Synthesis and crystal structure determination of [H2-cryptand 222](Br3)2: A unique tribromide catalyst for the catalytic chemoselective N-boc protection of amines

Article abstract of DOI:10.1002/jccs.201190018

The organic tribromide, [H₂-cryptand 222](Br₃) ₂ was synthesized and characterized by X-ray crystallography, and was utilized as an active catalyst for the N-boc protection of amines. The method is general for the preparation of N-boc derivatives of aliphatic (acyclic and cyclic), aromatic, primary and secondary amines. We also applied our new reaction protocols for the N-boc protection of some new amines and spectral and physical data for the obtained products are reported.

Full text of DOI:10.1002/jccs.201190018

538
Journal of the Chinese Chemical Society, 2011, 58, 538-543
Synthesis and Crystal Structure Determination of [H2-cryptand 222](Br3)2:
A Unique Tribromide Catalyst for the Catalytic Chemoselective N-Boc
Protection of Amines
Gholamabbas Chehardoli,a,* Mohammad Ali Zolfigol,b Vahid Khakyzadeh,b Reza Golbedaghi,c
Nikita A. Halld and Allan G. Blackmand
aSchool of Pharmacy, Hamedan University of Medical Sciences, Zip Code 65178, Hamedan, Iran
bFaculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
cPayame Noor University (PNU), Hamedan, Iran
dDepartment of Chemistry, University of Otago, P. O. Box 56, Dunedin, New Zealand
Received September 8, 2010; Accepted March 3, 2011; Published Online March 15, 2011
The organic tribromide, [H2-cryptand 222](Br3)2 was synthesized and characterized by X-ray crystal-
lography, and was utilized as an active catalyst for the N-boc protection of amines. The method is general
for the preparation of N-boc derivatives of aliphatic (acyclic and cyclic), aromatic, primary and secondary
amines. We also applied our new reaction protocols for the N-boc protection of some new amines and
spectral and physical data for the obtained products are reported.
Keywords: [H2-cryptand 222](Br3)2; diboc; N-Boc protection; Amine; Tribromide;
Chemoselective.
INTRODUCTION
Crown ethers have attracted significant attention
tribromide,18 pyridine hydrobromide perbromide,19 hexa-
methylenetetramine-bromine20 and DABCO-bromine.21
-
from various fields of science. Crown ether moieties are
popular host compounds in host-guest chemistry and these
ligands have shown a remarkable ability to form strong
complexes with organic and inorganic cations1-3 or an-
ions,4,5 selectively. Among the crown ethers, cryptand 222,
a macrobicyclic compound, has been used in a variety of
applications including the formation of a conductometric
mercury [II] sensor based on poly aniline,6 the encapsula-
tion of alkali metals, especially K+,7-9 use as an acceptor
ligand for the formation of complexes containing 7,7,8,8-
tetracyanoquinodimethane (TCNQ),10 extraction of ura-
nium(VI),11 exchanging the cations of micas12 and extrac-
tion of copper(II) with erythrosine B.13
Recently some ionic liquid tribromides (IL-Br3 ) for the
preparation of bromoesters from aromatic aldehydes22 and
bromination of aromatic substrates23 were reported. Very
recently, we reported {[K.18-crown-6]Br3}n, a unique tri-
bromide with a columnar nanotube-like structure.24
Given the usefulness of such compounds, the devel-
opment of further synthetic protocols for their synthesis is
an area of interest.25,26
Due to its great stability under the conditions used in
various base-catalyzed nucleophilic substitutions and cata-
lytic hydrogenation reactions, the tert-butoxycarbonyl
(boc) group is perhaps one of the most important protecting
groups, especially for amines and amine derivatives.27,28
The stability of N-boc to catalytic hydrogenation and its re-
sistance towards basic and nucleophilic attack make carba-
mates and benzyl esters ideal orthogonal partners for the
protection of amines during the synthesis of multifunc-
tional targets.29,30 Various reagents and methods have been
developed for N-tert-butoxycarbonylation of amines.31,32
Commercially available di-tert-butyl dicarbonate (diboc)
Organic tribromide reagents (OTBs) are preferable
as oxidants to molecular bromine, owing to the hazards
associated with elemental bromine. Several tribromides
have been reported i.e., tetramethylammonium tribro-
mide,14,15 phenyltrimethylammonium tribromide,16 cetyl-
trimethylammonium tribromide, tetrabutylammonium tri-
bromide,17 1,8-diazabicyclo[5,4,0]-tetrabutylammonium
* Corresponding author. Tel/Fax: +98(811)8257059; E-mail: chehardoli@umsha.ac.ir and cheh1002@gmail.com

[H2-cryptand 222](Br3)2 as Catalyst for the N-Boc Protection of Amines
J. Chin. Chem. Soc., Vol. 58, No. 4, 2011 539
is an efficient reagent for clean and rapid introduction of
the boc-protecting group.33-35
Table 1. Comparative performances of various solvents in the N-
boc protection of 4-methoxyaniline with diboc at room
temperature
In this paper, we report the synthesis and structural
characterization of [H2-cryptand 222](Br3)2 and show that
it is as an excellent catalyst for the selective tert-butoxycar-
bonylation of various amines using diboc.
[H2-cryptand 222](Br3)2
O
(0.1mol%)
H
NH2
N
O
O
O
O
O
O
O
O
RESULTS AND DISCUSSION
Solvent/rt
In continuation of our studies on the host-guest chem-
istry of crown ethers,36-38 the synthesis and application of
tribromide reagents24,39 and the protection of organic func-
tional groups,40-44 we found that addition of Br2 to cryptand
222 in ethanol as solvent gave the unique tribromide re-
agent [H2-cryptand 222](Br3)2 (I) which was isolated as red
crystals following recrystallization from acetonitrile,
(Scheme I).
Entry
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
CH3CN
CHCl3
CH2Cl2
1,4-dioxane
n-Hexane
Acetone
EtOAc
5
80
70
60
65
30
--
12
10
10
10
2
15
15
50
60
Ethanol
Scheme I
(Scheme II and Table 2).
A wide range of various amines undergo N-boc pro-
tection using this procedure to provide the corresponding
tert-butoxycarbonylated products in good to excellent
yields. Aliphatic amines generally react more rapidly than
aromatic. We also applied our reaction protocols to the N-
boc protection of some new amines (Table 2, entries 11, 14,
17, 19, 20, 21, 23, 25 and 26). Spectral and physical data
for the obtained products are consistent with their proposed
structures.
Crystallographic analysis at 89 K confirmed the for-
mulation of these crystals as [H2-cryptand 222](Br3)2. The
structure comprises a doubly protonated cryptand cation
and two tribromide anions. Diprotonated cryptands have
three possible conformers, namely exo-exo, endo-endo and
exo-endo.45 Like all but five of the 55 examples of dipro-
tonated cryptans 222 in the Cambridge Crystallographic
Database, [H2-cryptand 222](Br3)2 displays an endo-endo
conformation (Fig. 1) in which the two N-protons point
into the cavity of the cryptand.46
As the first application of these new structure, we
studied the conversion of 4-methoxyaniline (1 mmol) to its
corresponding N-boc protected derivative using the [H2-
cryptand 222](Br3)2 catalyst (0.001 mmol) and diboc (1
mmol) in a variety of solvents at room temperature (Table
1). The results show that acetonitrile is the best solvent
in terms of time and product yield.
We then prepared a range of tert-butoxycarbonylated
amines under the following reaction conditions: amine
compound (1 mmol), diboc (1-2 mmol), [H2-cryptand
222](Br3)2 (0.0015-0.003 mmol) and acetonitrile (4 mL)
Fig. 1. ORTEP diagram of [H2-cryptand 222](Br3)2. H
atoms have been omitted for clarity.

540 J. Chin. Chem. Soc., Vol. 58, No. 4, 2011
Chehardoli et al.
NMR (90 MHz, CDCl3): d = 1.3 (m, 22H), 1.9 (br, 4H), 3.2
(br, 2H), 4.8 (br, 2H, NH); IR (KBr): 3363, 2974, 1684
cm-1.
Scheme II
Entry 20: Colorless oil yield 85%; 1H NMR (90 MHz,
CDCl3): d = 1.2 (s, 9H), 2.2-2.4 (m, 6H), 3.3-3.5 (m, 7H,
CH); IR (KBr): 3450, 2976, 1680 cm-1.
Entry 21: Yellow oil yield 95%; 1H NMR (90 MHz,
CDCl3): d = 1 (d, J = 7 Hz, 3H), 1.2-1.3 (m, 15H), 2.5 (m,
1H), 3.6 (m, 1H), 4.1 (m, 1H); IR (Nujol): 2974, 1670 cm-1.
Chemoselectivity
1
Organic tribromide reagents are well known as bro-
minating agents for aromatic species.22-24 Our results for
the protection of aromatic amines further shows the chemo-
selectivity of the [H2-cryptand 222](Br3)2/diboc combina-
tion, as the N-boc protected amine is the only product ob-
served in all cases. This system thus appears superior to
other reported methods22-24 in that bromination of the aro-
matic ring in aromatic amines does not occur (Table 2,
Scheme III).
Entry 23: Pink oil yield 85%; H NMR (90 MHz,
CDCl3): d = 1.48 (s, 9H), 3.1 (t, J = 17 Hz, 4H), 3.5 (t, J =
17 Hz, 4H), 6.8-7.2 (m, 5H); IR (Nujol): 2978, 1700, 1597
cm-1.
Entry 25: Colorless solid yield 85%; Mp: 80 °C; 1H
NMR (90 MHz, CDCl3): d = 1.4 (s, 18H), 3.2-3.7 (m, 24H);
13C NMR (22.5 MHz, CDCl3): 28, 48, 65, 68, 83, 157; IR
(KBr): 2978, 1650, 1200 cm-1.
Entry 26: Colorless oil yield 90%; 1H NMR (90 MHz,
CDCl3): d = 1.4 (s, 9H), 3.4-3.7 (m, 24H); 13C NMR (22.5
MHz, CDCl3): 25, 55, 67, 70.1, 70.4, 70.7, 159; IR (Nujol):
2930, 1660, 1167 cm-1.
Spectroscopic data for unreported products
[H2-cryptand 222](Br3)2: Red crystals, yield 0.95%;
Mp: 145 °C, IR (KBr): 3320 (w), 2985 (w), 1450 (w), 1345
(m), 1125 (s). 1H NMR (90 MHz, CDCl3): d = 4.1 (s, 36H),
6.67 (br, 2H, NH).
Experimental description of structure
Suitable crystals of [H2-cryptand 222](Br3)2 were ob-
tained by slow evaporation of a CH3CN solution. Crystal
data and experimental parameters for the crystal structure
are reported in Table 3. The orange crystals (dimensions of
0.29 × 0.25 × 0.18 mm3) were mounted on a glass fibre and
used for data collection. X-ray data were collected at 89 K
on a Bruker Kappa APEX-II system using graphite-mono-
chromated Mo Ka radiation with exposures over 0.5o, and
were corrected for Lorentz and polarization effects using
SAINT.47 All structures were solved using SIR-9748 run-
ning within the WinGX package49 and weighted full-matrix
refinement on F2 was carried out using SHELXL-97.50 Hy-
drogen atoms attached to carbon and nitrogen, were in-
cluded in calculated positions, and were refined as riding
atoms with individual (or group, where appropriate) isotro-
Entry 11: Yellow solid, yield 65%; Mp: 188 °C; 1H
NMR (90 MHz, CDCl3): d = 1.4 (s, 18H), 3.8 (s, 2H), 6.4
(br, 2H, NH), 7.2 (m, 8H); IR (KBr): 3356, 2980, 1690,
1550 cm-1.
1
Entry 14: White solid, yield 70%; Mp: 150 °C; H
NMR (90 MHz, CDCl3): d = 1.4 (s, 18H), 2.2 (s, 3H), 6.5
(br, 1H, NH), 6.7-7.2 (m, 4H, NH, CH); 13C NMR (22.5
MHz, CDCl3): 20.9, 28.3, 80.5, 124.1, 124.2, 125.6, 127.1,
130.7, 135.4, 153.8; IR (KBr): 3278, 2978, 1700, 1541
cm-1.
1
Entry 17: Colorless oil, yield 95%; H NMR (90
MHz, CDCl3): d = 1.3-1.7 (m, 17H), 3.2 (br, 4H, CH2); IR
(KBr): 2978, 1690 cm-1.
1
Entry 19: White solid yield 90%; Mp: 163 °C; H
Scheme III
NH2
NHBoc
NHBoc
Br
NH2
NH2
[H2-Cryptand 222](Br3)2
NH2
+
Diboc/CH3CN
N
NH
N
NBoc
Br
N
NH
0%
100%

[H2-cryptand 222](Br3)2 as Catalyst for the N-Boc Protection of Amines
J. Chin. Chem. Soc., Vol. 58, No. 4, 2011 541
Table 2. Protection of amines (1) with diboc (2) using [H2-cryptand 222](Br3)2 as catalyst in acetonitrile at
room temperature
Catalyst
(mol %)
Diboc
(mmol)
Isolated yieldsa
(%)
Entry
Amine
Time (h)
Ref.
1
2
3
4
5
6
7
8
Ph-NH2
4-Cl-Ph-NH2
4-Br-Ph-NH2
4-OMe-Ph-NH2
4-OH-Ph-NH2
2-OH-Ph-NH2
2-Me-Ph-NH2
3-Me-Ph-NH2
3-Br-Ph-NH2
(PhCH2)2NH
(4-NH2Ph)2CH2
Ph-CH2NH2
Benzene-1,2-diamine
4-Methylbenzene-1,2-diamine
Naphthalen-1-amine
Azepane
0.1
0.15
0.2
0.1
0.1
0.1
0.15
0.1
0.2
0.1
0.2
0.1
0.3
0.2
0.15
--
0.1
0.1
0.15
0.1
--
0.1
0.2
0.1
1.1
1.1
1.1
1
1
1
1
1
1
1
2
1
2
2
1
1
1
2
5
4
8
5
5
4
4
7
10
0.5
4.5
2
10
8
80
80
85
80
90
85
65
85
75
98
65
80
85
70
80
80
95
70
90
85
95
95
85
75
34
33
33
34
32
27
33
33
33
27
--
34
32
--
33
--
--
32
--
--
--
--
--
28
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
6
0.75
0.25
1
Azepane
Piperazine
Cyclohexane-1,2-diamine
2-(Piperazin-1-yl)ethanol
2-Methylpiperidine
2-Methylpiperidine
1-Phenylpiperazine
1H-imidazole
2
1
1
1
1
1
1
0.25
0.75
0.33
0.33
2
O
O
NH
HN
25
26
0.1
0.1
2
1
0.33
0.16
85
--
--
O
O
O
O
O
O
O
83
H
N
Mixture of
products
Mixture of
products
Mixture of
products
--
27
28
29
3-(Trifluoromethyl)aniline
Pyridin-2-amine
0.3
0.2
0.2
1
1
2
--
--
--
--
34
--
4-Nitrobenzene-1,2-diamine
30
31
32
1H-indole
1H-pyrrole-3-carbaldehyde
Melamine
0.15
0.15
0.1
1
1
3
--
--
--
34
--
--
--
--
pic displacement parameters.
reaction is carried out under mild conditions and yields of
products are good to excellent.
In conclusions, we have prepared and characterized a
novel crystalline tribromide catalyst based on cryptand 222
which has high active bromine content per molecule and
which acts as an excellent bromine carrier capable of cata-
lyzing the chemoselective N-boc protection of amines. The
EXPERIMENTAL
General
Chemicals were purchased from Merck. N-Boc pro-

542 J. Chin. Chem. Soc., Vol. 58, No. 4, 2011
Chehardoli et al.
The solution was stirred at room temperature for one min-
ute. The amine (1 mmol) was then added and the solution
was stirred at room temperature for the appropriate time
(see Table 2). After completion of the reaction, CH3CN was
removed by water-bath distillation. To the residue was
added n-hexane or ethyl acetate (5 mL) and the mixture was
filtered. The solid was washed with n-hexane or ethyl ace-
tate (2 ´ 10 mL) and the combined filtrates were reduced to
dryness to yield pure products.
Table 3. Refinment and crystal structure data of compound [H2-
cryptand 222](Br3)2
Empirical formula
Formula weight
C18H38Br6N2O6
857.96
Temperature
89(2) K
Wavelength
0.71073
Crystal system
Space group
Monoclinic
C2/c
Unit cell dimensions
a (Å)
11.902(3)
b (Å)
15.671(3)
c (Å)
a
15.660(3)
90°
ACKNOWLEDGEMENTS
b
95.882(10)°
90°
2905.5(10)
4
1.961
8.324
1672
0.29 ´ 0.25 ´ 0.18
2.16 to 26.55
-14 £ h £ 14, -19 £ k £ 19,
-17 £ l £ 19
This paper was extracted from the MSc thesis of
Vahid Khakyzadeh. The authors acknowledge financial
support for this work from the research affairs of Hamedan
University of Medical Sciences, Hamedan, I.R. Iran and
partial support of this work by the Research Affairs Office
of Bu-Ali Sina University (Grant number 32-1716 entitled
development of chemical methods, reagent and molecules),
and also Center of Excellence in Development of Chemical
Method (CEDCM) Hamadan, I.R. Iran.
g
V(Å) 3
Z
Dcalc (Mg/m3)
Absorption coefficient (mm-1)
F(000)
Crystal size (mm3)
q range for data collection (°)
Index ranges
Reflections collected
Rint
Completeness to q = 26.55°
Absorption correction
26588
0.0419
98.9%
Semi-empirical from
equivalents
1.000000 and 0.646031
Full-matrix least-squares on F2
2998 / 0 / 151
1.054
R1 = 0.0208, wR2 = 0.0439
R1 = 0.0264, wR2 = 0.0454
REFERENCES
1. Huang, Z. B.; Chang, S. H. Synlett 2005, 1703.
2. Huang, Z. B.; Chang, S. H. Synlett 2005, 2257.
3. Huang, Z. B.; Kang, T. J.; Chang, S. H. Tetrahedron Lett.
2005, 46, 3461.
Max. and min. transmission
Refinement method
4. Lindoy, L. F. J. Iran. Chem. Soc. 2004, 1, 1.
5. Hua, J.; Wang, Y. G. Chem. Lett. 2005, 34, 98.
6. Muthukumar, C.; Kesarkar, S. D.; Srivastava, D. N. J.
Electroanal. Chem. 2007, 602, 172.
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R indices (all data)
Largest diff. peak and hole (e.Å-3) 0.414 and -0.399
7. Bushmann, H. J.; Wenz, G.; Schollmeyer, E.; Mutihac, L.
Inorg. Chem. Commun. 2001, 4, 211.
8. Letcher, T. M.; Mercer-Chalmers, J. D.; Kay, R. L. Pure
Appl. Chem. 1994, 66, 419.
tected products were characterized by comparison of their
1
spectral (IR, H-NMR and 13C-NMR) and physical data
9. Dhifet, M.; Belkhiria, M. S.; Daran, J.; Nasri, H. Acta Cryst.
2009, E65, m967.
with those of known samples.27,28,33-35
10. Pouretedal, H. R.; Semnani, A. Iran. J. Chem. Chem. Eng.
2005, 24, 53.
Preparation of [H2-cryptand 222](Br3)2
In a round-bottomed flask (100 mL) equipped with a
magnetic stirrer, bromine (0.494 g, 3.1 mmol) was added to
a solution of cryptand 222 (0.376 g, 1 mmol) in ethanol (30
mL) and the mixture was stirred for 0.5 hour. Filtration
through a sintered glass funnel gave a fine yellow powder
[0.81 g, 95% yield], which was recrystallized from CH3CN
to give red crystals [Mp: 145 °C].
11. Mathew, V. J.; Khopkar, S. M. J. Radioanal. Nucl. Chem.
Lett. 1995, 201, 281.
12. Bracke, G.; Satir, M.; Krau, P. Clays Clay Miner. 1995, 43,
732.
13. Gandhi, M. N.; Khopkar, S. M. Mikrochim. Acta 1993, 111,
93.
14. Cattaway, F. D.; Hoyle, G. J. Chem. Soc. 1923, 654.
15. Avramoff, M.; Weiss, J.; Schaechter, O. J. Org. Chem. 1963,
28, 3256.
General procedure for the N-boc protection of
amines
16. Kajigneshi, S.; Kakinami, T.; Tokiyama, H.; Hirakawa, T.;
Okamoto, T. Chem. Lett. 1987, 627.
To a solution of diboc (1-2 mmol) in CH3CN (4 mL)
was added [H2-cryptand 222](Br3)2 (0.001-0.003 mmol).
17. (a) Buckles, R. E.; Popov, A. I.; Zelezny, W. F.; Smith, R. J.

[H2-cryptand 222](Br3)2 as Catalyst for the N-Boc Protection of Amines
J. Chin. Chem. Soc., Vol. 58, No. 4, 2011 543
Am. Chem. Soc. 1951, 73, 4525. (b) Wu, L. Q.; Yang, C. G.;
Wu, Y. F.; Yang, L. M. J. Chin. Chem. Soc. 2009, 56, 606. (c)
Wu, L. Q.; Wang, X.; Ma, W. W.; Yan, F. L. J. Chin. Chem.
Soc. 2010, 57, 616.
37. Zolfigol, M. A.; Zebarjadian, M. H.; Chehardoli, G.;
Mallakpour, S. E.; Shamsipur, M. Tetrahedron 2001, 57,
1627.
38. Niknam, K.; Zolfigol, M. A. J. Iran. Chem. Soc. 2006, 3, 59.
39. (a) Zolfigol, M. A.; Chehardoli, G.; Ghaemi, E.; Madrakian,
E.; Zare, R.; Azadbakht, T.; Niknam, K.; Mallakpour, S.
Monatsh. Chem. 2008, 139, 261. (b) Ghorbani-Vaghei, R.;
Zolfigol, M. A.; Moshfeghifar, N.; Koukabi, N.; Chehardoli,
G. J. Chin. Chem. Soc. 2007, 54, 791.
18. Muathen, H. A. J. Org. Chem. 1992, 57, 2740.
19. Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis;
New York: Wiley, 1967.
20. Yavari, I.; Shaabani, A. J. Chem. Res. (S) 1994, 7, 274.
21. Heravi, M. M.; Derikvand, F.; Ghassemzadeh, M.; Neumuller,
B. Tetrahedron Lett. 2005, 46, 6243.
40. (a) Ghorbani-Vaghei, R.; Zolfigol, M. A.; Chegeny, M.; Veisi,
H. Tetrahedron Lett. 2006, 47, 4505. (b) Zolfigol, M. A.;
Khazaei, A.; Kolvari, E.; Koukabi, N.; Soltani, H.; Behjunia,
M.; Khakyzadeh, V. ARKIVOC 2009, xiii, 200.
22. Bao, W.; Wang, Z. Green Chem. 2006, 8, 1028.
23. Chiappe, C.; Leandri, E.; Pieraccini, D. Chem. Commun.
2004, 2536.
24. Zolfigol, M. A.; Chehardoli, G.; Salehzadeh, S.; Adams, H.;
Ward, M. D. Tetrahedron Lett. 2007, 48, 7969.
25. Chaudhuri, M. K.; Khan, A. T.; Patel, B. K. Tetrahedron Lett.
1998, 39, 8163.
41. Niknam, K.; Zolfigol, M. A.; Chehardoli, G.; Dehghanian,
M. Chin. J. Catal. 2008, 29, 901.
42. Zolfigol, M. A.; Chehardoli, G.; Dehghanian, M.; Niknam,
K.; Shirini, F.; Khoramabadi-Zad, A. J. Chin. Chem.
Soc. 2008, 55, 885.
26. Boeini, H. Z. J. Iran. Chem. Soc. 2009, 6, 547.
27. Heydari, A.; Khaksar, S.; Tajbakhsh, M. Synthesis 2008,
3126.
43. Niknam, K.; Zolfigol, M. A.; Saberi, D.; Khonbazi, M.
Chin. J. Chem. 2009, 27, 1548.
28. Heydari, A.; Shiroodi, K. S.; Hamadi, H.; Esfandyari, M.;
Pourayoubi, M. Tetrahedron Lett. 2007, 48, 5865.
29. Agami, C.; Couty, F. Tetrahedron 2002, 58, 2701.
30. Lutz, C.; Lutz, V.; Knochel, P. Tetrahedron 1998, 54, 6385.
31. Khaksar, S.; Heydari, A.; Tajbakhsh, M.; Vahdat, S. M. Tet-
rahedron Lett. 2008, 49, 3527.
44. Shirini, F.; Zolfigol, M. A.; Abedini, M. Monatsh. Chem.
2009, 140, 61.
45. Dantz, D. A.; Buschmann, H. J.; Schollmeyer, E. Polyhedron
1998, 17, 1891.
46. The room-temperature crystal structure of [H2-cryptand
222](Br3)2 has recently been reported; the unit cell parame-
ters are essentially identical to those reported herein, al-
though the present structure has been refined to a lower R
factor, and does not display the disorder present in the room
temperature structure. See Chekhlov, A. N. J. Struct. Chem.
2007, 48, 137.
32. Upadhyaya, D. J.; Barge, A.; Stefania, R.; Cravotto, G. Tet-
rahedron Lett. 2007, 48, 8318.
33. (a) Chankeshwara, S. V.; Chakraborti, A. K. Tetrahedron
Lett. 2006, 47, 1087. (b) Wang, G.; Li, C.; Li, J.; Jia, X. Tetra-
hedron Lett. 2009, 50, 1438.
34. Sunitha, S.; Kanjilal, S.; Reddy, P. S.; Prasad, R. B. N. Tetra-
hedron Lett. 2008, 49, 2527.
47. SAINT, Bruker AXS Inc., Madison: Wisconsin, USA 2001.
48. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori,
G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.
49. Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
50. Sheldrick, G. M. Acta Cryst. 2008, A64, 112.
35. Suryakiran, N.; Prabhakar, P.; Reddy, T. S.; Rajesh, K.;
Venkateswarlu, Y. Tetrahedron Lett. 2006, 47, 8039.
36. Zolfigol, M. A.; Zebarjadian, M. H.; Chehardoli, G.;
Keypour, H.; Salehzadeh, S.; Shamsipur, M. J. Org. Chem.
2001, 66, 3619.