2,5-Dimethylfuran, reactions with

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). 

The nature of the dipolar intermediate is crucial in the reaction with furans, since the product distribution is greatly influenced by the substituents present on the furan and vinylcarbenoid (Tab. 14.10) [84—86]. Electron-rich 2-methoxyfuran leads to exclusive formation of triene 89 with vinyldiazoacetate 42, whereas the corresponding reaction with 2,5-dimethylfuran affords only the [3+4] cycloaddition product 88 in 70% yield. 

Several 1,2,4-trioxolanes are known which contain a double bond linked in some way to the ring, with interest focusing on furan endoperoxides. The alkene moiety of 2,5-dimethylfuran endoperoxide (41) can be selectively functionalized in the presence of the 1,2,4-trioxolane ring. Reaction with diimide gives the saturated ozonide <81TL3509> and a single addition product was obtained with p-nitrophenylazide, although the stereochemistry of the reaction was not determined. 

Sulfur tetrafluoride fluorination of the methyl group has been reported.253 Thus, the reaction with 2,5-dimethylfuran-3,4-dicarboxylic acid gives, besides the expected acid fluoride 16 and 2,5-dimethyl-3,4-bis(trifluoromethyl)furan (17a), higher fluorinated compounds, 2-(difluoro-methyl)-5-methyl-3,4-bis(trifluoromethyl)furan (17b) and 2-methyl-3,4,5-tris(trifluoromethyl)-furan (17c). Low yields are due to considerable tar formation. 

Diels-Alder reaction.1 The first step in a synthesis of citreoviral (5), a metabolite of Penicillium citreoviride, from 2,4-dimethylfuran (2) is a Diels-Alder reaction with 1, to give a 7 5 mixture of endo- and exo-adducts (3). Both are converted in 3 steps to the diol (4), a precursor to 5. 

The reaction with simple, nonbenzenoid furans was less successful. Thus, reaction of tita-nium(III) chloride and lithium aluminum hydride with the adduct 8 (R = Me) of l-bromo-2-chlorocyclopropene and 2,5-dimethylfuran gave only 30% of the cycloheptatriene 10 (R = Me) and no cycloproparene. With the 2-methylfuran adduct 8 (R = H), an additional 30% of 2-methyl-l/f-cyclopropabenzene (9, R = H) was obtained. 

The Diels-Alder reaction of maleic anhydride with 3,4-dimethoxyfuran affords endo- and exo-adducts at about the same rate, in contrast to furan, where the endo-isomer is the product of kinetic control. In both cases the exo-adduct is thermodynamically more stable. 3,4-Dimethoxyfuran and p-benzoquinone give the eiufo-compound (37), whereas in the reaction with 2,3-dimethyl-1,4-benzoquinone only the exo-adduct (38) was detected. The Diels-Alder adduct (40) of methyl acrylate to 2-amino-3-cyano-4,5-dimethylfuran (39) is readily... 

While the acid forms of ZSM-5 produced dimethylfuran with nearly 100% selectivity, sodium-exchanged forms of ZSM-5 led to the formation of methy-cyclopentenone with more than 90% selectivity. However, further investigations into this reaction are needed, as there was no report about correlations of the rate of reaction with different basic strengths or basic site concentrations. 

The double furan 140 [173] [obtained in one step from 2,4-dimethylfuran (prepared in three steps from acetone) by reaction with acetaldehyde] adds to... 

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... 

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. ... 

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