Polycyclic systems including two

One Nitrogen Atom (it is self-sub divided into Monocyclic Pyrroles, Hydropyrroles, Porphyrins and Related Systems, Indoles, Carbazoles, Related Systems, and Hydrogenated Derivatives, Isoindoles Including Phthalocyanins and Porphyrazines, Polycyclic Systems Including Two Heterocycles). 

In addition to their work on tricyclic systems, Chmielewski and co-workers have used monosaccharides to obtain polycyclic derivatives of oxacepham. For instance, cyclization of 479 (R2 = Tos or TIBS) in a two-phase system including a phase-transfer catalyst and potassium carbonate gave 480 in 65-90% yields. The protecting group R1 was lost if it was a silyl group, for example, TMS, TBDMS <1998T14065>. 

Two interesting features of these models include the presence of an acid/base pair for organization of a well-defined six-membered transition state, and the role of the asymmetry adjacent to the basic group (X), which determines the face selectivity of the reaction. Note that for some catalysts (i.e. 85 and 87) the least-hindered site of coordination is not necessarily the convex face of a polycyclic system. 

The simplest polycycles stem from two triply-bridged points. These systems are exemplified by Trost et al. s 4,8-dihydrodibenzo[oi,g7z]pentalene (69) [87, 88], a precursor for a purturbed [12]annulene dianion, and Mislow et al. s double-bridged biphenyl derivatives (generally shown as 70) [89], where X is methylene, carbonyl, or various heteroatoms. Other longer bridged biphenyls include the triple-bridged cyclophanes 71 made by Hubert and Dale [90], their unsym-metrical relatives by Cram and Reeves [91], and the recent polyalkynyl cyclo-phane (72) made by Rubin et al. [92], a proposed fullerene precursor. 

A large number of polycyclic heterocycles containing two or more six-membered rings that share two or more carbon atoms are known. For the majority of these systems, only one of the six-membered rings contains the heteroatoms and the other rings are fused carbocyclic rings such as cyclohexane, benzene, naphthalene, and in rare examples, anthracene. Systems in which more than one of the six-membered rings contain heteroatoms are also briefly discussed these include spiro-cyclic compounds and substituted naphthalenes. 

Oxidation is intimately linked to the activation of polycyclic aromatic hydrocarbons (PAH) to carcinogens (1-3). Oxidation of PAH in animals and man is enzyme-catalyzed and is a response to the introduction of foreign compounds into the cellular environment. The most intensively studied enzyme of PAH oxidation is cytochrome P-450, which is a mixed-function oxidase that receives its electrons from NADPH via a one or two component electron transport chain (10. Some forms of this enzyme play a major role in systemic metabolism of PAH (4 ). However, there are numerous examples of carcinogens that require metabolic activation, including PAH, that induce cancer in tissues with low mixed-function oxidase activity ( 5). In order to comprehensively evaluate the metabolic activation of PAH, one must consider all cellular pathways for their oxidative activation. 

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