organic compounds
(S)-2-(Iodomethyl)-1-tosylpyrrolidine
aDepartment of Chemistry, State Key Laboratory of Applied Organic Chemstry, College of Chemical Engineering, Lanzhou University, Lanzhou 730000, People's Republic of China
*Correspondence e-mail: pengyu@lzu.edu.cn
In the title molecule, C12H16INO2S, the pyrrolidine ring is in an The dihedral angle between the four essentially coplanar atoms of the pyrrolidine ring and the benzene ring is 75.5 (4)°.
Related literature
For leading reviews, see: Allemann et al. (2004); List (2004); Notz et al. (2004); For related literature, see: Bahmanyar et al. (2003); List et al. (2000); Northrup & MacMillan, (2002); Sakthivel et al. (2001); Barbas et al. (1997); Dalko & Moisan (2004); Eder et al. (1971); Hajos & Parrish (1974); Machajewski & Wong (2000); Seayed & List (2005); Wagner et al. (1995).
Experimental
Crystal data
|
Data collection: SMART (Bruker, 2000); cell SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2000); software used to prepare material for publication: SHELXTL.
Supporting information
https://doi.org/10.1107/S1600536807059223/lh2560sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536807059223/lh2560Isup2.hkl
The title compound was prepared by the cascade reaction of p-toluenesulfonyl chloride with (S)-prolinol (commercial available) and iodine. 1H NMR (400 MHz, CDCl3): 7.73 (d, J = 6.8 Hz, 2H), 7.34 (d, J = 6.8 Hz, 2H), 3.77–3.71 (m, 1H), 3.63–3.60 (m, 1H), 3.51–3.46 (m, 1H), 3.23 (t, J = 9.6 Hz, 2H), 2.44 (s, 3H), 1.90–1.77 (m, 3H), 1.56–1.50 (m, 1H) p.p.m.; 13C NMR (100 MHz, CDCl3): 143.7, 134.2, 129.8 (2 C), 127.5 (2 C), 60.7, 50.0, 31.9, 23.8, 21.5, 11.5 p.p.m.. Single crystals suitable for X-ray determination were obtained by slow evaporation of a EtOAc solution over a period of several days.
All H atoms were placed geometrically (C—H distances were set to 0.98, 0.97, 0.96 and 0.93 A° for atoms CH, CH2, CH3, and CH (phenyl), respectively) and refined with a riding model, with Uiso(H) = 1.2 or 1.5 times Ueq(C).
During the past few years, the field of asymmetric catalysis, previously dominated by biocatalysis, has been complemented by organocatalysis (List, 2004; Notz et al., 2004; Allemann et al., 2004) using small organic molecules as a third powerful tool. Organocatalysis reagents are usually non-toxic, highly efficient and selective, readily available, metal-free and robust, explaining the growing interest in their use for organic synthesis (Dalko & Moisan, 2004; Seayed & List, 2005). Considering the above features, low cost and availability in both enantiomeric forms, proline is attractive especially to synthetic chemists. Developed by two industrial laboratories in the early 1970 s (Hajos & Parrish, 1974; Eder et al., 1971), a proline-catalyzed aldol reaction was reinvestigated recently and many novel results were obtained. For example, direct intermolecular asymmetric aldol reactions between
and the (List et al., 2000; Sakthivel et al., 2001) or (Northrup & MacMillan, 2002) afforded good to excellent The origin of stereoselectivity in this type of aldol reaction was examined in detail (Bahmanyar et al., 2003) and it was generally accepted this involved enamine intermediates. Similar mechanisms are found in type-1 aldolases (Machajewski & Wong, 2000) and catalytic antibodies that are type-1 aldolase mimics (Wagner et al., 1995; Barbas et al., 1997).The molecular structure of the title compound (Fig.1) contains a pyrrolidine ring, which exists in an
The dihedral angle between the plane of atoms N1–C1–C3–C5 and the benzene ring is 75.5 (4) °, which potentially provides enough space as a binding-site for substrates during asymmetric catalysis process.For leading reviews, see: Allemann et al. (2004); List (2004); Notz et al. (2004); For related literature, see: Bahmanyar et al. (2003); List et al. (2000); Northrup & MacMillan, (2002); Sakthivel et al. (2001); Barbas et al. (1997); Dalko & Moisan (2004); Eder et al. (1971); Hajos & Parrish (1974); Machajewski & Wong (2000); Seayed & List (2005); Wagner et al. (1995).
Data collection: SMART (Bruker, 2000); cell
SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXL97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2000); software used to prepare material for publication: SHELXTL (Bruker, 2000).Fig. 1. The molecular structure showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. |
C12H16INO2S | F(000) = 360 |
Mr = 365.22 | Dx = 1.710 Mg m−3 |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2yb | Cell parameters from 1240 reflections |
a = 7.6345 (16) Å | θ = 3.1–21.5° |
b = 7.7084 (16) Å | µ = 2.40 mm−1 |
c = 12.071 (3) Å | T = 294 K |
β = 93.17 (1)° | Block, colorless |
V = 709.3 (3) Å3 | 0.25 × 0.16 × 0.16 mm |
Z = 2 |
Bruker APEX CCD area-detector diffractometer | 2424 independent reflections |
Radiation source: fine-focus sealed tube | 1787 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.033 |
φ and ω scans | θmax = 27.9°, θmin = 1.7° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −9→9 |
Tmin = 0.586, Tmax = 0.701 | k = −6→9 |
4398 measured reflections | l = −15→15 |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.037 | w = 1/[σ2(Fo2) + (0.0387P)2 + 0.1584P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.092 | (Δ/σ)max = 0.001 |
S = 1.02 | Δρmax = 0.43 e Å−3 |
2424 reflections | Δρmin = −0.48 e Å−3 |
156 parameters | Extinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
1 restraint | Extinction coefficient: 0.0027 (10) |
Primary atom site location: structure-invariant direct methods | Absolute structure: Flack (1983), 664 Friedel pairs |
Secondary atom site location: difference Fourier map | Absolute structure parameter: 0.02 (5) |
C12H16INO2S | V = 709.3 (3) Å3 |
Mr = 365.22 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 7.6345 (16) Å | µ = 2.40 mm−1 |
b = 7.7084 (16) Å | T = 294 K |
c = 12.071 (3) Å | 0.25 × 0.16 × 0.16 mm |
β = 93.17 (1)° |
Bruker APEX CCD area-detector diffractometer | 2424 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 1787 reflections with I > 2σ(I) |
Tmin = 0.586, Tmax = 0.701 | Rint = 0.033 |
4398 measured reflections |
R[F2 > 2σ(F2)] = 0.037 | H-atom parameters constrained |
wR(F2) = 0.092 | Δρmax = 0.43 e Å−3 |
S = 1.02 | Δρmin = −0.48 e Å−3 |
2424 reflections | Absolute structure: Flack (1983), 664 Friedel pairs |
156 parameters | Absolute structure parameter: 0.02 (5) |
1 restraint |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
I1 | 0.74117 (5) | 1.0996 (2) | 0.25200 (3) | 0.0737 (2) | |
S1 | 0.26704 (16) | 0.6075 (3) | 0.31530 (11) | 0.0533 (3) | |
O2 | 0.4219 (6) | 0.5601 (6) | 0.2627 (4) | 0.0703 (15) | |
C2 | 0.3980 (7) | 0.9338 (7) | 0.3147 (5) | 0.0492 (14) | |
H2 | 0.3790 | 0.9188 | 0.2343 | 0.059* | |
C1 | 0.5919 (8) | 0.9208 (9) | 0.3477 (5) | 0.0572 (16) | |
H1A | 0.6320 | 0.8033 | 0.3355 | 0.069* | |
H1B | 0.6108 | 0.9470 | 0.4260 | 0.069* | |
C3 | 0.3090 (8) | 1.0976 (12) | 0.3511 (5) | 0.0749 (17) | |
H3A | 0.2155 | 1.1311 | 0.2977 | 0.090* | |
H3B | 0.3925 | 1.1922 | 0.3594 | 0.090* | |
C5 | 0.1722 (9) | 0.8691 (9) | 0.4444 (5) | 0.0579 (16) | |
H5A | 0.1685 | 0.8074 | 0.5143 | 0.069* | |
H5B | 0.0566 | 0.8668 | 0.4068 | 0.069* | |
C4 | 0.2361 (10) | 1.0518 (9) | 0.4619 (6) | 0.074 (2) | |
H4A | 0.3265 | 1.0578 | 0.5214 | 0.089* | |
H4B | 0.1406 | 1.1287 | 0.4788 | 0.089* | |
N1 | 0.3058 (6) | 0.7944 (6) | 0.3740 (4) | 0.0484 (11) | |
O1 | 0.1979 (6) | 0.4989 (6) | 0.3981 (4) | 0.0676 (12) | |
C6 | −0.0698 (7) | 0.5882 (12) | 0.2289 (4) | 0.0566 (15) | |
H6 | −0.0957 | 0.5381 | 0.2962 | 0.068* | |
C7 | 0.1002 (8) | 0.6359 (9) | 0.2101 (4) | 0.0491 (18) | |
C9 | −0.0007 (11) | 0.7369 (10) | 0.0301 (5) | 0.073 (2) | |
H9 | 0.0235 | 0.7888 | −0.0369 | 0.088* | |
C11 | −0.2011 (7) | 0.6151 (13) | 0.1476 (5) | 0.0652 (16) | |
H11 | −0.3147 | 0.5799 | 0.1605 | 0.078* | |
C10 | −0.1693 (9) | 0.6917 (9) | 0.0491 (5) | 0.0614 (17) | |
C8 | 0.1366 (10) | 0.7067 (9) | 0.1096 (5) | 0.0651 (19) | |
H8 | 0.2514 | 0.7343 | 0.0944 | 0.078* | |
C12 | −0.3186 (12) | 0.7276 (15) | −0.0368 (7) | 0.107 (3) | |
H12A | −0.3545 | 0.8465 | −0.0315 | 0.160* | |
H12B | −0.4160 | 0.6532 | −0.0233 | 0.160* | |
H12C | −0.2795 | 0.7057 | −0.1097 | 0.160* |
U11 | U22 | U33 | U12 | U13 | U23 | |
I1 | 0.0663 (3) | 0.0651 (3) | 0.0898 (3) | −0.0125 (3) | 0.00491 (18) | 0.0064 (3) |
S1 | 0.0550 (7) | 0.0350 (7) | 0.0701 (8) | 0.0009 (11) | 0.0039 (6) | −0.0016 (12) |
O2 | 0.062 (2) | 0.042 (4) | 0.107 (3) | 0.006 (2) | 0.007 (2) | −0.016 (2) |
C2 | 0.060 (4) | 0.032 (3) | 0.056 (3) | 0.001 (3) | 0.000 (3) | 0.003 (3) |
C1 | 0.062 (4) | 0.047 (4) | 0.062 (4) | −0.006 (3) | −0.002 (3) | 0.002 (3) |
C3 | 0.079 (4) | 0.036 (3) | 0.111 (5) | −0.002 (5) | 0.020 (3) | 0.004 (6) |
C5 | 0.067 (4) | 0.050 (4) | 0.058 (4) | 0.002 (3) | 0.009 (3) | −0.005 (3) |
C4 | 0.082 (5) | 0.050 (5) | 0.094 (5) | 0.000 (3) | 0.022 (4) | −0.025 (4) |
N1 | 0.052 (3) | 0.035 (3) | 0.058 (3) | 0.000 (2) | 0.003 (2) | −0.002 (2) |
O1 | 0.084 (3) | 0.042 (3) | 0.076 (3) | −0.006 (2) | −0.004 (2) | 0.016 (2) |
C6 | 0.064 (3) | 0.055 (4) | 0.052 (3) | −0.013 (4) | 0.014 (2) | −0.010 (4) |
C7 | 0.062 (3) | 0.036 (5) | 0.050 (3) | −0.006 (3) | 0.013 (2) | −0.004 (3) |
C9 | 0.109 (6) | 0.070 (5) | 0.042 (4) | −0.012 (4) | 0.007 (4) | −0.002 (3) |
C11 | 0.059 (3) | 0.067 (5) | 0.070 (4) | 0.004 (5) | 0.011 (3) | −0.012 (5) |
C10 | 0.075 (4) | 0.056 (4) | 0.053 (4) | −0.002 (3) | −0.002 (3) | −0.012 (3) |
C8 | 0.074 (4) | 0.063 (5) | 0.061 (4) | −0.024 (4) | 0.021 (3) | −0.005 (3) |
C12 | 0.110 (7) | 0.118 (8) | 0.089 (6) | −0.007 (6) | −0.028 (5) | −0.001 (5) |
I1—C1 | 2.163 (6) | C5—H5B | 0.9700 |
S1—O2 | 1.420 (4) | C4—H4A | 0.9700 |
S1—O1 | 1.427 (4) | C4—H4B | 0.9700 |
S1—N1 | 1.625 (5) | C6—C11 | 1.379 (8) |
S1—C7 | 1.762 (6) | C6—C7 | 1.380 (8) |
C2—N1 | 1.490 (7) | C6—H6 | 0.9300 |
C2—C3 | 1.511 (10) | C7—C8 | 1.372 (8) |
C2—C1 | 1.515 (8) | C9—C10 | 1.366 (10) |
C2—H2 | 0.9800 | C9—C8 | 1.401 (10) |
C1—H1A | 0.9700 | C9—H9 | 0.9300 |
C1—H1B | 0.9700 | C11—C10 | 1.361 (9) |
C3—C4 | 1.518 (9) | C11—H11 | 0.9300 |
C3—H3A | 0.9700 | C10—C12 | 1.523 (10) |
C3—H3B | 0.9700 | C8—H8 | 0.9300 |
C5—N1 | 1.480 (7) | C12—H12A | 0.9600 |
C5—C4 | 1.502 (9) | C12—H12B | 0.9600 |
C5—H5A | 0.9700 | C12—H12C | 0.9600 |
O2—S1—O1 | 120.8 (3) | C3—C4—H4A | 111.1 |
O2—S1—N1 | 106.7 (3) | C5—C4—H4B | 111.1 |
O1—S1—N1 | 106.3 (3) | C3—C4—H4B | 111.1 |
O2—S1—C7 | 107.2 (3) | H4A—C4—H4B | 109.1 |
O1—S1—C7 | 107.3 (3) | C5—N1—C2 | 110.8 (4) |
N1—S1—C7 | 108.1 (3) | C5—N1—S1 | 118.7 (4) |
N1—C2—C3 | 103.3 (5) | C2—N1—S1 | 120.6 (4) |
N1—C2—C1 | 107.9 (5) | C11—C6—C7 | 119.7 (6) |
C3—C2—C1 | 115.3 (5) | C11—C6—H6 | 120.1 |
N1—C2—H2 | 110.0 | C7—C6—H6 | 120.1 |
C3—C2—H2 | 110.0 | C8—C7—C6 | 119.3 (6) |
C1—C2—H2 | 110.0 | C8—C7—S1 | 120.8 (5) |
C2—C1—I1 | 110.7 (4) | C6—C7—S1 | 119.8 (4) |
C2—C1—H1A | 109.5 | C10—C9—C8 | 121.2 (6) |
I1—C1—H1A | 109.5 | C10—C9—H9 | 119.4 |
C2—C1—H1B | 109.5 | C8—C9—H9 | 119.4 |
I1—C1—H1B | 109.5 | C10—C11—C6 | 122.0 (6) |
H1A—C1—H1B | 108.1 | C10—C11—H11 | 119.0 |
C2—C3—C4 | 104.8 (6) | C6—C11—H11 | 119.0 |
C2—C3—H3A | 110.8 | C11—C10—C9 | 118.2 (6) |
C4—C3—H3A | 110.8 | C11—C10—C12 | 120.7 (7) |
C2—C3—H3B | 110.8 | C9—C10—C12 | 121.1 (7) |
C4—C3—H3B | 110.8 | C7—C8—C9 | 119.4 (6) |
H3A—C3—H3B | 108.9 | C7—C8—H8 | 120.3 |
N1—C5—C4 | 102.5 (5) | C9—C8—H8 | 120.3 |
N1—C5—H5A | 111.3 | C10—C12—H12A | 109.5 |
C4—C5—H5A | 111.3 | C10—C12—H12B | 109.5 |
N1—C5—H5B | 111.3 | H12A—C12—H12B | 109.5 |
C4—C5—H5B | 111.3 | C10—C12—H12C | 109.5 |
H5A—C5—H5B | 109.2 | H12A—C12—H12C | 109.5 |
C5—C4—C3 | 103.1 (6) | H12B—C12—H12C | 109.5 |
C5—C4—H4A | 111.1 | ||
N1—C2—C1—I1 | 173.7 (4) | C7—S1—N1—C2 | −72.0 (5) |
C3—C2—C1—I1 | −71.5 (6) | C11—C6—C7—C8 | −1.2 (12) |
N1—C2—C3—C4 | 24.5 (7) | C11—C6—C7—S1 | 178.1 (7) |
C1—C2—C3—C4 | −92.9 (7) | O2—S1—C7—C8 | −36.5 (7) |
N1—C5—C4—C3 | 36.7 (7) | O1—S1—C7—C8 | −167.6 (6) |
C2—C3—C4—C5 | −38.7 (7) | N1—S1—C7—C8 | 78.2 (6) |
C4—C5—N1—C2 | −22.3 (7) | O2—S1—C7—C6 | 144.1 (6) |
C4—C5—N1—S1 | −168.3 (5) | O1—S1—C7—C6 | 13.0 (7) |
C3—C2—N1—C5 | −1.4 (6) | N1—S1—C7—C6 | −101.2 (7) |
C1—C2—N1—C5 | 121.1 (5) | C7—C6—C11—C10 | −1.5 (14) |
C3—C2—N1—S1 | 143.9 (4) | C6—C11—C10—C9 | 2.3 (13) |
C1—C2—N1—S1 | −93.6 (5) | C6—C11—C10—C12 | −177.0 (8) |
O2—S1—N1—C5 | −174.4 (4) | C8—C9—C10—C11 | −0.3 (11) |
O1—S1—N1—C5 | −44.3 (5) | C8—C9—C10—C12 | 179.0 (7) |
C7—S1—N1—C5 | 70.6 (5) | C6—C7—C8—C9 | 3.1 (11) |
O2—S1—N1—C2 | 43.0 (5) | S1—C7—C8—C9 | −176.3 (5) |
O1—S1—N1—C2 | 173.1 (4) | C10—C9—C8—C7 | −2.4 (11) |
Experimental details
Crystal data | |
Chemical formula | C12H16INO2S |
Mr | 365.22 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 294 |
a, b, c (Å) | 7.6345 (16), 7.7084 (16), 12.071 (3) |
β (°) | 93.17 (1) |
V (Å3) | 709.3 (3) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 2.40 |
Crystal size (mm) | 0.25 × 0.16 × 0.16 |
Data collection | |
Diffractometer | Bruker APEX CCD area-detector |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.586, 0.701 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4398, 2424, 1787 |
Rint | 0.033 |
(sin θ/λ)max (Å−1) | 0.658 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.037, 0.092, 1.02 |
No. of reflections | 2424 |
No. of parameters | 156 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.43, −0.48 |
Absolute structure | Flack (1983), 664 Friedel pairs |
Absolute structure parameter | 0.02 (5) |
Computer programs: SMART (Bruker, 2000), SAINT (Bruker, 2000), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 2000).
Acknowledgements
We acknowledge financial support from the Research Fund for the new faculty at the State Key Laboratory of Applied Organic Chemistry.
References
Allemann, C., Gordillo, R., Clemente, F. R., Cheong, P. H. & Houk, K. N. (2004). Acc. Chem. Res. 37, 558–569. Web of Science CrossRef PubMed CAS Google Scholar
Bahmanyar, S., Houk, K. N., Martin, H. J. & List, B. (2003). J. Am. Chem. Soc. 125, 2475–2479. Web of Science CrossRef PubMed CAS Google Scholar
Barbas, C. F. III, Heine, A., Zhong, G., Hoffmann, T., Gramatikova, S., Björnestedt, R., List, B., Anderson, J., Stura, E. A., Wilson, I. A. & Lerner, R. A. (1997). Science, 278, 2085–2092. CrossRef CAS PubMed Web of Science Google Scholar
Bruker (2000). SMART, SAINT, SADABS and SHELXTL. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Dalko, P. L. & Moisan, L. (2004). Angew. Chem. Int. Ed. 43, 5138–5175. Web of Science CrossRef CAS Google Scholar
Eder, U., Sauer, G. & Wiechert, R. (1971). Angew. Chem. Int. Ed. Engl. 10, 496–497. CrossRef CAS Web of Science Google Scholar
Flack, H. D. (1983). Acta Cryst. A39, 876–881. CrossRef CAS Web of Science IUCr Journals Google Scholar
Hajos, Z. G. & Parrish, D. R. (1974). J. Org. Chem. 39, 1615–1621. CrossRef CAS Web of Science Google Scholar
List, B. (2004). Acc. Chem. Res. 37, 548–557. Web of Science CrossRef PubMed CAS Google Scholar
List, B., Lerner, R. A. & Barbas, C. F. III (2000). J. Am. Chem. Soc. 122, 2395–2396. Web of Science CrossRef CAS Google Scholar
Machajewski, T. D. & Wong, C.-H. (2000). Angew. Chem. Int. Ed. 39, 1352–1374. CrossRef CAS Google Scholar
Northrup, A. B. & MacMillan, D. W. C. (2002). J. Am. Chem. Soc. 124, 6798–6799. Web of Science CrossRef PubMed CAS Google Scholar
Notz, W., Tanaka, F. & Barbas, C. F. III (2004). Acc. Chem. Res. 37, 580–591. Web of Science CrossRef PubMed CAS Google Scholar
Sakthivel, K., Notz, W., Bui, T. & Barbas, C. F. III (2001). J. Am. Chem. Soc. 123, 5260–5267. Web of Science CrossRef PubMed CAS Google Scholar
Seayed, J. & List, B. (2005). Org. Biomol. Chem. 3, 719–724. Web of Science PubMed Google Scholar
Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany. Google Scholar
Wagner, J., Lerner, R. A. & Barbas, C. F. III (1995). Science, 270, 1797–1800. CrossRef CAS PubMed Web of Science Google Scholar
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During the past few years, the field of asymmetric catalysis, previously dominated by biocatalysis, has been complemented by organocatalysis (List, 2004; Notz et al., 2004; Allemann et al., 2004) using small organic molecules as a third powerful tool. Organocatalysis reagents are usually non-toxic, highly efficient and selective, readily available, metal-free and robust, explaining the growing interest in their use for organic synthesis (Dalko & Moisan, 2004; Seayed & List, 2005). Considering the above features, low cost and availability in both enantiomeric forms, proline is attractive especially to synthetic chemists. Developed by two industrial laboratories in the early 1970 s (Hajos & Parrish, 1974; Eder et al., 1971), a proline-catalyzed aldol reaction was reinvestigated recently and many novel results were obtained. For example, direct intermolecular asymmetric aldol reactions between aldehydes and the ketones (List et al., 2000; Sakthivel et al., 2001) or aldehydes (Northrup & MacMillan, 2002) afforded good to excellent enantioselectivity. The origin of stereoselectivity in this type of aldol reaction was examined in detail (Bahmanyar et al., 2003) and it was generally accepted this involved enamine intermediates. Similar mechanisms are found in type-1 aldolases (Machajewski & Wong, 2000) and catalytic antibodies that are type-1 aldolase mimics (Wagner et al., 1995; Barbas et al., 1997).
The molecular structure of the title compound (Fig.1) contains a pyrrolidine ring, which exists in an envelope conformation. The dihedral angle between the plane of atoms N1–C1–C3–C5 and the benzene ring is 75.5 (4) °, which potentially provides enough space as a binding-site for substrates during asymmetric catalysis process.