Heterocyclic analogs

In Table 29 the u(C=0) and other characteristic bands are given for some saturated five-membered heterocycles, and compared with the corresponding absorption frequencies for cyclopentanone. Adjacent NH groups and sulfur atoms have the expected bathochromic effect on r (C=0), whereas an adjacent oxygen atom acts in the reverse direction. The CHa vibrations of cyclopentanone are repeated to a considerable extent in the heterocyclic analogs. 

Several methods of quantitative description of molecular structure based on the concepts of valence bond theory have been developed. These methods employ orbitals similar to localized valence bond orbitals, but permitting modest delocalization. These orbitals allow many fewer structures to be considered and remove the need for incorporating many ionic structures, in agreement with chemical intuition. To date, these methods have not been as widely applied in organic chemistry as MO calculations. They have, however, been successfully applied to fundamental structural issues. For example, successful quantitative treatments of the structure and energy of benzene and its heterocyclic analogs have been developed. It remains to be seen whether computations based on DFT and modem valence bond theory will come to rival the widely used MO programs in analysis and interpretation of stmcture and reactivity. 

The replacement of carbon by other elements produces changes in several structural parameters and consequently affects the conformational characteristics of the molecule. In this section, we will first describe some stereochemical features of heterocyclic analogs of cycloalkanes. For the purpose of elaborating conformational principles, the discussion will focus on six-membered rings, so that the properties may be considered in the context of a ring system possessing a limited number of low-energy conformations. 

Fully unsaturated azocines are 7r-equivalent heterocyclic analogs of cy-clooctatetraene. Addition of two electrons to the completely unsaturated azocine (34) can lead to a dianion 35 and removal of a proton from a dihy-droazocine (36) to the monoanion 37. Both the mono- and the dianions are lOTT-electron systems, corresponding to 7r-equivalent and 7r-excess analogs of cyclooctatetraenide [84CHEC-I(7)653], Aromatic dianions related to 35 have been fully characterized by and NMR (87TL2517). 

Heterocyclic analogs of A-nitrosoureas as anticancer drugs 97CRV829. 

Noncovalent synthesis of organic nanostmctures, hydrogen-bonded ensembles including heterocyclic analogs of calix[4]arenes 98PAC1459. 

Just as there are heterocyclic analogs of benzene, there are also many heterocyclic analogs of naphthalene. Among the most common are quinoline, iso-quinoline, indole, and purine. Quinoline, isoquinoline, and purine all contain pyridine-like nitrogens that are part of a double bond and contribute one electron to the aromatic it system. Indole and purine both contain pyrrole-like nitrogens that contribute two - r electrons. 

Polyfarylene vinylene)s form an important class of conducting polymers. Two representative examples of this class of materials will be discussed in some detail here. There are poly(l,4-phenylene vinylcne) (PPV) 1, poly(l,4-thienylene viny-lenc) (PTV) 2 and their derivatives. The polymers are conceptually similar PTV may be considered as a heterocyclic analog of PPV, but has a considerably lowci band gap and exhibits higher conductivities in both its doped and undoped stales. The semiconducting properties of PPV have been shown to be useful in the manufacture of electroluminescent devices, whereas the potential utility of PTV has yet to be fully exploited. This account will provide a review of synthetic approaches to arylene vinylene derivatives and will give details an how the structure of the materials relate to their performance in real devices. 

Various heterocyclic analogs are also known, for example,... 

HETEROCYCLIC ANALOGS OF GLYPHOSATE 2.4.1 Connection Between the Ca and Nitrogen Centers... 

Amination of Aromatic Hydrocarbons and Heterocyclic Analogs Thereof , WO patent 0069804, to Bayer, 2000. 

The bioreductively-activated, hypoxia-selective DNA-damaging properties found in tirapazamine are not uniqne to this nitrogen heterocycle. Analogous properties have been observed for quinoxaline di-A-oxides snch as 99 and In addi-... 

Other heterocyclic analogs including those containing the tetrahy-drofuro [57], tetrahydropyrrolo [58], and tetrahydrothieno [59] moieties have also been disclosed. These analogs displayed PHD2 IC50 values in the range of < 10-100 nM. 

Its structure constitutes being a heterocyclic analog of naturally occurring tricyclic sesquiterpenes (Scheme 2.126). 

Palladium-catalyzed directed intramolecular activations of aryl C-H bonds have been reported, as in the phenyla-tion of heterocycle analogs. Palladacycles are proposed intermediates, acting as effective catalysts, and the mechanism is likely to proceed via oxidation of Pd(ll) to Pd(iv) by the iodonium salt, as for the Equation (57), which described the activation of benzylic i/-CH bonds (Equations (121)—(123).109... 

Other heterocycle analogs have been made by multiple arylations and in some cases a carbamoyl-directing group is cleaved during the reaction (Equations (140)—(142)).122 (For other multiple arylations, see Refs 122b-122d.)... 

An extensive study of the conformational behavior of perhydroazepine 66 was carried out by Espinosa and coworkers105. This pure force field based analysis, with no reference to experiment or other theoretical methods, was part of a series of studies on cycloheptane, cycloheptene and some of their oxygen, sulfur and nitrogen heterocyclic analogs. MM2... 

Cyclobutane and Heterocyclic Analogs, Stereochemistry of (Moriarty) Cyclohexyl Radicals, and Vinylic, The Stereochemistry of (Simamura)... 

IV. Heterocyclic Analogs of Annulenes and Monocyclic Conjugated Ions. 354... 

The fusion of a second aromatic ring results in subtle changes in reactivity. Halogenation of naphtho[l,2-c]-l,2,5-thiadiazole (42) occurs either by 4,5-addition of chlorine (43a) or by 5,6-substitution (44) by bromine. This heterocyclic analog of phenanthrene behaves like phenanthrene in that it gave the 4,5-addition product (43b) when treated with Br2 in glacial acetic acid (Scheme... 

Table 3. 4a,4b-Dihydrophenanthrenes. Heterocyclic analogs with three conjugated rings...

Another method for e preparation of aryl w-dimethoxyethyl sulfides was described by Pandya and Tilak. The procedure consists in allowing aryl lithium derivatives to react with 2,2,2, 2 -tetramethoxy-diethyl disulfide. Subsequent cyclization of the sulfides by polyphos-phoric acid yields 2-35% of condensed thiophenes and thiopyrans. By this method, thienothiophene 1 was prepared from 2-thienyllithium [Eq. (12)] and the previously unknown dithieno[2,3-6 3, 2 -i/]thiophene (5) was obtained from thienyl-2,5-dilithium. The possibility of synthesizing a heterocyclic analog (25) of pentacene from dithieno[2,3-6 3 2 -[Pg.130]

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