Aromatic compounds, fused alkenes

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. 

Fortunately, there is now a comprehensive body of knowledge on the metabolic reactions that produce reactive (toxic) intermediates, so the drug designer can be aware of what might occur, and take steps to circumvent the possibility. Nelson (1982) has reviewed the classes and structures of drugs whose toxicities have been linked to metabolic activation. Problem classes include aromatic and some heteroaromatic nitro compounds (which may be reduced to a reactive toxin), and aromatic amines and their N-acylated derivatives (which may be oxidized, before or after hydrolysis, to a toxic hydroxylamine or iminoquinone). These are the most common classes, but others are hydrazines and acyl-hydrazines, haloalkanes, thiols and thioureas, quinones, many alkenes and alkynes, benzenoid aromatics, fused polycyclic aromatic compounds, and electron-rich heteroaromatics such as furans, thiophenes and pyrroles. 

This may look like a rather specialised method but the biomimetic inspiration applies to much simpler compounds. Taxodione 261 is an antitumour compound from the swamp cypress Taxo-dium distichum. It has an extended quinone-like enone system and two trans fused six-membered rings. Livinghouse42 realised that the extended quinone might be derived by oxidation of a simpler aromatic compound 262 where X is an oxidisable group. He then saw a possible polyolefin cyclisation in which a tertiary cation derived from a simple alkene 263 starts the reaction and the aromatic ring terminates the sequence. 

A- Two alkenes suffer an isomerization through a base-catalysed deprotonation-protonation, yielding a compound with a greater stability due to the presence of two isolated benzenic and pyrrolic aromatic systems. These two aromatic systems fused as an indole would result in lower aromatic stabilization. 

To the organic chemists of the early 1900s and before, an aromatic compound was one that underwent substitution reactions, as opposed to the addition reactions of ordinary alkenes and polyenes. They also noted that if one had fused benzene rings in different arrangements, such compounds were by and large aromatic. Smaller members of this group included naphthalene, anthracene, phenanthrene, and coronene (Structure 4) ... 

Organic compounds that contain benzene rings as part of their molecular structure are called aromatic compounds. Nonaromatic hydrocarbons such as alkanes, alkenes, and alkynes are called aliphatic compounds. Some aromatic compounds contain two or more benzene rings fused together. Examples include naphthalene and anthracene. In these compounds, electrons are shared over all of the carbon atoms in the fused ring system. 

Similar to the benzynezirconocene, cyclohexyne, cyclopen-tyne, alkyne, alkene, cycloaUcene zirconocenes, and related species insert various substrates such as alkynes, alkenes, aldehydes, ketones, nitriles or phosphaalkynes. They lead in general five-membered zirconacycles, which can be converted by transmetalation or exchange reactions into fused-ring aromatic or heterocyclic compounds. The extension of this chemistry to heterobenzyne complexes can be realized, for instance, in phosphinine compounds. Consequently, under mild conditions, ) -phosphabenzyne-zirconocene complexes are formed and can be isolated either as PMes adducts or as dimers when the elimination reaction is carried out without added phosphane (Scheme 28). 

Unlike most other samples that have to be analysed, petrochemical samples generally contain a limited number of classes of compounds, notably, alkanes, alkenes, cyclic alkanes, and aromatics with a different number of fused rings. The sample dimensionality therefore is rather limited (see below). The absolute number of compounds, however, is not only tremendous, but they all need to be analysed. In other words, the matrix itself is the goal of the analysis. So instead of looking for the needle in the haystack, the haystack itself needs to be characterised. In that respect, it is not too surprising that GCxGC from the conception of the technique on, has been developed using petrochemical samples as a subject [1,2]. 

We have demonstrated that hydrocarbons and many related compounds are often used as fuels in our highly industrialized society but we have not looked closely at their structures and differences. At this point it is useful to take a closer look at the many types or classes of hydrocarbons and some related compounds as these have many uses beyond those as fuels. There are four classes of hydrocarbons the alkanes, which contain carbon—carbon single bonds the alkenes, which contain one or more carbon—carbon double bonds the alkynes, which contain carbon—carbon triple bonds and the aromatics, which consist of benzene, benzene derivatives, and fused benzene rings. 

Reactions of acylpalladium complexes involving acylpalladation with arenes or formally equivalent processes have been much less exploited compared with those involving acylpalladation with alkenes or alkynes discussed in the previous section, and to the best of our knowledge, their examples are limited to intramolecular reactions. A few reactions that may include the intramolecular acylmetallation with arenes are known in the case of a rhodium catalyst, but the products are limited to a narrow range of compounds such as indenones.t In contrast, the Pd-catalyzed carbonylation of 3-arylaUyl acetates or hahdes, most typically cinnamyl acetate, involving intramolecular acylpalladation with arenes results in the construction of 1-naphthol, which is a hiding member of cyclic aromatic ketones. The outline of the conversion is sketched in Scheme 1. In fact, this type of carbonylation-cyclization reaction (cyclocarbonylation) can be applied to the synthesis of a variety of fused aromatics, which is summarized in the following subsection. 

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