Benzothiophene analogues

The first example of a fused thiophene-based material was reported by Wudl et al. in 1984 [303]. In this pioneering work, poly(isothianaphthene) (PITN) (P3.1) was synthesized by electrochemical polymerization of isothianaphthene, also named benzo[c]thiophene. Both theoretical and experimental investigations [302, 304, 305] have demonstrated that the fused benzene ring in benzo[c]thiophene increases the quinoid character of the electronic ground-state in PITN, causing a bandgap of 1.0 eV, which is about half that 

Higher oligomers, such as dimer and trimer 3.6, were obtained as a mixture of isomers by oxidative coupling of the corresponding monomers with FeCls and were characterized by UV-Vis spectroscopy and 

In 2001, Meng and Wudl et al. reported the synthesis of poly(benzo[c]thiophene-A -2 -ethylhexyl-4,5-dicarbodiimide) P3.13 (Chart 1.45), which had a broad absorption band with a maximum at 832 nm and an onset absorption at 1000 nm corresponding to a bandgap of Eg = 1.24 eV [324]. Cyclic voltammograms of P3.13 exhibited an oxidation potential of 0.88 V and a reduction potential of -1.10 V vs SCE, showing p-and n-dopable properties of P3.13. Compared with the parent polymer PITN, both oxidation and reduction are shifted to positive potentials due to the electron-withdrawing effect of the imide group. 

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Recently, Minkin and coworkers31 have reported on thermal and photoinitiated E-Z isomerizations in a series of bicyclic N-monosubstituted 2-acylenamines (6). The E-Z equilibrium was found to be strongly dependent on the heteroatom X. While the indole derivative 6a exists only in the hydrogen-bonded E form both in solution and in the crystalline state, the benzofuran analogue 6b adopts the Z form in the crystal and in polar solvents. In chloroform and in hydrocarbon solvents, a slow transformation to the E form occurs, accelerated by heat and by catalytic amounts of acids and bases. The benzothiophene analogue 6c behaves similarly, and on irradiation a photostationary mixture of E and Z forms is established, which returns to the initial form in the dark. 

In 2006, Berens et al. reported the synthesis of novel benzothiophene-based DuPHOS analogues, which gave excellent levels of enantioselectivity when applied as the ligands to the asymmetric rhodium-catalysed hydrogenation of various olefins, such as dehydroamino acid derivatives, enamides and itaco-nates (Scheme 8.10). ... 

Scheme 8.10 Hydrogenations of olefins with benzothiophene-based DuPHOS analogue ligands.

Equilibrium and rate constants for the keto-enol tautomerization of 3-hydroxy-indoles and -pyrroles are collected in Table 32 (86TL3275). The pyrroles ketonize substantially (103-104 times) faster than their sulfur or oxygen analogues, and faster still than the benzo-fused systems, indole, benzofuran, and benzothiophene. The rate of ketonization of the hydroxy-thiophenes and -benzothiophenes in acetonitrile-water (9 1) is as follows 2-hydroxybenzo[b]thiophene > 2,5-dihydroxythiophene > 2-hydroxythiophene > 3-hydroxybenzo[/ Jthiophene > 3-hydroxythiophene. 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 (87PAC1577). 

The commonest five-membered heteroaromatic compounds containing one heteroatom are pyrrole (30), furan (31) and thiophene (32). Their substituted derivatives and the substituted derivatives of the corresponding benzo analogues [indole (33), benzofuran (34) and benzothiophene (35)] are widespread naturally-occurring compounds. 

A significant difference between the benzothiophenes (raloxifene and analogues) and the triphenylethylenes is the effect on the uterus, namely, whereas tamoxifen and its analogues exert relatively potent stimulatory effects on the uterus, raloxifene and its analogues have weak albeit statistically significant stimulatory effects (Ashby et at., 1997 Bryant, 1996 Sato et at., 1996). 

The last step in the synthesis of the sulfur- and selenium-containing psoralen analogues (174) (7/7-thieno[3,2- ][l]benzothiopyran-7-one, 7//-seleno[3,2-/][l]benzothiophen-7-one, 2//-selenolo [3,2- ][l]benzothiopyran-2-one, and 7//-selenolo[3,2-g][ 1 ]benzoselenopyran-7-one) was the poly-phosphoric acid silyl ether (PPSE)-mediated cyclization of benzol-thiophenes or selenophenes shown in Equation (76) <92H(34)lli9>. 

Furo- and thieno- analogues (187 X = O, S) of PQQ have been prepared via the cyclization of a 6-amino-5-hydroxybenzofuran or benzothiophene with the dimethyl ester of 4-ketoglutaconic acid, followed by oxidation (HN03) of the triesters (186) to the ort/to-quinones (Scheme 26) <94HCA100>. 

Equilibrium and rate constants for the keto-enol tautomerization of hydroxy heterocycles are summarized in Table 38 <1986TL3275>. The pyrroles ketonize (i.e., 226 — 230) substantially faster (103-104 times) than their sulfur or oxygen analogues, and still faster than the benzo-fused systems (indole, benzofuran, and benzothiophene). 

Some years ago a benzothiophene that exhibited some activity as a tubulin polymerization inhibitor and appeared to bind weakly to the colchicine binding domain of tubulin was reported. This finding stimulated the synthesis of several benzofuran and indole analogues, Fig. (17). 

Benzo[fc]thiophene and benzo[fc]furan, frequently (and in the rest of this chapter) referred to simply as benzothiophene and benzofuran, are respectively the sulfur and oxygen analogues of indole, but have been much less fully studied. 

Heterocyclic analogues of BINAP, such as the bis(benzothiophene) 108 as well as the 2,2, 5,5 -tetramethyl-4,4 -bis(diphenylphosphino)-3,3 -bithiophene, have been prepared and tested in the Heck reaction. Incorporation of a chiral o-(A, A dimethylamino)phenyl-sulhnyl group to a double bond elicits enantioselectivity at the p-carbon during the intramolecular Heck reaction. Optically active 5-arylcyclopenten-l-yl f-butyl sulfoxides are produced from (/f)-l-f-butylsulfinylcyclopentene. ... 

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