(SS,2S,3R)-2-(2-Methyl­propane-2-sulfin­amido)-3-phenyl­butyronitrile

Harms, K.; Marsch, M.; Oberthür, M.; Schüler, P.

doi:10.1107/S1600536809041233

organic compounds

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Volume 65| Part 11| November 2009| Page o2741

https://doi.org/10.1107/S1600536809041233

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(^SS,2S,3R)-2-(2-Methylpropane-2-sulfinamido)-3-phenylbutyronitrile

Klaus Harms,^a ^* Michael Marsch,^a Markus Oberthür ^a and Peter Schüler ^a

^aPhilipps-Universität Marburg, Fachbereich Chemie, Hans-Meerwein-Strasse, D-35032 Marburg, Germany
^*Correspondence e-mail: klaus.harms@chemie.uni-marburg.de

(Received 25 September 2009; accepted 9 October 2009; online 17 October 2009)

The absolute configuration has been determined for the title compound, C₁₄H₂₀N₂OS. Intermolecular N—H⋯O hydrogen bonds are observed in the crystal packing, forming infinitive one-dimensional chains with the base vector [100].

Related literature

For uses of tert-butanesulfinimines, see: Ferreira et al. (2009 ). For asymmetric Strecker reactions utilizing this auxiliary, see: Davis et al. (1994 ); Li et al. (2003 ). For the mannopeptimycin gene cluster, see: Magarvey et al. (2006 ). For a related structure, see: Harms et al. (2009 ).

Experimental

Crystal data

C₁₄H₂₀N₂OS
M_r = 264.38
Orthorhombic, P 2₁ 2₁ 2₁
a = 8.7892 (3) Å
b = 8.7967 (4) Å
c = 18.5217 (7) Å
V = 1432.02 (10) Å³
Z = 4
Mo Kα radiation
μ = 0.22 mm⁻¹
T = 100 K
0.36 × 0.18 × 0.15 mm

Data collection

STOE IPDS II diffractometer
Absorption correction: none
22029 measured reflections
3031 independent reflections
2624 reflections with I > 2σ(I)
R_int = 0.070

Refinement

R[F² > 2σ(F²)] = 0.029
wR(F²) = 0.064
S = 0.92
3031 reflections
244 parameters
All H-atom parameters refined
Δρ_max = 0.18 e Å⁻³
Δρ_min = −0.23 e Å⁻³
Absolute structure: Flack (1983 ), 1272 Friedel pairs
Flack parameter: 0.02 (6)

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H01⋯O1ⁱ	0.89 (2)	2.167 (19)	2.9511 (18)	146.5 (18)
Symmetry code: (i) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z]$ .

Data collection: X-AREA (Stoe & Cie, 2002 ); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: SIR2004 (Burla et al, 2005 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ); molecular graphics: DIAMOND (Brandenburg, 1999 ); software used to prepare material for publication: publCIF (Westrip, 2009 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536809041233/pv2212sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536809041233/pv2212Isup2.hkl

checkCIF report

Comment top

Chiral sulfinimines have proven to be powerful and versatile precursors for the synthesis of nonproteinogenic amino acids (Ferreira et al., 2008). They allow the stereoselective introduction of cyanide therefore representing an asymmetric modification of the Strecker reaction (Davis et al., 1994); Li et al., 2003). We have synthesized the title compound, (I), that can be hydrolyzed to give (2S,3R)-β-methylphenylalanine which is of practical use as reference substance in the investigation of the methyltransferase present in the mannopeptimycin gene cluster (Magarvey et al., 2006). In this paper we report the crystal structure and absolute configuration of (I).

The molecular structure of (I) is presented in Fig. 1. The structure exhibits intermolecular N—H···O hydrogen bonds [H···O = 2.167 (19) Å] resulting in infinitive one dimensional chains with the base vector [1 0 0] (details have have been provided in Table 1 and Fig. 2).

The crystal structure and absolute configuration of a closely related compound has just been reported (Harms et al., 2009).

Related literature top

For uses of tert-butanesulfinimines, see: Ferreira et al. (2009). For asymmetric Strecker reactions utilizing this auxiliary, see: Davis et al. (1994); Li et al. (2003). For the mannopeptimycin gene cluster, see: Magarvey et al. (2006). For a related structure, see: Harms et al. (2009).

Experimental top

Trimethylsilyl cyanide (TMSCN) (706 µL, 5.64 mmol) was added dropwise to a solution of (^SS)-(2-phenylpropyliden)-2-methyl-2-propansulfinylimin (1.12 g, 4.70 mmol) and CsF (858 mg, 5.64 mmol) in 50 ml n-hexane at 240 K. The mixture was stirred at this temperature for 14 h and subsequently quenched with semisaturated aqueous NH₄Cl solution. Extraction with EtOAc (2×50 ml) and drying of the combined organic phases (MgSO₄) yielded a crude mixture of 3S/3R epimers. Crystallization from petrolether/EtOAc yielded 370 mg (1.41 mmol, 35%) of a 1:1 mixture of the diastereomers. Flash column chromatography of the mother liquor yielded 80 mg (303 mmol, 6%) of the pure 3S isomer, which had a slightly higher R_f-value (R_f= 0.30 in petrol ether/EtOAc 2:1) than the 3R isomer of which 60 mg (227 mmol, 5%) could be isolated. The remaining fractions afforded 400 mg (1.53 mmol, 32%) of a roughly 1:1 mixture of the epimers. (^SS,2S,3R)-(2-Methylpropansulfinyl)-2-amino-3-phenylbutyronitril was crystallized from petrol ether/THF.

Structure description top

The crystal structure and absolute configuration of a closely related compound has just been reported (Harms et al., 2009).

For uses of tert-butanesulfinimines, see: Ferreira et al. (2009). For asymmetric Strecker reactions utilizing this auxiliary, see: Davis et al. (1994); Li et al. (2003). For the mannopeptimycin gene cluster, see: Magarvey et al. (2006). For a related structure, see: Harms et al. (2009).

Computing details top

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA (Stoe & Cie, 2002); data reduction: X-AREA (Stoe & Cie, 2002); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures top

	Fig. 1. A view of (I). Displacement ellipsoids are drawn at the 50% probability level. Symmetry operation (i): x+1/2, -y+1/2, -z.
	Fig. 2. Unit cell packing of (I) viewed down the b-axis. Dotted lines indicate hydrogen bonds.

(^SS,2S,3R)-2-(2-Methylpropane-2-sulfinamido)- 3-phenylbutyronitrile top

Crystal data top

C₁₄H₂₀N₂OS	F(000) = 568
M_r = 264.38	D_x = 1.226 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 22507 reflections
a = 8.7892 (3) Å	θ = 2.2–25°
b = 8.7967 (4) Å	µ = 0.22 mm⁻¹
c = 18.5217 (7) Å	T = 100 K
V = 1432.02 (10) Å³	Prism, colourless
Z = 4	0.36 × 0.18 × 0.15 mm

Data collection top

STOE IPDS II diffractometer	2624 reflections with I > 2σ(I)
Radiation source: sealed X-ray tube	R_int = 0.070
Graphite monochromator	θ_max = 26.8°, θ_min = 2.2°
area detetor, ω scans	h = −11→11
22029 measured reflections	k = −11→11
3031 independent reflections	l = −23→23

Refinement top

Refinement on F²	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F² > 2σ(F²)] = 0.029	w = 1/[σ²(F_o²) + (0.0378P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.064	(Δ/σ)_max < 0.001
S = 0.92	Δρ_max = 0.18 e Å⁻³
3031 reflections	Δρ_min = −0.23 e Å⁻³
244 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008)
0 restraints	Extinction coefficient: 0.0113 (13)
0 constraints	Absolute structure: Flack (1983), 1272 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.02 (6)

Crystal data top

C₁₄H₂₀N₂OS	V = 1432.02 (10) Å³
M_r = 264.38	Z = 4
Orthorhombic, P2₁2₁2₁	Mo Kα radiation
a = 8.7892 (3) Å	µ = 0.22 mm⁻¹
b = 8.7967 (4) Å	T = 100 K
c = 18.5217 (7) Å	0.36 × 0.18 × 0.15 mm

Data collection top

STOE IPDS II diffractometer	2624 reflections with I > 2σ(I)
22029 measured reflections	R_int = 0.070
3031 independent reflections

Refinement top

R[F² > 2σ(F²)] = 0.029	All H-atom parameters refined
wR(F²) = 0.064	Δρ_max = 0.18 e Å⁻³
S = 0.92	Δρ_min = −0.23 e Å⁻³
3031 reflections	Absolute structure: Flack (1983), 1272 Friedel pairs
244 parameters	Absolute structure parameter: 0.02 (6)
0 restraints

Special details top

Experimental. δ_H(300 MHz; DMSO) 1.13 (s, 9H, tBu), 1.28 (d, 3H, ³J_Me,CH= 7.0 Hz, CH₃), 3.14 (dq, 1H, ³J_CH,CHN= 9.9, J_CH,Me= 7.0 Hz, CH), 4.48 (pt, 1H, ³J_CHN,CH= 9.9 Hz, CHN), 6.37 (d, 1H, ³J_NH,CHN= 9.9 Hz, NH), 7.22 – 7.38 (m, 5H, CH_arom); δ_C(75 MHz; DMSO-d₆) 18.3 (CH₃), 22.5 (C(CH₃)₃), 43.6 (CH), 52.4 (CHN), 56.4 (C(CH₃)₃), 119.8 (CN), 127.2 (p-CH_arom), 127.8 (CH_arom),128.5 (CH_arom), 141.7 (i-C_arom).

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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

	x	y	z	U_iso*/U_eq
C1	0.43208 (18)	0.5330 (2)	−0.00956 (9)	0.0303 (4)
C2	0.56755 (17)	0.6458 (2)	−0.00597 (9)	0.0311 (4)
C3	0.40206 (16)	0.4817 (2)	−0.08405 (11)	0.0337 (4)
C4	0.57924 (19)	0.7071 (2)	0.07072 (10)	0.0343 (4)
C5	0.55157 (17)	0.7666 (2)	−0.06356 (9)	0.0322 (4)
C6	0.46159 (19)	0.8950 (2)	−0.05357 (10)	0.0362 (4)
C7	0.4397 (2)	0.9986 (2)	−0.10900 (12)	0.0451 (5)
C8	0.5075 (2)	0.9750 (3)	−0.17589 (12)	0.0480 (5)
C9	0.5996 (2)	0.8499 (3)	−0.18570 (11)	0.0467 (5)
C10	0.6223 (2)	0.7472 (2)	−0.13039 (10)	0.0394 (4)
C11	0.39529 (17)	0.2377 (2)	0.15401 (9)	0.0321 (4)
C12	0.4864 (3)	0.3546 (3)	0.19584 (12)	0.0498 (5)
C13	0.2643 (2)	0.1791 (3)	0.20040 (12)	0.0447 (5)
C14	0.4918 (2)	0.1082 (3)	0.12683 (12)	0.0459 (5)
N1	0.45589 (15)	0.40435 (17)	0.03876 (8)	0.0302 (3)
N2	0.37703 (17)	0.4385 (2)	−0.14134 (9)	0.0449 (4)
O1	0.23286 (12)	0.20929 (14)	0.03335 (7)	0.0376 (3)
S1	0.30144 (4)	0.33362 (5)	0.07741 (2)	0.03041 (11)
H2	0.6626 (19)	0.578 (2)	−0.0175 (9)	0.034 (5)*
H4A	0.655 (2)	0.795 (2)	0.0753 (11)	0.042 (5)*
H8	0.495 (2)	1.053 (3)	−0.2164 (11)	0.059 (6)*
H01	0.521 (2)	0.334 (2)	0.0226 (10)	0.038 (5)*
H4B	0.486 (2)	0.751 (2)	0.0859 (10)	0.041 (5)*
H10	0.689 (2)	0.649 (2)	−0.1366 (10)	0.049 (5)*
H1	0.3383 (18)	0.586 (2)	0.0075 (9)	0.030 (4)*
H13A	0.307 (3)	0.113 (3)	0.2399 (12)	0.064 (7)*
H6	0.417 (2)	0.910 (2)	−0.0079 (10)	0.040 (5)*
H14C	0.570 (2)	0.146 (2)	0.0968 (11)	0.053 (6)*
H12A	0.509 (3)	0.315 (3)	0.2468 (13)	0.063 (6)*
H14B	0.425 (2)	0.024 (3)	0.0969 (13)	0.059 (7)*
H4C	0.604 (2)	0.621 (2)	0.1034 (11)	0.051 (6)*
H13B	0.205 (3)	0.270 (3)	0.2212 (12)	0.067 (7)*
H12C	0.576 (3)	0.393 (3)	0.1711 (14)	0.080 (8)*
H7	0.379 (2)	1.088 (3)	−0.0992 (12)	0.053 (6)*
H12B	0.424 (3)	0.447 (3)	0.2040 (12)	0.060 (7)*
H9	0.650 (2)	0.827 (3)	−0.2315 (12)	0.060 (6)*
H14A	0.539 (3)	0.049 (3)	0.1672 (12)	0.061 (7)*
H13C	0.192 (3)	0.115 (3)	0.1726 (12)	0.061 (6)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0237 (8)	0.0324 (9)	0.0348 (9)	0.0004 (7)	−0.0002 (7)	−0.0003 (7)
C2	0.0230 (7)	0.0334 (10)	0.0368 (9)	−0.0003 (7)	0.0000 (6)	0.0008 (8)
C3	0.0232 (7)	0.0387 (9)	0.0394 (10)	−0.0018 (6)	0.0012 (7)	−0.0008 (9)
C4	0.0303 (8)	0.0346 (10)	0.0381 (10)	−0.0040 (7)	−0.0005 (7)	−0.0012 (8)
C5	0.0242 (7)	0.0346 (9)	0.0378 (9)	−0.0056 (7)	−0.0021 (6)	−0.0003 (8)
C6	0.0240 (8)	0.0381 (10)	0.0465 (10)	−0.0054 (7)	−0.0032 (7)	0.0046 (8)
C7	0.0304 (9)	0.0389 (11)	0.0661 (14)	−0.0059 (8)	−0.0134 (9)	0.0087 (10)
C8	0.0445 (10)	0.0477 (13)	0.0518 (12)	−0.0203 (9)	−0.0177 (9)	0.0157 (10)
C9	0.0468 (10)	0.0524 (13)	0.0408 (11)	−0.0187 (10)	−0.0043 (8)	0.0025 (11)
C10	0.0368 (9)	0.0407 (11)	0.0408 (10)	−0.0094 (8)	0.0004 (7)	0.0008 (9)
C11	0.0264 (8)	0.0318 (9)	0.0380 (9)	−0.0014 (7)	0.0002 (6)	−0.0011 (8)
C12	0.0603 (12)	0.0454 (13)	0.0436 (11)	−0.0135 (11)	−0.0102 (10)	0.0023 (11)
C13	0.0351 (9)	0.0486 (12)	0.0505 (11)	0.0009 (10)	0.0047 (8)	0.0134 (11)
C14	0.0428 (10)	0.0481 (12)	0.0466 (11)	0.0145 (9)	0.0039 (9)	0.0072 (10)
N1	0.0235 (6)	0.0296 (8)	0.0375 (8)	0.0017 (6)	0.0030 (6)	0.0012 (7)
N2	0.0350 (8)	0.0575 (11)	0.0421 (10)	−0.0049 (8)	0.0003 (7)	−0.0064 (8)
O1	0.0311 (6)	0.0367 (7)	0.0451 (7)	−0.0088 (5)	−0.0069 (5)	−0.0010 (6)
S1	0.02191 (15)	0.0315 (2)	0.0378 (2)	−0.00129 (16)	0.00057 (16)	0.0009 (2)

Geometric parameters (Å, º) top

C1—N1	1.458 (2)	C9—C10	1.380 (3)
C1—C3	1.476 (3)	C9—H9	0.98 (2)
C1—C2	1.551 (2)	C10—H10	1.05 (2)
C1—H1	0.998 (17)	C11—C14	1.507 (3)
C2—C5	1.512 (2)	C11—C12	1.517 (3)
C2—C4	1.523 (2)	C11—C13	1.526 (2)
C2—H2	1.046 (18)	C11—S1	1.8454 (17)
C3—N2	1.148 (2)	C12—H12A	1.02 (2)
C4—H4A	1.019 (19)	C12—H12C	0.97 (3)
C4—H4B	0.95 (2)	C12—H12B	0.99 (3)
C4—H4C	0.99 (2)	C13—H13A	1.01 (2)
C5—C6	1.391 (3)	C13—H13B	1.03 (2)
C5—C10	1.395 (2)	C13—H13C	0.99 (2)
C6—C7	1.386 (3)	C14—H14C	0.94 (2)
C6—H6	0.943 (19)	C14—H14B	1.10 (2)
C7—C8	1.390 (3)	C14—H14A	1.00 (2)
C7—H7	0.96 (2)	N1—S1	1.6560 (14)
C8—C9	1.378 (3)	N1—H01	0.89 (2)
C8—H8	1.02 (2)	O1—S1	1.4918 (12)

N1—C1—C3	111.21 (15)	C9—C10—C5	120.9 (2)
N1—C1—C2	111.10 (13)	C9—C10—H10	122.5 (11)
C3—C1—C2	111.90 (13)	C5—C10—H10	116.5 (11)
N1—C1—H1	106.6 (10)	C14—C11—C12	112.71 (17)
C3—C1—H1	106.9 (9)	C14—C11—C13	110.95 (17)
C2—C1—H1	108.8 (10)	C12—C11—C13	109.88 (17)
C5—C2—C4	114.53 (15)	C14—C11—S1	109.91 (13)
C5—C2—C1	110.36 (13)	C12—C11—S1	108.57 (14)
C4—C2—C1	108.55 (13)	C13—C11—S1	104.48 (11)
C5—C2—H2	109.2 (10)	C11—C12—H12A	110.1 (15)
C4—C2—H2	109.7 (9)	C11—C12—H12C	115.1 (16)
C1—C2—H2	104.0 (10)	H12A—C12—H12C	113 (2)
N2—C3—C1	178.3 (2)	C11—C12—H12B	109.8 (13)
C2—C4—H4A	112.9 (11)	H12A—C12—H12B	104 (2)
C2—C4—H4B	111.2 (11)	H12C—C12—H12B	104 (2)
H4A—C4—H4B	103.3 (15)	C11—C13—H13A	108.8 (13)
C2—C4—H4C	108.2 (12)	C11—C13—H13B	109.2 (12)
H4A—C4—H4C	112.6 (15)	H13A—C13—H13B	111.5 (17)
H4B—C4—H4C	108.6 (16)	C11—C13—H13C	112.4 (13)
C6—C5—C10	118.05 (17)	H13A—C13—H13C	106.7 (17)
C6—C5—C2	121.98 (15)	H13B—C13—H13C	108.3 (18)
C10—C5—C2	119.90 (16)	C11—C14—H14C	109.8 (13)
C7—C6—C5	120.94 (19)	C11—C14—H14B	112.1 (11)
C7—C6—H6	120.9 (12)	H14C—C14—H14B	109.4 (17)
C5—C6—H6	118.2 (12)	C11—C14—H14A	112.4 (13)
C6—C7—C8	120.2 (2)	H14C—C14—H14A	108.6 (17)
C6—C7—H7	118.1 (14)	H14B—C14—H14A	104.4 (18)
C8—C7—H7	121.7 (14)	C1—N1—S1	116.06 (11)
C9—C8—C7	119.2 (2)	C1—N1—H01	115.0 (12)
C9—C8—H8	120.2 (12)	S1—N1—H01	114.2 (13)
C7—C8—H8	120.4 (12)	O1—S1—N1	111.73 (7)
C8—C9—C10	120.6 (2)	O1—S1—C11	105.41 (7)
C8—C9—H9	122.8 (14)	N1—S1—C11	97.92 (7)
C10—C9—H9	116.6 (14)

N1—C1—C2—C5	172.20 (13)	C7—C8—C9—C10	1.3 (3)
C3—C1—C2—C5	47.23 (18)	C8—C9—C10—C5	0.6 (3)
N1—C1—C2—C4	−61.53 (18)	C6—C5—C10—C9	−2.1 (3)
C3—C1—C2—C4	173.50 (14)	C2—C5—C10—C9	174.84 (15)
N1—C1—C3—N2	31 (6)	C3—C1—N1—S1	−88.88 (15)
C2—C1—C3—N2	156 (6)	C2—C1—N1—S1	145.76 (12)
C4—C2—C5—C6	−39.8 (2)	C1—N1—S1—O1	90.88 (13)
C1—C2—C5—C6	83.09 (19)	C1—N1—S1—C11	−158.98 (12)
C4—C2—C5—C10	143.46 (15)	C14—C11—S1—O1	48.56 (14)
C1—C2—C5—C10	−93.69 (17)	C12—C11—S1—O1	172.26 (13)
C10—C5—C6—C7	1.6 (2)	C13—C11—S1—O1	−70.54 (14)
C2—C5—C6—C7	−175.21 (15)	C14—C11—S1—N1	−66.65 (14)
C5—C6—C7—C8	0.2 (3)	C12—C11—S1—N1	57.04 (15)
C6—C7—C8—C9	−1.7 (3)	C13—C11—S1—N1	174.25 (13)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H01···O1ⁱ	0.89 (2)	2.167 (19)	2.9511 (18)	146.5 (18)

Symmetry code: (i) x+1/2, −y+1/2, −z.

Experimental details

Crystal data
Chemical formula	C₁₄H₂₀N₂OS
M_r	264.38
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	100
a, b, c (Å)	8.7892 (3), 8.7967 (4), 18.5217 (7)
V (Å³)	1432.02 (10)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.22
Crystal size (mm)	0.36 × 0.18 × 0.15

Data collection
Diffractometer	STOE IPDS II
Absorption correction	–
No. of measured, independent and observed [I > 2σ(I)] reflections	22029, 3031, 2624
R_int	0.070
(sin θ/λ)_max (Å⁻¹)	0.634

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.029, 0.064, 0.92
No. of reflections	3031
No. of parameters	244
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.18, −0.23
Absolute structure	Flack (1983), 1272 Friedel pairs
Absolute structure parameter	0.02 (6)

Computer programs: X-AREA (Stoe & Cie, 2002), SIR2004 (Burla et al., 2005), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1999), publCIF (Westrip, 2009).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H01···O1ⁱ	0.89 (2)	2.167 (19)	2.9511 (18)	146.5 (18)

Symmetry code: (i) x+1/2, −y+1/2, −z.

Acknowledgements

The authors gratefully acknowledge funding by the Philipps-Universität Marburg, the Deutsche Forschungsgemeinschaft (PS & MO) and the Ernst-Schering-Foundation (PS).

References

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