Benzotriazole-Mediated 4-Position Derivatization of 2,6-Diarylpyrylium Cations by Electrophiles

Article abstract of DOI:10.1002/(SICI)1521-3897(199902)341:2<152::AID-PRAC152>3.0.CO;2-Y

2,6-Diaryl-4H-(benzotriazolyl)pyrans (7a-c) on treatment with n-butyllithium undergo smooth lithiation at the position α to the benzotriazolyl moiety. In contrast to fused and bridged pyranyl derivatives, these pyranyl anions react with electrophiles by t

Full text of DOI:10.1002/(SICI)1521-3897(199902)341:2<152::AID-PRAC152>3.0.CO;2-Y

FULL PAPER _________________________________________________________________________
Benzotriazole-Mediated 4-Position Derivatization of 2,6-Diarylpyrylium Cations by
Electrophiles
Alan R. Katritzky*, Weihong Du, and Sergey N. Denisenko
Gainesville (Florida, USA), Center for Heterocyclic Compounds, Department of Chemistry, University of Florida
Peter Czerney
Jena, Institut für Physikalische Chemie, Friedrich-Schiller-Universität
Peter J. Steel
Christchurch (New Zealand), Department of Chemistry, University of Canterbury
Received September 1st, 1998, respectively December 7th, 1998
Keywords: Cations, Heterocycles, Rearrangement, Benzotriazole, Indirect electrophilic substitutions, Pyrylium cations
Abstract. 2,6-Diaryl-4H-(benzotriazolyl)pyrans (7a–c) on
treatment with n-butyllithium undergo smooth lithiation at
the position α to the benzotriazolyl moiety. In contrast to
fused and bridged pyranyl derivatives, these pyranyl anions
react with electrophiles by two routes: i) the expected elec-
trophilic substitution resulting in various 4-alkyl- and 4-(ω-
alkylfunctionalized)-pyrylium salts (12–19) or ii) pyrylium
ring rearrangement of 2,6-diarylpyrylium anions (8a–c),
leading to 1,2-diaryl-2,4-cyclopentadien-1-ols (10a–c).
Recently, we introduced new methodology for the easy
indirect electrophilic derivatization of π-electron-defi-
cient heteronium salts [1], utilizing the properties of
benzotriazole as an efficient synthetic auxiliary [2]. Ben-
zo[b]pyrylium, xanthylium, thioxanthylium, acridinium
and 2',3-bridged pyrylium salts in this two pot, three
step procedure yield the corresponding heterocycles,
substituted at position 4 to the heteroatom (Scheme 1).
The success of this strategy was demonstrated [1] by
the preparation of a series of long chain (up to 22 car-
bons) alkyl-, ω-arylalkyl-, ω-halogenalkyl-,(α,ω-alkyl-
idene)bisheteronium salts, which are of interest for syn-
thetic, physico-organic and pharmaceutical applications
[3]. Significantly, only a few short-chain 4-alkyl deri-
vatives of simple, non-bridged pyrylium salts are known;
they were synthesized in low yield by condensations of
either acetaldehyde or alkyl acetates with aryl methyl-
ene ketones [4, p. 884]. Isolated examples of 4-(aryl-
methyl)- and 4-(hetarylmethyl)-2,6-diarylpyrylium salts
were obtained by reaction of pyranylphosphonate car-
banions with corresponding aldehydes [5]. 4-Alkyl-
pyrylium salts with a long-chain alkyl group were not
previously described. During our expansion of the new
methodology to the synthesis of 4-alkyl-2,6-diaryl-
pyrylium cations (6) we found that in some cases the
intermediate 2,6-diaryl-4-benzotriazolylpyran-4-yl an-
ions undergo rearrangement by ring contraction, and we
now report on this alternative reaction pathway.
Bt
H
R3
R4
R1
R2
R3
R4
R1
R2
BtNa
+
X
X
Y
1
2
Li+
R3
R
Bt
C
Bt
R1
R2
R1
R2
R3
R4
RCH2Z
n-BuLi
2
X
R4
X
4
3
HY
R
Results and Discussion
Following our normal procedure we prepared 2,6-dia-
ryl-4-benzotriazolylpyran analogues of compound 2 and
investigated the behavior of 2,6-diaryl-4-benzotriazol-
ylpyranyl anions in reaction with electrophiles. Easily
accessible 2,6-diarylpyrylium tetrafluoroborates (6a–
c) [6] underwent facile regiospecific addition of the ben-
R1
R2
R3
R4
N
N
+
N
N
or
Bt =
N
N
X
Y
5
Scheme 1
152 © WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 1436-9966/99/3410X-152 $ 17.50 + .50/0
J. Prakt. Chem. 1999, 341, No. 2

Benzotriazole-Mediated 4-Position Derivatization of 2,6-Diarylpyrylium Cations
___________________________________________________________________________ FULL PAPER
zotriazolyl anion in position 4 at room temperature in
THF (Scheme 2) to give the benzotriazole derivatives
7a–c. The mixtures of Bt-1 to Bt-2 isomers (ratio 9 to 1
gave only 10a–c, according to the NMR spectra of crude
reaction mixture, which were isolated in yields of 57%
to 66%. A mixture of both substitution and rearrange-
ment products was obtained for the reaction of 7a with
1-bromohexane. Lithiation of benzotriazole adducts 7a–
c in absence of an electrophile followed by quenching
the reaction mixtures with ammonium chloride solu-
tion leads to the same rearrangement products 10a–c in
yields of 54% to 66% (first three line in Table 1). The
products 10a–c are isomeric with the starting benzotri-
azole derivatives 7a–c according to the CHN analysis,
but the NMR spectra no longer show a plane of sym-
metry. Treatment of 10a with perchloric acid, or reflux
in ethanol in the presence of p-toluenesulphonic acid as
catalyst affords 4-hydroxy-3,4-diphenyl-2-cyclopenten-
1-one (11a) in high yield (Scheme 2).
The structure of compound 11a was confirmed by X-
ray analysis and is shown in Figure 1 along with select-
ed bond lengths and angles. In this structure the conju-
gated phenyl ring is approximately coplanar with the
enone system (angle between planes = 18.1(1)o), where-
as the C4 phenyl ring is approximately orthogonal to
the cyclopentenone ring (angle between planes =
103.4(1)o). The molecular packing is controlled by hy-
drogen bonds between the OH hydrogen and the carbo-
nyl oxygen of an adjacent molecule. The NMR spectra
and melting point are in agreement with literature data
for this compound [7].
1
by H NMR) were used without further purification,
but for analytical purposes the Bt-1 isomers were iso-
lated and characterized. Compounds 7a–c are colorless,
crystalline, and stable to neutral and basic conditions,
but easily eliminate benzotriazole to regenerate the high-
ly fluorescent cations 6 upon treatment with weak
acids.
Conversions of 7a–c to the carbanion 8a–c proceed
at low temperature (–78 °C) in THF with n-butyllithi-
um. In contrast to earlier investigations [1] the reactiv-
ity of anions 8a–c is more complex than that of other
fused or bridged anions of type 3, and the products of
their reaction with electrophiles depend dramatically on
the alkyl halide type. Alkyl and arylalkyl halides, or
alkylene dihalides with four or less carbon atoms in the
aliphatic chain give the normal products of substitution
12–19 in moderate to high yields (Scheme 2, Table 1).
However, aliphatic halides with a chain longer than 6
carbons unexpectedly gave the new products 10a–c in-
stead of alkyl substituted salts of type 5. Quenching the
reaction mixtures with ammonium chloride solution
Bt
H
BtNa
-
BF4
R
+
O
R
R
O
R
The tendency to form products of type 10 increases
with the electron-withdrawing nature of the para sub-
6a-c
7a-c
n-BuLi
Bt
Bt
O
C
C
R
O
R
R
R
8a-c
i) Alkyl halide
ii) NH4Cl sat.
iii) HClO4
Bt
O
R1
C
-
ClO4
R
+
R
O
R
R
9a-c
12-19
For assignment of R1
see Table 1
NH4Cl sat.
O
Bt
H+
Fig. 1 Perspective view of the X-ray crystal structure of 11a.
Selected bond lengths (Å) and angles (o): C1–O1 1.225(2);
C1–C2 1.455(2); C2–C3 1.341(2); C3–C4 1.542(2); C4–C5
1.544(2); C1–C5 1.504(2); C3–C31 1.469(2); C4–C41
1.521(2); C4–O4 1.428(2); C2–C1–C5 108.1(1); C1–C2–C3
111.4(1); C2–C3–C4 111.1(1); C3–C4–C5 103.2(1); C1–C5–
C4 105.8(1).
R
R
R
R
OH
OH
10a-c
11a
a: R = Ph, b: R = p-C6H4OMe, c: R = p-C6H4F
Scheme 2
J. Prakt. Chem. 1999, 341, No. 2
153

A. R. Katritzky et al.
FULL PAPER __________________________________________________________________________
type 10 was postulated, and at a higher temperature
(–30 °C) the cyclopentadiene dimer 22 was isolated in
unspecified yield (Scheme 3). The present rearrange-
ment differs by the absence of migration of phenyl
groups and no introduction of alkyl residue from n-butyl-
lithium into compound 21.
stituent in the aromatic ring at positions 2 and 6 of pyran
7. 2,6-(4'-Fluorophenyl)-4-benzotriazolylpyran (7c) fol-
lowing lithiation with n-butyllithium and treatment with
an electrophile forms exclusively 10c even if a very
active electrophile such as benzyl bromide was used.
Furthermore, we found that the anionic species 8b,c on
lithiation with n-butyllithium in the presence of HMPA
did not react with electrophiles but rearrange to 10b,c.
However, under these conditions the reactivity of anion
8a is greatly enhanced by the addition of two equiva-
lents of HMPA, so that reaction with weakly elec-
trophilic bromododecane gave the corresponding 2,6-
diphenyl-4-dodecylpyrylium perchlorate (18a) in 44%
yield.
Ph
Ph
n-BuLi
-80 °C
Bu
-
28%
Ph
O
20
Ph
Ph Ph
21
-30 °C
The formation of cyclopentadienols 10a–c originates
from a rearrangement of anion 8a–c through bicyclic
intermediates 9a–c followed by intramolecular oxirane
ring opening (Scheme 2). We conclude that most active
electrophiles attack anion 8 at the 4-position to form
substitution products (12–19), but, in the presence of
less reactive electrophiles, anion 8 transforms to 9 and
subsequently to 10 (Scheme 2). The mechanism pro-
posed is consistent with the fluoro-substituted pyran (7c)
rearranging in preference to treating with an electrophile.
Electron withdrawing substituents stabilize both the nC
and π*CC MOs involved in the formation of new (C-2)–
(C-6) bond. In the same time the energy gap between
Ph
Ph
OEt
HO
O
P
OEt
Ph
-
Ph
Ph
Ph
Ph
O
Ph
HO
23
22
Scheme 3
Anions of type 8 also behave differently from pyra-
nyl anion (23) stabilized by a diethyl phosphonate moi-
ety. Anion 23 does not rearrange but condenses with a
variety of aryl ketones and aldehydes to form exometh-
ylene substituted pyrans [5, 9].
In contrast to the pyran derivatives 7, the 2',3-bridged
pyran 24 on lithiation, in the absence of electrophile,
gave the imine 25 instead of the expected 27 (Scheme
4).
nC and σ*
MOs becomes larger and cause the in-
convenienCc–eHfaol r substitution process.
A similar rearrangement has been described for the
2,4,6-triphenyl-substituted pyranyl anion 20 [6a]
(Scheme 3). The action in of n-butyllithium large ex-
cess on 2,4,6-triarylpyran in THF at between –80 and
–120 °C gave less than 3% of the pyranyl anion 20 [8]
with 28% rearranged to product 21. An intermediate of
Table 1 Synthesis of 4-substituted 2,6-diaryl-pyrylium perchlorates 12–19 or rearrangement products 10 by indirect electrophilic substitu-
tion
Pyran educt
Electrophile
Substitution product
No
Rearrangement product
No
R
R1
Yield (%)
No
Yield (%)
7a
7b
7c
7a
7a
7c
7a
7a
7a
7a
7c
7a
7a
7b
7c
7c
7a
Ph
– a)
–
–
–
–
–
–
H
Ph
Ph
–
–
–
10a
10b
10c
66
54
66
p-C6H4OMe
p-C6H4F
Ph
Ph
p-C6H4F
Ph
Ph
Ph
Ph
p-C6H4F
– a)
– a)
CH3I
PhCH2Br
PhCH2Br
Cl(CH2)4Br
I(CH2)4I
n-C4H10
n-C6H13Br
n-C6H13Br
n-C12H25
n-C12 25
n-C12 25
n-C12 25
n-C12 25
I(CH2)4I
e
12a
13a
13c
14a
15a
16a
17a
17c
18a
18a
18b
18c
18c
19a
28 b)
81 b)
0
– )
e
– )
10c
62
e
(CH2)3Cl
(CH2)3I
n-C3H8
n-C5H11
n-C5H11
n-C11H23
n-C11H23
n-C11H23
n-C11H23
n-C11H23
(CH2)3R2 d
60
40
32
57
0
–
)
e
– )
e
I
– )
10a
10c
10a
43
60
Ph
Ph
I
I
I
I
I
0
57
e
H
H
H
H
44 c)
0
–
)
p-C6H4OMe
p-C6H4F
p-C6H4F
Ph
10a
10c
10c
60
0
0
66
22 c)
e
)
56
–
)
a) No electrophile was added. b) Literature yield for 12a 19% [12], 24–36% [4, p. 884], 13a – 16% [4, p. 885], 60% [5]. c) In the presence of HMPA (2 equiv).
d) R2 = 2,6-diphenylpyrylium perchlorate. e) No attempt to isolate the rearrangement product was undertaken.
154
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Benzotriazole-Mediated 4-Position Derivatization of 2,6-Diarylpyrylium Cations
___________________________________________________________________________ FULL PAPER
N
NH4Cl sat.
O
Bt
O
O
n-BuLi
25
O
Bt
Bt
O
O
24
-
O
HO
O
O
O
O
27
26
Scheme 4
Preparation of the 4H-(1H-Benzotriazol-1-yl)-2,6-di-
arylpyrans (7a–c, 24) (General Procedure)
In this case, steric compression in the polycyclic in-
termediate 26 disfavors rearrangement to 27. Instead,
the carbanion derived from 24 eliminates nitrogen as
known for numerous examples of benzotriazole stabi-
lized anions [2a].
To a solution of benzotriazole (1.19 g, 10 mmol) dissolved in
dry THF (50 mL) was added NaH (0.40 g of 60% in mineral
oil, 10 mmol). The reaction mixture was stirred at rt for
20 min before adding the 2,6-diarylpyrylium tetrafluorobo-
rate (6) (10 mmol) portionwise. The reaction mixture was
left stirring for 20 min before the precipitating inorganic by–
product was filtered off. Evaporation of the solvent yields
almost quantitative amount of the crude product containing
Bt-1 and Bt-2 isomers in ratio 9:1. The crude mixture was
used for further transformations without purification. Ana-
lytically pure samples of Bt-1 isomer were obtained by crys-
tallization.
Conclucion
We have described a novel rearrangement together with
further examples of simple indirect electrophilic sub-
stitutions of alkyl groups into position 4 of 2,6-di-
arylpyrylium cation 6. These include the synthesis of
hitherto inaccessible pyrylium derivatives with new, tai-
lored properties of potential interest in polymer chem-
istry, solid phase methods, Langmuir-Blodgett method-
ology and for other applications in analytical or sensor
chemistry [10].
4H-(1H-Benzotriazol-1-yl)-2,6-diphenylpyran (7a)
Yield 82%, m.p. 212–214 °C (from ethyl acetate/hexane). –
1H NMR (CDCl3): δ/ppm = 5.77 (d, J = 4.3 Hz, 2H), 6.73 (t,
J = 4.3 Hz, 1H), 7.25–7.33 (m, 2H), 7.34–7.50 (m, 7H), 7.68–
7.82 (m, 5H), 8.00–8.10 (m, 1H). – 13C NMR (CDCl3):
δ/ppm = 52.7, 94.9, 110.6, 120.0, 123.8, 125.1, 127.1, 128.6,
129.7, 132.8, 147.0, 152.3.
We gratefully acknowledge the financial support of DFG for
a stipend to P. C.
C23H17N3O calcd.: C 78.61 H 4.88 N 11.96
(351.41)
found: C 78.26 H 4.87 N 11.94.
4H-(1H-Benzotriazol-1-yl)-2,6-bis(4-methoxyphenyl) pyran
(7b)
Experimental
Yield 70%, m.p. 134–136 °C. –1H NMR (CDCl3): δ/ppm =
3.85 (s, 6H), 5.66 (d, J = 4.2 Hz, 2H), 6.70 (t, J = 4.2 Hz,
1H), 6.95 (d, J = 8.7 Hz, 4H), 7.28–7.42 (m, 2H), 7.42–7.55
(m, 1H), 7.68 (d, J = 8.7 Hz, 4H), 8.06 (m, 1H). – 13C NMR
(CDCl3): δ/ppm = 53.0, 55.3, 93.2, 110.8, 114.0, 119.9, 123.8,
125.4, 126.5, 127.0, 131.8, 146.9, 152.2, 160.7.
Melting points were determined on a Koefler hot stage appa-
ratus and are uncorrected. 1H and 13C NMR spectra were re-
corded at 300 MHz and 75 MHz respectively on a Varian XL
300 spectrometer in CDCl3, CDCl3/DMSO–d6 or CDCl3/
CF3CO2D referenced to Me4Si for the proton spectra and
CDCl3 for the carbon spectra. Elemental analyses were per-
formed on a Carlo Erba 1106 elemental analyzer. Tetrahy-
drofuran (THF) was distilled under nitrogen from sodium–
benzophenone immediately before use. All reactions with
water-sensitive compounds were carried out in dry nitrogen
atmospheres. 2,6-Diarylpyrylium tetrafluoroborates 6a–c
were prepared according to a literature procedure [6], 3,11-
dimethoxy-5H,6H,8H,9H–dibenzo[c,h]xanthenium perchlo-
rate for synthesis of 24 was prepared according to a literature
procedure [11].
C25H21N3O3 calcd.: C 72.97 H 5.15
(411.46) found: C 72.83 H 5.24
N 10.21
N 10.04.
4H-(1H-Benzotriazol-1-yl)-2,6-bis(4-fluorophenyl)pyran
(7c)
Yield 95%, m.p. 120–124 °C (from ether/ethyl acetate). –
1H NMR (CDCl3): δ/ppm = 5.74 (d, J = 4.2 Hz, 2H), 6.72 (t,
J = 4.2 Hz, 1H), 7.05–7.20 (m, 4H), 7.30–7.40 (m, 2H), 7.40–
7.48 (m, 1H), 7.65–7.80 (m, 4H), 8.05–8.13 (m, 1H). –
J. Prakt. Chem. 1999, 341, No. 2
155

A. R. Katritzky et al.
FULL PAPER __________________________________________________________________________
13C NMR (CDCl3): δ/ppm = 52.5, 94.8, 110.3, 115.8 (d, J =
21.7 Hz), 120.2, 123.9, 127.1 (d, J = 8.7 Hz), 127.2, 128.9 (d,
J = 3.2 Hz), 131.8, 147.0, 151.5, 163.6 (d, J = 250.6 Hz).
C23H15F2N3O calcd.: C 71.31 H 3.91 N 10.85
4-(4-Iodobutyl)-2,6-diphenylpyrylium Perchlorate (15a)
Yield 40%, m.p. 177–180 °C. – 1H NMR (CDCl3/CF3CO2D):
δ/ppm = 1.90–2.08 (m, 4H), 3.10–3.20 (m, 2H), 3.22–3.30
(m, 2H), 7.64–7.75 (m, 4H), 7.79 (d, J = 7.5Hz, 2H), 8.22 (d,
J = 7.8 Hz, 4H), 8.26 (s, 2H). – 13C NMR (CDCl3/CF3CO2D):
δ/ppm = 5.5, 29.6, 32.4, 36.5, 118.7, 128.0, 128.5, 130.4,
136.1, 171.1, 176.9. – HRMS: calcd. for C21H20IO: 415.0559
(M–ClO4); found: 415.0558.
(387.39)
found: C 71.08 H 3.73 N 10.87.
1-(3,11-Dimethoxy-5,7,8,9-tetrahydro-6H-dibenzo [c,h]
xanthen-7-yl)-1H-1,2,3-benzotriazole (24)
Yield 65%, m.p. 164–166 °C. – 1H NMR (CDCl3): δ/ppm =
1.76–2.00 (m, 2H), 2.31–2.48 (m, 2H), 2.50–2.67 (m, 2H),
2.72–2.87 (m, 2H), 3.83 (s, 6H), 6.38 (s, 1H), 6.69 (s, 2H),
6.87 (d, J = 8.7 Hz, 2H), 7.27 (t, J = 2.1 Hz, 2H), 7.42 (d, J =
6.9 Hz, 1H), 7.80 (d, J = 8.7 Hz, 2H), 8.05 (d, J = 6.9 Hz,
1H). – 13C NMR (CDCl3): δ/ppm = –23.4, 27.8, 55.3, 59.9,
101.8, 110.5, 111.5, 113.5, 119.9, 122.0, 123.3, 123.9, 127.1,
131.5, 138.3, 145.3, 146.9, 160.0.
4-n-Butyl-2,6-diphenylpyrylium Perchlorate (16a)
Yield 32%, m.p. 203 °C. – 1H NMR (CDCl3/CF3CO2D):
δ/ppm = 1.00 (t, J = 7.2 Hz, 3H), 1.45–1.57 (m, 2H), 1.79–
1.90 (m, 2H), 3.13 (t, J = 7.8 Hz, 2H), 7.68–7.74 (m, 4H),
7.78–7.84 (m, 2H), 8.17–8.25 (m, 6H). – 13C NMR (CDCl3/
CF3CO2D): δ/ppm = 13.4, 22.5, 31.3, 37.7, 118.7, 128.0,
128.4, 130.4, 136.1, 171.1, 178.1.
C29H25N3O3 calcd.: C 75.14 H 5.45
(463.54) found: C 74.99 H 5.48
N 9.07
N 9.07.
C21H21ClO5 calcd.: C 64.87 H 5.44
(388.85)
found: C 65.16 H 5.40.
4-Hexyl-2,6-diphenylpyrylium Perchlorate (17a)
Preparation of the Salts 12–19 (General Procedure)
Yield 57%, m.p. 149–153 °C. – 1H NMR (CDCl3/CF3CO2D):
δ/ppm = 0.89 (t, J = 6.6 Hz, 3H), 1.25–1.40 (m, 4H), 1.42–
1.54 (m, 2H), 1.78–1.92 (m, 2H), 3.07–3.18 (m, 2H), 7.65–
7.74 (m, 4H), 7.74–7.82 (m, 2H), 8.21 (d, J = 5.1 Hz, 4H),
8.22 (s, 1H). – 13C NMR (CDCl3/CF3CO2D): δ/ppm = 13.8,
22.3, 29.0, 29.2, 31.3, 38.0, 116.8, 128.0, 128.4, 130.4, 135.9,
170.9, 178.1.
To a solution of the 2,6-diphenyl-4H-(1H-benzotriazol-1-
yl)pyran (7) (1.25 mmol) in dry THF (30 mL), at –78 °C, was
added n-BuLi (0.78 mL, 1.25 mmol, 1.6M in hexane). The
solution was stirred at –78 °C for 0.5 h, before adding the
electrophile (1.25 mmol) as a solution in dry THF (10 mL).
The reaction mixture was stirred overnight and allowed to
warm up to rt, before being quenched with saturated aqueous
NH4Cl-solution (40 mL), and extracted with diethyl ether
(2 × 30 mL). The combined organic extract was washed with
brine and water and dried with MgSO4. The solvent was re-
moved in vacuo and to the resulting oil, acetic acid (20 mL)
and HClO4 (0.4 mL, 70%) added. The precipitate separating
after addition of water (50 mL) is filtered off and recrystal-
lized from glacial acetic acid/nitromethane (10/1, v/v).
C23H25ClO5 calcd.: C 66.26 H 6.06
(416.91)
found: C 66.31 H 5.83.
4-Dodecyl-2,6-diphenylpyrylium Perchlorate (18a)
Yield 44%, m.p. 128–132 °C (from ethanol/ether). –1H NMR
(CDCl3/CF3CO2D): δ/ppm = 0.89 (t, J = 6.2 Hz, 3H), 1.10–
1.50 (m, 16H), 1.57–1.75 (m, 2H), 1.78–1.93 (m, 2H), 3.19
(t, J = 6.7 Hz, 2H), 7.62–7.90 (m, 6H), 8.27 (d, J = 7.0 Hz,
4H), 8.37 (s, 2H). – 13C NMR (CDCl3/CF3CO2D): δ/ppm =
14.0, 22.6, 29.2, 29.3, 29.4, 29.5, 29.6, 29.7, 31.9, 38.0, 118.8,
128.0, 128.4, 130.3, 135.9, 170.8, 178.1.
4-Methyl-2,6-diphenylpyrylium Perchlorate (12a)
Yield 28%, m.p. 288 °C (lit. [12] 268 °C). –1H NMR (CDCl3/
CF3CO2D): δ/ppm = 2.89 (s, 3H), 7.67–7.74 (m, 4H), 7.77–
7.84 (m, 2H), 8.17–8.24 (m, 6H). – 13C NMR (CDCl3/
CF3CO2D): δ/ppm = 24.1, 120.0, 127.9, 128.4, 130.5, 136.1,
170.9, 180.0.
C29H37ClO5 calcd.: C 69.51 H 7.46
(501.07)
found: C 69.30 H 7.45.
4,4'-(1,4-Butyliden)-bis-2,6-diphenylpyrylium bis-Perchlo-
C18H15ClO calcd.: C 62.35 H 4.36
rate (19a)
(346.77)
found: C 62.47 H 4.27.
1
Yield 56%, m.p. 252.7–254 °C. – H NMR (CDCl3/
4-Benzyl-2,6-diphenylpyrylium Perchlorate (13a)
CF3CO2D): δ/ppm = 2.06–2.22 (m, 4H), 3.08–3.35 (m, 4H),
7.57–7.71 (m, 8H), 7.71–7.82 (m, 4H), 8.22 (d, J = 7.5 Hz,
8H), 8.35 (s, 4H). – 13C NMR (CDCl3/CF3CO2D): δ/ppm =
28.7, 37.2, 119.1, 128.0, 128.5,130.3, 135.9, 171.1, 176.9.
C38H32Cl2O10 calcd.: C 63.42 H 4.49
Yield 81%, m.p. 218 °C (lit. [5] 220 °C). – 1H NMR (CDCl3/
CF3CO2D): δ/ppm = 4.45 (s, 2H), 7.31–7.42 (m, 5H), 7.62–
7.69 (m, 4H), 7.72–7.78 (m, 2H), 8.11–8.16 (m, 6H). –
13C NMR (CDCl3/CF3CO2D): δ/ppm = 43.2, 118.7, 127.9,
128.4, 128.5, 129.7, 130.3, 134.1, 136.0, 171.2, 175.6.
C24H19ClO5 calcd.: C 68.17 H 4.53
(719.58)
found: C 63.51 H 4.56.
(422.86):
found: C 67.96 H 4.44.
Transformation of the 4-(1H-Benzotriazol-1-yl)-2,6-di-
arylpyrans to 10a–c and 25 (General Procedure)
4-(4-Chlorobutyl)-2,6-diphenylpyrylium Perchlorate (14a)
1
To a solution of 4H-(1H-benzotriazol-1-yl)-2,6-diarylpyran
(0.63 mmol) in THF (15 mL) was added n-BuLi (0.45 mL,
1.41M solution in hexane, 0.63 mmol) at –78 °C under argon.
After 30 minutes, the reaction mixture was allowed to warm
up to rt and stirred overnight, quenched with water, extracted
with ethyl acetate and dried over MgSO4. The solvent was
removed, and the residue was washed with diethyl ether to
give pure product.
Yield 60%, m.p. 174 – 175.5 °C. – H NMR (CDCl3/
CF3CO2D): δ/ppm = 1.90–2.20 (m, 4H), 3.18–3.30 (m, 2H),
3.60–3.72 (m, 2H), 7.70–7.90 (m, 6H), 8.35 (d, J = 7.5 Hz,
4H), 8.63 (s, 2H). – 13C NMR (CDCl3/CF3CO2D) : δ/ppm =
25.7, 31.1, 36.0, 43.7, 118.6, 127.5, 127.9, 129.6, 135.0, 169.9,
176.4.
C21H20Cl2O5 calcd.: C 59.59 H 4.76
(423.29)
found: C 59.52 H 4.70.
156
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Benzotriazole-Mediated 4-Position Derivatization of 2,6-Diarylpyrylium Cations
___________________________________________________________________________ FULL PAPER
amount of p-toluenesulfonic acid monohydrate (30 mg) in
acetic acid (10 mL) was refluxed for 30 min. The reaction
mixture was cooled and diluted with water (50 mL), extract-
ed with ethyl acetate (50 mL), washed with water, and dried
over MgSO4. The solvent was removed under vacuum, and
the residue was chromatographed through a silica gel column
using 10% (vol.) of ethyl acetate in hexanes to give pure prod-
uct as colorless crystals (yield 51%), m.p. 149.0–150.0 °C,
(Lit. [7] m.p. 147.0–148.0 °C). – 1H NMR (CDCl3): δ/ppm =
2.80–3.06 (m, 2H), 3.50 (s, 1H), 6.64 (s, 1H), 7.20–7.38 (m,
6H), 7.44 (d, J = 7.2 Hz, 2H), 7.53 (d, J = 7.2 Hz, 2H). –
13C NMR (CDCl3/CF3CO2D): δ/ppm = 56.5, 81.5, 124.2,
127.4, 128.7, 128.8, 129.2, 130.8, 131.4, 144.1, 174.3, 205.3.
4-(1H-Benzotriazol-1-yl)-1,2-diphenyl-2,4-cyclopentadien-
1-ol (10a)
Crude product was crystallized from ethyl acetate to give the
title compound as colorless crystals (yield 66%), m.p. 218–
219 °C. – 1H NMR (CDCl3/DMSO): δ/ppm = 5.38 (s, 1H),
5.66 (s, 1H), 5.94–6.16 (m, 6H), 6.26–6.39 (m, 3H), 6.47 (t,
J = 7.6 Hz, 1H), 6.54 (d, J = 7.2 Hz, 2H), 6.60 (s, 1H), 6.93
(d, J = 8.4 Hz, 1H), 7.01 (d, J = 8.4 Hz, 1H). – 13C NMR
(CDCl3/DMSO): δ/ppm = 85.7, 110.6, 119.1, 120.5, 123.9,
124.7, 126.1, 126.1, 127.0, 127.3, 127.4, 127.5, 127.7, 130.5,
131.5, 135.3, 139.4, 145.3, 153.0.
C23H17N3O calcd.: C 78.61 H 4.89
(351.41) found: C 78.30 H 4.83
N 11.96
N 11.97.
4-(1H-Benzotriazol-1-yl)-1,2-bis-(4-methoxyphenyl)-2,4-cy-
clopentadien-1-ol (10b)
X–Ray Crystallography
Intensity data were collected with a Siemens SMART CCD
area detector using monochromatized Mo Kα (λ = 0.71073 Å)
radiation. The crystal used was a colorless wedge of dimen-
sions 0.65 × 0.45 × 0.32 mm. A total of 10500 reflections
were collected, which after merging (Rint = 0.0456) gave 2 541
uniques reflections. The intensities were corrected for Lorentz
and polarization effects and for absorption (Tmax = 0.974, Tmin
= 0.948).
The structure was solved by direct methods using
SHELXS90 [13], and refined on F2 by full-matrix least-
squares procedures using SHELXL96 [14]. All non-hydro-
gen atoms were refined with anisotropic displacement coef-
ficients. Hydrogen atoms were included in calculated posi-
tions with isotropic displacement coefficients equal to 1.2
times the isotropic equivalent of their carrier carbons, except
for the OH hydrogen whose position was refined. The func-
Crude product was washed with diethyl ether to give the title
compound as colorless crystals (yield 54%), m.p. 200–
201 °C. – 1H NMR (CDCl3/DMSO): δ/ppm = 3.72 (s, 3H),
3.76 (s, 3H), 6.42 (s, 1H), 6.69 (s, 1H), 6.76–6.90 (m, 3H),
7.42 (d, J = 8.4 Hz, 2H), 7.46–7.58 (m, 2H), 7.60–7.72 (m,
3H), 8.06 (d, J = 8.1 Hz, 1H), 8.16 (d, J = 8.1 Hz, 1H). –
13C NMR (CDCl3): δ/ppm = 54.8, 54.9, 86.0, 111.9, 113.5,
113.6, 118.6, 119.7, 124.9, 125.1, 125.3, 125.9, 128.4, 128.7,
131.0, 132.5, 135.5, 145.7, 153.2, 158.1, 158.9.
C25H21N3O3 calcd.: C 72.97 H 5.15 N 10.21
(411.46)
found: C 73.15 H 5.41 N 9.98.
4-(1H-Benzotriazol-1-yl)-1,2-bis-(4-fluorophenyl)-2,4-cy-
clopentadien-1-ol (10c)
Crude product was washed with diethyl ether to give the title
compound as colorless crystals (yield 66%), m.p. 201–
202 °C. – 1H NMR (CDCl3/DMSO): δ/ppm = 6.26 (s, 1H),
6.57 (s, 1H), 6.91–7.05 (m, 4H), 7.48 (t, J = 7.8 Hz, 1H),
7.52–7.64 (m, 4H), 7.64–7.74 (m, 2H), 7.83 (d, J = 7.8 Hz,
1H), 8.12 (d, J = 8.1 Hz, 1H). – 13C NMR (CDCl3/DMSO):
δ/ppm = 85.6, 110.8, 114.5 (d, J = 21.6 Hz), 119.4, 120.5
(broad), 124.2, 124.3 (broad), 126.0 (d, J = 7.8 Hz), 128.0,
128.1 (d, J = 7.8 Hz), 130.7, 135.2, 135.6, 145.6, 152.0, 161.1
(d, J = 244 Hz), 161.5 (d, J = 247 Hz).
tion minimized was Σw(Fo – Fc ), with w = [σ2(Fo ) +
2
2
2
0.0396P2 + 0.402P]–1, where P = [max(Fo ) + 2Fc ]/3. A fi-
nal difference map showed no features greater or less than
0.25 e–/Å3. Full tabulations of atom coordinates, bond lengths
and bond angles, anisotropic thermal parameters and struc-
ture factors are available from the author PJS.
2
2
Crystal data at –110 °C : C17H14O2, Mr = 250.28, monoclin-
ic, space group P21/c, a = 9.6253(5), b = 18.3036(9), c =
7.4087(3) Å, β = 93.108(1), U = 1 302.2(1) Å3, F(000) = 528,
C23H15F2N3O calcd.: C 71.31 H 3.91
(387.39) found: C 70.86 H 3.94
N 10.85
N 10.56.
Z = 4, Dc = 1.277 g cm-3, µ(Mo–Kα) = 0.083 mm–1, 2θmax
=
53°, 175 parameters, wR2 = 0.1086 for all 2541 data, R1 =
0.0450 for 2 336 data with Fo > 4σ(Fo).
N-(3,11-Dimethoxy-5,6,8,9-tetrahydro-7H-dibenzo[c,h]
xanthen-7-ylidene)-N-phenylamine (25)
Crude product was washed with diethyl ether to give the title
compound as colorless crystals (yield 66%), m.p. 201–
203 °C. – 1H NMR (CDCl3/DMSO): δ/ppm = 1.90–2.25
(broad, 2H), 2.40–2.75 (broad, 2H), 2.75–3.20 (broad, 4H),
3.84 (s, 6H), 6.60–7.10 (m, 7H), 7.20 (t, J = 7.7 Hz, 2H),
7.77 (d, 2H, J = 8.5 Hz). – 13C NMR (CDCl3/DMSO): δ/ppm
= 28.06, 55.32, 112.02, 113.1 (broad), 120.08, 121.3, 122.2,
124.1 (broad), 128.2, 139.8 (broad), 151.8, 153.2, 160.8
(broad).
References
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[3] a) G. R. Geen, J. M. Evans, A. K. Vong in ‘Comprehensive
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C29H25NO3 calcd.: C 79.97 H 5.80
(435.53) found: C 79.59 H 5.93
N 3.22
N 3.21.
3,4-Diphenyl-4-hydroxy-cyclopent-2-enone (11a)
The mixture of 4-(benzotriazol-1-yl)-1,2-diphenyl-2,4-cy-
clopentadien-1-ol (10a) (0.52 g, 1.48 mmol) and catalytic
J. Prakt. Chem. 1999, 341, No. 2
157

A. R. Katritzky et al.
FULL PAPER __________________________________________________________________________
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Address for correspondence:
Prof. Dr. Alan R. Katritzky
Center for Heterocyclic Compounds
Department of Chemistry
University of Florida
Gainesville, Florida 32611–7200, USA
Fax: Intern. code (352) 392 9199
E–mail katritzky@chem.ufl.edu
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J. Prakt. Chem. 1999, 341, No. 2