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Acta Cryst. (2008). E64, o1933    [ doi:10.1107/S1600536808028717 ]

(2S)-Ethyl 2-[(Ss)-benzylsulfinylamino]-3,3-dimethylbutanoate

W. Zheng, X. Sun, J. Sun and B.-G. Wei

Abstract top

The title compound, C15H23NO3S, is an unexpected 1,3-migration product in the addition of benzylzinc bromide to N-tert-butanesulfinyl iminoacetate. In the crystal structure, molecules are linked by N-H...O hydrogen bonds and weak C-H...O hydrogen bonds.

Comment top

N-tert-Butanesulfinylamide has received considerable attention in the auxiliary-aided asymmetric synthesis of a broad range of chiral amines (Ellman et al., 2002; Stockman et al., 2006; Lin et al., 2008). In our research on the asymmetric addition of organozinc reagents to chiral N-tert-butanesulfinyl iminoacetates, an unexpected rearrangement product was obtained instead of the desired nucleophilic addition product. The structure of the compound obtained by 1,3-migration of the tert-butyl group was determined to be (2S)-ethyl 3,3-dimethyl-2-((Ss)-benzylsulfinylamino)butanoate. The reaction sequence (Sun et al., 2008) is briefly shown in Fig. 4. The absolute configuration at the sulfur atom (as determined by the Flack parameter) is S as in the starting material. The new chiral center at C1 also exhibits an S-configuration. We believe this unusual rearrangement reaction could be developed to be a novel and convenient approach to prepare tert-leucine.

The crystal packing in the title compound is stabilized by an intramolecular hydrogen interaction (C7—H7B···O1) and by two intermolecular hydrogen bonds (N1—H1A···O3i and C9—H9B···O3i, symmetry operator: (i) -x, y-1/2, -z+1) which lead to the formation of an one-dimensional hydrogen bonded chain along the b axis as shown in Fig. 3.

Related literature top

For related literature, see: Ellman et al. (2002); Lin et al. (2008); Sun et al. (2008); Daniel & Stockman (2006).

Experimental top

To a solution of ethyl N-(tert-butanesulfinyl)iminoacetate (1 mmol) and Ni(acac)2 (10 mol%) in anhydrous THF (10 ml) was added freshly prepared benzylzinc bromide (2.5 ml, 1 M in THF) at 195 K under an argon atmosphere. Then the mixture was allowed to warm to room temperature. After stirring for another 6 h, the reaction was quenched with saturated aqueous NH4Cl (4 ml). The mixture was extracted with EtOAc (10 ml) twice. The combined organic phases were washed with brine and dried with anhydrous Na2SO4. After concentrating under reduced pressure, the residue was purified by silica gel chromatography to give the title compound (yield: 47%). Suitable crystals were obtained by recrystallization from acetone (m.p. 421–423 K). [α]D25 132.2 (c = 0.60, CHCl3). 1H NMR (δ, CDCl3) 7.31-7.42 (m, 5H), 4.33 (d, J = 9.0, 1H), 4.12-4.20 (m, 2H), 4.03 (s, 2H), 3.48 (d, J = 9.0, 1H), 1.24 (t, J = 7.0, 3H), 0.83 (s, 9H). HRMS for (C15H23NO3S) found 289.1469, Calcd 289.1477.

Refinement top

Hydrogen atoms bonded to carbon were generated geometrically (C—H = 0.93, 0.98, 0.97 or 0.96 Å for phenyl, tertiary, methylene or methyl H atoms respectively) and refined in the riding model approximation. The hydrogen atom bound to the N atom was located from a difference density Fourier map, was refined isotropically and the N—H distance was restrained to 0.86 (2) Å. The displacement parameters of methyl H atoms were set to 1.5 times Ueq of the equivalent isotropic displacement parameters of their parent atoms, while those of other H atoms bound to C were set to 1.2 times Ueq.

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SMART (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Plot of C15H23NO3S with 50% probability levels. H atoms are drawn as spheres of arbitrary radius.
[Figure 2] Fig. 2. Hydrogen bonding in the title compound. Symmetry code: (i) -x, y-1/2, -z+1.
[Figure 3] Fig. 3. Molecular packing plot showing the one-dimensional polymeric chains of the title compound. Hydrogen bond interactions are shown as dashed lines.
[Figure 4] Fig. 4. Reaction sequence.
(2S)-Ethyl 2-[(Ss)-benzylsulfinylamino]-3,3-dimethylbutanoate top
Crystal data top
C15H23NO3SF(000) = 320
Mr = 297.40Dx = 1.189 Mg m−3
Monoclinic, P21Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ybCell parameters from 1845 reflections
a = 11.166 (2) Åθ = 3.4–23.9°
b = 7.1917 (14) ŵ = 0.20 mm−1
c = 11.460 (2) ÅT = 293 K
β = 115.473 (3)°Prismatic, colorless
V = 830.8 (3) Å30.49 × 0.41 × 0.17 mm
Z = 2
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer		3221 independent reflections
Radiation source: fine-focus sealed tube2661 reflections with I > 2σ(I)
graphiteRint = 0.120
φ and ω scansθmax = 27.0°, θmin = 2.0°
Absorption correction: multi-scan
(SADABS; Bruker, 2001)		h = −11→14
Tmin = 0.908, Tmax = 0.967k = −8→9
4782 measured reflectionsl = −14→13
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.055H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.134 w = 1/[σ2(Fo2) + (0.0662P)2]
where P = (Fo2 + 2Fc2)/3
S = 0.97(Δ/σ)max = 0.001
3221 reflectionsΔρmax = 0.43 e Å−3
189 parametersΔρmin = −0.23 e Å−3
2 restraintsAbsolute structure: Flack (1983), 1295 Friedel pairs
Primary atom site location: structure-invariant direct methodsFlack parameter: −0.09 (11)
Crystal data top
C15H23NO3SV = 830.8 (3) Å3
Mr = 297.40Z = 2
Monoclinic, P21Mo Kα radiation
a = 11.166 (2) ŵ = 0.20 mm−1
b = 7.1917 (14) ÅT = 293 K
c = 11.460 (2) Å0.49 × 0.41 × 0.17 mm
β = 115.473 (3)°
Data collection top
Bruker SMART APEX CCD area-detector
diffractometer		3221 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2001)		2661 reflections with I > 2σ(I)
Tmin = 0.908, Tmax = 0.967Rint = 0.120
4782 measured reflectionsθmax = 27.0°
Refinement top
R[F2 > 2σ(F2)] = 0.055H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.134Δρmax = 0.43 e Å−3
S = 0.97Δρmin = −0.23 e Å−3
3221 reflectionsAbsolute structure: Flack (1983), 1295 Friedel pairs
189 parametersFlack parameter: −0.09 (11)
2 restraints
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
S10.04167 (7)0.26178 (12)0.67424 (6)0.0442 (2)
O10.3061 (3)0.0339 (4)0.5596 (3)0.0741 (8)
O20.4124 (3)0.2630 (5)0.6946 (2)0.0696 (7)
O30.0313 (3)0.3869 (4)0.5670 (2)0.0665 (7)
N10.1252 (2)0.0717 (4)0.6804 (2)0.0420 (6)
C10.2690 (3)0.0814 (4)0.7500 (3)0.0397 (6)
H10.29010.18730.80940.048*
C20.3305 (3)0.1206 (5)0.6568 (3)0.0501 (8)
C30.4801 (5)0.3093 (8)0.6131 (5)0.0923 (17)
H3A0.53480.20580.61080.111*
H3B0.41550.33530.52550.111*
C40.5613 (6)0.4705 (9)0.6677 (5)0.108 (2)
H4A0.50560.57750.65470.162*
H4B0.61890.49000.62630.162*
H4C0.61360.45160.75860.162*
C50.3281 (3)−0.0954 (5)0.8332 (3)0.0478 (7)
C60.4791 (4)−0.0865 (6)0.8887 (4)0.0681 (10)
H6A0.5167−0.19120.94450.102*
H6B0.50990.02640.93710.102*
H6C0.5057−0.08920.81940.102*
C70.2792 (4)−0.2720 (5)0.7539 (4)0.0649 (10)
H7A0.3185−0.37810.80760.097*
H7B0.3039−0.27020.68330.097*
H7C0.1844−0.27910.72060.097*
C80.2833 (4)−0.0948 (6)0.9414 (3)0.0653 (10)
H8A0.1882−0.09090.90480.098*
H8B0.31910.01240.99520.098*
H8C0.3145−0.20550.99240.098*
C9−0.1205 (3)0.1504 (5)0.6172 (3)0.0513 (8)
H9A−0.18800.24550.59750.062*
H9B−0.13840.08340.53800.062*
C10−0.1293 (3)0.0198 (5)0.7130 (3)0.0494 (8)
C11−0.1140 (4)−0.1679 (6)0.7036 (4)0.0664 (10)
H11−0.1014−0.21450.63400.080*
C12−0.1169 (5)−0.2890 (6)0.7960 (5)0.0895 (15)
H12−0.1062−0.41610.78850.107*
C13−0.1357 (5)−0.2210 (10)0.8991 (5)0.0940 (15)
H13−0.1374−0.30230.96150.113*
C14−0.1515 (5)−0.0390 (8)0.9098 (5)0.0903 (16)
H14−0.16510.00560.97940.108*
C15−0.1479 (4)0.0835 (6)0.8193 (4)0.0702 (11)
H15−0.15790.21010.82890.084*
H1A0.102 (3)0.001 (3)0.614 (2)0.049 (7)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0470 (4)0.0432 (4)0.0420 (3)0.0052 (4)0.0189 (3)0.0057 (4)
O10.0850 (19)0.095 (2)0.0564 (14)−0.0256 (17)0.0441 (13)−0.0240 (15)
O20.0750 (16)0.0817 (16)0.0677 (13)−0.0294 (18)0.0455 (12)−0.0137 (18)
O30.0640 (16)0.0639 (16)0.0641 (15)0.0019 (13)0.0206 (12)0.0255 (13)
N10.0404 (14)0.0454 (15)0.0379 (12)−0.0008 (11)0.0146 (11)−0.0041 (11)
C10.0383 (15)0.0425 (17)0.0387 (14)−0.0046 (13)0.0168 (12)−0.0055 (13)
C20.0424 (17)0.060 (2)0.0489 (18)−0.0037 (16)0.0205 (14)−0.0013 (16)
C30.098 (4)0.119 (5)0.086 (3)−0.040 (3)0.065 (3)−0.019 (3)
C40.105 (4)0.132 (5)0.112 (4)−0.035 (4)0.070 (3)0.001 (3)
C50.0499 (18)0.0452 (17)0.0415 (16)0.0018 (15)0.0132 (13)−0.0001 (14)
C60.048 (2)0.073 (2)0.064 (2)0.0088 (19)0.0065 (17)0.002 (2)
C70.067 (2)0.048 (3)0.067 (2)0.0015 (18)0.0159 (17)−0.0079 (17)
C80.080 (3)0.067 (2)0.0490 (19)0.004 (2)0.0276 (18)0.0121 (18)
C90.0421 (17)0.065 (2)0.0451 (16)0.0087 (16)0.0174 (14)0.0066 (15)
C100.0369 (17)0.059 (2)0.0522 (18)−0.0030 (14)0.0190 (14)0.0005 (15)
C110.062 (2)0.070 (3)0.064 (2)−0.0145 (19)0.0243 (18)−0.0035 (18)
C120.092 (4)0.058 (3)0.113 (4)−0.018 (2)0.038 (3)0.011 (2)
C130.086 (3)0.108 (4)0.094 (3)−0.021 (4)0.044 (2)0.033 (4)
C140.095 (4)0.121 (5)0.077 (3)−0.006 (3)0.057 (3)0.012 (3)
C150.074 (3)0.075 (3)0.074 (2)−0.001 (2)0.043 (2)−0.002 (2)
Geometric parameters (Å, °) top
S1—O31.487 (2)C6—H6C0.9600
S1—N11.639 (3)C7—H7A0.9600
S1—C91.824 (4)C7—H7B0.9600
O1—C21.201 (4)C7—H7C0.9600
O2—C21.316 (4)C8—H8A0.9600
O2—C31.471 (4)C8—H8B0.9600
N1—C11.455 (4)C8—H8C0.9600
N1—H1A0.859 (17)C9—C101.480 (5)
C1—C21.523 (4)C9—H9A0.9700
C1—C51.555 (4)C9—H9B0.9700
C1—H10.9800C10—C111.371 (5)
C3—C41.439 (7)C10—C151.398 (5)
C3—H3A0.9700C11—C121.382 (6)
C3—H3B0.9700C11—H110.9300
C4—H4A0.9600C12—C131.375 (7)
C4—H4B0.9600C12—H120.9300
C4—H4C0.9600C13—C141.334 (8)
C5—C71.520 (5)C13—H130.9300
C5—C81.524 (5)C14—C151.374 (6)
C5—C61.526 (5)C14—H140.9300
C6—H6A0.9600C15—H150.9300
C6—H6B0.9600
O3—S1—N1112.37 (15)H6A—C6—H6C109.5
O3—S1—C9104.90 (15)H6B—C6—H6C109.5
N1—S1—C996.19 (15)C5—C7—H7A109.5
C2—O2—C3116.2 (3)C5—C7—H7B109.5
C1—N1—S1117.2 (2)H7A—C7—H7B109.5
C1—N1—H1A111.1 (19)C5—C7—H7C109.5
S1—N1—H1A120.2 (19)H7A—C7—H7C109.5
N1—C1—C2110.4 (2)H7B—C7—H7C109.5
N1—C1—C5111.9 (2)C5—C8—H8A109.5
C2—C1—C5112.4 (3)C5—C8—H8B109.5
N1—C1—H1107.3H8A—C8—H8B109.5
C2—C1—H1107.3C5—C8—H8C109.5
C5—C1—H1107.3H8A—C8—H8C109.5
O1—C2—O2123.9 (3)H8B—C8—H8C109.5
O1—C2—C1124.3 (3)C10—C9—S1112.7 (2)
O2—C2—C1111.8 (3)C10—C9—H9A109.1
C4—C3—O2107.8 (4)S1—C9—H9A109.1
C4—C3—H3A110.1C10—C9—H9B109.1
O2—C3—H3A110.1S1—C9—H9B109.1
C4—C3—H3B110.1H9A—C9—H9B107.8
O2—C3—H3B110.1C11—C10—C15117.5 (4)
H3A—C3—H3B108.5C11—C10—C9121.1 (3)
C3—C4—H4A109.5C15—C10—C9121.4 (3)
C3—C4—H4B109.5C10—C11—C12121.0 (4)
H4A—C4—H4B109.5C10—C11—H11119.5
C3—C4—H4C109.5C12—C11—H11119.5
H4A—C4—H4C109.5C13—C12—C11119.8 (4)
H4B—C4—H4C109.5C13—C12—H12120.1
C7—C5—C8109.2 (3)C11—C12—H12120.1
C7—C5—C6109.4 (3)C14—C13—C12120.2 (4)
C8—C5—C6110.6 (3)C14—C13—H13119.9
C7—C5—C1111.6 (2)C12—C13—H13119.9
C8—C5—C1107.2 (3)C13—C14—C15120.8 (5)
C6—C5—C1108.8 (3)C13—C14—H14119.6
C5—C6—H6A109.5C15—C14—H14119.6
C5—C6—H6B109.5C14—C15—C10120.8 (4)
H6A—C6—H6B109.5C14—C15—H15119.6
C5—C6—H6C109.5C10—C15—H15119.6
O3—S1—N1—C184.8 (2)N1—C1—C5—C6172.6 (3)
C9—S1—N1—C1−166.3 (2)C2—C1—C5—C647.8 (3)
S1—N1—C1—C2−95.2 (3)O3—S1—C9—C10−179.6 (3)
S1—N1—C1—C5138.8 (2)N1—S1—C9—C1065.2 (3)
C3—O2—C2—O1−2.6 (6)S1—C9—C10—C11−99.0 (4)
C3—O2—C2—C1178.3 (4)S1—C9—C10—C1578.2 (4)
N1—C1—C2—O1−51.2 (4)C15—C10—C11—C120.1 (6)
C5—C1—C2—O174.6 (4)C9—C10—C11—C12177.4 (4)
N1—C1—C2—O2128.0 (3)C10—C11—C12—C130.1 (7)
C5—C1—C2—O2−106.3 (3)C11—C12—C13—C140.2 (8)
C2—O2—C3—C4178.3 (4)C12—C13—C14—C15−0.7 (9)
N1—C1—C5—C751.8 (3)C13—C14—C15—C100.9 (7)
C2—C1—C5—C7−73.1 (4)C11—C10—C15—C14−0.5 (6)
N1—C1—C5—C8−67.8 (3)C9—C10—C15—C14−177.8 (4)
C2—C1—C5—C8167.4 (3)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C7—H7B···O10.962.613.234 (5)123.
C9—H9B···O3i0.972.483.296 (5)142.
N1—H1A···O3i0.86 (2)2.13 (2)2.932 (3)156 (3)
Symmetry codes: (i) −x, y−1/2, −z+1.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
C7—H7B···O10.962.613.234 (5)123.
C9—H9B···O3i0.972.483.296 (5)142.
N1—H1A···O3i0.86 (2)2.13 (2)2.932 (3)156 (3)
Symmetry codes: (i) −x, y−1/2, −z+1.
Acknowledgements top

The work was financially supported by the National Science Foundation of China (grant No. 20772017) and the Shanghai Municipal Committee of Science and Technology (grant No. 07DZ19713).

references
References top

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