Amino-Furans

Benzo[b]furan, 2-alkyl-2,3-dihydro-synthesis, 4, 680 Benzo[b]furan, 2-amino-synthesis, 4, 710 Benzo[b]furan, 3-amino-tautomerism, 4, 38 Benzo[b]furan, 2-amino-2,3-dihydro-applications, 4, 708... 

Furan, 2-alkenyl-3-hydroxytetrahydro-synthesis, 4, 677 Furan, alkyl-reactions, 4, 644 synthesis, 4, 710 Furan, 2-alkyl-mass spectra, 4, 21-22 synthesis, 4, 666 Furan, 3-alkyl-mass spectra, 4, 21-22 synthesis, 4, 665, 710 Furan, 5-alkyl-2-phenylthio-reactions, 4, 80 Furan, 2-alkyltetrahydro-synthesis, 4, 675, 711 Furan, 3-amido-synthesis, 4, 665 Furan, 2-amino-synthesis, 4, 74, 121, 661 tautomerism, 4, 38 Furan, 3-amino-tautomerism, 4, 38 Furan, 2-amino-3-cyano-synthesis, 4, 661, 689, 712 Furan, 3-amino-2-methyl-reaction, 4, 74 Furan, 2-aryl-reactions... 

Furan 3-(Amino-ethoxy-methyl)-5,5-dimethyl-2-oxo-tetrahydro-E15/2, 1775 [aus R —C(OR) = NH2]... 

Diacetates of 1,4-butenediol derivatives are useful for double allylation to give cyclic compounds. l,4-Diacetoxy-2-butene (126) reacts with the cyclohexanone enamine 125 to give bicyclo[4.3.1]decenone (127) and vinylbicy-clo[3.2.1]octanone (128)[85,86]. The reaction of the 3-ketoglutarate 130 with cij-cyclopentene-3,5-diacetate (129) affords the furan derivative 131 [87]. The C- and 0-allylations of ambident lithium [(phenylsulfonyl)methylene]nitronate (132) with 129 give isoxazoline-2-oxide 133, which is converted into c -3-hydroxy-4-cyanocyclopentene (134)[S8]. Similarly, chiral m-3-amino-4-hyd-roxycyclopentene was prepared by the cyclization of yV-tosylcarbamate[89]. 

The reaction of 2-amino-4(2-furyl)thiazole in acetic acid with bromine yields product 198 brominated on the furan ring (Scheme 126). The... 

The effect of substituents on the reactivity of heterocyclic nuclei is broadly similar to that on benzene. Thus mem-directing groups such as methoxycarbonyl and nitro are deactivating. The effects of strongly activating groups such as amino and hydroxy are difficult to assess since simple amino compounds are unstable and hydroxy compounds exist in an alternative tautomeric form. Comparison of the rates of formylation and trifiuoroacetylation of the parent heterocycle and its 2-methyl derivative indicate the following order of sensitivity to substituent effects furan > tellurophene > selenophene = thiophene... 

In many cases, substituents linked to a pyrrole, furan or thiophene ring show similar reactivity to those linked to a benzenoid nucleus. This generalization is not true for amino or hydroxyl groups. Hydroxy compounds exist largely, or entirely, in an alternative nonaromatic tautomeric form. Derivatives of this type show little resemblance in their reactions to anilines or phenols. Thienyl- and especially pyrryl- and furyl-methyl halides show enhanced reactivity compared with benzyl halides because the halogen is made more labile by electron release of the type shown below. Hydroxymethyl and aminomethyl groups on heteroaromatic nuclei are activated to nucleophilic attack by a similar effect. 

Benzo[c]furan, 6-amino-1,3-dihydro-1 -phenyl- H NMR, 4, 574 <75JA5160>... 

Furan, 2-amino-5-(5-amino-4-cyano-3-methyl-2,3-dihydro-2-furyl)-3-cyano-4-methyl-X-ray, 4, 548 <80LA1952)... 

Benzo[6]furan-2-carboxylic acid, 2-amino-tautomerism, 4, 648... 

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

Furan, 3-acetoxy-2,4,5-triphenyl-synthesis, 4, 659 Furan, 2-acetyl-isopropylation, 4, 607 rotamers, 4, 544 synthesis, 4, 665 toxicity, 1, 136 Furan, 3-acetyl-bromination, 4, 604 Furan, 3-acetyI-2-amino-reactions, 4, 74 Furan, 2-acetyl-3,5-dimethyl-synthesis, 4, 691 Furan, 2-acetyl-5-ethyl-synthesis, 4, 691 Furan, 2-acetyl-3-hydroxy-synthesis, 4, 649... 

Furan-2-carbaldehyde, 3-amino-Friedlander synthesis, 4, 648 Furan-2-carbaldehyde, 3-azido-reduction, 4, 647 Furan-2-carbaldehyde, 4-bromo-X-ray diffraction, 4, 543 Furan-2-carbaldehyde, 5-bromo-nucleophilic substitution, 4, 612 reactions... 

Furan-4-carbonitrile, 3-acetyl-2-amino-5-methyl-synthesis, 4, 647... 

Furan-2-carbonyl chloride, 5-alkyl-3,4-dichloro-synthesis, 4, 690 Furancarboxamides rotational isomerism, 4, 543 Furan-2-carboxylic acid, 5-acetylamino-ethyl ester reactions, 4, 647 Furan-2-carboxylic acid, amino-properties, 4, 708 Furan-2-carboxylic acid, 5-bromo-nitration, 4, 603, 711 Furan-2-carboxylic acid, 3-methyl-methyl ester bromination, 4, 604 Furan-2-carboxylic acid, 5-methyl-nitration, 4, 602... 

Phthalides — see Benzo[c]furan-l (3H)-one Phthalimide, 2-amino-pyridazine synthesis from, 3, 53 Phthalimide, N-cyclohexylthio-as vulcanization accelerator, 1, 404 Phthalimide. methylidine-polymerization, 1, 273 Phthalimide, N-(trichloromethylthio)-biocide, 1, 399 Phthalimide, 1-vinyl-polymerization, 1, 273 Phthalimide, N-vinyl-copolymer... 

Similarly, 1-alkylpyrroles, indoles, furans, thiophenes [60], a-picoline [61], enols, malonates [76], and organometallic compounds [56, 62] react with acyl imines of trifluoropyruvates to give derivatives of a-trifluoromethyl a-amino acids... 

Acyl-3-aminobenzo[6]furans also exist as amino tautomers (76JPR 313). 

Since Woodward s work on the synthesis of chlorophyll a (60JA3800) it is known that the intrinsic unstable thioformyl moiety can be stabilized by the delocalization effect of heterocyclic systems. Recently the synthesis of 2-amino- and 3-aminothioformylthiophenes (and furans) and the corresponding benzo derivatives (Scheme 19) has been reported (96S1185). These compounds exist as amino tautomers (91S609 96S1185). 

The amino form is usually much more favored in the equilibrium between amino and imino forms than is the hydroxy form in the corresponding keto-enol equilibrium. Grab and XJtzinger suggest that in the case of a-amino- and a-hydroxy-pyrroles, structure 89 increases the mesomeric stabilization and thus offsets the loss of pyrrole resonance energy, but the increase due to structure 90 is not sufficient to offset this loss. Similar reasoning may apply to furans and... 

The diazotization of heteroaromatic amines is basically analogous to that of aromatic amines. Among the five-membered systems the amino-azoles (pyrroles, diazoles, triazoles, tetrazoles, oxazoles, isooxazoles, thia-, selena-, and dithiazoles) have all been diazotized. In general, diazotization in dilute mineral acid is possible, but diazotization in concentrated sulfuric acid (nitrosylsulfuric acid, see Sec. 2.2) or in organic solvents using an ester of nitrous acid (ethyl or isopentyl nitrite) is often preferable. Amino derivatives of aromatic heterocycles without ring nitrogen (furan and thiophene) can also be diazotized. 

Alkoxy(carbene)iron(0) and amino(carbene)iron(0) complexes usually react with alkynes to give rj4-pyrone iron complexes and furans, respectively [54]. Nevertheless the chemoselective formation of naphthols was reported for alkoxy(carbene)iron(0) complexes with the electron-poor alkyne dimethyl... 

---