Preparation of onium salts of a reduced anthracenone crown ether macrocycle: A reactivity series involving pyridine, phosphine, thiophene, nitrile and primary amide nucleophiles

Article abstract of DOI:10.1002/poc.2902

Reaction of mineral acids with a cyclic macromolecule containing a secondary alcohol produces ammonium, phosphonium, thiophene, and amide adducts via a carbocation intermediate. X-ray crystallography confirms the structures of the products, including those when two competing nucleophiles are present. A reactivity series that mirrors the nucleophilicity index, where reactivity decreases in the order thiophene >pyridine >primary amides >alkyl nitriles >> aromatic nitriles (unreactive), results. Addition of metal ions to ammonium adducts dissolved in acetonitrile produces secondary amides via the Ritter amide synthesis. Copyright

Full text of DOI:10.1002/poc.2902

Research Article
Received: 26 August 2011,
Revised: 21 October 2011,
Accepted: 2 December 2011,
Published online in Wiley Online Library: 2011
(wileyonlinelibrary.com) DOI: 10.1002/poc.2902
Preparation of onium salts of a reduced
anthracenone crown ether macrocycle: a
reactivity series involving pyridine, phosphine,
thiophene, nitrile and primary
amide nucleophiles
Kadarkaraisamy Mariappan, Gerald Caple, Prem N. Basa and
Andrew G. Sykes*
Reaction of mineral acids with a cyclic macromolecule containing a secondary alcohol produces ammonium, phospho-
nium, thiophene, and amide adducts via a carbocation intermediate. X-ray crystallography confirms the structures
of the products, including those when two competing nucleophiles are present. A reactivity series that mirrors
the nucleophilicity index, where reactivity decreases in the order thiophene > pyridine > primary amides > alkyl
nitriles >> aromatic nitriles (unreactive), results. Addition of metal ions to ammonium adducts dissolved in acetonitrile
produces secondary amides via the Ritter amide synthesis. Copyright © 2012 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this paper.
Keywords: ammonium; crystallography; electrophilic addition; pyridinium; reactivity series
INTRODUCTION
EXPERIMENTAL
The synthesis of 1,8-oxybis(ethylenethoxyethylenethoxy)-10-hydroxy-10-
hydro-9-anthracenone (1) has previously been reported.[1] Pyridazine,
pyrimidine, phthalazine, benzo[c]cinnoline, triphenylphoshine, thiophene-
2-acetamide, and nicotinamide were purchased from Aldrich Milwaukee,
WI, USA and used without further purification. 1H (200MHz) and 13C NMR
(50MHz) spectra were obtained using a Varian 200MHz instrument Agilent
Technologies, Palo Alto, CA, USA at room temperature referenced to the
residual CHCl3 solvent peak. Elemental analyses were conducted using an
Exeter CE-440 Elemental Analyzer Chelmsford, MA, USA. Electrospray
ionization mass spectrometry (ESI-MS) was conducted using a Varian 500
Mass Spectrometer. Melting points were determined in an open capillary
and are uncorrected.
We have previously reported the reaction of nitriles with com-
pound 1 (Scheme 1, viii), which produces secondary amides in
the presence of an acid catalyst.[1] The production of amides
from nitriles was originally discovered by Ritter in the 1940s.[2,3]
In this case however, the amide carbonyl was itself protonated
and formed a stabilizing, intraannular hydrogen bond where,
upon deprotonation, a large amplitude change in geometry
occurred, leaving the macrocyclic pore unblocked. Unique
macrocyclic end-capped oligothiophene derivatives for the
colorimetric detection of Hg (II) have been reported previously
using similar chemistry.[4] We have extended this chemistry to
different nucleophiles, namely pyridine analogs (pyrazine, pyrim-
idine), phosphines, and primary amides, for the purpose of
designing novel host systems for the luminescence detection
of metal ions. Described within is the organic synthesis and X-ray
crystallographic characterization of a series of onium and amide
adducts of 1. Of special importance are the heterocyclic adducts
of 1, which have an additional nitrogen Lewis base present that
adds dimensionality to potential new hosts that could selec-
tively bind metal ions in near proximity to the polyether ring.
Whereas conversion of primary amides into secondary amides
by reaction with alcohols is fairly common,[5–10] ammonium
adduct formation using similar chemistry has only recently been
employed in the synthesis of surfactants,[11] new ionic
liquids,[12] novel heterocycles of pharmaceutical interest,[13,14]
and powerful methylating agents.[15]
General synthesis – liquid precursors
1,8-Oxybis(ethylenethoxyethylenethoxy)-10-hydroxy-10-hydro-9-anthracenone
(0.2g) (1) was dissolved in 5 mL of pyrimidine or pyrazine and mixed with
10 drops of 70% perchloric acid. The solution turned blue/green and fades
to yellow after 30 min. To this mixture was added 50 mL of diethyl ether,
and a yellow-colored solid was obtained, filtered, washed with diethyl
ether, and air dried.
* Correspondence to: A. G. Sykes, Department of Chemistry, University of South
Dakota, Vermillion, SD 57069, USA. E-mail: asykes@usd.edu
K. Mariappan, G. Caple, P. N. Basa, A. G. Sykes
Department of Chemistry, University of South Dakota, Vermillion, SD, 57069,
USA
J. Phys. Org. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.

K. MARIAPPAN ET AL.
O
O
O
+
N
+
N
+
H
H
N
N
O
O
O
O
H
O
O
O
O
O
O
O
O
N
N
O
O
O
3
2
4
O
ii
i
iii
No substitution
reaction
O
H
N
+
N
O
O
O
O
ix
iv
v
O
5
O
H
OH
O
O
O
viii
O
O
O
H
NH
O
O
O
1
O
vi
vii
R
O
H
PPh3
O
O
O
O
+
O
O
O
9
O
6
+
H
H
N
O
O
O
O
O
O
O
S
+
O
O
NH2
H3NOC
O
O
8
7
Scheme 1. (i) Pyrimidine, HClO4; (ii) pyridazine, HClO4; (iii) phthalazine, HClO4/C6H5CN; (iv) benzo(c)cinnoline, HClO4/C6H5CN; (v) triphenylphosphine,
HClO4/C6H5CN; (vi) thiophene-2-acetamide, H2SO4/C6H5CN; (vii) nicotinamide, HClO4/C6H5CN; (viii) alkyl nitrile, HClO4; and (ix) benzonitrile, HClO4.
Anions have been omitted for clarity
[1-Pyrimidinium](ClO4) (2): Yield = 20%; mp = 168–170 ꢀC (dec.).
Elemental analyses calculated for C26H27N2O10Cl.CH3CN: C, 55.70; H,
H, 4.83; N, 5.96%. Found: C, 61.11; H, 4.79; N, 5.81%. ESI MS calcd. for
[C34H32N2O6]+, M+, 563.3: Found 562.8.
4.96; N, 6.95%. Found: C, 55.58; H, 4.90; N, 6.82%. ESI MS calcd. for
[1-Triphenylphosphonium](ClO4) (6): Yield = 55%; mp = 115–118 ꢀC.
Elemental analyses calculated for C40H37O10ClP.2CH3CN: C, 63.98; H,
5.20; N, 3.39%: Found: C, 63.33; H, 5.61; N, 3.03%. ESI MS calcd. for
[C40H37O6P]+, M+, 644.7: Found 644.8.
[C26H27N2O6]+, M+, 463.3. Found 462.9.
[1-Pyridazinium](ClO4) (3): Yield = 15% mp = 185–190 ꢀC. Elemental
analyses calculated for C26H27N2O10Cl: C, 55.49; H, 4.79; N, 4.97%. Found:
C, 55.24; H, 4.74; N, 5.03%. ESI MS calcd. for [C26H27N2O6]+, M+, 463.3.
Found 462.6.
Competition studies
Thiophene versus primary amide nucleophiles
General synthesis – solid precursors
1 (0.5 mmol) and thiophene-2-acetamide (0.55 mmol) were dissolved in
5 mL of benzonitrile and mixed with five drops of sulfuric acid. The mix-
ture was stirred for 30 min and mixed with 50 mL of diethyl ether. The
crude solid was dissolved in 10 mL of acetonitrile, and diethyl ether
was diffused into the solution. Cream-colored crystals of (7), [1-
(5-(thiophene-2-acetamide))H](HSO4), were obtained in 20% yield
(melting point = 220 ꢀC (dec.)).
1 (0.5 mmol) and either phthalazine, benzo[c]cinnoline, or triphenylpho-
sphine (0.55 mmol) were dissolved in 5 mL of benzonitrile and mixed
with five drops of perchloric acid. The mixture was stirred for 30 min
and mixed with 50 mL of diethyl ether. A tan or yellow solid was
obtained, filtered, washed with diethyl ether, and air dried.
[1-Phthalazinium](ClO4) (4): Yield = 55%; mp = >210 ꢀC (dec.). Ele-
mental analyses calculated for C30H29O10N2Cl.0.5CH3CN: C, 58.67; H,
4.85; N, 5.53%. Found: C, 56.80; H, 4.68; N, 5.44%. ESI MS calcd. for
[C30H29O6N2]+, MH+, 513.3. Found 514.4.
Pyridine versus primary amide nucleophiles
[1-Benzo[c]cinnolinium](ClO4) (5): Yield = 75%; mp = 173–175 ꢀC
(dec.). Elemental analyses calculated for C34H31N2O10Cl.CH3CN: C, 61.43;
1 (0.5 mmol) and nicotinamide (0.55 mmol) were dissolved in 5 mL of
benzonitrile and mixed with five drops of 70% perchloric acid. The
wileyonlinelibrary.com/journal/poc
Copyright © 2012 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2012)

REACTION WITH A CYCLIC MACROMOLECULE
mixture was stirred for 30 min and mixed with 50 mL of diethyl ether. The
crude solid was dissolved in 10 mL of acetonitrile, and diethyl ether was
diffused into the solution. Cream-colored crystals of [1-(N-nicotinamide)]
(ClO4) (8) were obtained in 30% yield (melting point = 172–175 ꢀC).
molecule per asymmetric unit, which was used as the antisolvent during
crystallization. The anion is also rotationally disordered over two positions
in a ~60:40 ratio. The smaller occupancy was left isotropic. Because of the
anion disorder, neither of the hydrogen atoms around the sulfate anion
could be reliably located. SADI was used to restrain all sulfur–oxygen
distances within the anions as well.
Primary amide (benzamide) versus alkyl nitrile (acetonitrile) nucleophiles
1 (0.5 mmol) and benzamide (0.55 mmol) were dissolved in 5 mL of ace-
tonitrile and mixed with five drops of 70% perchloric acid. The mixture
was stirred for 30 min and mixed with 50 mL of diethyl ether. The crude
solid was dissolved in 10 mL of acetonitrile, and diethyl ether was dif-
fused into the solution. Cream-colored crystals (10) were obtained, and
the unit cell is identical to the secondary amide structure we reported
earlier[1] (yield: ~70%).
RESULTS – SYNTHESIS AND
CRYSTALLOGRAPHY
Pyrimidine and pyridazine, liquids at room temperature, react in
neat solution together with 1 and perchloric acid to yield the
ammonium adducts 2 and 3. Elemental analyses and mass
spectrometry results are consistent with the formation of the
ammonium salts. Phthalazine, benzo[c]cinnoline, and triphenyl-
phosphine starting materials are solids at room temperature, so
these reactants were dissolved in benzonitrile solvent (itself
unreactive) before addition of 1 and HClO4 to yield compounds
4–6. Chemical structures of 2–6 were also confirmed by X-ray
crystallography by recrystallization in acetonitrile diffused with
diethyl ether (Figs. 1–3). All the ammonium adducts (3, 4, and
5) with two adjacent nitrogens have the uncoordinated nitrogen
pointed towards the anthracenone. This eliminates steric inter-
ference that would occur between the phenyl hydrogen atom
and the anthracenone if the heterocyclic ring was rotated 180ꢀ
about the pyridyl C–N bond. The lower yield of products derived
from neat solution is likely due to a shift in the amount of free
base and acid catalyst towards the protonated salt associated
with the addition of the mineral acid.
We have previously determined that thiophene groups are
more susceptible to substitution at the aromatic alpha-position
when in the presence of alkyl nitriles as a competing nucleo-
phile.[4] We extend this chemistry to include competition reac-
tions between a pyridine or thiophene group in the presence
of primary amides. In either case, the primary amide is left
unreacted. Reaction of thiophene-2-acetamide with 1 in the
presence of sulfuric acid as catalyst produces the thiophene
substituted product 7 where the anthracenone substitutes at
the 2-position of the thiophene ring (crystal structure, Fig. 4).
This leaves a neutral molecule; however, it appears from bond
distances between heavy atoms in the crystal structure that the
amide oxygen is protonated by the catalyst after the reaction is
complete. The anion, hydrogen sulfate, is found rotationally dis-
ordered in a ~60:40 ratio, making it difficult to accurately locate
hydrogen atoms involved in the hydrogen bonding between the
anion and the amide group. However, it is apparent that a very
short O. . .H–O hydrogen bond exists between the hydrogen sul-
fate and the amide oxygen, O7. . .O8 = 2.555(7) Å. The hydrogen
bond distance for the smaller occupancy of the disordered anion
is even shorter, O7. . .O8′ = 2.420 Å. A second hydrogen bond is
Thiophene versus pyridine (benzo(c)cinnoline) nucleophiles
1 (0.5mmol), bithiophene (0.55mmol), and benzo(c)cinnoline (0.55 mmol)
were dissolved in 5 mL of benzonitrile and mixed with five drops 70% per-
chloric acid. The mixture was stirred for 30 min and mixed with 50mL of
diethyl ether. The crude solid was dissolved in 10 mL of acetonitrile, and
diethyl ether was diffused into the solution. Both a cream-colored solid
(11) and yellow-colored crystals (12) were obtained. Compound 11, the
macrocyclic end-capped bithiophene adduct (Scheme 2), has previously
been reported.[4] Compound 12 is protonated benzo(c)cinnoline and was
characterized by single-crystal X-ray analysis. Yield: ~20% of compound
11 and 30% of compound 12 (melting point: 219–222 ꢀC).
Crystallography
X-ray quality crystals were grown from samples dissolved in acetonitrile
and diffused with diethyl ether. Crystallographic data were collected at
100 K using MoKa radiation on a Bruker CCD APEXII diffractometer,
Madison, WI, USA. Cell constants were determined after integration from
typically more than 9000 reflections.[16] Structures were solved by direct
methods using SIR97[17] and refined using SHELXL-97.[18] Data reduction
and refinement were completed using the WinGX suite of crystallo-
graphic software.[19] All hydrogen atoms were placed in ideal positions
and refined as riding atoms with relative isotropic displacement param-
eters, with the exception of hydrogen-bonded protons, which were
found from the difference map. Table 1 lists additional crystallographic
and refinement information. Only the major occupancies of disordered
structures have been diagramed in Figs. 1–3.
[1-Pyridazinium](ClO4)ꢁ0.6H2O (2): There are two pyridazinium
adducts in the asymmetric unit along with one water of hydration with
a 60% occupancy. One perchlorate is disordered over two separate posi-
tions in a 74:26 ratio. The major fractions of the disordered water and
perchlorate participate in a hydrogen bond = 2.868(4) Å, 169(5)ꢀ.
[1-Phthalazinium](ClO4) (4): One-half of the polyether chain is disor-
dered over two positions in a 50:50 ratio.
[1-Benzo[c]cinnolinium](ClO4)ꢁCH3CN (5): One-half of the polyether
chain is disordered in a 60:40 ratio. Refinement of the smaller occupancy
was left isotropic.
[1-(5-(Thiophene-2-acetamide))H](HSO4) (7): Platon Squeeze removed
a disordered solvent molecule present in the structure equal to 140 Å3/61
electrons.[20] This is equivalent to approximately one-half a diethyl ether
O
O
O
O
Bithiophene
Benzo(c) cinnoline
Benzamide
N
S
S
H
ClO4
H
O
NH
Ph
H OH
H
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
+
N
HClO4, PhCN
H
HClO4, CH3CN
O
O
O
O
10
1
11
12
Scheme 2. Competition of bithiophene versus benzo(c)cinnoline derivative and benzamide versus acetonitrile with 1 in the presence of a strong acid
J. Phys. Org. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

K. MARIAPPAN ET AL.
wileyonlinelibrary.com/journal/poc
Copyright © 2012 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2012)

REACTION WITH A CYCLIC MACROMOLECULE
ammonium ion adduct and not the amide adduct 8 (crystal
structure, Fig. 5). An intramolecular hydrogen bond is formed
between the amide group and one of the polyether oxygens,
2.832(5) Å, and a second intermolecular hydrogen bond forms
between the second amide hydrogen and an ether oxygen of a
neighboring macrocycle, 2.957(5) Å.
DISCUSSION – RELATIVE REACTIVITY
Upon addition of a strong acid with 1, the secondary alcohol is
protonated, and the loss of water produces a transient carboca-
tion intermediate as shown in Scheme 3. Either concentrated
HClO4 or concentrated H2SO4 can generate the carbocation,
but we used concentrated H2SO4 for the thiophene derivatives
specifically because better yields are produced. In the other
cases, acid choice does not make any difference. Further reaction
of the short-lived carbocation with the nucleophilic pyridyl, thio-
phene, or phosphine lone pair produces onium and thiophene
adducts as characterized previously.
We have previously demonstrated that the reaction of 1 with
alkyl nitriles produces secondary amides via the Ritter amide
synthesis, and that aromatic nitriles, which contain a weaker
nucleophilic nitrogen, are unreactive towards 1 in the presence
of a strong acid (Scheme 1, ix).[1] Earlier work also showed that
activated aromatics such as pyrrole and thiophene are also more
reactive than alkyl nitriles,[4] and we have now determined that
pyridine analogs and thiophene are more reactive than primary
Figure 1. Thermal ellipsoid diagrams (30%) of [1-pyrimidinium]
(ClO4)ꢁCH3CN (2)
formed between the amide hydrogen (H1B) and the anion as
well, N1-H1B. . .O11 = 2.835(8) Å. A third hydrogen bond exists
in the structure between the second amide hydrogen and a
different neighboring anion, N1-H1A. . .O10 = 2.973(9) Å. These
competing amide hydrogen bonds may produce the different
occupancies of the rotationally disordered anion.
Nicotinamide contains both a heterocyclic aromatic ring and a
primary amide group, and reaction with 1 yields only the
Figure 2. Thermal ellipsoid diagrams (30%) of [1-pyridazinium](ClO4)ꢁ0.6H2O (3) – left (the water molecule has been omitted from the diagram), and
[1-phthalazinium](ClO4) (4) – right
Figure 3. Thermal ellipsoid diagrams (30%) of [1-benzo(c)cinnolinium](ClO4)ꢁCH3CN (5) – left, and [1-triphenylphosphonium](ClO4)ꢁ2CH3CN (6) – right.
Hydrogen atoms have been removed for clarity
J. Phys. Org. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

K. MARIAPPAN ET AL.
amides are more reactive than alkyl nitriles. As per Scheme 2,
another competition reaction was conducted by mixing one
equivalent of bithiophene with one equivalent of benzo[c]cinno-
line with 1 in benzonitrile/70% perchloric acid. We isolated two
different solids from this reaction. One is a bithiophene dimer,
1-C4H2S-C4H2S-1 (11), isolated as a powder, which was con-
firmed by 1H NMR. The molecular structure of 11 has previously
been reported.[4] The second yellow, crystalline product is the
mono-protonated form of benzo[c]cinnoline which was also
characterized by X-ray crystallography as [benzo(c)cinnolineH]
(ClO4) (thermal ellipsoid diagram not shown). A 2.890(4) Å hydro-
gen bond exists between the protonated benzo(c)cinnoline
nitrogen and the neighboring perchlorate anion. This experiment
clearly confirms that the activated aromatics such as thiophene
compete with pyridyl starting materials to form alpha-substituted
thiophene products, leaving the basic pyridyl groups protonated
and unreacted. The aforementioned reactions produce the follow-
ing reactivity series:
Figure 4. Thermal ellipsoid diagram (30%) of [1-(5-(thiophene-2-
acetamide))H](HSO4) (7). The thiophene group forms adduct rather than
a primary amide, which is in competition as the nucleophile. In this case,
the anion forms two hydrogen bonds to the amide, one via the amide
oxygen, O7. . .O8 = 2.555(7) Å and a second via one of the amide hydro-
gen, N1-H1B. . .O11 = 2.838(8) Å. The anion is spherically disordered, but
only the larger occupancy is shown
thiophenes > pyridines> primary amides > alkyl nitriles
≫ aromatic nitriles ðunreactiveÞ:
This series parallels the nucleophilic donor number for pyri-
dine (33.1), formamide (24.0), acetonitrile (14.1), and benzonitrile
(11.9), predicting that pyridine analogs are more reactive than
amides, which in turn are more reactive than nitriles.[21]
Although nucleophilicity is generally considered a kinetic para-
meter (i.e., the quality of an entering or leaving group), the sub-
stitution of thiophenes produces the most stable adducts in the
end because a full covalent C–C bond is formed between the
anthracenone and the heterocyclic ring. The anthracenone–
ammonium C–N bond almost certainly has some coordinate-
covalent character resulting in weaker bond formation. We have
observed this after attempting to coordinate metal ions within
macrocycles 3, 4, and 5.
Our original intent was to create an internal charge transfer
fluorescence sensor (Scheme 4) by coordination of metals to
the second, free nitrogen atom adjacent to the polyether ring.
This would tune the luminescence by altering internal charge
transfer within the lumophore, depending on the identity of
the metal, and would minimize vibrations that deactivate the
excited state, because the pyridyl group is also coordinated to
the metal. This phenomenon could be used as a novel chemodo-
simeter type approach for sensing metal ions. Using acetonitrile
as solvent, the addition of metal ions (nonspecific) to isolated
products 2–5 leads only to the production of the secondary
amide adduct, (9), shown in Scheme 1. Through coordinate-
covalent bonding, the metal likely helps dissociate the ammo-
nium adducts into a carbocation, which is attacked by the nitrile
group of the solvent, present in high concentration, followed by
rearrangement via the Ritter amide synthesis to yield a second-
ary amide. We are currently pursuing the luminescence sensor
Figure 5. Thermal ellipsoid diagram (30%) of [1-(N-nicotinamide)](ClO4)
(8) where the ammonium adduct rather than the amide is produced. The
intramolecular hydrogen bond formed has a typical N–H. . .O bond dis-
tance of 2.832(5) Å
amides because the primary amides are left unreacted in the
presence of either of these other two functional groups
(Scheme 1, vi and vii). In addition, we have run the competition
reaction (Scheme 2) of benzamide (C6H5C(O)NH2) with 1 in pure
acetonitrile, and the only product that is formed is the secondary
benzyl amide adduct, [1ꢁNHC(OH)C6H5](ClO4) (10). This product
has been structurally characterized previously.[1] Even though
the alkyl nitrile used as the solvent is by far in excess, the only
product isolated is the secondary amide obtained from the pri-
mary benzamide starting material. This indicates that primary
O
O
O
N
H+
+
- H2O
+
H
N
H
OH
H
Scheme 3. General mechanism of carbocation generation and onium ion formation
wileyonlinelibrary.com/journal/poc
Copyright © 2012 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2012)

REACTION WITH A CYCLIC MACROMOLECULE
REFERENCES
[1] M. Kadarkaraisamy, G. Caple, A. R. Gorden, A. G. Sykes, Inorg. Chem.
2008, 47, 11644.
[2] R. Ritter, P. P. Minieri, J. Am. Chem. Soc. 1948, 70, 4045–48.
[3] L. I. Krimin, D. J. Cota, The Ritter Reaction, Organic Reactions, Kreiger
Publishing, 1969, p. 213–325.
N
N
O
O
[4] M. Kadarkaraisamy, S. Thammavongkeo, P. N. Basa, G. Caple, A. G. Sykes,
Org. Lett. 2011, 13, 2364.
Mn+
O
O
[5] X. Lin, J. Wang, F. Xu, Y. Wang, J. Chem. Res. 2009, 638.
[6] H. Yang, L. Fang, M. Zhang, C. Zhu, Eur. J. Org. Chem. 2009, 666.
[7] G. W. Wang, Y. B. Shen, X. L. Wu, Eur. J. Org. Chem. 2008, 4367.
[8] S. Shirakawa, S. Shimizu, Synlett 2008, 1539.
O
O
Scheme 4. Proposed metal ion coordination to an ammonium adduct of 1
[9] U. Jana, S. Maiti, S. Biswas, Tetra. Letts. 2008, 49, 858.
[10] K. Motokura, N. Nakagiri, T. Mizugaki, K. Ebtani, K. Kadeda, J. Org.
Chem. 2007, 72, 6006.
[11] S. Singh, A. Bhadani, H. Kataria, G. Kaur, R. Kamboj, Ind. Eng. Chem.
Res. 2009, 48, 1673.
[12] S. Petit; R. Azzouz, C. Fruit, L. Bischoff, F. Marsais, Tet. Letts.
2008, 49, 3663.
chemistry of the aforementioned ammonium adducts in differ-
ent solvents that allow adequate solubility, but are not reactive,
and these details will be reported elsewhere.
[13] J. M. Bailey, G. Bruton, A. Huxley, V. Johnstone, P. H. Milner, B. S. Orlek,
G. Stemp, Synlett 2009, 1051.
SUPPORTING INFORMATION
[14] D. B. Gotchev, D. L. Comins, Tetrahedron 2004, 60, 11751.
[15] M. J. Corr, M. D. Roydhouse, K. F. Gibson, S. Z. Zhou, A. R. Kennedy,
J. A. Murphy, J. Am. Chem. Soc. 2009, 131, 17980.
[16] SAINT V6.1, Bruker Analytical X-ray Systems, Madison, WI, 1999.
[17] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Giacovazzo,
A. Guagliardi, A. G. G. Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst.
1999 32, 115.
Crystallographic files in CIF format can be obtained free of
charge from the Cambridge Crystallographic Data Center,
www.ccdc.cam.ac.uk/conts/retrieving.html.
[18] SHELX97 – Programs for Crystal Structure Analysis (Release 97–2).
G. M. Sheldrick, Institüt für Anorganische Chemie der Universität,
Tammanstrasse 4, D-3400 Göttingen, Germany, 1998.
[19] L. J. Farrugia, WinGX; An Integrated System of Windows Programs for
the Solution, Refinement, and Analysis of Single Crystal X-ray Diffrac-
tion Data, Ver. 1.70, J. Appl. Cryst. 1999, 32, 837.
Acknowledgements
The authors thank NSF-EPSCOR (EPS-0554609) and the South
Dakota Governor’s 2010 Initiative for the purchase of a Bruker
SMART APEX II CCD diffractometer. The elemental analyzer was
provided by funding from NSF-URC (CHE-0532242). P. N. B.
thanks NSF-EPSCOR (EPS-0903804) for financial support.
[20] A. L. Spek, J. Appl.Cryst. 2003, 36, 7.
[21] V. Gutmann, Coord. Chem. Rev. 1976, 18, 225.
J. Phys. Org. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc