Polymer, branched Cleavage

As follows from the comparison of the rates of oxidation and destruction of linear and branched polyalkenes, the branched form possesses more susceptible tertiary C—H bonds and oxidizes more rapidly (but degrade more slowly) than the linear form. This was observed for PS, PE, PP, polyfrt-isopropyl styrene), polymethylene, and polymers produced by the decomposition of diazomethane-diazoethane and diazomethane-diazobutane mixtures [125], The number of cleavages per oxygen molecule consumed at 403 K amounts to 0.25 for PE and to 0.04 for PP. 

The low molecular weight analogs, 3-chloropentane (3-CP) and 1-chloropentane (1-CP) were treated in exactly the same manner as the polymer glasses. Since these analogs were small molecules, no solvent was necessary to enhance resolution in the ESR. On irradiation, cleavage of the carbon-chlorine bond is expected for both. The 3-CP should serve as a model to indicate carbon-chlorine cleavage in the main PVC chain. The 1-CP molecule could be used to indicate formation of any primary radicals in PVC from branch points, chain cleavage, etc. 

Polymer-bound chiral hydrazines have been synthesized to furnish a-branched amides (Scheme 12.17) [13, 23], Enantiopure (i-methoxyamines 37 and 38, derived from readily available hydroxyproline and N,N-dibenzylleucinol, respectively, have been attached to solid support and transformed into the corresponding hydrazine auxiliaries 39 and 40 via several steps. The synthesis of a series of enantiomerically enriched a-branched amides required the coupling of aliphatic and aromatic aldehydes to form hydrazones 41 and 42 followed by the addition of different nucleophiles. Cleavage of the N-N bond of the resulting hydrazines 43 and 44 led to a-branched amines 45. Further conversion with benzoyl chloride or acetyl chloride furnished amides 46 in yields of 24—51% and 50-83% ee. 

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