Syntheses and photophysical properties of some 4-arylpyridinium salts

Article abstract of DOI:10.1002/jhet.5570380102

A number of 4-arylpyridines, many methoxy substituted, were prepared by an efficient two-step method involving aryl Grignard addition to 1-methyl-4-piperidone and direct aromatization of the resulting 4-aryl-4-piperidinols. The pyridines were N-alkylated to give sulfonate salts desired for their fluorescent properties. Study of selected compounds as laser dyes revealed several structures to be efficient dyes lasing in the 530-550 nm range. Two new diazaquaterphenyls were prepared and were quaternized. These salts exhibited intense fluorescence in the 420-450 nm range, but would not lase. A phenolic azaterphenyl suitably substituted for excited state intramolecular proton transfer (ESIPT) did not fluoresce at all.

Full text of DOI:10.1002/jhet.5570380102

Jan-Feb 2001
Syntheses and Photophysical Properties
of Some 4-Arylpyridinium Salts
11
Charles J. Kelley* [a], (the late) Kwabena Ansu [a], (the late) Wiranto Budisusetyo [a],
Alem Ghiorghis [a], Yuanxi Qin [a] and Joel M. Kauffman [b]
[a] Massachusetts College of Pharmacy and Health Sciences, 179 Longwood Ave, Boston MA 02115-5804
[b] University of the Sciences in Philadelphia, 600 South 43rd Street, Philadelphia PA 19104-4495
Received May 17, 2000
A number of 4-arylpyridines, many methoxy substituted, were prepared by an efficient two-step method
involving aryl Grignard addition to 1-methyl-4-piperidone and direct aromatization of the resulting 4-aryl-4-
piperidinols. The pyridines were N-alkylated to give sulfonate salts desired for their fluorescent properties.
Study of selected compounds as laser dyes revealed several structures to be efficient dyes lasing in the
530-550 nm range. Two new diazaquaterphenyls were prepared and were quaternized. These salts exhibited
intense fluorescence in the 420-450 nm range, but would not lase. A phenolic azaterphenyl suitably
substituted for excited state intramolecular proton transfer (ESIPT) did not fluoresce at all.
J. Heterocyclic Chem., 38, 11 (2001).
Introduction.
conjugation to the quaternized pyridinium ring. In a few
compounds electron release was provided without a
methoxy group by a dialkylmethylene bridged biphenyl
(a fluorene) or by a carbazole ring.
Most of these new 4-arylpyridines were quaternized by
alkylation with sulfonate esters, whose structures were
optimized in an earlier study on derivatives of 2 [6,7] and
were tested for fluorescence efficiency and as laser dyes in
alcohol-water mixtures. Compounds of this type have also
shown enhanced lasing properties in aqueous sodium
dodecyl sulfate solutions [8].
In initiating this study, we sought in three ways to
improve upon the lasing properties of 2C and its oxazole-
containing analogs to obtain laser beams better able to
penetrate sea water: (a) achieve a higher level of power
output; (b) induce a hypsochromic shift in the wavelength
of fluorescence (lasing) to more closely approach 490 nm,
the wavelength of maximum transmission of sea water,
and (c) to get (even) more service lifetime out of the dyes
in order to decrease the need for recurring solvent changes
in the dye laser.
In an attempt to discover whether the 4-arylpyridine
chromophore could experience excited state intra-
molecular proton-transfer (ESIPT) fluorescence, we
designed a molecule in which a phenolic hydroxyl group
could deliver a proton to the pyridine nitrogen.
The report [1] of the exceptional service lifetime as a
laser dye of 5-(4-methoxyphenyl)-2-(4-pyridyl)oxazole 1,
as its methyl p-toluenesulfonate quaternary salt 2C, has
inspired the synthesis of a number of heterocyclic analogs
of 1 in which both the pyridine and oxazole rings were
preserved [2]. In this paper, we report the synthesis of a
number of analogs of 1 which are 4-arylpyridines
(4-azaterphenyls) in which the central oxazole has been
replaced by a benzene ring. That the oxazole ring might be
a point of instability was suggested by early work in which
the presence of 2,5-disubstituted oxazole rings in known
fluorescent scintillators had been shown to lead to
photodecomposition of the chromophore on prolonged
irradiation in air [3]. Since we have previously reported on
the marked photochemical stability of oligophenylenes
under conditions of high intensity irradiation [4,5], we
sought to prepare a series of fluorescent pyridinium salts
which contained both unbridged and bridged carbocyclic
aromatic rings on C-4 of the pyridine ring. Most of these
salts contain a methoxy substituent placed so as to allow its
Discussion and Results.
Syntheses.
Our first target was the simplest analog azaterphenyl 3 in
which the oxazole ring in 1 was replaced with a phenylene
unit. For any synthesis of 4''-methoxyazaterphenyl 3, we
required 4-bromo-4'-methoxybiphenyl, 4f as the starting
material. Reaction of 4-methoxybiphenyl 4a in chloroform
with 1.0 equivalent of bromine gave 4f in the reported [9]
20% yield and melting range after two crystallizations
from chloroform. The byproducts, identified by HPLC as
major amounts of unreacted 4a, a monobromo derivative

12
Vol. 38
C. J. Kelley, (the late) K. Ansu, (the late) W. Budisusetyo,
A. Ghiorghis, Y. Qin and J. M. Kauffman
isomeric with 4f and a dibromo derivative of 4a, indicated
similar bromination rates in both the phenyl and the
methoxyphenyl rings of 4a.
a depressed melting range even after sublimation, most
likely because of the presence of a regioisomer [12], was
purified as its picrate salt 3D and re-isolated as the free
base 3 in just 9% yield.
Carbonate esters of 4b were known to brominate in the 4'-
position in halocarbon solvents [10,11]. We observed the
bromination of 4-benzoyloxybiphenyl 4c at 80° in acetic
acid exclusively in the 4'-position to give 4d in exceptional
yield. Experiments with 4-acetoxybiphenyl gave lower
yields and partial hydrolysis on oven drying. Hydrolysis of
4d gave phenol 4e [10] which upon O-methylation gave 4f.
To prepare the azaterphenyl 3, bromobiphenyl 4f was
converted to the corresponding Grignard reagent 4g in
concentrated tetrahydrofuran solutions. Formation of
Grignard 4g was not efficient in dilute solutions. In
Method I, 4g was reacted in the presence of a palladium
(II) catalyst with 4-chloropyridine (liberated in situ from
its hydrochloride salt 5 by the prior addition of methyl
Grignard) to give 3 directly in moderate yield. In Method
II following Comins and Abdullah [12], Grignard 4g was
reacted with pyrdine, which had been activated in situ with
ethyl chloroformate, to yield a crude N-acyl-1,4-
dihydropyridine which was aromatized directly by heating
with sulfur [12] in refluxing mesitylene [13]. The sample
of 3 which resulted from this two-step pathway possessed
In an attempt to eliminate regioisomer formation, we
reacted Grignard 4g with the highly sterically hindered
quaternary pyridinium salt 6 [14], Method III in Scheme 1.
No trace of 3 was isolated from this reaction.
Subsequently, we developed Method IV employing
classical pharmaceutical piperidinol [15,16] intermediates
in an efficient two-step synthesis of 3. The lithium

13
Jan-Feb 2001
Syntheses and Photophysical Properties of Some 4-Arylpyridinium Salts
derivative from transmetalation of bromobiphenyl 4f was
reacted at low temperature [16] with 1-methyl-4-
piperidone to give the 4-aryl-4-piperidinol 7.
Aromatization of the piperidinols over palladium on
carbon in diphenyl ether or diphenylmethane at elevated
temperatures gave pyridines 21 to 25 and bispyridines
(diazaquaterphenyls) 26 and 27. Azaterphenyls 22 and 23,
azaquaterphenyl 24 and diazaquaterphenyl 27 contained
bridging dipropylmethylene groups for greater coplanarity
of the multiaryl systems.
Correspondingly prepared by the sequences shown in
Scheme 3 were 6-methoxy-2-naphthyl derivative 29 and
carbazole derivative 33. Compounds 29 and 33 were
synthesized from 4-(4-chlorophenyl)pyridine 28. The
Grignard reagent from aryl bromide 11 produced 29 by
nickel-catalyzed coupling, while the Grignard reagents
from 31 gave 33 with palladium coupling. Although 28 is a
known compound, literature methods reported for its
synthesis gave mixtures of regioisomers [18,19]. Thus we
prepared 28 from 5 by the Method I of Scheme 1.
Aromatization of the saturated heterocyclic ring of 7,
which involves first the loss of water from the tertiary
benzylic alcohol and then loss of hydrogen and methane,
was first carried out in refluxing nitrobenzene. However,
azaterphenyl 3 could not be extracted into aqueous
hydrochloric acid. Aromatization of dihydroarenes over
palladium on carbon are well known [17]. We found that
piperidinol 7 was only partially aromatized during
72 hours in refluxing mesitylene. Aromatization was
completed by heating 7 overnight at higher temperatures in
refluxing diphenylmethane or diphenyl ether under a
nitrogen purge [17] to remove the water and gaseous
byproducts.
This two-step method was employed as shown in
Scheme 2 to convert aryl bromides 4h, 2-bromofluorenes
8-10, bromonaphthalene 11, and diaryl dibromides 12 and
13 to piperidinols 14-18 and bispiperidinols 19 and 20.
Each of the new pyridines (except 33) was quaternized
with methyl methanesulfonate and/or sultones in nitrile
solvents to give highly fluorescent salts soluble in polar

14
Vol. 38
C. J. Kelley, (the late) K. Ansu, (the late) W. Budisusetyo,
A. Ghiorghis, Y. Qin and J. M. Kauffman
Table 1
Absorption and Lasing Propertiesof 4-Arylpyridinium Salts in Methanol
Compound
Number
Longwave
Ultraviolet Absorption
max. (nm)
Lasing
Output [a]
(mJ)
Peak
Lasing
(nm)
2A
2B
3A
411 [b]
410 [b]
354
10.30 [c]
13.06 [c]
6.47
569 [c]
572 [c]
532
3B
357 [d]
361
380
370
367
15.3
0.8
9.4
2
548
≈455
530
481
481 [e]
22B
23B
25A
25B
no lasing
-4
[a] In methanolic solution at 2 x 10 . [b] In ethanol from ref. [7]. [c] From
-5
ref. [6]. [d] 2.1 x 10 M in ethanol. [e] Peak fluorescence emission.
solubility. The lower melting quaternary salts from methyl
methanesulfonate were in some cases more conveniently
isolated after their formation during extended periods of
reflux in acetonitrile.
To prepare a modification of azaterphenyl 3 that would
provide a suitable test of the effects of intramolecular
proton transfer, we converted 3 to its N-oxide 34 and used
the method of Webb [20] to activate the pyridine ring for
introduction of the p-anisyl group in the 2-position to give
35. Then we metalated methoxymethyl p-tolyl ether with
n-butyllithium, converted to the Grignard with magnesium
bromide, and reacted the Grignard with the activated
N-oxide to give the phenolic 38 directly, as the
methoxymethyl group from 37 was lost in the workup. The
product 38, obtained in only 2% yield, was fully
characterized by hi-field nmr.
Photophysical Properties.
The ultraviolet absorption spectra of bridged and
unbridged azaterphenyls resemble closely the published
data for similarly substituted terphenyls [21]. The
organic solvents. Quaternizations with 1,3-propane sultone
were conveniently completed within minutes in hot
benzonitrile in which the high melting salts had some

15
Jan-Feb 2001
Syntheses and Photophysical Properties of Some 4-Arylpyridinium Salts
quaternization of the pyridine ring in 4''-alkoxyazater-
phenyls causes a substantial bathochromic shift in their
ultraviolet absorption spectrum, presumably through the
enhanced contribution of resonance forms in which
oxygen releases non-bonding electrons to the pi system
with the positively charged nitrogen at its other terminus.
A comparison of the ultraviolet absorption data in
Table 1 for azaterphenyl quaternary salt 3A with a
phenylene middle ring to 2A with its oxazole ring reveals a
51 nm hypsochromic shift for the replacement of the
internal oxazole by a phenylene. A similar hypsochromic
shift is observed in comparing ring bridged analog 23B
with unbridged 3B. These shifts reflect both the electronic
nature of the oxazole [2] and the greater energy required for
the phenylene ring of 3A with four buttressing hydrogen
atoms in a six-membered ring to be converted from a
non planar ground state into a necessarily planar excited
state. In 23B only the pyridine ring needs to come into
planarity with the fluorene in the excited state. Fluorescent
carbocyclic chromophores exhibit similar relationships
between bridged and unbridged compounds [21].
the latter system, the methoxy is one double bond closer to
the pyridinium ring than in compound 3A. Much of the
50 nm hypsochromic shift in lasing could be attributed to
the missing double bond. The weak lasing observed for
25A frustrated our aim of obtaining useful compounds
lasing around 490 nm.
In an additional attempt to prepare compounds with
shorter wavelength fluorescence, we prepared two
diazaquaterphenyls 26 and 27 and their quaternary salts.
The ultraviolet spectra for these quaternary salts were
bathochromically shifted 45-50 nm from absorptions of
corresponding quaterphenyls, and exhibited comparable
extinction corefficients [21]. The fluorescence quantum
efficiency of 26A in methanol was about 1.0, while 27A
was 0.82, but neither would not lase flashlamp pumped
[24]. The durabiltiy of the fluorescence of these salts was
verified by our observation that a methanolic solution of
26A exposed to diffuse daylight was still exhibiting blue
fluorescence after 11 years. A similar solution of the
bridged analog 27A showed a substantial loss of
fluorescence during six years.
The quaternary salts of the 4-arylpyridines prepared in
this study were all fluorescent. Representative strongly
fluorescent compounds were subjected to lasing
experiments as shown in Table 1. As was anticipated, the
peak lasing occurred at shorter wavelengths for 3A/B and
23B than had been observed for the oxazoles 2A/B. This
paralleled closely the hypsochromic shift in peak lasing
reported for p-terphenyl versus 2,5-diphenyloxazole [3].
The energy output for 3B (15.3 mJ) was the highest output
yet observed in alcohol solvents among all compounds of
the quaternary 4-arylpyridinium class. Service lifetime
experiments were not conducted, but no deterioration in
output power was observed during the periods studied.
In a related experiment, 3B was observed to lase with
moderate efficiency at 545 nm in solid polymethyl
methacylate plastic rod when pumped with 355 nm light
from a YAG laser [22].
Although pyridine 35 was quite fluorescent, its phenolic
isomer 38 not only did not exhibit ESIPT fluorescence, but
it did not fluoresce at all. In known ESIPT fluors [25], the
proton transferred from the phenol in the excited state is
accepted by a heterocyclic nitrogen much less basic than a
pyridine ring. The failure of 38 to fluoresce may be related
to the proximity of pKa values between the phenol and the
pyridine nitrogen to which, as evidenced by its strongly
deshielded chemical shift (14.2 ppm) in the nmr, it is
strongly hydrogen bonded in the ground state. Indeed, it
appears that the effect of the intramolecular proton transfer
in 38 is to completely quench fluorescence.
EXPERIMENTAL
General.
Relative lasing efficiencies within the oxazole series
[6,7] were maintained in the phenylene series N-methyl to
N-methyl, and zwitterion to zwitterion, and there was no
loss of lasing efficiency. In these respects our original goal
was achieved. Ring bridging with dipropylmethylene
groups, however, showed none of the enhancements in
lasing which were observed with oligophenylenes [23]
either in wavelength or in efficiency, which actually
decreased for the compounds with bridging. The only
beneficial effect of ring bridging was qualitatively
demonstrated by the fluorescence of azaquaterphenyl salt
24a in which bridging of the central fluorene unit allowed
the transmission of electron donation by the methoxy
group to extend through 4 aromatic rings.
The methods employed in references [2], [4] and [5] were
followed with the following exceptions: 1-methyl-4-piperidone
was purchased from Aldrich or Lancaster and stored in a
refrigerator. On standing for more than one month, some samples
showed increased viscosity and coloration. Vacuum distillation
of older samples gave material of comparable quality to newly
purchased material. Palladium(II) couplings were catalyzed by
palladium(II) chloride 1,4-bis(diphenylphosphino)butane
[(PdCl2(dppb)] prepared from palladium(II) chloride in 6
mL/mmol of dimethylformamide containing one millimolar
equivalent of 1,4-bis(diphenylphosphino)butane by heating at
reflux for several hours as the color progressed from gray
through yellow to green, cooling, filtering, and washing with
ether. Anhydrous sodium sulfate, magnesium sulfate and calcium
chloride were used to dry solutions. 6-Bromo-2-naphthol
(Aldrich B7,340-6) was methylated by the procedure for 4f to
give 11; methyl methanesulfonate (Aldrich 12,992-
5),1,3-propane sultone (Aldrich P5,070-6), 1,4-butane sultone
(Aldrich B8,550-1) nickel acetylacetonate (Aldrich 28,365-7),
Weak lasing was observed for compounds 22B in which
a fluorene ring alone provided electron release to the
quaternary pyridinium, and also for 25A in which the
6-methoxy-2-naphthyl group was the electron releaser. In

16
Vol. 38
C. J. Kelley, (the late) K. Ansu, (the late) W. Budisusetyo,
A. Ghiorghis, Y. Qin and J. M. Kauffman
n-butyllithium as a solution in n-hexane (2.1 M, 2.5 M, Aldrich,
or 2.2 M, Alfa) were used as received. Pentene (technical, T418)
purchased from Eastman Kodak is no longer commercially
5 minutes. During the next 3 hours, 60 mL of tetrahydrofuran was
added in small portions to the refluxing mixture as the
magnesium dissolved to produce the solution of 4g.
1
available in useful quantities. Most H nmr spectra were recorded
In a separate flask was placed 2.87 g, (19.2 mmol) of 4-chloro-
pyridine hydrochloride 5 and 20 mL of tetrahydrofuran. The
mixture was stirred while 6.8 mL (19 mmol) of 2.85 M methyl-
magnesium bromide diluted with 20 mL of THF was added
slowly. The evolution of methane ceased when about 80% of the
solid had dissolved. To this mixture was added in one portion the
Grignard 4g. No change was observed during 10 minutes stirring
at room temperature. Palladium(II) chloride 1,4-bis(diphenyl-
phosphino)butane (0.174 g, 0.29 mmol) was added to the
mixture. All solids dissolved in 10 minutes, stirring was
continued for 12 hours, an additional 0.058 g of palladium
catalyst was added, and the solution was stirred for 24 hours.
Methanol (20 mL) was added dropwise, and all solvents were
evaporated. The semi-solid was dissolved in methylene chloride
and was pre-adsorbed on Silica Gel (20 g) under reduced
pressure. The dry mixture was placed atop 150 g of Silica Gel in
a large Ace-Kau column, and extracted with boiling pentene to
remove 2.54 g of 4-methoxybiphenyl (4a). Further extraction for
24 hours with methylene chloride gave traces of a fluorescent,
high-melting solid believed to be 4,4'''-dimethoxyquaterphenyl.
Continued extraction for another 24 hours with the azeotropic
mixture of ethyl acetate/methanol (51.4:48.6%) gave a semi-solid
after evaporation of solvents. Digestion with 30 mL of 95%
ethanol gave after filtration, 1.58 g of 3, mp 225-238°.
Recrystallization from 30 mL of 2-methoxyethanol gave 1.20 g
(24%) of 3, mp 229-230°.
at 60 MHz in deuteriochloroform with internal tetramethylsilane
except where stated that the solvent was trifluoroacetic acid
(non-deuterated) referenced to external tetramethylsilane in
choroform. Laser experiments were performed under conditions
stated [6].
4-Benzoyloxybiphenyl (4c).
A slurry of 4-phenylphenol (4b, 252 g, 1.48 mol) in benzoyl
chloride (172 mL, 208 g, 1.48 mol) was mechanically stirred as
300 mL of pyridine was added in small portions. The resulting
warm solution was heated to reflux for 30 minutes, was cooled,
filtered, washed with 2 L of 1% hydrochloric acid, and a larger
portion of water. The solid was air-dried to give 404 g (99%) of
4c, mp 150-152°; Lit. [26] mp 149-150.5°.
4-Benzoyloxy-4'-bromobiphenyl (4d).
A mixture of 400 g (1.46 mol) of 4c and 150 g, (1.82 mol)
sodium acetate in 0.9 L of acetic acid became homogeneous
on being heated to 90° with mechanical stirring. Bromine
(87 mL, 269 g, 1.68 mol) was added to the solution in portions
during 4 hours, and stirring and heating at 90° were
maintained for 20 hours. The solution was diluted with 0.6 L
of 10% aqueous sodium bisulfite and 1.0 L of water. The
precipitate collected by filtration was air-dried, to give 506 g
(98%) of 4d, mp 179-181°. A 250 g portion of crude 4d was
dissolved completely in 3 L of acetic acid upon boiling for
40 minutes. Crystallization overnight at room temperature
gave 242 g (97% recovery.) of 4d, mp 188-190°; Lit. [10] mp
187.5-188.5°.
Anal. Calc. for C
H NO: C, 82.73; H, 5.79; N, 5.36. Found:
18 15
C, 82.60; H, 6.08; N, 5.25
Method II.
A flask containing ground magnesium pieces (2.4 g, 0.1 mol)
was flame-dried under a stream of nitrogen and allowed to cool.
Tetrahydrofuran (30 mL) and 4f (26.3 g, 0.l mol) were added and
after ten minutes heating with stirring, the solid dissolved and the
mixture darkened as the exothermic reaction carried the
temperature to 74°. After the exotherm subsided, the mixture was
diluted with 30 mL of tetrahydrofuran and was refluxed for
3 hours to give the solution of 4g.
Into a separate flask equipped with a mechanical stirrer, under
nitrogen was added l.27 g of copper(I) iodide, 16.1 mL of pyridine
(0.20 mol, dried over KOH) and 200 mL of tetrahydrofuran. To
the stirred, cooled (-20°), yellow solution was added 12.8 mL
(0.134 mol) of ethyl chloroformate dropwise during 15 minutes.
The yellow precipitate which formed was vigorously stirred while
the solution of 4g was added dropwise during one hour at -20°.
During an additional hour of vigorous stirring, the temperature
was allowed to slowly rise to room temperature. Aqueous
ammonium chloride (20%, 75 mL) and ethyl acetate (200 mL)
were added and two layers separated. The lower aqueous layer
was discarded, and the organic layer was washed with 3x50 mL of
a mixture of 20% ammonium chloride and ammonium hydroxide
(1:1), 2x150 mL of water, 2x50 ml of 10% hydrochloric acid,
2x150 mL of water and saturated aqueous sodium chloride. The
solution was dried over calcium chloride, and the solvent was
removed under reduced pressure to give 27.0 g of a highly viscous
yellow oil. Crystallization from a mixture of 30 mL of absolute
ethanol and 50 mL of methanol gave 15.5 g of a yellow powder,
mp 80-142°. Recrystallization from boiling ethanol (40 mL)
4-(4-Bromophenyl)phenol (4e).
A mechanically stirred mixture of 336 g (0.94 mol) of 4d,
161 g of potassium hydroxide, 940 mL of dimethyl sulfoxide,
and 2 L of water was refluxed. After 1 hour all solids had
dissolved; after 4 hours the solution was cooled to 65°, and
200 mL of acetic acid was added in portions. The granular solid
which separated after the mixture had cooled to room
temperature was filtered, washed with 500 mL of 10% sodium
bicarbonate, with several liters of water, and air-dried to give
246 g (104%) of 4e, mp 143-145°; Lit. [10] mp 144-145.5°.
4-Bromo-4'-methoxybiphenyl (4f).
To a slurry of 148 g (0.6 mol) of 4e, 25 g of sodium hydroxide
in 700 mL of water and 1.8 L of dimethyl sulfoxide, was added
dropwise 56.8 mL (75.7 g, 0.6 mol) of dimethyl sulfate. The
mixture was refluxed for 3.5 hours, and all solids dissolved. The
mixture was diluted with water and filtered to give 141.2 g (89%)
of 4f, mp 144.5-146°; Lit. [9] mp 143-4°.
4-(4'-Methoxybiphenyl-4-yl)pyridine [4''-methoxy-4-azater-
phenyl] (3).
Method I.
A flask containing magnesium turnings (0.915g, 38 mmol),
was flame-dried under nitrogen purge, was cooled, and 10.0 g
(0.0380 mol) of 4f and 6 mL of tetrahydrofuran were added. The
mixture was heated to reflux, causing the color to darken within

17
Jan-Feb 2001
Syntheses and Photophysical Properties of Some 4-Arylpyridinium Salts
diluted with 40 mL of methanol at room temperature gave 9.7 g of
the crude dihydropyridine [1-ethoxycarbonyl-4-(4'-methoxy-
biphenylyl)-1,4-dihydropyridine] melting began at 140° and was
completed at 181-2° (dec.).
solvents were removed to give 72.1 g of a yellowish powder,
which was heated in 430 mL of boiling toluene, and the slurry
was cooled and filtered to give 60 g (75%) of 14, mp 181-183°.
Anal. Calc. for C
H NO : C, 80.76; H, 7.78; N, 3.49. Found:
27 31 2
C, 80.30; H, 7.70; N, 3.44.
A mixture of the dihydropyridine (1.0 g, 3.13 mmol) and
precipitated sulfur (0.12 g, 3.75 mmol, 20% excess) in 15 mL of
mesitylene was heated for 4 hours in an oil bath at 154°.
Filtration of the cooled mixture gave 400 mg of dark brown solid
which was sublimed at 0.01 torr to give 183 mg of yellow
material, mp 200-223°. The crude product was dissolved in
30 mL of boiling acetone, and a solution of 0.24 g of picric acid
in 5 mL of acetone was added to the warm solution. The yellow
precipitate was filtered and dried to give 207 mg of 3D, mp 222°
(dec). Recrystallization from acetone gave 143 mg of picrate 3D,
mp 224° (dec).
4-(9,9-Dipropylfluoren-2-yl)-4-hydroxy-1-methylpiperidine (15).
A mixture of 2-bromo-9,9-dipropylfluorene (8, 32.9 g,
0.094 mol, containing 6% of 2,7-dibromo-9,9-dipropylfluorene
13 [4]) and 100 mL of THF was cooled under nitrogen to
below -50° and n-butyllithium in hexane (47 mL, 0.1 mol) was
added dropwise during 20 minutes, as the temperature was held
below -50°. A solution of 1-methyl-4-piperidone (13.5 mL,
0.11 mol, 10% excess) in 25 mL of THF was added during
30 minutes below -50°. The mixture was warmed to -10° during
two hours, a solution of acetic acid (12 mL) and 1-propanol
(20 mL) was added, and all solvents were removed under reduced
pressure. The resulting semi-solid was dissolved in a mixture of
methylene chloride and 5% sodium hydroxide solution and
extracted 4 times with 30 mL portions of methylene chloride. The
solution was dried over sodium carbonate, and the solvent was
removed under reduced pressure to yield 37 g of a viscous yellow
oil. Crystallization from 60 mL of cyclohexane gave 17.0 g of a
white product, mp 137-139°. This product was dissolved in
35 mL of methanol and was diluted with 12 ml of water. The
16.0 g of crystals obtained, mp 140-141°, were recrystallized
from the same solvent system to give 14.36 g (42%) of 15, mp
139.5-140°; 1H nmr: δ 0.63 (s, broad, 10H, -CH CH CH ), 1.92
Anal. Calc. for C
11.08. Found: C, 57.03; H, 3.68; N, 10.91.
H NO.0.85 H2O: C, 57.00; H, 3.93; N,
26 23
Liberation of the free base with 5% NaOH solution allowed the
isolation of 70 mg (8.5%) of 3, mp 229-32°.
Method IV.
To 350 mL of diphenyl ether warmed to 140° was added 51.5 g
of 7 and 2.5 g of 10% palladium on carbon. Nitrogen gas was
bubbled through the mixture while it was heated at 230-255°
during 24 hours. On cooling to room temperature, the mixture
was filtered through a bed of Celite, and was washed with
hexane. The mixture was placed atop more Celite in a large
Ace Kau and was extracted with boiling methylene chloride
(0.75 L) for 16 hours. Chilling and filtration gave 12.5 g of 3, mp
225-7°. Successive concentration, chilling and filtration gave
three additional crops bringing the yield of 3 to 31.3 g (69%).
2
2
3
3
(m, 9H, -CH CH CH , OH and 3', 5'), 2.30 (s, 3H, -NCH ), 2.57
2
2
3
(t, very broad, J = 8 Hz, 4H, Hs 2', 6'), 7.13-7.43 (m, 3H, Hs 6-8),
7.50-7.83 (m, 4H, Hs 1, 3, 4, 5).
Anal. Calc. for C
H NO: C, 82.60; H, 9.15; N, 3.85. Found:
25 33
4-Hydroxy-4-(4'-methoxybiphenyl-4-yl)-1-methylpiperidine (7).
C, 82.44; H, 9.47; N, 3.59.
A slurry of 26.3 g, (0.1 mol) of 4f in 200 mL of tetrahydro-
furan dissolved on heating under nitrogen. As the solution was
cooled to -40°, a fine white precipitate separated, and 47.5 mL
(0.1 mol) of n-butyllithium in hexane was added dropwise during
15 minutes below -40°. As a solution of 1-methyl-4-piperidone
(13.5 mL, 10% excess) in 20 mL of tetrahydrofuran was added
dropwise during 10 minutes at -40 to -50°, the precipitate
dissolved. Stirring was continued for 30 minutes, and the solution
was allowed to warm slowly to -20° during one hour. A mixture
of acetic acid (12.0 mL) and 1-propanol (20 mL) was added, and
all solvents were removed under reduced pressure. The solid
residue was triturated with 5% aqueous sodium hydroxide,
filtered, washed several times with water and air dried to give
33.5 g of the yellow solid, mp 156-65°. Crystallization from
120 mL of toluene gave 21.3 g of 7 (72%), mp 180-181.5°.
4-Hydroxy-4-(7-methoxy-9,9-dipropylfluoren-2-yl)-1-
methylpiperidine (16).
A mixture of 17.95 g (0.05 mol) of bromide 9 [4] and 150 mL
of tetrahydrofuran under nitrogen was cooled to -50° and to the
homogeneous yellow solution was added n-butyllithium
(23.8 mL, 0.05 mol) dropwise during 15 minutes while the
temperature was maintained below -40°. No precipitate formed
during the addition. A solution of 1-methyl-4-piperidone
(6.8 mL, 0.055 mol) in 15 mL of tetrahydrofuran was added
dropwise during 15 minutes below -40°. The mixture was slowly
warmed to -15° during two hours. A mixture of acetic acid
(6 mL) and 1-propanol (15 mL) was added dropwise, and all
solvents were removed under reduced pressure. The resulting
viscous oil was dissolved in a mixture of 5% aqueous sodium
hydroxide and methylene chloride, and the aqueous phase was
extracted with four times with 30 mL of methylene chloride. The
combined organic extract was washed twice with water and once
with 30 mL of brine. The solution was dried with anhydrous
sodium carbonate, and the solvent was removed to give 20 g of a
yellow semi-solid which was triturated with 50 mL of
diisopropyl ether and filtered to give 8.0 g of 16, mp 168-170°.
Crystallization from methanol gave the analytical sample, mp
Anal. Calc. for C
H NO : C, 76.74; H, 7.80. Found: C,
19 23 2
76.78; H, 7.55.
4-Hydroxy-4-[4'-(3-phenylpropyloxy)biphenyl-4-yl]-1-
methylpiperidine (14).
To 4-bromo-4'-(3-phenylpropyloxy)biphenyl, 4h, 73.0 g
(0.2 mol) in 800 mL of tetrahydrofuran under nitrogen at -80°
was added via cannula n-butyllithium (100 ml in hexane). A
solution of 24.9 g (0.22 mol) of recently distilled 1-methyl-4-
piperidone in 800 mL of tetrahydrofuran was added dropwise,
and the solution was allowed to warm to room temperature
during six hours, whereupon 40 mL of methanol was added. The
1
171-172°; H nmr: δ 0.68 (s, broad, 10H, -CH CH CH ), 1.95
2
2
3
(m, 9H, -CH CH CH , OH and 3', 5'); 2.37 (s, 3H, -NCH ); 2.67
(t, very broad, J = 8 Hz, 4H, Hs 2', 6'); 3.87 (s, 3H, -OCH ); 6.85
(m, 2H, Hs 1, 3); 7.27-7.77 (m, 4H, H's 4, 5, 6, 8).
2
2
3
3
3

18
Vol. 38
C. J. Kelley, (the late) K. Ansu, (the late) W. Budisusetyo,
A. Ghiorghis, Y. Qin and J. M. Kauffman
Anal. Calc. for C
N, 3.52. Found: C, 78.79; H, 9.37; N, 2.69.
H
NO .0.15 methanol: C, 78.84; H, 9.01;
was recrystallized three times from a mixture of 60%
isopropyl acetate/40% methanol to give 45 g (37%) of 19,
mp 244-246°.
26 35
2
4-Hydroxy-4-[7-(4-methoxyphenyl)-9,9-dipropylfluoren-2-yl]-
1-methylpiperidine (17).
Anal. Calcd. for C
H N O : C, 75.75; H, 8.48; N, 7.36.
24 32 2 2
Found: C, 75.79; H, 8.47; N, 7.22.
To 6.5 g (14.9 mmol) of bromide 10 [4] in 40 mL of tetra-
hydrofuran was added dropwise 6 mL (15 mmol) of
n-butyllithium with stirring under nitrogen below -40°. The thick
mixture was stirred for 30 minutes with continued cooling and
1.9 g of 1-methyl-4-piperidone was added at such a rate that the
temperature did not exceed -30°. The temperature was warmed
gradually to -10° before 6 mL of methyl alcohol (MeOH) was
added. The mixture was concentrated, and the residue was
triturated with 100 mL of of 5% sodium hydroxide, filtered,
washed with water and dried under an ir lamp. The 6.46 g of
crude solid was recrystallized from 180 mL of toluene to give
2.38 g of very light yellow solid, mp 233-235°. The mother liquor
on concentration to 40% of its volume gave on cooling 1.5 g of a
second crop, mp 230-232°. The combined product was
recrystallized twice from toluene (35 mL/g) to give 3.45 g (49%)
of 17, mp 239.5-241°.
2,7-Bis(4-hydroxy-1-methyl-4-piperidinyl)-9,9-dipropyl-
fluorene (20).
A solution of 100 g (0.26 mol) of 13 [4] in 350 mL of tetra-
hydrofuran was cooled to -60° and 260 mL (0.572 mol, 10%
excess) of n-butyllithium in hexane was added dropwise at a
temperature below -50° during 40 minutes. To the resulting slurry
was added an additional 300 mL of tetrahydrofuran. After
30 minutes stirring, 65 mL (0.572 mol, 10% excess) of freshly
distilled 1-methyl-4-piperidone was added dropwise below -50°.
The reaction was then allowed to warm with stirring for 2 hours
before it was quenched by the addition of 17 mL of methanol and
subsequently 32 g of acetic acid at 15°. All solvents were
removed, and the semi-solid residue was dissolved in a mixture
of methylene chloride and aqueous 20% hydrochloric acid (HCl).
The organic layer was discarded. The aqueous layer was made
basic to pH =11 with 30% NaOH, and was extracted with
methylene chloride (3 x 40 mL). The organic layer was dried
with anhydrous sodium carbonate and the solvent was
concentrated under reduced pressure to give 65 g of a yellowish-
white solid which was recrystallized twice from 80% isopropyl
acetate/20% methanol to give 37 g (30%) of 20, mp 229-231°.
Anal. Calcd for C
H NO : C, 81.83; H, 8.37; N, 2.98.
32 39 2
Found: C, 81.58; H, 8.16; N, 2.82.
4-Hydroxy-4-(6-methoxynaphth-2-yl)-1-methylpiperidine (18).
To a dry-ice cooled paste of 11 (30 g, 0.127 mol) in 200 ml of
THF was added dropwise n-butyllithium (50.6 mL, 0.127 mol)
with magnetic stirring under nitrogen. During the addition the
temperature of the mixture was kept below -40°. After the
reaction mixture was stirred at -60 to-40° for one hour, 15.75 g,
(0.139 mol) of 1-methyl-4-piperidone was added at such a rate
that the temperature was maintained below -40°. Stirring was
continued for half an hour at that temperature and 10 mL of acetic
acid in 10 ml of methanol was added as the reaction mixture
warmed to -10°. After 5 minutes' stirring, the solvents were
removed under reduced pressure. The residue was washed with
10% sodium hydroxide and water, was dried, and was
recrystallized from 1.2 L of acetonitrile to give 19.37 g (56%) of
a light yellow solid 18, mp 178.5-180°. A second crop weighed
2.15 g, mp 172-174°.
Anal. Calcd. for C
H N O : C, 78.11; H, 9.30; N, 5.88.
31 44 2 2
Found: C, 78.30; H, 9.47; N, 5.78.
4-[4'-(3-Phenylpropyloxy)biphenyl-4-yl]pyridine (21).
In 25 mL of diphenyl ether was placed 5.0 g of 14 and 0.6 g of
10% Pd-charcoal. A stream of nitrogen gas was bubbled
continuously through the suspension as it was heated to 200°
with constant stirring during 52 hours. The mixture was filtered
hot through Celite and was filtered again on cooling to give a
greyish-green solid. The solid was boiled in 30 mL of butanone
and the slurry was allowed to cool and was filtered to give 2.74 g
(63%) of a greyish-green 21, mp 184-186°. Recrystallization of
2.37 g once from 40 mL of 2-methoxyethanol and once from
85 mL of ethyl acetate gave 1.82 g (50%) of 21, as an off-white
solid, mp 188-190°.
Anal. Calcd for C
H NO : C, 75.24; H, 7.80; N, 5.16.
17 21 2
Found: C, 75.54; H, 7.97; N, 5.24.
Anal. Calc. for C
C, 85.65; H, 6.14; N, 3.81.
H NO: C, 85.45; H, 6.36; N, 3.83. Found:
26 23
4,4'-Bis(4-hydroxy-1-methyl-4-piperidinyl)biphenyl (19).
A solution of 100 g (0.32 mol) of 12, in 350 mL of
tetrahydrofuran at room temperature under nitrogen was
cooled to -60° to give a slurry to which n-butyllithium
(305 ml, 0.67 mol,10% excess) was added dropwise
below -50° during an hour. Another 300 ml of THF was
added, and after 45 minutes freshly distilled 1-methyl-4-
piperidone (82 ml, 0.67 mol) was added dropwise below -50°.
The mixture was stirred for an additional 2 hours as it warmed
to 15° whereupon 21 mL (0.64 mol) of methanol was added.
Solvents were concentrated and the semi-solid was partitioned
between methylene chloride and aqueous 30% hydrochloric
acid. The organic layer was discarded while the aqueous layer
was made basic with 20% NaOH (pH = 11) and extracted
3 times with 80 mL portions of methylene chloride. The
combined organic layer was concentrated to a yellowish-white
solid which was washed in a sintered glass funnel 4 times with
water to give after drying 98 g of crude 19, mp 209-215°. This
4-(9,9-Dipropylfluoren-2-yl)pyridine (22).
A mixture of 10 g of 15, 0.8 g of 5% palladium on carbon, and
40 mL of diphenylmethane was heated for 51 hours at 240° while
nitrogen gas was bubbled through the mixture. The cooled
mixture was diluted with methylene chloride and filtered through
a bed of Celite. Methylene chloride was removed under reduced
pressure, and the diphenylmethane was distilled at 70-110°
(0.0l torr) to leave a viscous yellow oil. The residue was
dissolved in 10 mL of boiling hexane and crystallized to give
6.80 g (76%) of 22, mp 91-93°; uv (95% ethanol, c =
-5
2.45 x10 M): 317 nm (33,800); ir (KBr): 3050, 3024, 2952,
2860, 1590, 1450, 1400, 1220, 1152, 990, 810, 782, 740, 700
cm-1; 1H nmr (trifluoroacetic acid): δ 0.75 (s, 10H,
-CH2CH2CH3), 2.20 (t, broad, J = 7 Hz, 4H, -CH2CH2CH3),
7.45 (s br, 3H, Hs 6-8), 7.87 (s br, 4H, Hs 1, 3, 4, 5), 8.38 (d, J =
7 Hz, H-3',5'), 8.72 (t, J = 6 Hz, 2H, Hs 2', 6').

19
Jan-Feb 2001
Syntheses and Photophysical Properties of Some 4-Arylpyridinium Salts
Anal. Calc. for C
87.93; H, 7.88; N, 3.91.
H
N: C, 88.03; H, 7.70; N, 4.28. Found: C,
the mother liquors were combined to give a second crop of
3.3 g, mp 144-149°, of 25; uv (methanol, 1x10-5 M): 221 nm
(44,000), 262 (41,000), 309 (19,000).
24 25
4-(7-Methoxy-9,9-dipropylfluoren-2-yl)pyridine (23).
Anal. Calcd for C
H NO: C, 81.68; H, 5.57; N, 5.95. Found:
16 13
A mixture of 16 (7.0 g), 10% palladium on carbon (0.8 g) and
50 mL of diphenylmethane was heated at 240° for 72 hours while
a stream of nitrogen gas was bubbled through the mixture. The
cooled mixture was diluted with methylene chloride and filtered
through Celite, and was concentrated under reduced pressure.
Residual diphenylmethane was distilled at 90-95° (0.01torr) to
give a yellow oil which was crystallized from 30 mL of methanol
to remove 0.621 g of a brown, non-fluorescent product mp >240°
(dec). The parent liquor was concentrated and distilled at 230°
(0.01 torr). The distillate was crystallized from 10 ml of hexane
to give 2.034 g of 23, mp 110-112°. Recrystallization from 15 mL
of hexane gave 1.49 g of material which assayed 0.8% high for
carbon. This material (0.9 g) was used in the synthesis of 23B.
The remainder was crystallized from methanol-water to give
C, 81.60; H, 5.43; N, 5.83.
4,4'-Bis(4-pyridyl)biphenyl (26, 4,4'''-Diazaquaterphenyl).
A stirred slurry of l0 g, (0.026 mol) of 19 and 0.85 g of
palladium on carbon in 30 mL of diphenylmethane was purged
with nitrogen and heated at reflux (248°) for 72 hours. Methanol
(2 mL) was added and the mixture was filtered and washed with
15 mL of methylene chloride in a sintered glass funnel with a
celite bed. The volatile solvents were removed, and the
diphenylmethane was distilled (bp 70-100° at 0.01 torr). The
somewhat viscous residue was triturated in acetonitrile and
filtered. The solid, purified by extraction with acetonitrile from a
Soxhlet during 48 hours, was collected by filtration to give 5.2 g
(53%) of 26, mp 308-310°.
-5
analytically pure 23, mp 110-111°; uv (ethanol, 2.24 x10 M):
Anal. Calcd. for C
H N : C, 85.69; H, 5.23; N, 9.08. Found:
22 16 2
329 nm (39,300); ir (KBr): 3060, 3020, 2948, 2860, 1590, 1462,
1400, 1262, 1250, 1030, 812, 680 cm-1; 1H nmr: δ 0.72
(s, broad, 10H,-CH CH CH ), 1.87 (t, broad J = 7 Hz,
C, 85.84; H, 5.03; N, 8.96.
2,7-Bis(4-pyridyl)-9,9-dipropylfluorene (27).
2
2
3
4H, -CH CH CH ), 3.92 (s, 3H, OCH ), 6.77-7.17 (m, 2H,
A mixture of10 g (0.021 mol) of 20, 0.85 g of 10% palladium
on carbon and 35 mL of diphenylmethane was stirred and
refluxed at 248° for 72 hours while nitrogen gas was bubbled
continously through the hot mixture. The mixture was cooled,
diluted with 20 mL of methylene chloride and was filtered
through a bed of Celite in a sintered glass funnel. The filtrate was
concentrated and was distilled at 70-100° at 0.01 torr. The 9 g of
residual gum was triturated in acetonitrile and filtered. The crude
solid was extracted with acetonitrile for 48 hours in a Soxhlet
extractor. The solvent was concentrated, and the solid material
was washed with acetonitrile and dried to give 6.81 g (80%) of
27, mp 179-181°. (An earlier sample, mp 171-173° was used for
elemental analysis).
3
2
2
3
H-1; H-3), 7.40-7.80 (m, 6H, Hs 4, 5, 6, 8, 3', 5' ), 8.51-8.93
(m, 2H, Hs 2', 6').
Anal. Calcd. for C
H NO: C, 83.99; H, 7.61; N, 3.92. Found:
25 27
C, 83.69; H, 7.62; N, 3.78.
4-[7-(4-Methoxyphenyl)-9,9-dipropylfluoren-2-yl]pyridine (24).
A mixture of 17 (3.0 g, 6.59 mmol), 0.5 g of 10% Pd/C, and
40 mL of diphenylmethane was heated at 220-240° for
18 hours while a stream of nitrogen gas was bubbled through
the solution. The reaction mixture was cooled and filtered
through Celite/sintered glass, and the catalyst was washed
with several portions of methylene chloride. The filtrate was
evaporated, and the oil was distilled under reduced pressure
(bp 85° at 0.05 torr) to remove most of the diphenylmethane.
The residue was triturated with cold acetonitrile, and the solid
was filtered, washed with acetonitrile and dried to give 2.5 g
of 24, mp 179-205°. The solid was extracted from a Soxhlet
with ethanol for 64 hours. The extract was boiled down to
30 mL and was crystallized to give 1.44 g, mp 177-180°.
Recrystallization from acetonitrile gave 1.04 g (36%), of 24 as
a yellow solid, mp 180-182°.
Anal. Calcd. for C
H N : C, 86.10; H, 6.98; N, 6.92. Found:
29 28 2
C, 86.18; H, 6.91; N, 6.73.
4-(4-Chlorophenyl)pyridine (28).
Freshly ground magnesium turnings (16.5 g, 0.522 mol, 30%
excess) were flame-dried in a flask under nitrogen and allowed
to cool to 40°. Tetrahydrofuran (30 mL) was added, the mixture
was brought to reflux, and a solution of 100 g (0.522 mol) of
4-bromochlorobenzene in 150 mL of tetrahydrofuran was added
at such a rate as to maintain the reflux. After the addition, the
reaction was refluxed for an additional two hours. The
temperature was decreased to 30°, and salt 5 (28.0 g, 0.186 mol)
mixed with PdCl2.dppb (1.0 g, 0.0018 mol) was added in small
quantities, while the temperature was maintained below 50°.
Stirring was continued for 18 hours, and 100 mL of tetra-
hydrofuran was added in portions. Methanol 17 mL (1 equiv-
alent) was added and all solvents were removed under reduced
pressure. Hydrochloric acid (2 M) was added to the oily residue
until the pH was 2. The mixture was extracted with methylene
chloride (3 x 30 mL) and the extract was discarded. The aqueous
layer was treated with portions of saturated sodium bicarbonate
solution to pH 8. The mixture was then extracted with methylene
chloride (4 x 30 mL), and the organic layer was dried over
anhydrous sodium carbonate. The solution was filtered, and the
solvent removed under reduced pressure to leave 31.0 g of a
crude oil. The oil was distilled to give a forerun of
Anal. Calcd for C
H NO: C, 85.87; H, 7.21; N, 3.23. Found:
31 31
C, 86.11; H, 7.21; N, 3.18.
4-(6-Methoxynaphth-2-yl)pyridine (25).
A mixture of 18 (19.3 g, 71.1 mmol) and 10% Pd/C in
diphenylmethane (150 mL) was heated at 235-245° for
20 hours with stirring provided by a continuous purge of dry
nitrogen gas. The reaction mixture was cooled, filtered through
Celite in a sintered-glass funnel. The catalyst was washed
thoroughly with methylene chloride. The filtrate was distilled
under reduced pressure to remove the methylene chloride and
the diphenylmethane (bp 82-105°, 0.5 torr). Upon cooling, the
residue crystallized during two hours, and the liquid was
removed with a pipette. This solid which remained was
recrystallized twice from 1,2-dimethoxyethane to give 5.1 g of
light yellow solid, mp 153.5-156°. A third recrystallization
gave the analytical sample, 3.5 g (21%), mp 155-156.5°. All

20
Vol. 38
C. J. Kelley, (the late) K. Ansu, (the late) W. Budisusetyo,
A. Ghiorghis, Y. Qin and J. M. Kauffman
chlorobenzene (2 g) followed by 24 g of a fraction, bp 90-110°
(0.1 mm Hg). This liquid was dissolved in 10% hydrochloric
acid upon heating, was filtered hot, was cooled and was basified
with a saturated solution of sodium bicarbonate. Crystals, which
formed after ice was added, were filtered and washed with water.
The dried product (21.2 g) was recrystallized from 70 mL of
n-hexane to give 18 g (51%) of 28, mp 70-71°; lit. [18] mp
70-71°; readily sublimes as needles.
from methyl-t-butyl ether gave 10.93 g (92%) of 31, mp
91.5-92°. Recrystallization from 200 mL of methanol gave 9.17 g
(78%) of 32, mp 92-3°.
Anal. Calcd for C
H BrN: C, 61.33, H, 4.41, N, 5.11. Found:
14 12
C, 61.33, H, 4.51, N, 5.08.
2-[4-(4-Pyridyl)phenyl]-9-ethylcarbazole (33).
Magnesium turnings (0.71 g, 29 mmol) were heated to 110°
for 10 minutes, cooled and refluxed with 30 mL of tetrahydro-
furan. Solid 32 (8 g, 29 mmol) was added in small quantities
during 10 minutes. The magnesium dissolved during two
4-[4-(6-Methoxynaphth-2-yl)phenyl]pyridine (29).
A flask containing 1.02 g (42 mmol) of magnesium was heated
to 180° for 15 minutes, was cooled to room temperature, and
100 mL of tetrahydrofuran and 10 g (42 mmol) of 11 were added.
Almost all of the magnesium dissolved while the mixture was
refluxed with stirring for six hours. The solution was cooled to
room temperature and 4 g (21 mmol) of 28, 350 mg of nickel(II)
acetylacetonate and 30 mL of tetrahydrofuran were added. The
mixture was refluxed with stirring for 17 hours, was quenched
with methanol, and was evaporated to dryness under reduced
pressure. The residue was triturated with methanol and filtered to
give 9 g of solid. The solid was extracted with methylene
chloride (400 mL) in a Soxhlet extractor for 3 days. Evaporation
of the extract gave 7.25 g of solid. Extraction of the solid through
neutral alumina with boiling cyclohexane in a large Ace-Kau
column gave 4.2 g (32 %) of 29, mp 251-255°
hours reflux and PdCl -dppb (0.37g, 0.58 mmol) and 28
2
(4.36g, 0.024 mol), were added in small quantities during 15
minutes while reaction temperature was kept below 45°.
Tetrahydrofuran (20 mL) was added, the reaction was stirred
for 48 hours before it was quenched with 1 mL of methanol.
All solvents were removed, and the gum was acidified with
2 M hydrochloric acid and washed with methylene chloride
(3x10 mL) . The aqueous layer was made basic with saturated
sodium bicarbonate and was extracted with methylene
chloride (3x10 ml). The organic layer was dried over sodium
carbonate and filtered. The solvent was concentrated to a
semi-solid residue which was triturated in ethanol and filtered.
Three recrystallizations of the filtrate from toluene gave 0.8 g
(10%) of 33, mp 228-230°.
Anal. Calcd. for C
H N : C, 86.17; H, 5.79; N, 8.04. Found:
25 20 2
Anal. Calcd for C
H NO: C, 84.86; H, 5.50; N, 4.50. Found:
22 17
C, 86.01; H, 5.79; N, 7.89.
C, 85.00; H, 5.45; N, 4.35.
4-(4'-Methoxybiphenyl-4-yl)pyridine-N-oxide (34).
4-Bromo-2'-nitrobiphenyl (30).
To a solution of 10 g (38.3 mmol) of 3 in 600 mL of
chloroform was added 9.5 g of sodium bicarbonate and 23.3 g
(115 mmol) of m-chloroperoxybenzoic acid, and the mixture was
refluxed 15 hours. The suspension was twice extracted with
300 mL of 1 N sodium hydroxide, and the chloroform layer was
dried with brine followed by magnesium sulfate. The residue
after removal of the chloroform crystallized from methanol in
three crops to give 6.3 g of 34, mp 223-225°. Recrystallization
gave 34, mp 224-226°. The identity was confirmed by conversion
to 35 and 38.
A mixture of 177.4 g (0.89 mol) of 2-nitrobiphenyl, 7.9 g
(0.049 mol) of ferric chloride, and 200 mL of water was stirred
for one hour before 52 mL (1 mol) of bromine was added
dropwise during an hour. The reaction was heated, allowed to
cool and was stirred overnight. To the dark brown mixture was
added 5.8 g (56.3 mmol) of sodium bisulfite. The mixture was
washed with three times with 200 mL-portions of water, once
with 5% sodium hydroxide, twice with water, was dried over
calcium chloride and evaporated to a yellow oil which
crystallized slowly from 75 ml of methanol to give 51.5 g (37%)
of 30, mp 65-6°; lit. [27] mp 63-65°.
2-(4-Methoxyphenyl)-4-(4''-methoxybiphenyl-4-yl)pyridine (35).
To a suspension of 3.0 g (10.8 mmol) of 34 in 200 mL of
tetrahydrofuran was added 1.36 mL (13.8 mmol) of ethyl
chloroformate at 20° with mechanical stirring. After 20 minutes
the yellow mixture was cooled to -50° with a dry ice bath.
Anisylmagnesium bromide (14.4 mmol: 12 mL of a 1.2 M
solution in tetrahydrofuran) was added quickly. Most of the solid
dissolved as stirring was continued for 5 minutes at -50° and
30 minutes at -70°. The mixture was allowed to warm gradually
to room temperature, and 5 mL of methanol was added
cautiously. The precipitate was filtered (ca. 4 g) and was
recrystallized from 45 mL of 2-methoxyethanol to give 1.15 g of
35 as a yellow solid, mp 200-201°. The solid was extracted
through a bed of neutral alumina in an Ace-Kau extractor for
24 hours with methylene chloride. The solids obtained on
removal of the solvent were recrystallized from 40 mL of
2-methoxyethanol to give 0.74 g (24%) of white 35, mp
202-203°.
2-Bromocarbazole (31).
A solution of 27.8 g (0.1 mol) of 4-bromo-2'-nitrobiphenyl 30
and 66.5 mL (0.4 mol) of triethyl phosphite was refluxed for
12 hours under nitrogen. The yellowish-red solution was distilled
(68°, 1.25 torr), and the yellow residue was dissolved in 20 mL of
acetone, cooled, and filtered to give 15.3 g of crude 31, mp
234-43°. Recrystallization from 60 mL of butanone gave 6.2 g
(39%) of 31, mp 254-256°; lit. [28] mp 251-252°.
2-Bromo-9-ethylcarbazole (32).
To a dark brown solution of 10.61 g, (0.043 mol) of 31 in
120 mL of dimethyl sulfoxide was added 7.26 g (0.0467 mol) of
potassium t-butoxide under nitrogen was added dropwise during
20 minutes 5.2 mL of ethyl iodide while the temperature was held
at 40°. Stirring continued for an additional 1 hour before 140 mL
of water was added. This mixture was extracted 4 times with
40 mL-portions of methyl-t-butyl ether. The extract was dried
with calcium chloride and concentrated to a light yellow liquid
which crystallized at 10° to give 11.4 g of 32. Recrystallization
Anal. Calcd. for C
H NO (containing 0.1 mol of
25 21 2
2-methoxyethanol): C, 81.02; H, 5.86; N, 3.73. Found: C, 81.12;
H, 5.75; N, 3.70.

21
Jan-Feb 2001
Syntheses and Photophysical Properties of Some 4-Arylpyridinium Salts
2-(2-Hydroxy-5-methylphenyl)-4-(4'-methoxybiphenyl-4-
yl)pyridine (38).
1042, 1030 sh, 819 cm-1; 1H nmr (trifluoroacetic acid): δ 2.84
(br, pentet, 2H, NCH CH CH S), 3.53 (br. t, J = 7 Hz, 2H,
2
2
2
NCH CH CH S), 4.05 (s, 3H, OCH ), 4.96 (br. t, J = 7 Hz, 2H,
2
2
2
3
To a solution of 1.1 g (7.2 mmol) of methoxymethyl p-tolyl
ether in 20 mL of tetrahydrofuran at -60° was added 2.88 mL
(7.2 mmol) of n-butyllithium in hexane. The yellow solution was
stirred at -70° for 30 minutes, was allowed to warm to 20°, and
was transferred via cannula under nitrogen to a flask containing
1.33 g (7.2 mmol) of anhydrous magnesium bromide and was
stirred for 30 minutes to complete formation of Grignard 36. In a
separate flask, a suspension of 1.00 g (3.6 mmol of 34 in 100 mL
of tetrahydrofuran was stirred with 0.41 mL (4.2 mmol) of ethyl
chloroformate at 25° for 30 minutes and was cooled to -50°. The
solution of 36 was transferred under nitrogen, and the mixture
was stirred at -50° for three hours. The solution was allowed to
warm to room temperature, quenched with 5 mL of methanol,
concentrated to dryness, triturated with hexane and filtered. The
4.4 g of solid obtained was extracted from a Soxhlet with diethyl
ether for 16 hours. Concentration of the ether gave a solid which
was recrystallzed from 95% ethanol to give 0.15 g, mp 185-191°.
Two recrystalizations from small volumes of chloroform gave
25 mg (2%) of 38, mp 198-199°; 1H nmr (400 MHz, deuterio-
chloroform): δ 2.26 (s, 3.H), 3.77 (s, 3H), 6.95 (d, J = 9 Hz, 1H,
ortho to phenol), 7.01 (d, J = 9 Hz, 2H, ortho to methoxy), 7.13
(dd, J = 2, 9 Hz, 1H, ortho to methyl), 7.46 (dd, J = 2, 5 Hz, 1H,
H-5, pyridine), 7.58 (d, J = 9 Hz, 2H, meta to methoxy), 7.68
(s, br, 1H, ortho to methyl), 7.70 and 7.75 (two d, J = 9 Hz, 4H,
-C6H4-), 8.11, (s, br, 1H, H-3 on pyridine), 8.54 (d, J = 5 Hz, 1H,
H-6 on pyridine). and 14.12 (s, v br, 1H, OH).
NCH CH CH S), 7.20 (d, J = 9 Hz, 2H, H-3'', H-5''), 7.72 (d, J =
2
2
2
9 Hz, 2H, H-2'', H-6''), 7.90 (s, 4H, Hs 2',3',5',6'), 8.30 (d, J = 7
Hz, 2H, H-3,5), 8.93 (d, J = 7 Hz, 2H, H-2,6).
Anal. Calc. for C
H NO S: C, 65.77; H, 5.52; S, 8.36.
21 21 4
Found: C, 66.03; H, 5.70; S, 8.49.
4-(4'-Methoxybiphenyl-4-yl)-1-(3-sulfobutyl)pyridinium
Zwitterion (3C).
This was prepared in the manner of the sulfopropyl analog 3B.
The free base 3 (1.6 g, 0.0061 mol) and 1,4-butane sultone (1.04
g, 0.78 mL, 0.00763 mol) in 35 mL of benzonitrile were boiled
under reflux for 30 minutes. The mixture at 20° was filtered, the
product was washed with toluene and dried to give 2.06 g (85%)
of lemon-yellow solid, mp 359-360° (dec). uv (ethanol, 2.4 x10-
5 M) 203 nm (ε = 36,000); 248 (18,000); 360 (28,000).
Anal. Calc. for C
H NO S: C, 66.48; H, 5.83; N, 3.52.
22 23 4
Found: C, 66.51; H, 5.66; N, 3.56.
4-(9,9-Dipropylfluoren-2-yl)-1-(3-sulfopropyl)pyridinium
Zwitterion (22B).
To a warm solution of 1.0 g (3.07 mmol) of 22 in 10 mL of
benzonitrile was added 0.47 g (3.83 mmol) of 1,3-propane
sultone. The solution was heated to reflux for 15 minutes and
allowed to cool. Filtration of the suspension after two days gave
after washing twice with toluene and drying (110°, 30 torr,
3 hours) gave 1.34 g (98%) of 22B, mp 274-276.5°; uv
(methanol): 361 nm (33,000); ir (KBr): 3400 br, 3100 sh, 3007,
2950, 2920, 2862, 1627, 1604, 1510, 1450, 1423, 1280, 1180 s,
br, 1032, 861, 832, 787, 769, 740 cm-1.
Anal. Calcd. for C
H NO (containing 0.1 mol of
25 21 2
chloroform): C, 79.46; H, 5.81; N, 3.69. Found: C, 79.40; H,
5.65; N, 3.57.
Preparation of Quaternary Salts:
Anal. Calc. for C
H NO S: C, 72.13; H, 6.95; S, 7.13.
27 31 3
Found: C, 71.95; H, 6.72; S, 7.40.
4-(4'-Methoxybiphenyl-4-yl)-1-methylpyridinium
Methanesulfonate (3A).
4-(7-Methoxy-9,9-dipropylfluoren-2-yl)-1-sulfopropylpyridine
Zwitterion (23B).
To a solution of 3.92 g (15 mmol) of 3 in 40 mL of benzonitrile
heated to 105° was added 1.69 mL (2.0 g) of methyl methane-
sulfonate. A yellow solid, which separated in seconds,
redissolved as the temperature was raised to reflux. The solution
was immediately allowed to cool to room temperature overnight.
It was diluted with 25 mL of toluene, and the yellow solid was
filtered and was washed with toluene to give after vacuum drying
5.0 g (90%) of 3A, mp 258-260°.
By the method for 22B, 0.90 g (2.5 mmol) of 23 was converted
to 1.21 g of 23B, mp 260-270°. This was recrystallized from
20 mL of 1:1 benzonitrile/dibutyl ether to give 0.89 g (74%) of
23B, mp 267-269° which showed green fluorescence in
chloroform or methanol; uv (methanol) 385 nm (33,000); ir
(KBr): 3020 br, 3040, 2960, 2930, 2880, 2850 sh, 1625 sh, 1600,
1580 sh, 1518, 1460, 1425 sh, 1345, 1310 sh, 1180 s, br, 1100,
1035 s, 1005, 868, 817, 781, 755, 728 cm-1; 1H nmr
(trifluoroacetic acid): δ 0.7 (s, broad, 10H,-CH CH CH ), 2.18
Anal. Calc. for C
H NO S: C, 64.67; H, 5.70; S, 8.63.
20 21 4
Found: C, 64.94; H, 5.61; S, 9.04.
2
2
2
3
2
(m, 4H, -CH CH CH ), 2.82 (br, pentet, 2H, NCH CH CH S),
3
2
2
2
4-(4'-Methoxybiphenyl-4-yl)-1-(3-sulfopropyl)pyridinium
Zwitterion (3B).
3.53 (br. t, J = 7 Hz, 2H, NCH CH CH S), 4.13 (s, 3H, OCH ),
2
2
2
3
4.93 (br. t, J = 7 Hz, 2H, NCH CH CH S), 7.13 (m, 2H, H-6';
2
2
2
To a warm solution of 7.0 g (26.8 mmol) of 3 in 90 mL of
benzonitrile was added 3.9 mL (5.4 g, 44 mmol) of 1,3-propane
sultone. The solution was heated to reflux (187°) for 20 minutes,
and a precipitate separated. After cooling overnight the solution
was filtered and the chartreuse solid was washed with methyl
t-butyl ether to give 10.44 g (100%) of 3B, mp 360-361°.
Recrystallization of 9.4 g from 15 mL of acetic acid gave 7.01g
of 3B, mp 360-362°. A 1.65 g portion was preadsorbed on Silica
Gel and chromatographed on 30 g of Silica Gel. Elution with
25% methanol in methylene chloride gave, after recrystallization
from 200 mL of methanol, 1.07 g of 3B, mp 368-369°; ir (KBr):
3500, 3425, 3030, 2920 w, 1627, 1591, 1487, 1288, 1232, 1175 s,
H-8'), 7.90 (d, J = 9 Hz, 1H, H-5'), 7.95 (s, 3H, Hs 1', 3',4'), 8.30
(d, J = 7 Hz, 2H, H-3,5), 8.60 (d, J = 7 Hz, 2H, H-2,6).
Anal. Calc. for C
H NO S: C, 70.11; H, 6.77; S, 6.52.
28 33 4
Found: C, 68.61; H, 6.82; S, 6.87.
4-[7-(4-Methoxyphenyl)-9,9-dipropylfluoren-2-yl]-1-sulfo-
propylpyridinium Zwitterion (24B).
To a hot solution of 0.6 g (1.38 mmol) of 24 in 5 mL of
benzonitrile was added 0.5 g (4.0 mmol) of 1,3-propane sultone.
The mixture was stirred at 180° for 30 minutes and allowed to
cool slowly. The precipitate was filtered and washed with
acetonitrile to give 400 mg of 24B, mp 314-316°. The filtrate was

22
Vol. 38
C. J. Kelley, (the late) K. Ansu, (the late) W. Budisusetyo,
A. Ghiorghis, Y. Qin and J. M. Kauffman
diluted with 25 mL of methyl t-butyl ether and an additional
400 mg of yellow precipitate was obtained. The combined solids
on recrystallization from 20 mL of absolute ethanol gave 0.63 g
of 24B, mp 320.5-321° (dec).
Anal. Calcd. for C H N O S .1.5 CH CO H: C, 57.93; H,
28 28 2 6 2 3 2
5.33; N, 4.36. Found: C, 58.08; H, 5.48; N, 4.61.
2,7-Bis(1-methyl-4-pyridinium)-9,9-dipropylfluorene
Dimethanesulfonate (27A).
Anal. Calcd for C
H NO S: C, 73.48; H, 6.71; N, 2.52.
34 37 4
To a refluxing solution of 1.0 g (2.5 mmol) of 27 in 25 mL of
acetonitrile was added 0.6 g (5.5 mmol) of methyl methane-
sulfonate. Refluxing was maintained for an additional 8 hours
before the mixture was cooled, concentrated to dryness, and
crystallized from 10 mL of toluene to give 1.47 g (94%) of 27A,
mp 324-325°. uv (methanol) 377 nm. Fluorescence (methanol )
445 nm. Quantum efficiency 0.82 [24].
Found: C, 73.22; H, 6.77; N, 2.39.
4-(6-Methoxynaphth-2-yl)-1-methylpyridinium methane-
sulfonate (25A).
To a solution of 25 (1.5 g, 6.38 mmol) in 17 mL of acetonitrile
was added 2.1 g (19.1 mmol) methyl methanesulfonate. The
mixture was refluxed for 46 hours as the disappearance of the 25
was monitored by tlc (1,2-dimethoxyethane/Silica Gel). The
addition of toluene to the hot solution caused the separation of a
gum which was induced to crystallize. The solid was collected by
filtration and washed with toluene to give 1.2 g, mp 184-186°.
Recrystallization from 10 mL of acetonitrile gave 0.63 g of
yellow solid, 25A, mp 194-195°; uv (MeOH, 5x10-5 M): 225 nm
(42,000), 259 (16,000), 286 (17,000), 367 (20,000).
Anal. Calcd. for C
H N O S : C, 63.50; H, 6.46; N, 4.49.
33 40 2 6 2
Found: C, 63.53; H, 6.51; N, 4.39.
9,9-Dipropyl-2,7-bis(1-sulfopropyl-4-pyridinium)fluorene (27B).
A slurry of 1.0 g (2.5 mmol) of 27 in 15 mL of benzonitrile
was heated to 140° and 0.67 g (5.5 mmol) of melted 1,3-propane
sultone was added and the mixture was heated to reflux for
15 minutes. The yellowish crystals which formed immediately
were allowed to cool slowly to room temperature, were filtered,
and were washed with 20 mL of toluene. The crystals were dried
at 100°/26 torr to give 1.60 g (99%) of 27B, mp 359-361° (dec).
uv (methanol) 378 nm (58,000).
Anal. Calcd for C
H NO S: C, 62.59; H, 5.54; N, 4.06.
18 19 4
Found: C, 62.01; H, 5.75; N, 3.92.
4-(6-Methoxynaphth-2-yl)-1-(3-sulfopropyl)pyridinium
Zwitterion (25B).
Anal. Calcd. for C
Found: C, 64.68; H, 6.12; N, 4.16.
H N O S : C, 64.79; H, 6.21; N, 4.32.
35 40 2 6 2
To a hot solution of 25 (1.5 g, 6.38 mmol) in 5 mL of
benzonitrile was added 1.2 g (9.6 mmol) of 1,3-propane sultone.
The solution was heated to 180° for 10 minutes and was allowed to
cool slowly. The solid which separated was collected by filtration,
was washed with methyl t-butyl ether, and was recrystallized from
200 mL of absolute ethanol to give 1.90 g (83 %) of 25B as a
yellow solid, mp 295-297° (dec); uv (methanol, 5x10-5 M):
225 nm (40,000), 260 (15,000), 289 (15,000), 370 (20,000).
2-(1-Decyl-4-pyridinium)-7-(4-pyridyl)-9,9-dipropylfluorene
Bromide (27C).
To a refluxing solution of 0.20 g, (0.5 mmol, mp 171-173°) of
27 in 12 mL of acetonitrile was added 0.122 g, (0.55 mmol) of
1-bromodecane, and the solution was heated at reflux for 8 hours
while the color gradually changed from yellowish-green to light
yellow. The solvent was removed under reduced pressure and the
residue was crystallized from 2 mL of acetonitrile to give 0.3 g of
a yellow product, mp 184-189°. Recrystallization from 1.5 mL of
acetonitrile gave 0.28 g (90%) of 27C, mp 193-195°.
Anal. Calcd for C
H NO S: C, 63.85; H, 5.36; N, 3.92.
19 19 4
Found: C, 64.44; H, 5.61; N, 3.89.
4,4'-Bis(1-methyl-4-pyridinium)biphenyl Dimesylate (26A).
To a solution of 1.0 g (3.2 mmol) of 26 in 20 mL of
benzonitrile at 140° was added 0.7 g of methyl methanesulfonate.
A yellow solid immediately choked the stirring and 10 mL of
benzonitrile was added and the reaction mixture was heated for
another 15 minutes before it was slowly cooled to room
temperature. The precipitate was filtered, washed with toluene,
and then dried at 100°/20 torr for 30 hours to give 1.63 g (84%)
of 26A, mp 323-325° (dec). uv (methanol) 344 nm (52,600).
Fluorescence ca. 420 nm. Quantum efficiency 1.0 [24].
Anal. Calcd. for C
Found: C, 74.28; H, 7.78; N, 4.28.
H N Br: C, 74.86; H, 7.89; N, 4.48.
39 49 2
4-[4-(6-Methoxynaphth-2-yl)phenyl]-1-sulfopropylpyridinium
Zwitterion (29B).
A mixture of 1.0 g (3.21 mmol) of 29 and 25 mL of
benzonitrile was heated with mechanical stirring. After the solid
dissolved 1,3-propane sultone (1.0 g, 8.1 mmol) was added. A
yellow precipitate immediately separated from the hot solution,
and the mixture was stirred for 1 hour at ca. 80°. After standing at
room temperature overnight, the mixture was filtered. The solid
was washed with acetonitrile and diisopropyl ether to give 1.4 g
of 29B as a yellow solid, mp. 366-370° dec). A 1.17 g portion
was recrystallized from 400 mL of dimethylformamide with a hot
filtration to give on cooling 0.86 g (62%) of 29B, mp 268-270°.
Anal. Calcd. for C
H N O S : C, 59.07; H, 5.34; N, 5.30.
26 28 2 6 2
Found: C, 59.35; H, 5.40; N, 5.37.
4,4'-Bis(1-sulfopropyl-4-pyridinium)biphenyl (26B).
To 1.0 g (3.2 mmol) of 26 at 130° in 30 mL of benzonitrile was
added 0.78 g (6.4 mmol) of 1,3-propane sultone. Heating was
continued for 15 minutes to digest the yellowish crystals which
formed instantly. The crystals, were filtered, washed with 25 mL
of toluene, and dried (100°/20 torr/42 hours) to give 1.68 g (95%)
of 26B mp >400°. A 0.55 g portion of the yellow solid was placed
in a Soxhlet and extracted with boiling acetic acid for 36 hours.
The short, off-white needles suspended in the hot solution were
collected by filtration to give 0.28 g (44%) of 26B as the
sesquisolvate, browns 370-400°, sublimes partially 410-430° but
does not melt to 490°.
Anal. Calcd for C
H NO S: C, 69.26; H, 5.35; N, 3.23.
25 23 4
Found: C, 69.40, H, 5.37; N, 3.47.
Acknowledgement.
A large portion of this work was to have been the Masters thesis
of Kwabena Ansu. After his unfortunate death with Wiranto
Budisusetyo in a light plane crash on March 25, 1989, his degree
was awarded posthumously by MCPHS. The enthusiasm,
knowledge, and friendship shown us by James H. Bentley cannot

23
Jan-Feb 2001
Syntheses and Photophysical Properties of Some 4-Arylpyridinium Salts
[9] J. L. Abernathy and H. Pollock, J. Am. Chem. Soc., 73, 1351
(1951).
[10] S. E. Hazlet and R. A. Cory, J. Org. Chem., 27, 2671 (1962).
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(1993).
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[13] L. Pridgen, Personal communication, 1987, suggested that
mesitylene bp 163° allowed aromatization to proceed smoothly with sulfur.
[14] M. P. Sammes, H. K. Wah, A. R. Katritzky, J. Chem. Soc.,
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Soc., 355 (1940).
be overemphasized. Bentley's lasing data and that of his successor
at MICOM, Wayne Davenport were crucial to the objectives of
our work. The open exchange of information with Richard K. Hill,
(the late) Herbert Hall and (the late) Robert Kubin while they were
working on similar compounds is most appreciated. The origin of
some of "our" ideas in the work of Ted Pavlopoulos has not been
forgotten. The encouragement of Dr. John Ehrlich (Army Missile
Command) is greatly appreciated. Provision of time, credit, and
encouragement of the staff at both Colleges is appreciated. We
appreciate the cheerful and competent technical assistance of
Lisa Ruby, Jeffrey Adams and Ali Khalaj (at USP), and
Maria Lurantos, Thomas D. Van Deusen, Elizabeth Manyeneng,
Fariba Mojtabai, Punit Karnik and Dr. Naglaa Abd El-Rahman
(at MCPHS). We greatly acknowledge the financial support from
the U. S. Army Missile Command (MICOM) through Contracts
N66001-85-D-203 from San Diego State University Foundation
which were processed by the Naval Ocean Systems Center, San
Diego CA; Contracts DAAL03-89-K-0610 (to JMK) and
DAAL03-89-0159 (to CJK) from the United States Army
Research Office, Research Triangle Park, NC.
[19] T. J. Walter, U. S. Patent 4,405,792 (1983); Chem. Abstr., 100:
22582b.
REFERENCES AND NOTES
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[22] Personal communication from Dennis P. Pacheco, Spectra
Science, Warwick, RI, May 11, 1994.
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[24] Fluorescence quantum efficiencies for 26A and 27A were
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both methanol and methanol-water (1:1) by Dennis P. Pacheco, Avco
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