2.5- Dimethylfuran

CH3COCH2CH1COCH3. Colourless liquid which becomes yellow on standing b.p. I9PC. Obtained by boiling 2,5-dimethylfuran with dilute sulphuric acid. It readily condenses with a variety of substances to give derivatives of furan, thiophen and pyrrole, and is a solvent for cellulose acetate. 

The diacetoxylation of E,E)- and ( ,Z)-2.4-hexadiene (351 and 353) is stereospecific, and 2,5-dimethylfurans (352 and 354) of different stereochemistry have been prepared from the isomers. Two different carboxylates are introduced with high cis selectivity by the reaction of 1,3-cyclohexadiene and... 

Hexanedione [110-13-4] (acetonylacetone) is one of the most widely used 1,4-diketones. It is a colorless high boiling Hquid prepared by the hydrolysis of 2,5-dimethylfuran (332,333), by oxidation of 2,5-hexanediol (334) or 5-hexen-l-one (335), and from allylacetone (336). Its main use is in solvent systems and as a raw material for chemical synthesis. It is reportedly not highly toxic (336). 

Furan undergoes phenylation rather than diazo coupling on reaction with ben-zenediazonium salts, and thiophene similarly yields 2- or 2,5-diaryl derivatives rather than coupled products. However, 2,5-dimethylfuran and 2-/-butylfuran give coupled products with 2,4-dinitrobenzenediazonium ion (Scheme 26). 

Several groups have used the Paal-Knorr reaction to synthesize trialkylfurans. Ballini prepared a series of 3-alkyl-2,5-dimethylfurans (53) in 60-94% yield by treatment of the corresponding diones (52) with tosic acid. Weirsum produced the sterically congested tri-r-butylfuran 55 from dione 54, but was unable to use the same strategy to furnish the tetra-t-butyl derivative. ... 

Dimethylfuran, in a sensitized reaction, gave 1,3-dimethylcyclopropene (the main product), isoprene, cis- and rran.s-l,3-pentadiene, 2-pentyne, and 1-methylcyclopropenyl methyl ketone (Scheme 7) (70JPC574) the ring contraction showed a high selectivity. 

The irradiation of 2,5-dimethylfuran in the presence of mercury vapor gave a complex mixture of products. Carbon monoxide and propene were removed as gaseous products. Then, cis- and rran.s-l,3-pentadiene, isoprene, 1,3-dimethylcyclopropene, 2-pentyne, 2-ethyl-5-methylfuran, hexa-3,4-dien-2-one, 1-methyl-3-acetylcyclopropene, and 4-methylcyclopent-2-enone were obtained (Scheme 8) (68JA2720 70JA1824). The most abundantproduct was the cyclopentenone 19, the second was the 1,3-pentadiene 12, while the third product was the cyclopropenyl derivative 18. 

By contrast, direct irradiation of 2,5-dimethylfuran gave 2,4-dimethylfuran as the only isolated product (68JA2720). 

The enol ether double bond contained within the ds-fused dioxa-bicyclo[3.2.0]heptene photoadducts can also be oxidized, in a completely diastereoselective fashion, with mCPBA. Treatment of intermediate XXII, derived in one step from a Patemo-Buchi reaction between 3,4-dimethylfuran and benzaldehyde, with mCPBA results in the formation of intermediate XXIII. Once again, consecutive photocycloaddition and oxidation reactions furnish a highly oxygenated system that possesses five contiguous stereocenters, one of which is quaternary. Intermediate XXIII is particularly interesting because its constitution and its relative stereochemical relationships bear close homology to a portion of a natural product known as asteltoxin. 

Our journey begins with the photo-induced union of 3,4-dimethylfuran (19) and / -(benzyloxy)-propanal (18) (see Scheme 5). Irradiation of a solution of these two simple, achiral compounds in benzene with a 450 W Hanovia lamp equipped with a vycor filter results in the exclusive formation of head-to-head, exo photoadduct 17 in 63% yield. As a cw-fused dioxabicyclo[3.2.0]heptene system, intermediate 17 possesses a folded molecular framework to which access is obstructed on the concave face. In the presence of mCPBA, the less hindered convex face of the enol ether double bond is oxidized in a completely diastereoselective fashion, affording intermediate 16 in 80% yield after regioselective opening of... 

Treatment of 10-bromodibenz[fe,/]oxepin with potassium rm-butoxide at 100 C in dioxane results in elimination of hydrogen bromide to give 10,11-didehydrodibenz[6,/ oxepin. This highly strained alkyne intermediate can be trapped with dienophiles, for example, with 2,5-dimethylfuran to give 4.160... 

When 3,4-dichlorothiophene 1,1-dioxide (186) is treated with 2,5-dimethylfuran (187) at 50 °C, the adduct 188 can be obtained in 68% yield. Treatment of the reaction mixture at 93 °C gives the ketone 190 in 77% yield via extrusion of S02 from 188 a,nd the rearrangement of 189 (equation 124)117. Other examples are listed in Table 14. 

Heating of hexane-2,5-dione 1487 with TCS 14, Nal, and triethylamine for 36 h, to form 1488, followed by addition of triflic acid and heating to 140 °C affords, on distillation, a mixture of 2,5-dimethylfuran 1489 and HMDSO 7 containing 90%... 

Fig. 4.3. Potentiometric titration of phenol and salicylic acid. Solvent pyridine-dimethylfuran-diethylamine (4 7 9, v/v) titrant (C4H9)3CH3NOH, 0.1 Nin IPA glass-calomel electrode (aq.).

Temperature control during pressure hydrogenation of cis- or tram-isomers is essential, since at 155°C violent decomposition to carbon, hydrogen and carbon monoxide with development of over 1 kbar pressure will occur. The material should not be heated above 100°C, particularly if acid or base is present, to avoid exothermic polymerisation [1], The m-isomer is readily cyclised to 2,3-dimethylfuran, which promotes lire and explosion hazards. These were measured for the cis- and tram-isomers, and for fram-3-methyl-l-penten-4-yn-3-ol [2],... 

Moore and Hemmens [119] studied the photosensitization of primaquine and other antimalarial agents. The drugs were tested for in vitro photosensitizing capability by irradiation with 365 nm ultraviolet light in aqueous solutions. The ability of these compounds to photosensitize the oxidation of 2,5-dimethylfuran, histidine, trypotophan, or xanthine, and to initiate the free radical polymerization of acrylamide was examined in the pH range 2 12. Primaquine does not have significant photochemical activity in aqueous solution. 

Furans react readily with 4 in [4 + 2] cycloadditions, but the reactivity depends on the nature of the heterocyclic diene. Whereas the parent furan (7) reacts with neat 4 affording excellent yields of a 1.4 1 endo/exo mixture of cycloadducts 60c (entry 3, Table 5) [16], and 2-methylfuran (87a) afforded the corresponding endo-fSSa and exo-88a as a 1.5 1 mixture in 76% yield, 2,5-dimethylfuran (87b) reacted much more slowly, and after 120 h gave only 5% conversion to endo/exo- 88b (2 1) (Table 9). 

Needing 2,5-dimethylfuran as a masked 1,4-dicarbonyl equivalent, Scott and Naples found that the ion-exchange resin Amberlyst 15 is extremely effective in catalyzing the cyclization of hexane-2,5-dione to this compound.31 Some unusual Paal-Knorr reactions have been described. In one, phos-phorus(V) sulfide gave none of the expected thiophene when it acted upon the diketoester 3, the thioester 4 being obtained instead.32 Against all... 

The ease with which furans react with electrophiles is forcibly demonstrated by the reaction (in CHC13 at 25°C) of 2,4-dimethylfuran with trichloroacetyl isocyanate to give the amide 56a.129 Attack at the 3-position is not easy, but still the azide of 3-(2-furyl)propenoic acid at 230°C gives an isocyanate that... 

Alkyl migration has not been found in protonated furan derivatives. Neither 2,5-dimethylfuran nor 2,3,5-trimethylfuran undergo any change other than protonation in fluorosulfonic acid containing antimony pentafluoride. On the other hand, migrations will occur during cyclization until the product corresponds to a protonated furan (Scheme 29).19... 

Generated from diacetyl peroxide, methyl radicals attack 2-methylfuran at position 5 preferentially if both 2- and 5-positions are occupied as in 2,5-dimethylfuran there is still little or no attack at the 3(4)-position. If there is a choice of 2(5)-positions, as in 3-methylfuran, then that adjacent to the methyl substituent is selected.249 These orientation rules are very like those for electrophilic substitution, but are predicted for radical attack by calculations of superdelocalizability (Sr) by the simple HMO method. Radical bromination by IV-bromsuccinimide follows theory less closely, presumably because it does not occur through a pure radical-chain mechanism.249... 

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