organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

(±)-3-Benz­yl­oxy-1-(4-meth­­oxy­benz­yl)piperidine-2-thione

aMolecular Sciences Institute, School of Chemistry, University of the Witwatersrand, PO Wits 2050, Johannesburg, South Africa
*Correspondence e-mail: joseph.michael@wits.ac.za

(Received 26 November 2012; accepted 28 November 2012; online 5 December 2012)

The title mol­ecule, C20H23NO2S, adopts a twisted conformation in which the two aromatic rings connected to the central piperidine ring are orientated trans to each other. An intra­molecular C—H⋯S contact occurs. In the crystal, C—H⋯π and C—H⋯O inter­actions act to stabilize the structure in three dimensions.

Related literature

For the use of related piperidine­thio­nes in the synthesis of febrifugine analogues, see: Michael et al. (2006[Michael, J. P., de Koning, C. B. & Pienaar, D. P. (2006). Synlett, pp. 383-386.]). For information on the biological activity of febrifugine, see: Murata et al. (1998[Murata, K., Takano, F., Fushiya, S. & Oshima, Y. (1998). J. Nat. Prod. 61, 729-733.]).

[Scheme 1]

Experimental

Crystal data
  • C20H23NO2S

  • Mr = 341.45

  • Orthorhombic, P b c a

  • a = 18.371 (3) Å

  • b = 10.4844 (15) Å

  • c = 18.467 (3) Å

  • V = 3556.9 (9) Å3

  • Z = 8

  • Mo Kα radiation

  • μ = 0.19 mm−1

  • T = 173 K

  • 0.47 × 0.28 × 0.05 mm

Data collection
  • Bruker APEXII CCD area-detector diffractometer

  • 22717 measured reflections

  • 4286 independent reflections

  • 2949 reflections with I > 2σ(I)

  • Rint = 0.046

Refinement
  • R[F2 > 2σ(F2)] = 0.037

  • wR(F2) = 0.098

  • S = 1.01

  • 4286 reflections

  • 218 parameters

  • H-atom parameters constrained

  • Δρmax = 0.26 e Å−3

  • Δρmin = −0.26 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the C16–C21 ring.

D—H⋯A D—H H⋯A DA D—H⋯A
C7—H7A⋯S1 0.99 2.54 3.0760 (16) 114
C13—H13⋯O2i 0.95 2.59 3.4913 (19) 158
C6—H6BCg1i 0.99 2.54 3.5066 (19) 165
C14—H14ACg1ii 0.98 2.61 3.455 (2) 144
Symmetry codes: (i) [-x, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]; (ii) -x, -y, -z+1.

Data collection: APEX2 (Bruker, 2005[Bruker (2005). APEX2 and SAINT-NT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT-NT (Bruker, 2005[Bruker (2005). APEX2 and SAINT-NT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT-NT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]) and SCHAKAL99 (Keller, 1999[Keller, E. (1999). SCHAKAL99. University of Freiberg, Germany.]); software used to prepare material for publication: WinGX (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]) and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).

Supporting information


Comment top

The title piperidinethione was prepared as an intermediate for the total synthesis of febrifugine, a quinazoline alkaloid with potent antimalarial activity (Murata et al., 1998). Related thiolactam intermediates have been used in the synthesis of febrifugine analogues in ongoing investigations in our laboratories (Michael et al., 2006). It should be noted that, although an optically pure lactam was used in the synthesis of the title compound, racemization took place during the replacement of oxygen by sulfur with Lawesson's reagent.

The title organic compound (Fig. 1) crystallizes in the space group Pbca. The molecule adopts a twisted conformation in which the two aromatic rings connected to the piperidine ring are orientated trans to each other. The aromatic rings are also rotated with respect to each other such that the angle between least squares planes defined by the two rings is 59.04 (6)°. The most significant weak interactions in this structure are listed in Table 1. Two C—H···π interactions involving the ring defined by C16—C21 are present in the structure while no such interactions exist for the aromatic ring defined by C8—C13. These two C—H···π interactions act to bring three molecules together which interact further through the C—H···O interaction as shown in Fig. 2. No significant π···π interactions are present in the structure.

Related literature top

For the use of related piperidinethiones in the synthesis of febrifugine analogues, see: Michael et al. (2006). For information on the biological activity of febrifugine, see: Murata et al. (1998).

Experimental top

The title compound was synthesized by heating a mixture of (3S)-3-benzyloxy-1-(4-methoxybenzyl)piperidin-2-one (170 mg, 0.52 mmol) and Lawesson's reagent (106 mg, 0.26 mmol) in benzene (8 ml) under reflux for 4 h. After evaporation of the solvent in vacuo, the residue was purified by column chromatography on silica gel with hexane/ethyl acetate (4:1 v/v) as eluent to yield the racemic product as shiny colourless plates (174 mg, 98%), m.p. 349.5–351.5 K.

Refinement top

All H atoms attached to carbon were positioned geometrically, and allowed to ride on their parent atoms, with C—H bond lengths of 0.95 Å (CH), 0.99 Å (CH2) or 0.98 Å (CH3), and isotropic displacement parameters set to 1.2 (CH and CH2) or 1.5 times (CH3) the Ueq of the parent atom.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT-NT (Bruker, 2005); data reduction: SAINT-NT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and SCHAKAL99 (Keller, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. C—H···π and C—H···O interactions in the structure of (I). Only the aromatic ring defined by C16—C21 is involved in C—H···π interactions but these act to bring three molecules together.
(±)-3-Benzyloxy-1-(4-methoxybenzyl)piperidine-2-thione top
Crystal data top
C20H23NO2SF(000) = 1456
Mr = 341.45Dx = 1.275 Mg m3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2abCell parameters from 978 reflections
a = 18.371 (3) Åθ = 2.5–28.0°
b = 10.4844 (15) ŵ = 0.19 mm1
c = 18.467 (3) ÅT = 173 K
V = 3556.9 (9) Å3Plate, colourless
Z = 80.47 × 0.28 × 0.05 mm
Data collection top
Bruker APEXII CCD area-detector
diffractometer
2949 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.046
Graphite monochromatorθmax = 28.0°, θmin = 2.2°
phi and ω scansh = 2419
22717 measured reflectionsk = 1313
4286 independent reflectionsl = 2324
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)] = 0.037Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.098H-atom parameters constrained
S = 1.01 w = 1/[σ2(Fo2) + (0.0464P)2 + 0.5277P]
where P = (Fo2 + 2Fc2)/3
4286 reflections(Δ/σ)max = 0.003
218 parametersΔρmax = 0.26 e Å3
0 restraintsΔρmin = 0.26 e Å3
Crystal data top
C20H23NO2SV = 3556.9 (9) Å3
Mr = 341.45Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 18.371 (3) ŵ = 0.19 mm1
b = 10.4844 (15) ÅT = 173 K
c = 18.467 (3) Å0.47 × 0.28 × 0.05 mm
Data collection top
Bruker APEXII CCD area-detector
diffractometer
2949 reflections with I > 2σ(I)
22717 measured reflectionsRint = 0.046
4286 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0370 restraints
wR(F2) = 0.098H-atom parameters constrained
S = 1.01Δρmax = 0.26 e Å3
4286 reflectionsΔρmin = 0.26 e Å3
218 parameters
Special details top

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) top
xyzUiso*/Ueq
C20.00224 (8)0.06796 (14)0.61154 (8)0.0260 (3)
C30.02325 (8)0.19576 (13)0.58013 (8)0.0278 (3)
H30.01000.19910.52770.033*
C40.10388 (8)0.21947 (16)0.58763 (9)0.0339 (4)
H4A0.11530.30820.57330.041*
H4B0.13110.16110.55530.041*
C50.12655 (9)0.19740 (15)0.66565 (9)0.0371 (4)
H5A0.17900.21660.67150.045*
H5B0.09880.25480.69800.045*
C60.11198 (8)0.06000 (15)0.68586 (9)0.0339 (4)
H6A0.15110.00600.66540.041*
H6B0.11400.05180.73920.041*
C70.02107 (8)0.11296 (14)0.69241 (8)0.0310 (3)
H7A0.02930.13560.67820.037*
H7B0.02250.10570.74580.037*
C80.07247 (8)0.21843 (14)0.66849 (8)0.0265 (3)
C90.09864 (8)0.22570 (14)0.59808 (8)0.0293 (3)
H90.08460.16240.56400.035*
C100.14501 (8)0.32359 (14)0.57614 (8)0.0295 (3)
H100.16210.32730.52760.035*
C110.16592 (8)0.41589 (14)0.62622 (9)0.0311 (3)
C120.13904 (9)0.41094 (14)0.69669 (9)0.0353 (4)
H120.15220.47510.73060.042*
C130.09325 (9)0.31299 (14)0.71751 (9)0.0324 (4)
H130.07570.31000.76590.039*
C140.23736 (9)0.52714 (17)0.53823 (10)0.0434 (4)
H14A0.19530.53790.50610.065*
H14B0.26930.60170.53420.065*
H14C0.26430.45030.52430.065*
C150.02311 (8)0.40960 (13)0.58316 (9)0.0293 (3)
H15A0.02490.39730.53000.035*
H15B0.02050.46110.59480.035*
C160.09058 (8)0.47794 (13)0.60827 (8)0.0256 (3)
C170.15243 (8)0.41094 (14)0.62983 (8)0.0300 (3)
H170.15180.32030.63030.036*
C180.21487 (9)0.47569 (15)0.65056 (9)0.0359 (4)
H180.25670.42920.66540.043*
C190.21667 (9)0.60777 (16)0.64975 (9)0.0373 (4)
H190.25960.65180.66400.045*
C200.15566 (9)0.67528 (15)0.62815 (9)0.0351 (4)
H200.15690.76580.62700.042*
C210.09291 (8)0.61116 (14)0.60820 (8)0.0303 (3)
H210.05100.65820.59430.036*
N10.04038 (6)0.01121 (11)0.66005 (6)0.0267 (3)
S10.08302 (2)0.01240 (4)0.58307 (2)0.03658 (12)
O10.21278 (6)0.51478 (10)0.61136 (7)0.0413 (3)
O20.01884 (6)0.28903 (9)0.61845 (5)0.0299 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C20.0271 (8)0.0236 (7)0.0273 (8)0.0015 (6)0.0041 (6)0.0019 (6)
C30.0297 (8)0.0245 (7)0.0293 (8)0.0041 (6)0.0051 (6)0.0001 (6)
C40.0289 (8)0.0281 (8)0.0447 (10)0.0004 (6)0.0072 (7)0.0032 (7)
C50.0297 (9)0.0303 (9)0.0514 (10)0.0019 (7)0.0028 (7)0.0028 (7)
C60.0296 (8)0.0319 (8)0.0402 (9)0.0004 (7)0.0079 (7)0.0001 (7)
C70.0320 (8)0.0288 (8)0.0321 (8)0.0011 (6)0.0032 (7)0.0063 (6)
C80.0274 (8)0.0219 (7)0.0303 (8)0.0025 (6)0.0027 (6)0.0021 (6)
C90.0318 (8)0.0239 (7)0.0322 (8)0.0015 (6)0.0036 (6)0.0049 (6)
C100.0311 (8)0.0270 (8)0.0303 (8)0.0038 (6)0.0010 (6)0.0019 (6)
C110.0304 (8)0.0228 (8)0.0402 (9)0.0001 (6)0.0102 (7)0.0045 (6)
C120.0468 (10)0.0243 (8)0.0348 (9)0.0027 (7)0.0128 (7)0.0044 (7)
C130.0413 (9)0.0277 (8)0.0282 (8)0.0028 (7)0.0036 (7)0.0030 (6)
C140.0348 (9)0.0402 (10)0.0552 (11)0.0066 (7)0.0036 (8)0.0135 (8)
C150.0287 (8)0.0220 (7)0.0371 (9)0.0003 (6)0.0033 (6)0.0049 (6)
C160.0258 (7)0.0222 (7)0.0290 (7)0.0001 (6)0.0030 (6)0.0012 (6)
C170.0298 (8)0.0212 (7)0.0390 (9)0.0024 (6)0.0011 (6)0.0005 (6)
C180.0261 (8)0.0327 (9)0.0488 (10)0.0036 (7)0.0016 (7)0.0014 (7)
C190.0308 (9)0.0337 (9)0.0473 (10)0.0083 (7)0.0001 (7)0.0015 (7)
C200.0404 (10)0.0209 (8)0.0440 (10)0.0037 (7)0.0011 (7)0.0001 (7)
C210.0314 (8)0.0239 (8)0.0356 (8)0.0043 (6)0.0001 (6)0.0024 (6)
N10.0265 (6)0.0233 (6)0.0303 (7)0.0009 (5)0.0005 (5)0.0009 (5)
S10.0307 (2)0.0367 (2)0.0423 (2)0.00675 (17)0.00588 (17)0.00665 (18)
O10.0433 (7)0.0328 (6)0.0479 (7)0.0116 (5)0.0118 (5)0.0078 (5)
O20.0343 (6)0.0235 (5)0.0318 (6)0.0065 (4)0.0075 (5)0.0037 (4)
Geometric parameters (Å, º) top
C2—N11.3302 (19)C11—O11.3752 (19)
C2—C31.533 (2)C11—C121.393 (2)
C2—S11.6788 (15)C12—C131.382 (2)
C3—O21.4334 (17)C12—H120.9500
C3—C41.509 (2)C13—H130.9500
C3—H31.0000C14—O11.430 (2)
C4—C51.518 (2)C14—H14A0.9800
C4—H4A0.9900C14—H14B0.9800
C4—H4B0.9900C14—H14C0.9800
C5—C61.512 (2)C15—O21.4244 (17)
C5—H5A0.9900C15—C161.505 (2)
C5—H5B0.9900C15—H15A0.9900
C6—N11.4897 (19)C15—H15B0.9900
C6—H6A0.9900C16—C171.394 (2)
C6—H6B0.9900C16—C211.397 (2)
C7—N11.4756 (18)C17—C181.387 (2)
C7—C81.520 (2)C17—H170.9500
C7—H7A0.9900C18—C191.385 (2)
C7—H7B0.9900C18—H180.9500
C8—C91.388 (2)C19—C201.384 (2)
C8—C131.396 (2)C19—H190.9500
C9—C101.394 (2)C20—C211.384 (2)
C9—H90.9500C20—H200.9500
C10—C111.393 (2)C21—H210.9500
C10—H100.9500
N1—C2—C3117.77 (13)O1—C11—C10124.33 (15)
N1—C2—S1125.17 (12)C12—C11—C10119.78 (14)
C3—C2—S1117.04 (11)C13—C12—C11120.22 (14)
O2—C3—C4111.83 (12)C13—C12—H12119.9
O2—C3—C2104.16 (11)C11—C12—H12119.9
C4—C3—C2114.15 (12)C12—C13—C8120.93 (15)
O2—C3—H3108.8C12—C13—H13119.5
C4—C3—H3108.8C8—C13—H13119.5
C2—C3—H3108.8O1—C14—H14A109.5
C3—C4—C5109.36 (13)O1—C14—H14B109.5
C3—C4—H4A109.8H14A—C14—H14B109.5
C5—C4—H4A109.8O1—C14—H14C109.5
C3—C4—H4B109.8H14A—C14—H14C109.5
C5—C4—H4B109.8H14B—C14—H14C109.5
H4A—C4—H4B108.3O2—C15—C16109.08 (12)
C6—C5—C4109.33 (13)O2—C15—H15A109.9
C6—C5—H5A109.8C16—C15—H15A109.9
C4—C5—H5A109.8O2—C15—H15B109.9
C6—C5—H5B109.8C16—C15—H15B109.9
C4—C5—H5B109.8H15A—C15—H15B108.3
H5A—C5—H5B108.3C17—C16—C21118.62 (14)
N1—C6—C5113.86 (13)C17—C16—C15121.30 (13)
N1—C6—H6A108.8C21—C16—C15120.05 (13)
C5—C6—H6A108.8C18—C17—C16120.43 (14)
N1—C6—H6B108.8C18—C17—H17119.8
C5—C6—H6B108.8C16—C17—H17119.8
H6A—C6—H6B107.7C19—C18—C17120.40 (15)
N1—C7—C8112.02 (12)C19—C18—H18119.8
N1—C7—H7A109.2C17—C18—H18119.8
C8—C7—H7A109.2C20—C19—C18119.67 (15)
N1—C7—H7B109.2C20—C19—H19120.2
C8—C7—H7B109.2C18—C19—H19120.2
H7A—C7—H7B107.9C19—C20—C21120.17 (15)
C9—C8—C13118.27 (14)C19—C20—H20119.9
C9—C8—C7121.82 (13)C21—C20—H20119.9
C13—C8—C7119.89 (13)C20—C21—C16120.71 (14)
C8—C9—C10121.62 (14)C20—C21—H21119.6
C8—C9—H9119.2C16—C21—H21119.6
C10—C9—H9119.2C2—N1—C7121.73 (13)
C11—C10—C9119.16 (14)C2—N1—C6125.56 (13)
C11—C10—H10120.4C7—N1—C6112.68 (12)
C9—C10—H10120.4C11—O1—C14117.04 (13)
O1—C11—C12115.88 (14)C15—O2—C3114.16 (11)
N1—C2—C3—O2101.85 (14)C21—C16—C17—C180.2 (2)
S1—C2—C3—O276.83 (14)C15—C16—C17—C18177.91 (15)
N1—C2—C3—C420.40 (19)C16—C17—C18—C190.3 (2)
S1—C2—C3—C4160.92 (11)C17—C18—C19—C200.1 (3)
O2—C3—C4—C567.16 (16)C18—C19—C20—C210.7 (3)
C2—C3—C4—C550.78 (17)C19—C20—C21—C161.2 (2)
C3—C4—C5—C662.00 (17)C17—C16—C21—C200.9 (2)
C4—C5—C6—N143.34 (18)C15—C16—C21—C20177.18 (14)
N1—C7—C8—C939.1 (2)C3—C2—N1—C7178.97 (12)
N1—C7—C8—C13142.40 (14)S1—C2—N1—C72.5 (2)
C13—C8—C9—C100.6 (2)C3—C2—N1—C61.2 (2)
C7—C8—C9—C10179.13 (14)S1—C2—N1—C6179.75 (12)
C8—C9—C10—C110.4 (2)C8—C7—N1—C2112.23 (15)
C9—C10—C11—O1178.26 (14)C8—C7—N1—C665.82 (16)
C9—C10—C11—C121.5 (2)C5—C6—N1—C213.5 (2)
O1—C11—C12—C13178.11 (14)C5—C6—N1—C7168.55 (13)
C10—C11—C12—C131.7 (2)C12—C11—O1—C14175.93 (13)
C11—C12—C13—C80.7 (2)C10—C11—O1—C144.3 (2)
C9—C8—C13—C120.4 (2)C16—C15—O2—C3155.93 (12)
C7—C8—C13—C12179.00 (14)C4—C3—O2—C1576.17 (15)
O2—C15—C16—C1729.49 (19)C2—C3—O2—C15160.07 (12)
O2—C15—C16—C21152.48 (13)
Hydrogen-bond geometry (Å, º) top
Cg1 is the centroid of the C16–C21 ring.
D—H···AD—HH···AD···AD—H···A
C7—H7A···S10.992.543.0760 (16)114
C13—H13···O2i0.952.593.4913 (19)158
C6—H6B···Cg1i0.992.543.5066 (19)165
C14—H14A···Cg1ii0.982.613.455 (2)144
Symmetry codes: (i) x, y1/2, z+3/2; (ii) x, y, z+1.

Experimental details

Crystal data
Chemical formulaC20H23NO2S
Mr341.45
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)173
a, b, c (Å)18.371 (3), 10.4844 (15), 18.467 (3)
V3)3556.9 (9)
Z8
Radiation typeMo Kα
µ (mm1)0.19
Crystal size (mm)0.47 × 0.28 × 0.05
Data collection
DiffractometerBruker APEXII CCD area-detector
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
22717, 4286, 2949
Rint0.046
(sin θ/λ)max1)0.661
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.037, 0.098, 1.01
No. of reflections4286
No. of parameters218
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.26, 0.26

Computer programs: APEX2 (Bruker, 2005), SAINT-NT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012) and SCHAKAL99 (Keller, 1999), WinGX (Farrugia, 2012) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top
Cg1 is the centroid of the C16–C21 ring.
D—H···AD—HH···AD···AD—H···A
C7—H7A···S10.992.543.0760 (16)114
C13—H13···O2i0.952.593.4913 (19)158
C6—H6B···Cg1i0.992.543.5066 (19)165
C14—H14A···Cg1ii0.982.613.455 (2)144
Symmetry codes: (i) x, y1/2, z+3/2; (ii) x, y, z+1.
 

Acknowledgements

This work was supported by the University of the Witwatersrand and the National Research Foundation, Pretoria (grant number 78837).

References

First citationBruker (2005). APEX2 and SAINT-NT. Bruker AXS Inc., Madison, Wisconsin, USA.
First citationFarrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854.  Web of Science CrossRef CAS IUCr Journals
First citationKeller, E. (1999). SCHAKAL99. University of Freiberg, Germany.
First citationMichael, J. P., de Koning, C. B. & Pienaar, D. P. (2006). Synlett, pp. 383–386.  Web of Science CrossRef
First citationMurata, K., Takano, F., Fushiya, S. & Oshima, Y. (1998). J. Nat. Prod. 61, 729–733.  Web of Science CrossRef CAS PubMed
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals
First citationSpek, A. L. (2009). Acta Cryst. D65, 148–155.  Web of Science CrossRef CAS IUCr Journals

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