Synthesis, crystal structure, and high-resolution NMR spectroscopy of methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl-α-d-xylo- hexopyranoside

Article abstract of DOI:10.1016/j.carres.2004.10.016

Synthesis of methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl- and -6-O-p-tolylsulfonyl-α-d-xylo-hexopyranosides is presented. High-resolution ¹H and ¹³C NMR spectral data for both compounds and their precursors, and the single-crystal X-ray diffraction analysis for methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl-α-d-xylo- hexopyranoside are reported. The influence of the O-protective group on the chemical shift of adjacent atoms in the ¹H and ¹³C NMR spectra is discussed.

Full text of DOI:10.1016/j.carres.2004.10.016

Carbohydrate
RESEARCH
Carbohydrate Research 340 (2005) 143–147
Note
Synthesis, crystal structure, and high-resolution NMR
spectroscopy of methyl 3-azido-2,3-dideoxy-4,6-di-O-p-
tolylsulfonyl-a-D-xylo-hexopyranoside
Beata Liberek,a,* Artur Sikorskia and Antoni Konitza,b
a
´
´
Faculty of Chemistry, University of Gdansk, Sobieskiego 18, PL-80-952 Gdansk, Poland
´ ´
Department of Inorganic Chemistry, Gdansk University of Technology, G. Narutowicza 11/12, PL-80-952 Gdansk, Poland
b
Received 1 September 2004; accepted 20 October 2004
Available online 11 November 2004
Abstract—Synthesis of methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl- and -6-O-p-tolylsulfonyl-a-D-xylo-hexopyranosides is
presented. High-resolution 1H and 13C NMR spectral data for both compounds and their precursors, and the single-crystal
X-ray diffraction analysis for methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl-a-D-xylo-hexopyranoside are reported. The influ-
1
ence of the O-protective group on the chemical shift of adjacent atoms in the H and 13C NMR spectra is discussed.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Methyl 3-azido-2,3-dideoxy-a-D-xylo-hexopyranoside, tosylated; X-ray diffraction, single crystal; O-Protection, influence on chemical
shift
Although the hydroxyl group is poor leaving group in
nucleophilic substitution reactions, it is often convenient
to replace the OH group, particularly in carbohydrate
chemistry. The OH group is frequently converted to a
reactive ester, most commonly a p-toluenesulfonic ester,
to make the nucleophilic substitution possible. Due to
our interest in obtaining methyl 3-azido-2,3,6-trideoxy-
hex-5-eno-pyranosides, we synthesized 3-azido-2,3-dide-
oxy-4,6-di-O-p-tolylsulfonyl- (7) and -6-O-p-tolylsulfon-
yl-a-D-xylo-hexopyranosides (8).
As previously reported, addition of hydrazoic acid to
the a,b-unsaturated aldehyde derived from tri-O-acetyl-
D-galactal (1), followed by methyl glycosidation, led to a
mixture of 3-azido-2,3-dideoxy glycosides.1 Column
chromatography of this mixture gave in turn: methyl
4,6-di-O-acetyl-3-azido-2,3-dideoxy-a-D-lyxo- (2), -b-D-
xylo- (3), -a-D-xylo- (4), -b-D-lyxo-hexopyranosides (5).
Deacetylation of methyl 4,6-di-O-acetyl-3-azido-2,3-
solution of sodium methoxide in absolute methanol
yielded methyl 3-azido-2,3-dideoxy-a-D-xylo-hexopyr-
anoside (6). Tosylation of 6 with p-toluenesulfonyl chlo-
ride in pyridine at room temperature provided a mixture
of methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl-
(7) and -6-O-p-tolylsulfonyl-a-D-xylo-hexopyranosides
(8), which were separated by column chromatography
(Scheme 1).
Compounds synthesized in the sequence of reactions
of 4 ! 6 ! 7 and 8 differ solely in the type of OH group
protection: 4-OAc and 6-OAc (4), 4-OH and 6-OH (6),
4-OTs and 6-OTs (7), 4-OH and 6-OTs (8). The presence
of the above-mentioned protective groups in 4, 6, 7, and
8, respectively, was confirmed by IR (Table 1) and by 1H
(Table 2) and 13C NMR spectroscopy (Table 4). All
these compounds have the same a-D-xylo configuration
4
and also the same C1 conformation in CDCl3 solution,
which is demonstrated by respective coupling constants
(Table 3). As was reported earlier, the lack of coupling
between the equatorial H-1 and H-2 protons is charac-
dideoxy-a-D-xylo-hexopyranoside (4) with
a 0.1M
4
teristic for 2-deoxy-a-D-glycosides with the C1 confor-
mation.1,2 Additionally, the J4,5 coupling constant in a
range of 0–2Hz is diagnostic for a compound having
*
Corresponding author. Tel.: +48 58 3450344; fax: +48 58 3410357;
e-mail: beatal@chemik.chem.univ.gda.pl
0008-6215/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2004.10.016

144
B. Liberek et al. / Carbohydrate Research 340 (2005) 143–147
CH2OAc
O
AcO
OAc
1. a
2. b
3. c
AcO
AcO
AcO
AcO
N3
CH2OAc
CH2OAc
CH2OAc
CH2OAc
O
O
O
O
O
OM e
N3
OMe
4
5
2
3
N3
OMe
OMe N3
d
HO
TsO
HO
CH2OTs
CH2OH
CH2OTs
O
O
e
+
6
8
7
OMe
OMe
OMe
N3
N3
N3
Scheme 1. Reagents and conditions: (a) Hg2+, H3O+, dioxane; (b) NaN3, CH3COOH; (c) MsCl, MeOH, s-collidine; (d) MeONa, MeOH; (e) TsCl,
pyridine.
Table 1. Stretching frequencies (cmꢁ1) of some important groups in IR
spectra of 4 and 6–8
Table 3. The 1H–1H coupling constants (Hz) for compounds 4 and 6–8
0
0
J1,2a J1,2e J2a,2e J2a,3 J2e,3 J3,4 J4,5 J5,6 J5;6 J6;6
OH
N3
C@O
C6H4
CO–O
O@S@O
4
6
7
8
3.6
4.4
4.4
4.4
—
—
—
—
15.2 4.8
14.8 4.4
15.2 4.4
15.2 4.4
3.2
2.8
3.2
4.8
3.2 1.6 6.4 6.0 11.6
4
6
7
—
2111
2101
2114
1747
—
—
—
1231
—
—
—
3.2 1.2 3.6 3.6 11.6
3.6 0.8 7.2 4.8 10.8
3.6 1.2 6.8 5.6 10.4
3419
—
—
1598
—
1191
1178
1190
1176
8
3472
2108
—
1598
—
alter the position of the C-4 and C-6 carbon signals.
However, it seems that the 4-OH group has a deshield-
ing influence on the C-3 carbon. The signal of the C-3
carbon appears at ꢀ57ppm when the 4-OH group is
not protected (6 and 8) and at ꢀ54ppm, when 4-OH
group is protected by an acetyl (4) or a p-tolylsulfonyl
group (7).
Most important is that the X-ray structural analysis
of crystalline 7 fully confirmed the relative configuration
and conformation obtained from analysis of the NMR
spectra.
an anti-periplanar relationship of the H-4 proton and
ring oxygen atom in hexopyranoses of the D series.1,2
The differences in the 4- and 6-OH group protection of
the 4 and 6–8 glycosides are illustrated by the chemical
shifts of H-4 and H-6 protons as well as those of the
C-3, C-4, and C-6 carbons in their NMR spectra. The
most evident difference is the change of the chemical
shift of the H-4 proton with change of the 4-OH group
protection. A comparison of respective substituents
shows that their deshielding influence on the H-4 proton
decreases as follows: –OAc (d 4.73, 4), –OTs (d 4.18, 7),
–OH (d 3.72, 6 or 3.55, 8). Inversely in its 13C NMR
spectrum (Table 4), both the C-4 and C-6 carbons are
the most deshielding, while the p-tolylsulfonyl substitu-
ent protects respective OH groups (Dd ꢀ 4ppm). The
change of OAc into an OH group does not significantly
1. Experimental
1.1. General methods
Melting points are uncorrected. Optical rotations were
determined at room temperature with a Hilger-Watt
Table 2. Chemical shifts (ppm) in the 1H NMR spectra (CDCl3) of 4 and 6–8
H-1
H-2a
H-2e
H-3
H-4
H-5
H-6
H-60
OCH3
OAc
OTs
CH3
C6H4
—
4
4.81 (d) 2.15 (dt) 1.93 (dq)
3.88 (q) 4.73 (d)
4.34 (td)
4.15 (dd) 4.11 (dd) 3.40 (s) 2.08 (s)
2.13 (s)
—
6
7
4.81 (d) 2.28 (dt) 1.87 (dm) 3.81 (q) 3.72 (bd) 4.00 (td) 3.96 (dd) 3.91 (dd) 3.37 (s)
4.67 (d) 2.14 (dt) 1.86 (dm) 3.93 (q) 4.18 (d) 4.22 (ddd) 3.92 (dd) 3.73 (dd) 3.27 (s)
—
—
—
—
7.77 (d) 2.48 (s)
7.73 (d)
7.38 (d) 2.46 (s)
7.35 (d)
8
4.72 (d) 2.17 (dt) 1.87 (dm) 3.81 (q) 3.55 (b)
4.24 (td)
4.12 (dd) 4.19 (dd) 3.33 (s)
—
7.81 (d) 2.46 (s)
7.36 (d)

B. Liberek et al. / Carbohydrate Research 340 (2005) 143–147
Table 4. Chemical shifts (ppm) in the 13C NMR spectra (CDCl3) of 4 and 6–8
145
C-1
C-2
C-3
C-4
C-5
C-6
OCH3
OAc
OTs
C@O
CH3
C6H4
—
CH3
4
96.97
28.16
54.56
67.60
63.39
63.12
55.65
170.52
169.93
—
21.16
21.09
—
—
6
7
97.79
96.69
27.36
27.33
57.32
54.83
69.28
73.49
64.96
55.67
55.83
—
—
22.11
22.02
63.27
64.31
68.43
69.02
—
—
130.38
129.97
128.02
127.95
130.03
128.08
8
97.25
27.52
57.26
66.43
55.79
—
—
22.01
polarimeter in 1-dm tubes at the D line of sodium for
solutions in CHCl3. The IR spectra were recorded as
Nujol mulls with a Bruker IFS 66 spectrophotometer.
Column chromatography was performed on MN Kiesel-
gel 60 (<0.08mm).
1
The H and 13C NMR spectra (CDCl3, internal Me4Si)
were measured with a Varian Mercury 400 (400.49/
100.70MHz) instrument. Elemental analyses were con-
ducted with a Carlo Erba EA1108 elemental analyzer.
TLC was performed on the E. Merck Kieselgel 60 F-
254 plates using the following eluent systems (v/v): A,
4:1 petroleum ether–AcOEt; B, 4:1 Et2O–AcOEt; C,
1:4 petroleum ether–AcOEt; D, 2:1 toluene–AcOEt.
Table 5. Crystal data and structure refinement for 7
Empirical formula
Formula weight
Temperature (K)
C21H25N3O8N2
511.56
293(2)
0.71073
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions
Orthorhombic
P212121
Figure 1. Structure of 7 showing 50% probability displacement for
ellipsoids.
˚
a (A)
6.0130(10)
14.121(3)
28.399(6)
˚
b (A)
˚
c (A)
3
˚
V (A )
2411.3(8)
4
1.409
Z
Dcalcd (Mgmꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
Crystal size (mm)
)
0.272
1027
0.4 · 0.3 · 0.3
4.06–50.00
0 6 h 6 7, ꢁ16 6 k 6 0,
ꢁ33 6 l 6 0
2472/2472 (Rint = 0.0)
99.9
H range for data collection (ꢁ)
Limiting indices
Reflections collected/unique
Completeness 2H = 50.00ꢁ (%)
Refinement method
Full-matrix least-squares
on F2
Data/restraints/parameters
Goodness-of-fit on F2
2472/0/308
0.947
Final R indices [I > 2r(I)]
R1 = 0.0375
wR2 = 0.0641
R1 = 0.1414
wR2 = 0.0909
ꢁ0.02(14)
R indices (all data)
Absolute structure parameter
Extinction coefficient
Largest diff. peak and hole (eA
0.0016(3)
ꢁ3
˚
)
0.195 and ꢁ0.237
Figure 2. Molecular packing of 7 (view along x-axis).

146
B. Liberek et al. / Carbohydrate Research 340 (2005) 143–147
Table 6. Atomic coordinates (·104) and equivalent isotropic displace-
ment parameters (A · 10 ) for 7 Ueq is defined as one third of the trace
of the orthogonalized Uij tensor
Table 7. Selected bond lengths (A), valence angles (ꢁ), and torsion
angles (ꢁ) for 7
˚
2
3
˚
Bond lengths
Atom
x
y
z
Ueq
C-1–O-7
C-1–O-6
C-1–C-2
C-2–C-3
C-3–N-9
C-3–C-4
C-4–O-12
C-4–C-5
C-5–O-6
C-5–C-23
O-7–C-8
N-9–N-10
N-10–N-11
1.378(7)
1.423(7)
1.499(7)
1.509(6)
1.461(7)
1.547(6)
1.452(5)
1.497(6)
1.429(6)
1.509(6)
1.431(7)
1.205(7)
1.111(7)
C-1
C-2
ꢁ2727(12)
ꢁ1696(11)
ꢁ2543(7)
ꢁ2618(7)
ꢁ3669(10)
ꢁ2615(6)
ꢁ4876(8)
ꢁ5985(13)
ꢁ4809(10)
ꢁ5315(11)
ꢁ5984(15)
ꢁ349(6)
523(2)
775(4)
ꢁ133(4)
ꢁ486(3)
330(3)
1195(3)
1478(2)
590(3)
1400(5)
ꢁ860(4)
ꢁ1389(4)
ꢁ1894(5)
552(2)
132(1)
821(4)
515(4)
1116(4)
2016(4)
2311(4)
1722(4)
2702(4)
ꢁ822(2)
342(2)
2033(3)
2681(2)
3451(1)
4450(4)
4567(4)
5361(4)
6006(4)
5878(4)
5098(4)
6869(4)
3634(3)
3164(3)
1000
150(2)
314(2)
782(1)
1145(1)
937(2)
508(2)
9(2)
64(2)
71(2)
57(1)
43(1)
45(1)
54(1)
77(1)
102(3)
78(2)
86(2)
146(3)
50(1)
55(1)
44(1)
52(2)
58(2)
55(2)
63(2)
58(2)
88(2)
65(1)
76(1)
54(2)
64(1)
66(1)
54(2)
59(2)
65(2)
67(2)
74(2)
66(2)
100(3)
105(2)
82(2)
77
C-3
C-4
C-5
O-6
O-7
C-8
ꢁ183(2)
782(1)
467(2)
203(3)
1282(1)
1763(1)
2181(1)
2396(2)
2686(2)
2775(2)
2568(2)
2273(2)
3073(2)
1804(1)
1761(2)
1266(2)
1101(1)
1446(1)
1338(2)
1585(2)
1495(2)
1167(2)
915(2)
1005(2)
1068(2)
1269(2)
1915(1)
ꢁ118
N-9
N-10
N-11
O-12
S-13
Valence angles
O-7–C-1–O-6
O-7–C-1–C-2
O-6–C-1–C-2
C-1–C-2–C-3
N-9–C-3–C-2
N-9–C-3–C-4
C-2–C-3–C-4
O-12–C-4–C-5
O-12–C-4–C-3
C-5–C-4–C-3
O-6–C-5–C-4
O-6–C-5–C-23
C-4–C-5–C-23
C-1–O-6–C-5
C-1–O-7–C-8
N-10–N-9–C-3
N-11–N-10–N-9
C-14
C-15
ꢁ811(9)
ꢁ2739(10)
ꢁ3869(10)
ꢁ3149(10)
ꢁ1171(10)
ꢁ36(9)
112.6(5)
108.4(6)
110.8(5)
114.6(4)
115.8(4)
104.0(3)
110.6(2)
109.0(4)
108.1(2)
110.8(2)
112.2(4)
107.1(4)
112.4(4)
113.1(4)
113.4(5)
117.4(6)
172.5(9)
C-16
C-17
C-18
C-19
C-20
ꢁ4499(11)
ꢁ235(7)
2842(6)
ꢁ3587(9)
ꢁ5257(7)
ꢁ6203(3)
ꢁ4568(10)
ꢁ2625(10)
ꢁ1327(10)
ꢁ1917(12)
ꢁ3899(14)
ꢁ5216(11)
ꢁ508(13)
ꢁ8368(7)
ꢁ5887(9)
ꢁ1910
O-21
O-22
C-23
O-24
S-25
C-26
C-27
C-28
C-29
C-30
C-31
Torsion angles
C-32
O-7–C-1–C-2–C-3
O-6–C-1–C-2–C-3
C-1–C-2–C-3–N-9
C-1–C-2–C-3–C-4
N-9–C-3–C-4–O-12
C-2–C-3–C-4–O-12
N-9–C-3–C-4–C-5
C-2–C-3–C-4–C-5
O-12–C-4–C-5–O-6
C-3–C-4–C-5–O-6
O-12–C-4–C-5–C-23
C-3–C-4–C-5–C-23
O-7–C-1–O-6–C-5
C-2–C-1–O-6–C-5
C-4–C-5–O-6–C-1
C-23–C-5–O-6–C-1
O-6–C-1–O-7–C-8
C-2–C-1–O-7–C-8
C-2–C-3–N-9–N-10
C-4–C-3–N-9–N-10
C-3–N-9–N-10–N-11
H-1A–C-1–C-2–H-2A
H-1A–C-1–C-2–H-2B
H-2A–C-2–C-3–H-3A
H-2B–C-2–C-3–H-3A
H-3A–C-3–C-4–H-4A
H-4A–C-4–C-5–H-5A
H-5A–C-5–C-23–H-23A
H-5A–C-5–C-23–H-23B
ꢁ72.8(6)
51.2(7)
71.7(6)
ꢁ46.2(6)
162.3(4)
ꢁ72.8(4)
ꢁ78.3(4)
46.6(4)
64.8(5)
ꢁ54.1(4)
ꢁ56.0(5)
ꢁ174.9(3)
64.0(6)
ꢁ57.6(7)
60.9(6)
ꢁ175.4(5)
60.7(6)
ꢁ176.4(5)
45.1(6)
166.6(4)
170.9(6)
55.5
O-33
O-34
H-1A
H-2B
H-2A
H-3A
H-4A
H-5A
H-8A
H-8B
H-8C
H-15A
H-16A
H-18A
H-19A
H-20A
H-20B
H-20C
H-23A
H-23B
H-27A
H-28A
H-30A
H-31A
H-32A
H-32B
H-32C
ꢁ1752
ꢁ611
73
85
85
ꢁ162
18
ꢁ974
369
897
ꢁ1575
68
51
ꢁ3457
136
1068
1416
873
ꢁ5209
54
153
ꢁ6283
1846
1690
64
ꢁ417
ꢁ5056
153
153
ꢁ7361
1206
ꢁ109
ꢁ325
ꢁ3313
2338
2841
63
70
ꢁ5186
891
2942
ꢁ652
2630
2144
75
70
1356
ꢁ4100
1930
2630
3398
2974
132
132
ꢁ4194
3340
2571
ꢁ6054
3034
1254
132
65
ꢁ2153
2331
1834
ꢁ3902
1582
1808
65
70
ꢁ2161
4095
5438
63
ꢁ4303
1657
684
77
89
ꢁ60.9
6342
5007
ꢁ51.9
ꢁ6528
817
765
80
150
64.9
ꢁ72.4
ꢁ892
7123
7338
ꢁ772
1306
1070
150
150
ꢁ54.5
1035
6694
ꢁ159.5
79.1

B. Liberek et al. / Carbohydrate Research 340 (2005) 143–147
147
Table 8. Short contacts for 7
D–H
d(D–H)
d(Hꢃ ꢃ ꢃA)
2.45
2.49
<DHA
d(Dꢃ ꢃ ꢃA)
3.242(5)
3.377(7)
A
Symm. op.
C-4–H-4A
C-19–H-19A
0.96
0.96
140
153
O22
O34
[1 ꢁ x,y,z]
[1 + x,y,z]
1.2. Methyl 4,6-di-O-acetyl-3-azido-2,3-dideoxy-a-D-
lyxo-(2), -b-D-xylo- (3), -a-D-xylo- (4), and -b-D-lyxo-
hexopyranosides (5)
In the crystal, 7 adopts a 4C1 chair conformation with
puckering parameters Q = 0.512(4) and H = 6.8(4)ꢁ.7,8
The values of bond lengths and angles determined in this
work for 7 agree well with the expected ones.9,10 All H
atoms were placed geometrically and refined using a rid-
These were synthesized as previously reported.1
˚
ing model with C–H = 0.96A and Uiso(H) = 1.2 Ueq(C)
˚
(C–H = 0.96A and Uiso(H) = 1.5 Ueq(C) in the case of
the methyl H atoms).
1.3. Methyl 3-azido-2,3-dideoxy-a-D-xylo-hexopyrano-
side (6)
A mixture of 4 (2.84g, 8.1mM) and 0.1M NaOMe in abs
MeOH (35mL) was stirred for 0.5h at rt. The end of
deacetylation was verified by TLC (solvent A). The solu-
tion was then neutralized with Dowex-50W · 8 (H+) ion-
exchange resin and filtered, and the filtrate was evapo-
rated to give 6 (99%, solid); Rf 0.39 (solvent B).
Supplementary data
Full crystallographic details, excluding structure fea-
tures, have been deposited (deposition no. CCDC
247410) with the Cambridge Crystallographic Data
Centre. These data may be obtained, on request, from
The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (tel.: +44 1223 336408; fax: +44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk or <www:http:
//www.ccdc.cam.ac.uk>).
1.4. Methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl-
(7) and 6-O-p-tolylsulfonyl-a-D-xylo-hexopyranosides (8)
To a solution of 6 (1.39g, 6.84mM) in CH2Cl2 (50mL),
dry pyridine (2.8mL) and p-toluenesulfonyl chloride
(2.61g, 13.7mM) were added. The mixture was stirred
at rt for 24h. The end of the reaction was determined
by TLC (solvent C). The mixture was then diluted with
Et2O (50mL), and the precipitated salts were filtered
off. The filtrate was concentrated and diluted with CHCl3.
The organic solution was washed with satd NaHCO3 and
water and dried over Na2SO4. Concentration under re-
duced pressure led to the crude product, which was chro-
matographed (solvent D) to give first 7 (44%, mp 138–
Acknowledgements
This research was supported by the Polish State Com-
mittee for Scientific Research under grants DS/8361-4-
0134-4 and BW/8000-5-0200-4.
140ꢁC); ½aꢂ20 +58 (c 1, CHCl3); Rf 0.81 (solvent D). Anal.
References
D
Calcd for C21H25N3O8S2: C, 49.31; H, 4.93; N, 8.21; S,
12.54. Found: C, 49.68; H, 4.95; N, 8.10; S, 12.50.
1. Liberek, B.; Da˛browska, A.; Frankowski, R.; Matu-
szewska, M.; Smiatacz, Z. Carbohydr. Res. 2002, 337,
1803–1820.
2. Liberek, B.; Sikorski, A.; Melcer, A.; Konitz, A. Carbo-
hydr. Res. 2003, 338, 795–799.
20
D
Eluted second was 8 (36%, syrup); ½aꢂ +102 (c 1,
CHCl3); Rf 0.44 (solvent D). Anal. Calcd for
C14H19N3O6S: C, 47.05; H, 5.36; N, 11.76; S, 8.97.
Found: C, 47.38; H, 5.13; N, 11.52; S, 8.70.
3. Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467–
473.
4. Sheldrick, G. M. SHELXL-97; Program for the Refinement
of Crystal Structures; University of Goetingen: Goetingen,
1997.
1.5. Description of the crystal structure
5. Johnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge
National Laboratory: Oak Ridge, TN, 1976.
6. Motherwell, S.; Clegg, S. PLUTO-78; Program for Drawing
Crystal and Molecular Structure; University of Cambridge:
Cambridge, 1978.
7. Nardelli, M. Comput. Chem. 1983, 7, 95–97.
8. Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659.
9. Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.;
Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2
1987, S1–19.
The crystal structure of 7 was solved by the SHELXS pro-
gram and refined by SHELXL-97.3,4 A summary of crys-
tallographic data, data collection and structure
refinement is presented in Table 5. A view of 7 and its
molecular packing in the crystal are presented in Figures
1 and 2, respectively.5,6 The coordinates of atoms and
their isotropic temperature factors are presented in
Table 6. A selection of important geometric parameters
of 7 is tabulated in Table 7, and short contacts are sum-
marized in Table 8.
10. Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97,
1354–1358.