Michael core-functionalized dendrimers

All these experiments give dendrons possessing either a vinyl, a primary amino, a bisphosphino, or an azido group at the level of the core. Other functional groups can be incorporated [30,31]. These compounds are useful precursors of multidendritic systems. Various surface-block dendrimers can be prepared from these macromolecules. For instance, a Michael addition between dendron 17c-[G 3] (100% excess) and dendron 15b-[G 3] at 90°C induces the formation of dendrimer 20-[G 3]-[G 3] (Scheme 13). This dendrimer possesses two different faces 16 dimethylamino groups on one side, 16 nitrile groups on the other side. 

Tomalia presented the synthesis of dendrimers as Starburst polymers, which consisted of poly(amide-amine)s as shown in Scheme 1 [2]. The core molecule in this case was ammonia, and the building block was methylacrylate. First, ammonia reacted with methylacrylate by a Michael-type addition. The obtained ester-terminated molecule was treated with a large excess amount of ethylene-diamine to form amino groups at the terminal positions (generation 0, GO). In this reaction, the methylester is the protected form of the amine, and the treatment with ethylenediamine (ester-amide transformation) corresponds to the deprotection of the ester function. Treatment of this amine-terminated molecule again with methylacrylate results in the formation of another terminal methyl-ester group. The molecule can be extended by repeating these operations. 

FIGURE 4.16 The formation of a dendrimer using the divergent approach involving Michael addition of acrylonitrile to an amine core. Each addition step is followed by a hydrogenation to reform amine functions for subsequent addition of acrylonitrile. 

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