Benzothiophenes reduction

Thiophene-2-carbaldehyde, 3-bromo-synthesis, 4, 81 Thiophenecarbaldehydes benzothiophene synthesis from, 4, 906 reactions, 4, 807 synthesis, 4, 148 Wittig reactions, 4, 807 Thiophene-2-carb aldehydes bromination, 4, 753 conformation, 4, 33 halogenation, 4, 753 reactions, 4, 72-73 reactivity, 4, 72-73 reduction, 4, 776 Thiophene-3-carb aldehydes conformation, 4, 33 reactivity, 4, 72... 

Subsequently, Paquette and Johnson used LAH reductions to convert strained thietane or thiolane derivatives to their respective sulphides, generally in good yields. Whitney and Cram described the LAH reduction of a chiral derivative of benzothiophene sulphone, as outlined in equation (24). The authors also noted the formation of hydrogen gas and suggested that their results were consistent with those of Bordwell as outlined in equation (22), namely that reduction takes place by the formation of an aluminium oxide and hydrogen gas. In this case, the reduction clearly cannot involve the formation of an a-sulphonyl carbanion and it is unlikely that any C—S bond cleavage and reformation could have occurred. 

Rejnak M, Klima J, Svodoba J et al (2004) Synthesis and electrochemical reduction of methyl 3-halo-l-benzothiophene-2-carboxylates. Collect Czech Chem Commum 69 242-260... 

Reduction of 4-keto-l,2,3,4-tetrahydrodibenzothiophene (44a) with sodium borohydride followed by dehydration of the resultant carbinol by vacuum distillation in the presence of a trace of PPA yields 1,2-dihydro-dibenzothiophene (62) as a low-melting solid. Similarly, 3,4-dihydrodi-benzothiophene (63) has been prepared from the 1-keto compound (46) as an unstable liquid. ... 

The 4a,9b double bond in 1,2,3,4-tetrahydrodibenzothiophene 5,5-dioxide (68) and similar compounds, is essentially nonaromatic and in this respect resembles the 2,3 bond in benzo[6]thiophene 1,1-dioxide. Catalytic reduction of 68 results in the formation of l,2,3,4,4a,9b-hexahydrodibenzothiophene 5,5-dioxide (92 /o). Subsequent reduction of the sulfone with LAH yields 1,2,3,4,4a,9b-hexahydrodibenzothiophene (69) as an oil (78 /o). Oxidation of 4-keto-l,2,3,4-tetrahydrodi-benzothiophene (44a) to its sulfone with peracetic acid (63 /o) followed by... 

An improved synthesis of 2-(r-hydroxyethyl)dibenzothiophene has been reported involving Meerwein-Ponndorf reduction of 2-acetyldi-benzothiophene. An alternative synthetic route has been employed in the synthesis of 4-(l -hydroxyethyl)dibenzothiophene (101) involving treatment of 4-lithiodibenzothiophene with acetaldehyde (36%). Both of these compounds are readily dehydrated to the corresponding vinyl compounds, the polymerization of which is discussed in Section VII. 

Reductions of five-membered cyclic sulfones with lithium aluminum hydride were run in refluxing ether and of other sulfones in refluxing ethyl butyl ether (92°) (yields 12-92%). Benzothiophene-1,1-dioxide was reduced at the double bond as well, giving 2,3-dihydrobenzothiophene in 79% yield after 18 hours of refluxing in ether [687],... 

In this paper, the selectivity of the ECH method for the reduction of nitro compounds to the corresponding amines on RCu electrodes will be compared with that of reduction by RCu alloy powder in alkaline aqueous ethanol. In the latter method (termed chemical catalytic hydrogenation (CCH)), chemisorbed hydrogen is generated in situ but by reduction of water by aluminium (by leaching of the alloy) (equation [12]). The reductions by in situ leaching must be carried out in a basic medium in order to ensure the conversion of insoluble Al(OH)3 into soluble aluminate (equation [12]). The selectivity and efficiency of the electrochemical reduction of 5-nitro-indoles, -benzofurane, and -benzothiophene at RCu electrodes in neutral and alkaline aqueous ethanol will also be compared with that of the classical reduction with zinc in acidic medium. 

Benzo[6]thiophenes ran also be prepared indirectly by Friedel-Crafts cyclization of styrylsulfonyl chlorides (59JA2000) or 2-phenylethanesulfonyl chlorides (53JA3359). Since these cyclizations produce either benzothiophene sulfones or dihydrobenzothiophene sul-fones, further oxidative and/or reductive steps are required to obtain benzo[ Jthiophenes. 

The literature on conductivity in poly(p-phenylene sulfide) is confused. According to Shacklette et al.74) heavy doping with AsF5 causes reduction of the polymer with the formation of fused benzothiophene structures which are responsible for conjugation. This would more properly place poly(p-phenylene sulfide) in the category of precursor polymers, discussed later. On the other hand, Friend and Giles 75) proposed an intrinsic conduction mechanism, based on optical measurements and Tsukamoto et al. 76) have presented XPS and 13C NMR measurements to support this view. 

The catalysis cycle comprises the following steps oxidative addition of H2 to the metal coordination of the benzothiophene in the 77 -mode hydride migration and, finally, elimination of dihydrobenzo[3]thiophene by reductive coupling of the hydride and dihydrobenzothienyl ligands (Scheme 73). Based on this, various ruthenium and rhodium complexes have been developed, which exibit good catalytic activity. 

Reduction of enone 717 with diisobutylaluminium hydride (DIBAL) or thioindoxyls 719 with NaBH4 followed by spontaneous dehydration gives the thiophene 718 <2002TL8485> or benzothiophenes 720 <2002SL325, 2003T4767>, respectively. 

The only reduction of benzothiophenes involving metal hydrides is ionic hydrogenation utilizing EtsSiH/TFA (equation 120), The rate of reduction of benzothiophene itself is very sluggish and much slower than that of benzofuran (equation 113). 

Anodic methoxylation of aromatic ethers via the EEQCp mechanism has found its widest application in the synthesis of quinone bisketals (LXX) from para-dimethox-ybenzenes (LXIX) [79]. Yields are generally excellent, and the reaction is conveniently carried out at constant current in a single cell [42,80]. The reaction has also been shown to work well for naphthalenes [81] and benzothiophenes [82]. As shown in Table 4, a variety of substituents may be present on the ring. When substituents sensitive to cathodic reduction such as -CHO and -CH CHCO Me are present, a divided cell apparatus may be required to obtain reasonable yields of the corresponding bisketals. 

The reduction of benzothiophene by ammonium amalgams is discussed in Chapter 28. 

Benzothiophen-1,1-dioxide is polarographically reducible at about —1.3V at pH > 2 [197]. In alkaline solution the polarographic behavior is complicated by the addition of nucleophiles to the 2,3-double bond. Controlled potential reduction in acetate buffer produced 2,3-dihydrobenzothiophen-1,1-dioxide [198]. 

The catalytic properties of M0S2 and WS2 have been compared. In thiophen hds (673 K, 1 atm) the activity per unit area of WS2 was twice that of M0S2. This difference was attributed to the greater ease of reduction of WS2 in H2[AG (1100K) Mo, 120 W, 93.7kJmor ] giving more active sites (anion vacancies). However, in benzothiophen hds (523 K, 100 atm) M0S2 was more active than WS2 (areal activity ratio 2.66). ... 

C-S bond scission. Selective reductive bond scission is accomplished. For example, benzothiophene is converted to o-ethylbenzenethiol (99%) by Na in liquid ammonia. 

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