10.1002/cssc.201700241
ChemSusChem
FULL PAPER
By comparing the energy barrier of the both mechanisms, it
can be concluded that the CO2-activated mechanism had a
lower energy barrier in the first step, and thus was more
favorable than the amino-activated mechanism. This suggests
that the formation of ring-shaped carbonate intermediate could
decrease the activation energy for the formation of intermediate
3 , so that the reaction can proceed more easily. This made the
point that the formation of ring-shaped carbonate intermediate
might play an important role in the catalysis of the reaction. As
we known, primary and secondary amines can form ammonium
carbamates with CO2, which are more stable than carbonate.
This will potentially decrease the attack ability of N atom of
propargylic amine on carbamates and have a negative effect on
the reaction. Therefore, the catalytic activity of MEA and DEA for
this carboxylative cyclization reaction is lower than that of
tertiary amines, as shown in Table 1. When the TEOAs have
more hydroxyl groups and smaller steric hindrance, the best
catalytic activity has been found for the reaction among these
tertiary amines (Table 1).
oxazolidinone. The catalyst was recovered by drying under vacuum and
reused in the next run.
Characterization of the products
1H and 13C NMR analyses of the purified products were conducted in
CDCl3 on a Bruker Avance III HD 600 spectrometer (600 MHz for 1H
NMR and 150 MHz for 13C NMR), and the results are consistent with the
previous reported experimental results[15]
.
Compound 2a. Light yellow oil; 1H NMR (600 MHz, CDCl3): δ=7.581 (d,
J = 7.26 Hz, 2 H), 7.326 (t, J = 7.62 Hz, 2 H), 7.203 (t, J =7.44 Hz, 1 H),
5.465 (d, J = 1.74 Hz, 1 H), 4.524 (t, J = 1.8 Hz, 1 H), 3.633-3.582 (m, 1
H), 3.047-3.000 (m, 1 H), 1.886-1.826 (m, 1 H), 1.712−1.655 (m, 1 H),
1.622-1.520 (m, 2 H), 1.417-1.348 (m, 4 H), 0.958 (t, J = 7.32 Hz, 6 H)
ppm; 13C NMR (150 MHz, CDCl3): δ =155.17, 147.00, 133.62, 128.48,
128.28, 126.75, 102.32, 58.40, 41.13, 34.43, 29.26, 19.92, 15.84, 13.91,
13.68 ppm.
Compound 2b. Colorless oil; 1H NMR (600 MHz, CDCl3): δ=7.592 (d, J =
1.2 Hz, 1 H), 7.579 (s, 1 H), 7.341-7.315 (m, 2 H), 7.219-7.194 (m, 1 H),
5.462 (d, J = 1.74 Hz, 1 H), 4.559-4.543 (m, 1H), 3.641-3.590 (m, 1 H),
3.040-2.993 (m, 1 H), 1.962-1.913 (m, 1H), 1.771-1.729 (m, 1 H), 1.629-
1.529 (m, 3 H), 0.959 (t, J = 7.38Hz, 3 H), 0.902 (t, J = 7.32 Hz, 3 H) ppm;
13C NMR (150 MHz, CDCl3): δ= 155.29, 146.61, 133.62, 128.48, 128.28,
126.73, 102.35, 59.00, 41.06, 29.23, 24.90, 19.93, 13.68 ppm.
Compound 2c. Colorless oil; 1H NMR (400 MHz, CDCl3): δ=7.589 (d, J =
7.6 Hz, 2 H), 7.329 (t, J = 7.2 Hz, 2 H), 7.208 (t, J = 7.2Hz, 1 H), 5.476 (d,
J = 2.0 Hz, 1 H), 4.556-4.503 (m, 1 H), 3.583-3.507 (m, 1 H), 3.174-3.104
(m, 1 H), 1.645-1.512 (m, 2 H), 1.475 (d, J = 6.4 Hz, 3 H), 1.400-1.340 (m,
2 H), 0.960 (t, J = 7.2 Hz, 3 H), 0.902 (t, J = 7.32 Hz, 3 H) ppm; 13C NMR
(100 MHz, CDCl3): δ=154.80, 148.60,133.56, 128.49, 128.26, 126.80,
102.08, 54.65, 41.26, 29.36, 19.93, 19.74, 13.71 ppm.
Compound 2d. Colorless oil; 1H NMR (600 MHz, CDCl3): δ=7.591 (d, J =
7.56 Hz, 2 H), 7.328 (t, J = 7.44 Hz, 2 H), 7.210 (t, J =8.76 Hz, 1 H),
5.486 (s, 1 H), 4.306 (s, 1 H), 3.679-3.629 (m, 1 H), 3.075-3.030 (m, 1 H),
2.159-2.126 (m, 1 H), 1.631-1.538 (m, 2 H), 1.375-1.341 (m, 2 H), 1.099
(d, J = 6.96 Hz, 3 H), 0.955 (t, J = 7.26Hz, 3 H), 0.920 (d, J = 6.72 Hz, 3
H) ppm; 13C NMR (150 MHz, CDCl3): δ = 155.35, 145.02, 133.57, 128.47,
126.85, 104.20, 63.71, 41.37, 30.20, 29.18, 19.91, 17.52, 15.44, 13.68
ppm.
Compound 2e. Light yellow oil; 1H NMR (600 MHz, CDCl3): δ =7.594-
7.579 (m, 2 H), 7.335-7.309 (m, 2 H), 7.212-7.184 (m, 1 H), 5.452 (s, 1
H), 3.205 (t, J = 7.92 Hz, 2 H), 1.686-1.634 (m, 2 H), 1.493 (s, 6 H),
1.371-1.334 (m, 2 H), 0.958 (t, J = 7.38 Hz, 3 H)ppm; 13C NMR (150 MHz,
CDCl3): δ = 154.19, 153.51, 133.68, 128.46, 128.28, 126.71, 100.38,
62.17, 40.41, 31.52, 27.61, 20.24, 13.75 ppm.
Compound 2g. Colorless oil; 1H NMR (600 MHz, CDCl3): δ =7.480 (d, J
= 7.8 Hz, 2 H), 7.136 (d, J = 7.8 Hz, 2 H), 5.428 (d, J = 1.2 Hz, 1 H),
4.545-4.530 (m, 1 H), 3.635-3.585 (m, 1 H), 3.032-2.986 (m, 1 H), 2.334
(s, 3 H), 1.949-1.904 (m, 1 H), 1.754-1.712 (m, 1 H), 1.612-1.532 (m, 2
H), 1.398-1.347 (m, 2 H), 0.956 (t, J = 7.2 Hz, 3 H), 0.891 (t, J = 7.2 Hz, 3
H)ppm; 13C NMR (150 MHz, CDCl3): δ =155.44, 145.84, 136.56, 130.79,
129.18, 128.21, 102.29, 58.98, 41.05, 29.24, 24.92, 21.21, 19.94, 13.69,
6.49 ppm.
Compound 2h. Light yellow oil; 1H NMR (600 MHz, CDCl3): δ =7.589 (d,
J = 7.38 Hz, 2 H), 7.326 (t, J = 7.68 Hz, 2 H), 7.204 (t, J =14.82 Hz, 1 H),
5.466 (d, J = 1.68 Hz, 1 H), 4.531-4.516 (m, 1 H), 3.618-3.568 (m, 1 H),
3.042-2.996 (m, 1 H), 1.884-1.825 (m, 1 H), 1.712-1.655 (m, 1 H), 1.638-
1.588 (m, 1 H), 1.449-1.383 (m, 1 H), 1.349-1.310 (m, 7 H), 0.956 (t, J =
7.32 Hz, 3 H), 0.905-0.882 (m, 3H) ppm; 13C NMR (150 MHz, CDCl3): δ =
Conclusions
In summary, among the alkanolamines catalysts
investigated, TEOA was found to display the best catalytic
performance for the reactions of CO2 with propargylic amine,
and a series of desired products were synthesized in good to
excellent yields. Additionally, TEOA could be easily regenerated
and reused without obvious loss in its activity. The mechanistic
studies revealed that CO2 was activated by TEOA to form
unstable ring-shaped carbonate intermediate. This carbonate
intermediate could decrease the activation energy for the
formation of intermediate 3, so that the reaction can proceed
more easily. Considering the fact that TEOA is a cheap,
biodegradable, commercially available and recyclable catalyst,
we expect that more applications can be found for it in the
transformation of CO2 under mild conditions.
Experimental Section
Chemicals
CO2 was supplied by Beijing Analytical Instrument Factory with a purity of
99.999%. The deuterated solvents (DMSO-d6, CDCl3) were provided by
Cambridge Isotope Laboratories, Inc. All chemicals were of analytical
grade and used as received. The propargylic amine substrates were
synthesized by following the procedures described in literature[31]
.
General procedure for the synthesis of α-alkylidene cyclic
carbonates
In a 20 mL Schlenk flask, propargylic amine (1.0 mmol) and the indicated
amount of the catalyst were added. The air in the reactor was replaced
by bubbling of CO2. Then the reaction mixture was stirred at 90 °C for 12
h under the desired CO2 pressure. After the reaction was finished, the
product was extracted with n-hexane, leaving the catalyst alone in the
reactor. The crude mixture was purified by silica gel column
chromatography (EtOAc : petroleum ether = 1:20) to obtain the desired 2-
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