Imidazolidine ring aldehydes

Condensation reactions of aromatic aldehydes with a,cu-polyamines lead to Schiff bases, if the polyamine involved contains only primary amino groups or to imidazolidines, if the polyamine contains a secondary amino group. Condensation of 2-pyridinecarboxaldehyde 7V-oxide with triethylenetetramine yields derivative (31), with two imidazolidine rings, which in the presence of Cu11 undergoes a ring-opening reaction due to the formation of a complex.42... 

Tilting of the N-aryl ring of U relative to the imidazolidine ring positioned the ortfto-eyelohexyl substituent anti to the backbone phenyl group and distal to nickel. This orientation then positioned the ort/zo-methyl substituent syn to the backbone phenyl group and proximal to nickel. It was the ortho-methyl substituent that thus dictated the selectivity of aldehyde binding according to this model. Oxidative cyclisation of U to metallacycle V then led to the formation of the final product. 

The pyrazole ring is resistant to most reducing agents and survives intact when other heterocycles are cleaved. An illustration is provided by the reaction of the pyrazoloimidazolidinone (1) with LAH. Here the imidazolidine unit is sensitized to nucleophilic attack by the presence of a lactam carbonyl group, and the product formed is the monocyclic pyrazole (2). The stability of pyrazoles to reduction has been exploited in a synthesis of aldehydes from acyl halides. Thus N-acylpyrazoles (3) on reduction with LAH produce complexes of the type (4) these when hydrolyzed yield aldehydes and the parent pyrazoles (5). ... 

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