Chemistry Reference
In-Depth Information
SCHEME 16.2
particularly attractive for the synthesis of dendrimers. In our first methods, phos-
phorus dendrimers including these linkages necessitate three steps to build one
generation, starting from aldehyde groups: (i) condensation of methylhydrazine,
(ii) reaction with either Ph
2
PCl in basic conditions [21] or with Ph
2
PCH
2
OH [22], and
(iii) Staudinger reaction between the phosphine end groups and an azido dialdehyde,
which affords again aldehydes as end groups. The repetition of these three steps was
carried out up to the third generation
11-G
3
(Scheme 16.3). It must be emphasized that
this three-step method is fully compatible with the two-step method shown in
Scheme 16.1, because both afford aldehyde terminal groups. It means that the
P
¼
¼
S linkages can be introduced at one or several layers, where desired when
applying the two-step process.
The presence of P
¼
N
P
¼
S linkages inside dendrimers led to the most original
type of dendritic structures described up to now. Indeed, these linkages have a
mesomeric form (
þ
P
N
P
S
) in which a negative charge is located on sulfur.
Due to this particular structure, these linkages are able to undergo a specific alkylation
on sulfur with alkyl triflates [22], eventually functionalized [23]. This reaction is
N
¼
P
