Newkome

Newkome and co-workers have demonstrated the operation of a template effect in the formation of a pyrido-ester-crown. In the reaction shown in Eq. (2.8), they treated 2-clTloronicotinoyl cliloride with either the disodium or dipotassium salt of pentaethylene glycol. TJie two reactions were conducted under identical conditions except for the presence of sodium vs. potassium cations. Since the product is a six-oxygen macrocycle, its formation would be expected to be favored by K" rather than Na" counter ions for the glycolate. In fact, the yields of crown-lactone were 30% and 48% respectively when Na" and K" were the templating cations. 

Newkome and his group have pioneered in the synthesis of aliphatic macrocycles containing the pyridine subcyclic unit " . Like the furan systems discussed in Sect. 3.6, these are macrocycles containing a potentially coordinating subcyclic unit whose donor... 

Other, closely related, nicotinic acid derivatives and the unsubstituted system itself have also been studied and undergo similar reactions. Moreover, the approach may be extended to 2,2 -bipyridyls. Newkome and his collaborators have used the 2,2 -bipyridyl unit 19) as an electrophile in which ortho-hr ommes served as leaving groups. They have also used halomethyl systems and formed the macrocycles from these systems . A compound derived from the latter starting material 20) is reported to form a cobalt complex, in which both nitrogens and only one of the oxygen atoms participate in the binding . The two precursor units are shown below as 79 and 20, respectively. 

It should be stressed that there has been considerable interest in macrocycles containing the pyridine subcyclic unit, especially by Newkome and coworkers (see also Chap. 4). Most of his interest appears to have been focussed on polyethers rather than ester compounds. Bradshaw has also reported syntheses of compounds containing the pyridine subcyclic unit. ... 

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