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Acta Cryst. (2012). E68, o3392-o3393    [ doi:10.1107/S1600536812046776 ]

(2aR*,5S*,6aS*,8aS*,E)-Ethyl 5-hydroxy-7,7,8a-trimethyl-8-oxo-2,2a,6,6a,7,8,8a,8b-octahydro-1H-pentaleno[1,6-bc]oxepine-4-carboxylate

G. Mehta, C. S. A. Kumar and S. Sen

Abstract top

The title compound, C17H24O5, featuring a 2-carbethoxy-3-oxepanone unit in its intramolecularly O-H...O hydrogen-bonded enol form, was obtained via [(CF3CO2)2Rh]2-catalysed intramolecular O-H bond insertion in the [alpha]-diazo-[omega]-hydroxy-[beta]-ketoester, ethyl 4-[(1S,3aS,6R,6aS)-6-hydroxy-2,2,3a-trimethyl-3-oxo-octahydropentalen-1-yl]-2-diazo-3-oxobutanoate. The seven-membered oxacyclic ring, thus constructed on a cis-fused diquinane platform, was found to adopt a distorted boat-sofa conformation.

Comment top

Rhodium carbenoid mediated O—H insertion provides a facile means of transforming diazo-compounds into diverse range of functionalized ethers (Paulissen, et al., 1973; Cox, et al. 1994; Haigh, 1994; Aller et al., 1995; Shi et al., 1995; Bulugahapitiya et al., 1997; Moody & Miller, 1998; Morton et al., 2012). Hence the methodology has proven to be a useful stratagem in the synthetic acquisition of several natural products (Nelson et al., 2000; Medeiros & Wood, 2010; Freeman, et al. 2010). While not as extensively utilized or studied as the intermolecular variants, intramolecular interception of rhodium carbenoids by hydroxy nucleophiles can, nevertheless, afford an effective route to cyclic ethers and lactones (Paulissen et al., 1974; Moyer et al., 1985; Moody & Taylor, 1987; Heslin & Moody, 1988; Moody et al. 1992; Sarabia-García et al., 1994; Padwa & Sá, 1999; Im et al., 2005). Indeed, studies by Moody and co-workers have shown that rhodium(II) acetate catalysed cyclization in diazoalcohols may even be employed as a practical method for accessing medium-ring oxacycles - oxepanes, in particular, wherein interference from competing C—H insertion reactions do not appear to be significant (Heslin & Moody, 1988; Davies et al., 1990).

Against this background, we report herein the crystal structure of the title compound 1, a 2-carbethoxy-3-oxepanone embedded in a tricyclic framework, that was obtained as the sole isolable product in the rhodium(II) trifluroacetate mediated decomposition of the α-diazo-ω-hydroxy-β-ketoester 2 (Figure 1). Originally envisaged as an entry point to an angularly fused triquinane skeleton via Rh(II) catalyzed intramolecular C—H insertion (Doyle et al., 2010; Davies & Morton, 2011; Srikrishna et al., 2012) en route to the natural product penifulvin A (Shim et al., 2006; Gaich & Mulzer, 2009; Mehta & Khan, 2012), the diazoester 2 was prepared from the β-ketoester 3 via a diazo transfer reaction to the activated methylene group in 3 (Baum et al., 1987).

The crystal structure of 1 was solved and refined in the centrosymmetric orthorhombic space group Pbcn (Z = 8). The 2-carbethoxy-3-oxepanone moiety in 1 was found to exist in the intramolecularly O—H···O hydrogen bonded enol form (Figure 2). As indicated by its puckering parameters (q2 = 0.915 (3) Å, q3 = 0.310 (3) Å, φ2 = 193.59 (17)°, φ3 = 118.9 (5)°, QT = 0.967 (2) Å), the seven-membered oxacyclic ring adopted a distorted boat-sofa conformation (Cremer & Pople, 1975; Boessenkool & Boeyens, 1980). Crystal packing in 1 was effected primarily via the agency of weak van der Waals interactions, though short C—H···O contacts (C8—H8···O2) could be discerned among the molecules.

Related literature top

For rhodium carbenoid-mediated intermolecular O—H insertion reactions and their application to natural product synthesis, see: Paulissen et al. (1973); Cox et al. (1994); Haigh (1994); Aller et al. (1995); Shi et al. (1995); Bulugahapitiya et al. (1997); Moody & Miller (1998); Nelson et al. (2000); Medeiros & Wood (2010); Freeman et al. (2010); Morton et al. (2012). For rhodium-catalysed intramolecular O—H insertion reactions, see: Paulissen et al. (1974); Moyer et al. (1985); Moody & Taylor (1987); Heslin & Moody (1988); Davies et al. (1990); Moody et al. (1992); Sarabia-Garcá et al. (1994)9 Padwa & Sá (1999); Im et al. (2005). For recent reviews on rhodium-mediated C—H insertion reactions, see: Doyle et al. (2010); Davies & Morton (2011). For a recent report on the construction of an angularly fused triquinane skeleton via RhII-catalysed intramolecular C—H insertion, see: Srikrishna et al. (2012). For the isolation and synthesis of penifulvin A, see: Shim et al. (2006); Gaich & Mulzer (2009); Mehta & Khan (2012). For the application of p-acetamidobenzenesulfonyl azide as a diazo transfer reagent, see: Baum et al. (1987). For ring conformations, see: Cremer & Pople (1975); Boessenkool & Boeyens (1980).

Experimental top

As shown in Figure 1, the title compound 1 was prepared from the the β-ketoester 3 via the intermediate diazoester 2. Thus, 3, upon treatment with p-acetamidobenzenesulfonyl azide and triethylamine, afforded 2. The α-diazo-ω-hydroxy-β-ketoester 2 underwent smooth cyclization in presence of catalytic rhodium(II) trifluoroacetate dimer to deliver the oxepanone 1, which crystallized as thin colorless plates from 1:1 dichloromethane-hexanes.

Refinement top

The methine (CH) and methylene (CH2) H atoms were placed in geometrically idealized positions and allowed to ride on their parent atoms with C—H distances 0.93 and 0.97 Å respectively, and Uiso(H) = 1.2Ueq(C). The methyl (CH3) hydrogen atoms were constrained to an ideal geometry with C—H distances as 0.96 Å and Uiso(H) = 1.5Ueq(C). During refinement, each methyl group was however allowed to rotate freely about its C—C bond. The position of the hydroxyl hydrogen atom was refined freely, along with an isotropic displacement parameter.

Computing details top

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. Preparation of the title compound 1 from the β-ketoester 3.
[Figure 2] Fig. 2. View of the title compound 1, with the atom numbering scheme of the asymmetric unit. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level.
(2aR*,5S*,6aS*,8aS*,E)-Ethyl 5-hydroxy-7,7,8a-trimethyl-8-oxo-2,2a,6,6a,7,8,8a,8b-octahydro-1H- pentaleno[1,6-bc]oxepine-4-carboxylate top
Crystal data top
C17H24O5F(000) = 1328
Mr = 308.36Dx = 1.209 Mg m−3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2abCell parameters from 939 reflections
a = 8.447 (5) Åθ = 2.8–19.5°
b = 18.454 (14) ŵ = 0.09 mm−1
c = 21.735 (15) ÅT = 291 K
V = 3388 (4) Å3Plate, colorless
Z = 80.20 × 0.18 × 0.08 mm
Data collection top
Bruker APEXII CCD
diffractometer		3153 independent reflections
Radiation source: fine-focus sealed tube1408 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.087
φ and ω scansθmax = 25.5°, θmin = 1.9°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)		h = −10→7
Tmin = 0.983, Tmax = 0.993k = −22→18
14606 measured reflectionsl = −26→26
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.053Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.149H atoms treated by a mixture of independent and constrained refinement
S = 0.89 w = 1/[σ2(Fo2) + (0.0717P)2]
where P = (Fo2 + 2Fc2)/3
3153 reflections(Δ/σ)max < 0.001
207 parametersΔρmax = 0.17 e Å−3
0 restraintsΔρmin = −0.17 e Å−3
Crystal data top
C17H24O5V = 3388 (4) Å3
Mr = 308.36Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 8.447 (5) ŵ = 0.09 mm−1
b = 18.454 (14) ÅT = 291 K
c = 21.735 (15) Å0.20 × 0.18 × 0.08 mm
Data collection top
Bruker APEXII CCD
diffractometer		3153 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)		1408 reflections with I > 2σ(I)
Tmin = 0.983, Tmax = 0.993Rint = 0.087
14606 measured reflectionsθmax = 25.5°
Refinement top
R[F2 > 2σ(F2)] = 0.053H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.149Δρmax = 0.17 e Å−3
S = 0.89Δρmin = −0.17 e Å−3
3153 reflectionsAbsolute structure: ?
207 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

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
xyzUiso*/Ueq
O10.1027 (3)0.15812 (15)1.02261 (10)0.0990 (9)
O20.0947 (2)0.13477 (12)0.69261 (9)0.0655 (6)
H2O0.125 (4)0.0976 (18)0.6660 (15)0.090 (12)*
O30.1391 (2)−0.00529 (10)0.80956 (7)0.0545 (5)
O40.1993 (2)0.01550 (12)0.64764 (8)0.0717 (6)
O50.2612 (2)−0.07327 (12)0.71407 (8)0.0678 (6)
C10.0661 (3)0.12205 (14)0.86389 (11)0.0471 (7)
H1−0.00580.08100.86990.057*
C20.0332 (3)0.17697 (15)0.91600 (12)0.0544 (8)
C30.1256 (3)0.14428 (17)0.96932 (13)0.0623 (8)
C40.2513 (3)0.09177 (16)0.94596 (12)0.0568 (8)
C50.2035 (5)0.01234 (18)0.95976 (14)0.0888 (11)
H5A0.2518−0.00390.99780.107*
H5B0.08950.00830.96370.107*
C60.2602 (5)−0.03189 (19)0.90749 (14)0.0906 (12)
H6A0.1898−0.07260.90060.109*
H6B0.3655−0.05040.91580.109*
C70.2627 (3)0.01697 (15)0.85202 (12)0.0575 (8)
H70.36610.01390.83170.069*
C80.2347 (3)0.09461 (14)0.87520 (11)0.0474 (7)
H80.31250.12800.85740.057*
C90.4153 (4)0.1103 (2)0.97087 (15)0.0970 (12)
H9A0.44490.15800.95730.145*
H9B0.49080.07570.95590.145*
H9C0.41330.10901.01500.145*
C10−0.1415 (4)0.1859 (2)0.93120 (14)0.0795 (11)
H10A−0.18680.13940.94000.119*
H10B−0.19520.20720.89670.119*
H10C−0.15270.21680.96640.119*
C110.1093 (4)0.25222 (16)0.90386 (15)0.0781 (10)
H11A0.10310.28110.94050.117*
H11B0.05370.27610.87110.117*
H11C0.21830.24600.89250.117*
C120.0415 (3)0.14979 (16)0.79823 (11)0.0569 (8)
H12A−0.07040.15950.79250.068*
H12B0.09710.19550.79400.068*
C130.0951 (3)0.10042 (16)0.74780 (12)0.0510 (7)
C140.1445 (3)0.03157 (16)0.75362 (11)0.0512 (7)
C150.2038 (3)−0.00865 (17)0.70042 (13)0.0572 (8)
C160.3258 (4)−0.11534 (19)0.66252 (15)0.0833 (11)
H16A0.2406−0.13290.63660.100*
H16B0.3950−0.08520.63780.100*
C170.4146 (6)−0.1765 (2)0.68814 (18)0.1264 (17)
H17A0.4935−0.15870.71610.190*
H17B0.4650−0.20270.65540.190*
H17C0.3435−0.20810.70970.190*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.113 (2)0.137 (2)0.0465 (13)0.0369 (16)−0.0008 (12)−0.0152 (14)
O20.0791 (15)0.0722 (16)0.0452 (12)0.0013 (12)−0.0053 (10)0.0083 (12)
O30.0605 (13)0.0555 (13)0.0474 (11)−0.0043 (9)0.0016 (9)−0.0012 (9)
O40.0820 (16)0.0883 (16)0.0448 (12)0.0032 (12)0.0027 (10)−0.0031 (11)
O50.0850 (16)0.0645 (14)0.0540 (12)0.0051 (12)0.0061 (10)−0.0092 (11)
C10.0407 (18)0.0550 (17)0.0456 (16)−0.0004 (13)−0.0013 (12)−0.0012 (13)
C20.0495 (19)0.060 (2)0.0541 (17)0.0038 (15)−0.0001 (13)−0.0068 (15)
C30.063 (2)0.078 (2)0.0463 (18)−0.0012 (17)−0.0008 (15)−0.0052 (16)
C40.054 (2)0.073 (2)0.0438 (15)0.0052 (16)−0.0048 (13)−0.0029 (15)
C50.117 (3)0.085 (3)0.064 (2)0.019 (2)0.0199 (19)0.023 (2)
C60.128 (3)0.076 (2)0.067 (2)0.010 (2)−0.022 (2)0.013 (2)
C70.058 (2)0.0618 (19)0.0524 (16)0.0087 (15)−0.0061 (14)−0.0047 (15)
C80.0385 (17)0.0557 (18)0.0481 (15)0.0009 (14)−0.0004 (12)−0.0002 (13)
C90.060 (2)0.151 (4)0.080 (2)0.010 (2)−0.0213 (18)−0.031 (2)
C100.059 (2)0.103 (3)0.076 (2)0.0165 (19)0.0071 (17)−0.0200 (19)
C110.091 (2)0.063 (2)0.081 (2)−0.0007 (19)−0.0015 (18)−0.0131 (18)
C120.059 (2)0.0625 (19)0.0496 (16)0.0101 (15)−0.0062 (13)0.0010 (14)
C130.0500 (18)0.063 (2)0.0404 (15)−0.0043 (15)−0.0073 (12)0.0002 (15)
C140.0520 (19)0.063 (2)0.0388 (15)−0.0052 (15)0.0005 (12)−0.0016 (14)
C150.054 (2)0.064 (2)0.0535 (19)−0.0055 (17)0.0008 (14)−0.0021 (16)
C160.100 (3)0.077 (2)0.073 (2)0.005 (2)0.0090 (19)−0.026 (2)
C170.194 (5)0.076 (3)0.109 (3)0.047 (3)0.008 (3)−0.010 (2)
Geometric parameters (Å, º) top
O1—C31.202 (3)C6—H6B0.9700
O2—C131.357 (3)C7—C81.537 (4)
O2—H2O0.93 (3)C7—H70.9800
O3—C141.394 (3)C8—H80.9800
O3—C71.452 (3)C9—H9A0.9600
O4—C151.231 (3)C9—H9B0.9600
O5—C151.321 (3)C9—H9C0.9600
O5—C161.468 (3)C10—H10A0.9600
C1—C121.530 (3)C10—H10B0.9600
C1—C81.531 (3)C10—H10C0.9600
C1—C21.545 (3)C11—H11A0.9600
C1—H10.9800C11—H11B0.9600
C2—C101.521 (4)C11—H11C0.9600
C2—C31.522 (4)C12—C131.496 (4)
C2—C111.553 (4)C12—H12A0.9700
C3—C41.525 (4)C12—H12B0.9700
C4—C91.526 (4)C13—C141.343 (4)
C4—C81.545 (4)C14—C151.462 (4)
C4—C51.550 (4)C16—C171.465 (5)
C5—C61.479 (4)C16—H16A0.9700
C5—H5A0.9700C16—H16B0.9700
C5—H5B0.9700C17—H17A0.9600
C6—C71.505 (4)C17—H17B0.9600
C6—H6A0.9700C17—H17C0.9600
C13—O2—H2O102 (2)C4—C8—H8110.7
C14—O3—C7113.1 (2)C4—C9—H9A109.5
C15—O5—C16116.3 (2)C4—C9—H9B109.5
C12—C1—C8112.7 (2)H9A—C9—H9B109.5
C12—C1—C2116.1 (2)C4—C9—H9C109.5
C8—C1—C2105.5 (2)H9A—C9—H9C109.5
C12—C1—H1107.4H9B—C9—H9C109.5
C8—C1—H1107.4C2—C10—H10A109.5
C2—C1—H1107.4C2—C10—H10B109.5
C10—C2—C3112.0 (2)H10A—C10—H10B109.5
C10—C2—C1113.9 (2)C2—C10—H10C109.5
C3—C2—C1101.9 (2)H10A—C10—H10C109.5
C10—C2—C11110.0 (3)H10B—C10—H10C109.5
C3—C2—C11105.7 (2)C2—C11—H11A109.5
C1—C2—C11112.8 (2)C2—C11—H11B109.5
O1—C3—C2124.6 (3)H11A—C11—H11B109.5
O1—C3—C4124.6 (3)C2—C11—H11C109.5
C2—C3—C4110.8 (2)H11A—C11—H11C109.5
C3—C4—C9111.8 (2)H11B—C11—H11C109.5
C3—C4—C8104.3 (2)C13—C12—C1116.0 (2)
C9—C4—C8115.3 (2)C13—C12—H12A108.3
C3—C4—C5110.8 (2)C1—C12—H12A108.3
C9—C4—C5112.3 (3)C13—C12—H12B108.3
C8—C4—C5101.6 (2)C1—C12—H12B108.3
C6—C5—C4106.8 (3)H12A—C12—H12B107.4
C6—C5—H5A110.4C14—C13—O2121.7 (3)
C4—C5—H5A110.4C14—C13—C12127.0 (3)
C6—C5—H5B110.4O2—C13—C12111.3 (3)
C4—C5—H5B110.4C13—C14—O3122.2 (2)
H5A—C5—H5B108.6C13—C14—C15120.8 (3)
C5—C6—C7106.8 (3)O3—C14—C15117.0 (3)
C5—C6—H6A110.4O4—C15—O5123.2 (3)
C7—C6—H6A110.4O4—C15—C14122.9 (3)
C5—C6—H6B110.4O5—C15—C14114.0 (3)
C7—C6—H6B110.4C17—C16—O5107.9 (3)
H6A—C6—H6B108.6C17—C16—H16A110.1
O3—C7—C6109.2 (3)O5—C16—H16A110.1
O3—C7—C8111.2 (2)C17—C16—H16B110.1
C6—C7—C8107.1 (2)O5—C16—H16B110.1
O3—C7—H7109.8H16A—C16—H16B108.4
C6—C7—H7109.8C16—C17—H17A109.5
C8—C7—H7109.8C16—C17—H17B109.5
C1—C8—C7113.5 (2)H17A—C17—H17B109.5
C1—C8—C4104.8 (2)C16—C17—H17C109.5
C7—C8—C4106.3 (2)H17A—C17—H17C109.5
C1—C8—H8110.7H17B—C17—H17C109.5
C7—C8—H8110.7
C12—C1—C2—C1079.9 (3)C2—C1—C8—C435.4 (3)
C8—C1—C2—C10−154.5 (2)O3—C7—C8—C116.3 (3)
C12—C1—C2—C3−159.2 (2)C6—C7—C8—C1−103.0 (3)
C8—C1—C2—C3−33.6 (3)O3—C7—C8—C4131.0 (2)
C12—C1—C2—C11−46.3 (3)C6—C7—C8—C411.7 (3)
C8—C1—C2—C1179.3 (3)C3—C4—C8—C1−22.2 (3)
C10—C2—C3—O1−38.1 (4)C9—C4—C8—C1−145.2 (3)
C1—C2—C3—O1−160.2 (3)C5—C4—C8—C193.0 (3)
C11—C2—C3—O181.8 (4)C3—C4—C8—C7−142.7 (2)
C10—C2—C3—C4142.1 (3)C9—C4—C8—C794.4 (3)
C1—C2—C3—C420.0 (3)C5—C4—C8—C7−27.4 (3)
C11—C2—C3—C4−98.1 (3)C8—C1—C12—C1349.8 (3)
O1—C3—C4—C9−53.5 (4)C2—C1—C12—C13171.6 (2)
C2—C3—C4—C9126.4 (3)C1—C12—C13—C148.5 (4)
O1—C3—C4—C8−178.7 (3)C1—C12—C13—O2−169.0 (2)
C2—C3—C4—C81.1 (3)O2—C13—C14—O3−177.2 (2)
O1—C3—C4—C572.7 (4)C12—C13—C14—O35.5 (4)
C2—C3—C4—C5−107.5 (3)O2—C13—C14—C151.5 (4)
C3—C4—C5—C6144.6 (3)C12—C13—C14—C15−175.8 (3)
C9—C4—C5—C6−89.5 (3)C7—O3—C14—C13−75.6 (3)
C8—C4—C5—C634.3 (3)C7—O3—C14—C15105.7 (3)
C4—C5—C6—C7−28.1 (4)C16—O5—C15—O41.9 (4)
C14—O3—C7—C6−172.9 (2)C16—O5—C15—C14−178.6 (2)
C14—O3—C7—C869.1 (3)C13—C14—C15—O4−6.2 (4)
C5—C6—C7—O3−110.5 (3)O3—C14—C15—O4172.5 (2)
C5—C6—C7—C810.0 (4)C13—C14—C15—O5174.3 (3)
C12—C1—C8—C7−81.4 (3)O3—C14—C15—O5−7.0 (4)
C2—C1—C8—C7151.0 (2)C15—O5—C16—C17167.3 (3)
C12—C1—C8—C4163.1 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2O···O40.93 (3)1.69 (3)2.565 (4)155 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2O···O40.93 (3)1.69 (3)2.565 (4)155 (3)
Acknowledgements top

We thank the Department of Science and Technology (DST), India, for the CCD facility at the Indian Institute of Science (IISc), Bangalore. CSA thanks the University Grants Commission for the award of a Dr D. S. Kothari post-doctoral fellowship. GM thanks the Government of India for the award of a National Research Professorship and acknowledges the current research support from the Eli Lilly and Jubilant–Bhartia Foundations.

references
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