p-Quinoid compounds by nucleophilic aromatic substitution with hydride as leaving group

Article abstract of DOI:10.1002/ejoc.200700177

Triarylmethylium tetrafluoroborates with a sterically shielded cationic center react with selected C- and N-nucleophiles under nucleophilic aromatic substitution to give dipolar p-quinoid final products. The mechanistic rationale includes a hydride leavin

Full text of DOI:10.1002/ejoc.200700177

FULL PAPER
DOI: 10.1002/ejoc.200700177
p-Quinoid Compounds by Nucleophilic Aromatic Substitution with Hydride as
Leaving Group
Marcel Hagel,[a] Jianhui Liu,[a] Oliver Muth,[a] Hebert Jesus Estevez Rivera,[a]
Erik Schwake,[a] Lertnarong Sripanom,[a] Gerald Henkel,[b] and Gerald Dyker*[a]
Keywords: Triarylmethylium salts / Nucleophilic aromatic substitution / Hydride leaving group / p-Quinoid compounds
Triarylmethylium tetrafluoroborates with a sterically shielded
cationic center react with selected C- and N-nucleophiles un-
der nucleophilic aromatic substitution to give dipolar p-qui-
noid final products. The mechanistic rationale includes a hy-
dride leaving group in analogy to the Tschitschibabin reac-
tion.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
impossible with these nucleophiles, and indeed, p-quinoid
products of type 6 were isolated in good to excellent yields;
with one exception: in the case of the dipyridylmethane D –
the least acidic pronucleophile of Scheme 2 – we obtained
the triarylmethane 5.1D exclusively. As a mechanistic ra-
tionale we assume, that the cross-conjugated structures 4[5]
are intermediates for both, products of type 5 and 6. A
rearrangement analogous to the transformation of 4.1D to
5.1D was reported earlier by Zaugg et al.[6] refering to the
reaction of triphenylmethyl tetrafluoroborate with di-tert-
butyl malonate. If the basic reaction conditions are suitable
Introduction
Triarylmethylium salts – stabilized by an extensive delo-
calization of the cation – found widespread application in
various aspects of organic chemistry, for instance as dyes,
indicators, one-electron-oxidants and activators for olefin
polymerization.[1] In the course of our studies towards the
construction of extended π-systems with multiple coordina-
tion sites for transition metals we tested sterically hindered
triarylmethylium salts as substrates for nucleophilic aro-
matic substitution.[2] With methoxy- and with fluoro-sub-
stituents as leaving groups and with various pronucleophiles
we obtained satisfying yields of dipolar p-quinoid com-
pounds.[3] Herein we report on our observation, that this
type of products is also accessible with hydride as leaving
group.
Results and Discussion
Triarylmethyl alcohols 1 are easily synthesized from the
corresponding diaryl ketone and a metallated arene, gen-
erally with yields in the range of 60 to 80%, even for the
sterically rather crowded mesityl-substituted xanthenol
1.1[4] (Scheme 1). The transformation to the tetrafluorobo-
rate 2 also follows the standard procedure with tetrafluo-
roboric acid as reagent. Among the eight model electro-
philes 2.1 to 2.8 the reactivity of the mesityl-substituted tet-
rafluoroborate 2.1 was tested with all of our five model nu-
cleophiles A–E, including 8-aminoquinoline (E) as N-nu-
cleophile. Since the central carbon atom of 2.1 is sterically
rather shielded, formation of products of type 3 should be
[a] Fakultät für Chemie und Biochemie, Ruhr-Universität
Bochum,
Universitätsstrasse 150, 44780 Bochum, Germany
E-mail: gerald.dyker@ruhr-uni-bochum.de
[b] Department Chemie, Universität Paderborn,
Warburger Strasse 100, 33098 Paderborn, Germany
Scheme 1. Mechanistic rationale for the reactions of nucleophiles
with triarylmethylium salts of type 2.
Eur. J. Org. Chem. 2007, 3573–3582
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G. Dyker et al.
FULL PAPER
for a fast deprotonation of the HNu group of 4, the mech-
anistic pathway to 6 becomes possible: the anionic charge
of the Nu– group then activates hydride as leaving group,
thus generating the energetically favourable dipolar π-sys-
tem 6 with aromatic character. Presumably its a rather facile
process, judged from the immediate change to the intensive
characteristic color of the products. We consider this pro-
cess to be related to the Tschitschibabin reaction,[7,8] which
is known as an early example of a hydride elimination, also
energetically profiting from rearomatization.
Figure 1. Structure of p-quinoid dibenzopyran 6.2A in the crys-
tal.[9]
Scheme 2. List of the tested C- and N-nucleophiles (or prenucleo-
philes, respectively).
ine 6.1E during chromatographic work-up on silica gel
(Table 1).
In order to further demonstrate the generality of this ap-
Since the cycloheptanylium tetrafluoroborate 2.5 seemed
proach to products of type 6 we also varied the electrophile to be sensitive to oligomerization, we chose a special pro-
1, this time constantly with malononitrile (A) as nucleo- cedure for the synthesis of 6.5: directly starting from the
phile: as long as the central carbon of the triarylmethyl sys- tertiary alcohol 1.5 and malononitrile in DMF as polar sol-
tem is shielded by two methyl groups as in 2.2 to 2.5 (with vent at elevated temperature, thus saving one preparative
unreactive bridging units) the p-quinoid compounds 6 are step. In this case dissociation delivers the basic hydroxide,
always isolated as the main products. The structure of 6.2A which deprotonates malononitrile. However, the 37% yield
was confirmed by X-ray crystal structure analysis (Fig- of 6.5 is only moderate: main reaction pathway is the trans-
ure 1).[9,10] The extended length of 140.1 pm of the exocyclic formation to the olefinic product 9 in 59% yield; obviously
double bond indicates its distinct push-pull character.[11]
the intermediary cation is deprotonated at the ethandiyl
In the case of the thioxanthenylium salt 2.4 a test reac- bridge to give a highly reactive o-quinoid compound, which
tion in the NMR tube at –40 °C clearly showed the interme- rearranges to the final product (Scheme 3).
1
diary cross-conjugated system 4.4A, with the diagnostic H
The unbridged model compound 2.6 also reacts with ma-
NMR signals of the alkyl and vinyl hydrogens at 3.75, 4.04, lononitrile to the corresponding p-quinoid product 6.6.
5.58, 5.72 and 6.14 ppm. On a preparative scale we ob- Most interestingly, the xylyl-substituted xanthenylium salt
tained the quinonmethide 7 as a by-product, presumably a 2.7 with just one shielding methyl group is still sterically
result of basic hydrolization of 2.4. The related compound hindered enough for the formation of the quinoid com-
8 we isolated after partial hydrolization of the sensitive im- pound 6.7A. The 4-tolyl-substituted xanthenylium salt 2.8
Table 1. Yield (%) of products for the reactions of Scheme 1.
Entry
X
O
Ar
1[a]
2
Nucleophile
3
5
6
1
2
3
4
5
6
7
8
2,4,6-trimethylphenyl
79 (1.1)
98
A
B
C
D
E
A
A
A
A
A
A
A
96
94
61
93
32
58
90
49
37
30
15
O
O
S
4-methoxy-2,6-dimethylphenyl
4-(dimethylamino)-2,6-dimethylphenyl
4-methoxy-2,6-dimethylphenyl
4-methoxy-2,6-dimethylphenyl
15 (1.2)
71 (1.3)
71 (1.4)
76 (1.5)
60 (1.6)
94 (1.7)
43 (1.8)
90
88
93
9
C2H4
not isol.
86
10
11
12
H···H[b] 4-methoxy-2,6-dimethylphenyl
O
O
2,4-dimethylphenyl
4-methylphenyl
92
95
37
65
[a] Yield of 1 synthesized by the reaction of the aryl-Li species with the specific ketone. [b] No bridging group X.
3574 Eur. J. Org. Chem. 2007, 3573–3582
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Functionalized p-Quinoid π-Systems
FULL PAPER
(70 eV, EI): m/z (%) = 316 (14) [M+], 299 (33), 197 (100). C22H20O2
(316.40): calcd. C 83.52, H 6.37; found C 83.55, H 6.45.
9-Hydroxy-9-(4-methoxy-2,6-dimethylphenyl)xanthene (1.2): To a
solution of 500 mg (2.25 mmol) of 4-bromo-3,5-dimethylanisol in
10 mL of dry THF was added 1.6 mL (2.5 mmol) of n-butyllithium
(15% in hexane) at –30 °C. The colorless solution was stirred for
1 h and a solution of 455 mg (2.32 mmol) xanthone in 20 mL of
dry dioxane was added dropwise within 15 min. The reaction mix-
ture was stirred at reflux temperature for 21 h and was hydrolyzed
with 20 mL of saturated aqueous diammonium hydrogen phos-
phate solution. After extraction with CH2Cl2 (three times 20 mL)
and concentration of the combined organic layer in vacuo the crude
product was purified by flash chromatography (silica, n-hexane/
Et2O, 4:1, Rf = 0.44 (1.2), 0.37 (xanthone)) and dried in vacuo
(50 °C, 0.5 mbar, 4 h): 110 mg (15%) of a brownish needles 1.2 with
m.p. 183–185 °C (in addition to 340 mg (75%) recovered starting
material xanthone). IR (KBr): ν = 3512 (s), 3071 (w), 2937 (w),
˜
2835 (w), 1601 (s), 1571 (m), 1477 (s), 1447 (s), 1315 (s), 1302 (s),
1241 (m), 1193 (w), 1138 (m), 1124 (m), 1099 (w), 1071 (w), 1043
(w), 1005 (w), 894 (w), 874 (w), 750 (s) cm–1. UV (acetonitrile):
λmax (log ε) = 194 (4.73, sh), 203 (4.79), 239 (4.35), 281 (3.59), 290
(3.59) nm. 1H NMR (CDCl3, 300 MHz): δ = 2.06 (s, 1 H, OH),
2.13 (s, 6 H, CH3), 3.77 (s, 3 H, OCH3), 6.54 (s, 2 H, 3-H/5-H),
7.01 (“dt”, “J” = 8.0, 7.3, 1.1 Hz, 2 H), 7.13–7.19 (m, 4 H), 7.29
(ddd, J = 8.4, 7.2, 1.7 Hz, 2 H) ppm. 13C NMR {1H} (CDCl3,
75.5 MHz): δ = 24.61 (q), 54.96 (q), 74.11 (s, C–OH), 115.90 (d),
116.39 (d), 123.58 (d), 128.06 (s), 128.33 (d), 129.08 (d), 133.80 (s),
139.06 (s), 149.40 (s), 157.85 (s) ppm. MS (70 eV, EI): m/z (%) =
333 (8) [M+ + 1], 332 (34) [M+], 316 (10), 315 (37), 198 (19),
197 (100), 136 (43). C22H20O3 (332.40): calcd. C 79.50, H 6.06;
found C 79.50, H 6.05.
Scheme 3. Additional isolated and identified products.
finally is sterically open for the classical reaction pathway
to 3.8A.
Our results represent a straightforward and efficient ac-
cess to polar p-quinoid π-systems, attached with functional
groups which can trigger the electronic properties: we in-
tend to test these products as bidentate redoxactive ligands
in transition metal catalysis.
Experimental Section
9-(4-Dimethylamino-2,6-dimethylphenyl)-9-hydroxyxanthene (1.3):
To a solution of 550 mg (2.00 mmol) of 3,5,N,N-tetramethyl-4-
iodoaniline in 5 mL of dry THF was added 0.88 mL (2.2 mmol) of
n-butyllithium (2.5  in hexane) at –78 °C. The colorless solution
was stirred for 0.5 h and a solution of 314 mg (1.60 mmol) xan-
thone in 10 mL of dry dioxane was added at –60 °C. The reaction
mixture was stirred at reflux temperature for 6 h and was hy-
drolyzed with 25 mL of saturated aqueous ammonium chloride
solution. After extraction with diethyl ether (twice 20 mL) and con-
centration of the combined organic layer in vacuo the crude prod-
uct was purified by flash chromatography (silica, petroleum ether/
Et2O, 5:1, Rf = 0.63 (1.3), 0.35 (xanthone)): 390 mg (71%) of a
General Remarks: Melting points (uncorrected): Reichert Thermo-
var. IR: Perkin–Elmer 841 and 983. NMR: Bruker DPX-200, WM-
300, DRX-400, AM-500. 1H NMR spectra were recorded in CDCl3
with TMS as the internal standard. 13C NMR spectra were mea-
sured by using CDCl3 as the solvent and the internal standard.
MS: MAT 700 ITD (70 eV) and Varian MAT 311 A. For analytical
TLC precoated plastic sheets “POLYGRAM SIL G/UV254” from
“Macherey–Nagel” were used. EA: Elementar/Hanau Vario EL.
9-Hydroxy-9-(2,4,6-trimethylphenyl)xanthene (1.1): To a solution of
1.49 g (1.13 mL, 7.50 mmol) 2-bromomesitylene in 17 mL of dry
THF was added 3.30 mL (8.26 mmol) of n-butyllithium (2.5  in
hexane) at –30 °C. The colorless solution was stirred for 30 min
and a solution of 0.98 g (5.00 mmol) xanthone in 28 mL of dry
dioxane was added dropwise within 15 min. The reaction mixture
was stirred at room temperature for 24 h and hydrolyzed with
20 mL of saturated aqueous diammonium hydrogen phosphate
solution. After extraction with CH2Cl2 (3ϫ20 mL) and concentra-
tion of the combined organic layer in vacuo the crude product was
purified by flash chromatography (silica, PE/Et2O, 10:1, Rf = 0.25)
and dried in vacuo (50 °C, 0.5 mbar, 4 h): 1.24 g (79%) of the color-
less solid 1.1 with m.p. 193–194 °C (ref.[4,12] m.p. 192.5–193.5 °C
colorless solid 1.3 which decomposes at 182–185 °C. IR (KBr): ν =
˜
3407 (m), 3079 (w), 2963 (m), 2930 (m), 1657 (m), 1606 (s), 1574
(m), 1477 (s), 1459 (s), 1447 (s), 1347 (m), 1332 (m), 1311 (m), 1239
(s), 1113 (s), 830 (m), 758 (s) cm–1. UV (acetonitrile): λmax (log ε)
= 213 (4.72), 244 (4.33), 265 (3.65) nm. 1H NMR (CDCl3,
500 MHz): δ = 2.02 (s, 1 H), 2.12 (br. s, 6 H), 2.93 (s, 6 H), 6.38
(s, 2 H), 6.99–7.02 (m, 2 H), 7.16–7.21 (m, 4 H), 7.28 (“t”, “J” =
7.73 Hz, 2 H) ppm. 13C NMR {1H} (CDCl3, 125 MHz): δ = 24.79
(q), 40.24 (q), 74.03 (s), 114.61 (d), 116.23 (d), 123.45 (d), 128.40
(d), 128.41 (d), 128.84 (s), 129.80 (s), 138.15 (s), 148.92 (s), 149.33
(s) ppm. MS (70 eV, EI): m/z (%) = 345 (10) [M+], 328 (38), 312
(14), 197 (100), 149 (93), 134 (16). C23H23NO2 (345.44): calcd. C
79.97, H 6.71, N 4.05; found C 79.99, H 6.97, N 4.00.
dec.). IR (KBr): ν = 3518 (s), 3037 (w), 2970 (m), 2921 (m), 2859
˜
(w), 1602 (s), 1574 (m), 1479 (s), 1446 (s), 1315 (s), 1293 (s), 1242
(s), 1203 (m), 1099 (m), 1043 (m), 1026 (m), 1002 (s), 894 (s), 874
1
(s), 747 (s), 629 (m) cm–1. H NMR (CDCl3, 500 MHz): δ = 2.08
(s, 1 H), 2.13 (br. s, 6 H), 2.28 (s, 3 H), 6.83 (br. s, 2 H), 7.02 9-Hydroxy-9-(4-methoxy-2,6-dimethylphenyl)thioxanthene (1.4): To
(“t”, “J” = 7.5 Hz, 2 H), 7.16 (dd, J = 7.8, J = 1.65 Hz, 2 H), 7.20
(dd, J = 8.25, J = 1.2 Hz, 2 H), 7.31 (“t”, “J” = 7.7 Hz, 2 H) ppm.
a solution of 1.00 g (4.51 mmol) of 4-bromo-3,5-dimethylanisol in
20 mL of dry THF was added 2.8 mL (4.5 mmol) of n-butyllithium
13C NMR {1H}: δ = (CDCl3, 125 MHz): δ = 20.58 (q), 24.20 (q, (15% in hexane) at –45 °C. The colorless solution was stirred for
br.), 74.31 (s), 116.39 (d), 123.60 (d), 127.94 (s), 128.35 (d), 129.10
(d), 131.75 (d), 136.61 (s), 137.35 (s), 138.40 (s), 149.45 (s) ppm. MS
1 h and a solution of 637 mg (3.00 mmol) thioxanthone in 25 mL
of dry dioxane/THF (4:1) was added dropwise within 15 min. The
Eur. J. Org. Chem. 2007, 3573–3582
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3575

G. Dyker et al.
FULL PAPER
orange suspension was stirred at reflux temperature for 5 d and was
hydrolyzed with 20 mL of saturated aqueous diammonium hydro-
gen phosphate solution. After extraction with CH2Cl2 (three times
20 mL) and concentration of the combined organic layer in vacuo
a crude product was obtained, containing 750 mg (71%) of thiox-
anthenol 1.4. Purification by flash chromatography (silica, n-hex-
ane/acetone, 10:1, Rf = 0.31 (thioxanthone), 0.20 (1.4)) gave an
analytically pure sample of 133 mg (13%) of the greenish solid 1.4
–60 °C. The reaction mixture was stirred at room temperature for
3 h and at reflux temperature for 18 h and was hydrolyzed with
20 mL of saturated aqueous diammonium hydrogen phosphate
solution. After extraction with diethyl ether (three times 20 mL)
and with CH2Cl2 (three times 20 mL) and concentration of the
combined organic layer in vacuo the crude product was purified by
flash chromatography (silica, diethyl ether/n-hexane, 1:5): Rf
=
0.42, 0.28 (1.6)) and dried in vacuo (50 °C, 0.5 mbar, 4 h): 428 mg
with m.p. 132 °C. IR (KBr): ν = 3520 (m), 3059 (w), 2963 (w), 2937
(60%) of colorless crystals 1.6 with m.p. 110–115 °C. IR (KBr): ν
˜
˜
(w), 2835 (w), 1600 (s), 1467 (s), 1438 (s), 1305 (s), 1270 (m), 1159
(w), 1140 (m), 1125 (m), 1069 (m), 1043 (w), 995 (w), 957 (w), 867
= 3503 (s), 3054 (w), 3011 (w), 2983 (w), 2961 (w), 2935 (w), 2917
(w), 2836 (w), 1598 (br. s, sh), 1449 (br. s, sh), 1341 (m), 1299 (s),
(w), 769 (s), 738 (s), 632 (s) cm–1. UV (acetonitrile): λmax (log ε) = 1163 (s), 1132 (s), 1067 (s), 1045 (m), 1030 (m), 1008 (m), 1001 (m),
197 (4.78), 205 (4.74, sh), 241 (4.12, sh), 271 (4.15), 285 (3.95, sh), 959 (m), 851 (s), 772 (s), 698 (s) cm–1. UV (acetonitrile): λmax (log
378 (2.21) nm. 1H NMR (CDCl3, 300 MHz): δ = 2.09 (s, 6 H), 2.17 ε) = 198 (4.83), 207 (4.77, sh), 235 (3.96, sh) nm. 1H NMR (CDCl3,
(s, 1 H, OH), 3.81 (s, 3 H, OCH3), 6.59 (s, 2 H, 3-H/5-H), 7.04– 300 MHz): δ = 1.87 (s, 6 H), 2.73 (s, 1 H, OH), 3.78 (s, 3 H), 6.54 (s,
7.13 (m, 4 H), 7.22 (ddd, J = 8.8, 6.6, 2.0 Hz, 2 H), 7.35 (dd, J =
7.9, 0.9 Hz, 2 H) ppm. 13C NMR {1H} (CDCl3, 75.5 MHz): δ =
24.65 (q, CH3), 55.01 (q, OCH3), 79.94 (s, C-OH), 115.84 (d),
125.40 (d), 126.31 (d), 127.70 (d), 128.96 (s), 129.02 (d), 133.80 (s),
138.61 (s), 139.31 (s), 157.87 (s) ppm. MS (70 eV, EI): m/z (%) =
349 (8) [M+ + 1], 348 (33) [M+], 332 (14), 331 (50), 214 (16),
213 (100), 212 (21), 184 (21), 136 (17). C22H20O2S (348.46): calcd.
C 75.83, H 5.79; found C 75.78, H 5.80.
2 H, 3-H/5-H), 7.21–7.34 (m, 10 H) ppm. 13C NMR {1H} (CDCl3,
75.5 MHz): δ = 24.71 (q, CH3), 54.99 (q, OCH3), 83.38 (s, C-OH),
115.51 (d), 127.30 (d), 127.87 (d), 128.18 (d), 136.67 (s), 139.89 (s),
147.85 (s), 157.64 (s) ppm. MS (70 eV, EI): m/z (%) = 319 (10) [M+
+ 1], 318 (38) [M+], 301 (29), 300 (11), 241 (31), 223 (24), 183 (26),
165 (19), 163 (25), 136 (21), 105 (100), 77 (35). C22H22O2 (318.42):
calcd. C 82.99, H 6.96; found C 83.07, H 6.95.
9-(2,6-Dimethylphenyl)-9-hydroxyxanthene (1.7): To a solution of
5.55 g (30.0 mmol) of 1-bromo-2,4-dimethylbenzene in 30 mL of
dry THF was added 40.9 mL (60.0 mmol) of n-butyllithium (1.6 
in n-hexane) at –78 °C within 15 min. The colorless suspension was
stirred for 1 h and 5.88 g (30.0 mmol) of xanthone was added in
one portion. The reaction mixture was stirred at room temperature
for 2 h and was hydrolyzed with 30 mL of water. After extraction
with CH2Cl2 (three times 30 mL) the combined organic layer was
dried with sodium sulfate and was concentrated in vacuo. The
crude product was purified by flash chromatography (silica, ethyl
acetate/petroleum ether, 1:5: Rf = 0.27) and dried in vacuo (70 °C,
0.5 mbar, 1 h): 8.49 g (94%) of 1.7 as colorless crystals with m.p.
10,11-Dihydro-5-(4-methoxy-2,6-dimethylphenyl)-5H-dibenzo[a,d]-
cyclohepten-5-ol (1.5): To a solution of 2.50 g (11.3 mmol) of 4-
bromo-3,5-dimethylanisol in 20 mL of dry THF was added
15.3 mL (22.5 mmol) of tert-butyllithium (15% in n-pentane) at
–60 °C. The yellow suspension was stirred for 1 h and a solution
of 2.42 (11.3 mmol) of 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-
5-one in 100 mL of dry dioxane was added dropwise within 30 min
at –40 °C. The reaction mixture was stirred at reflux temperature
for 6 d and was hydrolyzed with 20 mL of saturated aqueous diam-
monium hydrogen phosphate solution. After extraction with di-
ethyl ether (three times 20 mL) and with CH2Cl2 (three times
20 mL) and concentration of the combined organic layer in vacuo
the crude product was purified by flash chromatography (silica, n-
hexane/toluene, 1:1, Rf = 0.26 (diaryl ketone), 0.14 (1.5)) and dried
in vacuo (50 °C, 0.5 mbar, 4 h): 2.95 (76%) of colorless solid 1.5
172–173 °C. IR (KBr): ν = 3510 (m), 2914 (m), 1924 (w), 1700 (w),
˜
1601 (m), 1573 (m), 1477 (s), 1446 (m), 1380 (m), 1357 (m), 1312
(s), 1291 (s), 1237 (s), 1205 (s), 1176 (m), 1153 (m), 1116 (m), 1001
(m), 1040 (m), 991 (s), 946 (m), 929 (m), 896 (m), 874 (s), 824 (m),
798 (m), 759 (s) cm–1. UV (acetonitrile): λmax (log ε) = 239 (3.64),
with m.p. 143–145 °C. IR (KBr): ν = 3493 (s), 3056 (w), 3003 (w),
˜
1
2963 (m), 2935 (m), 2838 (w), 1599 (s), 1476 (s), 1443 (s), 1304 (s),
281 (3.45), 289 (3.51) nm. H NMR (CDCl3, 400 MHz): δ = 1.48
1196 (m), 1166 (m), 1140 (m), 1108 (m), 1070 (m), 1033 (m), 1017 (s, 3 H), 2.41 (s, 3 H), 2.44 (s, 1 H, OH), 6.90 (br. s, 1 H), 7.06 (“t”,
(m), 962 (w), 944 (w), 852 (m), 781 (w), 764 (m), 753 (s) cm–1. UV “J” = 7.8 Hz, 2 H), 7.15 (dd, J = 7.8, 1.8 Hz, 2 H) 7.24–7.28 (m,
(acetonitrile): λmax (log ε) = 205 (4.85), 238 (4.19, sh) nm. 1H NMR 3 H), 7.37 (“t”, “J” = 7.8 Hz, 2 H), 8.28 (d, J = 7.8 Hz, 1 H) ppm.
(CDCl3, 300 MHz): δ = 1.75 (s, 6 H, CH3), 2.39 (s, 1 H, OH), 2.70– 13C NMR {1H} (CDCl3, 125 MHz): δ = 20.52 (q), 20.93 (q), 69.85
2.80 (m, 4 H, CH2), 3.77 (s, 3 H, OCH3), 6.48 (s, 2 H, 3-H/5-H),
(s), 116.29 (d), 123.52 (d), 125.88 (d), 125.90 (d), 126.05 (s), 128.77
6.92 (dd, J = 7.3, 1.4 Hz, 2 H), 7.04–7.16 (m, 4 H), 7.79 (“d”, “J” (d), 129.21 (d), 132.83 (d), 135.46 (s), 137.34 (s), 140.98 (s), 150.10
= 6.6 Hz, 2 H, br.) ppm. 13C NMR {1H} (CDCl3, 75.5 MHz): δ = (s) ppm. MS (70 eV, EI): m/z (%) = 302 (13) [M+], 286 (4), 285 (20),
24.03 (q), 31.66 (t), 55.01 (q, OCH3), 115.83 (d), 124.30 (s, br.),
126.44 (d), 126.92 (d), 130.62 (d), 135.87 (s, br.), 139.72 (s),
148.15 (s, br.), 158.00 (s) ppm. MS (70 eV, EI): m/z (%) = 344 (16)
[M+], 209 (10), 208 (28), 207 (7), 179 (6), 165 (9), 164 (23), 163
(100), 103 (8). C24H24O2 (344.45): calcd. C 83.69, H 7.02; found C
83.86, H 7.03. An attempt to synthesize the corresponding cyclo-
heptenylium tetrafluoroborate 2.5 by treating the tertiary alcohol
1.5 with HBF4·O(C2H5)2 led to the isolation of a brown to black
presumably polymeric material, which exhibited only broad signals
198 (13), 197 (100), 181 (3), 141 (4), 115 (4), 77(6). C12H18O2
(194.27): calcd. C 83.42, H 6.00; found C 83.38, H 5.98.
9-Hydroxy-9-(4-methylphenyl)xanthene (1.8): To
a solution of
3.70 mL (30.0 mmol) of 4-bromotoluene in 80 mL of dry THF was
added 23.4 mL (37.5 mmol) of n-butyllithium (15% in hexane) at
–78 °C within 5 min. After 30 min additional stirring 5.89 g
(30.0 mmol) of xanthone was added and the reaction mixture was
warmed up to room temperature overnight. After hydrolysis with
20 mL of water and extraction with CH2Cl2 (three times 20 mL)
the organic layer was concentrated to dryness and the residue
recrystallized from pentane. After drying in vacuo for (2 h at
0.5 mbar and 70 °C) 3.75 g (43%) of xanthenol 1.8 as a colorless
solid with m.p. 140–141 °C was obtained (ref.[13–15] m.p. between
141 and 150 °C). 1H NMR (CDCl3, 400 MHz): δ = 2.29 (s, 3H),
2.59 (s, 1 H, OH), 7.09–7.03 (m, 4 H), 7.19 (dd, J = 8.3, 1.0 Hz, 2
H), 7.31–7.26 (m, 5 H), 7.38 (dd, J = 8.1, 1.8 Hz, 2 H) ppm. 13C
1
in the H NMR spectroscopy.
(4-Methoxy-2,6-dimethylphenyl)diphenylmethanol (1.6): To a solu-
tion of 500 mg (2.25 mmol) of 4-bromo-3,5-dimethylanisol in
10 mL of dry THF was added 1.55 mL (2.5 mmol) of n-butyllith-
ium (15% in n-hexane) at –60 °C. The colorless suspension was
stirred for 1 h and a solution of 424 mg (2.33 mmol) of benzophe-
none in 20 mL of dry THF was added dropwise within 5 min at
3576
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Eur. J. Org. Chem. 2007, 3573–3582

Functionalized p-Quinoid π-Systems
FULL PAPER
NMR {1H} (CDCl3, 100 MHz): δ = 21.03 (q), 70.44 (s), 116.43 (d),
1.4 in 2 mL of dry dichloromethane was added 0.13 mL
123.58 (d), 126.17 (d), 127.48 (s), 128.72 (d), 128.98 (d), 129.03 (d), (0.96 mmol) of HBF4·OEt2 (15% in Et2O). After 10 min of stirring
136.40 (s), 145.22 (s), 149.77 (s) ppm.
at room temperature a layer of 15 mL of diethyl ether is carefully
placed on the reaction mixture. Slow diffusion (1 d) led to the for-
mation of a red precipitate, which was collected, washed with Et2O
and dried in vacuo (80 °C, 0.04 mbar, 2 h): 123 mg (93%) of the
9-(2,4,6-Trimethylphenyl)xanthenylium Tetrafluoroborate (2.1):
0.98 g (3.10 mmol) of xanthenol 1.1 in 40 mL of dry diethyl ether
was treated with 1 mL (7.4 mmol) of HBF4 etherate (15% in Et2O).
After 1 h of stirring at room temperature, the slightly yellow pre-
cipitate was collected, washed with Et2O and dried in vacuo
(100 °C, 0.5 mbar, 2 H): 1.16 g (98%) of the yellow solid 2.1 with
deep red solid 2.4 with m.p. 255–260 °C. IR (KBr): ν = 3047 (w),
˜
3003 (w), 2965 (w), 2935 (w), 1632 (w), 1604 (m), 1544 (w), 1451
(m), 1372 (m), 1320 (m), 1198 (w), 1157 (m), 1124 (m), 1084 (s,
br.), 1037 (m), 859 (w), 803 (w), 743 (m), 624 (w) cm–1. UV (aceto-
nitrile): λmax (log ε) = 201 (4.76), 225 (4.43), 247 (4.12, sh), 280
(4.88), 361 (3.74, sh), 381 (4.29), 495 (3.60), 521 (3.57) nm. 1H
NMR (CDCl3, 300 MHz): δ = 1.73 (s, 6 H), 3.96 (s, 3 H, OCH3),
6.92 (s, 2 H, 3-H/5-H), 8.07 (ddd, J = 7.9, 6.8, 1.1 Hz, 2 H), 8.19
(dd, J = 8.7, 0.7 Hz, 2 H), 8.44 (ddd, J = 8.2, 6.8, 1.3 Hz, 2 H),
8.94 (d, J = 8.5 Hz, 2 H) ppm. 13C NMR {1H} (CDCl3, 75.5 MHz):
δ = 20.43 (q, CH3), 55.54 (q, OCH3), 114.06 (d), 125.89 (s), 128.82
(d), 130.25 (s), 132.03 (d), 133.76 (d), 137.29 (s), 138.14 (d), 148.25
(s), 161.34 (s), 172.80 (s) ppm. MS (70 eV, EI): m/z (%) = 333 (8),
332 (327), 331 (100) [M+ – BF4], 273 (13), 271 (10), 197 (7).
C22H19BF4OS (418.26): calcd. C 63.18, H 4.58; found C 63.15, H
4.50.
m.p. 251–254 °C. IR (KBr): ν = 3075 (vw), 1623 (w), 1599 (s), 1576
˜
(w), 1536 (w), 1508 (s), 1436 (w), 1373 (s), 1084 (s), 1053 (s), 761
(m) cm–1. UV (acetonitrile): λmax (log ε) = 197 (4.42), 258 (4.30),
1
372 (4.20), 444 (3.23) nm. H NMR (CDCl3, 200 MHz): δ = 1.83
(s, 6 H), 2.48 (s, 3 H), 7.18 (s, 2 H), 7.27–8.00, (m, 4 H), 8.56–8.67
(m, 4 H) ppm. 13C NMR (CDCl3, 100 MHz): {1H} δ = 20.13 (q),
21.25 (q), 121.11 (d), 124.43 (s), 127.42 (s), 129.23 (d), 129.93 (d),
130.11 (d), 135.34 (s), 141.71 (s), 145.12 (d), 158.49 (s), 177.90 (s)
ppm. MS (70 eV, EI): m/z (%) = 299 (100) [M+ – BF4], 154 (20),
136 (14). C22H19BF4O (386.20): calcd. C 68.42, H 4.96; found C
68.20, H 4.91.
9-(4-Methoxy-2,6-dimethylphenyl)xanthenylium Tetrafluoroborate
(2.2): To a solution of 180 mg (0.542 mmol) of xanthenol 1.2 in
4 mL of dry dichloromethane was added 0.25 mL (1.8 mmol) of
HBF4·OEt2 (15% in Et2O). After 5 min of stirring at room tem-
perature a layer of 10 mL of diethyl ether is carefully placed on
the reaction mixture. Slow diffusion led to the formation of a red
precipitate (2 d), which was collected, washed with Et2O and dried
in vacuo (60 °C, 0.5 mbar, 2 h): 195 mg (90%) of the red solid 2.2
(4-Methoxy-2,6-dimethylphenyl)diphenylmethyl Tetrafluoroborate
(2.6): To a solution of 210 mg (0.66 mmol) of triarylmethanol 1.6
in 5 mL of dry dichloromethane was added 0.25 mL (1.8 mmol) of
HBF4·OEt2 (15% in Et2O). After 5 min of stirring at room tem-
perature a layer of 15 mL of diethyl ether is carefully placed on the
reaction mixture. Slow diffusion (1 d) led to the formation of a red
with m.p. 293–296 °C. IR (KBr): ν = 3050 (w), 3013 (w), 2963 (w), precipitate, which was collected, washed with Et2O and dried in
˜
1621 (w), 1600 (s), 1576 (m), 1535 (m), 1501 (m), 1467 (m), 1371 vacuo (80 °C, 0.04 mbar, 2 h): 219 mg (86%) of violet crystals 2.6
(m), 1352 (w), 1314 (m), 1200 (w), 1166 (w), 1145 (w), 1125 (m), with m.p. 139–142 °C. IR (KBr): ν = 3059 (w), 2936 (w), 1598 (s),
˜
1084 (s, br.), 882 (w), 805 (w), 764 (m) cm–1. UV (acetonitrile): λmax
(log ε) = 202 (4.80), 225 (4.41, sh), 257 (4.70), 274 (3.80), 354 (4.24),
372 (4.63), 443 (3.53) nm. H NMR (CDCl3, 300 MHz): δ = 1.85
(s, 6 H, CH3), 3.95 (s, 3 H, OCH3), 6.95 (s, 2 H, 3-H/5-H), 7.99
(“d”, “J” = 4.0 Hz, 4 H), 8.51 (d, J = 8.8 Hz, 2 H), 8.60–8.66 (m,
2 H) ppm. 13C NMR {1H} (CDCl3, 75.5 MHz): δ = 20.42 (q), 55.65
1583 (s), 1482 (w), 1450 (m), 1352 (m), 1291 (s, sh), 1182 (m), 1155
(m), 1124 (m), 1084 (s, br.), 1038 (m), 995 (w), 771 (w) cm–1. UV
(acetonitrile): λmax (log ε) = 199 (4.80), 253 (3.93), 310 (3.65), 413
1
1
(4.31), 528 (4.26) nm. H NMR (CDCl3, 300 MHz): δ = 1.81 (s, 6
H, CH3), 4.12 (s, 3 H), 7.01 (s, 2 H), 7.59 (d, J = 7.2 Hz, 4 H), 7.80
(t, J = 7.7 Hz, 4 H), 8.13 (t, J = 6.9 Hz, 2 H) ppm. 13C NMR {1H}
(q), 114.20 (d), 120.55 (d), 122.47 (s), 124.68 (s), 130.35 (d), 130.76 (CDCl3, 75.5 MHz): δ = 23.42 (q), 57.33 (q), 118.84 (d), 130.50 (s),
(d), 137.44 (s), 145.37 (d), 158.34 (s), 162.19 (s), 178.76 (s) ppm.
130.89 (d), 139.49 (d), 139.80 (s), 141.67 (d), 142.33 (s), 152.36 (s),
MS (70 eV, EI): m/z (%) = 334 (4) [M+ – BF3], 316 (32), 315 (100)
170.53 (s) ppm. MS (70 eV, EI): m/z (%) = 302 (38), 301 (82) [M+
–
[M+ – BF4], 313 (5), 300 (6), 299 (5), 272 (9), 271 (6), 257 (8), 256 BF4], 300 (46), 299 (100), 287 (20), 285 (20), 284 (16), 269 (11), 253
(5), 255 (10), 199 (12), 181 (8). C22H19BF4O2 (402.20): calcd. C (13), 252 (15), 241 (14), 239 (20), 223 (13), 179 (20), 166 (13), 165
65.70, H 4.76; found C 65.54, H 4.81.
(39), 126 (12). C22H21BF4O (388.21): calcd. C 68.07, H 5.45; found
C 68.01, H 5.39.
9-(4-Dimethylamino-2,6-dimethylphenyl)xanthenylium
Tetrafluo-
roborate (2.3): To a solution of 104 mg (0.300 mmol) of xanthenol
1.3 in 5.5 mL of dry dichloromethane was added 0.041 mL
(0.3 mmol) of HBF4·OEt2 (15% in Et2O). After 5 min of stirring
at room temperature a layer of 12 mL of diethyl ether is carefully
placed on the reaction mixture. Slow diffusion led to the formation
of a red precipitate (24 h), which was collected, washed with Et2O
and dried in vacuo (60 °C, 0.5 mbar, 2 h): 110 mg (88%) of green
9-(2,4-Dimethylphenyl)xanthenylium Tetrafluoroborate (2.7): To a
solution of 300 mg (0.99 mmol) of triarylmethanol 1.7 in 10 mL of
dry dichloromethane was added 0.41 mL (2.9 mmol) of HBF4·OEt2
(15% in Et2O). After 10 min of stirring at room temperature a layer
of 20 mL of diethyl ether is carefully placed on the reaction mix-
ture. Slow diffusion (1 d) led to the formation of a yellow precipi-
tate, which was collected, washed with Et2O and dried in vacuo
(100 °C, 0.5 mbar, 3 h): 280 mg (92%) of 2.7 as yellow solid with
crystals 2.3 with m.p. 260 °C (dec.). IR (KBr): ν = 3060 (w), 2536
˜
(w), 2440 (w), 1623 (m), 1598 (s), 1534 (m), 1508 (s), 1480 (m),
1374 (s), 1084 (vs, br.), 767 (m) cm–1. UV (acetonitrile): λmax (log
ε) = 201 (4.76), 275 (3.80), 374 (4.63) nm. 1H NMR (CDCl3,
400 MHz): δ = 1.88 (s, 6 H), 3.15 (s, 6 H), 6.66 (s, 2 H), 7.80–
8.00 (m, 4 H), 8.40–8.50 (m, 4 H) ppm. 13C NMR {1H} (CDCl3,
125 MHz): δ = 21.33 (q), 40.40 (q), 112.15 (d), 120.75 (d), 124.87
(s), 129.61 (d), 131.15 (d), 137.53 (s), 144.11 (d), 152.29 (s), 157.86
(s), 178.41 ppm. MS (70 eV, EI): m/z (%) = 328 (72) [M+ – BF4],
312 (20), 181 (100), 163 (20), 49 (52).
m.p. 225–230 °C. IR (KBr): ν = 3511 (w), 3073 (w), 1625 (m), 1599
˜
(s), 1577 (m), 1537 (m), 1508 (s), 1436 (m), 1402 (s), 1373 (m), 1285
(w), 1234 (w), 1211 (w), 1150 (m), 1097 (s), 1053 (s), 879 (s), 829
(w), 805 (w), 759 (s) cm–1. UV (acetonitrile): λmax (log ε) = 205
(4.57), 258 (4.60), 290 (2.76), 368 (4.45), 371 (4.45), 449 (3.74) nm.
1H NMR (CDCl3, 400 MHz): δ = 1.99 (s, 3 H), 2.52 (s, 3 H), 7.30–
7.36 (m, 3 H), 7.90–7.97 (m, 4 H), 8.47 (“d”, J = 8.6 Hz, 2 H), 8.54
(“t”, J = 8.6 Hz, 2 H) ppm. 13C NMR {1H} (CDCl3, 125 MHz): δ
= 20.16 (q), 21.51 (q), 120.61 (d), 124.37 (s), 127.24 (d), 127.87 (s),
129.53 (d), 129.83 (d), 131.14 (d), 131.98 (d), 135.87 (s), 142.48 (s),
144.45 (d), 158.63 (s), 176.67 (s) ppm. MS (70 eV, EI): m/z (%) =
9-(4-Methoxy-2,6-dimethylphenyl)thioxanthenylium Tetrafluorobo-
rate (2.4): To a solution of 110 mg (0.316 mmol) of thioxanthenol
Eur. J. Org. Chem. 2007, 3573–3582
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3577

G. Dyker et al.
FULL PAPER
304 (29) [M+ – BF4], 286 (18), 285 (63), 269 (11), 255 (6), 199 (100),
400 MHz): δ = 1.25 (s, 6 H), 1.34 (s, 6 H), 1.90 (s, 6 H, o-CH3),
181 (16), 49 (10). C21H17BF4O (372.17): calcd. C 67.74, H 4.56; 2.28 (s, 3 H, p-CH3), 4.24 (“d”, 4 H, CH2), 6.27 (d, J = 9 Hz, 1
found C 67.74, H 4.74.
H), 6.65 (d, J = 9 Hz, 1 H), 6.84 (m, 1 H), 6.90 (s, 2 H), 7.07 (d, J
= 8 Hz, 1 H), 7.23 (m, 2 H), 7.37 (“d”, 1 H) ppm. 13C NMR {1H}
(CDCl3, 100 MHz): δ = 19.64 (q), 21.14 (q), 28.20 (q), 28.45 (q),
67.61 (s), 67.81 (s), 74.75 (s), 78.08 (t), 78.32 (t), 103.66 (d), 105.53
(s), 116.02 (d), 122.20 (s), 123.60 (d), 124.23 (s), 125.81 (d), 125.94
(d), 128.42 (d), 128.80 (d), 128.75 (s), 131.02 (d), 136.69 (s), 137.44
(s), 138.16 (s), 144.55 (s), 152.99 (s), 153.14 (s), 161.12 (s) ppm. MS
(FAB): m/z (%) = 507 (47), 507 (100), 506 (43) [M+], 136 (60).
C33H34N2O3 (506.64): calcd. C 78.23, H 6.76, N 5.53; found C
77.91, H 6.67, N 5.49.
9-(4-Methylphenyl)xanthenylium Tetrafluoroborate (2.8): 3.72 g
(12.9 mmol) of xanthenol 1.8 was dissolved in 25 mL of dry
CH2Cl2 and 5.0 mL (36 mmol) of HBF4·OEt2 (15% in diethyl
ether) was added. After 10 min of stirring at room temperature a
layer of 40 mL of diethyl ether was carefully placed on the reaction
mixture. Slow diffusion (1 d) led to the formation of a yellow to
orange precipitate, which was collected, washed with diethyl ether
and dried in vacuo (50 °C, 0.5 mbar, 4 h): The formed yellow solid
was removed by filtration, washed with diethyl ether (3ϫ10 mL)
and dried in vacuo (100 °C, 0.5 mbar, 3 h): 4.60 g (95%) of the
orange solid (a hydrate according to NMR) with m.p. 210–215 °C
Reaction of 2.1 with Nucleophile C. S,S-3-Bis[(4-isopropyl-2-methyl-
4,5-dihydrooxazolyl)methylene]-9-(2,4,6-trimethylphenyl)-3H-
xanthene (6.1C): 57 mg (0.24 mmol) of bisoxazoline E in 2.5 mL of
dry DMF was treated with 11 mg of NaH (60% in mineral oil,
0.28 mmol) for 30 min at room temperature. 78 mg (0.2 mmol) of
the mesityl-substituted xanthenylium salt 2.1 in 1.5 mL DMF was
added and the red solution stirred at 70 °C for 6 h. After hydrolysis
with 20 mL of water and extraction with CH2Cl2 (three times
25 mL) the organic layer was washed with water (20 mL), brine
(20 mL), dried with Na2SO4 and concentrated and the residue was
fractionated by flash chromatography (silica, petroleum ether/di-
ethyl ether/methanol, 50:25:2; Rf = 0.78, 0.69, 0.31). The fraction
with Rf = 0.69 gave 65 mg (61%) of the p-quinoid compound 6.1C
(ref.[13] m.p. 200 °C, dec.). H NMR (CDCl3, 200 MHz): δ = 2.59
(s, 3 H), 2.80 (broad s, hydrate), 7.58 (“d”, J = 8.0 Hz, 2 H), 7.62
(“d”, J = 8.0 Hz, 2 H), 7.92 (“t”, J = 7.7 Hz, 2 H), 8.18 (dd, J =
8.2, 1.3 Hz, 2 H), 8.33 (d, J = 8.7 Hz, 2 H), 8.36–8.54 (m, 4 H) ppm.
1
Reaction of 2.1 with Nucleophile A. 2-[9-(2,4,6-Trimethylphenyl)-
xanthen-3-yliden]malononitrile (6.1A): To 132 mg (2.00 mmol) of
malononitrile (A) in 20 mL of dry THF at –78 °C 1.0 mL of n-
butyllithium (2.5  in hexane) were slowly added and the reaction
mixture was stirred for 30 min. 750 mg (2.00 mmol) of the mesityl-
substituted xanthenylium salt 2.1 was added in the cold and the
reaction mixture was stirred for 24 h at room temperature. After
hydrolysis with 20 mL of saturated aqueous diammonium hydrogen
phosphate solution and extraction with CH2Cl2 (three times
20 mL) the organic layer was concentrated and the residue was
purified by flash chromatography (silica, petroleum ether/ethyl ace-
tate, 1:1, Rf = 0.29): 695 mg (96%) of the p-quinoid compound
as a deep red solid with m.p. 226–231 °C. IR (KBr): ν = 2963 (s),
˜
2909 (m), 1622 (m), 1470 (s), 1351 (m), 1312 (m), 1265 (m), 1201
(m), 1113 (w), 992 (m), 850 (w), 756 (w), 653 (w), 616 (w) cm–1.
UV (acetonitrile): λmax (log ε) = 211 (4.21), 361 (3.75), 506 (3.95)
1
nm. H NMR (CDCl3, 500 MHz): δ = 0.91 (d, J = 5.9 Hz, 3 H),
0.98 (t, J = 6.8 Hz, 6 H), 1.07 (d, J = 6.65 Hz, 3 H), 1.87–1.92 (m,
2 H), 1.97 (s, 6 H), 2.36 (s, 3 H), 4.00–4.13 (m, 4 H), 4.27–4.34 (m,
2 H), 6.33 (d, J = 9.7 Hz, 1 H), 6.71 (dd, J = 7.85, 1.45 Hz 1 H),
6.93 (td, J = 7.25, 1.05 Hz, 1 H), 6.98 (s, 2 H), 7.14 (dd, J = 8.3,
1.0 Hz, 1 H), 7.28–7.32 (m, 2 H), 7.42 (dd, J = 9.8, 1.75 Hz, 1
H) ppm. 13C NMR {1H} (CDCl3, 125 MHz): δ = 18.36 (q), 18.43
(q), 19.09 (q), 19.64 (q), 21.12 (q), 32.83 (d), 32.94 (d), 69.34 (t),
69.52 (t), 72.77 (d), 103.53 (d), 105.68 (s), 115.96 (d), 122.12 (s),
123.58 (d), 124.07 (s), 125.66 (d), 125.90 (d), 128.39 (d), 128.72 (d),
129.64 (s), 131.00 (d), 136.62 (s), 136.69 (s), 137.46 (s), 138.12 (s),
143.89 (s), 152.91 (s), 152.96 (s), 162.57 (s) ppm. MS (70 eV, EI):
m/z (%) = 535 (63), 491 (100) [M+], 405 (37), 380 (21), 337 (11),
314 (25), 299 (12), 285 (14), 237 (18), 41 (13). C35H38N2O3 (534.70)
+ 0.5H2O: calcd. C 77.32, H 7.23, N 5.15; found C 76.95, H 7.47,
N 4.97.
6.1A as a deep purple solid with m.p. 228–231 °C. IR (KBr): ν =
˜
2923 (w), 2203 (s), 1635 (m), 1599 (m), 1469 (s), 1414 (m), 1322
(m), 1152 (m), 843 (m), 754 (m) cm–1. UV (acetonitrile): λmax (log
ε) = 197 (4.82), 292 (3.97), 370 (3.81), 529 (4.39), 568 (4.48), 617
1
(4.31) nm. H NMR (CDCl3, 500 MHz): δ = 1.94 (s, 6 H), 2.42 (s,
3 H), 6.84 (d, J = 9.4 Hz, 1 H), 7.04 (d, J = 1.8 Hz, 1 H), 7.06 (s,
2 H), 7.09 (dd, J = 8.1 Hz, J = 1.5 Hz, 1 H), 7.21 (dd, J = 9.4 Hz,
J = 1.8 Hz, 1 H), 7.24(“t”, “J” = 8.2 Hz, 1 H), 7.51 (dd, J = 8.5 Hz,
J = 0.8 Hz, 1 H), 7.67 (“t”, “J” = 7.8 Hz, 1 H) ppm. 13C NMR
{1H} (CDCl3, 125 MHz): δ = 19.80 (q), 21.17 (q), 64.55 (d), 102.52
(d), 115.90 (s), 116.07 (s), 117.23 (d), 121.23 (s), 122.74 (s), 125.48
(d), 125.93 (s), 127.66 (s), 128.22 (d), 128.84 (d), 128.96 (d), 134.60
(d), 135.90 (s), 139.53 (s), 150.65 (s), 153.06 (s), 155.98 (s), 157.35
(s) ppm. MS (70 eV, EI): m/z (%) = 362 (22) [M+], 332 (7), 299 (30),
181 (25), 66 (100). C25H18N2O (362.43): calcd. C 82.85, H 5.01, N
7.73; found C 82.63, H 5.04, N 7.72.
Reaction of 2.1 with Nucleophile D. 3-(Dipyridin-2-ylmethyl)-9-
(2,4,6-trimethylphenyl)xanthene (5.1D): To 900 mg (5.30 mmol) of
2-(pyridin-2-ylmethyl)pyridine D in 20 mL of dry THF at –78 °C
was added 2.1 mL (5.30 mmol) of n-butyllithium (2.5  in hexane)
within 2 min, then the reaction mixture was stirred for 30 min. A
suspension of 772 mg (2.00 mmol) of the mesityl-substituted xan-
thenylium salt 2.1 in of dry THF was added and the reaction mix-
ture was stirred at room temperature for 16 h. After hydrolysis with
25 mL of aqueous ammonium chloride solution and extraction
with diethyl ether (three times 25 mL) the organic layer was dried
with Na2SO4 and concentrated. 370 mg of starting material D were
recovered by distillation in the kugelrohr oven at 160 °C and
0.3 mbar. The residue was fractionated by flash chromatography
(silica, petroleum ether/ethyl acetate, 1:3; Rf = 0.71, 0.46, 0.23,
0.11): The fraction with Rf = 0.23 gave 870 mg (93%) of compound
Reaction of 2.1 with Nucleophile B. 3-Bis[(4,4-dimethyl-4,5-dihy-
drooxazol-2-yl)methylene]-9-(2,4,6-trimethylphenyl)-3H-xanthene
(6.1B): 210 mg (1.00 mmol) of bis(4,4-dimethyl-4,5-dihydrooxazol-
2-yl)methane (D) in 20 mL of dry THF was treated with 40 mg of
NaH (60% in mineral oil, 1.00 mmol) for 30 min at room tempera-
ture. 386 mg (1.00 mmol) of the mesityl-substituted xanthenylium
salt 2.1 was added and the reaction mixture stirred for 24 h at room
temperature. After hydrolysis with 20 mL of saturated aqueous di-
ammonium hydrogen phosphate solution and extraction with
CH2Cl2 (three times 20 mL) the organic layer was concentrated and
the residue was purified by flash chromatography (silica, petroleum
ether/ethyl acetate, 1:1, Rf = 0.46): 475 mg (94%) of the p-quinoid
compound 6.1B as a deep red solid with m.p. 226 °C. IR (KBr): ν
˜
= 2963 (w), 1656 (m), 1605 (m), 1577 (m), 1473 (s), 1260 (m), 1187
(m), 1011 (m), 725 (m) cm–1. UV (acetonitrile): λmax (log ε) = 261
(4.12), 268 (4.10), 355 (3.83), 577 (3.90) nm. 1H NMR (CDCl3,
5.1D as a colorless solid with m.p. 200 °C. IR (KBr): ν = 3427 (m,
br.), 3005 (w), 2963 (w), 2917 (w), 2868 (w), 1588 (s), 1567 (s), 1484
(s), 1470 (m), 1456 (m), 1419 (s), 1322 (m), 1272 (m), 1244 (m),
˜
3578
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3573–3582

Functionalized p-Quinoid π-Systems
FULL PAPER
1102 (w), 996 (w), 979 (w), 859 (w), 788 (w), 752 (s), 699 (w), 620 (3.88), 296 (3.95), 311 (3.98), 345 (4.36), 388 (3.77), 460 (3.82, sh),
(w) cm–1. UV (acetonitrile): λmax (log ε) = 220 (4.68, sh), 257 (4.18),
489 (4.13, sh), 528 (4.39), 569 (4.49), 619 (4.31) nm. 1H NMR
(CDCl3, 300 MHz): δ = 1.96 (s, 6 H, CH3), 3.89 (s, 3 H, OCH3),
270 (4.02, sh), 285 (3.57), 295 (3.59) nm. 1H NMR (CDCl3,
500 MHz): δ = 1.63 (s, 3 H), 2.27 (s, 3 H), 2.50 (s, 3 H), 5.77 (s, 1 6.79 (s, 2 H, 3-H/5-H), 6.86 (d, J = 9.4 Hz, 1 H), 7.04 (s, 1 H, 4-
H), 5.83 (s, 1 H), 6.67 (dd, J = 7.9, 1.1 Hz, 1 H), 6.73 (m, 2 H), H), 7.11 (dd, J = 8.0, 1.4 Hz, 1 H), 7.20–7.28 (m, 2 H), 7.51 (d, J
6.79 (dd, J = 8.1, 1.7 Hz, 1 H), 6.85 (td, J = 7.5, 1.3 Hz, 1 H), 6.95
(br. s, 1 H), 6.96 (d, J = 1.8 Hz, 1 H), 6.98 (dd, J = 8.2, 1.3 Hz, 1
= 8.4 Hz, 1 H), 7.67 (“t”, “J” = 8.5 Hz, 1 H) ppm. 13C NMR {1H}
(CDCl3, 75.5 MHz): δ = 20.25 (q), 55.33 (q), 64.82 (s), 102.61 (d),
H), 7.11–7.15 (m, 3 H), 7.25–7.27 (m, 2 H), 7.63 (m, 2 H), 8.58 (m, 113.60 (d), 115.91 (s), 116.08 (s), 117.30 (d), 121.62 (s), 123.27 (s),
2 H) ppm. 13C NMR {1H} (CDCl3, 125 MHz): δ = 20.77 (q), 20.88 123.46 (s), 125.53 (d), 126.06 (d), 127.75 (d), 129.05 (d), 134.60 (d),
(q), 21.21 (q), 36.97 (d), 61.28 (d), 115.99 (d), 116.77 (d), 121.63
137.77 (s), 150.39 (s), 153.15 (s), 156.07 (s), 157.39 (s), 160.41 (s)
(d), 122.18 (s), 123.06 (d), 123.78 (s), 124.03 (d), 124.16 (d), 127.59 ppm. MS (70 eV, EI): m/z (%) = 379 (28), 378 (100) [M+], 335
(d), 128.09 (d), 128.18 (d), 128.62 (d), 131.42 (d), 136.48 (s), 136.54 (3), 320 (8), 319 (6), 318 (4), 305 (3), 255 (3), 189 (10). C25H18N2O2
(d), 137.01 (s), 137.34 (s), 137.75 (s), 141.56 (s), 149.46 (d), 150.87 (378.43): calcd. C 79.35, H 4.79, N 7.40; found C 79.40, H 4.75, N
(s), 150.89 (s), 161.90 (s) ppm. MS (70 eV, EI): m/z (%) = 469 (33),
468 (100) [M+], 389 (22), 349 (75), 299 (69), 270 (54), 174 (26), 169
(6). C33H28N2O (468.60): calcd. C 84.59, H 6.02, N 5.98; found C
84.51, H 6.02, N 5.99.
7.37.
Reaction of 2.3 with Nucleophile A. 2-{9-[2,6-Dimethyl-4-(dimeth-
ylamino)phenyl]xanthen-3-ylidene}malononitrile
(6.3A):
13 mg
(0.20 mmol) of malononitrile (A) in 2 mL of dry THF was treated
with 9 mg (60% in mineral oil, 0.225 mmol) of NaH for 30 min at
room temperature. 34 mg (0.10 mmol) of the [2,6-dimethyl-4-(di-
methylamino)phenyl]-substituted xanthenylium salt 2.3 was added
and the reaction mixture was stirred at room temperature for 21 h.
After hydrolysis with 20 mL of saturated aqueous diammonium hy-
drogen phosphate solution and extraction with CH2Cl2 (three times
20 mL) the organic layer was concentrated and the residue was
purified by flash chromatography (silica, petroleum ether/diethyl
ether, 1:1, Rf = 0.25): 35 mg (90%) of the p-quinoid compound
Reaction of 2.1 with Nucleophile E. Quinolin-8-yl-[9-(2,4,6-trimeth-
ylphenyl)xanthen-3-ylidene]amine (6.1E): 288 mg (2.00 mmol) 8-
aminoquinoline (E) in 20 mL of dry THF was treated with 80 mg
of NaH (60% in mineral oil, 2.00 mmol) for 4 h at room tempera-
ture. 388 mg (1.00 mmol) of the xanthenylium salt 2.8 was added
and the reaction mixture was stirred at room temperature for 24 h.
After hydrolysis with a saturated aqueous solution of Na2HPO4,
extraction with CH2Cl2 (3ϫ20 mL) and removal of the solvent and
the excess of nucleophile in vacuo (100 °C, 0.5 mbar), the product
was isolated by flash chromatography (silica, methyl tert-butyl
ether/CH2Cl2, 1:10, Rf = 0.44): 139 mg (32%) of the metallic shiny
6.3A as purple solid with m.p. 238–242 °C. IR (KBr): ν = 3050 (w),
˜
2628 (w), 2208 (s), 1678 (m), 1634 (s), 1594 (s), 1530 (w), 1471 (s),
1416 (m), 1205 (s), 1143 (s), 842 (w), 799 (w), 743 (w) cm–1. UV
(acetonitrile): λmax (log ε) = 216 (4.57), 261 (4.36), 309 (4.19), 370
(3.86), 528 (4.40), 568 (4.48), 621 (4.32) nm. 1H NMR (CDCl3,
500 MHz): δ = 1.93 (s, 6 H), 3.05 (s, 6 H), 6.56 (s, 2 H), 6.94(d, J
= 9.35 Hz, 1 H), 7.03 (d, J = 1.95 Hz, 1 H), 7.20(“t”, “J” = 8 Hz,
1 H), 7.24 (dd, J = 7 Hz, J = 1 Hz, 1 H), 7.26 (s, 1 H), 7.50 (dd, J
= 8.5 Hz, J = 0.7 Hz, 1 H), 7.66 (“t”, “J” = 7.8 Hz, 1 H) ppm. 13C
NMR {1H} (CDCl3, 125 MHz): δ = 20.53 (q), 40.27 (q), 63.61(s),
102.36 (d), 111.40 (d), 116.16 (s), 116.31 (s), 117.14 (s), 118.83 (d),
122.04 (s), 123.37 (s), 125.33 (d), 125.58 (d), 128.16 (d), 129.49 (d),
134.41 (d), 136.86 (s), 151.03 (s), 152.15 (s), 153.06 (s), 156.17 (s),
157.47 (s) ppm. MS (70 eV, EI): m/z (%) = 392 (27), 391 (100) [M+],
375 (11), 195 (22). C26H21N3O (391.47): C 79.77, H 5.41, N 10.73;
found C 79.70, H 5.06, N 10.55.
black solid 6.1E with m.p. 172–174 °C. IR (KBr): ν = 2921 (vw),
˜
1637 (s), 1596 (s), 1559 (m), 1542 (m), 1507 (s), 1490 (a), 1486 (s),
1472 (s), 1386 (m), 1326 (m), 1326 (m), 1149 (m), 1058 (m), 827
(w), 759 (w) cm–1. UV (CHCl3) λmax (log ε): 243 (4.17), 274 (3.90),
1
362 (3.77), 515 (4.02) nm. H NMR (CDCl3, 400 Hz): δ = 1.90 (s,
6 H, o-CH3), 2.43 (s, 3 H, p-CH3), 7.10 (s, 2 H), 7.35–7.53 (m, 5
H), 7.68 (t, J = 8.6 Hz, 1 H), 7.83–7.86 (m, 2 H), 7.95 (t, J =
8.6 Hz, 1 H), 8.05 (d, J = 8.60 Hz, 1 H), 8.25 (dd, J = 8.3, 1.5 Hz,
1 H), 8.90 (dd, J = 8.3, 1.5 Hz, 1 H) ppm. 13C NMR {1H} (CDCl3,
100 MHz): δ = 19.97 (d), 21.24 (d), 118.49 (d), 120.86 (d), 121.08
(s), 122.46 (d), 123.91 (q), 126.90 (d), 126.95 (d), 127.63 (s), 127.86
(s), 128.81 (d), 129.10 (d), 129.14 (d), 131.79 (s), 133.44 (s), 135.52
(d), 136.61 (d), 137.60 (d), 140.54 (s), 141.74 (q), 150.44 (d), 154.34
(s), 161.60 (s) ppm, two signals are missing. MS (70 eV, EI): m/z
(%) = 442 (37), 441 (100) [M + H+], 154 (27), 136 (25). C31H24N2O
(440.54): calcd. C 84.52, H 5.49, N 6.36; found C 84.49, H 5.41, N
6.74.
Reaction of 2.4 with Nucleophile A. 2-[9-(4-Methoxy-2,6-dimeth-
ylphenyl)thioxanthen-3-ylidene]malononitrile (6.4A) and 9-(4-Meth-
oxy-2,6-dimethylphenyl)thioxanthen-3-one (7): 26 mg (0.39 mmol)
of malononitrile (A) in 3 mL of dry THF was treated with 18 mg
(60% in mineral oil, 0.45 mmol) of NaH for 20 min at room tem-
perature. 100 mg (0.239 mmol) of the thioxanthenylium salt 2.4 was
added and the reaction mixture was stirred at room temperature
for 18 h. After hydrolysis with 20 mL of saturated aqueous diam-
monium hydrogen phosphate solution and extraction with CH2Cl2
(three times 20 mL) the organic layer was concentrated and the
residue was purified by flash chromatography (silica, n-hexane/di-
ethyl ether, 1:1, Rf = 0.29, 0.10).
Reaction of 2.2 with Nucleophile A. 2-[9-(4-Methoxy-2,6-dimeth-
ylphenyl)xanthen-3-ylidene]malononitrile (6.2A): 26 mg (0.39 mmol)
of malononitrile (A) in 3 mL of dry THF was treated with 18 mg
(60% in mineral oil, 0.45 mmol) of NaH for 20 min at room tem-
perature. 100 mg (0.249 mmol) of the (4-methoxy-2,6-dimeth-
ylphenyl)-substituted xanthenylium salt 2.2 in 5 mL of THF was
added and the reaction mixture was stirred at room temperature
for 18 h. After hydrolysis with 20 mL of saturated aqueous diam-
monium hydrogen phosphate solution and extraction with CH2Cl2
(three times 20 mL) the organic layer was concentrated and the
residue (91 mg of a slightly impure crude product) was purified by
flash chromatography (silica, n-hexane/diethyl ether, 2:3, Rf = 0.35):
56 mg (58%) of the p-quinoid compound 6.2A as dark green crys-
1st Fraction: Rf = 0.29, 46 mg (49%) of the p-quinoid compound
6.4A as brown metallic shiny crystals with m.p. 249–254 °C. IR
(KBr): ν = 3060 (w), 2917 (w), 2840 (w), 2202 (s), 1605 (s), 1583
˜
tals with m.p. 239–243 °C. IR (KBr): ν = 3067 (w), 2936 (w), 2841
(s), 1490 (s), 1444 (s), 1408 (s), 1316 (m), 1287 (m), 1236 (m), 1195
˜
(w), 2204 (s), 1630 (s), 1596 (s), 1546 (w), 1525 (w), 1467 (s), 1413 (m), 1161 (m), 1146 (m), 1128 (m), 1083 (m), 1054 (m), 912 (w),
(m), 1361 (m), 1325 (m), 1311 (s), 1251 (w), 1211 (w), 1196 (w), 850 (w), 747 (w), 639 (w) cm–1. UV (acetonitrile): λmax (log ε) =
1149 (m), 1131 (m), 1112 (w), 1063 (w), 843 (w), 758 (w) cm–1. UV 201 (4.77), 228 (4.23), 253 (4.41), 270 (4.05, sh), 306 (3.93, sh), 360
(acetonitrile): λmax (log ε) = 201 (4.79), 229 (4.51), 261 (3.88), 282 (4.45), 405 (3.92, sh), 427 (4.00), 490 (3.66, sh), 523 (4.02, sh), 565
Eur. J. Org. Chem. 2007, 3573–3582
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3579

G. Dyker et al.
FULL PAPER
(4.30), 610 (4.42), 664 (4.27) nm. 1H NMR (CDCl3, 300 MHz): δ
= 1.90 (s, 6 H), 3.90 (s, 3 H), 6.79 (s, 2 H, 3-H/5-H), 7.02 (d, J =
737 (m) cm–1. UV (acetonitrile): λmax (log ε) = 203 (4.80), 224
(4.49), 237 (4.29, sh), 256 (3.76), 288 (3.99) nm. 1H NMR (CDCl3,
9.6 Hz, 1 H), 7.22 (dd, J = 9.6, 1.9 Hz, 2 H), 7.28–7.36 (m, 2 H), 300 MHz): δ = 2.27 (s, 6 H), 3.86 (s, 3 H), 5.66 (s, 1 H, 5Ј-H), 6.78
7.55 (“dt”, “J” = 7.0, 1.4 Hz, 1 H), 7.64 (dd, J = 8.1, 7.3 Hz, 1 (s, 2 H), 6.96 (s, 2 H), 7.05–7.30 (m, 8 H) ppm. 13C NMR {1H}
H) ppm. 13C NMR {1H} (CDCl3, 125 MHz): δ = 20.13 (q), 55.30
(q), 63.46 (s), 113.53 (d), 113.55 (d), 115.99 (s), 116.25 (s), 125.76
(d), 126.09 (s), 126.38 (d), 126.78 (s), 127.71 (d), 128.80 (s), 131.17
(d), 131.96 (d), 132.99 (d), 135.70 (s), 137.65 (s), 142.61 (s), 152.93
(s), 153.00 (s), 160.04 (s) ppm. MS (70 eV, EI): m/z (%) = 396 (11),
(CDCl3, 75.5 MHz): δ = 23.54 (q), 46.63 (d), 55.12 (q), 114.71 (d),
126.10 (d), 127.52 (d), 128.86 (d), 129.35 (s), 129.44 (d), 132.74 (d),
136.46 (s), 140.13 (s, presumably 2 s), 157.94 (s) ppm. MS (70 eV,
EI): m/z (%) = 327 (19), 326 (71) [M+], 312 (10), 311 (16), 192 (16),
191 (56), 190 (11), 189 (18), 149 (15), 148 (100). C24H22O (326.44):
395 (39), 394 (100) [M+], 378 (6), 336 (8), 335 (6), 334 (4), 321 (5). calcd. C 88.31, H 6.79; found C 88.34, H 6.75.
C25H18N2OS (394.49): calcd. C 76.12, H 4.60, N 7.10; found C
2nd Fraction: 83 mg (37%) of the p-quinoid compound 6.5A as deep
76.00, H 4.68, N 7.01.
red solid with m.p. 230–233 °C. IR (KBr): ν = 2961 (w), 2209 (s),
˜
2nd Fraction: Rf = 0.10, ca. 37 mg (45%) of thioxanthenone 7 as
dark orange oil, which still contains THF after 2 h at 150 °C in
1604 (s), 1527 (w), 1451 (w), 1412 (s), 1378 (w), 1316 (s), 1299 (m),
1265 (m), 1192 (m), 1172 (m), 1148 (m), 1107 (w), 1062 (w), 870
(w), 851 (w), 815 (w), 789 (w), 766 (w) cm–1. UV (acetonitrile): λmax
(log ε) = 199 (4.81), 233 (4.06, sh), 283 (3.86), 347 (3.68, sh),
vacuo. IR (KBr): ν = 2941 (s), 2857 (s), 1608 (m), 1588 (w), 1486
˜
(w), 1454 (w), 1383 (w), 1317 (w), 1115 (s, br.), 811 (w) cm–1. UV
(acetonitrile): λmax (log ε) = 200 (4.56), 238 (4.29), 271 (4.03, sh),
283 (4.09), 295 (4.12), 306 (4.07), 360 (3.91), 377 (3.80, sh), 496
1
487 (4.52) nm. H NMR (CDCl3, 500 MHz): δ = 1.90 (br. s, 6 H),
3.09 (br. s, 4 H), 3.86 (s, 3 H), 6.69 (s, 2 H), 6.85–6.97 (m, 4 H),
7.09 (“t”, “J” = 7.7 Hz, 1 H), 7.25 (“d”, “J” = 7.3 Hz, 1 H), 7.32
(dt, J = 7.4, 1.0 Hz, 1 H) ppm. 13C NMR {1H} (CDCl3, 125 MHz):
δ = 20.14 (q), 33.67 (t), 37.80 (t), 55.23 (q, OCH3), 71.38 (s), 113.29
(d), 114.61 (s), 114.77 (s), 122.46 (d), 122.54 (d), 127.00 (d), 128.53
(d), 131.63 (d), 133.12 (s), 133.86 (d), 134.31 (s), 136.74 (s), 137.32
(s), 139.18 (d), 144.79 (s), 149.59 (s), 155.83 (s), 159.25 (s), 159.45
(s) ppm. MS (70 eV, EI): m/z (%) = 391 (27), 390 (100) [M+], 375
(9), 360 (5), 254 (11), 195 (3), 180 (3). C27H22N2O (390.48): calcd.
C 83.05, H 5.68, N 7.17; found C 82.76, H 5.74, N 7.02.
1
(3.74), 609 (4.08) nm. H NMR (CDCl3, 300 MHz): δ = 1.91 (s, 6
H), 3.89 (s, 3 H, OCH3), 6.65 (dd, 1 H), 6.78 (s, 2 H, 3-H/5-H),
6.86 (“d”, “J” = 3.6 Hz, 1 H), 7.17–7.27 (m, 3 H), 7.50 (dd, 1 H),
7.61 (dd, 1 H) ppm. 13C NMR {1H} (CDCl3, 125 MHz): δ = 20.14
(q), 26.50 (t), 55.26 (q), 70.61 (t), 113.33 (d), 118.17 (d), 123.44 (s),
125.49 (d), 126.85 (d), 127.45 (s), 128.06 (s), 130.92 (d), 131.08 (d),
131.29 (d), 135.46 (s), 135.51 (d), 137.59 (s), 144.36 (s), 152.17 (s),
159.82 (s), 181.73 (s) ppm. MS (70 eV, EI): m/z (%) = 348 (10), 347
(28), 346 (100) [M+], 319 (13), 318 (49), 317 (36), 303 (20), 285 (10),
271 (7), 259 (13), 258 (9), 245 (7), 129 (8). HMRS calcd. for
C22H18O2S: 346.10275; found 346.1021.
Reaction of 2.6 with Nucleophile A. 2-{4-[(4-Methoxy-2,6-dimeth-
ylphenyl)phenylmethylene]cyclohexa-2,5-dienylidene}malononitrile
(6.6A): 44 mg (0.65 mmol) of malononitrile (A) in 4 mL of dry
THF was treated with 28 mg (60% in mineral oil, 0.70 mmol) of
NaH for 10 min at room temperature. 150 mg (0.386 mmol) of the
triarylmethylium salt 2.6 in 6 mL of dry THF was added and the
reaction mixture was stirred at room temperature for 20 h. After
hydrolysis with 20 mL of saturated aqueous diammonium hydrogen
phosphate solution and extraction with CH2Cl2 (three times
20 mL) the organic layer was concentrated and the residue was
fractionated by flash chromatography (silica, n-hexane/diethyl
ether, 1:1, Rf = 0.42 (1.6), 0.24 (6.6A)): The fraction with Rf = 0.24
gave 42 mg (30%) of the p-quinoid compound 6.6A as a red to
brown solid with m.p. 192–194 °C (crystallized from THF/n-pen-
NMR Spectroscopic Test for the Intermediate 2-[9-(4-Methoxy-2,6-
dimethylphenyl)-3H-thioxanthen-3-yl]malononitrile (4.4A): To
a
solution of 6 mg (0.09 mmol) of malononitrile (A) in 2 mL of dry
CDCl3 was added 4 mg (60% in mineral oil, 0.1 mmol) of NaH at
–40 °C. After 10 min 35 mg (0.084 mmol) of the thioxanthenylium
salt 2.4 was added and the reaction mixture was kept at –40 °C for
additional 20 min, before a 1H NMR spectrum of the red to brown
reaction mixture was measured, which is in accord with structure
1
4.4A. H NMR (CDCl3, 300 MHz): δ = 2.00 (s, 3 H, CH3) 2.04 (s,
3 H, CH3), 3.75 (d, J = 5.2 Hz, 1 H), 3.84 (s, 3 H, OCH3), 4.02–
4.06 (m, 1 H, 3Ј-H), 5.58 (dd, J = 4.8, 2.0 Hz, 1 H, 4Ј–H), 5.69–
5.75 (m, 1 H), 6.14 (dd, J = 10.0, 1.2 Hz, 1 H), 6.57 (d, J = 7.9 Hz,
1 H), 6.69 (s, 2 H, 3-H/5-H), 6.86–6.91 (m, 1 H), 7.07–7.13 (m, 2
H) ppm. After 2 weeks at room temperature the colour of the reac-
tane, 1:3). IR (KBr): ν = 3058 (w), 2961 (w), 2839 (w), 2211 (s),
˜
1604 (s), 1449 (s), 1432 (s), 1346 (w), 1313 (s), 1201 (m), 1193 (m),
1173 (s), 1144 (m), 1064 (w), 841 (w), 775 (w), 748 (w), 705 (w),
699 (w) cm–1. UV (acetonitrile): λmax (log ε) = 195 (4.84), 235 (4.07,
sh), 282 (4.08), 371 (3.97), 484 (4.56) nm. 1H NMR (CDCl3,
300 MHz): δ = 1.96 (s, 6 H, CH3), 3.84 (s, 3 H, OCH3), 6.68 (s, 2H.
3Ј-H/5Ј-H), 6.87 (dd, J = 9.6, 1.8 Hz, 1 H, 6-H), 7.08 (dd, J = 9.6,
2.0 Hz, 1 H, 5-H), 7.21 (dd, J = 9.7, 2.0 Hz, 1 H, 3-H), 7.28 (dd, J
= 9.3, 1.6 Hz, 2 H, 2-H), 7.40–7.48 (m, 3 H), 7.55 (dd, J = 9.7,
1.9 Hz, 1 H) ppm. 13C NMR {1H} (CDCl3, 75.5 MHz): δ = 20.81
(q), 55.23 (q), 71.73 (s), 113.61 (d), 114.48 (s), 114.54 (s), 124.42
(d), 124.49 (d), 128.74 (d), 130.91 (d), 131.55 (s), 131.67 (d), 133.15
(s), 136.26 (d), 136.84 (d), 138.53 (s), 138.63 (s), 155.69 (s), 160.14
(s), 161.94 (s) ppm. MS (70 eV, EI): m/z (%) = 365 (28), 364 (100)
[M+], 349 (6), 334 (5), 228 (6), 223 (5), 182 (3), 165 (4), 136 (4), 90
(4). C25H20N2O (364.45): calcd. C 82.39, H 5.53, N 7.69; found C
82.16, H 5.55, N 7.65.
1
tion mixture had changed to blue and the H NMR revealed that
a clean transformation to 6.4A had taken place.
Reaction of 1.5 with Nucleophile A. 2-[5-(4-Methoxy-2,6-dimeth-
ylphenyl)-10,11-dihydro-dibenzo[a,d]cyclohepten-2-ylidene]malono-
nitrile (6.5A) and 5-(4-Methoxy-2,6-dimethylphenyl)-5H-dibenzo-
[a,d]cycloheptene (8). Special Procedure: 200 mg (0.581 mmol) of
triarylmethanol 1.5 and 157 mg (2.32 mmol) malononitrile in
10 mL abs. DMF were stirred at 150 °C for 19 h. The deep orange
red solution was cooled to room temperature and 100 mL of H2O
was added. The aqueous layer was extracted with diethyl ether (5
times 50 mL) and the combined organic layer was reextracted with
water (4 times 50 mL) and dried with sodium sulfate. After evapo-
ration of the solvent in vacuo 215 mg of a reddish residue was
obtained, which was fractionated by flash chromatography; TLC
(silica, diethyl ether/n-hexane, 1:1): Rf = 0.64, 0.35.
1st Fraction: 112 mg (59%) of dibenzocycloheptatriene 8 as a yellow
Reaction of 2.7 with Nucleophile A. 2-[9-(2,4-Dimethylphenyl)-9H-
xanthen-9-yl]malononitrile (3.7A) and 2-[9-(2,4-Dimethylphenyl)-
xanthen-3-ylidene]malononitrile (6.7A): 264 mg (4.00 mmol) of ma-
solid with 256–262 °C. IR (KBr): ν = 3012 (w), 2935 (w), 2837 (w),
˜
1601 (m), 1580 (w), 1482 (m), 1378 (w), 1306 (s), 1284 (w), 1140
(m), 1066 (m), 996 (w), 857 (w), 836 (w), 813 (w), 802 (m), 780 (w), lononitrile (A) in 20 mL of dry THF was treated with 160 mg (60%
3580
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3573–3582

Functionalized p-Quinoid π-Systems
FULL PAPER
in mineral oil, 4.00 mmol) of NaH for 1 h at room temperature.
372 mg (1.00 mmol) of the xanthenylium salt 2.7 was added and
the reaction mixture was stirred at reflux temperature for 2 d. After
hydrolysis with 20 mL of saturated aqueous diammonium hydrogen
phosphate solution and extraction with CH2Cl2 (three times
50 mL) the organic layer was concentrated and the residue was
fractionated by flash chromatography (silica, toluene: Rf = 0.67,
0.14).
(d), 138.15 (s), 151.36 (s) ppm, one s is missing. MS (70 eV, EI):
m/z (%) = 336 (0.72) [M+], 271 (100), 255 (16), 181 (8), 128 (14).
C23H16N2O (336.39): calcd. C 82.12, H 4.79, N 8.33; found C
81.92, H 5.03, N 7.86.
Acknowledgments
1st Fraction: Rf = 0.67, 274 mg (78%) of 3.7A as a white solid with
This work was financially supported by the Fonds der Chemischen
Industrie and by the European Union, in the framework of the
project INTCHEM (MEST-CT-2005-020681).
m.p. 165 °C. IR (KBr): ν = 3044 (vw), 2969 (w), 2932 (m), 2265
˜
(vw), 1600 (w), 1573 (w), 1479 (s), 1143 (s), 1310 (m), 1294 (w),
1250 (m), 1229 (m), 1189 (vw), 1129 (vw), 940 (vw), 908 (vw), 874
(m), 812 (vw), 745 (s) cm–1. UV (acetonitrile): λmax (log ε) = 220
(4.32), 247 (4.08), 290 (3.58) nm. 1H NMR (400 MHz, CDCl3,
25 °C): mixture of rotamers; δ = 1.44 (s, 3 H, CH3), 2.39 (br. s, 3
H, CH3), 4.08 (br. s, 0.38 H), 4.51 (br. s, 0.62 H), 6.94–7.05 (m, 5
H), 7.24–7.28 (m, 3 H), 7.37–7.42 (t, 2 H), 7.51 (br. s, 0.62 H), 7.90
(br. s, 0.38 H) ppm. 13C NMR (400 MHz, CDCl3, 25 °C): mixture
of rotamers, δ = 20.82 (q), 21.59 (q, br.), 34.88 (br.), 38.93 (br.),
50.11 (br.), 111.60 (s), 116.98 (d), 120.68 (br.), 124.00 (d), 125.62
(br.), 126.32 (br.), 128.26 (br.), 129.07 (br.), 130.40 (d), 135.01 (d,
br.), 137.53 (s), 138.00 (s), 151.20 (s) ppm. MS (EI, 70eV): m/z (%)
= 351 (0.3), 350 (1.2) [M+], 285 (100), 255 (5), 181 (5), 134 (4).
C24H18N2O (350.41): calcd. C 82.26, H 5.18, N 7.99; found C
82.17, H 5.30, N 7.80.
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[9] X-ray crystal structure analysis of 6.2A: A single crystal was
mounted on top of a glass capillary. Diffraction data were col-
2nd Fraction: 53 mg (15%) of the p-quinoid compound 6.7A as deep
violet solid with m.p. 280–285 °C. IR (KBr): ν = 2922 (w), 2203
˜
(s), 1631 (m), 1595 (m), 1523 (w), 1467 (s), 1414 (m), 1361 (w),
1320 (w), 1139 (w), 1113 (w), 840 (w), 754 (w) cm–1. UV (acetoni-
trile): λmax (log ε) = 228 nm (4.38), 297 (3.94), 308 (3.97), 349 (4.09),
369 (3.81), 390 (3.79), 528 (4.35), 562 (4.37), 618 (4.22) nm.
1HnNMR (400 MHz, CDCl3, 25 °C): δ = 2.02 (s, 3 H), 2.46 (s, 3
H), 6.89 (d, J = 9.6 Hz, 1 H), 7.02–7.06 (m, 2 H), 7.16 (dd, J =
8.1, 1.5 Hz, 1 H), 7.19–7.26 (m, 4 H), 7.48 (d, J = 8.3 Hz, 1 H),
7.65 (“t”, “J” = 7.8 Hz, 1 H) ppm. 13C NMR (400 MHz, CDCl3,
25 °C): δ = 19.63 (q), 21.29 (q), 64.63 (s), 102.53 (d), 115.89 (s),
116.04 (s), 117.10 (d), 121.77 (s), 122.77 (s), 125.23 (d), 125.66 (d),
127.08 (d), 128.46 (d), 128.73 (s), 129.17 (d), 129.51 (d), 131.61 (d),
134.43 (d), 136.09 (s), 140.06 (s), 150.39 (s), 152.95 (s), 156.07 (s),
157.26 (s) ppm. MS (EI, 70 EV): m/z (%) = 349 (28), 348 (100)
[M+], 332 (4), 318 (4), 166 (4), 59 (6). C24H16N2O (348.40) +
0.5H2O: calcd. C 80.65, H 4.79, N 7.84; found: C 81.01, H 5.00, N
7.45.
Reaction of 2.8 with Nucleophile A. 2-[9-(4-Methylphenyl)-9H-
xanthen-9-yl]malononitrile (3.8A): 264 mg (4.00 mmol) of malono-
nitrile (A) in 20 mL of dry THF was treated with 160 mg (60% in
mineral oil, 4.00 mmol) of NaH for 30 min at room temperature.
357 mg (1.00 mmol) of the 4-methylphenyl-substituted xanthenyl-
ium salt 2.2 was added and the reaction mixture was stirred at
reflux temperature for 2 h. After hydrolysis with 50 mL of water
and extraction with CH2Cl2 (three times 50 mL) the organic layer
was concentrated and the residue was purified by flash chromatog-
raphy (silica, petroleum ether/methyl tert-butyl ether 1:10, Rf =
0.67): 229 mg (68%) of compound 3.8A as a colorless solid with
lected at 150 K with a Siemens P4RA four-cyrcle dif-
fractometer utilizing monochromated Mo-Kα radiation. The
data were corrected for absorption (ψ-scan method) as well as
for Lorentz and polarisation effects. The structure was solved
by direct methods and refined by full-matrix least-squares
methods based on F2 with anisotropic displacement parameters
for all non-hydrogen atoms using the SHELX-97* program
suite. Hydrogen atoms were fixed on ideal positions and refined
with a common isotropic temperature factor. The final refine-
ment converged to R1 = 0.0431 for 3201 data with Fo Ͼ 4σ(Fo)
and wR2 = 0.1229 for all 4099 data and 263 parameters.
CCDC-644405 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
m.p. 83–85 °C. IR (KBr): ν = 2032 (w), 2901 (w), 2265 (vw), 1600
˜
(w), 1673 (w), 1478 (s), 1443 (s), 1313 (m), 1280 (m), 874 (w), 756
(s) cm–1. UV (acetonitrile): λmax (log ε) = 231 (4.47), 243 (4.44),
268 (3.83), 274 (3.89), 290 (3.99) nm. 1H NMR (CDCl3, 400 MHz):
δ = 2.40 (s, 3 H), 4.40 (s, 1 H), 6.98 (d, J = 8.2 Hz, 2 H), 7.07 (m,
2 H), 7.2–7.3 (m, 6 H), 7.39 (m, 2 H) ppm. 13C NMR {1H} (CDCl3,
100 MHz): δ = 21.04 (q), 36.09 (s), 50.70 (d), 111.43 (d), 117.05
(d), 122.37 (s), 123.85 (d), 128.63 (s), 129.47 (d), 129.87 (d), 130.28
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crystal structures, University of Göttingen, Germany, 1997.
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Eur. J. Org. Chem. 2007, 3573–3582
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3581

G. Dyker et al.
FULL PAPER
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Received: February 26, 2007
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Published Online: June 5, 2007
3582
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3573–3582