Accelerated methods of synthesis of phosphorus-containing dendrimers

In order to shorten the long and tedious synthesis of dendrimers, several improvements have been proposed. This paper is a review of the improved methods recently published concerning the synthesis of phosphorus-containing dendrimers. It describes first the synthesis of hyperbranched polymers and their comparison with real dendrimers obtained from the same monomer. Then, the influence of the modification of the core of dendrimers is shown. In a third part, the use of dendrons is illustrated by several examples; they allow for instance to built a generation 8 directly from a generation 3 dendrimer. The last part describes the use of branched monomers of types AB₂ and CD₂, in which A reacts only with D and B reacts only with C. These reactions do not need any protecting groups, and the only by-products are H₂O and N₂. Using these monomers, the 4th generation is obtained in only four steps, instead of 8 for classical methods. This method has been improved by using more branched monomers AB₅ and CD₅, built from the cyclotriphosphazene. In this case, a dendrimer having 750 end groups is obtained in only three steps. The A (NH₂), B (PPh₂), C (N₃) and D (CHO) functions are identical in all cases, and they allow a real “Lego” chemistry, as shown by the synthesis of CA₂ and DB₂ monomers, also used for the accelerated synthesis of dendrimers.