Benzo furan-3-carboxylate

As 2-vinylfuran rapidly polymerizes even in a nitrogen atmosphere in the presence of a stabilizer, yields obtained for these Diels-Alder reactions were very low. In fact, when the more stable 5-(4-nitrophenyl)-2-vinylfuran lb reacted with DMAD, the yield of the aromatized cycloadduct, dimethyl 2-(4-nitrophenyl)benzofuran-4,5-dicarboxylate 4b, was 50%. The 4-nitrophenyl group not only deactivated the vinylfuran for oxidation and polymerization, but also deactivated the diene system toward cycloadditions, and the reaction was successful only when conducted in boiling xylene. The decrease in reactivity of the reactive diene may account for the relatively low yield of methyl 2-(4-nitrophenyl)benzo-furan-4-carboxylate 6b obtained in a similar reaction with MP (73-AJC1059). 

Furan is resinified by sulfuric acid but it can be sulfonated with the complex of sulfur trioxide with pyridine or dioxane. Depending on conditions the 2-sulfonic or the 2,5-disulfonic acid may be obtained. Furan-2-carboxylic acid can be sulfonated with oleum. Benzo[ >]furan is polymerized by sulfuric acid. The 2-sulfonic acid has been obtained by oxidation of the sulfinic acid available in turn by treatment of the lithio derivative with sulfur dioxide. Benzo[6]furan with the sulfur trioxide-pyridine complex allegedly affords the 3-sulfonic acid. 

Benzo[, ]furan 82 with sodium sand in the presence of 1-chlorooctane gave the 2-sodium salt of benzo[, ]furan, which with CO2 gave the carboxylic acid 93 (Equation 87) <2002AGE340>. 

Copper-mediated decarboxylation was observed to convert benzo [. ]furan-2-carboxylic acid into its corresponding benzoMfuran, albeit in low yield (Equation 174) <2002EJ01937>. 

Perkin rearrangement. Formation of benzo-furan-2-carboxylic acids and benzofurans by heating 3-halocoumarins with alkali. 

In contrast to furan, the benzene ring in benzo[ ]furan (because of its large resonance energy) is dominant to such an extent that [4+2] cycloadditions are not possible. On the other hand, photochemical [2+2] cycloaddition occurs readily on the C-2/C-3 double bond leading, e.g. with an acetylene di-carboxylic ester, to the cyclobutene derivative 1 ... 

Benzo[b]furan-2-carboxylic acid, 3,6-dimethoxy-, methyl ester UV, 4, 589 <71AJC1883> Benzo[b]furan-2-carboxylic acid, 5,6-dimethyl-, methyl ester... 

H NMR, 4, 561 <65MI31002> Benzo[b]furan-2-carboxylic acid, methyl ester UV, 4, 589 Benzo[b]furan-3-carboxylic acid, 6-chloro-4,5,7-trifluoro-2-methyl-, ethyl ester C NMR, 4, 568 <72JCS(P2)1733> Benzo[b]furan-3-carboxylic acid, 6-cyano-4,5,7-trifluoro-2-methyl-, ethyl ester C NMR, 4, 568 <72JCS(P2)1733>, 569 <72JCS(P2)1733>... 

F NMR, 4, 569 <72JCS(P2)1733> Benzo[b]furan-3-carboxylic acid, 2-methyl-, methyl ester... 

H NMR, 4, 561 <720MR(4)343> Benzo[b]furan-4-carboxylic acid, methyl ester UV, 4, 589 (73AJC1059)... 

Benzo[6]furan-2-carboxylic acid, 5-acyl-2,3-dihydro-applications, 4, 708... 

Benzo[b]furan-2-carboxylic acid, 6,6 -[(2-hydroxy-l,3-propanediyl)bis(oxy)]bis(3-hydroxy-diethyl ester trisodium salt trihydrate applications, 4, 709... 

Benzo[b]furan-3-carboxylic acid, 2-amino-esters... 

C- F coupling constants, 4, 569 Benzo[b]furan-5-carboxylic acid, 4-hydroxy-2-isopropyl-synthesis, 3, 698... 

Benzo[b]furan-2-carboxylic acids bromination, 4, 602 chloromethylation, 4, 602 from coumarins, 3, 686 IR spectra, 4, 590 methyl ester... 

Benzo[b]furan-3-carboxylic acids methyl esters, 4, 646 Benzofuranofurans H NMR, 4, 572 5-Benzo[ b]furanol esters... 

Whereas the degradation of the carboxylates of the monocyclic furan, thiophene, and pyrrole is initiated by hydroxylation, degradation of their benzo analogs is generally carried out by dioxygenation. The degradation of the analogs dibenzofuran and dibenzo-[l,4]-dioxin is discussed in Part 2 of this chapter. 

The treatment of 2-fluorophenyl-2-iodophenyl ethers, amines, and thioethers with 3.3 equivalents of f-BuLi and further reaction with selected electrophiles gave rise to functionalized carbazoles, dibenzofurans, and dibenzothiophenes in a direct and regioselective manner. A selected example is illustrated below <06JOC6291>. Benzyl 2-halophenyl ethers was treated with f-BuLi, and then reacted with carboxylic esters to give 2,3-disubstituted benzo[t>]furans <06JOC4024>. 

Electron-withdrawing substituents seem to stabilize the benzo[cjfuran system as they do in the analogous benzo[c]thiophene and benzo [c]indole series. l-Cyano-3-phenylbenzo[c]furan (128) was obtained from the aldehyde 127 as stable yellow needles hydrolysis with base yields the carboxylic acid (129). Catalyzed hydrogenation of these cornpounds leads to 1,3-dihydrobenzo[c]furans (130, R = CH2NH2, COOH = Ph). Increased... 

Phenylbenzo[c ]furan-3-carbonitrile and the corresponding carboxylic acid are catalyti-cally reduced in a cis manner to the expected 1,3-dihydro compounds. 1,3-Diaryl-benzo[c]furans are also reduced to phthalans with sodium amalgam. 

Methyl benzo[6]furan-3-carboxylate is more easily hydrolyzed than its 2-isomer. 

Aminobenzo[6]furan-2-carboxylates and 2-acylbenzo[6]furan-3-amines exist as the amino tautomers. 3-Pyrrolidinobenzo[6]furan is available from benzo[Z>]furan-3(2//)-one (74RTC321). 

Electron withdrawing substituents stabilize the benzo[c]furan system. l-Cyano-3-phenyl-benzo[c]furan (247) can be obtained from the benzophenone (246) (70TL707) as a crystalline solid. The carboxylic acid (248) could be isolated on base catalyzed hydrolysis of (247), while catalytic hydrogenation led to the l,3-dihydrobenzo[c]furans (249). 

---