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DOI: 10.1055/s-0028-1087950
Novel l-Tartaric Acid Derived Pyrrolidinium Cations for the Synthesis of Chiral Ionic Liquids
Publication History
Publication Date:
24 February 2009 (online)
Abstract
Novel pyrrolidinium salts based on l-(+)-tartaric acid were designed and synthesized in very good yields with a simple and practical strategy. Twelve new chiral ionic potential task-specific catalysts, two of which are room-temperature chiral ionic liquids (RTCIL), were obtained, and their properties are discussed.
Key words
chiral pool - green solvents - ionic liquid - microwaves - chiral molecular recognition
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References and Notes
(3
R
,4
R
)-1-Benzyl-3,4-dihydroxy-2,5-pyrrolidinedione (13)
Benzylamine (11 mL, 100 mmol)
were added to a 250 mL round-bottom flask containing a suspension
of l-(+)-tartaric acid (15.0 g,
100 mmol) in xylene (80 mL). The mixture was refluxed in a Dean-Stark
apparatus for 4 h, and H2O (3.6 mL, 200 mmol) was collected.
Then the solid was filtered off, washed with acetone, and recrystallized
from EtOH (12.5 g, 57 mmol, 57%).
(3
S
,4
S
)-1-Benzyl-3,4-pyrrolidinediol (14)
To a cooled (0 ˚C)
suspension of LiAlH4 (2.28 g, 60 mmol) in dry THF (100
mL) in a 500 mL round-bottom flask the pyrrolidinedione 13 (4.42 g, 20 mmol) was added portionwise,
and the mixture was heated at reflux for 12 h. The mixture was then
cooled to 0 ˚C, and a sat. solution of Na2SO4 was
added until no gas evolution was observed, then additional anhyd
Na2SO4 was added, and the mixture was filtered
through Celite washing with EtOAc. Evaporation of the solvent yielded
a white solid (1.97 g, 10.2 mmol, 51%). Spectral data were
identical to those reported in the literature, see ref. 9.
This two-step procedure has been reported to give higher yields. However, in our hands, these yields were not reproducible, and we introduced some slight modifications to render the synthesis reliable when extended to a multigram scale.
12
General Procedure
for Quaternization under Conventional Heating
In a
round-bottom flask the pyrrolidinediol 14 and
alkyl or benzyl bromide (1.5 equiv) were suspended in MeCN. The mixture
was heated at 90 ˚C until disappearance of the starting
material (TLC control). The reaction mixture was cooled at 0 ˚C,
and Et2O was added to crystallize the pure product as
a white solid.
General Procedure for
Quaternization under Microwave Heating
In a microwave
reactor, the pyrrolidinediol 14 and alkyl
or benzyl bromide (1.5 equiv) were suspended in MeCN. The reaction
was carried out at 90 ˚C, 150 W for 10 min (TLC control),
then the reaction mixture was cooled to 0 ˚C,
and the pure product crystallizes as a white solid.
Crystal Data for
1
MW = 364.3, trigonal,
space group P31, Z = 3, D
c = 1.46, a = b = 10.686
(1) Å, c = 12.580
(1) Å, α = β = 90˚, γ = 120˚, V = 1244.1
(2) ų. The X-ray CIF file for this structure
has been deposited at the Cambridge Crystallographic Data Centre
(CCDC), deposition number 710820.
Crystal Data for
5
MW = 544.5, orthorhombic,
space group P212121, Z = 4, D
c = 1.37, a = 9.767
(1) Å, b = 9.805
(1) Å, c = 27.605
(1) Å, α = β = γ = 90˚, V = 2643.6
(4) ų. The X-ray CIF file for this
structure has been deposited at the CCDC, deposition number 710821.
Anion Exchange
(Procedure A)
In a round-bottom flask the pyrrolidinium
bromide 1 or 5
(1-5
mmol) were suspended in H2O-EtOAc (1:1), then
the appropriate potassium or lithium salt was added. After 5 min the
two phases became limpid, and the reaction was finished. The organic
phase was separated and dried with anhyd Na2SO4.
Solvent evaporation gave the pure product.
Upon addition of a slight excess of AgNO3 the solution became yellow due to formation of Ag2CrO4.
19Anion Exchange (Procedure B) In a round-bottom flask the pyrrolidinium bromide 9 was suspended in H2O, then the appropriate potassium or lithium salt was added. The mixture was left to react overnight at r.t., and the formation of a pale yellow oil, insoluble in H2O, was observed. Ethyl acetate was then added. The organic phase was separated and dried with anhyd Na2SO4. Solvent evaporation gave the pure product.
20
Data for Ionic
Liquid 8
Pale yellow viscous liquid. ¹H
NMR (400 MHz, CDCl3): δ = 7.47-7.43
(m, 10 H), 7.35-7.32 (m, 6 H), 7.22-7.19 (m, 4 H),
4.73 (A part of an AB system, J = 13.1
Hz, 2 H), 4.63 (B part of an AB system, J = 13.1
Hz, 2 H), 4.46 (A part of an AB system, J = 11.9
Hz, 2 H), 4.42 (B part of an AB system, J = 11.9
Hz, 2 H), 4.24 (br s, 2 H), 3.85 (dd, J = 13.5,
5.6 Hz, 2 H), 3.71 (dd, J = 13.5,
2.6 Hz, 2 H). ¹³C NMR (50 MHz, CDCl3): δ = 135.9
(s, 2 C), 133.3 (d, 4 C), 131.0 (d, 2 C), 129.4 (d, 4 C), 128.5
(d, 4 C), 128.3 (d, 2 C), 127.9 (d, 4 C), 126.6 (s, 2 C), 119.9
(q, 2 C, CF3, J = 319.9
Hz), 80.2 (d, 2 C), 72.3 (t, 2 C), 66.9 (t, 2 C), 60.8 (t, 2 C). ¹9F
NMR (188 MHz, acetone-d
6,): δ = -79.9
(s). IR (CDCl3): 3090 (w), 3068 (m), 3034 (m), 2923 (w),
2872 (w), 2260 (m), 1497 (m), 1456 (s), 1350 (s), 1199 (s), 1134
(s), 1059 (s) cm-¹. MS: m/z (%) = 464
(0.4), 160 (9), 120 (19), 91 (100), 69 (46), 41 (52). Anal. Calcd
for C34H34F6N2O6S2:
C, 54.83; H, 4.60; N, 3.76. Found: C, 54.82; H, 4.86; N, 3.86. [α]D
²³ +0.9
(c 1.00, CH2Cl2).
Data for Ionic
Liquid 12
Pale yellow viscous liquid. ¹H
NMR (400 MHz, CDCl3): δ = 7.51-7.41
(m, 5 H), 4.66-4.53 (m, 4 H), 4.17 (br s, 1 H), 4.09 (dd, J = 13.1,
4.0 Hz, 1 H), 3.98 (br s, 1 H), 3.79 (d, J = 12.8 Hz,
1 H), 3.73 (dd, J = 12.8,
4.0 Hz, 1 H), 3.37 (d, J = 13.1 Hz,
1 H), 3.30-3.15 (m, 2 H), 1.95-1.84 (m, 2 H),
1.32-1.25 (m, 18 H), 0.87 (t, J = 6.8
Hz, 3 H). ¹³C NMR (50 MHz, CDCl3): δ = 132.1
(d, 2 C), 130.9 (d, 1 C), 129.4 (d, 2 C), 127.4 (s, 1 C), 119.5
(q, 2 C, CF3, J = 318.7
Hz), 75.8 (d, 1 C), 75.5 (d, 1 C), 68.6 (t, 1 C), 67.7 (t, 1 C),
66.9 (t, 1 C), 63.8 (t, 1 C), 31.9 (t, 1 C), 29.6 (t, 2 C), 29.5
(t, 1 C), 29.4 (t, 1 C), 29.3 (t, 1 C), 29.0 (t, 1 C), 26.2 (t,
1 C), 23.7 (t, 1 C), 22.8 (t, 1 C), 14.2 (q, 1 C). ¹9F
NMR (188 MHz, acetone-d
6): δ =
-79.8
(s, 6 F). IR (CHCl3): 3507 (m), 3033 (w), 2927 (m), 2855
(w), 1457 (w), 1349 (s), 1192 (s), 1133 (m), 1059 (m) cm-¹.
MS: m/z (%) = 362
(35), 288 (12), 270 (11), 206 (6), 193 (7), 134 (5), 116 (100),
91 (45), 69 (11), 55 (15). Anal. Calcd for C25H40F6N2O6S2:
C, 46.72; H, 6.27; N, 4.36. Found: C, 46.70; H, 6.55; N, 4.35. [α]D
²² -5.1
(c 0.985, MeOH).
Data for Ionic
Liquid 4
Pale yellow solid; mp 50-53 ˚C. ¹H
NMR (200 MHz, CD3OD): δ = 7.63-7.50
(m, 10 H), 4.89 (br s, 2 H), 4.71 (br s, 2 H), 4.32-4.24
(m, 2 H), 3.87 (dd, J = 12.5,
5.1 Hz, 2 H), 3.60 (dd, J = 13.2,
1.5 Hz, 2 H). ¹³C NMR (50 MHz, CDCl3): δ = 133.2
(d, 4 C), 131.1 (d, 2 C), 129.5 (d, 4 C), 127.1 (s, 2 C), 119.6
(q, 2 C, CF3, J = 320.5
Hz), 76.1 (d, 2 C), 67.4 (t, 2 C), 63.3 (t, 2 C). ¹9F
NMR (188 MHz, acetone-d
6): δ =
-79.9
(s). IR (CH2Cl2): 3593 (w), 3502 (m), 3059
(w), 3032 (w), 2923 (w), 1494 (w), 1457 (w), 1351 (s), 1199 (s),
1134 (m), 1060 (m) cm-¹. MS: m/z (%) = 284
(22), 210 (7), 193 (6), 133 (11), 120 (11), 91 (100), 65 (25), 51
(7). Anal. Calcd for C20H22F6N2O6S2:
C, 42.55; H, 3.93; N, 4.96. Found: C, 42.36; H, 4.12; N, 4.95. [α]D
²³ -24.5
(c 1.01, CH2Cl2).