2-Methyl furan, addition

Chlorination of furan at -40 °C with 1.6 mol of chlorine affords 2-chloro- (64%), 2,5-dichloro- (29%) and 2,3,5-trichloro-furan (7%). By use of more chlorine the addition product 2,2,3,4,5,5-hexachloro-2,5-dihydrofuran and tetrachlorofuran are obtained. The chlorination of methyl furan-2-carboxylate obeys second order kinetics, when the 5-chloro compound is the only product. 

Matsuda 1992 PC/LiC104 Effect of additives benzene, methyl furan 92... 

Treatment of 1,3-dicarbonyl compounds with DBP in a methoxide/methanol system affords 2-alkyl-4-[(phenylsulfonyl)methyl]furans, where reaction proceeds by Initial addition-elimination on the vinyl sulfone moiety. In contrast, silyl enol ethers in the presence of silver tetrafluoroborate resulted in products derived from Sn2 displacement at the allylic site.11 Anions derived from 1,3-dicarbonyls substituted at the C-2 position are found to induce a complete reversal in the mode of ring closure.12 The major products obtained are 3-[(phenylsulfonyl)methyl]-substituted cyclopentenones. The internal displacement reaction leading to the furan ring apparently encounters an unfavorable Ai -interaction in the transition state when a substituent group is present at the 2-position ol the dicarbonyl compound. This steric Interaction is not present in the transition state leading to the cyclopentenone ring. 

Dielectrophilic species are 1,4-diketones, certain 1,3-dienes, a,B-unsaturated isocyanates, isothiocyanates, cyanates, and thiocyanates bearing electron-withdrawing (e.g., polyfluorinated and perfluorinated) substituents the most frequently used 1,1-dinucleophiles are water, potassium sulfide, primary amines, and ammonia. From this repertoire of building blocks many combinations are possible. Tetrakis(trifluoro-methyl)furans, thiophenes, and pyrroles have been synthesized from per-fluoro-3,4-dimethylhexa-2,4-diene on addition of water, potassium sulfide, or aniline (90CC1127) (Scheme 39). 

Photoadducts could also be formed when the alkenes are replaced by benzene and methyl-substituted benzenes (equation 35) and heterocyclic arenes such as furans, pyrrole and thiophene (equation 36)196. It should be noted that the arylation took place at the a position of these heterocycles, but at the /9 position when both the a positions are methylated. In addition, hexamethylbenzene could also lead to photoadducts. The reactions of 91a and 91b are efficient with the quantum yields for decomposition of 91a and 91b being 0.44 and 0.87, respectively. Thus, these reactions offer alternative methods for the synthesis of biarylamines and 4-alkylanilines. 

Already in the thirties, copper-chromite promoted by addition of an alkaline earth oxide, was a favourite commercial catalyst for various hydrogenations. In the gas-phase hydrogenation of furfural copper catalysts have been used mainly to avoid hydrogen addition on the furan ring. However, an imdesired further reduction of the furfuryl alcohol to 2-methyl-furan can sometimes occur. Bremner et al. [9] studied in details the reaction of furfural over a number of copper catalysts. These studies showed that in the hydrogenation of furfural, high temperatures (> 300°C) or the addition of chromite to the copper catalyst favoured the formation of 2-methyl-furan, whereas low temperatures (< 200°C) or the addition of alkali-metal containing compoimds favoured the formation of furfuryl alcohol. 

Cycloadducts, formed by addition of hexafluorobut-2-yne to 2-methyl furan or 2-hydroxymethyl furan can be transformed into bis(trifluoromethyl)furan derivatives. For example, compounds 59 and 60 were prepared using this approach. " ... 

The observed 100% regiochemistry of the addition of 2-methylfuran and methyl furan-2-carboxylate to all thiophene 1,1-dioxides was explained in terms of the frontier orbital theory using the calculated orbital coefficients (Scheme 93) [116]. 

The final variation of the Feist-Benary furan synthesis encompasses reactions of 1,3-dicarbonyls with 1,2-dibromoethyl acetate (52). For example, treatment of ethyl acetoacetate (9) with sodium hydride followed by addition of 52 at 50°C yields dihydrofuran 53. The product can be easily converted into the corresponding 2-methyl-3-furoate upon acid catalyzed elimination of the acetate, thus providing another strategy for the synthesis of 2,3-disubstituted furans. 

The second group of reactions is called vicinal difunctionalization. They embrace the C2 and C3 positions of the furan ring simultaneously. Thus, complex 3 (X = O, R = R = R = H) reacts with benzaldehyde dimethyl acetal to give 4H-furanium cation (the product of electrophile addition at C4), which experiences further attack by the methoxide group with formation of the acetal 8 (950M2861). This reaction is possible in the presence of the Lewis acid (BF3—OEt2). Reaction with methyl vinyl ketone in methanol, when run in identical conditions. 

The presence of methyl groups in the 2- and 3-position directs bromination to the adjacent carbon. When both positions are substituted by methyl there is an initial addition process, but the ultimate products are bromi-nated in a side chain. Even 3-methylbenzo[h]furan reacted with NBS to give 2-bromo-3-bromomethylbenzo[h]furan (48HCA78 84BAU445). The 2-phenyl derivative of 1 gave a mixture of 3-bromo and 3,6-dibromo... 

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