R. T. A. Mayadunne et al. / Tetrahedron Letters 43 (2002) 6811–6814
6813
Br
O
HO
O
Ph
Ph
Ph
O
OH
Ph
S
b
HO
Br
O
Br
HO
− +
S Na
O
Br
O
H3CS
O
a
O
OH
O
2
O
HO
O
OH
Ph
O
O
O
Br
Br
Ph
Ph
7
O
Br
Scheme 2. Reagents and conditions: (a) p-TsOH, toluene, 110°C, 6 h; (b) EtOAc, rt.13
erythritol and dipentaerythritol for the four and six
arms, respectively) with 2-mercaptopropanoic acid in
the presence of p-toluenesulfonic acid as a catalyst
(Scheme 1). The reaction was carried out in toluene at
reflux with Dean–Stark water separation. The interme-
diate tetra- or hexamercapto derivatives were obtained
in near quantitative yield. These mercapto derivatives
were converted to the desired multi-trithiocarbonate
derivatives by treatment with carbon disulfide, triethyl-
amine and benzyl bromide.
products are obtained in high yields using convenient
reaction conditions and inexpensive commercially avail-
able substrates and reagents. The present route is read-
ily adapted to the synthesis of initiators for other
controlled radical polymerization methods, e.g. ATRP.
The use of these multi arm RAFT agents in the prepa-
ration of star polymers will be the subject of a forth-
coming paper.
Multi arm chain-transfer agents 2, 3, 4, and 6 were
prepared13 similarly (Scheme 2). a-Bromophenylacetic
acid was condensed with the appropriate core to form
tri, tetra, hexa, and octa bromo derivatives in high
isolated yield (see Table 1). The purified bromo deriva-
tives were subsequently treated with freshly prepared
sodium methyl trithiocarbonate14 (prepared from
sodium methyl thiolate and carbon disulfide) in ethyl
acetate to afford the macromolecule 2 and the variants
3, 4, and 6 as yellow oils.
References
1. (a) Mishra, M. K.; Kobayashi, S. Star and Hyper-
branched Polymers; Marcel Dekker: New York, 1999; (b)
Mishra, M. K.; Shirodkar, S. M.; Jung, A. K. PCT Int.
Appl. WO96-US753 19960122; (c) Bennett, S. L.; Jiang,
Y.; Gruskin, E. A.; Connolly, K. M. Eur. Pat. Appl.
EP693294 A2 19960124, EP 95-111520 19950721; Chem.
Abstr. 1996, 124, 242385; (d) Hoxmeier, R. J.; Spence, B.
A.; Southwick, J. G. US 5461116 A 19951024; Chem.
Abstr. 1996, 124, 58780; (e) Spinelli, H. J. Eur. Pat. Appl.
EP420686 A2 19910403.
Non-esterified arms, if any, in the reaction products are
clearly distinguishable in the 1H NMR spectra. The
methylene groups a to the hydroxy groups of the
starting cores appear at l 3.45. Complete disappearance
of this signal from the NMR spectrum of the crude
mixtures and the appearance of a sharp singlet at l
4.20, integrating to the expected number of protons was
observed in each case confirming the completeness of
the reaction.
2. Matyjaszewski, K. Comparison and classification of con-
trolled/living radical polymerization. In Controlled Radi-
cal Polymerization; Matyjaszewski, K., Ed.; ACS
Publishing: Washington, DC, 2000, ACS Symposium
Series c768, pp. 2–26.
3. (a) Le, T. P.; Moad, G.; Rizzardo, E.; Thang, S. H. PCT
Int. Appl. WO9801478 A1 980115; Chem. Abstr. 1998,
128, 115390; (b) Chiefari, J.; Chong, Y. K.; Ercole, F.;
Krstina, J.; Jeffery, J.; Le, T. P. T.; Mayadunne, R. T. A.;
Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.;
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1999, 131, 45250.
Final proof of the completeness of the reaction comes
from analysis of the star polymers prepared using type
1 as RAFT agents (e.g. 1 and 5). The arms of these star
polymers can be cleaved at the core (trithiocarbonate
link) to result in linear polymer (the arms). The fact
that the polydispersity of the resulting polymer
remained similar to that of the starting material (consis-
tent propagation at each arm) and the molecular weight
was equal to the molecular weight of the original star
polymer divided by the number of arms confirms that
each arm of the RAFT agent was composed of a
thiocarbonyl thio group.
5. Rizzardo, E.; Chiefari, J.; Mayadunne, R. T. A.; Moad,
G.; Thang, S. H. Synthesis of defined polymers by
reversible addition—fragmentation chain-transfer: the
RAFT process. In Controlled Radical Polymerization;
Matyjaszewski, K., Ed.; ACS Publishing: Washington,
DC, 2000, ACS Symposium Series c768, pp. 278–296.
6. Mayadunne, R. T. A.; Rizzardo, E.; Chiefari, J.; Chong,
Y. K.; Moad, G.; Thang, S. H. Macromolecules 1999, 32,
6977–6980.
In conclusion, organic molecules having three, four, six
and eight arms, each functionalized with a trithiocar-
bonate moiety have been synthesized for use as chain-
transfer agents in RAFT polymerization. These
7. Mayadunne, R. T. A.; Rizzardo, E.; Chiefari, J.; Krstina,
J.; Moad, G.; Postma, A.; Thang, S. H. Macromolecules
2000, 33, 243–245.