Article
Macromolecules, Vol. 43, No. 3, 2010 1275
NMR (600 MHz, CDCl3): δ 7.43-7.31 (m, 20H), 6.68 (d, J = 2
Hz, 4H), 6.59-6.55 (m, 5H), 5.04 (s, 8H), 4.98 (s, 4H), 4.26 (s,
2H). 13C NMR (125 MHz, CDCl3): δ 160.11, 160.07, 139.0,
137.6, 136.7, 128.5, 128.0, 127.5, 107.2, 106.3, 101.8, 101.6, 70.1,
70.0, 54.8.
70.03, 69.98, 69.91, 67.7, 58.0, 54.0, 30.8, 24.8. MS (MALDI in
-
N6O36: C, 76.67; H, 5.62; N, 2.25. Found: C, 76.90; H, 6.00;
N, 2.20.
dithranol) m/z 3728.3 [M þ H]þ. Anal. Calcd for C238H208
[G-1] DA Adduct (8). [G-1] bisfuran 6a (100 mg, 84.6 μmol)
and N-phenylmaleimide 7 (14.7 mg, 84.6 μmol) were dissolved in
CDCl3 (500 μL), and the mixture was heated to 50 °C in an open
vial. Every 24 h, fresh CDCl3 (500 μL) was added. After 10 days,
the residue was purified by flash chromatography (silica gel, 9:1
CH2Cl2-acetone) to give 8 (75 mg, 65% yield,34 93% exo
[G-3] Azide (5c)30. To a 250 mL round-bottom flask under an
N2 atmosphere was added [G-3]-OH33 (2.50 g, 1.57 mmol),
DBU (353 mg, 2.35 mmol), and CH2Cl2 (50 mL). The mixture
was cooled to 0 °C in an ice bath, followed by dropwise addition
of diphenylphosphoryl azide (645 mg, 2.35 mmol). The reaction
was allowed to warm to rt and was stirred for 16 h. The solvent
was removed under reduced pressure, followed by purification
by flash chromatography (silica gel, CH2Cl2) to give 5c (2.46 g,
76% yield) as a white, waxy solid. 1H NMR (600 MHz, CDCl3):
δ 7.41-7.30 (m, 40H), 6.68-6.66 (m, 12H), 6.58-6.54 (m, 9H),
5.02 (s, 16H), 4.97 (s, 12H), 4.23 (s, 2H). 13C NMR (125 MHz,
CDCl3): δ 160.1, 160.0, 139.1, 139.0, 137.6, 136.7, 128.5, 127.9,
127.5, 107.2, 106.4, 101.8, 101.63, 101.59, 70.1, 70.04, 70.00,
54.8.
1
isomer) as a white foam. Data for exo-exo isomer: H NMR
(600 MHz, CDCl3): δ 8.04 (s, 2H), 7.93 (s, 2H), 7.41-7.28 (m,
26H), 7.21-7.20 (m, 4H), 6.59-6.57 (m, 2H), 6.55 (d, J = 2 Hz,
4H), 6.50 (d, J = 5 Hz, 2H), 6.32 (d, J = 6 Hz, 2H), 5.49 (s, 4H),
5.31 (s, 2H), 4.99 (s, 8H), 4.85 and 4.50 (AB pattern, J = 13 Hz,
4H), 4.18 (t, J = 6 Hz, 4H), 3.06 and 2.97 (AB pattern, J = 6 Hz,
4H), 2.46 (t, J = 4 Hz, 4H), 2.19-2.10 (m, 4H). 13C NMR (150
MHz, CDCl3): δ 174.7, 173.3, 172.4, 160.3, 149.1, 143.1, 137.6,
137.2, 137.1, 136.4, 131.5, 129.0, 128.7, 128.5, 128.0, 127.5,
126.4, 123.6, 119.4, 110.9, 107.0, 101.9, 89.6, 81.4, 70.1, 67.8,
61.4, 53.9, 49.9, 48.3, 30.8, 29.4, 24.8. MS (ESI) m/z 1550.0 [M þ
Na]þ, 1375.9 [M - maleimide þ Na]þ, 1203.3 [6a þ Na]þ. Anal.
Calcd for C90H78N8O16: C, 70.76; H, 5.15; N, 7.34. Found: C,
70.28; H, 5.38; N, 7.46.
[G-1] Bisfuran (6a). In a small vial equipped with a stirbar, 4
(200 mg, 0.406 mmol), Cu(PPh3)3Br (76 mg, 0.0812 mmol), 5a
(308 mg, 0.893 mmol), DIEA (262 mg, 2.03 mmol), and CH2Cl2
(3.0 mL) were combined. The mixture was stirred at rt for 48 h,
at which point the solvent was removed under reduced pressure.
The residue was purified by flash chromatography (silica gel,
95:5 CH2Cl2-acetone) to give 6a (460 mg, 96% yield) as an off-
NMR Studies. To monitor assembly of DA adduct 8, [G-1]
bisfuran 6a (100 mg, 84.6 μmol) and N-phenylmaleimide (7)
(14.7 mg, 84.6 μmol) were dissolved in CDCl3 (500 μL), and the
mixture was heated to 50 °C in an open vial. Every 24 h, fresh
CDCl3 (500 μL) was added. At time intervals aliquots were
removed from the vial, and 1H NMR spectra were collected at
ambient temperature. To monitor disassembly, a solution
of purified bis-DA adduct 8 in TCE-d2 (1 mM) was heated to
110 °C in a sealed NMR tube. At time intervals the reaction was
removed from the heating bath, and 1H NMR spectra were
collected at ambient temperature. To monitor the reassembly,
the same disassembled sample of DA adduct 8 was concentrated
to dryness and redissolved in a minimal quantity of CDCl3. The
sample was heated to 50 °C in an open vial. At time intervals
aliquots were removed from the vial, and 1H NMR spectra were
collected at ambient temperature.
GPC Studies. To measure the assembly of dendritic DA
polymers 10a-10c, [G-n] bisfurans 6a-6c (1.0 equiv) and bisma-
leimide 9 (1.0 equiv) were dissolved in a minimal quantity of
CHCl3 and heated to 50 °C in open vials. Every 24 h, a fresh
minimal quantity of CHCl3 was added to each vial. At time
intervals aliquots were taken, dissolved in THF, and analyzed by
GPC. To monitor disassembly, each crude polymer mixture of
10a-10c was precipitated from CH2Cl2 and hexanes and heated to
110 °C in TCE (1 mM based on polystyrene-equivalent Mn values).
Aliquots were taken out at time intervals, diluted with THF, and
analyzed by GPC. To monitor reassembly, the same disassembled
polymer samples were concentrated to dryness and dissolved in a
minimal quantity of CHCl3. Every 24 h, a fresh minimal quantity
of CHCl3 was added to each vial. At time intervals aliquots were
taken, dissolved in THF, and analyzed by GPC.
1
white cotton-like solid: mp 162-164 °C. H NMR (500 MHz,
CDCl3): δ 8.08 (s, 2H), 7.97 (s, 2H), 7.39-7.28 (s, 22H), 6.59-
6.56 (m, 6H), 6.34-6.33 (m, 2H), 6.31-6.30 (m, 2H), 5.51 (s,
4H), 5.00 (s, 12H), 4.19 (t, J = 6 Hz, 4H), 2.45 (t, J = 7 Hz, 4H),
2.20-2.10 (m, 4H). 13C NMR (125 MHz, CDCl3): δ 172.4,
160.3, 149.2, 149.1, 143.1, 137.1, 136.4, 128.5, 128.0, 127.4,
123.5, 119.3, 110.8, 110.6, 110.5, 107.0, 102.0, 70.1, 67.8, 58.1,
54.0, 30.8, 24.8. MS (ESI) m/z 1203.4 [M þ Na]þ. Anal. Calcd
for C90H78N8O16: C, 71.17; H, 5.46; N, 7.11. Found: C, 70.91; H,
5.65; N, 7.39.
[G-2] Bisfuran (6b). In a small vial equipped with a stirbar, 4
(100 mg, 0.204 mmol), Cu(PPh3)3Br (38 mg, 0.0410 mmol), 5b
(346 mg, 0.449 mmol), DIEA (132 mg, 1.02 mmol), and CH2Cl2
(3.0 mL) were combined. The mixture was stirred at rt for 48 h,
at which point the solvent was removed under reduced pressure.
The residue was purified by flash chromatography (silica gel,
97:3 CH2Cl2-acetone) to give 6b (390 mg, 94% yield) as an off-
1
white foam: mp 145-148 °C. H NMR (500 MHz, CDCl3): δ
8.06 (s, 2H), 7.92 (s, 2H), 7.41-7.29 (m, 42H), 6.64 (d, J = 2 Hz,
8H), 6.56-6.54 (m, 10H), 6.31-6.30 (m, 2H), 6.27-6.26 (m,
2H), 5.49 (s, 4H), 5.01 (s, 16H), 4.97 (s, 4H), 4.94 (s, 8H), 4.09 (t,
J = 6 Hz, 4H), 2.41 (t, J = 7 Hz, 4H), 2.15-2.05 (m, 4H). 13C
NMR (125 MHz, CDCl3): δ 172.5, 160.3, 160.1, 149.3, 149.1,
143.1, 138.9, 137.2, 136.7, 128.5, 127.9, 127.5, 123.5, 110.9,
110.6, 110.5, 107.2, 106.4, 102.1, 101.7, 70.12, 70.05, 67.8,
58.1, 54.1, 30.9, 29.7, 24.9. MS (MALDI in dithranol) m/z
2030.0 [M þ H]þ. Anal. Calcd for C126H112N6O20: C, 74.54;
H, 5.56; N, 4.14. Found: C, 74.41; H, 5.34; N, 4.11.
[G-3] Bisfuran (6c). In a small vial equipped with a stirbar, 4
(50 mg, 0.102 mmol), Cu(PPh3)3Br (19 mg, 0.0203 mmol), 5c
(362 mg, 0.224 mmol), DIEA (66 mg, 0.510 mmol), and CH2Cl2
(3.0 mL) were combined. The mixture was stirred at rt for 48 h,
at which point the solvent was removed under reduced pressure.
The residue was purified by flash chromatography (silica gel,
98:2 CH2Cl2-acetone) to give 6c (340 mg, 90% yield) as an off-
white foam: mp 62-64 °C. 1H NMR (500 MHz, CDCl3): δ 8.07
(s, 2H), 7.93 (s, 2H), 7.43-7.29 (m, 82H), 6.69 (d, J = 2 Hz,
16H), 6.65-6.64 (m, 8H), 6.58-6.57 (m, 14H), 6.55-6.53 (m,
4H), 6.30-6.29 (m, 2H), 6.26-6.25 (m, 2H), 5.45 (s, 4H),
5.01-4.93 (m, 60H), 4.07 (t, J = 6 Hz, 4H), 2.39 (t, J = 7 Hz,
4H), 2.13-2.05 (m, 4H). 13C NMR (125 MHz, CDCl3): δ 172.5,
160.2, 160.0, 159.9, 149.2, 149.0, 143.1, 139.1, 138.8, 137.1,
136.7, 128.5, 128.31, 128.28, 127.9, 127.6, 127.5, 127.2, 123.5,
119.3, 110.7, 110.6, 110.5, 107.1, 106.3, 102.0, 101.54, 101.49,
Acknowledgment. This work was supported by the United
States Department of Energy (US DOE) under Contract DE-
AC04-94AL85000. Sandia is a multiprogram laboratory oper-
ated by Sandia Corporation, a Lockheed Martin Company, for
the US DOE. Certain trade names and company products are
identified in order to specify experimental procedures adequately.
In no case does such identification imply recommendation or
endorsement by the National Institute of Standards and Tech-
nology, nor does itimply that the productsare necessarily the best
available for the purpose.
Supporting Information Available: 1H NMR spectra of the
assembly of DA adduct 8. This material is available free of