Ring compounds fused bicyclic molecules, structure

In 1999, Katritzky reported a novel [3+2+1] synthesis of 2,4,6-trisubstituted pyridine derivatives that used the Michael addition of a-benzotriazolyl ketones to a,P-unsaturated carbonyl compounds. This reaction resembles the Krohnke pyridine synthesis and is an extension of Katritzky s earlier studies with benzotriazolyl derivatives that provided access to pyridones, 2-thiopyridones, 5-alkyl-2,4-diphenylpyridines and 2-aminopyridines. This approach is attractive as both components are readily synthesized or commercially available. The availability of these starting materials allows for an efficient access to structurally diverse 2,4,6-triaryl pyridines when combined with ammonium acetate in acetic acid at reflux. In addition, it is possible to access fused 2,3,4,6-tetrasubstituted pyridines from the requisite fused bicyclic ketone starting material. The preparation of the pyridine ring via benzotriazole methodology has resulted in improved yields for many compounds and the opportunity to synthesize molecules with a substitution pattern that would be difficult to prepare by other methods. 

Bicyclic molecules in which two rings share two or more carbons are even more important than the spirocyclic compounds. The simplest way in which two rings can share more than one carbon is for two adjacent carbons to be shared in a fused structure. The fusion positions, or bridgeheads (p. 121), are shown in red (Fig. 5.50). 

Diamondoid molecules are cagelike saturated hydrocarbons. These molecules are ringed compounds, that have a diamondlike structure consisting of a number of six-member carbon rings fused together. They are called diamondoid because they can be assumed as repeating units of the diamond. The most famous member of this group, adamantane, is a bicyclic saturated hydrocarbon (tricyclo [3.3.1.1]decane). 

Our approach was to use the unsaturated bromodeoxylactones in an intramolecular radical reaction, since these compounds possess both the radical precursor and the radical trap within the same molecule. Thus, reacting the unsaturated bromodeoxyheptonolactone 20 (Scheme 14) with tributyltin hydride and a radical initiator, the bicyclic lactone 65 a was obtained in a quantitative yield within 1 h. The stereocontrol in the reaction was determined by the structure of the product, since the compound obtained has two fused cyclopentane rings which can only be cis anellated. The radical A, which is the intermediate, was trapped by the tin hydride. The stereochemistry of the newly formed chiral center is determined by the configuration at C-4 in the educt 20 [45]. 

Naphthalene is a bicyclic aromatic compound with the formula CioHg and structure 122. It was the main constituent of mothballs for many years, but toxicity led to its replacement with 1,4-dichlorobenzene (characterized as an insecticidal fumigant). Naphthalene is planar, with 10 7t-electrons in a ji-cloud above and below the plane of the 10 carbon atoms like benzene, it is aromatic and particularly stable. Another polycyclic aromatic compound has three rings fused together, as in 123 this aromatic molecule (14 7i-electrons) is called anthracene (formula C14H10). It is an important starting material in the synthesis of dyes such as the red dye alizarin (125) and is used in wood preservatives and insecticides. 

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