Dendritic molecule divergent synthesis

The synthesis of uniform dendritic molecules can proceed in two major iterative ways the divergent-iterative pathway (Fig. 7), which was used in the early work in 1978, starts from an initial core with one or more functional... 

Fig. 2.8 Divergent synthesis of dendritic molecules on a solid phase (C=coupling group, F= functional group P= protective group)...

Lambert et al. succeeded in developing second-generation dendritic polysilanes [71]. The repetitive steps of this divergent synthesis consist in cleavage of silicon-methyl bonds by trifluorosulphonic acid (CF3SO3H) and subsequent formation of silicon-silicon bonds (Fig. 4.39). Starting from tetrasilanes, up to second-generation starfish-like dendritic molecules with a molecular mass of 1832.9 g/mol could be prepared in this way [72]. 

Poly(propylene imine) (PPI or POPAM) dendrimers are the first dendritic stmctures found in literature. They were first reported by Buhleier etal, who presented a divergent synthesis of branched and dendritic-like molecules. These simple structures were accomplished using controlled organic chemistry. In this case, a Michael reaction between a primary amine and two equivalents of acrylonitrile resulted in a dinitrile. Further reduction through Co(II)-catalyzed hydrogenolysis led to a terminal diamine (Figure 16). An iterative protocol allowed the con-stmction of what today is defined as a second-generation... 

In the series for synthesizing dendritic molecules, they prepared various monomers to achieve a directional divergent cascade synthesis. For instance, as shown in Scheme 5, aminotriol 1 was prepared as follows [Eq. (1)] [7] Michael-type addition of nitromethane to acrylonitrile afforded the trisnitrile 2. which was subsequently transformed to the triacid 5. Alternatively, triacid 3 was obtained via a Michael-type addition of nitromethane to methyl acrylate and subsequent hydrolysis of triester 4. Reduction of the acid moieties with di-borane gave nitrotriol 5. Further reduction with Raney nickel yielded the desired aminotriol 1. 

The first correctly dendritically branched molecules were termed cascade molecules and could be prepared divergently by a cascade synthesis (Section 1.1). 

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