Cyclic nitrogen-metal ring

With this section, the classification in the Handbook of Heterocyclic Chemistry has been followed thus a general survey of the effect of rings on the reactions of substituents is followed by a survey of the effect of rings on reactions of individual substituents in the order fused benzene rings, C-linked, AMinked, <9-linked, S-linked substituents, halogens, and metals. Substituents attached to cyclic nitrogen and sulfur are dealt with as described below. 

Organometallic reagents and alkali metal amides can react via a cyclic transition state (Section II, B, 5) beginning with electrophilic attack at the most basic ring-nitrogen. As a result, sodamide (in dimethylaniline, 145°, 2 hr) yields the 4-amino derivatives (40% yield S)) methyl- or phenyl-magnesium iodides give the 4-adduct quantitatively.s ... 

Chls and all tetrapyrroles are heteroaromatic compounds and the aromatic character of the underlying tetrapyrrole moiety and the reactivity of the functional groups in the side chains govern their chemistry. Three different classes of tetrapyrroles, differentiated by their oxidation level, occur in nature porphyrins (11, e.g. hemes), chlorins (12, e.g. chls) and bacteriochlorins (13, e.g. bchls). As a cyclic tetrapyrrole with a fused five-membered ring, the overall reactivity of chi is that of a standard phytochlorin 7. Such compounds are capable of coordinating almost any known metal with the core nitrogen atoms. Together with the conformational flexibility of the macrocycle and the variability of its side chains, this accounts for their unique role in photosynthesis and applications ... 

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