Benzo thiophene 5-oxides

Benzo[Z>]thiophen 5-Oxides. - Mild methods for the oxidation of 2,3-dihydrobenzo[Z>] thiophens to the sulphoxide have been developed. The photochemical reactions of various 2- and 3-substituted benzo[ ]-thiophen 1-oxides led to different photodimers. From 3-chlorobenzo[b]-thiophen-2-carboxylic acid 1,1-dioxide, 1,3-oxazinones of biological interest were obtained through cyclization reactions with cyanamides and carbodi-imides. Secondary amines add to 2-phenylbenzo [b] thiophen 1,1-dioxide to give 3-amino-substituted 2,3-dihydro-2-phenylbenzo[b]thiophen 1,1-dioxides. " ... 

The oxidation of benzo[( ]thiophene by strains of pseudomonads produces the sulfoxide that undergoes an intramolecular Diels-Alder reaction followed by further transformation to benzo[fc]naphtho[l,2- (]thiophene (Figure 2.2b) (Kropp et al. 1994). 

The benzo[fc]thiophene sulfoxides, such as (142), generated from the parent benzo-thiophene on the H202-TFA-mediated oxidation, undergoes Michael-type nucleophilic addition of oxygen and sulfur nucleophiles in acidic media to produce 3-substituted benzo[fc]thiophenes (143). This method provides an easy two-step functionalization of 2-acylbenzo[fc]thiophene derivatives. ... 

Pathway III of Fig. 26 has been demonstrated for thiophene and benzo-thiophene with Ir complexes (4) and for all thiophenes, including dibenzo-thiophene, with Rh complexes (94, 95). These oxidative additions appear to be influenced by substituents present on the carbon atoms adjacent to the sulfur atom. Insertion between sulfur and the unsubstituted carbon is highly preferred. For 2-methylthiophene the exclusive product is the 1-5 bond insertion product, whereas for 3-methylthiophene, no preference for insertion was observed (1-2 and 1-5 bond insertion products were equal). In competitive studies, thiophene was found to be about twice as reactive as 2,5-dimethylthiophene. This behavior is similar to that observed for relative reaction rates of substituted thiophenes observed with conventional HDS catalysts. Thus steric limitations can occur, even with monomeric, homogeneous catalysts. 

Benzo[ >]thiophene dianion (173) has been prepared by reduction of benzo[ >J thiophene with sodium metal at - 78°C in [2H8]THF. The H and 13C NMR spectra of the purple solution obtained prove that it is the dianion and not a radical anion. This is the first example of a sulfur-containing (4n)Tr polycyclic dianion. The dianion undergoes oxidation to benzo[ ]thiophene with oxygen (85CC1033). 

Dihydrobenzo[6]thiophene 426 and its 2-methyl derivative182 are readily dehydrogenated with sulfur to the corresponding benzo[ ]-thiophene. 2,3-Dihydrobenzo[6]thiophenes are oxidized by peracetic acid to the corresponding sulfones (Section VI, P, 2), and give crystalline complexes with mercuric chloride. 

The most widely used routes to benzo[ >]thiophene-2-carboxylic acids are (a) successive lithiation and carbonation of the parent benzo[ >]thiophene,42,76 90 98,183,477, 481>487,521,685-687 (ft) oxidation of the corresponding aldehyde,90,91,106,189 424, 477,640 (c) hypohalite oxidation of the corresponding methyl ketone,82 °8,189,424 and (d) cyclization reactions (Section IV,D, and E). Acids prepared by these routes are listed in Table XV. Oxidation of aldehydes usually proceeds almost quantitatively with moist silver oxide,90,91,105, 189,424 hut potassium permanganate is satisfactory.477, 640... 

See Nitric acid Benzo[ >]thiophene derivatives See other ARENEDIAZONIUM OXIDES... 

On converting l-phenylbenzo[ ]thiophene into 1-phenyl-1-benzo[ ]thiophenium triflate 123, this salt becomes a dienophile and reacts readily with cyclopentadiene or l,3-diphenylbenzo[r]furan to give the adduct 124 (Scheme 9) <19990L257>. This example of the dienophilic nature of the double bond in the benzo[/ ]thiophene ring arises from reduced aromaticity. Thiophene 1-oxide and 1-substituted thiophenium salts present reduced aromaticity <1970JA7610>. 

Biocatalytic asymmetric oxidation of 2,3-dihydrobenzo[. ]thiophene to (—)-(lJ)-sulfoxide in excellent yield has been reported. The enzyme used is a chloroperoxidase from the marine fungus Caldariomycesfumago. This enzyme is relatively stable and does not require any cofactor. Hydrogen peroxide was the oxygen source. Using this system, 2,3-dihydro-benzo[. ]thiophene was converted to the (—)-(i )-sulfoxide in 99.5% yield, with an ee of 99%. Similarly, 1,3-dihydro-benzo[f]thiophene could be oxidized to the corresponding sulfoxide in 80% yield <1998CH246>. 

Several benzologs of furan and thiophene are conveniently formed by procedures of ring closure over dehydrogenation catalysts. o-Ethylphenol is cyclized at 620° over a palladium catalyst to benzofuran (11%). Chromium oxide on alumina at 450° converts o-ethylthiophenol to benzo-thiophene (42%). Alkyl groups in the alpha and beta positions are obtained by suitable variation of structure in the alkyl side chain. For the... 

For instance in benzene and some of its homologs, carbazolyl-N-oxides 246 are detected, in thiophene the heteroanalog radical 247 is formed. On the other hand in furan a 1.4-addition takes place giving product radical 248. Analogously, reaction with anthracene leads to formation of 250. Furthermore reaction of 245 with benzo-nitrile oxides 6 yields benzimidazolyl-N.N -dioxides 249. 

Oxidation of benzo[b] thiophene 1,1-dioxide with KMn04 affords the sulfonic acid 172 [189], while oxidation with alkaline H202 yields the ketone 173 (Scheme 97) [244]. Oxidation of 3-substituted benzo[ ]thiophene 1,1-dioxides 174 with alkaline H202 affords the alcohols 175 as the principal product (Scheme 98) [244]. Compounds 173 and 175 are presumably formed through Michael addition of HOO to the 3-position of the substrates. Indeed, the reaction of 3,4-di-ferf-butylthiophene 1,1-dioxide 83 with H202 under alkaline conditions at room temperature afforded the Michael adduct 177 in 91 % yield, while the reaction carried out at 50-60 °C gave the ring-opened product 178 in 15% yield in addi-... 

Several refractory thiophenes, that are often not reductively removable by conventional refining processes, can be oxidized under these conditions, e.g. benzo-thiophenes are oxidized to the corresponding sulfoxides and sulfones using ultrasonic and microwave irradiation, respectively, in the presence of NaI04-silica [129]. A noteworthy feature of the procedure is its applicability to long-chain fatty... 

Reaction at Sulphur.— The kinetics of the oxidation of benzo[/>]thiophen and its 3-substituted derivatives by perbenzoic acid in dichloromethane at 30 °C have been studied. The rate constants obtained for the first step, the oxidation to the sulphoxide, have been correlated with values, whereas the rate constants for the second step, of oxidation to the sulphone, have been correlated with values. A number of benzo[ft]thiophen and dibenzothiophen derivatives and their sulphoxides have been S- and O-alkylated, respectively, with silver perchlorate and alkyl halides. 5-Methoxydibenzothiophenium perchlorate reacted with amines to give 5-aminosulphonium salts, and with certain carbanions to give zwitterionic compounds such as (394). 

In a recent paper the interaction of tert-butyl hydroperoxide with oxide catalysts was investigated. This oxidant is used, with the aid of oxide catalysts, for the oxidation of (benzo) thiophenes to the corresponding sulfones in liquid phase, but also for other liquid-phase oxidation and epoxidation reactions. The adsorption of tert-butyl hydroperoxide on zirconia from the gas-phase is reported to produce an undissociated adsorbed species as well as a terbutylperoxide species whose 00 stretching frequency is observed at 867 cm i.e. shifted to higher frequencies with respect to the undissociated compound (845 cm ). The presence of vanadium at the surface of the catalyst increases the reactivity of this species. 

Thiophene is isoelectronic with benzene and has an aromatic character. The smallest fused thiophenes, benzothiophenes (BTs) and thienothiophenes (TTs) (Figure 11.1), are isoelectronic with naphthalene. The former has two isomeric structures, benzo[ ]thiophene (thianaphthene, BTl) and benzo[c]thiophene (isothianaphthene, BT2). Although both of them are lOit electron systems, BT2 is unstable because of the quinoid structure and very sensitive toward oxidation,... 

Reaction at Sulphur.—The oxidation of benzo[6]thiophens to sulphoxides by t-butyl hypochlorite has been studied. In the presence of a ruthenium catalyst, dibenzothiophen was oxidized by oxygen to the sulphone. The reactions of benzo[ >]thiophen 1,1-dioxides with various reagents such as amines, amino-alcohols,3-aminopropylsilanes, and aromatic sulphonyl chlorides have been studied. Four detailed papers on the reaction of dibenzophenonium salts with aryl-lithiums have appeared in which the mechanism of ligand exchange was elucidated. " ... 

Benzo[6]thiophene, 4,7-dialkoxy-synthesis, 4, 930 Benzo[6]thiophene, 2,3-dialkyl-synthesis, 4, 877-878 Benzo[6]thiophene, 3 -(dialkylamino)-synthesis, 4, 925 Benzo[c]thiophene, 1,3-diaryl-oxidative ring opening, 4, 768 Benzo[6]thiophene, 2,3-dibromo-reactions, 4, 830... 

Benzo[b]thiophene, 3-mercapto-2-methyl-synthesis, 4, 931 Benzo[6]thiophene, 2-methoxy-lithiation, 4, 773 synthesis, 4, 929 Benzo[6]thiophene, 3-methoxy-alkylation, 4, 765 synthesis, 4, 929 Benzo[6]thiophene, 4-methoxy-anodic oxidation, 4, 798 Benzo[6]thiophene, 5-methoxy-synthesis, 4, 929 Benzo[6]thiophene, 6-methoxy-synthesis, 4, 929 Benzo[6]thiophene, 7-methoxy-synthesis, 4, 929-930... 

Benzo[6]thiophene, methoxynitro-Meisenheimer complexes, 4, 816 Benzo[6]thiophene, 2-methyl-cycloaddition reactions, 4, 793 protonation, 4, 47 sulfonation, 4, 764 synthesis, 4, 879, 915 Benzo[6]thiophene, 3-methyl-cycloaddition reactions, 4, 793 1-oxide... 

Benzo[c]thiophene, 1,3-diphenyl-oxidative ring opening, 4, 768 synthesis, 4, 141-142... 

Benzo[b]thiophene-2,3-quinone, 5-chloro-oxidation, 4, 824 Benzothiophenes, 4, 863-934 biological activity, 4, 911-913 intramolecular acylation, 4, 761 mass spectrometry, 4, 739 metabolism, 1, 242 phosphorescence, 4, 16 reactivity, 4, 741-861 spectroscopy, 4, 713-740 structure, 4, 713-740 substituents reactivity, 4, 796-839... 

Iodination of 4 with molecular iodine in the presence of mercuric oxide formed the 3-iodo derivative (52JA4951 66CJC2283). Iodine in tetrahydro-furan oxidatively cyclized /3-(3-benzo[b]thienyl)-a-mercaptoacrylic acids rather than iodinating the thiophene ring [70JCS(C)2431]. 

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