Synthesis of Poly(aryl benzyl ether) Dendrimers on Solid Support

Abstract

Dendronized supports, combining core Wang resin and poly(aryl benzyl ether) dendrons, were prepared using a novel route. Employing a dimethyl 5-hydroxyisophthalate module and a Mitsunobu condensation/ester reduction iterative sequence, the dendrimer was cleanly and efficiently prepared to the third generation. The synthesis was monitored using gel-phase 13 C NMR and acidolytic cleavage, followed by 1 H NMR. Gel-phase NMR and swelling experiments demonstrated that the behavior of the dendronized resins in various solvents is strongly influenced by the peripheral functional groups. Synthesis of a cinnamate derivative (via Mitsunobu and Heck reactions) and of a tripeptide demonstrated suitability of the dendronized support for solid-phase synthesis.

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

“…The increase depends on the nature of the dendron and the polymeric core and ranges between 6 and 25% (Table 1). 25(b), 42,43 For beads with a diameter of approximately 100 m, this increase greatly exceeds that which may be expected from the addition of a thin dendritic layer. Thus, we may assume that, as Bradley 38(a) suggested, the dendrons, gradually filling the pores of the microporous resin, try to position themselves as far apart as possible, and this weakens the interaction between the polymer chains, separates them, and inflates the bead.…”

“…41 Accordingly, poly- ether dendron synthesis on solid supports was targeted and reported, initially by Bradley et al 42 and later by our group. 43 Instead of the 3,5-dihydroxy benzyl alcohol derivatives used in Fréchet-type dendrimers, prepared in solution, a more SPOS-suitable 3,5-bis(hydroxymethyl) phenol unit was conceived as a building block for dendron construction.…”

“…An alternative synthetic strategy enabled us to prepare the dendron, again via two repetitive steps, with the dimethyl-5-hydroxyisophthalate itself, without any need for building block preparation in solution (Scheme 8). 43 Although the special betain reagent 6 leads to very high conversion and purity at the Mitsunobu coupling step, it has to be prepared from costly starting materials and has a limited shelf life. 44 To avoid this obstacle, we recently elaborated the synthetic scheme (Scheme 9).…”

“…Synthesis of polyether dendrons by Dahan and Portnoy. 43 The reagents and conditions are as follows: (i) CH 2 Cl 2 and (ii) LiBH 4 , B(OMe) 3 , and tetrahydrofuran.…”

“…The dendronized resins swell to a lesser degree than the parent resins in polar and apolar aprotic solvents. 37,38,42,43 This can be partially explained by strong mutual interactions of the terminal groups impeding their separation and swelling (e.g., hydroxyl-terminated polyether dendrons). In addition, the swelling-like inflation of the beads during the dendron growth process reduces the potential of swelling.…”