Thiophenes 5-aryl-3-hydroxy

Benzo[6]thiophene, 2-acetyl-3-hydroxy-synthesis, 4, 892 Benzo[6]thiophene, 2-acyl-synthesis, 4, 918 Benzo[6]thiophene, 3-acyl-synthesis, 4, 918- 19 Benzo[6]thiophene, acylamino-synthesis, 4, 815 Benzo[6]thiophene, alkenyl-synthesis, 4, 917 Benzo[6]thiophene, 2-alkoxy-synthesis, 4, 929 Benzo[6]thiophene, 3-alkoxy-synthesis, 4, 929 Benzo[6]thiophene, 4-alkoxy-synthesis, 4, 930 Benzo[6]thiophene, 2-alkyl-synthesis, 4, 877-878 Benzo[6]thiophene, 2-alkylthio-synthesis, 4, 931 Benzo[6]thiophene, 2-amino-diazotization, 4, 810 reactivity, 4, 797 stability, 4, 810 synthesis, 4, 869, 924-925 tautomerism, 4, 38 Benzo[6]thiophene, 3-amino-cycloaddition reactions, 4, 68 synthesis, 4, 109, 881, 925 Benzo[6]thiophene, 4-amino-synthesis, 4, 925 Benzo[6]thiophene, 5-amino-synthesis, 4, 925 Benzo[6]thiophene, 7-amino-synthesis, 4, 925 Benzo[6]thiophene, 3-t-amyl-synthesis, 4, 915 Benzo[6]thiophene, 2-aryl-synthesis, 4, 881... 

Thiobenzophenone can also serve as a C3S intermediate in the synthesis of some benzo[c]thiophenes. The carbon source in this case is carbon monoxide. Reaction of various thiobenzophenones with diiron enneacarbonyl in benzene at room temperature produced a complex, Ar2CSFe2(CO)6, which could be oxidized to form 2-hydroxy-5-aryl-benzo[c]thiophenes (226e) in 60-80% yield (73JA4905). 

The relative rates of ketonization of hydroxythiophenes and hydroxybenzo[A]thiophenes in acetonitrile-water (9 1) are as follows 2-hydroxybenzo[A]thiophene > 2,5-dihydroxythiophene > 2-hydroxythiophene > 3-hydroxy-benzo[A]thiophene > 3-hydroxythiophene (Table 38). 3-Hydroxythiophene does not ketonize readily in the above solvent system but in 1 1 acetonitrile-water it ketonizes 6.5 times slower than 2-hydroxythiophene <1987PAC1577>. The solvent has a significant effect on the equilibrium constants <1989JA5346>. In general, for the benzo b systems, increasing solvent polarity favors the hydroxy tautomer, which becomes the almost exclusive species in 2-acetyl <1965T3331> and 2-aryl <1976CS(9)216> derivatives, even in nonpolar media. 

The rate of acetylation of 0-(hydrox3Tnethyl)cellulose (and other hydroxy compounds) by mixtures of carboxylic acids and their anhydrides has been found to increase greatly in the presence of trifluoroacetic acid. The acceleration is very much less with mono- and tri-chloroacetic acids, presumably because they form unsymmetrical anhydrides which are less effective acylating agents than acyl trifluoroacetates. The exceptional acylating power of the latter anhydrides is shown by their use in the synthesis of alkyl aryl ketones from polyalkylbenzenes, phenyl ethers, furan, and thiophene under mild conditions. The principle has been extended to include acids... 

Benzo[e]thiophene, 5-aryl-2-hydroxy-synthesis, 4, 893 Benzo[e]thiophene, 1,3-dihydro-... 

Tautomerism of 2-hydroxythieno[2,3-Zi]- and -[3,2-Zi]thiophenes, 2,5-dihydrox-ythieno[3,2-Zi]thiophene and their alkyl- and aryl-substituted derivatives was also examined by NMR spectroscopy (75JOC3384, 78JOC2197). These compounds were demonstrated to occur predominantly as thiolactones rather than in the hydroxy form. For the thieno[2,3-Zi]thiophene system, this equilibrium is completely shifted to thieno[2,3-Zi]thiophen-2(3//)-ones, whereas the forms B and D were found for [3,2-Zi]-fused systems. The effect of the nature and positions of the substituents on the tautomeric equilibrium was discussed. 

Alkyl- and aryl-substituted 2,5-dihydroxythieno[3,2-Zi]thiophenes appeared to occur exclusively as dithiolactones. In no case was the hydroxy form of these compounds detected (78JOC2197). NMR spectroscopy demonstrated that 2,3-dihydrothieno[3,2-Zi]thiophene-2,5-dione (E) is a favourable structure. Tautomer F was detected only for the unsubstituted compound. However, this tautomer is readily transformed into tautomer E. For 6-substituted compounds, two stereoisomers of the form G are observed these stereoisomers have opposite configurations at the C(6) atom. 

A very promising new route to substituted thiophens has recently been developed by Hartmann. The reaction of 2-aryl-1,3-oxathiolium salts such as (33) with malononitrile in the presence of base yields 3-amino-4-cyanothiophens (34), with ethyl malonate or ethyl cyanoacetate 3-hydroxy-thiophens (34a), and finally with nitromethane 3-nitrothiophens (34b). The... 

The Structures and Reactions of Hydroxy- and Mercapto-thiophens and their Simple Derivatives.—2-Hydroxythiophens can in principle exist in three tautomeric forms, the hydroxy-form (110) and the 3- (111) and 4-thiolen-2-one (111a) forms. During recent years a series of derivatives of the 2-hydroxythiophen system, substituted with halogen, methoxy, aryl, and... 

As in the examples described earlier, the alkenylations are usually performed in acidic solvents such as acetic and propionic acids, which limits coexisting functional groups in substrates. In contrast, the authors developed a reaction system, Pd(OAc)2/Cu(OAc)2/LiOAc/dimethylformamide (DMF), which is applicable to the reaction of thiophenes and furans possessing acid-sensitive substituents [42]. For example, the diphenyl(hydroxy)methyl function in diphenyl(2-thienyl)methanol is tolerable under the weakly basic conditions, as shown in Scheme 18.41. The function can be subsequently substituted by Pd-catalyzed arylation with aryl bromides via C-C bond cleavage to produce the corresponding 2-alkenyl-5-arylthiophenes. 

Reactions.—All the mono- and poly-bromo-derivatives, as well as iodo-derivatives, of thieno[2,3-h]thiophen have been prepared by direct bromination or iodination, or from the lithium compounds, and characterized by their n.m.r. spectra. Boronic acids were obtained from several alkyl- and aryl-thienothiophens via lithiation and were converted by hydrogen peroxide oxidation into the tautomeric hydroxy-derivatives. It was shown by n.m.r. that all thieno[2,3-h]-thiophen systems exist as thieno[2,3-h]thiophen-2(3 )-ones, while in the case of... 

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