LETTER
Guanidinium Salt Functionalized PEG
3061
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(13) The pentaalkylguanidine 3 was synthesized from 1,3-
dimethylimidazolidin-2-one(1), POCl3 and BuNH2 by the
methods reported in the literature;12b colorless liquid; yield:
71% (lit.12b 85%). 1H NMR (300 MHz, CDCl3): d = 0.91 (t,
J = 14.4 Hz, 3 H, Me), 1.33–1.41 (m, 2 H, CH2), 1.48–1.58
(m, 2 H, CH2), 2.79 (s, 6 H, Me), 3.14 (s, 4 H, NCH2), 3.34
(s, 2 H, CH2).
(14) Procedure for the Synthesis of PEG-Supported
Guanidinium Bromide 4: To a solution of polyethylene
glycol bromide (12 g, 0.002 mol) in toluene (150 mL),
pentaalkylguanidine 3 (3.38 g, 0.02 mol) was added, and the
resulting solution was stirred at 65 °C for 72 h. After the
reaction was completed, the solvent was removed under
reduced pressure, and then anhyd Et2O (40 mL) was added.
The product was precipitated and isolated by filtration, then
washed by anhyd Et2O and dried to obtain the product 4
(94%); white powder; mp 53–55 °C. IR: 1638 (C=N) cm–1.
1H NMR (400 MHz, CDCl3): d = 0.89 (t, J = 14.7 Hz, 6 H,
2 × Me), 1.29–1.36 (m, 4 H, 2 × CH2), 1.62–1.72 (m, 4 H,
2 × CH2), 3.11 (s, 6 H, 2 × Me), 3.60 (m, 4 H, OCH2CH2O).
13C NMR (75 MHz, CDCl3): d = 13.08, 19.13, 31.69, 34.85,
43.08, 49.02, 69.90, 158.72.
(15) Representative Procedure for the Cycloaddition
Reaction of Epoxide with CO2: In a 25-mL inner volume
stainless-steel autoclave equipped with a magnetic stirrer,
isopropyl glycidyl ether (15.8 mmol) and PEG-supported
hexaalkylguanidinium bromide (0.5 mol%) were added, and
CO2 (liquid, 3.0 MPa) was charged into the reactor at r.t. The
initial pressure was generally adjusted to 4 MPa at 110 °C.
The reactor was heated at that temperature for 4 h. After
cooling, the products were separated by adding Et2O and
analyzed by a gas chromatograph (Shimadzu GC-2014)
equipped with a capillary column (RTX-5, 30 m × 0.25 mm)
using a flame ionization detector and the side-products were
detected by GC–MS. All of the products were further
identified using GC–MS by comparing the retention times
and fragmentation patterns with authentic samples. The
structures of the isolated products were also characterized by
1H NMR and 13C NMR spectroscopy. Spectral
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characteristics of cyclic carbonates shown in Table 2 are as
follows:
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4-Methyl-1,3-dioxolan-2-one (6a): 1H NMR (400 MHz,
CDCl3): d = 1.43 (d, J = 6.0 Hz, 3 H, Me), 3.98 (t, J = 8.4 Hz,
1 H, OCH2), 4.51 (t, J = 8.4 Hz, 1 H, OCH2), 4.82 (m, 1 H,
CHO). 13C NMR (100.4 MHz, CDCl3): d = 19.15, 70.53,
73.49, 154.95. 1,3-Dioxolan-2-one (6b): 1H NMR (400
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Synlett 2007, No. 19, 3058–3062 © Thieme Stuttgart · New York