Thiophenes hydroxy-, alkylation

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... 

Hydroxy group of 8-hyd oxy-2-cycloalkyl-2,3,4,6,ll,lla-hexahydro-l//-pyrazino[l,2-i]isoquinoline-l,4-diones was alkylated with allyl bromide, 2-(bromodifluoromethyl)pyridines, l-(bromodifluoromethyl)- and l-(bro-momethyl)benzenes, halomethyl derivatives of different heterocycles (pyridine, pyrazine, pyrazole, pyrrole, thiazole, thiophene) in the presence of CS2CO3 or K2CO3 (98MIP7). Hydroxy group of 8-hydroxy-2-cyclopentyl-... 

Alkoxybenzo[6]thiophenes and 4,7-dialkoxybenzo[6 jthiophenes are best obtained by alkylation of the available hydroxy derivatives (Section 3.15.9.4.1.iii). 

Hydroxy-6-y-cyclohexylpropylbenzo[6]thiophene-4,7-quinone is obtained by radical alkylation of 5-hydroxybenzo[6]thiophene-4,7-quinone.636... 

Hydrodesulfurization of certain hydroxy-437 and methoxy-sub-stituted615 alkybenzo[6]thiophenes is a useful means of preparing some otherwise inaccessible alkyl-substituted phenols [e.g., Eq. (15)].015 Various p-methoxyphenylbenzo[6]thiophenes have been employed similarly to prepare the corresponding hydroxydiphenyl-alkanes.464 Catalytic hydrodesulfurization of a-alkyl-/ -(3-benzo[6]-thienyl)propionic acids affords a convenient method of preparing a,y-disubstituted y-phenylbutyric acids.636 Treatment of / -(3-benzo[6]thienyl)acrylic acid with Raney nickel alloy, sodium meth-oxide, and deuterium oxide affords the deuterated acid (366).667... 

Menon presented a set of interesting liquid crystals 48 (Scheme 25) based on dibenzo[18]crown-6 modified with 2-hydroxy-3-methoxybenzene (48a), 3,4,5-trimethoxybenzene (48b), thiophene (48c), and pyrrole (48d) linked via a Schiff base [63]. All compounds are lacking long alkyl chains in the periphery. Nonetheless, broad mesophases with different geometries (SmC, SmA, N) were observed. 

All of the above described hydroxy thiophenes and hydroxybenzo[6]thiophenes can of course be alkylated with conventional phenolic alkylating agents to yield the corresponding alkoxy derivatives. However, many of the alkoxy derivatives can be obtained directly by ring closure reactions, and can indeed serve as sources of the hydroxy derivatives by dealkylation (Section 3.14.3.6). 

Both 2- and 3-alkoxybenzo(7>]thiophenes may be obtained by alkylation of the appropriate hydroxy derivative, but there are competing side reactions (70AHC(11)177). 2-Methoxy-benzo[7>] thiophene can be prepared by heating 2-bromobenzo[6]thiophene with sodium methoxide, and 3-methoxybenzo[6]thiophene is obtained by similar treatment of 3-bromobenzo[7>]thiophene. Alkylation of 3-hydroxybenzo[6]thiophene-2-carboxylic ester is more efficient, giving the 3-alkoxy derivative in good yield, and this in turn can be hydrolyzed and decarboxylated in adequate yields (equation 81). 

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... 

HC(44/3)l>. The two most important methods are (i) conversion of thienyllithium to a thienyl-boronic acid by reaction with alkyl borate, followed by oxidation with H2O2, and (ii) reaction of thienylmagnesium derivatives with t-butylperbenzoate, followed by dealkylation of the /-butyl ethers with acid. The boronic acid method has been used for the synthesis of several pyridine-substituted hydroxy thiophenes <92ACS654>. 

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. 

In connection with the elucidation of the structures of the products obtained upon reaction of the tropone (496) with perchloric acid, the 6-methoxy-substituted derivatives have been prepared by reaction of (496) with methyl iodide and silver fluoroborate. -Comparison of u.v. spectra indicated that the salts between the tropones (496) and perchloric acid were 6-hydroxy-derivatives of the perchlorate of (497). U.v. and n.m.r. spectra of the systems (496)—(499) are discussed and their properties and reactivities compared with the corresponding JV-phenyl-pyrrole analogue. A preliminary report of the polarographic, i.r., and u.v. spectroscopic properties, as well as the dipole moments, of both the C-annelated systems (496) and (497) without methyl groups in the thiophen ring and also the ion (500) with alkyl, hydroxy, and methoxy-groups in the seven-membered ring has been published. Values of piirR+ between 6 and 7 have been obtained for this system. The spectroscopic properties of metallocene derivatives such as (501)—(503) have also... 

A new thiophen synthesis is based on deprotonation and cyclization of the resultant carbanion (65) of a keten dimethylthioacetal. Other applications of cr-(phenylthio)- or cr-(alkylthio)-alkyl-lithiums include preparations of disparlure (the sex pheromone of the gypsy moth) and other chiral epoxides,of an anti-peptic-ulcer diterpene from Croton sublyratus, of carbene-thiometal chelates through reaction with fCr(CO)gl or fW(CO)jl, of olefins via )ff-hydroxy-sulphides, and of Michael adducts of enones. In other work, the chiral solvent l,4-dimethylamino-2,3-dimethoxybutane is employed in enantioselective addition reactions of cr-thio-carbanions with ketones and Michael acceptors. a,P -Elimination of cr-thio-carbanions such as (66) provides a useful synthesis of olefins, and a 2-(lithiomethylthio)-A -oxazoline (67) has been used to prepare a C-labelled thiiran for a microwave study of the valence tautomerism of allene episulphide. ... 

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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