Poli Cyclic Imines

A new active-iron reducing system - iron(II) chloride tetrahydrate-excess lithium powder-5 mol% 4,4 -di-f-butylbiphenyl in THF - reduces ketones and imines.326 (g) Mono- and poly-cyclic ketones in particular are reduced with good to excellent ee. 

Poly(ethylene imine). Poly(ethylene amine) (PEI) is the simplest polybase. It can be prepared directly via the acid-catalyzed polymerization of ethyleneimine (aziridine, 24C) (Fig. 40). 24C may be prepared via a number of routes with ethanolamine being a convenient precursor (223). The cationic polymerization of 24C is very rapid due to the release of the ring strain associated with the monomer. However, the synthesis of PEI under these conditions leads to highly branched structnres dne to chain transfer reactions involving the —NH— species in the polymer backbone. Cyclic products can also be prodnced nnder these conditions. Copol5nnerization with an appropriate comonomer can rednce the degree of chain branching (224). 

Cyclic amines (referred to as imines) are polymerized by acids and other cationic initiators [Goethals, 1984, 1989a,b Hauser, 1969 Kubisa, 1996 Tomalia and Killat, 1985]. The 3-membered imines (IUPAC aziridines) are the most studied of the cyclic amines. Polyethy-leneimine [IUPAC name poly(iminoethylene)] had been commercially available and used in the treatment of paper and textiles. It is no longer available in the United States because of the high toxicity of the monomer. 

Cyclic ethers are not the only heterocycles that can be polymerized. Poly(eth-ylene imine) can be prepared by the ring opening of aziridine, which can be initiated by protonic acids, followed by nucleophilic attack of the monomer to give the dimer. Further addition of the monomer can lead to linear polymer formation, but the dimer... 

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