Chemistry within megamolecules:: Regiospecific functionalization after construction of phosphorus dendrimers

The synthesis of dendrimers including P=N-P=S linkages specifically placed at some generations within the dendrimeric architecture allows the grafting of several types of functional groups at site- and depth-specific locations in the internal layers. The synthesis is carried out up to the fourth generation starting from a difunctional core, or up to the third generation starting from a hexafunctional core. These dendrimers include 2, 6, or 18 P=N-P=S groups, depending on the type of core and the generation considered. The functional groups are introduced by several types of reactions. First, the strong polarization of the P=N-P=S linkage induces a facile reactivity with various alkyl triflates such as methyl, allyl, and propargyl triflates, leading to the formation of functionalized phosphonium salts [P=N=P-S-R](+). The alkylation induces a weakening of the P-S bond which is cleaved with P(NMe2)(3), leading to the formation of internal aminophosphite groups [P=N-P:]. These highly reactive tricoordinated phosphorus atoms are alkylated by methyl or allyl iodide, leading to a second series of functionalized dendrimers including phosphonium salts at some precise internal layers. A third series of internally functionalized dendrimers is obtained by the Staudinger reaction of functionalized azides with the aminophosphite internal groups. Isothiocyanate, aldehyde, and primary amine derivatives have been grafted regiospecifically in this way [P=N-P=N-R]. The reactivity of the aldehyde internal functions leading to the grafting of azides or crown-ethers is also described.