Benzil Knoevenagel reaction

We thus obtain defined, monodisperse, defect-free functionalized dendrim-ers, which are easily purified due to the high mass differences between the cyclopentadienone and the final dendrimer. However, for each new functionality, an appropriate cyclopentadienone building unit has to be synthesized. This can be achieved via a double Knoevenagel reaction of an already functionalized benzil 35 and diphenylacetone 24. For example, 4,4 -dibromobenzil (35a) as well as 4,4 -dimethoxybenzil (35 b) are commercially available and give the cyclopentadienone building unit with two bromo- or methoxy substituents in high yields [30, 34]. Furthermore the bromo substituent of the dibromocyclopenta-dienone can be quantitatively converted into a cyano (37) or amino (38) function (Scheme 13) [52]. 

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