PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of actaeInternational Union of Crystallographysearchopen accessarticle submissionjournal home pagethis article
 
Acta Crystallogr Sect E Struct Rep Online. 2008 February 1; 64(Pt 2): o455.
Published online 2008 January 16. doi:  10.1107/S1600536808000652
PMCID: PMC2960361

5,5′,7,7′-Tetra­meth­oxy-2,2′-ethano-1,1′-spiro­biindane

Abstract

In the title compound, C23H26O4, there is a dihedral angle of 83.7 (6)° between the two benzene rings. The five-membered rings have chair conformations.

Related literature

For related literature, see: Bandin et al. (2000 [triangle]); Birman et al. (1999 [triangle]); Lan et al. (2006 [triangle]); Zhu et al. (2005 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-64-0o455-scheme1.jpg

Experimental

Crystal data

  • C23H26O4
  • M r = 366.44
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-64-0o455-efi1.jpg
  • a = 12.7089 (11) Å
  • b = 10.0905 (8) Å
  • c = 16.1664 (13) Å
  • β = 104.306 (2)°
  • V = 2008.9 (3) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.08 mm−1
  • T = 298 (2) K
  • 0.33 × 0.21 × 0.15 mm

Data collection

  • Bruker APEXII area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Sheldrick, 2004 [triangle]) T min = 0.974, T max = 0.988
  • 9884 measured reflections
  • 3576 independent reflections
  • 2013 reflections with I > 2σ(I)
  • R int = 0.028

Refinement

  • R[F 2 > 2σ(F 2)] = 0.039
  • wR(F 2) = 0.101
  • S = 1.08
  • 3576 reflections
  • 249 parameters
  • H-atom parameters constrained
  • Δρmax = 0.13 e Å−3
  • Δρmin = −0.10 e Å−3

Data collection: APEX2 (Bruker, 2004 [triangle]); cell refinement: SAINT (Bruker, 2004 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: SHELXTL (Bruker, 2004 [triangle]); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808000652/cs2064sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808000652/cs2064Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors gratefully acknowledge financial support of this work by the National Natural Science Foundation of China (grant No. 20572066).

supplementary crystallographic information

Comment

The symmetric chiral ligands, such as BINOL (1,1'-binaphthalene-2,2'-diol), BINAP [2,2'-bis(diphenylphosphino)-1,1'-binaphthyl], SPINOL (1,1'-spirobiindane-7,7'-diol), etc, are widely used in catalytic asymmetric synthesis (Lan et al., 2006; Birman et al., 1999; Zhu et al., 2005). Even minor modifications of the chiral ligands were found to enhance manifold functional capability of these ligands in asymmetric catalysis (Bandin et al., 2000). We also report the synthesis of the title compound here.

The title compound (Fig. 1) was obtained in three steps (experimental section). The molecule has an approximate C2 symmetry. Two phenyl groups make a dihedral angle of 83.7 (6)°.

Experimental

A solution of 3,5-dimethoxybenzaldehyde (7.9 g, 47.6 mmol) and cyclopentanone (2 g, 23.8 mmol) in 20 ml of ethanol was added to a solution of 0.8 g of NaOH in 30 ml 50% aqueous ethanol over a period of 30 min and stirred for 8 h at room temperature. The yellow solid obtained was filtered and washed with water and the product vacuum dried (7.2 g, 85%). The yellow product is 2,6-bis(3,5-dimethoxybenzylidene)cyclopentanone, which was dissolveed in 30 ml of acetone and then stirred with Raney nickel (3 g) under hydrogen atmosphere at room temperature and the reaction progress monitored by TLC. Upon disappearance of the starting material in TLC (ca 12 h, rotary evaporator), the reaction mixture was carefully filtered off without allowing the Raney nickel to become dry by washing with acetone and the filtrate was concentrated in a rotary evaporator. The crude product was crystallized from 95% ethanol to yield 2,6-bis(3,5-dimethoxybenzyl)cyclopentanone (2.8 g, 92.4%). This compound (2 g, 5.56 mmol) and H3PW12O40 (2.57 g, 0.834 mmol) in 20 ml toluene were charged in a 50 ml flask with water segregator and reflux condenser, followed by reflux and dehydration until no water was separated for 12 h when the solution turned red slowly, then cooled, filtered and washed with CHCl3. The organic phase was combined, evaporated and the residue was recrystallized from a hexane–ethyl acetate (3:1) mixture to give 1.8 g of the title compound (88.7% yield).

1H NMR: (CDCl3) 1.23–1.29 (m, 2H), 1.96–2.00 (m, 2H), 2.61–2.66 (m, 4H), 3.36–3.44 (m, 2H), 3.55 (s, 6H), 3.77 (s, 6H), 6.20 (s, 2H), 6.34 (s,2H).

Refinement

The H atoms (pyridine ring) were placed in calculated positions [Csp2—H = 0.93 Å] and refined using a riding model, with Uiso(H) = 1.2Ueq(C).

Figures

Fig. 1.
The asymmetric unit of the title compound, showing 30% probability displacement ellipsoids.

Crystal data

C23H26O4F000 = 784
Mr = 366.44Dx = 1.212 Mg m3
Monoclinic, P21/cMo Kα radiation λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3576 reflections
a = 12.7089 (11) Åθ = 1.7–25.1º
b = 10.0905 (8) ŵ = 0.08 mm1
c = 16.1664 (13) ÅT = 298 (2) K
β = 104.306 (2)ºBlock, colourless
V = 2008.9 (3) Å30.33 × 0.21 × 0.15 mm
Z = 4

Data collection

Bruker APEXII area-detector diffractometer3576 independent reflections
Radiation source: fine-focus sealed tube2013 reflections with I > 2σ(I)
Monochromator: graphiteRint = 0.028
T = 298(2) Kθmax = 25.1º
[var phi] and ω scansθmin = 1.7º
Absorption correction: multi-scan(SADABS; Sheldrick, 2004)h = −15→15
Tmin = 0.974, Tmax = 0.988k = −12→11
9884 measured reflectionsl = −11→19

Refinement

Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-atom parameters constrained
R[F2 > 2σ(F2)] = 0.039  w = 1/[σ2(Fo2) + (0.0439P)2] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.101(Δ/σ)max < 0.001
S = 1.09Δρmax = 0.13 e Å3
3576 reflectionsΔρmin = −0.10 e Å3
249 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0095 (8)
Secondary atom site location: difference Fourier map

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/Ueq
O10.01787 (11)0.00651 (13)0.11905 (9)0.0934 (5)
O20.11557 (9)0.45860 (11)0.10743 (7)0.0615 (3)
O30.26734 (10)0.31122 (11)−0.09967 (7)0.0720 (4)
O40.21271 (10)0.76096 (12)−0.18685 (8)0.0753 (4)
C10.48840 (15)0.4601 (2)0.18491 (13)0.0857 (6)
H1A0.52800.50930.15080.103*
H1B0.51610.48370.24450.103*
C20.49705 (15)0.3121 (2)0.17181 (13)0.0844 (6)
H2A0.47160.26250.21450.101*
H2B0.57130.28650.17430.101*
C30.42396 (14)0.28916 (18)0.08308 (11)0.0666 (5)
H30.46210.31180.03920.080*
C40.37550 (15)0.14983 (17)0.06805 (12)0.0730 (6)
H4A0.37000.12140.00980.088*
H4B0.41980.08660.10680.088*
C50.26458 (14)0.16203 (17)0.08514 (10)0.0574 (5)
C60.19459 (17)0.06072 (17)0.09508 (11)0.0671 (5)
H60.2143−0.02770.09300.081*
C70.09506 (15)0.09546 (18)0.10816 (11)0.0641 (5)
C80.06579 (14)0.22698 (17)0.11182 (10)0.0597 (5)
H8−0.00190.24830.12040.072*
C90.13625 (13)0.32636 (15)0.10281 (10)0.0505 (4)
C100.23758 (13)0.29369 (15)0.08937 (9)0.0496 (4)
C110.32709 (12)0.38749 (16)0.07973 (9)0.0514 (4)
C120.29743 (12)0.47861 (16)0.00341 (10)0.0503 (4)
C130.26767 (13)0.44407 (16)−0.08266 (10)0.0517 (4)
C140.24065 (13)0.54127 (17)−0.14428 (10)0.0566 (5)
H140.22070.5184−0.20180.068*
C150.24339 (13)0.67340 (17)−0.11997 (11)0.0571 (5)
C160.27449 (13)0.71002 (16)−0.03510 (12)0.0604 (5)
H160.27740.7988−0.01920.072*
C170.30128 (13)0.61047 (17)0.02569 (10)0.0543 (4)
C180.33526 (15)0.62685 (17)0.12096 (11)0.0685 (5)
H18A0.27580.66100.14250.082*
H18B0.39640.68700.13730.082*
C190.36713 (14)0.48682 (17)0.15539 (10)0.0619 (5)
H190.33210.46650.20150.074*
C200.03804 (18)−0.13115 (18)0.11287 (13)0.0989 (7)
H20A0.0585−0.14850.06060.148*
H20B−0.0265−0.18010.11350.148*
H20C0.0957−0.15780.16040.148*
C210.01061 (14)0.49516 (17)0.11711 (13)0.0794 (6)
H21A−0.04420.46000.07040.119*
H21B0.00490.59000.11760.119*
H21C0.00060.46000.16980.119*
C220.2423 (2)0.27137 (19)−0.18592 (13)0.1168 (9)
H22A0.16920.2970−0.21320.175*
H22B0.24910.1769−0.18900.175*
H22C0.29150.3131−0.21430.175*
C230.22177 (17)0.89829 (17)−0.16809 (13)0.0850 (6)
H23A0.17520.9208−0.13160.127*
H23B0.20060.9480−0.22020.127*
H23C0.29560.9190−0.13980.127*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
O10.0960 (11)0.0534 (9)0.1336 (13)−0.0154 (7)0.0338 (9)−0.0010 (8)
O20.0575 (8)0.0496 (8)0.0802 (8)0.0036 (6)0.0222 (6)−0.0009 (6)
O30.1176 (11)0.0527 (8)0.0469 (8)0.0052 (7)0.0223 (7)−0.0020 (6)
O40.0980 (10)0.0589 (9)0.0687 (9)0.0035 (7)0.0202 (7)0.0151 (7)
C10.0645 (14)0.1059 (18)0.0789 (15)−0.0058 (12)0.0033 (11)−0.0021 (12)
C20.0551 (12)0.1137 (18)0.0815 (15)0.0141 (11)0.0117 (11)0.0149 (13)
C30.0684 (13)0.0810 (14)0.0559 (12)0.0144 (10)0.0260 (10)0.0110 (10)
C40.0853 (15)0.0739 (14)0.0629 (12)0.0268 (11)0.0244 (10)0.0095 (10)
C50.0708 (13)0.0570 (12)0.0452 (10)0.0114 (10)0.0158 (9)0.0050 (8)
C60.0936 (15)0.0490 (11)0.0570 (12)0.0103 (11)0.0150 (10)0.0018 (9)
C70.0725 (14)0.0558 (13)0.0621 (12)−0.0061 (10)0.0130 (10)0.0008 (9)
C80.0612 (12)0.0526 (12)0.0639 (12)0.0025 (9)0.0129 (9)0.0014 (9)
C90.0619 (12)0.0422 (11)0.0453 (10)0.0049 (9)0.0093 (8)0.0016 (8)
C100.0590 (11)0.0530 (11)0.0365 (9)0.0064 (8)0.0114 (8)0.0041 (7)
C110.0552 (10)0.0601 (11)0.0411 (10)0.0052 (9)0.0160 (8)0.0031 (8)
C120.0525 (10)0.0556 (11)0.0446 (10)−0.0001 (8)0.0152 (8)0.0001 (8)
C130.0617 (11)0.0474 (11)0.0487 (11)0.0002 (8)0.0188 (8)−0.0004 (8)
C140.0679 (12)0.0579 (12)0.0459 (10)−0.0014 (9)0.0178 (8)0.0029 (9)
C150.0644 (12)0.0541 (12)0.0558 (12)0.0005 (9)0.0208 (9)0.0129 (10)
C160.0721 (12)0.0498 (11)0.0639 (13)−0.0045 (9)0.0256 (10)−0.0033 (10)
C170.0582 (11)0.0578 (12)0.0496 (11)−0.0054 (8)0.0183 (9)−0.0032 (9)
C180.0790 (13)0.0717 (13)0.0561 (12)−0.0113 (10)0.0190 (10)−0.0101 (9)
C190.0584 (12)0.0783 (13)0.0483 (10)−0.0052 (10)0.0119 (9)−0.0031 (9)
C200.1240 (19)0.0513 (14)0.1129 (18)−0.0128 (12)0.0132 (15)0.0006 (11)
C210.0659 (13)0.0621 (13)0.1158 (17)0.0110 (10)0.0329 (12)−0.0006 (11)
C220.235 (3)0.0622 (14)0.0548 (14)−0.0128 (15)0.0381 (16)−0.0153 (10)
C230.1083 (17)0.0570 (14)0.0975 (16)0.0083 (11)0.0403 (13)0.0200 (11)

Geometric parameters (Å, °)

O1—C71.373 (2)C10—C111.517 (2)
O1—C201.420 (2)C11—C121.510 (2)
O2—C91.3656 (17)C11—C191.566 (2)
O2—C211.4294 (18)C12—C171.376 (2)
O3—C131.3682 (18)C12—C131.393 (2)
O3—C221.410 (2)C13—C141.380 (2)
O4—C151.3759 (19)C14—C151.388 (2)
O4—C231.4171 (19)C14—H140.9300
C1—C21.516 (3)C15—C161.381 (2)
C1—C191.521 (2)C16—C171.388 (2)
C1—H1A0.9700C16—H160.9300
C1—H1B0.9700C17—C181.502 (2)
C2—C31.522 (2)C18—C191.536 (2)
C2—H2A0.9700C18—H18A0.9700
C2—H2B0.9700C18—H18B0.9700
C3—C41.530 (2)C19—H190.9800
C3—C111.572 (2)C20—H20A0.9600
C3—H30.9800C20—H20B0.9600
C4—C51.507 (2)C20—H20C0.9600
C4—H4A0.9700C21—H21A0.9600
C4—H4B0.9700C21—H21B0.9600
C5—C101.378 (2)C21—H21C0.9600
C5—C61.390 (2)C22—H22A0.9600
C6—C71.378 (2)C22—H22B0.9600
C6—H60.9300C22—H22C0.9600
C7—C81.383 (2)C23—H23A0.9600
C8—C91.376 (2)C23—H23B0.9600
C8—H80.9300C23—H23C0.9600
C9—C101.397 (2)
C7—O1—C20118.91 (16)C17—C12—C11112.92 (14)
C9—O2—C21117.11 (13)C13—C12—C11127.96 (15)
C13—O3—C22117.84 (13)O3—C13—C14124.30 (15)
C15—O4—C23117.87 (15)O3—C13—C12115.63 (14)
C2—C1—C19103.52 (16)C14—C13—C12120.07 (15)
C2—C1—H1A111.1C13—C14—C15119.61 (15)
C19—C1—H1A111.1C13—C14—H14120.2
C2—C1—H1B111.1C15—C14—H14120.2
C19—C1—H1B111.1O4—C15—C16124.39 (16)
H1A—C1—H1B109.0O4—C15—C14114.33 (16)
C1—C2—C3103.46 (15)C16—C15—C14121.29 (15)
C1—C2—H2A111.1C15—C16—C17118.02 (15)
C3—C2—H2A111.1C15—C16—H16121.0
C1—C2—H2B111.1C17—C16—H16121.0
C3—C2—H2B111.1C12—C17—C16121.87 (15)
H2A—C2—H2B109.0C12—C17—C18110.93 (15)
C2—C3—C4114.65 (15)C16—C17—C18127.19 (16)
C2—C3—C11103.13 (14)C17—C18—C19104.68 (14)
C4—C3—C11107.07 (14)C17—C18—H18A110.8
C2—C3—H3110.6C19—C18—H18A110.8
C4—C3—H3110.6C17—C18—H18B110.8
C11—C3—H3110.6C19—C18—H18B110.8
C5—C4—C3104.71 (14)H18A—C18—H18B108.9
C5—C4—H4A110.8C1—C19—C18115.66 (15)
C3—C4—H4A110.8C1—C19—C11103.89 (14)
C5—C4—H4B110.8C18—C19—C11107.47 (13)
C3—C4—H4B110.8C1—C19—H19109.9
H4A—C4—H4B108.9C18—C19—H19109.9
C10—C5—C6121.93 (16)C11—C19—H19109.9
C10—C5—C4110.09 (16)O1—C20—H20A109.5
C6—C5—C4127.97 (16)O1—C20—H20B109.5
C7—C6—C5117.93 (16)H20A—C20—H20B109.5
C7—C6—H6121.0O1—C20—H20C109.5
C5—C6—H6121.0H20A—C20—H20C109.5
O1—C7—C6124.43 (17)H20B—C20—H20C109.5
O1—C7—C8114.43 (17)O2—C21—H21A109.5
C6—C7—C8121.14 (17)O2—C21—H21B109.5
C9—C8—C7120.37 (16)H21A—C21—H21B109.5
C9—C8—H8119.8O2—C21—H21C109.5
C7—C8—H8119.8H21A—C21—H21C109.5
O2—C9—C8124.55 (15)H21B—C21—H21C109.5
O2—C9—C10115.87 (14)O3—C22—H22A109.5
C8—C9—C10119.57 (15)O3—C22—H22B109.5
C5—C10—C9119.04 (15)H22A—C22—H22B109.5
C5—C10—C11113.21 (14)O3—C22—H22C109.5
C9—C10—C11127.74 (14)H22A—C22—H22C109.5
C12—C11—C10114.94 (13)H22B—C22—H22C109.5
C12—C11—C19102.46 (13)O4—C23—H23A109.5
C10—C11—C19115.23 (12)O4—C23—H23B109.5
C12—C11—C3116.61 (12)H23A—C23—H23B109.5
C10—C11—C3101.74 (13)O4—C23—H23C109.5
C19—C11—C3106.06 (13)H23A—C23—H23C109.5
C17—C12—C13119.12 (14)H23B—C23—H23C109.5
C19—C1—C2—C345.85 (18)C10—C11—C12—C17117.93 (15)
C1—C2—C3—C4−153.35 (15)C19—C11—C12—C17−7.82 (17)
C1—C2—C3—C11−37.33 (18)C3—C11—C12—C17−123.13 (16)
C2—C3—C4—C595.86 (17)C10—C11—C12—C13−61.8 (2)
C11—C3—C4—C5−17.87 (17)C19—C11—C12—C13172.49 (15)
C3—C4—C5—C1012.87 (18)C3—C11—C12—C1357.2 (2)
C3—C4—C5—C6−167.74 (16)C22—O3—C13—C142.9 (2)
C10—C5—C6—C71.0 (2)C22—O3—C13—C12−177.36 (17)
C4—C5—C6—C7−178.31 (17)C17—C12—C13—O3179.06 (14)
C20—O1—C7—C6−3.0 (3)C11—C12—C13—O3−1.3 (2)
C20—O1—C7—C8177.41 (15)C17—C12—C13—C14−1.2 (2)
C5—C6—C7—O1−179.96 (16)C11—C12—C13—C14178.52 (15)
C5—C6—C7—C8−0.4 (3)O3—C13—C14—C15179.81 (15)
O1—C7—C8—C9179.30 (14)C12—C13—C14—C150.0 (2)
C6—C7—C8—C9−0.3 (3)C23—O4—C15—C165.2 (2)
C21—O2—C9—C8−4.0 (2)C23—O4—C15—C14−174.92 (14)
C21—O2—C9—C10177.12 (14)C13—C14—C15—O4−178.73 (14)
C7—C8—C9—O2−178.43 (15)C13—C14—C15—C161.1 (2)
C7—C8—C9—C100.4 (2)O4—C15—C16—C17178.73 (15)
C6—C5—C10—C9−0.9 (2)C14—C15—C16—C17−1.1 (2)
C4—C5—C10—C9178.50 (14)C13—C12—C17—C161.2 (2)
C6—C5—C10—C11178.08 (14)C11—C12—C17—C16−178.55 (14)
C4—C5—C10—C11−2.48 (18)C13—C12—C17—C18−179.81 (14)
O2—C9—C10—C5179.15 (13)C11—C12—C17—C180.47 (19)
C8—C9—C10—C50.2 (2)C15—C16—C17—C12−0.1 (2)
O2—C9—C10—C110.3 (2)C15—C16—C17—C18−178.90 (16)
C8—C9—C10—C11−178.65 (14)C12—C17—C18—C197.32 (19)
C5—C10—C11—C12118.32 (15)C16—C17—C18—C19−173.73 (16)
C9—C10—C11—C12−62.8 (2)C2—C1—C19—C18−152.31 (15)
C5—C10—C11—C19−122.85 (14)C2—C1—C19—C11−34.81 (18)
C9—C10—C11—C1956.1 (2)C17—C18—C19—C1103.58 (17)
C5—C10—C11—C3−8.63 (16)C17—C18—C19—C11−11.91 (17)
C9—C10—C11—C3170.29 (15)C12—C11—C19—C1−111.14 (14)
C2—C3—C11—C12128.93 (16)C10—C11—C19—C1123.31 (15)
C4—C3—C11—C12−109.76 (16)C3—C11—C19—C111.61 (17)
C2—C3—C11—C10−105.22 (15)C12—C11—C19—C1811.92 (16)
C4—C3—C11—C1016.09 (16)C10—C11—C19—C18−113.63 (15)
C2—C3—C11—C1915.64 (17)C3—C11—C19—C18134.67 (14)
C4—C3—C11—C19136.95 (13)

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CS2064).

References

  • Bandin, M., Casolari, S., Cozzi, P. G., Proni, G., Schmohel, E. & Spada, G. P. (2000). J. Org. Chem.491, 494–497.
  • Birman, V. B., Rheingold, A. L. & Lam, K. C. (1999). Tetrahedron Asymmetry, 10, 125–131.
  • Bruker (2004). APEX2 and SMART Bruker AXS Inc, Madison, Wisconsin, USA.
  • Lan, K., Shan, Z. X. & Fan, S. (2006). Tetrahedron Lett.47, 4343–4345.
  • Sheldrick, G. M. (2004). SADABS University of Göttingen, Germany.
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Zhu, S.-F., Yang, Y., Wang, L.-X., Liu, B. & Zhou, Q.-L. (2005). Org. Lett.7, 2333–2335. [PubMed]

Articles from Acta Crystallographica Section E: Structure Reports Online are provided here courtesy of International Union of Crystallography