research communications
N-isopropyl-N-(phenyl)phenylglyoxylamide
ofaDepartment of Liberal Arts (Sciences & Mathematics), National Institute of, Technology, Kurume College, Fukuoka 830-8555, Japan, bMaterial Engineering Advanced Course, National Institute of Technology, Kurume College, Fukuoka 830-8555, Japan, and cDepartment of Chemistry, School of Science, Tokyo Institute of Technology, Ookayama 2-12-1-H62, Meguro-ku, Tokyo 152-8551, Japan
*Correspondence e-mail: h-miya@kurume-nct.ac.jp
The title compound [systematic name: 2-oxo-N,2-diphenyl-N-(propan-2-yl)acetamide], C17H17NO2, was synthesized and its photoreactive properties in the crystalline state were investigated. In the molecule, the carbonyl group attached to the phenyl ring adopts an s-trans configuration with respect to the isopropyl group. Moreover, the distance between the C atom of the carbonyl group and the N-bound C atom of the isopropyl group is 3.845 (2) Å, which is much longer than 3.2 Å, the threshold for photoreactions to take place in the molecule. As a result, the crystal did not photoreact upon UV light irradiation. In the crystal, the molecules are linked via weak intermolecular C—H⋯O hydrogen bonds, forming a layer structure parallel to the ab plane.
Keywords: crystal structure; photoreaction.
CCDC reference: 1870320
1. Chemical context
An achiral molecule of N,N-diisopropylarylglyoxylamide 1a having two isopropyl groups crystallizes in the P212121 and is transformed to the optically active β-lactam derivative 2a upon UV light irradiation (Fig. 1; Toda et al., 1987, 1993; Sekine et al., 1989; Hashizume et al., 1995, 1996, 1998). Likewise, N-ethyl-N-isopropylphenylglyoxylamide 1b, having an ethyl group and an isopropyl group, forms a chiral crystal (P212121), and its photoirradiation in the solid state yields the optically active β-lactam derivative 2b (Fig. 1; Toda et al., 1997). Therefore, we synthesized the title compound 1c having a phenyl group and an isopropyl group, and investigated whether an optically active β-lactam derivative could be obtained by photoreaction of its crystals. It was found that the photoreaction did not proceed in the solid state. In this paper, an explanation for the lack of photoreactivity is presented based on single crystal X-ray structural analysis.
2. Structural commentary
In the molecule of 1c, the carbonyl group (C7=O1) adopts an s-trans configuration with respect to the isopropyl group (Fig. 2), in contrast to 1a and 1b, which have s-cis configurations. The torsion angles C7—C8—N1—C15 and O1—C7—C8—O2 are −179.43 (13) and −112.09 (19)°, respectively, in 1c. The corresponding torsion angles are −5.1 (4) and 88.0 (4)°, respectively, in 1a, and −10.4 (3) and 90.7 (2)°, respectively, in 1b; in the case of 1a, which has two isopropyl groups, the torsion angle including the reacting carbon atom was calculated.
In order for the Norrish–Yang reaction to take place, the reacting atoms in the molecular structure must be in close proximity. In the 1c, the distance between the γ-hydrogen atom H15 and the carbonyl oxygen atom O1 is 4.565 Å. This interatomic distance is much longer than the ideal value of up to about 2.7 Å, at which photoreaction can proceed in the crystal (Konieczny et al., 2018). Moreover, the distance between the reacting C7 and C15 carbon atoms is 3.845 (2) Å, which is outside the range of ideal values of up to about 3.2 Å. These interatomic distances in 1c are large enough to prevent the photoreaction from taking place. In contrast, the corresponding distances are 2.78 (4) and 2.871 (4) Å in 1a, and 2.81 (3) and 2.897 (3) Å in 1b. As those distances are close to the ideal values, the photoreaction could occur in the crystalline state.
of3. Supramolecular features
In the crystal of 1c, the molecules are linked by weak intermolecular C—H⋯O interactions (C10—H10⋯O1i and C13—H13⋯O2ii; symmetry codes as in Table 1), forming a layer structure parallel to the ab plane (Fig. 3).
4. Database survey
A search of the Cambridge Structural Database (Version 5.39, last update August 2018; Groom et al., 2016) generates nine hits for compounds based on the N-isopropylphenylglyoxylamide fragment shown in Fig. 1. These results include five structural analogues including an isopropyl group (JAGLAE; Sekine et al., 1989), a methacryloyl group (NUKSOB; Sakamoto et al., 1997), an ethyl group (POWMIX; Toda et al., 1997), a tigloyl group (WEPCID01; Sakamoto et al., 1997) and a 2-tert-butylphenyl group (QUPWEE; Jesuraj & Sivaguru, 2010). The last compound has a similar molecular structure to that of 1c, with a corresponding torsion angle of 174.6 (1)°. Of the remaining compounds, three are co-crystals of N,N-diisopropylarylglyoxylamide with other organic compounds (ZEDJOH and ZEDJUN; Hashizume et al., 1994; POWMET; Toda et al., 1997).
5. Synthesis and crystallization
The title compound was prepared according to a reported method (Toda et al., 1987,1997; Sekine et al., 1989): chlorination of the phenylglyoxylic acid with thionyl chloride followed by reaction with N-isopropylaniline and triethylamine. Thus, to an ice-cooled solution of N-isopropylaniline (0.72 ml, 5 mmol) and triethylamine (0.70 ml, 5 mmol) in dry diethyl ether (2 ml) was added a solution of benzoylformyl chloride (0.84 g, 5 mmol) in dry diethyl ether (2 ml), and the reaction mixture was stirred for 3 h in an ice bath. After filtration of triethylammonium chloride, the filtrate was washed with dilute HCl and aqueous NaHCO3 and dried over MgSO4. The crude product was recrystallized from benzene to give 1c as colourless prisms (0.5968 g, 22.4% yield, m.p. 397–401 K); IR (KBr): νmax 1643 and 1681 cm−1; 1H NMR (CDCl3): δH 1.21 (d, 6H, CHMe2), 5.10 (sep, 1H, N—CH), 7.07–7.80 (m, 10H, ArH). Single crystals of 1c suitable for X-ray diffraction were grown from a benzene solution.
6. Photoreaction in the solid state
1c (51.3 mg, 0.21 mmol) was pulverized in a mortar and irradiated with a 400 W high pressure mercury lamp for 20 h. No reaction took place, as determined by TLC, IR and NMR spectroscopy.
7. Refinement
Crystal data, data collection and structure . All H atoms were positioned in geometrically calculated positions (C—H = 0.95–0.98 Å) and refined using a riding model with Uiso(H) = 1.2Ueq(C) and 1.5Ueq(C-methyl).
details are summarized in Table 2Supporting information
CCDC reference: 1870320
https://doi.org/10.1107/S2056989018013762/is5500sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989018013762/is5500Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989018013762/is5500Isup3.cml
Data collection: RAPID-AUTO (Rigaku, 1998); cell
RAPID-AUTO (Rigaku, 1998); data reduction: RAPID-AUTO (Rigaku, 1998); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010).C17H17NO2 | F(000) = 568 |
Mr = 267.31 | Dx = 1.220 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71075 Å |
a = 5.8354 (5) Å | Cell parameters from 13857 reflections |
b = 16.5123 (14) Å | θ = 3.7–27.5° |
c = 15.1330 (12) Å | µ = 0.08 mm−1 |
β = 93.837 (2)° | T = 93 K |
V = 1454.9 (2) Å3 | Block, colorless |
Z = 4 | 0.25 × 0.18 × 0.14 mm |
Rigaku R-AXIS RAPID diffractometer | 3316 independent reflections |
Radiation source: rotating anode X-ray | 2572 reflections with I > 2σ(I) |
Detector resolution: 10.0 pixels mm-1 | Rint = 0.043 |
ω–scan | θmax = 27.5°, θmin = 3.7° |
Absorption correction: multi-scan (ABSCOR; Higashi, 1995) | h = −7→6 |
Tmin = 0.642, Tmax = 0.989 | k = −21→21 |
13857 measured reflections | l = −19→19 |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.054 | H-atom parameters constrained |
wR(F2) = 0.143 | w = 1/[σ2(Fo2) + (0.0737P)2 + 0.1802P] where P = (Fo2 + 2Fc2)/3 |
S = 1.13 | (Δ/σ)max < 0.001 |
3316 reflections | Δρmax = 0.36 e Å−3 |
183 parameters | Δρmin = −0.21 e Å−3 |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.9019 (2) | 0.43953 (8) | 0.30276 (9) | 0.0606 (4) | |
O2 | 0.6189 (3) | 0.53493 (7) | 0.14588 (8) | 0.0580 (4) | |
N1 | 0.5441 (2) | 0.40017 (7) | 0.15732 (7) | 0.0296 (3) | |
C1 | 0.7452 (3) | 0.54690 (9) | 0.42792 (9) | 0.0349 (3) | |
H1 | 0.890380 | 0.521888 | 0.440442 | 0.042* | |
C2 | 0.6582 (3) | 0.59840 (10) | 0.48934 (10) | 0.0419 (4) | |
H2 | 0.742860 | 0.608701 | 0.544010 | 0.050* | |
C3 | 0.4469 (3) | 0.63490 (10) | 0.47073 (11) | 0.0444 (4) | |
H3 | 0.386515 | 0.670465 | 0.512701 | 0.053* | |
C4 | 0.3231 (3) | 0.61973 (10) | 0.39107 (11) | 0.0416 (4) | |
H4 | 0.178359 | 0.645041 | 0.378623 | 0.050* | |
C5 | 0.4093 (2) | 0.56796 (9) | 0.32967 (9) | 0.0324 (3) | |
H5 | 0.323566 | 0.557451 | 0.275295 | 0.039* | |
C6 | 0.6215 (2) | 0.53134 (8) | 0.34761 (9) | 0.0270 (3) | |
C7 | 0.7246 (2) | 0.47610 (8) | 0.28442 (10) | 0.0328 (3) | |
C8 | 0.6187 (3) | 0.47218 (8) | 0.18929 (10) | 0.0341 (3) | |
C9 | 0.5209 (2) | 0.33160 (7) | 0.21501 (8) | 0.0244 (3) | |
C10 | 0.3298 (2) | 0.32551 (9) | 0.26361 (9) | 0.0306 (3) | |
H10 | 0.216281 | 0.366815 | 0.260071 | 0.037* | |
C11 | 0.3046 (3) | 0.25880 (10) | 0.31762 (9) | 0.0424 (4) | |
H11 | 0.173330 | 0.254294 | 0.351177 | 0.051* | |
C12 | 0.4701 (3) | 0.19876 (9) | 0.32281 (10) | 0.0463 (4) | |
H12 | 0.451759 | 0.152802 | 0.359426 | 0.056* | |
C13 | 0.6617 (3) | 0.20564 (9) | 0.27481 (11) | 0.0444 (4) | |
H13 | 0.776465 | 0.164769 | 0.279285 | 0.053* | |
C14 | 0.6880 (2) | 0.27157 (9) | 0.22024 (10) | 0.0345 (3) | |
H14 | 0.819139 | 0.275831 | 0.186591 | 0.041* | |
C15 | 0.4431 (3) | 0.39643 (8) | 0.06438 (9) | 0.0357 (4) | |
H15 | 0.509044 | 0.442544 | 0.031566 | 0.043* | |
C16 | 0.1885 (4) | 0.40866 (18) | 0.06136 (13) | 0.0788 (8) | |
H16A | 0.128132 | 0.413824 | −0.000383 | 0.118* | |
H16B | 0.154033 | 0.458040 | 0.093861 | 0.118* | |
H16C | 0.116587 | 0.362105 | 0.088643 | 0.118* | |
C17 | 0.5082 (4) | 0.31954 (11) | 0.01865 (11) | 0.0496 (5) | |
H17A | 0.454587 | 0.322180 | −0.044054 | 0.074* | |
H17B | 0.436796 | 0.273184 | 0.046472 | 0.074* | |
H17C | 0.675558 | 0.313261 | 0.023782 | 0.074* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0388 (7) | 0.0666 (9) | 0.0745 (9) | 0.0178 (6) | −0.0104 (6) | −0.0379 (7) |
O2 | 0.1117 (11) | 0.0272 (6) | 0.0356 (6) | −0.0214 (6) | 0.0097 (7) | −0.0026 (5) |
N1 | 0.0430 (7) | 0.0230 (6) | 0.0231 (5) | −0.0042 (5) | 0.0039 (5) | −0.0016 (4) |
C1 | 0.0364 (8) | 0.0353 (7) | 0.0318 (7) | 0.0036 (6) | −0.0059 (6) | −0.0020 (6) |
C2 | 0.0518 (9) | 0.0446 (9) | 0.0286 (7) | 0.0014 (7) | −0.0024 (7) | −0.0067 (6) |
C3 | 0.0558 (10) | 0.0418 (9) | 0.0365 (8) | 0.0068 (7) | 0.0099 (7) | −0.0095 (7) |
C4 | 0.0378 (8) | 0.0411 (8) | 0.0458 (9) | 0.0109 (6) | 0.0025 (7) | −0.0034 (7) |
C5 | 0.0344 (7) | 0.0327 (7) | 0.0294 (7) | 0.0003 (6) | −0.0029 (6) | 0.0005 (5) |
C6 | 0.0313 (7) | 0.0229 (6) | 0.0267 (6) | −0.0019 (5) | 0.0017 (6) | 0.0001 (5) |
C7 | 0.0318 (7) | 0.0289 (7) | 0.0379 (8) | −0.0024 (5) | 0.0025 (6) | −0.0080 (6) |
C8 | 0.0470 (9) | 0.0261 (7) | 0.0301 (7) | −0.0068 (6) | 0.0103 (6) | −0.0050 (5) |
C9 | 0.0296 (7) | 0.0215 (6) | 0.0216 (6) | −0.0004 (5) | −0.0011 (5) | −0.0024 (5) |
C10 | 0.0318 (7) | 0.0350 (7) | 0.0250 (6) | 0.0047 (5) | 0.0023 (6) | 0.0006 (5) |
C11 | 0.0506 (9) | 0.0487 (9) | 0.0283 (7) | −0.0114 (7) | 0.0058 (7) | 0.0063 (7) |
C12 | 0.0755 (12) | 0.0301 (8) | 0.0312 (8) | −0.0093 (7) | −0.0121 (8) | 0.0097 (6) |
C13 | 0.0600 (11) | 0.0278 (7) | 0.0427 (8) | 0.0139 (7) | −0.0162 (8) | −0.0033 (6) |
C14 | 0.0325 (7) | 0.0347 (7) | 0.0359 (7) | 0.0066 (6) | −0.0003 (6) | −0.0067 (6) |
C15 | 0.0603 (10) | 0.0256 (7) | 0.0211 (6) | −0.0041 (6) | 0.0022 (6) | 0.0004 (5) |
C16 | 0.0715 (14) | 0.128 (2) | 0.0338 (9) | 0.0442 (14) | −0.0149 (9) | −0.0091 (11) |
C17 | 0.0712 (12) | 0.0450 (9) | 0.0318 (8) | 0.0037 (8) | −0.0030 (8) | −0.0123 (7) |
O1—C7 | 1.2141 (18) | C9—C14 | 1.3890 (18) |
O2—C8 | 1.2269 (18) | C10—C11 | 1.385 (2) |
N1—C8 | 1.3451 (17) | C10—H10 | 0.9500 |
N1—C9 | 1.4417 (16) | C11—C12 | 1.382 (2) |
N1—C15 | 1.4893 (17) | C11—H11 | 0.9500 |
C1—C2 | 1.381 (2) | C12—C13 | 1.378 (3) |
C1—C6 | 1.3952 (19) | C12—H12 | 0.9500 |
C1—H1 | 0.9500 | C13—C14 | 1.381 (2) |
C2—C3 | 1.385 (2) | C13—H13 | 0.9500 |
C2—H2 | 0.9500 | C14—H14 | 0.9500 |
C3—C4 | 1.386 (2) | C15—C16 | 1.497 (3) |
C3—H3 | 0.9500 | C15—C17 | 1.507 (2) |
C4—C5 | 1.382 (2) | C15—H15 | 1.0000 |
C4—H4 | 0.9500 | C16—H16A | 0.9800 |
C5—C6 | 1.3883 (19) | C16—H16B | 0.9800 |
C5—H5 | 0.9500 | C16—H16C | 0.9800 |
C6—C7 | 1.4781 (19) | C17—H17A | 0.9800 |
C7—C8 | 1.529 (2) | C17—H17B | 0.9800 |
C9—C10 | 1.3796 (19) | C17—H17C | 0.9800 |
C8—N1—C9 | 121.17 (11) | C11—C10—H10 | 120.2 |
C8—N1—C15 | 118.33 (11) | C12—C11—C10 | 120.15 (15) |
C9—N1—C15 | 119.47 (10) | C12—C11—H11 | 119.9 |
C2—C1—C6 | 120.50 (14) | C10—C11—H11 | 119.9 |
C2—C1—H1 | 119.8 | C13—C12—C11 | 119.95 (14) |
C6—C1—H1 | 119.8 | C13—C12—H12 | 120.0 |
C1—C2—C3 | 119.57 (14) | C11—C12—H12 | 120.0 |
C1—C2—H2 | 120.2 | C12—C13—C14 | 120.43 (14) |
C3—C2—H2 | 120.2 | C12—C13—H13 | 119.8 |
C2—C3—C4 | 120.23 (14) | C14—C13—H13 | 119.8 |
C2—C3—H3 | 119.9 | C13—C14—C9 | 119.41 (14) |
C4—C3—H3 | 119.9 | C13—C14—H14 | 120.3 |
C5—C4—C3 | 120.31 (14) | C9—C14—H14 | 120.3 |
C5—C4—H4 | 119.8 | N1—C15—C16 | 110.62 (13) |
C3—C4—H4 | 119.8 | N1—C15—C17 | 111.89 (12) |
C4—C5—C6 | 119.86 (13) | C16—C15—C17 | 112.32 (16) |
C4—C5—H5 | 120.1 | N1—C15—H15 | 107.2 |
C6—C5—H5 | 120.1 | C16—C15—H15 | 107.2 |
C5—C6—C1 | 119.53 (13) | C17—C15—H15 | 107.2 |
C5—C6—C7 | 122.58 (12) | C15—C16—H16A | 109.5 |
C1—C6—C7 | 117.90 (12) | C15—C16—H16B | 109.5 |
O1—C7—C6 | 122.44 (13) | H16A—C16—H16B | 109.5 |
O1—C7—C8 | 118.59 (13) | C15—C16—H16C | 109.5 |
C6—C7—C8 | 118.61 (12) | H16A—C16—H16C | 109.5 |
O2—C8—N1 | 124.45 (13) | H16B—C16—H16C | 109.5 |
O2—C8—C7 | 116.97 (12) | C15—C17—H17A | 109.5 |
N1—C8—C7 | 118.47 (12) | C15—C17—H17B | 109.5 |
C10—C9—C14 | 120.44 (13) | H17A—C17—H17B | 109.5 |
C10—C9—N1 | 119.48 (11) | C15—C17—H17C | 109.5 |
C14—C9—N1 | 120.07 (12) | H17A—C17—H17C | 109.5 |
C9—C10—C11 | 119.61 (13) | H17B—C17—H17C | 109.5 |
C9—C10—H10 | 120.2 | ||
C6—C1—C2—C3 | −0.2 (2) | O1—C7—C8—N1 | 64.3 (2) |
C1—C2—C3—C4 | 0.2 (3) | C6—C7—C8—N1 | −122.42 (15) |
C2—C3—C4—C5 | 0.1 (3) | C8—N1—C9—C10 | 80.08 (17) |
C3—C4—C5—C6 | −0.4 (2) | C15—N1—C9—C10 | −88.16 (15) |
C4—C5—C6—C1 | 0.4 (2) | C8—N1—C9—C14 | −101.03 (16) |
C4—C5—C6—C7 | −179.31 (14) | C15—N1—C9—C14 | 90.73 (16) |
C2—C1—C6—C5 | −0.1 (2) | C14—C9—C10—C11 | −0.3 (2) |
C2—C1—C6—C7 | 179.61 (14) | N1—C9—C10—C11 | 178.59 (12) |
C5—C6—C7—O1 | −174.46 (15) | C9—C10—C11—C12 | 0.1 (2) |
C1—C6—C7—O1 | 5.9 (2) | C10—C11—C12—C13 | 0.6 (2) |
C5—C6—C7—C8 | 12.5 (2) | C11—C12—C13—C14 | −1.1 (2) |
C1—C6—C7—C8 | −167.15 (13) | C12—C13—C14—C9 | 0.9 (2) |
C9—N1—C8—O2 | −171.72 (15) | C10—C9—C14—C13 | −0.2 (2) |
C15—N1—C8—O2 | −3.3 (2) | N1—C9—C14—C13 | −179.05 (12) |
C9—N1—C8—C7 | 12.2 (2) | C8—N1—C15—C16 | −91.50 (19) |
C15—N1—C8—C7 | −179.43 (13) | C9—N1—C15—C16 | 77.08 (19) |
O1—C7—C8—O2 | −112.09 (19) | C8—N1—C15—C17 | 142.45 (15) |
C6—C7—C8—O2 | 61.20 (19) | C9—N1—C15—C17 | −48.97 (18) |
D—H···A | D—H | H···A | D···A | D—H···A |
C10—H10···O1i | 0.95 | 2.32 | 3.2140 (18) | 157 |
C13—H13···O2ii | 0.95 | 2.48 | 3.2895 (18) | 143 |
Symmetry codes: (i) x−1, y, z; (ii) −x+3/2, y−1/2, −z+1/2. |
Funding information
A part of this work was supported by JSPS KAKENHI Grant Nos. JP17K05745 and JP18H04504.
References
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CSD CrossRef IUCr Journals Google Scholar
Hashizume, D., Kogo, H., Ohashi, Y., Miyamoto, H. & Toda, F. (1998). Anal. Sci. 14, 1187–1188. Web of Science CrossRef Google Scholar
Hashizume, D., Kogo, H., Sekine, A., Ohashi, Y., Miyamoto, H. & Toda, F. (1995). Acta Cryst. C51, 929–933. CrossRef Web of Science IUCr Journals Google Scholar
Hashizume, D., Kogo, H., Sekine, A., Ohashi, Y., Miyamoto, H. & Toda, F. (1996). J. Chem. Soc. Perkin Trans. 2, pp. 61–66. CrossRef Web of Science Google Scholar
Hashizume, D., Uekusa, H., Ohashi, Y., Matsugawa, R., Miyamoto, H. & Toda, F. (1994). Bull. Chem. Soc. Jpn, 67, 985–993. CrossRef Web of Science Google Scholar
Higashi, T. (1995). ABSCOR. Rigaku Corporation, Tokyo, Japan. Google Scholar
Jesuraj, J. L. & Sivaguru, J. (2010). Chem. Commun. 46, 4791–4793. Web of Science CrossRef Google Scholar
Konieczny, K., Ciesielski, A., Bąkowicz, J., Galica, T. & Turowska-Tyrk, I. (2018). Crystals, 8, 299–311. Web of Science CrossRef Google Scholar
Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453–457. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Rigaku (1998). RAPID-AUTO. Rigaku Corporation, Tokyo, Japan. Google Scholar
Sakamoto, M., Takahashi, M., Fujita, T., Watanabe, S., Nishio, T., Iida, I. & Aoyama, H. (1997). J. Org. Chem. 62, 6298–6308. CrossRef Web of Science Google Scholar
Sekine, A., Hori, K., Ohashi, Y., Yagi, M. & Toda, F. (1989). J. Am. Chem. Soc. 111, 697–699. CrossRef Web of Science Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Toda, F. & Miyamoto, H. (1993). J. Chem. Soc. Perkin Trans. 1, pp. 1129–1132. CrossRef Web of Science Google Scholar
Toda, F., Miyamoto, H., Koshima, H. & Urbanczyk-Lipkowska, Z. (1997). J. Org. Chem. 62, 9261–9266. Web of Science CrossRef Google Scholar
Toda, F., Yagi, M. & Sōda, S. (1987). J. Chem. Soc. Chem. Commun. pp. 1413–1414. CrossRef Web of Science Google Scholar
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.