Furan 3- lithio

Benzo[b]furan, 3-(2-hydroxy-3,5-dichlorophenyl)-5,7-dichloro-properties, 4, 708 Benzo[b]furan, 2-lithio-synthesis, 4, 652 Benzo[i]furan, 3-lithio-ring opening, 4, 79 Benzo[b]furan, methoxy-mass spectrometry, 4, 583 Benzo[b]furan, 6-methoxy-2,3-diphenyl-synthesis, 4, 679... 

Furan, 2-(p-hydroxyphenyI)-2,5-dihydro-synthesis, 4, 677 Furan, 3-hydroxytriphenyl-tautomerism, aromaticity and, 4, 595 Furan, iodo-synthesis, 4, 712 Furan, 2-iodo-Grignard reagents, 4, 79 Furan, 5-iodo-2-nitro-synthesis, 4, 711 Furan, 2-isopropyl-cycloaddition reactions with ff, ,a, ff -tetrabromoacetone, 1, 418 Furan, 2-lithio-5-methyl-synthesis, 1, 419 Furan, 2-mercapto-tautomerism, 4, 38 Furan, 3-mercapto-tautomerism, 4, 38 Furan, methoxy-planarity, 4, 544 synthesis, 4, 664 Furan, 2-methoxy-synthesis, 4, 648 Furan, 3-methoxy-Diels-Alder reaction, 1, 416 synthesis, 4, 649... 

The first proton to be removed from iV-methylpyrrole by w-butyllithium is from an a-position a second deprotonation occurs to give a mixture of 2,4- and 2,5-dilithiated derivatives. The formation of a 2,4-dilithio derivative is noteworthy since in the case of both furan and thiophene initial abstraction of a proton at C-2 is followed by proton abstraction from C-5 (77JCS(P1)887). iV-Methylindole, benzo[6]furan and benzo[6]thiophene are also deprotonated at C-2. Selenophene and benzo[6]selenophene and tellurophene and benzo[6]tellurophene similarly yield 2-lithio derivatives (77AHC(21)119). 

Directive effects on lithiation have also been studied. The regiospecific /3-metallation of A-methylpyrrole derivatives and 2-substituted furans has been effected by employing the directive effect of the oxazolino group (82JCs(Pl)1343). 2-Substituted furans and thiophenes are metallated in the 5-position. The formation of 2-lithio-3-bromofuran on treatment of... 

Furan, 2,5-di hydro-2,5-dimethoxy- C NMR, 4, 573 heat of hydrogenation, 4, 592 Furan, 2,5-dihydro-3,4-dimethylene- H NMR, 4, 577 Furan, 2,3-dihydro-3-hydroxy-synthesis, 4, 685 Furan, 2,3-dihydro-5-lithio- C NMR, 4, 572 Furan, 2,3-dihydro-3-methyl- H NMR, 4, 570... 

The synthesis of phosphonium iodide 24, the precursor of phos-Br phorus ylide 12, begins with the alkylation of 5-lithio-2-methyl- furan,10 derived from the action of n-butyllithium on 2-methylfuran 17 (16), with 1,4-dibromobutane (17) to give 15 in 75% yield (see... 

The lithio derivatives of dibenzofuran undergo the expected reactions. Carbonation yields carboxylic acids,reaction with sulfur dioxide yields sulfinic acids, and reaction with methyl sulfate yields methyl compounds. Alkylation can also be achieved by treatment of 4-lithio-dibenzofuran with alkyl halides. Silylation can be achieved with chlorotrimethyl- or chlorotriphenylsilane. " " Reaction of lithiodibenzo-furans with acetaldehyde and with benzonitrile take the expected course. 

Auf diese Weise erhalt man z. B. aus Phenyl-magnesiumbromid Anilin und aus 2- bzw. 3-Lithio-furan 2- bzw. 3-Amino-furan. 

Although a limited range of Grignard reagents is available, the most widely used group is undoubtedly the lithio group introduced by direct lithiation (see Section 3.3.1.6.2). The ready formation of the lithio derivatives of pyrroles, furans and thiophenes and their benzo-fused derivatives has had a most important impact on the chemistry of these heterocyclic systems. Reaction of the... 

The reactions of the lithio derivatives of benzo[ >]-fused systems indole, benzo[6]furan and benzo[h]thiophene are similarly diverse. Since indole and benzo[h]thiophene undergo electrophilic substitution mainly in the 3-position, the ready availability of 2-lithio derivatives by deprotonation with n-butyllithium is particularly significant and makes available a wide range of otherwise inaccessible compounds. The ready availability of 3-iodoselenophene and hence of 3-lithioselenophene (73CHE845) provides a convenient route to 3-substituted selenophenes. 2-Lithiotellurophenes are especially important precursors of tellurophene derivatives because of the restricted range of electrophilic substitution reactions which are possible on tellurophenes (77AHC(2l)ll9). 

The tendency for the 3-lithio derivatives of furans and thiophenes to undergo ring opening has been exploited for the synthesis of polyunsaturated acyclic compounds. A trimethylsilyl group in the... 

N-Substituted pyrroles, furans and thiophenes can be 2-lithiated, and these lithio derivatives are important synthetic intermediates (Section 3.3.3.8). 2-Mercuri and 2-palladio derivatives are also important (Sections 3.3.3.8.8 and 3.3.3.8.9). 

Disubstituted furans can be prepared by the 3-lithiation of 2-phenylthio-5-alkylfurans, followed by reaction with an electrophile and then desulfurization with Raney nickel (Section 3.3.3.8.4). 3-Furylmercuri acetate can be obtained from furan-2-carboxylic acid (CHEC 3.11.3.9) and transformed to other 3-substituted furans via the lithio compound. 

Naphthofurans have been synthesized from the corresponding naphthols thus 2-methoxy-3-allylnaphthalene (from allyl bromide and 3-lithio-2-methoxynaphthalene) gives 2-methyl-2,3-dihydronaphtho-[2,3-6]furans,435 and l-allyl-2-naphthol gives (with pyridine hydrochloride) 2-methyl-2,3-dihydronaphtho[2, l-6]furan.438... 

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[6]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. 

The halo-furans and -benzo[f>]furans are particularly important as precursors of the lithio derivatives (Section 3.11.3.9). Direct halogenation of furan (Section 3.11.2.2.5) is unsatisfactory, and halofurans are prepared by decarboxylation of halofurancarboxylic acids, from chloromercurio compounds, by decarboxylative halogenation of furancarboxylic acids or by partial dehalogenation of polyhalofurans. 

Grignard reagents are difficult to prepare in both the furan and benzo[f ]furan series and their use has been superseded by the more tractable lithio compounds. Bromofurans are best converted into the Grignard reagents by treatment with a copper-magnesium alloy in THF (80JOC3125). 

Butylpotassium and butylcesium deprotonate furan at the 2-position (75BSF1302), but butyllithium is the reagent of choice. When furan is treated with butyllithium the reactions in Scheme 114 occur (77JCS(P1)887>. The conditions, however, may be controlled to yield predominantly the mono- or the di-lithio derivative. By carbonation and esterification of the reaction mixture obtained by treatment of furan with butyllithium and TMEDA (1 1 1) in ether at 25 °C for 30 min, a 98% yield of methyl furan-2-carboxylate is obtained. Similarly, a butyllithium TMEDA furan ratio of 2.5 2.5 1 in boiling hexane for 30 min results in 91% of dimethyl furan-2,5-dicarboxylate and 9% of the monoester. Competition experiments indicate that furan reacts with butyllithium faster than thiophene under non-ionizing conditions but that the order is reversed in ether or in the presence of TMEDA. 

N-methyl pyrrole 2.34, thiophene, and furan can be metallated at the C2 position with alkyl lithium reagents. This position is more activated to deprotonation than the C3 position because of the electron-withdrawing inductive effect of the heteroatom. The nucleophilic 2-lithio species can then be reacted with various electrophiles, as in the preparation of 2.37, 2.38,... 

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