Heterocyclic aromatic compounds fused

Other kinds of aromatic eom])ounds exist besides simple benzene derivatives. Two common types will be covered in this chapter polycyclic fused benzenoid hydrocarbons and other cyclic conjugated polyenes with either more or less than six carbons in the ring. In Chapter 25, a third common class, heterocyclic aromatic compounds, will be pre.sented. 

Nature abounds with compounds having a heterocyclic aromatic ring fused to one or more other rings. Two such compounds especially important in the biological world are indole and purine ... 

The latter reagent also methylates certain heterocyclic compounds (e.g., quinoline) and certain fused aromatic compounds (e.g., anthracene, phenanthrene). The reactions with the sulfur carbanions are especially useful, since none of these substrates can be methylated by the Friedel-Crafts procedure (11-12). It has been reported that aromatic nitro compounds can also be alkylated, not only with methyl but with other alkyl and substituted alkyl groups as well, in ortho and para positions, by treatment with an alkyllithium compound (or, with lower yields, a Grignard reagent), followed by an oxidizing agent such as Bra or DDQ (P- 1511). 

There are two distinct classes of compounds that fit the criteria mentioned above alkene-functionalized chalcone derivatives (Fig. IB) and enone-functionalized chalcone derivatives (Fig. 1C). Within each class, both aromatic and non-aromatic compounds exist. Those compounds functionalized at the alkene include i) 3-membered heterocycles, e.g., epoxide and aziri-dine compounds, ii) 5-membered aromatic derivatives including fused and non-fused compounds, and iii) 6-membered aromatic pyrazine compounds. The enone-functionalized compounds include i) 5-membered aromatics such as pyrazole and isoxazole compounds, ii) 5-membered non-aromatic compounds for example pyrazolines and isoxazolines, and iii) 6-membered non-aromatics where a discussion of heterocyclic and non-heterocyclic compounds will be given for completeness. 

The peripheral selenodiazole rings of porphyrazine (169) can be opened upon treatment with H2S with the proposed formation of the octaaminoporphyrazine (184), which was not isolated and instead converted into the tetrakis(pyrazino)porphyrazine (185) (Scheme 34) (171). Other heterocycles have been fused on the periphery of porphyrazines, such as l,3-dithiol-2-thione in order to extend the aromatic core (172). Macrocyclization of 4,5-dicyano-l,3-dithiole-2-thione (186) under Linstead conditions in the presence of magnesium butoxide produced the symmetrically substituted tetrakis(l,3-dithiol-2-thiono)porphyrazine (187) (Scheme 35). Due to the low solubility of porphyrazine 181, a consequence of the planar aromatic molecular structure, a full characterization of this compound could not be accomplished. 

Fused heterocyclic compounds are similar to polycyclic aromatic compounds except that one or more of the fused rings is a heterocycle. Explain whether or not the heterocyclic rings of these compounds are aromatic. 

Purine is one of many fused heterocyclic compounds whose rings share two atoms and the bond between them. For example, the following compounds all contain fused heterocyclic aromatic rings ... 

Recognize fused aromatic systems such as polynuclear aromatic hydrocarbons and fused heterocyclic compounds, and use the theory of aromatic compounds to explain their properties. 

Aromatic compounds with two or more fused aromatic rings. Naphthalene is a polynuclear aromatic hydrocarbon (PAH or PNA). Indole is a polynuclear aromatic heterocycle, (p. 735)... 

Considerable research effort has been directed towards the generation, detection, and isolation of oxirenes, a highly strained class of antiaromatic heterocycles <83CRV519>. Although the unsaturated oxiranes are called oxirenes, much confusion is generated by the fact that Chemical Abstracts denotes oxiranes fused onto a polycyclic aromatic compound as oxirenes also (e.g., compound (16), Figure 9 <91JHC473 . 

Preparation of an appropriately disubstituted aromatic compound is the first step in the synthesis of fused aromatic heterocyclic compounds. Thus a method for the synthesis of benzofurans, coumarins etc. involves the preparation of the salicyl aldehydes as the first step. Standard methods are then used to add one or more carbon atoms and to effect cyclisation to complete the synthesis. 

Benzoxazole is a heterocyclic aromatic organic compound with a fused benzene-oxazole ring structure. Benzoxazole (l-oxa-3-azaindene) and several alkylated benzoxazoles have been identified in tobacco smoke. Benzoxazoles found in... 

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