A-Terthiophene

Advantage has been taken of the aforementioned observations in the synthesis of a terthiophene natural product, arctic acid (147) [123]. Pd-catalyzed carbonylation of bromobisthiophene 25, obtained from the Kumada coupling of 2-thienylmagnesium bromide and 2,5-dibromothiophene, gave bithiophene ester 144, which was converted to iodide 145 by reaction with iodine and yellow mercuric oxide. Subsequent propynylation of 145 was then realized using the Sonogashira reaction with prop-l-yne to give bisthienyl alkyne 146, which was subsequently hydrolyzed to 5 -(l-propynyl)-2,2 -bithienyl-5-carboxylic acid (147), a natural product isolated from the root of Arctium lappa. 

The highest values were obtained for bis-alanines 611a, 611b, and 611d, with a thiophene, bithiophene, and a phenylthiophene at position 2 of the benzoxazole, respectively, which were found to be strongly emissive (0.59 < Of < 0.89) while 611c, with a terthiophene bridge, displayed much lower quantum yield (F = 0.14). 

Non-plant reference terthiophene a-Terthiophene carboxaldehyde [phototoxic, photodermatitic] 8. In... 

Sulfuration of dithiophene-1,4-diketone 598 using Steliou s reagent [(Bu3Sn)2S, BCI3] or Lawesson s reagent affords a-terthiophene 599 (Equation 29) <1998BML2695>. 

Four new natural products, namely 5,5"-dichloro-a-terthiophene, 5-chloro-a-terthiophene, 5-acetyl-a-terthio-phene, and 5-carboxyl bithiophene, together with seven known thiophenes were isolated and purified from ethanol extract of roots of Echinops grijisii Hance <2002M1175>. 

Less effort was spent recently on perfecting the conditions of electrodeposition in conventional or related conditions, except when a subsequent application was aimed at, which is indicative of, either a rising lack of interest in electropolymerization conditions, or that this technique has reached its limits. However, De Paoli et al. have recently investigated the optimization of the deposition conditions of a terthiophene derivative on indium tin oxide (ITO), with the further purpose to make a LED device [58]. 

Block copolymer 2.34 with a low polydispersity of 1.1 was prepared by ring closure of 1,4-dicarbonyl precursor 2.33 using an excess of Lawesson s reagent (Scheme 1.8) [99]. The latter compound was synthesized by coupling of two equivalents of formylated a-terthiophene 2.32 endowed with a polystyrene chain at other a-terminus with the bis-Mannich base 5,5 -bis[3-(dimethylamino)propionyl]-2,2 5, 2 -terthiophene. TEM and scanning force microscopy (SFM) showed that 2.34 is self-assembled into spherical, micellar structures with average diameters of 12 nm, which corresponds to about 60 block copolymer molecules per aggregate. 

A terthiophene-functionalized guanine base 2.203 was synthesized for its incorporation into the minor grove of DNA without alteration of duplex stability (Chart 1.41) [293]. Pulse radiolysis measurements of 2.203-modifled oligodeoxynucleotides showed the formation of a stable terthiophene radical cation in DNA. The authors further proposed that the incorporation of several terthiophene moieties along the DNA sequence may be useful to carry holes along the modified DNA. 

Higgins et al. synthesized a biotin-functionalized terthiophene 2.210 by reaction of biotin hydrazide and a terthiophene which was functionalized by a succinimidyl active ester (Chart 1.43) [299]. The copolymerization of 2.210 with terthiophene on a Pt electrode formed poly(terthiophene) films containing intact biotin moieties. The binding of 5 x 10 " mol of the glycoprotein avidin to the pendant biotin units of the polymer film resulted in a positive shift of the oxidation potential due to specific inferactions and blocking of the ion transport to and from the polymer by the bound protein. 

Thiophene-Thiazole. Copolymers of thiophene or 3-methoxy-thiophene with methylthiazole have been electrochemically synthesized from a-linked four-ring monomers. The conductivity and redox potential of this copolymer appear to be comparable to those observed for poly(a-terthiophene) [787] (Fig. 49e). 

Thiophene-Benzo[c]thiophene (or Isothianaphthene). Polymers derived from a-terthiophenes bearing a variety of fused central ring systems have been prepared. These materials were synthesized in the context of smaU-bandgap polymers. The insertion of a specific ring system into the middle of a trimeric precursor presents several advantages such as the construction of alternate donor and acceptor moieties or the stabilization of rather unstable fused ring systems. 

Bithiophene and a-terthiophene monomers containing jS-aryl substituents have also been polymerized. A material derived from XL has been used in blends with other poly(3-substituted thiophene)s to afford electroluminescent devices whose emission color depended on the applied voltage [62]. Monomers in which the central ring of a-terlhiophene has been substituted with phenyl-157,63], p-cyanophenyl-, p-methoxyphenyl-, p-pyridyl-, 2-thienyl-, or 3-methyl-2-thienyl [63] have been electro-chemically oxidized to yield mixtures of oligomers in all cases [63]. 

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