Conjugated heterocycles

In conjugated heterocyclic systems (partial double bond) 135.3(5)... 

Chemistry of conjugated heterocycles built from furan pyrrole, or thiophene ring fused with bicyclic (norbomadiene, bomene, or azanorbomene) skeletons 98YGK192. 

D. Pseudo-cross-conjugated Heterocyclic Mesomeric Betaines. 131... 

Benzo[c]phenanthridine alkaloids are widespread in Papaveraceae, Fumariaceae, and Rutaceae. Fagaridine (118), the structure of which had to be revised, is a derivative of the unknown 5-methyl-benzo[c]phenan-thridine-8-olate (119) which is isoconjugate with the 2-methyl-chrysene anion (Scheme 43). Thus, Fagaridine is a member of class 1 of conjugated heterocyclic mesomeric betaines, which are isoconjugate with odd alternant hydrocarbon anions. 

Roseophilin (273), a deeply red-colored pentacyclic compound isolated from the culture broth of Streptomyces griseoviridis, is a novel antitumor antibiotic. Compound 273 possesses a topologically unique pentacyclic skeleton, consisting of a 13-membered macrocycle incorporated in an ansa-bridged azafulvene, which in turn is linked to a conjugated heterocyclic ring system. The absolute stereochemistry of roseophilin, as depicted in Fig. 9, was unknown until the first total synthesis published by Tius and Harrington in 2001 [125]. All syn-... 

In general, conjugated heterocyclic mesomeric betaines are associated with 1,3-dipoles and cross-conjugated heterocyclic mesomeric betaines are associated with 1,4-dipoles. The dipolar cycloaddition reactions of both types of heterocyclic mesomeric betaines have been widely investigated and its use for the preparation of a diverse variety of heterocyclic compounds was duly covered in CHEC-II(1996) <1996CHEC-II(8)747>. 

This route remains an unknown approach to the fully conjugated heterocycle. The synthesis of 1,2,4-oxadiazolidines is detailed in Section 5.04.10.4. 

Irnidazo[ 1,2-tf ]py ridines were covered in CHEC(1984) <1984CHEC(6)613> along with others imidazoles fused to six-membered rings and they were reviewed together with imidazo[l,5- ]pyridines in CHEC-II(1996) <1996CHEC-II(8)249>. The chemical literature on this heterocycle is very abundant, due to its easy synthesis (most of the preparations use readily available 2-aminopyridines) and to the very broad spectrum of bioactivities displayed by many derivatives. A simple Beilstein search on the fully conjugated heterocycle (free sites everywhere) disclosed ca. 3000 hits for the past decade. Therefore, this chapter cannot be exhaustive in view of space limitations, but will mainly focus on the original synthetic methods that have appeared in the last decade. 

C.C. Wu, P.Y. Tsay, H.Y. Cheng, and S.J. Bai, Polarized luminescence and absorption of highly oriented, fully conjugated, heterocyclic aromatic rigid-rod polymer poly-p-phenylenebenzoxazole, J. Appl. Phys., 95 417 123, 2004. 

Research is also focused on non-precious metal catalysts synthesized with conjugated heterocyclic conducting polymers such as Ppy, Pani and poly (3-methylthiophene (P3MT)) [166, 219-223]. 

Dihydro derivatives are readily formed in reactions with aldehydes and ketones, and aldehyde addition products can be dehydrogenated to the fully conjugated heterocycles <1981RCR816, 1995AQ151>. In a new procedure, palladium iodide-catalyzed carbonylation of 1,8-naphthalenediamine 918 gave 2(l//)-perimidinone 921 in 91% yield <2004JOC4741>. 

Fluorescence spectroscopy is reported for a benzo[4,5]thieno[2,3- / thiazolium iodide salt <2004SAA129>. A wide variety of structural variants of the nonconjugated heterocycles have reported X-ray crystallographic data however, perhaps surprisingly, only very limited X-ray structural information has been reported for the fully conjugated heterocycles. 

There are relatively few fully conjugated heterocycles within the scope of this chapter. Compound 7 is one of a number of similar structures which undergo an intramolecular aza-Diels-Alder reaction followed by extrusion of molecular nitrogen to give fused pyridine derivatives such as 8 (Equation 1) <2003T8489>. 

Coverage is restricted to halogenation of conjugated heterocycles. Although not all of these can be classified as aromatic (e.g., pyranones, fulvalenes), there are aspects of their reactivities that have parallels in the series traditionally classified as heteroaromatic. Processes that produce a halogenoaromatic product from a nonaromatic substrate (e.g., quinolone to chloroquinoline) are usually included. 

CONDENSED OR CONJUGATED HETEROCYCLIC CHELATING LIGANDS 13.2.6.1 Introduction... 

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