Choice of strategies for the divergent synthesis of phosphorus- containing dendrons, depending on the function located at the core

Article abstract of DOI:10.1039/b001835j

The use of divergent strategies is a fruitful approach for the synthesis of phosphorus-containing dendrons (dendritic wedges). Different synthetic processes have been devised, depending on the type of function located at the core (alkenyl groups, pyridine derivatives, chloromethyl or azidomethyl groups). In all cases, the divergent strategy easily allows one to have very reactive functional groups such as P-Cl, amine, phosphine or aldehyde groups on the surface of the dendron.

Full text of DOI:10.1039/b001835j

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Choice of strategies for the divergent synthesis of
phosphorus-containing dendrons, depending on the function located
at the core¤
Valerie Maraval, Delphine Prevote–Pinet, Regis Laurent, Anne-Marie Caminade* and
Jean-Pierre Majoral*
L aboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077, T oulouse
cedex 4, France. E-mail: caminade=lcc-toulouse.fr and majoral=lcc-toulouse.fr;
Fax: ]33 5 61 55 30 03
Received (in Strasbourg, France) 28th February 2000, Accepted 11th April 2000
Published on the Web 14th June 2000
The use of divergent strategies is a fruitful approach for the synthesis of phosphorus-containing dendrons (dendritic
wedges). Di†erent synthetic processes have been devised, depending on the type of function located at the core
(alkenyl groups, pyridine derivatives, chloromethyl or azidomethyl groups). In all cases, the divergent strategy easily
allows one to have very reactive functional groups such as PÈCl, amine, phosphine or aldehyde groups on the
surface of the dendron.
Numerous publications dealing with dendrimers1 have
appeared in the last Ðfteen years, due to the wide range of
unique chemical and physical properties of these hyper-
branched macromolecules. Among these papers, the construc-
tion of multidendritic systems by connecting preconstructed
dendrons2 (dendritic wedges) appears as an area of growing
interest due to the possibilities for controlling the structure
and topology of very complex frameworks. Dendrimers and
dendrons are built using either divergent or convergent pro-
cesses, the former being mainly used for dendrimers and the
latter for dendrons. Scheme 1 illustrates both processes
applied to the synthesis of dendrons. In convergent growth,
the periphery of the dendron never reacts, only one reaction
occurs at the level of the core, and each generation is created
by associating two dendrons, which become larger at each
generation. However, in divergent growth the periphery reacts
at each step, no reaction occurs at the core, and each gener-
ation is created by associating a large number of small mol-
ecules to the dendron. The consequence is that it is much
easier to have a variety of functional groups on the periphery
of a dendron using divergent growth than with convergent
growth. Thus, divergent growth ought to be the most widely
used for the synthesis of dendrons, but this feeling is in sharp
contrast with reality.2l,2t,2u,3 Indeed, the drawback of diver-
gent growth is that the function located at the core must not
react during the synthesis of the dendron, but must be reactive
enough to be activated after the synthesis, despite the steric
hindrance of the core.
We have already reported several methods of synthesis of
P-containing dendrimers using divergent strategies.4 We
present here our e†orts to apply these methods to the synthe-
sis of dendrons, and the modiÐcations needed, depending on
the type of functional group located at the core.
Results and discussion
Most of the synthetic methods we developed for dendrimers
are based on the reactivity of aldehydes.4 Thus, in order to
¤ Electronic supplementary information (ESI) available: full spectro-
scopic data and elemental analyses of all compounds. See http://
www.rsc.org/suppdata/nj/b0/b001835j/
Scheme 1 Schematized convergent and divergent growth schemes for dendrons.
DOI: 10.1039/b001835j
New J. Chem., 2000, 24, 561È566
561
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Scheme 2 Synthesis of dendrons from alkenylphosphines.
synthesize a dendron having a particular functional group at
the core, we decided to design molecules possessing on one
side two aldehyde groups and on the other side the desired
functional group. The Ðrst type of function we tried to have
was alkenes, due to the wide range of reactions (additions,
substitutions, polymerizations, . . .) that could be carried out
later with these functions. For this purpose, we have chosen
alkenylphosphines such as allyldiphenylphosphine 1a, 1-
phenylphosphol-3-ene 1b, and diphenylstyrylphosphine 1c, for
use in Staudinger reactions with the azidodialdehyde 2
(Scheme 2). Such reactions lead to the formation of com-
fact, the basicity of pyridine rapidly appeared to be a problem.
Indeed, the reaction of pyridine-4-carboxaldehyde with phos-
phorhydrazide 3 does not give the expected condensation
product, but induces the formation of a precipitate (Scheme 3).
This precipitate has not been fully characterized, but it seems
to correspond to the polymerization of 3, which occurs in
basic conditions, accompanied by the formation of the
chlorhydrate of pyridine-4-carboxaldehyde. In order to avoid
this reaction, the pyridine is alkylated by methyl iodide in
THF, leading to the pyridinium salt 5, which precipitates.
Starting from 5, we tried to apply the method of synthesis
pounds 1aÈc-G@ , possessing one alkenyl and two aldehyde
used for dendrons 1-G , but in a di†erent solvent
0
n
groups, and characterized in 31P NMR by the presence of two
(acetonitrile). The Ðrst step, that is the condensation with
doublets, typical of the P2NÈP2S linkage. The dendrons are
phosphorhydrazide 3, occurs without any problem, leading to
grown from 1aÈc-G@ , with the alternating use of
5-G . However, the next step, the reaction with
0
0
H NNMeP(S)Cl (3) in CHCl ÈTHF and NaOC H CHO in
NaOC H CHO, is not quantitative. The expected product
2
2
3
6
4
6 4
THF, both reactions being quantitative before work-up as we
have already shown for dendrimers.4ahc,4ehf In all cases, the
dendrons are characterized by 1H, 13C, 31P NMR and IR
spectroscopies, as well as elemental analyses. In particular,
31P NMR is a precious tool at each step to check the total
reaction of the outer layer, and the P2NÈP2S group at the
core is a sensitive probe to ensure that no reaction occurs at
this level. The growth of the dendron has been stopped at the
Ðrst generations 1b-G@ and 1c-G@ (4 aldehyde groups) from
5-G@ is obtained but it appears difficult to isolate from side
0
products, probably due to a reaction with iodide. Thus, we
decided to change the type of pyridine derivative used as start-
ing product. Pyridine-2,6-dicarboxaldehyde, 6, appears as a
good candidate, because the nitrogen is hindered and partially
deactivated by the inductive e†ect of both aldehydes. The use
of phosphorhydrazide 3 and NaOC H CHO in alternation
6
4
allows us to grow the dendron starting from 6, by applying
exactly the method used for the synthesis of 1-G . The con-
1
1
n
phenylphosphol-3-ene and diphenylstyrylphosphine, respec-
tively. However, the growth could have been pursued to
higher generations, as illustrated by the formation of the third
struction has been successfully carried out up to the second
generation dendron 6-G@ , which possesses 16 aldehyde end
2
groups (Scheme 4). However, it must be noted that a strictly
generation dendron 1a-G@ from allyldiphenylphosphine. The
quantitative amount of phosphorhydrazide 3 must be used in
the condensation step. Indeed, an excess induces the poly-
3
synthesis has been stopped at this step in order to be able to
detect easily the signals corresponding to the P2NÈP2S group
of the core in 31P NMR. Dendron 1a-G@ possesses one allyl
3
function at the core and 16 aldehyde functions on the periph-
ery. The presence of aldehyde groups is important since they
o†er a wide range of possibilities to graft other functions onto
the surface of the dendron.4bhc,4ehf,4k,4o However, it could be
interesting also, for technical reasons, to have non reactive
groups on the surface, in order to study more easily the reacti-
vity of the core. This is achieved using NaOC H instead of
6
5
NaOC H CHO in the last step. For instance, the reaction of
6
4
1a-G with sodium phenate gives dendron 4a-G@ , possessing
a protected surface and only one allyl group at the core
(Scheme 2).
2
2
The second type of functional group that we intended to
introduce at the core of dendrons was pyridine derivatives,
whose complexing and basic properties could be used later. In
Scheme 3 Attempted synthesis of a dendron from a monosubstituted
pyridine.
562
New J. Chem., 2000, 24, 561È566

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merization of 3 and the formation of pyridinium chlorhydrate,
which is the type of problem already encountered with
pyridine-4-carboxaldehyde. Furthermore, we have not isolated
compounds 6-G@ (n \ 0È2) with P(S)Cl end groups, but used
n
2
them immediately to react with NaOC H CHO. Thus, only
6
4
compounds with aldehyde end groups 6-G@ (n \ 0È2) are iso-
lated and fully characterized in this series.
n
The third type of function we tried to graft at the core of
dendrons is a chloromethyl group, which could be used in
various substitution reactions. The starting compound is chlo-
romethylphosphonic acid dichloride 7. The expected di†erence
in reactivity between the PÈCl and CÈCl groups is observed
when hydroxybenzaldehyde sodium salt is reacted with com-
pound 7, only substitutions on the P(O)Cl group occur to
2
yield 7-G@ (Scheme 5). The CÈCl is much less reactive, but it
0
reacts for instance with NaN , even if it is under drastic con-
3
ditions (70 ¡C in pyridine for 20 days). The azide 8-G@ is iso-
0
lated, and characterized in particular by the presence of the l
N band at 2101 cm~1 in IR spectroscopy. Compounds 7-G@
3
0
and 8-G@ could be starting products for the synthesis of den-
0
drons functionalized with CÈCl and CÈN groups, respec-
3
tively. Thus we tried Ðrst to react phosphorhydrazide 3 with
both compounds. These reactions occur without any problem
Scheme 4 Synthesis of a dendron from a disubstituted pyridine.
to yield 7-G and 8-G , respectively. However, the next step
1
1
to grow the dendron, the reaction with hydroxybenzaldehyde
sodium salt, does not lead cleanly to the expected dendron
with four aldehyde groups. Indeed, 31P NMR indicates in
both cases that a reaction occurred also at the level of the
core. We did not try to isolate any compound, since the
growing of dendrons or dendrimers necessitates absolutely
clean and quantitative reactions. Thus, we decided to apply
another method to synthesize dendrons from compound
7-G@ , avoiding the use of any sodium salt.
0
We have already described
a three-step synthesis of
branches within dendrimers, which necessitates the alternating
use of methylhydrazine, Ph PCH OH, and the azide 2.4g Such
2
2
a process for the growing of dendrons from 7-G@ is depicted in
0
Scheme 6. The repetition of these three steps has been carried
Scheme 5 Attempted synthesis of dendrons from a chloromethyl or
azidomethyl phosphine oxide derivative.
out up to the formation of the fourth generation dendron
Scheme 6 Synthesis of a dendron from a chloromethyl phosphine oxide derivative up to the fourth generation.
New J. Chem., 2000, 24, 561È566
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9-G@ , possessing 32 aldehyde end groups. In this series, only
H PO for 31P NMR, SiMe for 1H and 13C NMR. The
4
3
4
4
compounds 9-G@ (n \ 1È4) with aldehyde end groups have
attribution of 13C NMR signals has been done using Jmod,
two dimensional HMBC, and HMQC, broad band or CW
31P decoupling experiments when necessary. The labelling
scheme used for NMR is depicted on Scheme 7. Only 31P
NMR data are given in this section. Full spectroscopic data
and elemental analyses are deposited as Electronic Supple-
mentary Information. Compounds 1a,6 1b,7 1c,8 29 and
Ph PCH OH10 were prepared according to published pro-
n
been isolated and fully characterized. In all cases, the reactions
are monitored by 31P NMR, which indicates a slight shifting
of the signals corresponding to the phosphorus of the outer
layer. The condensation step with methylhydrazine is charac-
terized by a slight shielding of the doublet corresponding to
Ph P2N from d \ 13.1 to d \ 11.7, and a slight deshielding
2
for the doublet corresponding to NÈP2S from d \ 50.9 to
2
2
d \ 52.6 for the 9-G@ ] 9-GA reaction. The condensation step
cedures. The reactions are carried out at room temperature,
unless otherwise stated.
n
n
with Ph PCH OH is characterized by the appearance of a
2
2
singlet at d \ [23.4 for the diphenylphosphino group grafted
to the dendron, and a very slight shifting of both doublets
corresponding to the P2NÈP2S linkage (*d \ 0.1) for the 9-
GA ] 9-GÓ reaction. The Staudinger reaction with the azide 2
induces the disappearance of the singlet of the
diphenylphosphino group and the appearance of two doublets
corresponding to the formation of the new P2NÈP2S linkages
at d \ 13.2 and 50.9 for the 9-GÓ ] 9-G@ reaction.
General procedure for the synthesis of 1a–c-Gº
0
To a solution of phosphine 1a–c (a: 1.5 g, 6.631 mmol; b: 1.5
g, 9.248 mmol, c: 1.5 g, 5.202 mmol) in CH Cl (15 mL) was
n
n
2
2
slowly added at 0 ¡C 1 equiv. of the azide 2 (a: 2.303 g, 6.631
mmol; b: 3.212 g, 9.248 mmol, c: 1.807 g, 5.202 mmol) in
CH Cl (15 mL). Ten minutes after the addition was ended,
n
n`1
2
2
the solution temperature was raised to room temperature. The
evolution of nitrogen ceased after 3 h. The solvent was elimi-
nated under vacuum to yield an oil, which was washed 5 times
with THFÈpentane (1 : 5).
Conclusion
We have demonstrated in this paper that the use of the diver-
gent strategy is not only a fruitful approach for the synthesis
of dendrimers but also for the synthesis of dendrons. The
main drawback of this method is that di†erent synthetic pro-
cesses have to be devised, depending on the type of function
located at the core, and no general procedure can be applied.
However, the divergent strategy easily allows having very
reactive functional groups on the surface of the dendron such
as PÈCl, amine, phosphine, and aldehyde groups, whose reac-
tivities were fully studied on the surface of dendrimers.1h,4k
Furthermore, the variety of functional groups located at the
core should o†er a versatile reactivity, leading to new means
to synthesize multidendritic systems with complex architec-
tures, as we have recently demonstrated for dendrons of type
1a-Gº . White powder, 72% yield. 31P M1HN NMR (CDCl ):
0
3
d \ 17.8 (d, 2J \ 32.9 Hz, P@ ), 50.8 (d, 2J \ 32.9 Hz, P ).
PP
0
PP
0
1b-Gº . Yellow oil, 80% yield. 31P M1HN NMR (CDCl ):
0
3
d \ 40.8 (d, 2J \ 29.8 Hz, P@ ), 52.3 (d, 2J \ 29.8 Hz, P ).
PP PP
0
0
1c-Gº . Pale beige powder, 93% yield. 31P M1HN NMR
0
(CDCl ): d \ 13.3 (d, 2J \ 31.3 Hz, P@ ), 49.9 (d, 2J \ 31.3
3
Hz, P ).
0
PP
0
PP
General procedure for the synthesis of dendrons 1-G (n = 1–3)
n
with P(S)Cl end groups
1-G having a vinyl group at the core.5 Work is in progress to
2
n
study the synthetic properties of the core and of the outer
To a solution of dendron 1-G@
n~1
in THF (10 mL) was added
(CHO end groups) (5 mmol)
solution of dichloro-
layer of these phosphorus-containing dendrons.
a
methylhydrazinothiophosphine 3 (10% excess) in CHCl . The
3
Experimental
resulting mixture was stirred for 12 h, then evaporated to
dryness. The residue was washed several times with THFÈ
General
pentane (1 : 5) to a†ord 1-G .
n
All manipulations were carried out with standard high
vacuum and dry-argon techniques. 1H, 13C, 31P NMR spectra
were recorded with Bruker AC 200, AC 250 or AMX 400
spectrometers. References for NMR chemical shifts are 85%
1a-G . White powder, 88% yield. 31P M1HN NMR (CDCl ):
1
3
d \ 18.0 (d, 2J \ 33.5 Hz, P@ ), 52.4 (d, 2J \ 33.5 Hz, P ),
PP
0
PP
0
63.5 (s, P ).
1
Scheme 7 Labelling scheme used for NMR.
564
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1b-G . Pale beige powder, 95% yield. 31P M1HN NMR
powder in 97% yield. 31P M1HN NMR (CD CN): d \ 61.6 (s,
1
3
(THF): d \ 40.1 (d, 2J \ 30.2 Hz, P@ ), 53.5 (d, 2J \ 30.2
P ).
PP
0
PP
1
Hz, P ), 62.1 (s, P ).
0
1
5-Gº . To a solution of 5-G (0.2 g, 0.49 mmol) in MeCN (20
0
0
1c-G . Pale beige powder, 92% yield. 31P M1HN NMR
mL) was added hydroxybenzaldehyde sodium salt (0.14 g, 0.98
mmol). The resulting mixture was stirred for 12 h, then centri-
fuged. The solution was evaporated to dryness to give a
yellow powder, which could not be perfectly puriÐed by
1
(THF): d \ 12.4 (d, 2J \ 31.3 Hz, P@ ), 51.0 (d, 2J \ 31.3
PP
0
PP
Hz, P ), 62.1 (s, P ).
0
1
1a-G . White powder, 82% yield. 31P M1HN NMR (THF):
washing (with diethyl ether). 31P M1HN NMR (CH CN):
2
3
d \ 16.6 (d, 2J \ 33.5 Hz, P@ ), 51.9 (d, 2J \ 33.5 Hz, P ),
d \ 58.9 (s, P ).
PP
0
PP
0
1
61.5 (s, P ), 62.1 (s, P ).
1
2
General procedure for the synthesis of dendrons 6-Gº
n
1a-G . White powder, 92% yield. 31P M1HN NMR (CDCl ):
To a solution of dialdehyde 6 (5.000 mmol) or dendron 6-
3
3
0
d \ 17.6 (d, 2J \ 33.6 Hz, P@ ), 52.4 (d, 2J \ 33.6 Hz, P ),
PP PP
62.1 (s, P ), 62.3 (s, P ), 63.2 (s, P ).
G@
(2.000 mmol) in a minimum amount of THF (10 mL)
0
n~1
was added compound 3 (10.000 mmol for 6-G ; 8.000 mmol
1
2
3
0
for 6-G ; 16.000 mmol for 6-G ). The reaction was monitored
General procedure for the synthesis of dendrons 1-Gº (n = 1–3)
1
2
n
by 31P NMR until the disappearance of the signal corre-
sponding to compound 3 (70.5 ppm), then a slight excess of
hydroxybenzaldehyde sodium salt was added. The resulting
mixture was stirred for 12 h, then centrifuged. The solution
was evaporated to dryness to a†ord a powder, which was
washed several times with THFÈpentane (1 : 5). Dendrons
with CHO end groups
To a solution of dendron 1-G [P(S)Cl end groups] (5 mmol)
n
2
in THF (10 mL) was added hydroxybenzaldehyde sodium salt
(10% excess). The resulting mixture was stirred overnight,
then centrifuged. The solution was then evaporated to dryness
to a†ord a powder, which was washed several times with
THFÈpentane (1 : 5).
6-G@ were isolated as white powders.
n
6-Gº . 82% yield. 31P M1HN NMR (CDCl ): d \ 60.0 (s, P ).
0
3
0
1a-Gº . White powder, 93% yield. 31P M1HN NMR (CDCl ):
1
3
0
6-Gº . 90% yield. 31P M1HN NMR (CDCl ): d \ 60.5 (s, P ),
d \ 17.6 (d, 2J \ 33.5 Hz, P@ ), 52.6 (d, 2J \ 33.5 Hz, P ),
1
61.8 (s, P ).
0
3
1
PP
0
PP
60.7 (s, P ).
1
6-Gº . 92% yield. 31P M1HN NMR (THF): d \ 60.0 (s, P ),
1b-Gº . Pale beige powder, 96% yield. 31P M1HN NMR
2
2
1
61.2 (s, P ), 61.4 (s, P ).
(THF): d \ 39.9 (d, 2J \ 30.4 Hz, P@ ), 53.6 (d, 2J \ 30.4
0
1
PP
0
PP
Hz, P ), 60.2 (s, P ).
0
1
Synthesis of 7-Gº and 7-G
0 1
1c-Gº . Pale beige powder, 90% yield. 31P M1HN NMR
7-Gº . To a solution of ClCH P(O)Cl (2.00 g, 11.97 mmol)
1
0
2
2
(THF): d \ 12.4 (d, 2J \ 32.1 Hz, P@ ), 51.5 (d, 2J \ 32.1
in THF (20 mL), was added 4-hydroxybenzaldehyde sodium
salt (3.43 g, 23.94 mmol). The resulting mixture was stirred for
2 h, then centrifuged. The solution was evaporated under
PP
0
PP
Hz, P ), 59.7 (s, P ).
0
1
1a-Gº . White powder, 91% yield. 31P M1HN NMR (CDCl ):
vacuum to a†ord 7-G@ as a yellow oil in 80% yield. 31PM1HN
2
3
0
0
d \ 16.6 (d, 2J \ 35.0 Hz, P@ ), 52.6 (d, 2J \ 35.0 Hz, P ),
PP PP
60.6 (s, P ), 62.5 (s, P ).
NMR (THF): d \ 12.2 [s, P (O)].
0
0
2
1
7-G . To a solution of 7-G@ (0.200 g, 0.591 mmol) in THF (5
1
0
1a-Gº . White powder, 92% yield. 31P M1HN NMR (CDCl ):
mL), was added a solution of 3 (1.182 mmol) in chloroform
(concentration 0.32 M). The resulting solution was stirred for
3 h, then evaporated to dryness to a†ord a powder. Washing
this powder twice with diethyl etherÈpentane (2 : 1) a†orded
3
3
0
d \ 17.6 (d, 2J \ 32.0 Hz, P@ ), 52.6 (d, 2J \ 32.0 Hz, P ),
PP PP
60.5 (s, P ), 62.4 (s, P ), 62.5 (s, P ).
0
3
2
1
Synthesis of dendron 4a-Gº
2
7-G as a yellow powder in 70% yield. 31PM1HN NMR (THF):
1
To a solution of 1a-G (3.000 g, 1.618 mmol) in THF (30 mL)
d \ 12.0 [s, P (O)], 61.9 [s, P(S)Cl ].
2
0
2
was added phenol sodium salt (1.520 g, 13.106 mmol). The
Synthesis of 8-Gº and 8-G
resulting mixture was stirred overnight, then centrifuged. The
solution was evaporated to dryness to a†ord a powder, which
was washed 3 times with THFÈpentane (1 : 5). Dendron
0
1
8-Gº . To a solution of 7-G@ (2.00 g, 5.904 mmol) in pyridine
0
0
(40 mL) was added a large excess of sodium azide. The
resulting mixtured was heated at 70 ¡C for 20 days, then cen-
trifuged. The solution was evaporated under vacuum, and the
residue was puriÐed on silica gel (eluent diethyl ether, then
4a-G@ was obtained as a white powder in 95% yield. 31P M1HN
2
NMR (CDCl ): d \ 17.4 (d, 2J \ 33.2 Hz, P@ ), 52.6 (d,
3
PP
0
2J \ 33.2 Hz, P ), 62.5 (s, P ), 62.7 (s, P ).
PP
0
1
2
methanol) to a†ord 8-G@ as a yellow oil in 60% yield.
Synthesis of 5,5-G and 5-Gº
0
0
0
31PM1HN NMR (THF): d \ 7.3 [s, P (O)].
0
5. To a solution of pyridine-4-carboxaldehyde (1.0 mL,
10.46 mmol) in THF (10 mL) were added 5 equiv. of methyl
iodide (3.3 mL, 52.38 mmol). The resulting mixture was stirred
for 1 day. A precipitate appeared, which was recovered and
dried under vacuum, to a†ord compound 5 as an orange
8-G . To a solution of 8-G@ (0.065 g, 0.188 mmol) was
1
0
a solution of 3 (0.376 mmol) in chloroform
added
(concentration 0.32 M). The solution was stirred for 3 h, then
evaporated to dryness to a†ord a powder, which was washed
twice with Et OÈpentane (2 : 1). Compound 8-G was
powder in 99% yield. 1H NMR (CD CN): d \ 4.4 (s, 3H,
2
1
3
4
obtained as a yellow powder in 71% yield. 31PM1HN NMR
(THF): d \ 6.8 [s, P (O)], 62.1 [s, (S)PCl ].
CH ), 8.4 (d, 3J \ 6.4 Hz, 2H, o-C H N), 8.7 (d, 3J \ 6.4
3
HH
5
HH
Hz, 2H, m-C H N), 10.3 (s, 1H, CHO).
0
2
5
4
General procedure for the synthesis of dendrons 9-Gº (n = 1–4)
5-G . To a solution of 5 (1.00 g, 4.01 mmol) in CH CN (40
n
0
3
mL) at 0 ¡C was added a solution of 3 (4.42 mmol) in CHCl
To a solution of 7-G@ or dendron 9-G@
(n \ 2È4), in THF
3
0
n~1
(15.8 mL). The resulting mixture was stirred for 12 h, then
evaporated to dryness to give a powder, which was washed
(30 mL) was added a stoichiometric amount of methyl-
hydrazine. The resulting mixture was stirred overnight, then
evaporated to dryness. The residue was washed two or three
several times with pentane. 5-G was obtained as a yellow
0
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times with diethyl ether to a†ord dendron 9-GA . To a THF
n~1
solution of this compound was added a slight excess of
Ph PCH OH. The resulting mixture was stirred overnight at
2
2
40 ¡C, then evaporated to dryness. The residue was washed at
least 4 times with pentaneÈEt O (3 : 1), then with pure Et O
2
2
to a†ord dendron 9-GÓ . To a THF solution of this com-
n~1
pound was added a slight excess of the azide 2. The solution
was stirred till the evolution of nitrogen ceased (30 min), then
evaporated to dryness. The residue was washed with
CH CNÈEt O to a†ord 9-G@ as a white powder. Only den-
3
2
n
drons 9-G@ were isolated and fully characterized.
n
9-Gº . White powder, 50% yield. 31PM1HN NMR (THF):
1
d \ 11.6 [s, P (O)], 13.1 (d, 2J \ 32 Hz, P@ ), 50.9 (d, 2J
\
0
PP
1
PP
32 Hz, P ).
1
9-Gº . White powder, 55% yield. 31PM1HN NMR (THF):
2
d \ 11.6 [s, P (O)], 11.9 (d, 2J \ 32 Hz, P@ ), 13.2 (d, 2J
PP PP
\
0
1
32 Hz, P@ ), 50.9 (d, 2J \ 32 Hz, P ), 52.5 (d, 2J \ 32 Hz,
2
PP
2
PP
P ).
1
9-Gº . White powder, 57% yield. 31PM1HN NMR (THF):
3
d \ 12.0 (br d, 2J \ 32 Hz, P@ , P@ ), 13.3 (d, 2J \ 32 Hz,
PP
1
2
PP
3
4
P@ ), 50.9 (d, 2J \ 32 Hz, P ), 52.5 (d, 2J \ 32 Hz, P , P ).
3
PP
3
PP
1
2
9-Gº . White powder, 50% yield. 31PM1HN NMR (THF):
4
d \ 11.9 (br d, 2J \ 32 Hz, P@ , P@ , P@ ), 13.2 (d, 2J \ 32
PP
PP
1
4
2
3
PP
Hz, P@ ), 50.8 (d, 2J \ 32 Hz, P ), 52.4 (d, 2J \ 32 Hz, P ,
4
PP
1
P , P ).
2
3
Acknowledgements
Thanks are due to the CNRS and to the European Union
(INCO-Copernicus project ERBIC15CT960746) for Ðnancial
support.
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