X. Liang, C. Qi / Catalysis Communications 12 (2011) 808–812
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Scheme 1. The synthesis route of the novel ionic liquid.
(400 MHz, D2O, TMS): δ 1.75 (m, 2H), 2.17 (m, 2H), 2.90 (t, JH–H
=
anticipated, all carbonyl compounds were successfully transformed to
the corresponding products. The results in Table 1 clearly demon-
strated that the novel ionic liquid was very efficient, with high yields
for most reactions. Aliphatic aldehydes transformed to the
corresponding acetals smoothly under the reaction conditions
(entries 1–5). The ketalization reactions were also examined under
the same condition. Cyclohexanone worked well with almost
complete conversion and selectivity for less steric hindrance of the
carbonyl group (entries 6–8). The linear ketones such as butanone
owned relatively low activity for the reactions with moderate yields
(entries 9–10). Aromatic aldehyde, such as benzaldehyde could also
be acetalized to afford the corresponding 1,3-acetals with high yields
(entries 11–13). The groups attached to aromatic ring were also very
important for the reactivities. Aromatic aldehydes with electron-
donating groups such as methyl or methoxyl groups showed
relatively low activity, which reduced the reactivity of the carbonyl
groups (entries 14–19). On the other hand, electron-withdrawing
groups enhanced the nucleophilicity and the aromatic aldehydes with
F and nitro groups showed higher activities (entries 20–23). Different
diols such as 1,2-ethanediol, 1,2-propylene glycol and neopentyl
glycol were all transformed to products smoothly. The reactivities
reduced as follows: 1,2-ethanediolN1,2-propylene glycolNneopentyl
glycol for the steric hindrance of the diols.
7.2 Hz, 2H), 4.67 (d, 2H), 7.91 (t, 1H), 8.10 (q, 2H), 8.29 (t, 2H), 8.41 (d,
1H), 9.60 (s, 1H). IR(KBr): 1037 cm−1 and 907 cm−1 (―SO3H),
1166 cm−1 (C―N), and 3409 cm−1 (O–H).
2.2. Acetalization of carbonyl compounds
Acetals were synthesized via the acetalization of carbonyl com-
pounds with diols. In the typical procedure (Scheme 2): carbonyl
compounds (0.1 mol), 10 mL cyclohexane, diols (0.15 mol) and the
catalyst (0.05 g, 0.138 mmol) were mixed together in a three necked
round bottomed flask equipped with a magnetic stirrer and thermom-
eter. Here a Dean–Stark apparatus was used to remove the water
continuously from the reaction mixture. The mixture was refluxed for
the specified time. The progress of the reaction was monitored by GC
analysis of the small aliquots withdrawn. On completion, the catalyst
was recovered by centrifugation, washing with acetone and drying in an
oven at 80 °C for about 1 h.
2.3. Conjugate addition of amines to electron deficient alkenes
Typical procedure for the conjugate addition of amines (Scheme 3)
was shown as follows: A mixture of amine (20 mmol), alkene
(24 mmol) and the catalyst (0.05 g, 0.138 mmol) were stirred at room
temperature for certain time as shown in Table 2. The process of the
reaction was monitored by GC analysis. The reaction mixture was
extracted with ethyl acetate (2×20 ml) and the combined extract was
dried over anhydrous Na2SO4 and evaporated to leave a crude product,
which was separated by column chromatography using neutral alumina
as stationary phase and petroleum ether/ethyl acetate mixture (95: 5)
as eluent to give the corresponding product.
Selected NMR data for the compounds in Table 1
Entry 2 1H NMR (400 MHz, CDCl3, TMS): δ 1.23 (d, 3H), 3.61 (d,
2H), 3.81 (d, 2H), 4.08 (m, 1H), 5.20 (t, JH–H =7.2 Hz, 1H). 13C NMR
(400 MHz, CDCl3, TMS): 18.8, 50.7, 74.6, 75.8, 111.5.
Entry 5 1H NMR (400 MHz, CDCl3, TMS): δ 0.95 (t, JH–H =7.2 Hz,
3H), 1.12 (s, 6H), 1.64 (m, 2H), 3.68 (s, 4H), 4.68 (t, JH–H =7.3 Hz,
1H). 13C NMR (400 MHz, CDCl3, TMS): 4.8, 20.7, 29.6, 31.8, 77.9,
105.5.
Entry 8 1H NMR (400 MHz, CDCl3, TMS): δ 1.11 (s, 6H), 1.44(t, JH–H
=
3. Results and discussions
7.2 Hz, 4H), 3.72 (s, 4H). 13C NMR (400 MHz, CDCl3, TMS): 16.2, 20.1,
29.0, 32.1, 35.6, 75.4.
3.1. Acetalization of carbonyl compounds
Entry 9 1H NMR (400 MHz, CDCl3, TMS): δ 0.97 (t, JH–H=7.2 Hz, 3H),
1.22 (d, 3H), 1.46 (s, 3H), 3.74 (d, 2H), 4.08 (m, 1H). 13C NMR
(400 MHz, CDCl3, TMS): 2.3, 19.2, 23.6, 31.8, 72.3, 74.1, 109.5.
The acetalization of various carbonyl compounds and diols
catalyzed by the novel ionic liquid was performed first (Table 1). As
Scheme 2. Catalytic acetalization of carbonyl compounds.
Scheme 3. Conjugate addition of amines to electron deficient alkenes.