Chemistry fused ring systems

Finally, a section is devoted to developments in (5-lactam chemistry. Fused-ring systems are not included though often the purpose of the work on monocyclic systems is to develop synthons for fused-ring compounds. Recent reviews on the use of (5-lactams... 

Interest in (5,5)-fused ring systems developed in separate, albeit closely related, directions. In the first, chemists continue their quest for new compounds having unique biological, chemical and physical properties. In the second, emphasis is on the classification of aromaticity based upon molecular conformity with Hiickel s rule. An increasing understanding of the fundamental chemistry of heterocyclic ring systems has led to considerable advances in this field, as evidenced by the growing list of applications as biocides and in industrial processes. 

The progress in synthesis and chemistry of pyrroles, indoles, and related fused ring systems are the subjects of this chapter. Due to space limitations, only a selection of the recent advances reported during the period of January-December 2003 has been included in this text. However, several specialized reviews on the chemistry of indoles and pyrroles have appeared during the reporting period of this account, providing more in-depth coverage. 

The three monoepoxides of humulene, i.e. (136), (150) and (162), occur in nature, and there is every reason to assume that each epoxide is involved separately in transannulation processes leading to various fused-ring systems found amongst the sesquiterpenes. All three humulene monoepoxides have been synthesized and their individual chemistry with Lewis acids has been examined in an effort to effect their biogenetic conversions to natural teipenes. 

Selenazoles were first prepared in 1889, but intensive research did not begin in this area until 1940 <79AHC(24)109>. For the most part the Hantzsch approach has been used as the method of choice to prepare analogues of selenazole. The majority of the literature is concerned with applications and improvements in this basic methodology. Reactions of selenazole systems involve substitution of the ring and manipulation of attached functionality. The chemistry of the benzo- and hetero-fused ring systems has continued to develop with new analogues and uses reported. 

Synthesis of coumarins with 3,4-fused ring systems and their physiological activity , Darbarwar, M. and Sundaramurthy, V., Synthesis, 1982, 337 Naturally occurring coumarins . Dean, F. M., Fortschr. Chem. Org. Naturst, 1952, 9, 225 Naturally occurring plant coumarins , Murray, R. D. H., Fortschr. Chem. Org. Naturst, 1978, 35, 199 The natural coumarins occurrence, chemistry and biochemistry , Murray, R. D. H., Mendez, J. and Brown, S. A., Chichester, Wiley, 1982. 

After developing some aspects of this chemistry, it became important to us to synthesize one or more of a number of natural products that possess a five-eight fused ring system. However, we also recognized the... 

Carbon-hydrogen bond activation by transition metals has found its way to becoming an important aspect of organic synthesis. Metals have been found to break C-H bonds and then participate in follow-up reactions, oftentimes insertions of olefins or alkynes, that permit functionalization of a substrate or the formation of fused-ring systems. As this chemistry is developed, it is clear that selectivity in C-H bond activation is a critical issue that must be controlled to make a given functionalization reaction valuable. 

A. Padwa, A.D. Woolhouse, Aziridines, azirines and fused ring systems, in A.R. Kalrizky, C.W. Rees (Eds.), Comprehensive Heterocyclic Chemistry, vol. 7, Pergamon Press, Oxford, UK, 1984, pp. 47-93. Part 5. 

Heterocyclic amines are compounds that contain one or more nitrogen atoms as part of a ring. Saturated heterocyclic amines usually have the same chemistry as their open-chain analogs, but unsaturated heterocycles such as pyrrole, imidazole, pyridine, and pyrimidine are aromatic. All four are unusually stable, and all undergo aromatic substitution on reaction with electrophiles. Pyrrole is nonbasic because its nitrogen lone-pair electrons are part of the aromatic it system. Fused-ring heterocycles such as quinoline, isoquinoline, indole, and purine are also commonly found in biological molecules. 

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