9210
J . Org. Chem. 2000, 65, 9210-9213
The core of the monomers was synthesized following
the strategy proposed by Newkome et al.,19 which is based
on the pentaerythritol and acrylonitrile reaction. As
depicted retrosynthetically in Scheme 1, two strategies
were used for the synthesis of multiacrylic dendrimer 1:
disconnection aa′ based on a divergent synthetic path-
way, and disconnection b, which involves a convergent
strategy. In this report we analyze these approaches, both
of which had challenging features.
This new kind of dendritic monomer with reactive
acrylic double bonds on its surface would be of particular
interest if it could be used to obtain new materials
through simple and available polymerization processes.
We expect that deprotection of the hydroxyl groups
after free radical polymerization of the monomer would
lead to a macromolecular structure possessing numerous
hydroxyl groups, which should give the resulting material
a very pronounced hydrophilicity and reactivity with
some further chemical modifications. We are currently
attempting to transform these ideas into reality.
Syn th esis a n d Ch a r a cter iza tion of a Novel
Den d r itic Acr ylic Mon om er
A. Halabi and M. C. Strumia*
Departamento de Quı´mica Orga´nica, Facultad de Ciencias
Quı´micas, Universidad Nacional de Co´rdoba,
Ciudad Universitaria (5000) Co´rdoba, Argentina
mcs@dqo.fcq.unc.edu.ar
Received February 14, 2000
In tr od u ction
Over the past decade, dendrimers and their controlled
cascade architecture have attracted considerable atten-
tion. These three-dimensional molecules have three
architectural regions: a core, an interior, and a highly
functionalized surface, all of which are spatially defined
by branch cells tethered to the core by chemical bonds.1-3
These versatile molecules with controllable sizes are
some of the most powerful synthetic building blocks
available today for the construction of giant macro-
molecules and supramolecular systems with a complete
architecture, precise shape, and functionality. New ma-
terials with potentially significant and scarcely explored
properties may be obtainable using these compounds. 4-10
These structural features have aroused the interest of
synthetic organic chemists, and several valuable contri-
butions to the synthesis and characterization have been
reported over the past few years.11-15 Current studies are
mainly focused on their potential properties and applica-
tions in such diverse areas as organic chemistry, analyti-
cal chemistry, biology, medicine, materials science, phar-
macology, agrochemistry, environmental chemistry, and
chemical engineering.16-18
Resu lts a n d Discu ssion
(I) Mon om er Syn th esis. Two pathways for the syn-
thesis of the desired dendritic monomer were studied, as
shown in Scheme 2.
Our first choice for the synthesis of product 11 was
made through stages A, B, C, and D. Various experimen-
tal conditions were tested to maximize the yields of the
different steps. Thus, pentaerythritol 2 and acrylonitrile
3 in dioxane/water gave tetranitrile 4 in 85% yield by
the Michael reaction. Tetramethyl ester 5 was then
obtained in 50% yield by methanolysis of 4 in an acidic
medium. The hydroxyl-functionalized monomer 7 was
obtained from nucleophilic substitution amidation be-
tween 5 and 6 in DMSO, base-catalyzed with K2CO3.
Once 7 was obtained, we sought to protect 1,3-diol pairs
by reaction with benzaldehyde, acetone, or 2,2-dimethoxy-
propane (DMP) 9 in different solvents and acid-catalyzed
with HCl or p-toluenesulfonic acid (p-TSA). Despite the
various conditions used to protect the diol moiety in 7
by condensation with a carbonyl function, complete
acetalization was not achieved.
The relatively low reactivity of the hydroxyl groups of
7 could be explained by a clear-cut tendency to develop
aggregation which leads to gelation through hydrogen-
bonding interactions. We confirmed that self-assembly
of dendrimers with hydroxyl groups on the surface leads
to gelation depending on the balance of external hydro-
philic and internal hydrophobic groups.20,21 Similar re-
sults were obtained when the reaction with acryloyl
chloride was attempted to form random acrylic end
groups. The yields were much lower than expected
(>15%).
In view of the increasing interest in these new com-
pounds, we report the synthesis and characterization of
a new dendrimer (1) bearing acrylic functions and
masked hydroxyl groups.
(1) Dvoric, P. R.; Tomalia, D. A. Macromol. Symp. 1994, 88, 123.
(2) Fre´chet, J . M. J . Science 1994, 263, 1710.
(3) Dvoric, P. R.; Tomalia, D. A. Curr. Opin. Colloid Interface Sci.
1996, 1, 221.
(4) Tsukruk, V. V. Prog. Polym. Sci. 1997, 22, 247.
(5) Frey, H. Angew. Chem., Int. Ed. 1998, 37, 16, 2193.
(6) Ingerl, A.; Neubert, I.; Klopsch, R.; Schluter, D. Eur. J . Org.
Chem. 1998, 2551.
(7) Schluter, D. Topics Curr. Chem. 1998, 197, 165.
(8) Wenfang, S.; Ranby, B. J . Appl. Polym. Sci. 1996, 59, 1937.
(9) Wenfang, S.; Ranby, B. J . Appl. Polym. Sci. 1996, 59, 1945.
(10) Wenfang, S.; Ranby, B. J . Appl. Polym. Sci. 1996, 59, 1951.
(11) Newkome, G. R.; Moorefield, C. N.; Baker, G. R. Aldrichimica
Acta 1992, 25, 31.
(12) Hawker, C.; Frechet, J . M. J . J . Chem. Soc., Chem. Commun.
1990, 1010.
(13) Tomalia, D. A.; Naylor, A. M.; Goddard, W. A. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 138.
(14) Frechet, J . M. J .; Hawker, C. J .; Wooley, K. L. Macromolecules
1992, 25, 2401.
(15) Ardoin, N.; Astruc, D. Bull. Soc. Chim. Fr. 1995, 132, 875.
(16) J ansen, J . F.; de Brabender-van den Berg, E. M.; Meijer, E. W.
Science 1994, 266, 1226.
To overcome the problem encountered in the first
approach, a convergent synthetic pathway (E + F + G)
(19) Newkome, G. R.; Lin, X. Macromolecules 1991, 24,1443.
(20) Newkome, G.; Baker, G.; Arai, S.; Saunders, M.; Russo, P.;
Theriot, K.; Moorefield, C.; Rogers, E.; Miller, J .; Lieux, R.; Murray,
M.; Phillips, B.; Pascal, L. J . Am. Chem. Soc. 1990, 112, 8458.
(21) Newkome, G. R.; Lin, X.; Yaxiong, C.; Escamilla, G. H. J . Org.
Chem. 1993, 58, 3123.
(17) Knapen, J . W.; van der Made, A. W.; de Wilde J . C.; van
Leeuwen, A. W.; Wijkens, P.; Grove D.; van Koten, G.; Nature 1994,
372, 659.
(18) Newkome, G.; Moorefield, C.; Epperson, Strumia, M.; Halabi,
A.; Pucci, P. J . Polym. Sci. Polym. Chem. Ed. 2000, 38, 2779.
10.1021/jo000202d CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/28/2000