Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199012962/bk1479sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270199012962/bk1479Isup2.hkl |
CCDC reference: 140974
To prepare the title compound, a stirred solution of a mixture of (4S,5S)-dimethyl 2-(3',4'-dimethoxyphenyl)-2-ethyl-1,3-dioxolane-4,5-dicarboxylate, (1.20 g, 33.9 mmol), easily obtained from the available 3,4-dimethoxypropylphenone in the presence of (-)-(4S,5S)-dimethyl tartrate, methyl orthoformate and methanesulfonic acid (Castaldi et al., 1987), was treated in carbon tetrachloride with 2-methoxynaphtalene (8 mg, 0.05 mmol) followed by bromine (0.55 g, 34.4 mmol) at 263 K for 2 h. After pH neutralization, the solution was extracted with dichloromethane and the extract washed with water, dried over magnesium sulfate and evaporated to dryness to give a diastereomeric mixture of (Ia/Ib) with 1.38 g, 88% chemical yield and diasteromeric ratio 7:93. The title compound was isolated by slow crystallization, m.p. 369–372 K (from diethyl ether); [α]D20 − 39.2° (CHCl3): νmax (KBr)/cm−1 1772 and 1745; δH (250 MHz; CDCl3; Me4Si) 1.65 (3H, d, J = 7.0, 2'-H), 3.60 (3H, s, 5-CO2CH3), 3.85 (3H, s, 4-CO2CH3), 3.88 (3H, s, 3"-OCH3), 3.90 (3H, s, 4"-OCH3), 4.40 (1H, d, J = 9.0, 5"-H), 7.05–7.15 (2H, m, 2",6"-H); δC (63 MHz; CDCl3;Me4Si) 20.7 (C-2'), 59.7 (C-1'); m/z (EI) 434 [M+ +2], <1%), 432 [M+], <1), 325 [M+ - C2H4Br], 100).
All H atoms were placed in calculated positions using a riding model [C—H = 0.93 Å, U(H) = 1.2Ueq(C) for Csp2; C—H = 0.96 Å, U(H) = 1.5Ueq(C) for Csp3]. A previous refinement with Br and C11 atoms at their full occupancy factors gave distances C10—C11 of 1.664 (10) Å and Br—C10 of 1.928 (8) Å. Consulting the Cambridge Structural Database (1999) we found that the Br—C10 distance was shorter than the mean value (1.962 Å). Furthermore, the displacment ellipsoid for C11 was too small and somewhat oddly shaped. These facts indicated that a small fraction of the molecules have the other configuration at C10. the best of the several disorder models tried gave a lower R(F) index and lower s.u.'s for most parameters. Each of the disordered disordered Br/C11 sites was treated as being composed of Br and C11 atoms are the same positions using SHELXL97, EXYZ and EADP instructions (Sheldrick, 1997). The site occupancies for major component (Br B and C11 B) refined to 0.901 (2). The values of R1 and wR2 for the refinement without disorder (NV = 236) were 0.050 and 0.158. A l l calculations were performed on a DEC 3000 AXP and PC/Pentium II computer running LINUX.
Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: SET4 in CAD-4 EXPRESS; data reduction: HELENA (Spek, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ZORTEP (Zsolnai et al., 1996); software used to prepare material for publication: SHELXL97..
C17H21BrO8 | Dx = 1.507 Mg m−3 |
Mr = 433.25 | Melting point: 369-372 K K |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71073 Å |
a = 9.728 (2) Å | Cell parameters from 25 reflections |
b = 8.414 (2) Å | θ = 19.6–23.0° |
c = 11.674 (2) Å | µ = 2.19 mm−1 |
β = 92.23 (3)° | T = 293 K |
V = 954.8 (3) Å3 | Irregular, colourless |
Z = 2 | 0.50 × 0.43 × 0.40 mm |
F(000) = 444 |
Nonius CAD-4 diffractometer | 1916 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.018 |
Graphite monochromator | θmax = 28.0°, θmin = 2.7° |
ω–2θ scans | h = −12→12 |
Absorption correction: ψ scan (PLATON; Spek, 1990) | k = −5→11 |
Tmin = 0.39, Tmax = 0.42 | l = 0→15 |
3275 measured reflections | 3 standard reflections every 60 min |
3024 independent reflections | intensity decay: 0.4% |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.035 | Calculated w = 1/[σ2(Fo2) + (0.0352P)2 + 0.4675P]
where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.086 | (Δ/σ)max = 0.001 |
S = 1.00 | Δρmax = 0.35 e Å−3 |
3024 reflections | Δρmin = −0.31 e Å−3 |
237 parameters | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
1 restraint | Extinction coefficient: 0.022 (2) |
Primary atom site location: structure-invariant direct methods | Absolute structure: Flack (1983) |
Secondary atom site location: difference Fourier map | Absolute structure parameter: −0.018 (11) |
C17H21BrO8 | V = 954.8 (3) Å3 |
Mr = 433.25 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 9.728 (2) Å | µ = 2.19 mm−1 |
b = 8.414 (2) Å | T = 293 K |
c = 11.674 (2) Å | 0.50 × 0.43 × 0.40 mm |
β = 92.23 (3)° |
Nonius CAD-4 diffractometer | 1916 reflections with I > 2σ(I) |
Absorption correction: ψ scan (PLATON; Spek, 1990) | Rint = 0.018 |
Tmin = 0.39, Tmax = 0.42 | 3 standard reflections every 60 min |
3275 measured reflections | intensity decay: 0.4% |
3024 independent reflections |
R[F2 > 2σ(F2)] = 0.035 | H-atom parameters constrained |
wR(F2) = 0.086 | Δρmax = 0.35 e Å−3 |
S = 1.00 | Δρmin = −0.31 e Å−3 |
3024 reflections | Absolute structure: Flack (1983) |
237 parameters | Absolute structure parameter: −0.018 (11) |
1 restraint |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
BrB | 0.54926 (6) | 0.04609 (8) | 0.81288 (5) | 0.0828 (3) | 0.901 (2) |
O1 | 1.1420 (4) | 0.7514 (4) | 0.8648 (3) | 0.0623 (9) | |
O2 | 1.1838 (3) | 0.4675 (4) | 0.9401 (3) | 0.0586 (9) | |
O3 | 0.8245 (3) | 0.1382 (3) | 0.7033 (2) | 0.0414 (7) | |
O4 | 0.6568 (3) | 0.3171 (3) | 0.6628 (2) | 0.0442 (8) | |
O5 | 1.0803 (3) | 0.1891 (4) | 0.6251 (3) | 0.0542 (8) | |
O6 | 0.9934 (4) | 0.3537 (4) | 0.4926 (3) | 0.0707 (12) | |
O7 | 0.6687 (3) | 0.1899 (4) | 0.3744 (3) | 0.0647 (10) | |
O8 | 0.4967 (4) | 0.1832 (6) | 0.4926 (3) | 0.1003 (15) | |
C1 | 0.8541 (4) | 0.4051 (5) | 0.7796 (3) | 0.0398 (11) | |
C2 | 0.9709 (5) | 0.3721 (5) | 0.8483 (3) | 0.0422 (10) | |
H2 | 0.9850 | 0.2699 | 0.8769 | 0.051* | |
C3 | 1.0652 (5) | 0.4888 (5) | 0.8743 (3) | 0.0425 (11) | |
C4 | 1.0426 (5) | 0.6443 (6) | 0.8325 (4) | 0.0451 (12) | |
C5 | 0.9267 (5) | 0.6753 (6) | 0.7649 (4) | 0.0538 (13) | |
H5 | 0.9114 | 0.7771 | 0.7361 | 0.065* | |
C6 | 0.8329 (4) | 0.5559 (6) | 0.7395 (3) | 0.0470 (10) | |
H6 | 0.7543 | 0.5786 | 0.6946 | 0.056* | |
C7 | 1.2217 (5) | 0.3085 (6) | 0.9685 (4) | 0.0629 (14) | |
H7A | 1.3051 | 0.3091 | 1.0153 | 0.094* | |
H7B | 1.2360 | 0.2497 | 0.8995 | 0.094* | |
H7C | 1.1497 | 0.2595 | 1.0099 | 0.094* | |
C8 | 1.1307 (7) | 0.9056 (6) | 0.8163 (5) | 0.0830 (17) | |
H8A | 1.2057 | 0.9703 | 0.8450 | 0.124* | |
H8B | 1.0452 | 0.9527 | 0.8366 | 0.124* | |
H8C | 1.1337 | 0.8981 | 0.7343 | 0.124* | |
C9 | 0.7530 (4) | 0.2699 (5) | 0.7509 (3) | 0.0397 (10) | |
C10 | 0.6795 (4) | 0.2119 (6) | 0.8554 (4) | 0.0533 (13) | |
H10 | 0.7486 | 0.1660 | 0.9090 | 0.064* | |
C11B | 0.5998 (4) | 0.3583 (5) | 0.9237 (3) | 0.0986 (19) | 0.901 (2) |
H11A | 0.6625 | 0.4449 | 0.9376 | 0.148* | 0.901 (2) |
H11B | 0.5686 | 0.3191 | 0.9954 | 0.148* | 0.901 (2) |
H11C | 0.5225 | 0.3946 | 0.8772 | 0.148* | 0.901 (2) |
BrA | 0.5998 (4) | 0.3583 (5) | 0.9237 (3) | 0.0986 (19) | 0.099 (2) |
C11A | 0.54926 (6) | 0.04609 (8) | 0.81288 (5) | 0.0828 (3) | 0.099 (2) |
H11D | 0.5511 | −0.0332 | 0.8716 | 0.124* | 0.099 (2) |
H11E | 0.5744 | 0.0002 | 0.7417 | 0.124* | 0.099 (2) |
H11F | 0.4591 | 0.0915 | 0.8048 | 0.124* | 0.099 (2) |
C12 | 0.7187 (4) | 0.2876 (6) | 0.5561 (3) | 0.0431 (11) | |
H12 | 0.7525 | 0.3874 | 0.5243 | 0.065* | |
C13 | 0.8410 (4) | 0.1763 (5) | 0.5873 (3) | 0.0421 (10) | |
H13 | 0.8313 | 0.0789 | 0.5417 | 0.063* | |
C14 | 0.6119 (4) | 0.2134 (6) | 0.4734 (4) | 0.0516 (12) | |
C15 | 0.5804 (5) | 0.1188 (7) | 0.2837 (4) | 0.0763 (17) | |
H15A | 0.6320 | 0.1052 | 0.2160 | 0.115* | |
H15B | 0.5034 | 0.1874 | 0.2669 | 0.115* | |
H15C | 0.5480 | 0.0173 | 0.3088 | 0.115* | |
C16 | 0.9790 (5) | 0.2530 (6) | 0.5634 (4) | 0.0447 (11) | |
C17 | 1.2159 (5) | 0.2473 (8) | 0.6055 (5) | 0.0808 (18) | |
H17A | 1.2813 | 0.1924 | 0.6548 | 0.121* | |
H17B | 1.2198 | 0.3591 | 0.6217 | 0.121* | |
H17C | 1.2373 | 0.2293 | 0.5270 | 0.121* |
U11 | U22 | U33 | U12 | U13 | U23 | |
BrB | 0.0631 (4) | 0.0985 (5) | 0.0866 (5) | −0.0312 (4) | −0.0007 (3) | 0.0309 (4) |
O1 | 0.082 (2) | 0.039 (2) | 0.065 (2) | −0.0110 (19) | −0.0049 (18) | −0.0035 (17) |
O2 | 0.061 (2) | 0.047 (2) | 0.0657 (19) | −0.0022 (17) | −0.0209 (17) | −0.0010 (16) |
O3 | 0.0392 (16) | 0.0388 (17) | 0.0462 (17) | 0.0006 (14) | 0.0014 (13) | 0.0046 (13) |
O4 | 0.0377 (16) | 0.055 (2) | 0.0400 (16) | 0.0113 (14) | −0.0005 (13) | 0.0029 (14) |
O5 | 0.0328 (16) | 0.062 (2) | 0.0679 (19) | −0.0011 (16) | 0.0002 (15) | 0.0096 (17) |
O6 | 0.052 (2) | 0.092 (3) | 0.068 (2) | −0.007 (2) | 0.0058 (17) | 0.032 (2) |
O7 | 0.0491 (19) | 0.098 (3) | 0.0473 (18) | −0.0205 (19) | 0.0013 (15) | −0.0120 (18) |
O8 | 0.0436 (19) | 0.189 (5) | 0.069 (2) | −0.027 (3) | 0.0067 (16) | −0.028 (3) |
C1 | 0.043 (3) | 0.045 (3) | 0.032 (2) | 0.004 (2) | 0.0064 (19) | 0.001 (2) |
C2 | 0.050 (3) | 0.036 (3) | 0.040 (2) | 0.000 (2) | 0.001 (2) | 0.004 (2) |
C3 | 0.048 (3) | 0.042 (3) | 0.037 (2) | 0.000 (2) | 0.000 (2) | −0.004 (2) |
C4 | 0.061 (3) | 0.033 (3) | 0.042 (2) | −0.007 (3) | 0.004 (2) | −0.006 (2) |
C5 | 0.067 (3) | 0.042 (3) | 0.053 (3) | 0.006 (3) | 0.006 (3) | 0.006 (2) |
C6 | 0.054 (3) | 0.043 (3) | 0.044 (2) | 0.006 (3) | −0.0005 (18) | 0.008 (3) |
C7 | 0.054 (3) | 0.053 (4) | 0.080 (3) | 0.002 (3) | −0.016 (3) | 0.011 (3) |
C8 | 0.110 (5) | 0.043 (4) | 0.095 (4) | −0.015 (3) | −0.010 (3) | 0.001 (3) |
C9 | 0.037 (2) | 0.042 (3) | 0.040 (2) | 0.008 (2) | −0.0001 (19) | 0.007 (2) |
C10 | 0.041 (3) | 0.074 (4) | 0.045 (3) | −0.001 (2) | 0.004 (2) | 0.016 (2) |
C11B | 0.082 (3) | 0.143 (4) | 0.072 (2) | 0.015 (2) | 0.0172 (16) | 0.012 (2) |
BrA | 0.082 (3) | 0.143 (4) | 0.072 (2) | 0.015 (2) | 0.0172 (16) | 0.012 (2) |
C11A | 0.0631 (4) | 0.0985 (5) | 0.0866 (5) | −0.0312 (4) | −0.0007 (3) | 0.0309 (4) |
C12 | 0.036 (2) | 0.051 (3) | 0.042 (2) | −0.002 (2) | 0.0032 (19) | 0.000 (2) |
C13 | 0.038 (2) | 0.046 (3) | 0.043 (2) | 0.000 (2) | 0.0006 (18) | −0.005 (2) |
C14 | 0.033 (3) | 0.075 (4) | 0.047 (3) | −0.004 (2) | 0.003 (2) | 0.001 (2) |
C15 | 0.066 (3) | 0.108 (5) | 0.054 (3) | −0.013 (3) | −0.011 (2) | −0.014 (3) |
C16 | 0.039 (3) | 0.053 (3) | 0.042 (3) | 0.000 (2) | 0.005 (2) | −0.004 (2) |
C17 | 0.041 (3) | 0.116 (5) | 0.086 (4) | −0.005 (3) | 0.009 (3) | 0.010 (4) |
BrB—C10 | 1.936 (5) | O8—C14 | 1.179 (5) |
O1—C4 | 1.364 (5) | C1—C6 | 1.366 (6) |
O1—C8 | 1.418 (6) | C1—C2 | 1.393 (6) |
O2—C3 | 1.373 (5) | C1—C9 | 1.532 (6) |
O2—C7 | 1.424 (5) | C2—C3 | 1.369 (6) |
O3—C13 | 1.407 (5) | C3—C4 | 1.410 (6) |
O3—C9 | 1.432 (5) | C4—C5 | 1.376 (6) |
O4—C9 | 1.420 (5) | C5—C6 | 1.381 (7) |
O4—C12 | 1.427 (5) | C9—C10 | 1.518 (5) |
O5—C16 | 1.312 (5) | C10—C11B | 1.673 (6) |
O5—C17 | 1.434 (5) | C12—C14 | 1.524 (6) |
O6—C16 | 1.196 (5) | C12—C13 | 1.547 (6) |
O7—C14 | 1.315 (5) | C13—C16 | 1.525 (6) |
O7—C15 | 1.464 (5) | ||
C4—O1—C8 | 116.8 (4) | O3—C9—C10 | 108.3 (3) |
C3—O2—C7 | 117.2 (3) | O4—C9—C1 | 110.5 (3) |
C13—O3—C9 | 105.8 (3) | O3—C9—C1 | 110.0 (3) |
C9—O4—C12 | 107.2 (3) | C10—C9—C1 | 112.4 (3) |
C16—O5—C17 | 116.6 (4) | C9—C10—C11B | 112.8 (3) |
C14—O7—C15 | 116.2 (3) | C9—C10—BrB | 110.5 (3) |
C6—C1—C2 | 119.5 (4) | C11B—C10—BrB | 110.0 (3) |
C6—C1—C9 | 121.8 (4) | O4—C12—C14 | 108.9 (3) |
C2—C1—C9 | 118.7 (4) | O4—C12—C13 | 104.3 (3) |
C3—C2—C1 | 120.6 (4) | C14—C12—C13 | 113.6 (4) |
C2—C3—O2 | 124.8 (4) | O3—C13—C16 | 114.0 (3) |
C2—C3—C4 | 119.6 (4) | O3—C13—C12 | 104.4 (3) |
O2—C3—C4 | 115.5 (4) | C16—C13—C12 | 112.0 (4) |
O1—C4—C5 | 126.1 (4) | O8—C14—O7 | 124.7 (4) |
O1—C4—C3 | 114.7 (4) | O8—C14—C12 | 126.7 (4) |
C5—C4—C3 | 119.2 (4) | O7—C14—C12 | 108.6 (4) |
C4—C5—C6 | 120.3 (4) | O6—C16—O5 | 124.3 (4) |
C1—C6—C5 | 120.8 (4) | O6—C16—C13 | 123.6 (4) |
O4—C9—O3 | 104.6 (3) | O5—C16—C13 | 111.9 (4) |
O4—C9—C10 | 110.7 (3) | ||
C6—C1—C2—C3 | −1.1 (6) | C2—C1—C9—C10 | 67.5 (5) |
C9—C1—C2—C3 | 178.8 (4) | O4—C9—C10—C11B | −69.5 (4) |
C1—C2—C3—O2 | −179.3 (4) | O3—C9—C10—C11B | 176.4 (3) |
C1—C2—C3—C4 | 1.1 (6) | C1—C9—C10—C11B | 54.6 (4) |
C7—O2—C3—C2 | 10.2 (6) | O4—C9—C10—BrB | 54.1 (4) |
C7—O2—C3—C4 | −170.2 (4) | O3—C9—C10—BrB | −60.0 (4) |
C8—O1—C4—C5 | −5.6 (7) | C1—C9—C10—BrB | 178.2 (3) |
C8—O1—C4—C3 | 174.2 (4) | C9—O4—C12—C14 | 137.1 (4) |
C2—C3—C4—O1 | 179.2 (4) | C9—O4—C12—C13 | 15.5 (4) |
O2—C3—C4—O1 | −0.5 (6) | C9—O3—C13—C16 | 95.0 (4) |
C2—C3—C4—C5 | −1.0 (6) | C9—O3—C13—C12 | −27.6 (4) |
O2—C3—C4—C5 | 179.4 (4) | O4—C12—C13—O3 | 7.6 (4) |
O1—C4—C5—C6 | −179.3 (4) | C14—C12—C13—O3 | −110.9 (4) |
C3—C4—C5—C6 | 0.8 (6) | O4—C12—C13—C16 | −116.3 (4) |
C2—C1—C6—C5 | 1.0 (6) | C14—C12—C13—C16 | 125.2 (4) |
C9—C1—C6—C5 | −178.9 (4) | C15—O7—C14—O8 | −0.9 (8) |
C4—C5—C6—C1 | −0.9 (6) | C15—O7—C14—C12 | −180.0 (4) |
C12—O4—C9—O3 | −33.0 (4) | O4—C12—C14—O8 | −0.5 (7) |
C12—O4—C9—C10 | −149.4 (4) | C13—C12—C14—O8 | 115.2 (6) |
C12—O4—C9—C1 | 85.4 (4) | O4—C12—C14—O7 | 178.6 (4) |
C13—O3—C9—O4 | 38.1 (4) | C13—C12—C14—O7 | −65.7 (5) |
C13—O3—C9—C10 | 156.2 (3) | C17—O5—C16—O6 | 0.7 (7) |
C13—O3—C9—C1 | −80.6 (4) | C17—O5—C16—C13 | 177.2 (4) |
C6—C1—C9—O4 | 11.5 (5) | O3—C13—C16—O6 | −144.9 (4) |
C2—C1—C9—O4 | −168.3 (3) | C12—C13—C16—O6 | −26.6 (6) |
C6—C1—C9—O3 | 126.5 (4) | O3—C13—C16—O5 | 38.6 (5) |
C2—C1—C9—O3 | −53.3 (5) | C12—C13—C16—O5 | 157.0 (4) |
C6—C1—C9—C10 | −112.7 (4) |
Experimental details
Crystal data | |
Chemical formula | C17H21BrO8 |
Mr | 433.25 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 293 |
a, b, c (Å) | 9.728 (2), 8.414 (2), 11.674 (2) |
β (°) | 92.23 (3) |
V (Å3) | 954.8 (3) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 2.19 |
Crystal size (mm) | 0.50 × 0.43 × 0.40 |
Data collection | |
Diffractometer | Nonius CAD-4 diffractometer |
Absorption correction | ψ scan (PLATON; Spek, 1990) |
Tmin, Tmax | 0.39, 0.42 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3275, 3024, 1916 |
Rint | 0.018 |
(sin θ/λ)max (Å−1) | 0.659 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.035, 0.086, 1.00 |
No. of reflections | 3024 |
No. of parameters | 237 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.35, −0.31 |
Absolute structure | Flack (1983) |
Absolute structure parameter | −0.018 (11) |
Computer programs: CAD-4 EXPRESS (Enraf-Nonius, 1994), SET4 in CAD-4 EXPRESS, HELENA (Spek, 1996), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ZORTEP (Zsolnai et al., 1996), SHELXL97..
BrB—C10 | 1.936 (5) | O4—C12 | 1.427 (5) |
O3—C13 | 1.407 (5) | C9—C10 | 1.518 (5) |
O3—C9 | 1.432 (5) | C10—C11B | 1.673 (6) |
O4—C9 | 1.420 (5) | C12—C13 | 1.547 (6) |
C13—O3—C9 | 105.8 (3) | C10—C9—C1 | 112.4 (3) |
C9—O4—C12 | 107.2 (3) | C9—C10—C11B | 112.8 (3) |
O4—C9—O3 | 104.6 (3) | C9—C10—BrB | 110.5 (3) |
O4—C9—C10 | 110.7 (3) | C11B—C10—BrB | 110.0 (3) |
O3—C9—C1 | 110.0 (3) | ||
C12—O4—C9—O3 | −33.0 (4) | O4—C12—C13—O3 | 7.6 (4) |
C13—O3—C9—O4 | 38.1 (4) | C14—C12—C13—C16 | 125.2 (4) |
C9—O4—C12—C13 | 15.5 (4) | O4—C12—C14—O8 | −0.5 (7) |
C9—O3—C13—C12 | −27.6 (4) | O3—C13—C16—O6 | −144.9 (4) |
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Single crystals of (Ib) were obtained by a synthetic route (Castaldi et al., 1987) using the 3,4-dimethoxypropylphenone as starting material which requires, in an intermediate step, an acid-promoted bromination of the enol ether by a substrate-controlled diasteroselective synthesis of the bromoketal with an observed stereochemistry, as confirmed also by present X-ray studies of the title diastereomer. The crystal structure determination was undertaken to establish the absolute stereochemistry of the newly formed chiral center at C10 in the reaction product, (Ib), according to the scheme below. The absolute configuration of the other asymmetric centres at C12 and C13 being already known. These findings are important in understanding the mechanism of diasterofacial selectivity induced by a chiral auxiliary in the halogenation of aryl enol ethers (Castaldi et al., 1986, 1987; Giordano et al., 1990), which is the key step in the industrial asymmetric synthesis of α-arylpropionic acid derivatives (Giordano et al., 1989; Elks & Gamellin, 1990), the non-steroidal anti-inflammatories drugs widely prescribed as an analgesic and in the treatment of rheumatoid arthritis (Reuben & Wittcoff, 1989), and also in the enantiomeric synthesis of sulfur analogue of 8,4'-oxyneolignan derivative showing selective antagonistic activity in Platelet Activating Factor-induced platelet aggregation (Lariucci et al., 1995).
A ZORTEP (Zsolnai et al., 1996) plot of the molecule and the atomic numbering is shown in Fig. 1. Selected bond distances and angles are given in Table 1.
All distances are within their typical values except for C10—C11B [1.673 (6) Å], which is longer than expected and BrB-C10 [1.936 (5) Å] which is shorter than expected (cf. value quoted by Allen et al., 1987). These differences are due to the disorder of the Br and C11 atom sites with BrA and BrB (C11A and C11B) in the proportions of 9.9% and 90.1%, respectively (see Experimental).
With regard to the bond lengths in the 1,3-dioxolane ring, the distance C9—O3 [1.432 (5) A], is significantly longer than O3—C13 [1.407 (5) A], while the difference between C9—O4 [1.420 (5) A] and O4—C12 [1.427 (5) A] is not significant, showing a smaller distortion than those strongly distorted 1,4-dioxaspiro structures (Ianelli et al., 1992). Within the limits of experimental error, the ring's carbon atoms are situated in the aromatic ring plane, mean deviations being close to 0.003 Å. The methoxyl oxygen atoms are almost coplanar with the respective ring [O1, 0.012 (6) Å; O2, −0.011 (6) Å], while the methoxyl carbons atoms C7 and C8 are not [−0.233 (8) and −0.109 (9) Å, respectively]. The ring O3→ C13→ ···C9 shows a twisted conformation, with the Cremer & Pople (1975) puckering parameters Q2 = 0.334 (4) Å and ϕ2 = 347.7 (7)°. The orientation of the two methoxycarbonyl substituents is near to the anticlinal oriented with respect to one another, as indicated by the C16—C13—C12—C14 torsion angle of 125.2 (4)°. However, the torsion angles of O3—C13—C16—O6 [−144.9 (4)°] and O4—C12—C14—O8 [−0.5 (7)°] show that the situation of these groups are not the same, presumably as a result of a short intramolecular contact between the C12 and O6 atoms with a geometry that would qualify as a C—H···O bond (Desiraju, 1996): C12—H12···O6 [C—H···O 107.5°, O···H 2.40 and C···O 2.856 (6) Å]. The application of semiempirical (AM1, PM3 MNDO), molecular mechanics, and ab initio methods carried out with the MOPAC6.0 (Stewart, 1990), DISCOVER-CFF91 force field) (Molecular Simulations, 1997), and GAUSSIAN94 (Frisch et al., 1994; Hehre et al., 1986) packages, respectively, show that these torsion angles are similar [81.5 and 3.2°, respectively]. Additionally, the CFF91 force field computations show that 1,3-dioxolane ring adopts a C13β-envelope conformation which is 16.8 kJ.mol1 more stable than the C13α-conformer obtained in the solid state. These different situations have shown that packing interactions are the most important factors determining the conformation of these groups in the crystal. There are another intramolecular and two intermolecular C—H···O interactions: C6—H6···O4 [C—H···O 102.1°, O···H 2.42 and C···O 2.767 (5) Å]; C10—H10···O2i [C—H···O 150.4°, O···H 2.50 and C···O 3.384 (5) Å]; C13—H13···O6ii [C—H···O 130.2°, O···H 2.59 and C···O 3.308 (6) Å] with symmetry codes (i) 2 − x, −1/2 + y, 2 − z; (ii) 2 − x, −1/2 + y, 1 − z.