Organoiron route to a new dendron for fast dendritic syntheses using divergent and convergent methods

Full text of DOI:10.1021/ja983868m

J. Am. Chem. Soc. 1999, 121, 2929-2930
2929
Scheme 1a
Organoiron Route to a New Dendron for Fast
Dendritic Syntheses Using Divergent and Convergent
Methods
Vale´rie Sartor,† Laurent Djakovitch,† Jean-Luc Fillaut,†
Franc¸oise Moulines,† Fre´de´ric Neveu,† Vale´rie Marvaud,†
Joe¨lle Guittard,‡ Jean-Claude Blais,‡ and Didier Astruc*,†
Groupe de Chimie Supramole´culaire des
Me´taux de Transition, LCOO, UMR CNRS No. 5802
UniVersite´ Bordeaux I, 33405 Talence Cedex, France
Laboratoire de Chimie Structurale
Organique et Biologique, UniVersite´ Paris VI
75352 Paris Cedex 04, France
ReceiVed NoVember 9, 1998
The construction of dendrimers by organic1 and inorganic2 paths
is well established. Although organotransition-metal moieties have
been fixed onto the termini of dendrimers3 for catalytic applica-
tions,4 the only known organotransition-metal synthesis of den-
drimers is Puddephatt’s oxidative addition of benzyl halides to
Pd(0) complexes.5 The syntheses of large dendrimers usually
require a number of steps, which overtakes those involved in the
total syntheses of natural products, thus the search for fast
syntheses of large dendrimers is timely. We are reporting here
the organoiron synthesis of a dendron inVolVing eight steps of
four different kinds in a one-pot reaction and the use of this
dendron for the fast synthesis of dendrons and dendrimers using
divergent and convergent routes.
a (i)t-BuOK, THF, CH2)CH-CH2Br, 10d, -50 °C-rt, 50%; (ii) hνvis
,
MeCN, 4h, rt, 70%; (iii) t-BuOK, THF, CH2)CH-CH2Br, 5d, -50 °C-
rt, 60%.
C-O bond of aryl ethers6c (Scheme 1). The iron complex 1 is
easily available on a very large scale by quantitative reaction of
ethanol and K2CO3 with [FeCp(η5-p‚CH3C6H5Cl)][PF6].6b,7 Reac-
tion of 1 with t-BuOK and allylbromide in THF directly provides
good yields of either the iron complex 2 or the free phenol deriv-
ative 3, depending on the reaction conditions. Note that this flex-
ible and powerful combination is unprecedented. From 1, the three
deprotonation-allylation sequences occur before heterolytic cleav-
age of the C-O bond, giving 2, a red oil, in 50% yield. Altern-
atively, addition of t-BuOK in situ instead of extraction of 2 pro-
vokes its decomplexation giving 3, a light-brown solid, in 60%
overall yield from 1 (after chromatography) in this one-pot reac-
tion. Photolysis of isolated 2 in MeCN also leads to 3 (70%
yield).8
We already know that the CpFe+-induced perfunctionalization
of permethylaromatics by reaction with a base and a functional
halide provides a clean and efficient route to dendritic cores (Cp
) η5-C5H5).6a,b We have now been able to combine this reaction
with the CpFe+-induced heterolytic cleavage of the exocyclic
† Universite´ Bordeaux I.
‡ Universite´ Paris VI (mass spectrometry).
The divergent construction starts from the nona-ol 6 synthesized
by CpFe+ induced nona-allylation of mesitylene followed by
hydroboration and oxidation of the nona-borane using H2O2/
NaOH6c (Scheme 2). Reaction of SiMe3Cl, then NaI, with 6 gives
the nona-iodo dendritic core 7, a light-yellow solid, in 89% yield.
Reaction of 7 with 3 and CsF in DMF leads to the first-generation
27-allyl dendrimer 9 which is purified by chromatography and
characterized inter alia by the molecular peak in the MALDI TOF
mass spectrum (MNa+ ) 2558). However, peaks corresponding
to the 24- and 21-allyl dendrimers are also observed, correspond-
ing to some dehydroiodation of iodoalkyl branches. Thus, we
switched to the mesylation of 6 using mesylchloride, which gives
the nona-mesylate 8 (95% yield). Reaction of 8 with 3 and CsF
in DMF followed by column chromatography gives 9 (27% yield)
whose MALDI TOF mass spectrum shows only tiny amounts of
impurities. Iteration of this reaction sequence followed by chroma-
tography gives the second-generation 81-allyl dendrimer 10 whose
MALDI TOF mass spectrum shows the molecular peak MNa+
at 5989, although several other less intense peaks were also found,
corresponding mainly to the side deshydromesylation. The synthe-
sis of the third dendritic generation, 243-allyl dendrimer 11 was
also attempted. Monitoring by NMR the reaction of the 81-
mesylate dendrimer (obtained in 45% overall yield from 10)
showed the progressive disappearance of the mesylate functional
groups until completion and their replacement by phenate triallyl
(1) (a) Tomalia, D. A.; Dupont Durst, H. Topics Curr. Chem. 1993, 165,
193. (b) AdVances in Dendritic Molecules; Newkome, G. R., Ed., JAI:
Greenwich, CT, 1994-1996; Vols. 1-3. (c) Fre´chet, J. M. J. Science 1994,
263, 1710; Jansen, J. F. G. A.; de Brabander-van den Berg, E. M. M.; Meijers,
E. W. Science 1994, 266, 1226. (d) Ardoin, N.; Astruc, D. Bull. Soc. Chim.
Fr. 1995, 132, 875. (e) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F.
Dendritic Molecules: Concepts, Syntheses and PerspectiVes; VCH: New York,
1996; (f) Zeng, F.; Zimmerman, F. C. Chem ReV. 1997, 97, 1681. (g)
Matthews, O. A.; Shipway, A. N.; Stoddart, J. F. Prog. Polym. Sci. 1998, 23,
1. (h) Gorman, C. AdV. Mater. 1998, 10, 295.
(2) (a) Serroni, S.; Denti, G.; Campagna, S.; Juris, A.; Ciano, M.; Balzani,
V. Angew Chem., Int. Ed. Engl. 1992, 31, 1493. (b) Constable, E. C. Chem.
Commun. 1997, 1073. (c) Balzani, V.; Campagna, S.; Denti, G.; Juris, A.;
Serroni, S.; Venturi, M. Acc. Chem. Res. 1998, 31, 26.
(3) (a) Moulines, F.; Gloaguen, B.; Astruc, D. Angew. Chem., Int. Ed. Engl.
1992, 28, 458. (b) Liao Y.-H., Moss J.-R. J. Chem. Soc., Chem. Commun.
1993, 1774. (c) Liao, Y.-H.; Moss, J.-R. Organometallics 1995, 14, 2130. (d)
Slany, M.; Bardaji, M.; Casanove, M.; Caminade, A.-M.; Majoral, J.-P.;
Chaudret, B. J. Am. Chem. Soc. 1995, 117, 9764. (e) Cuadrado, I.; Mora´n,
M.; Casado, C. M.; Alonso, B.; Lobete, F.; Garcia, B.; Ibisate, M.; Losada, J.
Organometallics 1996, 15, 5278. (f) Cuadrado, I.; Casado, C. M.; Alonso,
B.; Mora´n, M.; Losada, J.; Belsky, V. J. Am. Chem. Soc. 1997, 119, 7613.
(g) Castro, R.; Cuadrado, I.; Alonso, B.; Casado, C. M.; Mora´n, M.; Kaifer,
A. E J. Am. Chem. Soc. 1997, 119, 5760. (h) Takada, K.; Diaz, D. J.; Abrun˜a,
H. D.; Cuadrado, I.; Casado, C. M.; Alonso, B.; Mora´n, M.; Losada, J. J. Am.
Chem. Soc. 1997, 119, 10763. (i) Hummelen, J. C.; van Dongel, J. L. J.; Meijer,
E. W. Chem. Eur. J. 1997, 3, 1489. (j) Bosman, A. W.; Schenning, A. P. H.
J.; Janssen, R. A. J.; Meijers, E. W. Chem. Ber. 1997, 130, 725. (k) Vale´rio,
C.; Fillaut, J.-L.; Ruiz, J.; Guittard, J.; Blais, J.-C.; Astruc, D. J. Am. Chem.
Soc. 1997, 119, 2588. (l) Larre´, C.; Donnadieu, B.; Caminade, A.-M.; Majoral,
J.-P. Chem. Eur. J. 1998, 4, 2031.
(4) (a) Brunner, H.; Altmann, S. Chem. Ber. 1994, 127, 2285. (b) Knapen,
J. W. J.; van der Made, A. W.; de Wilde, J. C.; van Leeuwen, P. W. N. M.;
Wijkens, P.; Grove, D. M.; van Koten, G. Nature 1994, 372, 659. (c) Miedaner,
A.; Curtis, C. J.; Barkley, R. M.; Dubois, D. L. Inorg. Chem. 1994, 33, 5482.
(d) Herring, A. M.; Steffey, B. D.; Miedaner, A.; Wander, S. A.; Dubois, D.
L. Inorg. Chem. 1995, 34, 1100. (e) Reetz, M. T.; Lohmer, G.; Schwickardi,
R. Angew. Chem., Int. Ed. Engl. 1997, 36, 1526. (f) Rigaut, S.; Delville, M.-
H.; Astruc, D. J. Am. Chem. Soc. 1997, 119, 11132.
(6) (a) Moulines, F.; Djakovitch, L.; Boese, R.; Gloaguen, B.; Thiel, W.;
Fillaut, J.-L.; Delville, M.-H.; Astruc, D. Angew. Chem., Int. Ed. Engl. 1993,
32, 1075; (b) Astruc, D. Top. Curr. Chem. 1991, 160, 47. (c) Moulines, F.;
Djakovitch, L.; Astruc, D. New J. Chem. 1996, 20, 1071.
(7) Nesmeyanov, N. A.; Vol’kenau, N. A.; Bolesova, I. N. Dokl. Akad.
Nauk. SSSR 1967, 175, 606.
(5) (a) Achar, S.; Puddephatt, R. J. Angew. Chem., Int. Ed. Engl. 1994,
33, 847. (b) Achar, S.; Puddephatt, R. J. J. Chem. Soc., Chem. Commun. 1994,
1895.
(8) A related dendron, 4-triallylsilylphenol, has recently been reported:
Gossage, R. A.; Munoz-Martinez, E.; van Koten, G. Tetrahedron Lett. 1998,
39, 2397.
10.1021/ja983868m CCC: $18.00 © 1999 American Chemical Society
Published on Web 03/16/1999

2930 J. Am. Chem. Soc., Vol. 121, No. 12, 1999
Scheme 2. Divergent Dendrimer Synthesesa
Communications to the Editor
Scheme 3. Convergent Dendrimer Routesa
a Routes involve the following steps for the synthesis of the protected
trifunctional dendron which reacts with 3 to provide the protected
precursor of 16:
3
9
(i)8 MeOPhC(CH2-CHdCH2)3
9
(ii)8 MeOPhC-
{(CH2)3OH}3 (iii)8 HOPhC{(CH2)3I}3 (iii)8 C2H5C(O)OPhC{(CH2)3I}3
(i) MeI, KOH, DMSO, 2 h, rt, 91%. (ii) Disiamylborane, THF, then H2O2,
NaOH 3 N, 50 °C, 89%. (iii) Me3SiCl, NaI, MeCN, 12 h, 80 °C, 87%.
(iv) EtC(O)I, NEti-Pr2 (1 equiv), CH2Cl2, 16 h, rt, 94%. (v) 3, K2CO3,
DMF, 2 d, rt, 30%, then K2CO3, H2O. (vi) K2CO3, Me2CO, 2 d, reflux,
2,4,6-tri(bromomethyl)mesitylene, 33%. (vii) 15, K2CO3, DMF, then
K2CO3, H2O, 2 d, rt, 35%.
iodoalkyl-protected phenol does not lead to the expected 27-allyl
dendron but to the 19-allyl dendron 17 (35% yield after chro-
matography) resulting from the selective dehydroiodation of one
iodoalkyl branch. Thus, condensation of 16 is faster than dehydro-
iodation for the first two branches, but this latter reaction is faster
than the condensation of 16 onto the third branch for steric rea-
sons. The selectivity is remarkable, as shown by the purity of
the product disclosing a clean MALDI TOF mass spectrum with-
out side peaks ([M + Na+] ) 2077.7). Finally another example
of the rich potential of the dendrons 3 and 16 is provided by the
reaction of 16 with 2,4,6-tri(bromomethyl)mesitylene giving the
27-allyl dendrimer 18 (MALDI TOF mass spectrum: MK+
)
2935.9). The polyolefin dendrimers are colorless or light-brown
oils, the polymesylate dendrimers are colorless oils, and the polyol
dendrimers are white solids.
In conclusion, using a one-pot organoiron-mediated reaction
which involves eight successive steps, we have synthesized a new
tripodal dendron and shown its broad synthetic potential for the
fast divergent and convergent syntheses of polyallyl dendrons and
dendrimers. Exploration of the numerous facets of the synthetic
potential of this dendritic chemistry is currently underway in our
laboratories.
Acknowledgment. The Institut Universitaire de France, Rhoˆne-
Poulenc, the Universite´ Bordeaux I and the Centre National de la
Recherche Scientifique are gratefully acknowledged for financial support.
This paper is dedicated to our colleague and friend Professor Helmut
Werner on the occasion of his 65th birthday.
a Syntheses involve the following steps from one generation to the
next: RCHdCH2
9
(ii)8 RCH2CH2OH (iv)8 RCH2CH2OSO2Me
9
(v)8
RCH2CH2OPhC(allyl)3 (i) KOH, DME, CH2dCH-CH2Br, 10 d, rt; then
hνvis, PPh3, MeCN, 12 h, rt. (ii) Disiamylborane, THF 0 °C, then H2O2,
NaOH 3 N, 50 °C, 88%. (iii) Me3SiCl, NaI, MeCN, 80 °C, 12 h, 89%.
(iv) MeSO2Cl, py, 0 °C, 5 h, 95%. (v) 3, CsF, DMF, rt.
1
moieties. Although the H and 13C NMR spectra were finally in
agreement with the 243-allyl structure of 11, a clean mass spec-
trum could not be obtained, possibly due to the polydispersity9
of this dendrimer.
The successful convergent synthesis of the nona-allyl dendron
16 is achieved by reaction of 3 with the tri-iodoalkyl derivative
obtained according to Scheme 3 (30% overall yield of 16 from 3
after chromatography; MALDI TOF mass spectrum: [M + Na+]
) 935.6, no side peak). Reaction of 16 with this same tri-
Supporting Information Available: Experimental procedures, spec-
1
troscopic and analytical data, and MALDI TOF and H and 13C NMR
(9) Recently, Newkome et al. introduced the terms monomolecular and
monodisperse dendrimers for structures with 100 and <100% dendritic purity,
respectively: Newkome, G. R.; Weiss, C. D.; Morefield, C. N. Macromolecules
1997, 30, 2300.
spectra for the new compounds (PDF). This material is available free of
charge via the Internet at http://pubs.acs.org.
JA983868M