Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100014955/qa0411sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270100014955/qa0411Isup2.hkl |
CCDC reference: 156207
Benzyl bromide (2.7 g, 15.8 mmol) was added to a mixture of ethyl nitroacetate (1.0 g. 7.5 mmol), tetrabutylammonium bromide (0.24 g, 0.75 mmol) and diisopropylethylamine (2.0 g, 15.8 mmol) dissolved in 5 ml of dry dimethylformamide. The reaction was stirred for 2 h, and the precipitated diisopropylethylammonium bromide salt was removed by filtration and washed with diethyl ether (100 ml). The resulting filtrate was washed with water (5 × 50 ml). The organic layer was dried over sodium sulfate, filtered, and the ether removed by evaporation at 273 K to provide a yellow oil (2.0 g, 88% crude yield). Silica-gel column chromatography with pentane/diethyl ether provided a white crystalline solid following removal of solvents (1.48 g, 63% yield). The compound was crystallized (in the dark under argon) from hot pentane by slow cooling.
H atoms were placed in calculated positions with C—H bond distances of 0.95 Å for phenyl, 0.99 Å for methylene and 0.98 Å for methyl, and thereafter treated as riding. A torsional parameter was refined for the methyl group. Uiso = 1.2Ueq of the attached C atom (1.5 for methyl groups).
Data collection: KappaCCD Software (Nonius, 1998); cell refinement: DENZO and SCALEPAK; data reduction: DENZO and SCALEPAK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXL97.
C18H19NO4 | F(000) = 664 |
Mr = 313.34 | Dx = 1.292 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 18.0850 (6) Å | Cell parameters from 7336 reflections |
b = 6.0670 (2) Å | θ = 2.5–27.5° |
c = 15.9830 (6) Å | µ = 0.09 mm−1 |
β = 113.280 (2)° | T = 120 K |
V = 1610.90 (10) Å3 | Lath, colourless |
Z = 4 | 0.50 × 0.10 × 0.05 mm |
KappaCCD (with Oxford Cryosystems Cryostream cooler) diffractometer | 2576 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.038 |
Graphite monochromator | θmax = 27.5°, θmin = 3.4° |
ω scans with κ offsets | h = −23→23 |
7336 measured reflections | k = −7→7 |
3662 independent reflections | l = −20→20 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.039 | H-atom parameters constrained |
wR(F2) = 0.094 | w = 1/[σ2(Fo2) + (0.0388P)2 + 0.1307P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max = 0.001 |
3662 reflections | Δρmax = 0.27 e Å−3 |
210 parameters | Δρmin = −0.22 e Å−3 |
0 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0152 (17) |
C18H19NO4 | V = 1610.90 (10) Å3 |
Mr = 313.34 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 18.0850 (6) Å | µ = 0.09 mm−1 |
b = 6.0670 (2) Å | T = 120 K |
c = 15.9830 (6) Å | 0.50 × 0.10 × 0.05 mm |
β = 113.280 (2)° |
KappaCCD (with Oxford Cryosystems Cryostream cooler) diffractometer | 2576 reflections with I > 2σ(I) |
7336 measured reflections | Rint = 0.038 |
3662 independent reflections |
R[F2 > 2σ(F2)] = 0.039 | 0 restraints |
wR(F2) = 0.094 | H-atom parameters constrained |
S = 1.04 | Δρmax = 0.27 e Å−3 |
3662 reflections | Δρmin = −0.22 e Å−3 |
210 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.19690 (6) | 0.44747 (15) | 0.81248 (6) | 0.0344 (2) | |
O2 | 0.26130 (5) | 0.77258 (14) | 0.83315 (6) | 0.0267 (2) | |
O3 | 0.24154 (5) | 0.95503 (15) | 0.62506 (6) | 0.0336 (2) | |
O4 | 0.15004 (6) | 0.98732 (15) | 0.67960 (6) | 0.0331 (2) | |
N1 | 0.19922 (6) | 0.87969 (18) | 0.66197 (7) | 0.0252 (3) | |
C1 | 0.20260 (7) | 0.6323 (2) | 0.68295 (8) | 0.0211 (3) | |
C2 | 0.21764 (7) | 0.6072 (2) | 0.78347 (9) | 0.0238 (3) | |
C3 | 0.28908 (8) | 0.7509 (2) | 0.93147 (8) | 0.0317 (3) | |
H3A | 0.3184 | 0.6102 | 0.9522 | 0.038* | |
H3B | 0.2429 | 0.7542 | 0.9500 | 0.038* | |
C4 | 0.34387 (9) | 0.9424 (3) | 0.97160 (10) | 0.0430 (4) | |
H4A | 0.3874 | 0.9419 | 0.9497 | 0.064* | |
H4B | 0.3668 | 0.9307 | 1.0382 | 0.064* | |
H4C | 0.3133 | 1.0800 | 0.9533 | 0.064* | |
C5 | 0.11964 (7) | 0.5389 (2) | 0.62068 (8) | 0.0239 (3) | |
H5A | 0.1183 | 0.3795 | 0.6332 | 0.029* | |
H5B | 0.0776 | 0.6118 | 0.6359 | 0.029* | |
C6 | 0.10002 (7) | 0.5703 (2) | 0.52041 (8) | 0.0223 (3) | |
C7 | 0.06529 (7) | 0.7666 (2) | 0.47761 (8) | 0.0262 (3) | |
H7 | 0.0529 | 0.8784 | 0.5116 | 0.031* | |
C8 | 0.04857 (7) | 0.8012 (2) | 0.38620 (9) | 0.0299 (3) | |
H8 | 0.0250 | 0.9361 | 0.3580 | 0.036* | |
C9 | 0.06622 (7) | 0.6395 (2) | 0.33618 (9) | 0.0312 (3) | |
H9 | 0.0551 | 0.6635 | 0.2736 | 0.037* | |
C10 | 0.09997 (8) | 0.4427 (2) | 0.37699 (9) | 0.0319 (3) | |
H10 | 0.1117 | 0.3311 | 0.3424 | 0.038* | |
C11 | 0.11678 (7) | 0.4080 (2) | 0.46869 (9) | 0.0280 (3) | |
H11 | 0.1399 | 0.2723 | 0.4964 | 0.034* | |
C12 | 0.27142 (7) | 0.5200 (2) | 0.66547 (9) | 0.0237 (3) | |
H12A | 0.2592 | 0.3606 | 0.6560 | 0.028* | |
H12B | 0.2721 | 0.5796 | 0.6081 | 0.028* | |
C13 | 0.35516 (7) | 0.5457 (2) | 0.73967 (8) | 0.0248 (3) | |
C14 | 0.38473 (8) | 0.3836 (2) | 0.80657 (9) | 0.0308 (3) | |
H14 | 0.3528 | 0.2577 | 0.8045 | 0.037* | |
C15 | 0.46038 (8) | 0.4052 (3) | 0.87614 (10) | 0.0380 (4) | |
H15 | 0.4799 | 0.2944 | 0.9216 | 0.046* | |
C16 | 0.50754 (8) | 0.5872 (3) | 0.87959 (10) | 0.0387 (4) | |
H16 | 0.5591 | 0.6023 | 0.9277 | 0.046* | |
C17 | 0.47938 (8) | 0.7465 (3) | 0.81288 (9) | 0.0354 (3) | |
H17 | 0.5121 | 0.8704 | 0.8146 | 0.042* | |
C18 | 0.40359 (7) | 0.7269 (2) | 0.74330 (9) | 0.0287 (3) | |
H18 | 0.3846 | 0.8379 | 0.6978 | 0.034* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0439 (6) | 0.0298 (5) | 0.0319 (5) | −0.0065 (5) | 0.0174 (4) | 0.0046 (4) |
O2 | 0.0314 (5) | 0.0255 (5) | 0.0224 (4) | −0.0006 (4) | 0.0099 (4) | 0.0000 (4) |
O3 | 0.0358 (5) | 0.0265 (5) | 0.0388 (6) | −0.0061 (4) | 0.0150 (4) | 0.0070 (4) |
O4 | 0.0420 (5) | 0.0239 (5) | 0.0333 (5) | 0.0089 (4) | 0.0147 (4) | −0.0008 (4) |
N1 | 0.0292 (6) | 0.0193 (6) | 0.0237 (5) | −0.0007 (5) | 0.0068 (5) | 0.0005 (5) |
C1 | 0.0255 (6) | 0.0139 (6) | 0.0245 (6) | 0.0006 (5) | 0.0104 (5) | 0.0017 (5) |
C2 | 0.0240 (6) | 0.0216 (7) | 0.0275 (7) | 0.0026 (5) | 0.0120 (5) | 0.0011 (6) |
C3 | 0.0342 (7) | 0.0390 (8) | 0.0208 (7) | 0.0020 (6) | 0.0096 (5) | 0.0014 (6) |
C4 | 0.0398 (8) | 0.0600 (11) | 0.0279 (7) | −0.0124 (8) | 0.0121 (6) | −0.0082 (8) |
C5 | 0.0233 (6) | 0.0194 (6) | 0.0289 (7) | −0.0013 (5) | 0.0104 (5) | 0.0008 (5) |
C6 | 0.0183 (6) | 0.0204 (7) | 0.0274 (6) | −0.0026 (5) | 0.0082 (5) | −0.0014 (5) |
C7 | 0.0253 (6) | 0.0229 (7) | 0.0291 (7) | 0.0015 (5) | 0.0093 (5) | −0.0020 (6) |
C8 | 0.0279 (6) | 0.0267 (7) | 0.0296 (7) | −0.0002 (6) | 0.0057 (5) | 0.0036 (6) |
C9 | 0.0273 (7) | 0.0399 (8) | 0.0250 (7) | −0.0072 (6) | 0.0088 (5) | −0.0031 (7) |
C10 | 0.0272 (6) | 0.0352 (8) | 0.0334 (8) | −0.0021 (6) | 0.0121 (6) | −0.0102 (7) |
C11 | 0.0255 (6) | 0.0219 (7) | 0.0340 (7) | 0.0012 (6) | 0.0091 (5) | −0.0026 (6) |
C12 | 0.0256 (6) | 0.0196 (6) | 0.0266 (7) | −0.0002 (5) | 0.0111 (5) | −0.0006 (6) |
C13 | 0.0255 (6) | 0.0260 (7) | 0.0253 (6) | 0.0026 (6) | 0.0127 (5) | −0.0013 (6) |
C14 | 0.0301 (7) | 0.0307 (8) | 0.0340 (7) | 0.0032 (6) | 0.0153 (6) | 0.0030 (6) |
C15 | 0.0354 (8) | 0.0474 (10) | 0.0305 (7) | 0.0102 (7) | 0.0123 (6) | 0.0077 (7) |
C16 | 0.0257 (7) | 0.0562 (10) | 0.0304 (7) | 0.0020 (7) | 0.0072 (6) | −0.0049 (7) |
C17 | 0.0281 (7) | 0.0412 (9) | 0.0378 (8) | −0.0074 (6) | 0.0140 (6) | −0.0077 (7) |
C18 | 0.0268 (6) | 0.0301 (7) | 0.0310 (7) | −0.0012 (6) | 0.0134 (5) | 0.0002 (6) |
O1—C2 | 1.1966 (15) | C8—C9 | 1.3802 (19) |
O2—C2 | 1.3286 (15) | C8—H8 | 0.9500 |
O2—C3 | 1.4544 (14) | C9—C10 | 1.382 (2) |
O3—N1 | 1.2245 (13) | C9—H9 | 0.9500 |
O4—N1 | 1.2228 (13) | C10—C11 | 1.3901 (19) |
N1—C1 | 1.5336 (16) | C10—H10 | 0.9500 |
C1—C2 | 1.5276 (17) | C11—H11 | 0.9500 |
C1—C12 | 1.5384 (17) | C12—C13 | 1.5181 (17) |
C1—C5 | 1.5435 (16) | C12—H12A | 0.9900 |
C3—C4 | 1.497 (2) | C12—H12B | 0.9900 |
C3—H3A | 0.9900 | C13—C18 | 1.3924 (18) |
C3—H3B | 0.9900 | C13—C14 | 1.3942 (18) |
C4—H4A | 0.9800 | C14—C15 | 1.3867 (19) |
C4—H4B | 0.9800 | C14—H14 | 0.9500 |
C4—H4C | 0.9800 | C15—C16 | 1.383 (2) |
C5—C6 | 1.5102 (17) | C15—H15 | 0.9500 |
C5—H5A | 0.9900 | C16—C17 | 1.379 (2) |
C5—H5B | 0.9900 | C16—H16 | 0.9500 |
C6—C7 | 1.3934 (17) | C17—C18 | 1.3873 (18) |
C6—C11 | 1.3936 (18) | C17—H17 | 0.9500 |
C7—C8 | 1.3859 (18) | C18—H18 | 0.9500 |
C7—H7 | 0.9500 | ||
C2—O2—C3 | 116.57 (10) | C9—C8—C7 | 119.93 (13) |
O4—N1—O3 | 124.18 (11) | C9—C8—H8 | 120.0 |
O4—N1—C1 | 116.22 (10) | C7—C8—H8 | 120.0 |
O3—N1—C1 | 119.48 (10) | C8—C9—C10 | 120.07 (12) |
C2—C1—N1 | 107.63 (10) | C8—C9—H9 | 120.0 |
C2—C1—C12 | 109.04 (10) | C10—C9—H9 | 120.0 |
N1—C1—C12 | 111.04 (10) | C9—C10—C11 | 120.01 (13) |
C2—C1—C5 | 111.42 (10) | C9—C10—H10 | 120.0 |
N1—C1—C5 | 105.89 (9) | C11—C10—H10 | 120.0 |
C12—C1—C5 | 111.73 (10) | C10—C11—C6 | 120.69 (12) |
O1—C2—O2 | 125.69 (12) | C10—C11—H11 | 119.7 |
O1—C2—C1 | 122.39 (12) | C6—C11—H11 | 119.7 |
O2—C2—C1 | 111.70 (10) | C13—C12—C1 | 116.21 (10) |
O2—C3—C4 | 106.28 (11) | C13—C12—H12A | 108.2 |
O2—C3—H3A | 110.5 | C1—C12—H12A | 108.2 |
C4—C3—H3A | 110.5 | C13—C12—H12B | 108.2 |
O2—C3—H3B | 110.5 | C1—C12—H12B | 108.2 |
C4—C3—H3B | 110.5 | H12A—C12—H12B | 107.4 |
H3A—C3—H3B | 108.7 | C18—C13—C14 | 118.73 (11) |
C3—C4—H4A | 109.5 | C18—C13—C12 | 122.03 (11) |
C3—C4—H4B | 109.5 | C14—C13—C12 | 119.24 (11) |
H4A—C4—H4B | 109.5 | C15—C14—C13 | 120.41 (14) |
C3—C4—H4C | 109.5 | C15—C14—H14 | 119.8 |
H4A—C4—H4C | 109.5 | C13—C14—H14 | 119.8 |
H4B—C4—H4C | 109.5 | C16—C15—C14 | 120.32 (14) |
C6—C5—C1 | 113.51 (10) | C16—C15—H15 | 119.8 |
C6—C5—H5A | 108.9 | C14—C15—H15 | 119.8 |
C1—C5—H5A | 108.9 | C17—C16—C15 | 119.69 (12) |
C6—C5—H5B | 108.9 | C17—C16—H16 | 120.2 |
C1—C5—H5B | 108.9 | C15—C16—H16 | 120.2 |
H5A—C5—H5B | 107.7 | C16—C17—C18 | 120.38 (14) |
C7—C6—C11 | 118.29 (12) | C16—C17—H17 | 119.8 |
C7—C6—C5 | 120.00 (11) | C18—C17—H17 | 119.8 |
C11—C6—C5 | 121.70 (11) | C17—C18—C13 | 120.46 (13) |
C8—C7—C6 | 121.01 (12) | C17—C18—H18 | 119.8 |
C8—C7—H7 | 119.5 | C13—C18—H18 | 119.8 |
C6—C7—H7 | 119.5 | ||
O4—N1—C1—C2 | −55.88 (13) | C5—C6—C7—C8 | 178.40 (11) |
O3—N1—C1—C2 | 127.90 (11) | C6—C7—C8—C9 | 0.15 (18) |
O4—N1—C1—C12 | −175.15 (10) | C7—C8—C9—C10 | 0.46 (19) |
O3—N1—C1—C12 | 8.62 (14) | C8—C9—C10—C11 | −0.49 (18) |
O4—N1—C1—C5 | 63.39 (13) | C9—C10—C11—C6 | −0.08 (18) |
O3—N1—C1—C5 | −112.83 (11) | C7—C6—C11—C10 | 0.67 (18) |
C3—O2—C2—O1 | 3.02 (17) | C5—C6—C11—C10 | −178.42 (11) |
C3—O2—C2—C1 | −171.58 (10) | C2—C1—C12—C13 | −38.54 (14) |
N1—C1—C2—O1 | 154.00 (11) | N1—C1—C12—C13 | 79.89 (13) |
C12—C1—C2—O1 | −85.46 (14) | C5—C1—C12—C13 | −162.13 (10) |
C5—C1—C2—O1 | 38.32 (16) | C1—C12—C13—C18 | −86.16 (15) |
N1—C1—C2—O2 | −31.19 (13) | C1—C12—C13—C14 | 93.66 (14) |
C12—C1—C2—O2 | 89.35 (12) | C18—C13—C14—C15 | 1.11 (19) |
C5—C1—C2—O2 | −146.87 (10) | C12—C13—C14—C15 | −178.72 (12) |
C2—O2—C3—C4 | 173.68 (11) | C13—C14—C15—C16 | −0.4 (2) |
C2—C1—C5—C6 | 177.05 (10) | C14—C15—C16—C17 | −0.7 (2) |
N1—C1—C5—C6 | 60.31 (13) | C15—C16—C17—C18 | 1.0 (2) |
C12—C1—C5—C6 | −60.70 (13) | C16—C17—C18—C13 | −0.3 (2) |
C1—C5—C6—C7 | −85.52 (13) | C14—C13—C18—C17 | −0.76 (19) |
C1—C5—C6—C11 | 93.56 (14) | C12—C13—C18—C17 | 179.06 (12) |
C11—C6—C7—C8 | −0.71 (17) |
Experimental details
Crystal data | |
Chemical formula | C18H19NO4 |
Mr | 313.34 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 120 |
a, b, c (Å) | 18.0850 (6), 6.0670 (2), 15.9830 (6) |
β (°) | 113.280 (2) |
V (Å3) | 1610.90 (10) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.50 × 0.10 × 0.05 |
Data collection | |
Diffractometer | KappaCCD (with Oxford Cryosystems Cryostream cooler) diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7336, 3662, 2576 |
Rint | 0.038 |
(sin θ/λ)max (Å−1) | 0.650 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.039, 0.094, 1.04 |
No. of reflections | 3662 |
No. of parameters | 210 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.27, −0.22 |
Computer programs: KappaCCD Software (Nonius, 1998), DENZO and SCALEPAK (Otwinowski & Minor, 1997), SIR92 (Altomare et al., 1994), SHELXL97 (Sheldrick, 1997), SHELXL97.
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The ability of α,α-disubstituted-α-amino acids to modulate the chemical and physical properties of peptides (Olson et al., 1990) has given rise to an increased interest in their synthesis and subsequent incorporation into peptides (Trost & Arisa 1997; Dyker, 1997). One synthon of particular interest to the preparation of amino acids, as well as to other compounds of biological relevance, is the alkyl nitroacetates (Shipchandler, 1979). For the synthesis of mono- and disubstituted α-amino acids from these precursors, the ability to undergo electrophilic substitution reactions at the α-methylene of nitroacetate is of primary importance. However, the synthesis of the title compound, (I), representing dialkylation at this position, as opposed to competing O-alkylation, has previously required two separate synthetic steps to accomplish in moderate yield (Gogte et al., 1987). We have conducted the synthesis in one synthetic step, and herein the structure of the title compound is reported. Further structural comparisons with other α,α-disubstituted alkyl nitroacetates, as well as their conversion to novel prochiral α,α-disubstituted glycines, will be reported elsewhere (Fu et al., 2000). \scheme
The molecule potentially has mirror symmetry; however, it is crystallographically asymmetric, with benzyl groups forming torsion angles of the same sign with the nitro N atom, N1—C1—C5—C6 60.31 (13)° and N1—C1—C12—C13 79.89 (13)°. One is anti to the ester substituent [C2—C1—C5—C6 177.05 (10)°] while the other is more nearly syn [C2—C1—C12—C13 − 38.54 (14)°]. The phenyl rings thus form a dihedral angle of 74.04 (7)°.