Bi- and Poly-heterocycles

Nord n, R. H ansson, and M. Sundbom, Acta Chem. Scand., 1972, 26, 429. 

Semtsova, P. L. Trakhtenberg, A. E. Lipkin, and T. B. Ryskina, Khim.-farm. Zhur., 

Ribereau, G. Queguiner, and P. Pastour, Bull. Soc. chim. France, 1972, 1581. 

Bi- and Poly-heterocycles.—Extensive work on the synthesis, optical resolution, and conformation of 3,3 -bithienyls, as well as detailed studies of their c.d. curves, has appeared. Most 3,3 -bithienyls were prepared by the coupling of 3-thienyl-lithium derivatives followed by the introduction of the appropriate substituents by electrophilic substitution or by the modification of substituents by reduction, - ° oxidation, - - or side-chain bromination. In particular, halogen-metal exchange in bromo-substituted 3,3 -bithienyls was very useful for the modification of substituents. - - Ullman coupling of 3-bromo-2,4-dimethoxycarbonylthiophen was used for the synth is of 2,2, 4,4 -tetra- 

A new promising method for the synthesis of mixed biaryls consists in the reaction of the ethanolamine esters of diarylboronic acids with NBS in dichloro-methane/aqueous buffer at pH 9. In this way, 2- and 3-phenylthiophen, 2,2 -bi-thienyl, and 2-(2-thienyl)furan were obtained. The nitration of 2,3 -bithienyl has been studied. 2-Nitro-2 -amino-3,3 -bithienyl and 3-nitro-3 -amino-2,2 -bithienyl have been found to be stable. Carbonyl derivatives of 2-aryl-thiophens have been prepared, and reactivity constants for 2-aryl-thiophens determined. Some 2,5-bis(4 -n-alkyldiphenyl-4 -yl)thiophens, which are liquid crystals, have been prepared from the corresponding 1,4-diketones and P4S10. Various naphthyl-thiophens have been synthesized in order to study their anti-inflammatory and antibacterial properties.  

A large amount of work on compounds where the thiophen ring is connected to another five-membered aromatic heterocycle has appeared. Reacting thioamides, e.g. 2-thiocarbamoyl-thiophens or -selenophens, with oc-halogeno-ketones, according to the method of Hantzsch, led to a variety of 2-(thienyl)-thiazoles and 2-(selenienyl)thiazoles. Thiophens attached to two thiazolyl rings, and 2-(5-nitro-2-thienyl)thiazole, needed for a study of antiprotozoal activity, have been prepared similarly. The somewhat exotic thienylthiazole (182) 

Dell Erba, G. Guanti, and G. Garbarino, /. Heterocyclic Chetn., 1974,11, 1017. 

Polyakov, Z. P. 2 piyuisvechka, and S. V. Tsukerman, Khim. geterotsikl. Soedinenii, 

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Finally, E. S. H. El Ashry, A. Mousaad, and N. Rashed (University of Alexandria, Egypt) cover the chemistry of 2,3,4,-furantriones and their conversion into a very wide variety of bi- and poly-heterocyclic systems. 

The survey of the literature data has shown that nitroarenes with unsubstituted orf/io-position relative to the nitro group can be functionalized directly by using various types of C-H functionalizations to give nitrogen heterocycles or their precursors. The results presented in this chapter may provide a good basis for the directed synthesis of diversely functionalized nitrogen bi- and poly heterocyclic systems. The general features and plausible pathways for these chemical transformations have been described. 

Tellurophene aldehydes and ketones readily undergo reduction reactions typical of carbonyl compounds. The Wittig reaction of 2,5-bis(dodecyloxy)- -xylene-bis(triphenylphosphonium bromide) with tellurophene-2,5-dicarbaldehyde leads to poly(2,5-tellurophenediylvinylene) (MW 7000-29000 Da) in 65% yield <1995MM8363>. The condensation reactions of 2,5-diphenyl-3,4-diformyltellurophene 15 have been employed for the synthesis of a number of bi- and polycyclic heterocycles with a fused tellurophene ring (Scheme 8) <1976CB3886>. 

The most likely prospects have been the compounds having heterocyclic moieties, including selenafulvalenes and -conjugated polyselenophenes. Some examples are tetramethylselenafulvalene (TMTSF) (175), bis(ethylenedithio)tetraselenafulvalene (BETS) (176), and poly(3-alkylselenophenes) (177) (Fig. 14) [5, 25, 278],... 

Poly(arylene ether benzimidazole)s have received more attention than any other PAE containing heterocyclic units. This is due primarily to their unique combination of properties even at relatively low molecular weights and their potential for use in several high performance applications. The initial report in 1991 involved polymers from the reaction of 3 different bis[(4-hydroxy-phenyl)benzimidazole]s with various activated aromatic difluoro monomers as shown in Eq. (10) [37]. The bis[(4-hydroxyphenyl)benzimidazole]s were prepared from the reaction of aromatic bis(o-diamines) and phenyl-4-hydroxybenzoate in diphenyl sulfone. The use of 4-hydroxybenzoic acid would obviously reduce the... 

Considerable research effort has been devoted in recent years to the use of chloral derivatives for the synthesis of linear heterocyclic polymers. Of these, the most common are aromatic polyimides [1-12], Many of these polymers have been synthesised from compounds like 4,4 -diaminobenzophenone, and other diamines, which, as demonstrated in the previous chapter, can be obtained from chloral. Polyimides prepared from these diamines were largely synthesised by the conventional two-step procedure [11, 12] involving mild reaction of the diamines with the bis(phthalic)anhydrides, isolation of poly(o-carboxy)amide (PCA) prepolymers, and then processing into products followed by thermal or chemical imidisation [13—16] (Scheme 3.1). Some properties of polyimides prepared from 4,4 -diaminobenzophenone are provided in Table 3.1. 

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