Synthesis of low generation phenylenealkylene dendrons as nonpolar building blocks for a dendrimer construction set

Article abstract of DOI:10.1055/s-2003-36263

The gram scale syntheses of first and second generation (G1 and G2) dendrons 1-4, and 35, based on aryl and alkyl moieties, by Suzuki-Miyaura cross-coupling are presented. Both a divergent and an accelerated convergent route are applied. In addition, first results on the synthesis of hyperbranched oligomers of AB₂ monomer 19 are reported.

Full text of DOI:10.1055/s-2003-36263

PAPER
79
Synthesis of Low Generation Phenylenealkylene Dendrons as Nonpolar
Building Blocks for a Dendrimer Construction Set
S
yntehsis of Phenylene
a
alkylene
D
t
e
ndron
t
s
hias Beinhoff, Birol Karakaya, A. Dieter Schlüter*
Freie Universität Berlin, Institut für Chemie/Organische Chemie, Takustr. 3, 14195 Berlin, Germany
Fax +49(30)83853357; E-mail: adschlue@chemie.fu-berlin.de
Received 30 July 2002; revised 25 September 2002
Here we describe gram scale procedures for the synthesis
of nonpolar aryl/alkyl G1 and G2 dendrons employing
both divergent and convergent routes. The main synthetic
tool is the Suzuki–Miyaura cross-coupling of alkyl bor-
Abstract: The gram scale syntheses of first and second generation
(G1 and G2) dendrons 1–4, and 35, based on aryl and alkyl moi-
eties, by Suzuki–Miyaura cross-coupling are presented. Both a di-
vergent and an accelerated convergent route are applied. In
addition, first results on the synthesis of hyperbranched oligomers anes with aryl bromides and iodides.15 This tool was also
of AB2 monomer 19 are reported.
applied to one of the new AB2 type monomers to test
whether hyperbranched polymers with reasonable molar
Key words: dendrimers, dendrons, Suzuki–Miyaura cross-cou-
pling, iododesilylation, building blocks
mass and branching degree can be obtained.16
Results and Discussion
Introduction
Figure 1 shows the four main target dendrons 1–4. They
are characterized by threefold benzene branching units
which are connected by trimethylene (1, 2) and tetrameth-
ylene bridges (3, 4), respectively. Dendrons 1 and 2 each
carry two trimethylsilyl (TMS) placeholder functions per
terminal phenyl unit and a benzyl protected hydroxyethyl
group at the focal point. Dendrons 3 and 4 carry two silyl-
protected hydroxypropyl groups per terminal phenyl unit
and 1-but-3-enyl groups at the focal point which results in
a very efficient, step economic growth reaction (see be-
low). The syntheses for 1 and 2 are divergent, that for 3
and 4 convergent.
One of our aims is to develop a construction set consisting
of first (G1) and second generation (G2) dendritic build-
ing blocks which carry orthogonally protected functional
groups to allow a wide range of combinations.1 Such a set
is of considerable interest not only for the modular and
combinatorial synthesis of a variety of spherical dendri-
mers and dendronized polymers2 but also for surface mod-
ifications.3 Up to now, we have developed G1 and G2
dendrons with the following orthogonal protecting group
patterns (periphery/focal point/connectivity): hydroxy/
isocyanate/urethane,4 hydroxy/acid/amides,5 amines/acid/
amides,6 and amines/olefin (allyl)/amides.7 Besides these,
dendrons with two differently protected amine groups in
the periphery were also constructed.8 Properties of den- Divergent Procedure
drimers like solubility, glass transition temperature, melt-
The synthesis of dendrons 1 and 2 started from 1,3,5-tri-
ing behavior, etc., are very dependent on the nature of
their periphery. For applications as energy or electron
transfer agents or their ability to act as a host for guest up-
take (and release), the interior of dendrimers is also im-
portant. Recently we started a project aiming at the
creation of a polarity gradient in the interior of dendri-
mers.6b,9 For such a goal the construction set lacks nonpo-
lar representatives, like hydrocarbons, with appropriate
connecting functions in the periphery and/or at the focal
point. Unfortunately, the known all-hydrocarbon den-
drons on the basis of oligo(phenylene)s,10 oligo(phenyle-
neacetylene)s,11 oligo(phenylenevinylene)s,12 and oligo-
(alkylene)s13 are not suitable, since they are too different
in flexibility and/or in spacer lengths between two phe-
nylene branching units in comparison to other dendrons in
our set.14
bromobenzene (5) which was silylated to give compound
617,18 in 80% yield by performing twice the metal–halogen
exchange sequence and quenching the generated anion
with chlorotrimethylsilane (Scheme 1). The ethanol de-
rivative 7 was obtained by reacting parent oxirane with
the Grignard derivative of 6. Its benzyl protection gave 8.
Subsequent ipso-iododesilylation19 at the position carry-
ing the TMS place holder group20 with iodine monochlor-
ide at –60 °C led to the diiodo compound 9 on a 30 g scale.
The G1 dendron 1 was synthesized from bromide 6
(Scheme 2). Its conversion into the terminal olefin 10 was
achieved through reductive metalation and allylation with
allyl bromide. Isomerization to the conjugated isomer (not
shown) was not observed (high-field NMR) under the
conditions applied. In situ hydroboration of 10 with 9-
BBNH cleanly furnished the expected anti-
Markownikow21 borane 11, which was not isolated. For
the following Suzuki–Miyaura cross-coupling 2.2–2.3
equivalents of borane 11 were reacted with the diiodo
compound 9 in the presence of 1–3 mol% of Pd(Ph3P)4 as
Synthesis 2003, No. 1, 30 12 2002. Article Identifier:
1437-210X,E;2003,0,01,0079,0090,ftx,en;T08602SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

80
M. Beinhoff et al.
PAPER
TMS
TMS
TMS
TMS
TMS
TMS
TMS
TMS
OBn
TMS
OBn
TMS
1
2
TMS
OTBDMS
TMS
TBDMSO
TBDMSO
OTBDMS
OTBDMS
OTBDMS
4
3
Figure 1 Structures of target dendrons 1–4
R1
R1
R
R
b
TMS
TMS
TMS
TMS
Br
a
b
6
OR2
7: R1 = TMS, R2 = H
8: R1 = TMS, R2 = Bn
5: R = Br
6: R = TMS
a
c
9: R1 = I,
R2 = Bn
d
9BBN
Scheme 1 Reagents and conditions: (a) i. BuLi (1 equiv), anhyd
Et2O, –78 °C, ii. TMSCl, –78 °C to r.t., iii. repetition of i and ii, 80%;
(b) i. Mg, anhyd THF, reflux, ii. oxirane, 83%; (c) i. t-BuONa, anhyd
THF, r.t., ii. benzyl bromide, r.t., 95%; (d) ICl, CHCl3, –60 °C, 87%
11
10
R1
R1
R1
R1
catalyst precursor to afford G1 dendron 1 in 85–88%
yield. The slight excess of borane 11 could easily be sep-
arated by column chromatography because it became con-
verted into the more polar corresponding hydroxyborate
under the basic coupling conditions. The next step leading
to the tetraiodoarene 12 required iododesilylation which is
normally conveniently achieved by the addition of iodine
monochloride. Even when the reaction was carried out
avoiding any excess of ICl and at a temperature as low as
–78 °C, the formation of a side product could not be pre-
vented (up to 8% by 1H NMR). Repeated recrystallization
or reversed phase HPLC gave the pure byproduct and was
characterized as the pentaiodo compound 13 (mass spec-
trometry, 2D HMQC NMR,22 see Figure 3 in the experi-
mental section for structure and signal assignment).
Obviously the central branching unit is activated by its
c
2 x 11
R3
OR2
1: R1 = TMS, R2 = Bn, R3 = H
d
12: R1 = I,
13: R1 = I,
R2 = Bn, R3 = H
R2 = Bn, R3 = I
14: R1 = TMS, R2 = H, R3 = H
e
Scheme 2 Reagents and conditions: (a) i. Mg, anhyd THF, reflux,
ii. allyl bromide, 85%; (b) 9-BBNH, anhyd THF, r.t.; (c) i. aq NaOH,
ii. 9, toluene, degas, iii. cat. Pd(Ph3P)4, reflux, 87%; (d) ICl, CHCl3,
–60 °C, 94% of 12; (e) cyclohexa-1,4-diene, Pd/C (10%), THF, re-
flux, quant
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Synthesis of Phenylenealkylene Dendrons
81
TMS
TMS
TMS
TMS
a
4 x 11
TMS
OR
TMS
TMS
TMS
2: R = Bn
15: R = H
b
Scheme 3 Reagents and conditions: (a) i. aq NaOH, ii. 12, toluene, degas, iii. cat. Pd(Ph3P)4, reflux, 77%; (b) cyclohexa-1,4-diene, Pd/C
(10%), THF, reflux, quant
three alkyl substituents to such a degree that it is attacked Low generation dendrons were obtained by an accelerated
by the electrophilic iodine monochloride. Recently, con- convergent approach whereby every isolated step produc-
ditions were found which allow suppression of this side es a new generation.23,24 It uses the fact that the focal ole-
reaction by applying a solvent combination.14
finic group is inactive during the Pd-catalyzed growth
reaction performed at the periphery and can then be easily
converted into a coupling functionality by hydroboration.
This allows the entire growth step to be performed as a
one-pot reaction.
The coupling procedure was repeated with G1 dendron 12
and 4.5–5.0 equivalents of borane 11 to give the G2 den-
dron 2 in reproducible isolated yields of 77–78% and
quantities of about 8 g (Scheme 3). Thus, every step of
this fourfold coupling proceeds with at least 94%.
Pd-catalyzed cross-coupling reactions with iodoarenes
usually proceed faster and with higher yields than the cor-
responding bromo compunds. Though 1-allyl 3,5-dibro-
mobenzene has been employed in a convergent dendron
synthesis,7,25 the diiodo derivative 19 was considered su-
perior and synthesized instead (Scheme 4).26
Preliminary experiments showed that the benzylic pro-
tecting group can be cleanly removed in the presence of
peripheral TMS group. Catalytic hydrogenation of 1 and
2 with Pd/C and cyclohexa-1,4-diene gave deprotected
G1-dendron 14 (Scheme 2) and G2-dendron 15, respec-
1
tively (Scheme 3). H NMR integration did not indicate 1,3,5-Trichlorobenzene (16) was silylated threefold in a
any loss of TMS.
one-pot reaction in the presence of magnesium and
chlorotrimethylsilane to the 1,3,5-tris(trimethylsilyl)ben-
zene (17).27 Subsequent ipso-iododesilylation19 with io-
dine monochloride at room temperature led to 1,3,5-
Convergent Procedure
Figure 2 shows the general structure of the used AiB2 triiodobenzene (18) in an overall yield of 63% on a 100 g
monomer where i denotes the inactivity of the focal func- scale which was purified by recrystallization. Both this
tion A in the coupling step and its potential for an in situ high yield and the simple purification procedure renders
activation. Here, A is an olefinic group whereas B are this route to triiodobenzene 18 superior to other proto-
halogens. The construction methodology starts with the cols.28 Allyl derivative 19 was obtained in up to 86% yield
replacement of the peripheral halogens by protected hy- on a 60 g scale by coupling the in situ prepared monolithi-
droxyalkyl moieties. Hydroxy groups were chosen mainly ation product of 18 with allyl bromide (Scheme 4). The
for two reasons. First, they can serve as suitable connect- lithiation was performed with butyllithium in toluene.
ing units to already existing other dendritic building When the same reaction was conducted in diethyl ether or
blocks in the construction set of which many have benzoic tetrahydrofuran, even at –78 °C, the product always con-
acid groups at their focal point. Secondly, the varying tained butylated and twofold allylated compounds (NMR)
number of protected hydroxy groups in different dendri- which were rather difficult to remove. A reason for this
mer generations should facilitate column purification by may be the low solubility of the mono lithiated intermedi-
polarity differences.
ate in toluene which seems to protect it from the side re-
actions mentioned. It precipitates immediately after
addition of butyllithium as finely dispersed particles. This
lithiation in toluene is very slow and it took several days
to reach completion. Besides small amounts of unaffected
18, 1,3-diiodobenzene (not shown) was detected as a
byproduct, presumably resulting from quenching of unre-
acted organolithium compound with water.
B
B
Ai
Figure 2 Structure of AiB2 monomer
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82
M. Beinhoff et al.
PAPER
of its bis(hydroxypropyl) functionalized derivative to po-
lymerize. This route was, therefore, not continued.
R
R
I
I
c
Finally, the homoallyl variants 28 and 32 led to success
(Schemes 6 and 7). The bromo derivative was considered
more attractive for lower generation dendrons regarding
overall effort, whereas for higher generation the diiodo
analogue was also prepared to exploit its generally higher
coupling efficiency.
R
16: R = Cl
17: R = TMS
18: R = I
a
b
19
Scheme 4 Reagents and conditions: (a) Mg, TMSCl, anhyd THF,
reflux, 70%; (b) ICl, CH2Cl2, 0 °C, 90%; (c) i. BuLi (1 equiv), anhyd
toluene, r.t., ii. allyl bromide, 86%
Both compounds were prepared according to four step se-
quences starting from bromide 5 or 6. 1,3-Dibromo-5-io-
dobenzene (24)14,29 was obtained by monolithiation of
tribromobenzene 5 in diethyl ether30 and electrophilic
trapping of the resulting organolithium derivative with
1,2-diiodoethane. In situ hydroboration of vinyl acetal 25
with 9-BBNH and Pd-catalyzed coupling of the resulting
borane with 24 exploiting the known chemoselectivity of
C–I over C–Br groups yielded acetal 26 (Scheme 6). Hy-
drolysis of 26 to the aldehyde 27 proceeded quantitatively
(TLC) with catalytic amounts of DDQ in aqueous aceto-
nitrile solution.31 Various other conditions, including
treatment with acidic resin Amberlyst®-1532 or tin(II)
chloride,33 only led to partial deprotection. In the case of
the dioxolane derivative (not shown) the results were even
worse. Aldehyde 27 was unstable on silica gel. The reac-
tion mixture was therefore filtered through Celite to re-
move DDQ. Standard Wittig reaction produced dibromo
olefin 28 in an overall yield of 35% on a 10 g scale.34 At-
tempts to obtain aldehyde 27 by selective Heck coupling
of iodoarene 24 and allyl alcohol35 (not shown) yielded a
low yield mixture with the twofold coupled byproduct.
Monomer 19 was converted into the G1 dendron 22 in
70% yield by reacting it with the in situ prepared 21,
which is the hydroborated derivative of the benzyl-pro-
tected allylic alcohol 20 (Scheme 5). Unfortunately the
desired allylic product 22 was accompanied by varying
amounts of its styryl isomer 23. These compounds could
easily be differentiated by 1H NMR spectroscopy (see ex-
perimental section). Compound 23 was typically formed
in yields below 10%, in some cases, however, even 50%
was observed. No reaction conditions could be found
which suppressed this isomerization in a reproducable
manner.18 Thus, in principle compound 19 should work as
a AiB2 monomer, the purification requirements for 22,
however, were considered too unattractive to follow this
route further.
BnO
20
a
Br
Br
Br
Br
c
BnO
9BBN
R
21
5: R = Br
24: R =I
R
a
b
26: R = HC(OCH3)2
27: R = HC=O
28: R = HC=CH2
d
e
OBn
OBn
OBn
OBn
O
O
b
+
25
Scheme 6 Reagents and conditions: (a) i. BuLi (1 equiv) , anhyd
Et2O, –78 °C; ii. 1,2-diiodoethane, –78 °C to r.t., 92%; (b) 9-BBNH,
anhyd THF, r.t.; (c) i. THF, aq NaOH, degas, ii. cat. Pd(Ph3P)4, reflux,
68%; (d) DDQ, MeCN–H2O (9:1), r.t., 90%; (e) i. Ph3PCH2I, BuLi,
anhyd THF, 0 °C, ii. 27, r.t., 63%
23
22
Scheme 5 Reagents and conditions: (a) 9-BBNH, anhyd toluene,
r.t.; (b) i. aq NaOH, ii. 19, toluene, degas, iii. cat. Pd(Ph3P)4, reflux,
70%
A similar strategy was applied for the synthesis of 1-but-
3-enyl-3,5-diiodobenzene (32) (Scheme 7). The bro-
moarene 6 was converted into acetal 29, again by coupling
with the hydroboration product of vinylacetal 25. The io-
dodesilylation step gave the diiodoacetal 30, which was
accompanied by some deprotected aldehyde 31. It was
crucial to perform the iododesilylation at low temperature
(–78 °C). At room temperature or 0 °C some -chlorina-
Two alternative AiB2 monomers were, therefore, consid-
ered, one with a methylene group less (a dihalostyrene)
and one with an additional methylene group (dihalo-
homoallylbenzene). Orienting experiments with 3,5-di-
bromostyrene revealed an unexpectedly high propensity
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PAPER
Synthesis of Phenylenealkylene Dendrons
83
tion of the alkyl chain occurred as indicated by a 13C NMR
signal at = 63.8 and the corresponding molecular ion in
the mass spectrum. Acetal 30 was not separated, but rather
a mixture of 30 and aldehyde 31 was reacted with DDQ to
give 31 in a clean conversion. Wittig reaction of 31 result-
ed in the diiodo olefin 32.
RO
20: R = Bn
33: R = TBDMS
a
RO
9BBN
21: R = Bn
34: R = TBDMS
R1
R1
a
25
b
OR
RO
R2
29: R1 = TMS, R2 = HC(OCH3)2
b
c
30: R1 = I,
31: R1 = I,
32: R1 = I,
R2 = HC(OCH3)2
R2 = HC=O
R2 = HC=CH2
d
RO
OR
Scheme 7 Reagents and conditions: (a) i. 9-BBNH, anhyd THF, r.t.,
ii. aq NaOH, iii. 6, degas, iv. cat. Pd(Ph3P)4, reflux, 76%; (b) ICl,
CH2Cl2, –78 °C; (c) DDQ, MeCN–H2O (9:1), r.t.; (d) i. triphenylme-
thylphosphonium iodide, BuLi, anhyd THF, 0 °C, ii. 31, r.t., 62%
35: R = Bn
3: R = TBDMS
c
RO
OR
Both homoallylbenzene derivatives 28 and 32 acted suc-
cessfully as AiB2 monomers. Functionalization of the pe-
ripheral halogens proceeded without affecting the
homoallyl goup (Scheme 8). Three equivalents of allyl
benzyl ether 20 or allyl TBDMS ether 33 were both hy-
droborated in situ with 9-BBNH to boranes 21 and 34, re-
spectively, and coupled under standard Suzuki–Miyaura
cross-coupling conditions with either the dibromo 28 or
the diiodo monomer 32.36 The benzylether 35 was isolated
in a yield of about 95%, the TBDMS ether 3 80 (from 28)
and 85% (from 32). G2 dendron 4 was obtained from G1
building block 3 and iodo monomer 32 in 75% on a 2 g
scale. The excess of unreacted borane derivative 34 was
easily removed by column chromatography. For the TB-
DMS ether dendrons 3 and 4, the desired polarity differ-
ences were so small that chromatographic separation of
the pure compounds from the monocoupled products re-
sulted in lower isolated yields.37
4: R = TBDMS
Scheme 8 Reagents and conditions: (a) 9-BBNH, anhyd THF, r.t.;
(b) i. aq NaOH, ii. 28 or 32 (0.5 equiv), degas, iii. cat. Pd(Ph3P)4, re-
flux, 80–95%; (c) i. 9-BBNH, anhyd THF, r.t., ii. aq NaOH, iii. 32,
degas, iv. cat. Pd(Ph3P)4, reflux, 75%
(Scheme 9). In several runs under different conditions,
polymeric material was obtained in yields of 78–95%
which was only slightly soluble in common organic sol-
vents. Size exclusion chromatography (SEC) analyses of
the THF soluble fractions gave Mn of about 2.000 to 3.000
g/mol, and PDI between 1.35 and 1.50 (polystyrene stan-
dard, THF as eluent, r.t.) which corresponds to relatively
low degrees of polymerization (DP) of 8–12.39 In some
SEC fractions of masses up to 10 000 g/mol were deter-
mined. MALDI TOF mass spectrometric analysis con-
firmed at least oligomers with a DP of 9. The degree of
branching (DB) was determined on the basis of 1H NMR
integration using the method by Frey.40 The aromatic sig-
nals were assigned by comparison with the ones of the
parent molecular compounds, diiodotoluene, iodoxylene,
and mesitylene. The resonances at = 7.82 (H-1) and 7.42
Hyperbranched Oligomer
In contrast to dendrons/dendrimers where a few all-hydro-
carbon representatives have been reported, there is only
one such example for a hyperbranched polymer. This is a
poly(phenylene), which was synthesized by Suzuki cross-
coupling of 3,5-dibromophenylboronic acid.38 Consider-
ing the importance of unpolar highly branched molecules
with a polar surface specifically for transport of unpolar
guests in polar media, the AiB2 monomer 19 was tested
with regard to its ability to polymerize. Activation of its
olefinic group by 9-BBN hydroboration followed by typ-
ical cross-coupling of the resulting borane [(1–3 d reflux
in THF or toluene, NaOH or Ba(OH)2 as base, 1–2 mol%
of the freshly prepared catalyst precursor Pd(Ph3P)4] gave
a polymeric material to which tentatively the poly(phe-
nylenepropenylene) structure 36 was assigned
(H-2) stem from the terminal moiety, the signals at
=
7.30 (H-3) and 6.88 (H-4) from the linear unit and the one
at = 6.76 (H-5) belong to the dendritic part. Values of
about DB = 0.65 were obtained. The compared aromatic
signals were not completely baseline separated, and the
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84
M. Beinhoff et al.
PAPER
sodium/benzophenone ketyl or potassium/benzophenone ketyl; in
the cross-coupling reactions toluene used was of p.a. quality. The
solvents used in the column chromatography were distilled prior to
use. Experiments under a protective atmosphere were carried out
under N2 with a purity of 4.0 and 5.0, purchased from Linde or
Messer Griesheim. All reactions with moisture sensitive reagents
(e. g., lithiations and hydroborations) were performed in dried
glassware. The apparatus was evacuated ( 15 mbar), heated with an
electric dryer ( 500 °C), and flushed with N2. After cooling, this
procedure was repeated. All palladium-catalyzed cross-coupling re-
actions were carried out under oxygen-free conditions. For this a
stream of N2 was run through the stirred mixture (15–30 min). All
reactions were monitored by TLC on silica gel alumina sheets.
Some of the compounds were spotted by spraying the TLC plate ei-
ther with an anisaldehyde stain (solution of 0.5 mL p-methoxybenz-
aldehyde, 50 mL glacial AcOH, and 1 mL concd H2SO4) and
heating it up to 100 °C (for boranes, alcohols and ethers), or with
an aqueous solution of KMnO4 (0.5%, for olefins). Melting points:
Büchi SMP 510 (open capillaries, uncorrected values). NMR: Bruk-
er WH 270, AC 500 (1H: CDCl3 at = 7.24, 13C: CDCl3 at = 77.00
as internal standards, 20 °C). MS: Perkin-Elmer Varian Type MAT
771 and CH6 (EI), Type CH5DF (FAB), or Bruker Reflex (MAL-
DI-TOF) respectively. MALDI-TOF: UV-Laser (337 nm), delayed
extraction source, reflector mode. 2,5-Dihydroxybenzoic acid
(DHB) was used as matrix. The high resolution mass spectra were
obtained according to the peak match method (MAT 771). Elemen-
tal analyses: Perkin-Elmer EA 240. Column chromatography: Mer-
ck silica gel 60, 0.040–0.063 mm (230–400 mesh). Analytical TLC:
Merck silica gel Si 60, F254, on aluminum sheets. Preparative RP-
HPLC: Machery-Nagel, Nucleosil® 5 m C18, 32 250 mm, UV de-
tection at 254 nm. Analytical SEC: Waters Styragel HR 1 or HR 3
columns, Waters 2487 UV/VIS detector at 254 nm.
DB can therefore only be considered a reasonable estima-
tion. The oligomer 36 shows a broad endothermic transi-
tion from 35–55 °C (differential scanning calorimetry)
and decomposition at 290 °C (thermogravimetric analy-
sis).
I
I
19
a
I
1
5
3
I
I
I
I
2
2
5
5
3
4
=
n, hb
B
36
Scheme 9 Reagents and conditions: Typical procedure: (a) i. 9-
BBNH, anhyd THF, r.t., ii. aq NaOH, degas, iii. cat. Pd(Ph3P)4, reflux,
94%. Due to its hyperbranched (hb) nature, polymer 36 consists of
three different units, the terminal, linear, and dendritic units (from
left)
Conclusion and Outlook
1-Bromo-3,5-bis(trimethylsilyl)benzene (6)
To a solution of 1,3,5-tribromobenzene (5; 100.0 g, 318.0 mmol) in
Et2O (1.4 L) was added BuLi (210.0 mL of a 1.6 M solution in hex-
The gram scale syntheses of all-hydrocarbon G1 and G2
dendrons by Suzuki–Miyaura cross-coupling of alkyl bo- ane, 336.0 mmol, 1.06 equiv) within 30 min at –40 °C. After the
mixture had been stirred at –78 °C for 30 min, Me3SiCl (50.0 mL,
ranes with aryl halides were presented. Both a divergent
400.7 mmol, 1.19 equiv) was added all at once, and the mixture was
and convergent procedure were successfully applied. The
allowed to warm up to r.t. The suspension was cooled to –78 °C and
BuLi (250.0 mL of a 1.6 M solution in hexane, 400.0 mmol, 1.19
equiv) was added within 15 min. After the addition of chlorotrime-
latter approach seems to be capable of yielding higher
generation dendrons in an accelerated manner since every
isolated step yields a new generation. Depending on
whether their hydroxy groups are at the periphery or the
focal point, the dendrons presented have the promising
potential to be used for the construction of higher genera-
tions both with a polarity gradient going from the interior
to the exterior and the other way around, respectively. For
example, the convergently grown dendrons with (protect-
ed) hydroxyl groups in the periphery will be connected to
some of the dendrons with carboxylic acids at the focal
point.5,6 First results in the synthesis of hyperbranched oli-
gomers of an AiB2 monomer by Suzuki–Miyaura cross-
coupling were also reported.
thylsilane (60.0 mL, 480.8 mmol, 1.43 equiv) all at once, the mix-
ture was allowed to warm up to r.t. Aq 10% NaHCO3 solution (100
mL) was added, followed by extractive workup with Et2O (3 100
mL), drying (MgSO4), evaporation of the volatile components, and
distillation through a vigreux column. Recrystallization of the resi-
due from EtOH (70 mL) at –22 °C gave 81.0 g (85%) of the desired
6 as colorless crystals; bp 65 °C/0.02 mbar.
1H NMR (270 MHz, CDCl3): = 0.30 (s, 18 H), 7.58 (s, 2 H), 7.65
(s, 1 H).
13C NMR (68 MHz, CDCl3,): = –1.16, 123.41, 136.19, 136.33,
142.95.
MS (EI, 70 eV, 40 °C): m/z (%) = 302 (17, [M]+), 287 (100, [M –
CH3]+).
Anal. Calcd for C12H21BrSi2 (301.37): C, 47.82; H, 7.02. Found: C,
47.59; H, 6.87.
All chemicals were purchased from Acros, Aldrich, Fluka, Janssen,
or Lancaster and used without further purification. Several com-
pounds were prepared according to literature procedures and gave
satisfactory NMR and MS data: 17,27 20,41 triphenylmethylphos-
phonium iodide.42 Pd(Ph3P)4 was prepared according to Ref.,43
stored in a glove box (O2: <2.0 ppm, H2O: <0.3 ppm) and used with-
out further characterization. Compounds 6,17,44 10,14 1828 and 2414,29
were prepared in ways different to the literature procedures, and are
described in full detail. All other compounds have not been previ-
ously reported. Anhyd toluene, Et2O, and THF were distilled from
2-[3,5-Bis(trimethylsilyl)phenyl]ethanol (7)
Ethylene oxide (oxirane, 15 mL) was condensed into THF (20 mL),
and added dropwise to an ice-cold Grignard solution prepared from
1-bromo-3,5-bis(trimethylsilanyl)benzene (6; 65.7 g, 218.0 mmol)
and Mg (6.4 g, 263.3 mmol, 1.2 equiv) in THF (150 mL). The solu-
tion was stirred overnight, and brine (200 mL) was added. After
acidification with AcOH ( pH 5), the separated aqueous phase was
extracted with Et2O (3 100 mL), the combined organic phases
Synthesis 2003, No. 1, 79–90 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Phenylenealkylene Dendrons
85
were dried (MgSO4), and evaporated. The crude product was dis-
tilled to give the alcohol 7 as a colorless oil in 83% yield (48.2 g);
bp 95 °C/0.014 mbar.
1H NMR (270 MHz, CDCl3): = 0.30 [s, 18 H, Si(CH3)3], 1.56 (s,
1 H, OH), 3.38 (t, 3J = 7.0 Hz, 2 H, Ar-CH2), 3.88 (t, 3J = 7.0 Hz, 2
H, CH2OH), 7.36 (s, 2 H, Ar-H), 7.55 (s, 1 H, Ar-H).
extracted with Et2O (3 100 mL), the combined organic phases
were dried (MgSO4), and the resulting oil obtained after evapora-
tion of the solvent was distilled in vacuo to give 27.2 g (85%) of a
colorless oil 10; bp 53 °C/0.010 mbar.
1H NMR (270 MHz, CDCl3): = 0.41 [s, 18 H, Si(CH3)3], 3.54 (d,
3J = 7.5 Hz, 2 H, Ar-CH2), 5.19–5.29 (m, 2 H, CH=CH2), 6.13 (m,
1 H, CH=CH2), 7.41 (s, 2 H, Ar-H), 7.61 (s, 1 H, Ar-H).
13C NMR (68 MHz, CDCl3,): = –1.44, 39.27, 63.26, 134.28,
135.77, 136.69, 138.92.
13C NMR (68 MHz, CDCl3): = -1.03, 40.51, 115.72, 134.15,
135.97, 137.59, 138.22, 139.59.
MS (EI, 70 eV, 40 °C): m/z (%) = 266 (16, [M]+), 251 (100, [M –
CH3]+).
MS (EI, 80 eV, 20 °C): m/z (%) = 262 (16; [M]+, 247 (100, [M –
CH3]+).
Anal. Calcd for C14H26OSi2 (266.53): C, 63.09; H, 9.83. Found: C,
62.85; H, 9.69.
Anal. Calcd for C15H26Si2 (262.54): C, 68.62; H, 9.98. Found: C,
68.31; H, 9.71.
1-(2-Benzyloxyethyl)-3,5-bis(trimethylsilyl)benzene (8)
To a stirred solution of alcohol 7 (21.9 g, 82.2 mmol) and t-BuONa
(21.1 g, 219.5 mmol, 2.7 equiv) in THF (150 mL) was slowly added
benzyl bromide (20.0 mL, 168.4 mmol, 2.05 equiv) via a syringe.
After stirring overnight, brine (200 mL) was added. The separated
aqueous phase was extracted with Et2O (3 100 mL), the combined
organic phases were dried (MgSO4), and the resulting oil was dis-
tilled in vacuo to give 27.7 g (95%) of a colorless oil; bp 131 °C/
0.014 mbar.
1-(2-Benzyloxyethyl)-3,5-bis{3-[3,5-bis(trimethylsilyl)phenyl]-
propyl}benzene (1); Typical Procedure
A solution of 10 (16.9 g, 64.4 mmol) and 9-BBNH (7.9 g, 64.7
mmol, 1.01 equiv) in THF (180 mL) was stirred overnight. After re-
moving the solvent toluene (130 mL), aq 1 M NaOH (80 mL), and
9 (13.3 g, 28.7 mmol, 0.45 equiv) were added to the degassed solu-
tion. The catalyst precursor Pd(Ph3P)4 (980 mg, 0.85 mg, 1.5 mol%)
was added, and the resulting suspension was refluxed overnight. Af-
ter cooling to r.t., the phases were separated, the aqueous phase was
extracted with toluene (3 50 mL), the combined organic phases
were washed with H2O (50 mL) and dried (MgSO4). After removal
of the solvent, the residual oil was chromatographed on silica gel
(EtOAc–hexanes, 1:20) to give 1 as a viscous oil; yield: 18.4 g
(87%); Rf 0.64 (EtOAc–hexanes, 1:6).
1H NMR (270 MHz, CDCl3): = 0.39 [s, 18 H, Si(CH3)3], 3.04 (t,
3
3J = 7.0 Hz, 2 H, Ar-CH2), 3.82 (t, J = 7.0 Hz, 2 H, CH2CH2O),
4.62 (s, 2 H, Ar-CH2), 7.40 (m, 5 H, Ar-H), 7.48 (s, 2 H, Ar-H), 7.63
(s, 1 H, Ar-H).
13C NMR (68 MHz, CDCl3): = –1.06, 36.61, 71.50, 72.93, 127.45,
127.54, 128.29, 134.55, 136.06, 137.20, 138.44, 139.41.
1H NMR (270 MHz, CDCl3): = 0.32 [s, 36 H, Si(CH3)3], 2.00
MS (EI, 70 eV, 60 °C): m/z (%) = 356 (22, [M]+), 73 (100,
3
(quintet, J = 7.5 Hz, 4 H, CH2CH2CH2), 2.70 (m, 8 H, Ar-CH2),
[SiMe3]+).
2.95 (t, 3J = 7.5 Hz, 2 H, Ar-CH2), 3.73 (t, 3J = 7.0 Hz, 2 H,
CH2CH2O), 4.57 (s, 2 H, Ar-CH2), 6.95 (s, 3 H, Ar-H), 7.25–7.37
(m, 5 H, Ar-H), 7.41 (s, 4 H, Ar-H), 7.56 (s, 2 H, Ar-H).
Anal. Calcd for C21H32OSi2 (356.65): C, 70.72; H, 9.04. Found: C,
70.40; H, 8.76.
13C NMR (68 MHz, CDCl3): = –1.00, 33.21, 35.60, 35.89, 36.36,
71.37, 72.95, 126.59, 127.50, 127.60, 128.32, 134.05, 135.63,
138.41, 138.82, 139.34, 140.50, 142.36.
1-(2-Benzyloxyethyl)-3,5-diiodobenzene (9); Typical Procedure
A stirred solution of 8 (27.6 g, 77.4 mmol) in CHCl3 (100 mL) was
cooled to –60 °C, and a solution of ICl (26.4 g, 162.6 mmol, 2.1
equiv) in CHCl3 (50 mL) was added dropwise. After stirring 1.5 h
at this temperature, a solution of Na2S2O5 (20 g) in H2O (100 mL)
was added, and the mixture was stirred for additional 30 min. The
separated aqueous phase was washed with CHCl3 (3 50 mL), the
collected organic phases were dried (MgSO4), and the solvent was
evaporated. The diiodo compound 9 was recrystallized from
CH2Cl2, and 31.1 g (87%) were obtained as colorless, long needles;
mp 82 °C.
MS (EI, 70 eV, 150 °C): m/z (%) = 736 (1, [M]+).
Anal. Calcd for C45H68OSi4 (737.38): C, 73.30; H, 9.29. Found: C,
73.09; H, 9.12.
1-(2-Benzyloxyethyl)-3,5-bis[3-(3,5-diiodophenyl)propyl]-
benzene (12)
Following the typical procedure described for the preparation of 9,
the reaction was carried out with 1 (12.5 g, 16.9 mmol), ICl (17.0
g, 104.7 mmol, 6.2 equiv), CHCl3 (200 mL), and worked up with
Na2S2O5 (20 g) in H2O (100 mL). Recrystallization from Et2O gave
15.1 g (94%) of the tetraiodo compound 12 as colorless, short nee-
dles; mp 83 °C. The pentaiodo compound 13 was obtained as a side
product (see below).
1H NMR (270 MHz, CDCl3): = 2.78 (t, 3J = 7.0 Hz, 2 H,
3
CH2CH2O), 3.63 (t, J = 7.0 Hz, 2 H, CH2CH2O), 4.49 (s, 2 H,
ArCH2O), 7.29 (m, 5 H, Ar-H), 7.53 (s, 2 H, Ar-H), 7.89 (s, 1 H, Ar-
H).
13C NMR (67 MHz, CDCl3): = 35.31, 69.95, 72.99, 94.66, 127.58,
127.63, 128.40, 137.25, 137.96, 142.81, 143.40.
MS (EI, 70 eV, 100 °C): m/z (%) = 464 (29), 91 (100, [C7H7]+).
1H NMR (270 MHz, CDCl3): = 1.92 (m, 4 H, CH2CH2CH2), 2.50
3
3
(t, J = 7.5 Hz, 4 H, Ar-CH2), 2.60 (t, J = 7.5 Hz, 4 H, Ar-CH2),
2.93 (t, 3J = 7.0 Hz, 2 H, Ar-CH2), 3.73 (t, 3J = 7.0 Hz, 2 H,
CH2CH2O), 4.57 (s, 2 H, Ar-CH2), 6.83 (s, 1 H, Ar-H), 6.89 (s, 2 H,
Ar-H), 7.32 (m, 5 H, Ar-H), 7.49 (s, 4 H, Ar-H), 7.89 (s, 2 H, Ar-H).
Anal. Calcd for C15H14I2O (464.08): C, 38.82; H, 3.04. Found: C,
38.71; H, 2.73.
13C NMR (68 MHz, CDCl3): = 32.38, 34.49, 35.05, 36.25, 71.23,
72.89, 94.83, 126.41, 126.71, 127.48, 127.53, 127.66, 128.25,
139.07, 140.37, 141.61, 142.38, 146,48.
1-Allyl-3,5-bis(trimethylsilyl)benzene (10)
To a refluxing Grignard solution prepared from 1-bromo-3,5-
bis(trimethylsilyl)benzene (6; 36.6 g, 121.4 mmol) and Mg (3.1 g,
127.6 mmol, 1.05 equiv) in THF (100 mL), was added dropwise a
solution of allyl bromide (15.0 mL, 181.8 mmol, 1.5 equiv) in THF
(50 mL). After refluxing overnight, the mixture was cooled to r.t.,
and brine (200 mL) was added. The separated aqueous phase was
MS (EI, 70 eV, 250 °C): m/z (%) = 952 (100, [M]+).
Anal. Calcd for C33H32I4O (952.23): C, 41.62; H, 3.39. Found: C,
41.49; H, 3.27.
Synthesis 2003, No. 1, 79–90 ISSN 0039-7881 © Thieme Stuttgart · New York

86
M. Beinhoff et al.
PAPER
1-(2-Benzyloxyethyl)-4-iodo-3,5-bis[3-(3,5-diiodophenyl)-
propyl]benzene (13)
Anal. Calcd for C93H140OSi8 (1498.79): C, 74.53; H, 9.41. Found:
C, 74.35; H, 9.16.
Pentaiodo compound 13 (Figure 3) was obtained as a side product
in the synthesis of G1 12. It was separated either by recrystallization
(EtOAc–toluene) or reversed phase HPLC: tR 5.3 min at 28 mL/min
vs tR 4.7 min of 12; mp 92–93 °C.
1H NMR (500 MHz, CDCl3): = 1.88 (m, 4 H, H-6, H-6 ), 2.52 (m,
4 H, H-5, 7), 2.59 (t, 2 H, 3J = 7.7 Hz, H-7 ), 2.75 (t, 3J = 7.7 Hz, 2
H, H-5 ), 3.12 (t, 3J = 7.0 Hz, 2 H, H-12), 3.70 (t, 3J = 7.0 Hz, 2 H,
H-13), 4.56 (s, 2 H, H-14), 6.81 (d, 4J = 2.0 Hz, 1 H, H-4), 6.92 (s,
4J = 2.0 Hz, 1 H, H-2), 7.31 (m, 5 H, H-16, 17, 18), 7.45 (d, 4J = 1.3
Hz, 2 H, H-9), 7.53 (d, 4J = 1.3 Hz, 2 H, H-9 ), 7.87 (d, 4J = 1.3 Hz,
2 H, H-11, 11 ).
13C NMR (126 MHz, CDCl3): = 31.19 (C-6 ), 32.09 (C-6), 34.25,
34.32 (C-5, 7), 34.60 (C-7 ), 41.43 (C-5 ), 42.13 (C-12), 69.54 (C-
13), 72.78 (C-14), 94.87, 94.89 (C-10, 10 ), 104.20 (C-2 ), 127.49
(C-16, 18), 127.56 (C-4), 128.15 (C-2), 128.27 (C-17), 136.72,
136,76 (C-9, C-9 ), 138.21 (C-15), 141.18 (C-3), 142.11 (C-1),
142.36 (C-11, 11 ), 144.94 (C-3 ), 146.11, 146.14 (C-8, 8 ).
MS (EI, 70 eV, 270 °C): m/z (%) = 1078 (2, [M]+), 987 (3, [M –
C7H7]+), 972 (2, [M – C7H7O]+), 952 (2, [M – I]+), 845 (100, [M –
C7H7O – I]+).
Cleavage of Benzyl Group; General Procedure
A mixture of the respective benzyl ether 1 or 2, cyclohexa-1,4-diene
and 10% Pd/C in THF was refluxed overnight. The cooled suspen-
sion was filtered through Celite, and the volatile components were
evaporated at elevated temperature in high vacuo to give an analyt-
ically pure, colorless, highly viscous oil in virtually quantitative
yield.
2-(3,5-Bis{3-[3,5-bis(trimethylsilyl)phenyl]propyl}phenyl)-
ethanol (14)
This compound was prepared starting from 1 (3.0 g, 4.1 mmol), cy-
clohexa-1,4-diene (6.4 g, 80 mmol), and 10% Pd/C (0.3 g); yield:
2.63 g (99%).
1H NMR (500 MHz, CDCl3): = 0.38 [s, 36 H, Si(CH3)3], 1.77 (s,
1 H, OH), 2.13 (m, 4 H, CH2CH2CH2), 2.83 (m, 8 H, Ar-CH2), 2.97
(t, 3J = 7.0 Hz, 2 H, Ar-CH2), 3.98 (t, 3J = 7.0 Hz, 2 H, CH2CH2O),
7.06 (s, 2 H, Ar-H), 7.10 (s, 4 H, Ar-H), 7.48 (s, 4 H, Ar-H), 7.67 (s,
2 H, Ar-H).
13C NMR (126 MHz, CDCl3): = –1.01, 33.19, 35.62, 35.87, 39.15,
63.68, 126.09, 126.57, 134.05, 135.61, 139.33, 140.50, 142.27,
142.67.
Anal. Calcd for C33H31I5O (1078.12): C, 36.76; H, 2.90. Found: C,
36.88; H, 2.88.
MS (EI, 70 eV, 180 °C): m/z (%) = 646 (6, [M]+).
Anal. Calcd for C38H62OSi4 (647.25): C, 70.52; H, 9.65. Found: C,
70.30; H, 9.30.
11'
11
I
I
I
I
10
10'
9'
9
2-{3,5-Bis[3-(3,5-bis{3-[3,5-bis(trimethylsilyl)phenyl]propyl}-
phenyl)propyl]phenyl}ethanol (15)
This compound was prepared strating from 2 (3.0 g, 2.0 mmol), cy-
clohexa-1,4-diene (3.2 g, 40 mmol), and 10% Pd/C (0.3 g); yield:
2.80 g (99%).
8'
8
5
5'
I
4
3'
2'
3
7
7'
6'
6
2
1
12
1H NMR (500 MHz, CDCl3): = 0.36 [s, 72 H, Si(CH3)3], 1.45 (s,
1 H, OH), 2.05 (m, 12 H, CH2CH2CH2), 2.70 (m, 24 H, Ar-CH2),
2.80 (t, 3J = 7.0 Hz, 2 H, Ar-CH2), 3.87 (t, 3J = 7.0 Hz, 2 H,
CH2CH2O), 6.95 (m, 9 H, Ar-H), 7.43 (s, 8 H, Ar-H), 7.60 (s, 4 H,
Ar-H).
13C NMR (126 MHz, CDCl3): = –0.98, 31.21, 31.73, 32.46, 35.66,
35.54, 35.86, 39.13, 63.63, 126.61, 126.66, 126.81, 126.87, 134.01,
138.33, 138.93, 139.07, 139.58, 139.82, 141.52, 142.34.
13
O
14
15
16
17
18
Figure 3 Structure of byproduct 13, elucidated by 2D NMR
MS (EI, 70 eV, 350 °C): m/z (%) = 1408 (4, [M]+).
1-(2-Benzyloxyethyl)-3,5-bis[3-(3,5-bis{3-[3,5-bis(trimethyl-
silyl)phenyl]propyl}phenyl)propyl]benzene (2)
Anal. Calcd for C86H134OSi8 (1408.69): C, 73.33; H, 9.59. Found:
C, 73.21; H, 9.36.
Following the typical procedure described for the preparation of 1,
the reaction was carried out with 10 (8.5 g, 32.4 mmol), 9-BBNH
(4.0 g, 32.8 mmol, 1.01 equiv), THF (150 mL), toluene (75 mL), aq
1 M NaOH (75 mL), 12 (6.5 g, 6.8 mmol, 0.21 equiv), and
Pd(Ph3P)4 (844 mg, 0.73 mmol, 2.7 mol%). The resulting viscous
oil was dried at 80 °C in high vacuo to give 2 as a resin-like sub-
stance; yield: 7.8 g (77%); Rf 0.71 (EtOAc–hexanes, 1:6).
1H NMR (270 MHz, CDCl3): = 0.32 [s, 72 H, Si(CH3)3], 2.03 (m,
12 H, CH2CH2CH2), 2.70 (m, 24 H, ArCH2), 2.93 (t, 3J = 7.0 Hz, 2
H, Ar-CH2), 3.72 (t, 3J = 7.0 Hz, 2 H, CH2CH2O), 4.56 (s, 2 H, Ar-
CH2), 7.02 (s, 9 H, Ar-H), 7.42 (m, 5 H, Ar-H), 7.49 (s, 8 H, Ar-H),
7.66 (s, 4 H, Ar-H).
1,3,5-Triiodobenzene (18)
To a solution of 17 (66.0 g, 224.0 mmol) in CH2Cl2 (1000 mL) was
added a solution of ICl (122.4 g, 754.0 mmol, 3.4 equiv) in CH2Cl2
(400 mL) at r.t. within 3 h. Cooling with an ice/water bath was nec-
essary. The product precipitated, and the suspension was stirred
overnight. After removal of excess ICl with aq Na2S2O5 solution,
the layers were separated and the aqueous layer was washed with
CH2Cl2. The combined organic layers were dried (MgSO4) and fil-
tered. Some of the solvent was evaporated and the precipitated
product was filtered under suction. Recrystallization from the con-
centrated filtrate was repeated three times to yield 91.7 g (90%) of
18 as colorless crystals. The product was stored under exclusion of
light to avoid brownish discoloring; mp. 183 °C (Lit.28a mp 184 °C,
Lit.28c mp 183 °C).
13C NMR (68 MHz, CDCl3): = –1.00, 33.21, 35.60, 35.69, 35.86,
36.32, 71.39, 72.91, 125.84, 126.09, 126.52, 126.89, 127.46,
127.57, 128.29, 128.66, 134.06, 135.60, 138.39, 138.70, 139.30,
139.69, 139.82, 140.50, 142.25, 142.32.
1H NMR (270 MHz, CDCl3): = 7.98 (s).
13C NMR (63 MHz, CDCl3): = 95.21, 144.42.
MS (EI, 80 eV, 50 °C): m/z (%) = 456 (100, [M]+).
MS (EI, 70 eV, 350 °C): m/z (%) = 1489 (1, [M]+), 325 (100), 73
(70, [TMS]+).
Synthesis 2003, No. 1, 79–90 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Phenylenealkylene Dendrons
87
anal. Calcd for C6H3I3 (455.80): C, 15.81; H, 0.66. Found: C, 15.98;
H, 0.60.
1H NMR (270 MHz, CDCl3): = 7.62 (s, 4J = 1.7 Hz, 1 H), 7.77 (s,
4J = 1.7 Hz, 2 H).
13C NMR (63 MHz, CDCl3): = 94.43, 123.34, 133.60, 138.46.
MS (EI, 80 eV, 60 °C): m/z (%) = 362 (100, [C6H379Br81BrI]+).
1-Allyl-3,5-diiodobenzene (19)
To a suspension of 1,3,5-triiodobenzene (18; 84.4 g, 185.2 mmol)
in toluene (1000 mL) was added a 1.6 M solution of BuLi in hexane
(116.0 mL, 185.6 mmol, 1.00 equiv) within 60 min at r.t. After 3 d,
allyl bromide (25.0 mL, 303.6 mmol, 1.64 equiv) was added all at
once and the mixture was stirred for an additional one day with a
mechanical stirrer. H2O (500 mL) was added, the phases separated,
and the aqueous layer was extracted with toluene twice. The com-
bined organic layers were dried (MgSO4), and evaporated to give 70
g of a brownish oil. Distillation utilizing a vigreux column gave
58.7 g (86%) of the desired 19 as a colorless, mobile oil. Long,
colorless needles were obtained by recrystallization from EtOH at
–22 °C, but these crystals were not stable at r.t. (22 °C); bp 75 °C/
0.008 mbar. 1,3-Diiodobenzene was identified as a side product.
Anal. Calcd for C6H3Br2I (361.80): C, 19.92; H, 0.84. Found C,
19.82; H, 0.89.
1,3-Dibromo-5-(3,3-dimethoxypropyl)benzene (26); Typical
Procedure
3,3-Dimethoxypropene (25;10.2 mL, 88.6 mmol) was added to a
0.5 M solution of 9-BBNH in THF (200.0 mL, 100.0 mmol, 1.13
equiv) at 0 °C, and the mixture was stirred for 20 h at r.t. After ad-
dition of 1,3-dibromo-5-iodobenzene (24; 32.1 g, 88.7 mmol, 1.00
equiv), the catalyst precursor Pd(Ph3P)4 (1.00 g, 8.65 10–4 mol,
0.98 mol%), aq NaOH (3 M, 85 mL) and additional THF (50 mL),
the suspension was stirred under reflux for 20 h. The mixture was
cooled with ice/water, and 30% aq H2O2 (35 mL) was added care-
fully. Extractive workup with Et2O and column chromatography on
silica gel (hexanes, then hexanes–EtOAc, 15:1) gave 20.4 g (68%)
of 26 as a colorless oil; Rf 0.23 (hexanes–EtOAc, 10:1).
1H NMR (500 MHz, CDCl3): = 3.25 (d, 3J = 6.5 Hz, 2 H), 5.03–
4
5.14 (m, 2 H), 5.86 (m, 1 H), 7.49 (d, J = 1.3 Hz, 2 H), 7.87 (d,
4J = 1.3 Hz, 1 H).
13C NMR (126 MHz, CDCl3): = 39.08, 94.91, 117.22, 135.57,
136.87, 142.72, 144.11.
MS (EI, 70 eV, 25 °C): m/z (%) = 370 (100, [M]+).
3
1H NMR (270 MHz, CDCl3): = 1.85 (m, 2 H), 2.59 (d, J = 7.5
Hz, 2 H), 3.33 (s, 6 H), 4.39 (t, 3J = 6.0 Hz, 1 H), 7.25 (s, 2 H), 7.48
(s, 1 H).
Anal. Calcd for C9H8I2 (369.97): C, 29.22; H, 2.18. Found: C,
28.92; H, 1.69.
13C NMR (63 MHz, CDCl3): = 30.17, 33.58, 52.80, 103.26,
122.76, 130.25, 131.56, 145.58.
MS (EI, 80 eV, 40 °C): m/z (%) = 338 (7, [C11H1479Br81BrO2]+), 75
1-Allyl-3,5-bis(3-benzyloxypropyl)benzene (22); Typical
Procedure
(100, [HC(OCH3)2]+).
Allyl benzyl ether (20; 7.6 g, 51.1 mmol, 2.07 equiv) and 9-BBNH
(6.3 g, 51.4 mmol, 2.08 equiv) were suspended in toluene (100 mL)
and stirred for one day at r.t. After addition of aq NaOH (1 M, 60
mL) and 1-allyl-3,5-diiodobenzene (19; 9.1 g, 24.7 mmol), the sus-
pension was degassed. The catalyst precursor Pd(Ph3P)4 (1.07 g, 9.3
10–4 mol, 1.8 mol% per coupling) was added and the suspension
was stirred under gentle reflux for 16 h. Usual extractive workup
with toluene and purification by column chromatography on silica
gel (hexanes–EtOAc, 20:1) yielded 7.1 g (70%) of 22 as a colorless
oil; Rf 0.52 (hexanes–EtOAc, 6:1). The product was accompanied
by varying amounts of the styrene derivative 23, identified by the
signals in the 1H NMR spectra [ = 1.88 (d, 3 H), 6.21 (m, 1 H), 6.38
(d, 3J = 15 Hz, 1 H)].
HRMS: m/z Calcd for C11H14Br2O2 335.97605; found 335.93298.
3-(3,5-Dibromophenyl)propionaldehyde (27)
1,3-Dibromo-5-(3,3-dimethoxypropyl)benzene (26; 9.4 g, 27.8
mmol) was dissolved in a mixture of MeCN (120 mL) and H2O (13
mL). After addition of DDQ (0.6 g, 2.7 mmol, 0.1 equiv), the dark
red suspension was stirred at r.t. for 18 h. After filtration of the mix-
ture through Celite to remove DDQ and elution with CH2Cl2 the
product was not further purified, since aldehyde 27 was unstable on
silica gel. The solvent was evaporated to give 7.3 g (90%) of 27 as
a colorless oil; Rf 0.20 (hexanes–EtOAc, 6:1).
1H NMR (270 MHz, CDCl3): = 2.78 (m, 4 H), 7.24 (s, 2 H), 7.44
(s, 1 H), 9.74 (s, 1 H).
13C NMR (63 MHz, CDCl3): = 27.13, 44.38, 122.80, 130.10,
131.81, 144.30, 199.98.
1H NMR (250 MHz, CDCl3): = 1.96 (m, 4 H), 2.71 (t, 3J = 6.5 Hz,
4 H), 3.37 (d, 3J = 6.5 Hz, 2 H), 3.53 (t, 3J = 7.0 Hz, 4 H), 4.58 (s, 4
H), 5.06–5.17 (m, 2 H), 6.00 (m, 1 H), 6.89 (s, 3 H), 7.27–7.44 (m,
10 H).
1-But-3-enyl-3,5-dibromobenzene (28); Typical Procedure
To a suspension of triphenylmethylphosphonium iodide (9.3 g, 23.1
mmol) in THF (100 mL) was added BuLi (14.3 mL of a 1.6 M so-
lution in hexane, 22.9 mmol, 0.99 equiv) at 0 °C within 5 min, and
the resulting orange solution was stirred for an additional 45 min. A
solution of 3-(3,5-dibromophenyl)propionaldehyde (27; 6.1 g, 20.9
mmol, 0.90 equiv) in THF (20 mL) was added dropwise and the re-
action mixture was stirred at r.t. for 2 h. The solution was decanted,
the residue was washed with Et2O (3 ), the combined organic lay-
ers were dried (MgSO4). Purification by column chromatography
on silica gel (hexanes) gave 3.8 g (63%) of 28 as a colorless oil;
Rf 0.58 (hexanes); bp 65 °C/0.01 mbar.
1H NMR (270 MHz, CDCl3): = 2.33 (q, 3J = 8.0 Hz, 2 H), 2.64 (t,
3J = 8.0 Hz, 2 H), 5.02 (m, 2 H), 5.78 (m, 1 H), 7.25 (s, 2 H), 7.47
(s, 1 H).
13C NMR (63 MHz, CDCl3): = 34.63, 34.79, 115.70, 122.67,
130.27, 131.48, 136.84, 145.65.
13C NMR (63 MHz, CDCl3): = 31.35, 32.01, 40.12, 69.53, 72.81,
115.54, 126.17, 126.38, 127.42, 127.55, 128.26, 137.54, 138.52,
139.90, 142.03.
MS (EI, 80 eV, 170 °C): m/z (%) = 414 (2, [M]+), 91 (100, [C7H7]+).
Anal. Calcd for C29H34O2 (414.58): C, 84.02; H, 8.27. Found: C,
83.59; H 7.98.
1,3-Dibromo-5-iodobenzene (24)
To a solution of 1,3,5-tribromobenzene (5; 13.4 g, 42.7 mmol) in
Et2O (300 mL) was added BuLi (27.0 mL of a 1.6 M solution in hex-
ane, 43.2 mmol, 1.01 equiv) within 30 min at –78 °C. After an ad-
ditional hour, solid 1,2-diiodoethane (12.2 g, 43.1 mmol, 1.01
equiv) was added all at once, and the mixture was allowed to warm
up to r.t. H2O (100 mL) was added, followed by usual extractive
workup with CH2Cl2. Recrystallization from Et2O gave 14.2 g
(92%) of the desired 24 as colorless crystals. The product was stored
under exclusion of light to avoid brownish discoloring; mp
118 °C.45
MS (EI, 80 eV, 40 °C): m/z (%) = 290 (30, [C10H1079Br81Br]+), 249
(100, [C7H579Br81Br]+).
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88
M. Beinhoff et al.
PAPER
Anal. Calcd for C10H10Br2 (289.99): C, 41.42; H, 3.48. Found: C,
41.41; H, 3.07.
Anal. Calcd for C10H10I2 (384.00): C, 31.28; H, 2.62. Found: C,
31.52; H, 2.48.
1,3-Bis(trimethylsilyl)-5-(3,3-dimethoxypropyl)benzene (29)
Following the typical procedure described for the preparation of 26,
the reaction was carried out with 3,3-dimethoxypropene (25; 17.0
mL, 147.7 mmol), 9-BBNH (18.1 g, 148.6 mmol, 1.01 equiv), THF
(200 mL), 1-bromo-3,5-bis(trimethylsilyl)benzene (6; 41.9 g, 139.0
mmol, 0.94 equiv), Pd(Ph3P)4 (1.60 g, 1.39 mmol, 1.0 mol%), aq
NaOH (3 M, 100 mL), and 30% aq H2O2 (60 mL); yield: 36.6 g
(76%); colorless oil; Rf 0.26 (hexanes–EtOAc, 10:1).
1-But-3-enyl-3,5-bis-(3-benzyloxypropyl)benzene (35)
Following the typical procedure described for the preparation of 22,
the reaction was carried out with allyl benzyl ether (20; 1.51 g,
10.19 mmol, 3.08 equiv), 9-BBNH (20.0 mL of a 0.5 M solution in
THF, 10.0 mmol, 3.7 equiv), aq NaOH (1 M, 20 mL), 1-but-3-enyl-
3,5-dibromobenzene (28; 0.78 g, 2.69 mmol), and Pd(Ph3P)4 (0.23
g, 0.11 mmol, 2.04 mol% per coupling) by refluxing for 5 d; yield:
1.10 g (95%); colorless oil; Rf 0.34 (hexanes–EtOAc, 10:1).
1H NMR (270 MHz, CDCl3): = 0.27 (s, 18 H), 1.95 (m, 2 H), 2.68
(m, 2 H), 3.46 (s, 6 H), 4.42 (t, 3J = 6.0 Hz, 1 H), 7.35 (s, 2 H), 7.51
(s, 1 H).
13C NMR (63 MHz, CDCl3): = –1.06, 31.15, 34.47, 52.80, 104.03,
133.99, 135.77, 139.54, 139.82.
1H NMR (250 MHz, CDCl3): = 1.84 (m, 4 H, CH2CH2CH2O),
2.26 (m, 2 H, CH2CH2CH), 2.59 (m, 6 H, Ar-CH2), 3.37 (t, 3J = 7.0
Hz, 4 H, CH2CH2CH2O), 4.39 (s, 2 H, PhCH2O), 4.86–4.98 (m, 2
H, CH=CH2), 5.77 (m, 1 H, CH=CH2), 6.92 (s, 3 H, Ar-H), 7.32–
7.44 (m, 10 H, Ar-H).
13C NMR (63 MHz, CDCl3): = 31.33, 32.27, 35.27, 35.47, 69.45,
72.81, 114.75, 125.76, 125.88, 127.53, 128.16, 128.57, 138.04,
138.55, 141.86, 141.86.
MS (EI, 80 eV, 130 °C): m/z (%) = 324 (2, [M]+), 291 (4, [M –
HOCH3]+), 276 (17, [M – CH3 – HOCH3]+), 73 (100, [SiMe3]+).
HRMS: m/z Calcd for C11H12Br2O2: 324.194087. Found:
324.19732.
MS (EI, 80 eV, 130 °C): m/z (%) = 428 (2, [M]+), 337 (100, [M –
C7H7]+).
Anal. Calcd for C11H12Br2O2 (324.60): C, 62.90; H, 9.94. Found: C,
62.46; H, 9.95.
HRMS: m/z Calcd for C30H36O2: 428.27153. Found: 428.27158.
1-But-3-enyl-3,5-bis[3-(tert-butydimethylsiloxy)propyl]benzene
(3)
3-(3,5-Diiodophenyl)propionaldehyde (31)
To
a solution of 1,3-bis(trimethylsilyl)-5-(3,3-dimethoxypro-
Following the typical procedure described for the preparation of 22,
the reaction was carried out with (allyloxy)(tert-butyl)dimethylsi-
lane (33; 11.0 mL, 51.8 mmol, 3.01 equiv), 9-BBNH (6.3 g, 51.7
mmol, 3.01 equiv), THF (60 mL), aq NaOH (1 M, 150 mL), 1-but-
3-enyl-3,5-dibromobenzene (28; 5.0 g, 17.2 mmol), Pd(Ph3P)4 (0.44
g, 3.8 10–4 mol, 1.1 mol% per coupling), and an additional amount
THF (100 mL) by refluxing for 17 h; yield: 8.8 g (85%); colorless
oil; Rf 0.64 (hexanes–EtOAc, 20:1).
pyl)benzene (29; 30.8 g, 94.9 mmol) in CH2Cl2 (250 mL) at 0 °C
was added a solution of ICl (42.9 g, 264.4 mmol, 2.79 equiv) in
CH2Cl2 (50 mL) within 2 h. After stirring for an additional 30 min,
an aq sat. solution of Na2S2O5 was added, and the layers were sepa-
rated. The aqueous layer was washed with CH2Cl2 (2 20 mL) and
the combined organic layers were dried (MgSO4), filtered and the
solvent was removed. 1H NMR analysis of the residue indicated for-
mation of a mixture of acetal 30 and aldehyde 31. It was not further
purified, but dissolved in a mixture of MeCN (250 mL) and H2O (30
mL). After addition of DDQ (2.15 g, 9.5 mmol, 0.10 equiv based on
29), the dark red suspension was stirred at r.t. for 4 h. Chromogra-
phy through a short column of silica gel (hexanes–EtOAc, 20:1) and
precipitation from CH2Cl2–MeOH yielded 9.2 g (25%) of 31 as a
pale yellow solid; mp 65–66 °C; Rf 0.23; (hexanes–EtOAc, 6:1).
Compound 31 was not stable on silica gel leading to considerable
loss. The mass spectra indicated the formation of the corresponding
acid.
1H NMR (250 MHz, CDCl3): = 0.08 [s, 12 H, Si(CH3)2], 0.94 [s,
18 H, t-C4H9], 1.86 (m, 4 H, CH2CH2CH2O), 2.36 (m, 2 H,
3
CH2CH2CH), 2.66 (m, 6 H, Ar-CH2), 3.66 (t, J = 7.0 Hz, 4 H,
CH2CH2CH2O), 4.98–5.11 (m, 2 H, CH=CH2), 5.89 (m, 1 H,
CH=CH2), 6.87 (s, 3 H, Ar-H).
13C NMR (63 MHz, CDCl3): = –5.26, 18.35, 25.99, 32.03, 34.49,
35.41, 35.62, 62.48, 114.69, 126.03, 126.24, 138.31, 141.75,
142.14.
MS (EI, 80 eV, 60 °C): m/z (%) = 476 (<1, [M]+), 418 (33, [M – t-
1H NMR (500 MHz, CDCl3): = 2.74 (m, 2 H), 2.80 (m, 2 H), 7.48
(s, 2 H), 7.86 (s, 1 H), 9.77 (s, 1 H).
13C NMR (125 MHz, CDCl3): = 26.09, 44.62, 94.86, 136.67,
142.96, 144.58, 200.31.
Bu]+), 346 (61, [M – OSi(CH3)2Bu-t]+, 75 (100, [OSi(CH3)2]+).
Anal. Calcd for C28H52O2Si2 (476.88): C, 70.52; H, 10.99. Found:
C, 70.74; H, 10.75.
MS (EI, 80 eV, 90 °C): m/z (%) = 386 (100, [M]+).
1-But-3-enyl-3,5-bis(3-{3,5-bis-[3-(tert-butyldimethylsiloxy)-
propyl]phenylpropyl)benzene (4)
Anal. Calcd for C9H8I2O (385.97): C, 28.01; H, 2.09. Found: C,
27.99; H, 2.05.
Following the general procedure described for the preparation of
22, the reaction was carried out with G1 dendron 3 (3.1 g ,6.5 mmol,
3.09 equiv), 9-BBNH (13.0 mL of a 0.5 M solution in THF, 6.5
mmol, 3.09 equiv), aq NaOH (1 M, 25 mL), 1-but-3-enyl-3,5-dibro-
mobenzene (28; 0.61 g, 2.10 mmol), and Pd(Ph3P)4 (0.15 g, 1.3
10–4 mol, 3.09 mol% per coupling) in additional THF (20 mL);
yield: 1.7 g (75%); colorless oil; Rf 0.38 (hexanes–EtOAc, 20:1).
1H NMR (250 MHz, CDCl3): = 0.01 [s, 24 H, Si(CH3)2], 0.96 (s,
36 H, t-C4H9), 1.70 (m, 8 H, CH2CH2CH2CH2), 1.86 (m, 8 H,
CH2CH2CH2O), 2.40 (m, 2 H, CH2CH2CH), 2.63–2.70 (m, 18 H,
Ar-CH2), 3.68 (t, 3J = 7.0 Hz, 8 H, CH2CH2CH2O), 5.00–5.10 (m, 2
H, CH=CH2), 5.91 (m, 1 H, CH=CH2), 6.87–6.88 (m, 9 H, Ar-H).
1-But-3-enyl-3,5-diiodobenzene (32)
Following the typical procedure described for the preparation of 28,
the reaction was carried out with triphenylmethylphosphonium io-
dide (0.70 g, 1.73 mmol), THF (20 mL), BuLi (1.05 mL of a 1.6 M
solution in hexane, 1.68 mmol, 1.14 equiv), and 3-(3,5-diiodophe-
nyl)propionaldehyde (31; 0.57 g, 1.48 mmol) in THF (10 mL);
yield: 0.53 g (62%); oil; Rf 0.70 (hexanes–EtOAc, 6:1).
1H NMR (270 MHz, CDCl3): = 2.32 (m, 2 H), 2.57 (t, 3J = 8.0 Hz,
2 H), 5.01 (m, 2 H), 5.78 (m, 1 H), 7.50 (s, 2 H), 7.86 (s, 1 H).
13C NMR (63 MHz, CDCl3): = 34.36, 34.85, 94.76, 115.68,
136.79, 136.89, 142.51, 145.96.
13C NMR (63 MHz, CDCl3): = –5.27, 18.33, 25.98, 26.19, 31.34,
32.03, 34.47, 35.38, 35.61, 35.81, 62.48, 114.70, 125.75, 125.91,
126.02, 126.68, 138.28, 141.67, 142.07, 142.53 (2 signals missing).
MS (EI, 80 eV, 40 °C): m/z (%) = 384 (66, [M]+), 343 (100, [M –
C3H5]+).
Synthesis 2003, No. 1, 79–90 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Phenylenealkylene Dendrons
89
MS (EI, 80 eV, 200 °C): m/z (%) = 1085 (1, [M]+), 1070 (8, [M –
CH3]+), 1028 (100, [M – t-Bu]+).
(9) Beinhoff, M.; Weigel, W.; Jurczok, M.; Rettig, W.;
Modrakowski, C.; Brüdgam, I.; Hartl, H.; Schlüter, A. D.
Eur. J. Org. Chem. 2001, 3819.
(10) (a) Miller, T. M.; Neenan, T. X.; Zayas, R.; Bair, H. E. J. Am.
Chem. Soc. 1992, 114, 1018. (b) Wiesler, U.-M.; Weil, T.;
Müllen, K. Top. Curr. Chem. 2001, 212, 1.
(11) See for example: (a) Xu, Z.; Moore, J. S. Acta Polym. 1994,
45, 83. (b) Bharati, P.; Patel, U.; Kawaguchi, T.; Pesak, D.
J.; Moore, J. S. Macromolecules 1995, 28, 5955.
(12) (a) Deb, S. K.; Maddux, T. M.; Yu, L. J. Am. Chem. Soc.
1997, 119, 9079. (b) Pillow, J. N. G.; Halim, M.; Lupton, J.
M.; Burn, P. L.; Samuel, I. D. W. Macromolecules 1999, 32,
5985. (c) Meier, H.; Lehmann, M.; Kolb, U. Chem.–Eur. J.
2000, 6, 2462. (d) Segura, J. L.; Gomez, R.; Martin, N.;
Guldi, D. M. Org. Lett. 2001, 3, 2645.
(13) Newcome, G. R.; Moorefield, C. N.; Baker, G. R.; Johnson,
A. L.; Behera, R. K. Angew. Chem., Int. Ed. Engl. 1991, 30,
1176; Angew. Chem. 1991, 103, 1205.
(14) In a similar approach phenylenealkylene dendrons with m-
terphenylene branching units were constructed: Bo, Z.;
Schlüter, A. D. J. Org. Chem. 2002, 67, 5327.
(15) (a) Miyaura, N.; Ishiyama, T.; Sasaki, H.; Ishikawa, M.;
Satoh, M. J. Am. Chem. Soc. 1989, 111, 314. (b) Chemler,
S. R.; Trauner, D.; Danishefsky, S.Angew. Chem., Int. Ed.;
2001, 40: 4544; Angew. Chem. 2001, 113, 4676.
(16) (a) Voit, B. I. Acta Polym. 1995, 46, 87. (b) Hult, A.;
Johansson, M.; Malmstöm, E. Adv. Polym. Sci. 1999, 143, 1.
(17) Wang, F.; Kon, A. B.; Rauh, R. D. Macromolecules 2000,
33, 5300.
(18) For a statistical one-pot procedure, see: Wrobel, D.;
Wannagat, U. J. Organomet. Chem. 1982, 225, 203.
(19) (a) Félix, G.; Dunoguès, J.; Pisciotti, F.; Calas, R. Angew.
Chem. 1977, 89, 502. (b) Weber, W. P. Reactivity and
Structure, Vol. 14; Springer: Berlin, 1983, 115–118.
(20) Since TMS groups are not protective groups in the common
sense, we prefer to use the term place holder, which
precisely defines their function.
(21) (a) Brown, H. C. Organic Synthesis via Boranes; Wiley:
New York, 1975, 41. (b) For an overview concerning
hydroborations, see: Zaidlewicz, M. In Comprehensive
Organometallic Chemistry, Vol. 7; Wilkinson, G., Ed.;
Pergamon: Oxford, 1982, 143–160.
Anal. Calcd. for C66H116O4Si4 (1085.97): C, 73.00; H, 10.77.
Found: C, 72.97; H, 10.69.
Poly-{9-[3-(3,5-diiodophenyl)propyl]-9-borabicyclo[3.3.1]-
nonane} (36); Typical Procedure
A mixture of 9-BBNH (3.20 mL of a 0.5 M solution in THF, 1.60
mmol, 1.02 equiv) and 1-allyl-3,5-diiodobenzene (19; 0.58 g, 1.57
mmol) was stirred for one day at r.t. After addition of aq NaOH (3
M, 1.50 mL, 4.50 mmol, 2.87 equiv) and additional THF (10 mL),
the suspension was degassed. The catalyst precursor Pd(Ph3P)4
(38.3 mg, 3.31 10–5 mol, 1.05 mol% per coupling) was added and
the suspension was stirred under gentle reflux for 20 h. The reaction
mixture was poured into MeOH (200 mL), and the polymer was al-
lowed to stand for one day for precipitatation. The turbid suspension
was centrifuged, and the resulting solid was lyophilized from ben-
zene to yield 0.38 g (94%) of polymer 36 as a creamy white solid.
The solubilty of polymer 36 was too low to obtain a well resolved
13C NMR spectra.
1H NMR (500 MHz, CDCl3): = 1.85 (s, 2 H, H-7), 2.52 (s, br, 4 H,
H-6), 6.76 (s, br, H-5), 6.88 (s, br, H-4), 7.30 (s, br, H-3), 7.42 (s,
br, H-2), 7.82 (s, br, H-1).
MS (MALDI-TOF, DHB): m/z = 2333 [Mn (n = 9)]+, 2207
[Mn (n = 9) – I]+, 2089 [Mn (n = 8)]+, 1963 [Mn (n = 8) – I]+,
1845 [Mn (n = 7)]+, 1719 [Mn (n = 7) – I]+, 1601 [Mn (n = 6)]+,
1475 [Mn (n = 6) – I]+, 1357 [Mn (n = 5)]+, 1231 [Mn (n = 5) – I]+,
1113 [Mn (n = 4)]+, 987 [Mn (n = 4) – I]+, 869 [Mn (n = 3)]+, 743
[Mn (n = 3) – I]+.
Anal. Calcd for (C10H11I)n (258.20): C, 44.29; H, 3.72. Found: C,
46.46; H, 3.89.
Acknowledgements
Support of this work by the Deutsche Forschungsgemeinschaft (Sfb
448, Teilprojekt A1) and the Fonds der Chemischen Industrie is
gratefully acknowledged. We wish to thank Dr. A. Schäfer for help
with 2D NMR spectroscopy.
References
(22) Two-dimensional Heteronuclear Multiple Quantum
Coherence NMR experiment.
(1) For general information about dendrimers, see for example:
(a) Newkome, G. R.; Moorefield, C. N.; Vögtle, F.
Dendrimers and Dendrons - Concepts, Syntheses,
Applications; Wiley-VCH: Weinheim, 2001.
(b) Dendrimers and other Dendritic Polymers; Fréchet, J. M.
J.; Tomalia, D. A., Eds.; Wiley: New York, 2001.
(2) For a review, see: Schlüter, A. D.; Rabe, J. P. Angew. Chem.
2000, 112, 860; Angew. Chem., Int. Ed. 2000, 39, 864.
(3) Peez, R. F.; Dermody, D. L.; Franchina, J. G.; Jones, S. J.;
Bruening, M. L.; Bergbreiter, D. E.; Crooks, R. M.
Langmuir 1998, 14, 4232; and references cited therein.
(4) Klopsch, R.; Franke, P.; Schlüter, A. D. Chem.–Eur. J. 1996,
1330.
(5) Klopsch, R.; Schlüter, A. D. Eur. J. Org. Chem. 1998, 2551.
(6) (a) Klopsch, R.; Koch, S.; Schlüter, A. D. Eur. J. Org. Chem.
1998, 1275. (b) Modrakowski, C.; Camacho Flores, S.;
Beinhoff, M.; Schlüter, A. D. Synthesis 2001, 2143.
(c) Zhang, A.; Vetter, S.; Schlüter, A. D. Macromol. Chem.
Phys. 2001, 202, 3301.
(7) (a) Shu, L.; Schäfer, A.; Schlüter, A. D. Macromolecules
2000, 33, 4321. (b) Shu, L.; Schlüter, A. D. Macromol.
Chem. Phys. 2000, 201, 239.
(23) For recent overviews on(accelerated) convergent methods,
see: (a) Grayson, S. M.; Fréchet, J. M. J. Chem. Rev. 2001,
101, 3819. (b) Freeman, A. W.; Fréchet, J. M. J. Dendrimers
and other Dendritic Polymers; Fréchet, J. M. J.; Tomalia, D.
A., Eds.; Wiley: New York, 2001, 91–110.
(24) Recently a one-pot synthesis of an almost defect-free G4
dendron was reported: (a) Brauge, L.; Magro, G.;
Caminade, A.-M.; Majoral, J.-P. J. Am. Chem. Soc. 2001,
123, 6698. (b) Brauge, L.; Magro, G.; Caminade, A.-M.;
Majoral, J.-P. J. Am. Chem. Soc. 2001, 123, 8446.
(25) For 3,5-dibromoallylbenzene, see also: Ek, F.; Wistrand, L.
G. EP1013636, 2000; Chem. Abstr. 2000, 133, 58600.
(26) A more practical reason was the unfavorable synthesis
protocol of the dibromo compound by Pd-catalyzed
allylation of (3,5-dibromophenyl)trimethylstannane. In
order to avoid the handling of tin compounds the diiodo
analog was prepared by a different procedure.
(27) Boudjouk, P.; Kapfer, C. A. J. Organomet. Chem. 1985, 296,
339.
(28) (a) Willgerodt, C.; Arnold, E. Ber. Dtsch. Chem. Ges. 1901,
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Fleischer, F.; Pflug, J. L.; Schwab, P. F. H.; Meng, X.;
(8) Vetter, S.; Koch, S.; Schlüter, A. D. J. Polym. Sci. Part A:
Polym. Chem. 2001, 39, 1940.
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M. Beinhoff et al.
PAPER
Lipiak, D.; Noll, B. C.; Allured, V. S.; Rudalevige, T.; Lee,
S.; Michl, J. J. Am. Chem. Soc. 1997, 119, 3907.
(c) Nishide, H.; Miyasaka, M.; Tsuchida, E. J. Org. Chem.
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(37) Preliminary investigations on the corresponding G3 dendron
(not shown) encountered the additional problem that the
molar mass of this molecule could not be confirmed, since
the applied methods (EI, FAB, MALDI-TOF) only showed
much smaller fragments. The mass spectral analyses of
TBDMS-protected dendrons 3 and 4 point to the sensitivity
of the silyl group with the loss of methyl and tert-butyl
groups.
(29) (a) Benkeser, R. A.; Hickner, R. A.; Hoke, D. J.; Thomas, O.
H. J. Am. Chem. Soc. 1958, 80, 5289. (b) McDonagh, A.
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Organometallics 1999, 18, 5195. (c) Lustenberger, P.;
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(38) Kim, Y. H.; Webster, O. W. Macromolecules 1992, 25,
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(39) The molar mass distribution of hyperbranched
poly(phenylene)s, obtained by Suzuki cross-coupling of 3,5-
dibromophenylboronic acid, was reported to show a large
dependence from the used solvent system. The average
number of repeating units was between 13 and 42 (7
examples), in one example 206 repeating units were
achieved.38
(33) (a) Ford, K. L.; Roskamp, E. J. Tetrahedron Lett. 1992, 33,
1135. (b) Ford, K. L.; Roskamp, E. J. J. Org. Chem. 1993,
58, 4142.
(34) Target molecule 28 was also synthesized by reaction of
the(expensive) 3,5-dibromobenzyl bromide with
allylmagnesium bromide.
(40) According to: Hölter, D.; Burgath, A.; Frey, H. Acta Polym.
1997, 48, 30.
(41) Nicolaou, K. C.; Patron, A. P.; Ajito, K.; Richter, P. K.;
Khatuya, H.; Bertinato, P.; Miller, R. A.; Tomaszewski, M.
J. Chem.–Eur. J. 1996, 2, 847.
(42) Day, G. M.; Howell, O. T.; Metzler, M. R.; Woodgate, P. D.
Austr. J. Chem. 1997, 50, 425.
(43) Coulson, D. R. Inorg. Synth. 1972, 13, 121.
(44) For an analogous procedure, see: Chen, G. J.; Tamborski, C.
J. Organomet. Chem. 1983, 251, 149.
(35) See for example: (a) Jefferey, T. J. Chem. Soc., Chem.
Commun. 1984, 1287. (b) Kang, S.-K.; Lee, H.-W.; Jang,
S.-B.; Kim, T.-H.; Pyun, S.-J. J. Org. Chem. 1996, 61, 2604.
(36) The Suzuki–Miyaura cross-coupling of 34 with vinylic
halides has been previously described: (a) Ridgway, B. H.;
Woerpel, K. A. J. Org. Chem. 1998, 63, 458. (b) Trost, B.
M.; Probst, G. D.; Schoop, A. J. Am. Chem. Soc. 1998, 120,
9228.
(45) No reference data were found.
Synthesis 2003, No. 1, 79–90 ISSN 0039-7881 © Thieme Stuttgart · New York