Chemistry Reference
In-Depth Information
FIGURE 16.6
Influence of cocatalyst and generation for catalyzed asymmetric allylic
alkylation.
(water/heptane)-catalyzed isomerization of allylic alcohols to ketones (from 38% of
conversion with the monomer
33
, 63% with the first-generation dendrimer
33-G
1
,to
98% with the third generation
33-G
3
). The products were easily isolated and the
catalyst could be reused several times, even the first generation (Figure 16.7) [42].
The best example of positive dendritic effect was obtained for the coupling of
pyrazole, catalyzed by the copper complexes of pyridineimine-ended phosphorus
dendrimers. Copper is a cheap and practically nontoxic metal, which is a very
attractive alternative to transition metals. However, the monomer
34
is totally
inefficient to catalyze this reaction, starting from either iodo- or bromobenzene. In
sharp contrast, the dendrimers
34-G
n
enabled quantitative conversion of substrate into
FIGURE 16.7
Role of the generation and recycling in aqueous media for alcohols
isomerization.
