Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807022428/hb2377sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807022428/hb2377Isup2.hkl |
CCDC reference: 651442
Key indicators
- Single-crystal X-ray study
- T = 173 K
- Mean (C-C) = 0.002 Å
- R factor = 0.044
- wR factor = 0.102
- Data-to-parameter ratio = 14.1
checkCIF/PLATON results
No syntax errors found
Alert level G PLAT793_ALERT_1_G Check the Absolute Configuration of C2 = ... R PLAT793_ALERT_1_G Check the Absolute Configuration of C7 = ... R
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 0 ALERT level C = Check and explain 2 ALERT level G = General alerts; check 2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 0 ALERT type 2 Indicator that the structure model may be wrong or deficient 0 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check
For related literature, see: Albarella et al. (2001); Brown & Keily (2001); de Champdoré et al. (1998); Charlsen et al. (1981); Donohoe & Butterworth (2003); Luger et al. (1991); Matsumura et al. (2000); Piccialli (2000); Piccialli & Cavallo (2001); Roth & Stark (2006); Roth et al. (2005).
For related literature, see: Hoberg (1988); Piccialli & Caserta (2004).
The oxidative cyclization was accomplished as shown in Scheme 1. Ru-catalyzed oxidative cyclizations of dienes are generally conducted in solvent mixtures containing water (e.g EtOAc/CH3CN/H2O, 3:3:1) to dissolve NaIO4 that acts as the final oxidant. However, exclusion of water from the reaction mixture has recently been demonstrated to increase the yields of the THF diols obtained from the oxidation of 1,5-dienes. (Roth et al., 2005). Therefore, after some experimentation, the process was run in EtOAc/CH3CN (1:1) with NaIO4 (7 equiv.) supported on wet silica. These conditions proved very effective giving trans-oxepane (I) in an isolated 63% yield (HPLC, hexane/EtOAc, 7:3, Rt= 34 min) with >95% stereoselectivity level.
In particular, to a suspension of NaIO4 supported on wet silica (7 eqiv, 1.90 g) in EtOAc/CH3CN (1:1, 5.8 ml) was added 2,9-dimethyldeca-2,8-diene in EtOAc/CH3CN (1:1, 0.5 ml). Then, RuCl3 (160 µL of a 0.1 M stock solution in EtOAc, 5 mol %) was added via syringe, at 273 K under stirring. After 15 min reaction, TLC analysis (I2) showed complete consumption of the diene and formation of a product at Rf 0.6 (EtOAc/hexane, 7:3). The process was quenched by addition of a few drops of isopropylalcohol. The mixture was filtered and the solid washed with EtOAc and MeOH and the crude mixture chromatographed over a Si-gel column (25 × 0.5 cm). Elution with EtOAc-petroleum ether (1:1, 50 ml) gave 20 mg (63%) of the pure oxepane diol (I).
1H-NMR (500 MHz, CDCl3): δ 3.63 (1H, dd, J=10.6, 2.2, H-3/H-8), 1.94, 1.87 (2H each, H2-4/H2-7), 1.52, 1.37 (2H each, H2-5/H2-6), 1.22, 1.16 (6H each, 4 x Me). 13C NMR (75 MHz, CDCl3) δ 82.6, 73.9, 29.6, 27.8, 27.7, 24.2.
Single crystals of (I) suitable for structure determination were obtained from a chloroform solution by slow evaporation at room temperature.
The H atoms were located in difference maps and their coordinates were refined with Uiso(H) = Ueq(carrier).
Ruthenium tetroxide is able to catalyze the stereoselective synthesis of 2,5-bishydroxyalkyl-substituted THF and/or THP rings from 1,5- and 1,6-dienes, respectively, via oxygen transfer to the diene system, in the presence of sodium periodate as reoxidant (Charlsen et al., 1981; Piccialli, 2000; Piccialli & Cavallo, 2001; Albarella et al., 2001; Roth et al., 2005; Roth & Stark, 2006). Related oxidative cyclization processes, mediated by other transition metal-oxo species such as OsO4, MnO4-, RuO4-, are also known (Brown & Keily, 2001; de Champdoré et al., 1998; Piccialli & Caserta, 2004; Donohoe & Butterworth, 2003). We decided to investigate the same oxidative transformation on 1,7-dienes envisaging that the process could lead to the formation of oxepane rings as well.
Seven-membered oxacycles are present in many biologically active natural products such as Laurencia acetogenin metabolites and ether marine toxin. In these compounds the oxepane ring is very often 2,7 dialkylsubstituted. While some efficient methods toward the stereoselective synthesis of 2,7-cis-oxepanes have been developed, few methods have been so far devised to generate the 2,7-trans-oxepane system (Hoberg, 1998; Matsumura et al., 2000). Thus, taking into account the electrophilic character of RuO4, and precedents from the oxidation of 1,5- and 1,6-dienes, 2,9-dimethyldeca-2,8-diene was initially selected as a good substrate to test this possibility.
In this paper we report that the ruthenium-catalyzed oxidative cyclization of 2,9-dimethyldeca-2,8-diene gives the trans-oxepane diol product, (I). The X-ray analysis showed that the (R,R), (S,S) racemic mixture is formed, with the molecule in trans-configuration (Fig. 1 and Table 1). The oxepane ring adopts a twisted-chair conformation (Table 1) as usually found in oxepane derivatives (Luger et al., 1991). This conformation appears also to be the one adopted by mono-p-bromobenzoate derivative of (I) in solution as indicated by NOE data and J values.
This is the first report dealing with the synthesis of an oxepane product through oxidative cyclization of an 1,7-diene.
Crystal packing with indication of H bonds is shown in Fig. 2. Hydrogen bonds are summarized in Table 2. There is an intramolecular hydrogen bond, whose graph set descriptor is S(8), from O3 donor to O2 acceptor, leading to the formation of an eight-membered ring.
Molecules in the crystals are linked through intermolecular O—H···O bonds forming chains running along a, whose graph set descriptor is C22(4). The rows are generated by the glide planes normal to c axis.
For related literature, see: Albarella et al. (2001); Brown & Keily (2001); de Champdoré et al. (1998); Charlsen et al. (1981); Donohoe & Butterworth (2003); Luger et al. (1991); Matsumura et al. (2000); Piccialli (2000); Piccialli & Cavallo (2001); Roth & Stark (2006); Roth et al. (2005).
For related literature, see: Hoberg (1988); Piccialli & Caserta (2004).
Data collection: COLLECT (Nonius, 1999); cell refinement: DIRAX/LSQ (Duisenberg et al., 2000); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
C12H24O3 | F(000) = 960 |
Mr = 216.31 | Dx = 1.119 Mg m−3 |
Orthorhombic, Pbca | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2ab | Cell parameters from 86 reflections |
a = 8.4400 (16) Å | θ = 3.4–19.5° |
b = 16.473 (3) Å | µ = 0.08 mm−1 |
c = 18.470 (5) Å | T = 173 K |
V = 2567.9 (10) Å3 | Prism, colourless |
Z = 8 | 0.25 × 0.20 × 0.10 mm |
Bruker-Nonius KappaCCD diffractometer | 2926 independent reflections |
Radiation source: fine-focus sealed tube | 1811 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.082 |
Detector resolution: 9 pixels mm-1 | θmax = 27.5°, θmin = 3.3° |
CCD rotation images, thick slices scans | h = −10→10 |
Absorption correction: multi-scan (SADABS; Bruker–Nonius, 2002) | k = −17→21 |
Tmin = 0.978, Tmax = 0.988 | l = −23→21 |
20554 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.044 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.102 | Only H-atom coordinates refined |
S = 1.02 | w = 1/[σ2(Fo2) + (0.038P)2 + 0.5591P] where P = (Fo2 + 2Fc2)/3 |
2926 reflections | (Δ/σ)max < 0.001 |
208 parameters | Δρmax = 0.24 e Å−3 |
0 restraints | Δρmin = −0.17 e Å−3 |
C12H24O3 | V = 2567.9 (10) Å3 |
Mr = 216.31 | Z = 8 |
Orthorhombic, Pbca | Mo Kα radiation |
a = 8.4400 (16) Å | µ = 0.08 mm−1 |
b = 16.473 (3) Å | T = 173 K |
c = 18.470 (5) Å | 0.25 × 0.20 × 0.10 mm |
Bruker-Nonius KappaCCD diffractometer | 2926 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker–Nonius, 2002) | 1811 reflections with I > 2σ(I) |
Tmin = 0.978, Tmax = 0.988 | Rint = 0.082 |
20554 measured reflections |
R[F2 > 2σ(F2)] = 0.044 | 0 restraints |
wR(F2) = 0.102 | Only H-atom coordinates refined |
S = 1.02 | Δρmax = 0.24 e Å−3 |
2926 reflections | Δρmin = −0.17 e Å−3 |
208 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 | 0.00809 (12) | 0.04118 (6) | 0.90900 (5) | 0.0255 (3) | |
O2 | −0.10634 (13) | 0.07424 (7) | 0.77014 (6) | 0.0345 (3) | |
H2O | −0.185 (2) | 0.0479 (11) | 0.7584 (9) | 0.035* | |
O3 | 0.15740 (14) | −0.01681 (7) | 0.78139 (5) | 0.0312 (3) | |
H3O | 0.072 (2) | 0.0072 (11) | 0.7781 (8) | 0.031* | |
C2 | 0.15237 (18) | −0.00501 (9) | 0.91339 (8) | 0.0270 (4) | |
H2 | 0.1361 (17) | −0.0388 (10) | 0.9560 (8) | 0.027* | |
C3 | 0.2978 (2) | 0.04707 (11) | 0.92827 (9) | 0.0323 (4) | |
H3A | 0.3339 (18) | 0.0754 (10) | 0.8836 (9) | 0.032* | |
H3B | 0.382 (2) | 0.0112 (10) | 0.9424 (9) | 0.032* | |
C4 | 0.2726 (2) | 0.10787 (11) | 0.98981 (9) | 0.0379 (4) | |
H4A | 0.207 (2) | 0.0818 (10) | 1.0290 (8) | 0.038* | |
H4B | 0.377 (2) | 0.1205 (10) | 1.0105 (9) | 0.038* | |
C5 | 0.1973 (2) | 0.18820 (11) | 0.96685 (10) | 0.0385 (4) | |
H5A | 0.265 (2) | 0.2133 (10) | 0.9287 (9) | 0.039* | |
H5B | 0.199 (2) | 0.2266 (10) | 1.0091 (9) | 0.039* | |
C6 | 0.0286 (2) | 0.18288 (10) | 0.93785 (9) | 0.0320 (4) | |
H6A | −0.0038 (19) | 0.2358 (10) | 0.9216 (8) | 0.032* | |
H6B | −0.044 (2) | 0.1686 (9) | 0.9770 (8) | 0.032* | |
C7 | 0.01118 (18) | 0.12087 (9) | 0.87740 (8) | 0.0253 (3) | |
H7 | 0.1026 (19) | 0.1262 (9) | 0.8431 (8) | 0.025* | |
C8 | −0.13765 (18) | 0.12793 (10) | 0.82998 (8) | 0.0291 (4) | |
C9 | −0.2878 (2) | 0.10296 (12) | 0.86928 (10) | 0.0355 (4) | |
H9A | −0.283 (2) | 0.0472 (11) | 0.8852 (9) | 0.035* | |
H9B | −0.307 (2) | 0.1363 (10) | 0.9119 (9) | 0.035* | |
H9C | −0.378 (2) | 0.1079 (10) | 0.8360 (9) | 0.035* | |
C10 | −0.1541 (3) | 0.21341 (12) | 0.79847 (12) | 0.0451 (5) | |
H10A | −0.186 (2) | 0.2511 (12) | 0.8354 (10) | 0.045* | |
H10B | −0.237 (2) | 0.2126 (11) | 0.7604 (9) | 0.045* | |
H10C | −0.052 (2) | 0.2298 (11) | 0.7752 (9) | 0.045* | |
C11 | 0.16319 (19) | −0.06260 (9) | 0.84775 (8) | 0.0295 (4) | |
C12 | 0.3197 (2) | −0.10858 (12) | 0.84672 (11) | 0.0413 (4) | |
H12A | 0.409 (2) | −0.0726 (11) | 0.8373 (9) | 0.041* | |
H12B | 0.333 (2) | −0.1365 (11) | 0.8936 (10) | 0.041* | |
H12C | 0.312 (2) | −0.1483 (11) | 0.8092 (9) | 0.041* | |
C13 | 0.0240 (2) | −0.12139 (11) | 0.84791 (10) | 0.0368 (4) | |
H13A | 0.027 (2) | −0.1555 (10) | 0.8037 (9) | 0.037* | |
H13B | 0.029 (2) | −0.1577 (10) | 0.8913 (9) | 0.037* | |
H13C | −0.073 (2) | −0.0938 (11) | 0.8474 (8) | 0.037* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0243 (6) | 0.0224 (5) | 0.0297 (5) | −0.0022 (4) | 0.0025 (4) | 0.0020 (4) |
O2 | 0.0261 (6) | 0.0472 (7) | 0.0303 (6) | −0.0026 (5) | −0.0022 (5) | −0.0071 (5) |
O3 | 0.0292 (6) | 0.0370 (6) | 0.0273 (5) | 0.0035 (5) | 0.0049 (5) | 0.0028 (5) |
C2 | 0.0270 (9) | 0.0261 (8) | 0.0277 (8) | 0.0022 (6) | 0.0017 (6) | 0.0056 (7) |
C3 | 0.0276 (9) | 0.0351 (9) | 0.0343 (9) | 0.0010 (7) | −0.0036 (7) | 0.0039 (7) |
C4 | 0.0336 (10) | 0.0432 (10) | 0.0370 (9) | −0.0037 (8) | −0.0111 (8) | −0.0037 (8) |
C5 | 0.0402 (11) | 0.0325 (9) | 0.0429 (10) | −0.0081 (8) | −0.0085 (8) | −0.0067 (8) |
C6 | 0.0356 (10) | 0.0237 (9) | 0.0365 (9) | −0.0020 (7) | −0.0015 (7) | −0.0013 (7) |
C7 | 0.0262 (8) | 0.0214 (8) | 0.0284 (8) | −0.0036 (6) | 0.0007 (7) | 0.0025 (6) |
C8 | 0.0261 (9) | 0.0314 (8) | 0.0298 (8) | −0.0001 (7) | 0.0000 (6) | −0.0021 (7) |
C9 | 0.0255 (9) | 0.0433 (11) | 0.0376 (10) | −0.0003 (8) | 0.0025 (7) | −0.0068 (8) |
C10 | 0.0416 (12) | 0.0424 (11) | 0.0515 (11) | 0.0029 (9) | −0.0118 (9) | 0.0111 (9) |
C11 | 0.0328 (9) | 0.0273 (8) | 0.0284 (8) | 0.0019 (7) | 0.0047 (7) | 0.0038 (6) |
C12 | 0.0433 (11) | 0.0372 (10) | 0.0434 (10) | 0.0118 (9) | 0.0052 (9) | 0.0008 (9) |
C13 | 0.0450 (11) | 0.0290 (9) | 0.0365 (10) | −0.0052 (8) | 0.0051 (8) | −0.0043 (8) |
C7—O1 | 1.4368 (17) | C6—H6B | 0.978 (17) |
C2—O1 | 1.4382 (18) | C7—C8 | 1.536 (2) |
O2—C8 | 1.4399 (18) | C7—H7 | 1.002 (16) |
O2—H2O | 0.819 (18) | C8—C9 | 1.518 (2) |
O3—C11 | 1.4400 (18) | C8—C10 | 1.530 (2) |
O3—H3O | 0.824 (18) | C9—H9A | 0.965 (18) |
C2—C3 | 1.523 (2) | C9—H9B | 0.973 (17) |
C2—C11 | 1.542 (2) | C9—H9C | 0.982 (17) |
C2—H2 | 0.974 (16) | C10—H10A | 0.963 (19) |
C3—C4 | 1.530 (2) | C10—H10B | 0.990 (19) |
C3—H3A | 0.995 (16) | C10—H10C | 1.000 (19) |
C3—H3B | 0.958 (17) | C11—C12 | 1.522 (2) |
C4—C5 | 1.528 (3) | C11—C13 | 1.523 (2) |
C4—H4A | 1.006 (17) | C12—H12A | 0.972 (19) |
C4—H4B | 0.982 (18) | C12—H12B | 0.986 (18) |
C5—C6 | 1.523 (2) | C12—H12C | 0.956 (18) |
C5—H5A | 0.997 (18) | C13—H13A | 0.992 (17) |
C5—H5B | 1.004 (18) | C13—H13B | 1.001 (17) |
C6—C7 | 1.520 (2) | C13—H13C | 0.938 (18) |
C6—H6A | 0.961 (17) | ||
C7—O1—C2 | 119.40 (11) | C8—C7—H7 | 105.2 (8) |
C8—O2—H2O | 112.4 (12) | O2—C8—C9 | 110.73 (13) |
C11—O3—H3O | 110.0 (11) | O2—C8—C10 | 106.86 (14) |
O1—C2—C3 | 113.24 (12) | C9—C8—C10 | 110.82 (15) |
O1—C2—C11 | 109.35 (12) | O2—C8—C7 | 103.95 (12) |
C3—C2—C11 | 116.16 (13) | C9—C8—C7 | 112.94 (13) |
O1—C2—H2 | 103.2 (9) | C10—C8—C7 | 111.16 (14) |
C3—C2—H2 | 106.9 (9) | C8—C9—H9A | 111.7 (10) |
C11—C2—H2 | 107.0 (9) | C8—C9—H9B | 111.7 (10) |
C2—C3—C4 | 113.03 (14) | H9A—C9—H9B | 107.3 (13) |
C2—C3—H3A | 111.2 (9) | C8—C9—H9C | 108.9 (10) |
C4—C3—H3A | 110.5 (9) | H9A—C9—H9C | 107.6 (14) |
C2—C3—H3B | 107.3 (10) | H9B—C9—H9C | 109.5 (14) |
C4—C3—H3B | 107.7 (10) | C8—C10—H10A | 110.5 (11) |
H3A—C3—H3B | 106.7 (13) | C8—C10—H10B | 108.7 (10) |
C5—C4—C3 | 114.74 (14) | H10A—C10—H10B | 108.3 (15) |
C5—C4—H4A | 109.9 (10) | C8—C10—H10C | 109.5 (11) |
C3—C4—H4A | 109.3 (10) | H10A—C10—H10C | 112.0 (15) |
C5—C4—H4B | 107.3 (10) | H10B—C10—H10C | 107.7 (14) |
C3—C4—H4B | 107.7 (10) | O3—C11—C12 | 106.22 (13) |
H4A—C4—H4B | 107.6 (13) | O3—C11—C13 | 107.98 (13) |
C6—C5—C4 | 115.89 (15) | C12—C11—C13 | 110.66 (15) |
C6—C5—H5A | 108.1 (10) | O3—C11—C2 | 110.18 (12) |
C4—C5—H5A | 108.4 (10) | C12—C11—C2 | 111.54 (14) |
C6—C5—H5B | 108.8 (10) | C13—C11—C2 | 110.12 (13) |
C4—C5—H5B | 108.9 (9) | C11—C12—H12A | 111.6 (11) |
H5A—C5—H5B | 106.2 (13) | C11—C12—H12B | 108.6 (10) |
C7—C6—C5 | 112.79 (14) | H12A—C12—H12B | 110.7 (14) |
C7—C6—H6A | 110.7 (9) | C11—C12—H12C | 106.9 (11) |
C5—C6—H6A | 108.9 (10) | H12A—C12—H12C | 109.8 (14) |
C7—C6—H6B | 108.7 (9) | H12B—C12—H12C | 109.0 (14) |
C5—C6—H6B | 110.0 (10) | C11—C13—H13A | 109.8 (10) |
H6A—C6—H6B | 105.6 (13) | C11—C13—H13B | 110.6 (10) |
O1—C7—C6 | 108.51 (12) | H13A—C13—H13B | 108.7 (13) |
O1—C7—C8 | 106.62 (12) | C11—C13—H13C | 111.5 (11) |
C6—C7—C8 | 116.56 (13) | H13A—C13—H13C | 106.8 (14) |
O1—C7—H7 | 110.6 (9) | H13B—C13—H13C | 109.4 (14) |
C6—C7—H7 | 109.3 (9) | ||
C7—O1—C2—C3 | 35.73 (17) | C6—C7—C8—O2 | 168.50 (13) |
C7—O1—C2—C11 | −95.51 (14) | O1—C7—C8—C9 | 49.88 (17) |
O1—C2—C3—C4 | 47.03 (18) | C6—C7—C8—C9 | −71.42 (18) |
C11—C2—C3—C4 | 174.81 (13) | O1—C7—C8—C10 | 175.18 (13) |
C2—C3—C4—C5 | −85.78 (19) | C6—C7—C8—C10 | 53.88 (19) |
C3—C4—C5—C6 | 64.5 (2) | O1—C2—C11—O3 | 58.09 (16) |
C4—C5—C6—C7 | −52.3 (2) | C3—C2—C11—O3 | −71.58 (17) |
C2—O1—C7—C6 | −95.30 (14) | O1—C2—C11—C12 | 175.81 (13) |
C2—O1—C7—C8 | 138.41 (12) | C3—C2—C11—C12 | 46.14 (19) |
C5—C6—C7—O1 | 77.03 (17) | O1—C2—C11—C13 | −60.91 (16) |
C5—C6—C7—C8 | −162.67 (14) | C3—C2—C11—C13 | 169.41 (14) |
O1—C7—C8—O2 | −70.20 (14) |
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H2O···O3i | 0.819 (18) | 1.859 (18) | 2.6705 (16) | 170.7 (17) |
O3—H3O···O2 | 0.824 (18) | 1.873 (18) | 2.6921 (17) | 172.4 (17) |
Symmetry code: (i) x−1/2, y, −z+3/2. |
Experimental details
Crystal data | |
Chemical formula | C12H24O3 |
Mr | 216.31 |
Crystal system, space group | Orthorhombic, Pbca |
Temperature (K) | 173 |
a, b, c (Å) | 8.4400 (16), 16.473 (3), 18.470 (5) |
V (Å3) | 2567.9 (10) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.08 |
Crystal size (mm) | 0.25 × 0.20 × 0.10 |
Data collection | |
Diffractometer | Bruker-Nonius KappaCCD |
Absorption correction | Multi-scan (SADABS; Bruker–Nonius, 2002) |
Tmin, Tmax | 0.978, 0.988 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 20554, 2926, 1811 |
Rint | 0.082 |
(sin θ/λ)max (Å−1) | 0.650 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.044, 0.102, 1.02 |
No. of reflections | 2926 |
No. of parameters | 208 |
H-atom treatment | Only H-atom coordinates refined |
Δρmax, Δρmin (e Å−3) | 0.24, −0.17 |
Computer programs: COLLECT (Nonius, 1999), DIRAX/LSQ (Duisenberg et al., 2000), EVALCCD (Duisenberg et al., 2003), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), WinGX (Farrugia, 1999).
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H2O···O3i | 0.819 (18) | 1.859 (18) | 2.6705 (16) | 170.7 (17) |
O3—H3O···O2 | 0.824 (18) | 1.873 (18) | 2.6921 (17) | 172.4 (17) |
Symmetry code: (i) x−1/2, y, −z+3/2. |
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Ruthenium tetroxide is able to catalyze the stereoselective synthesis of 2,5-bishydroxyalkyl-substituted THF and/or THP rings from 1,5- and 1,6-dienes, respectively, via oxygen transfer to the diene system, in the presence of sodium periodate as reoxidant (Charlsen et al., 1981; Piccialli, 2000; Piccialli & Cavallo, 2001; Albarella et al., 2001; Roth et al., 2005; Roth & Stark, 2006). Related oxidative cyclization processes, mediated by other transition metal-oxo species such as OsO4, MnO4-, RuO4-, are also known (Brown & Keily, 2001; de Champdoré et al., 1998; Piccialli & Caserta, 2004; Donohoe & Butterworth, 2003). We decided to investigate the same oxidative transformation on 1,7-dienes envisaging that the process could lead to the formation of oxepane rings as well.
Seven-membered oxacycles are present in many biologically active natural products such as Laurencia acetogenin metabolites and ether marine toxin. In these compounds the oxepane ring is very often 2,7 dialkylsubstituted. While some efficient methods toward the stereoselective synthesis of 2,7-cis-oxepanes have been developed, few methods have been so far devised to generate the 2,7-trans-oxepane system (Hoberg, 1998; Matsumura et al., 2000). Thus, taking into account the electrophilic character of RuO4, and precedents from the oxidation of 1,5- and 1,6-dienes, 2,9-dimethyldeca-2,8-diene was initially selected as a good substrate to test this possibility.
In this paper we report that the ruthenium-catalyzed oxidative cyclization of 2,9-dimethyldeca-2,8-diene gives the trans-oxepane diol product, (I). The X-ray analysis showed that the (R,R), (S,S) racemic mixture is formed, with the molecule in trans-configuration (Fig. 1 and Table 1). The oxepane ring adopts a twisted-chair conformation (Table 1) as usually found in oxepane derivatives (Luger et al., 1991). This conformation appears also to be the one adopted by mono-p-bromobenzoate derivative of (I) in solution as indicated by NOE data and J values.
This is the first report dealing with the synthesis of an oxepane product through oxidative cyclization of an 1,7-diene.
Crystal packing with indication of H bonds is shown in Fig. 2. Hydrogen bonds are summarized in Table 2. There is an intramolecular hydrogen bond, whose graph set descriptor is S(8), from O3 donor to O2 acceptor, leading to the formation of an eight-membered ring.
Molecules in the crystals are linked through intermolecular O—H···O bonds forming chains running along a, whose graph set descriptor is C22(4). The rows are generated by the glide planes normal to c axis.