

Dimedone has a trivial name because its preparation is so easy that it was discovered early in the history of organic chemistry. The first step is a conjugate addition of diethyl malonate to the unsaturated ketone mesityl oxide (4-methylpent-3-en-2-one given a trivial name for the same reason). Ethoxide ion is the base for the usual reason that nucleophilic substitution at the ester group simply regenerates starting material. 

With the morpholino enaminone derived from dimedone the oxidized enamine adduct shown in Scheme 41 could be isolated. 

The oxidative cyclisation of the disulfide 71 derived from a Willgerodt-Kindler thiolation of dimedone affords the 4,1,2-oxadithiin 72 <07HCA1606>. 

The condensation of 3-substituted catechols with dimedone under electrochemical oxidation in aqueous medium leads to benzofurans (Equation 120) <2004JOC2637>. 

Cyclohexadienes. The last steps in a recent novel synthesis of /3-damascenone (3) from dimedone by way of 1 required oxidation of an allylic hydroxyl group and 1,4-elimination of acetic acid. Activated Mn02 proved to be superior to pyridinium chlorochromate (40% yield) and to NCS-S(CH3)2 (4,87-89), which caused elimination of the hydroxyl group. The last step was effected by DBU at reflux for 20 seconds in 79% yield. ... 

Dimedone (5,S-Dlmethylcyclohexane-M-illone). Mol. wt. 14(1.18. m.p. 149°. Suppliers F.. B. Di(jac, Light. Prepared by condcnxalion of diethyl mulonule with mesityl oxide, hydrolysis, and decarboxylation. The product is almost entirely enolic. 

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