Synthesis of some new functionalized 2,4,4,6-tetraphenyl-4H-thiopyrans and study on their photocolouration

Article abstract of DOI:10.1135/cccc19980662

A series of nineteen new 2,4,4,6-tetraphenyl-4H-thiopyrans both symmetrically and asymmetrically functionalized in the 3- and 5-positions of the 4H-thiopyran ring (-Br, -NO₂, -CN) and/or in the 4-positions of the 2- and 6-phenyl groups (-Br, -C

Full text of DOI:10.1135/cccc19980662

662
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
SYNTHESIS OF SOME NEW FUNCTIONALIZED 2,4,4,6-TETRAPHENYL-
4H-THIOPYRANS AND STUDY ON THEIR PHOTOCOLOURATION
a1
a
b
c
Jiri KROULIK , Martin CHADIM , Miroslav POLASEK , Stanislav NESPUREK
a2
and Josef KUTHAN
a Department of Organic Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6,
Czech Republic; e-mail: 1 jiri.kroulik@vscht.cz, 2 josef.kuthan@vscht.cz
b J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
182 23 Prague 8, Czech Republic; e-mail: vladimir.hanus@jh-inst.cas.cz
c Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic,
162 06 Prague 6, Czech Republic; e-mail: nespurek@imc.cas.cz
Received January 8, 1998
Accepted March 27, 1998
A series of nineteen new 2,4,4,6-tetraphenyl-4H-thiopyrans both symmetrically and asymmetrically
functionalized in the 3- and 5-positions of the 4H-thiopyran ring (–Br, –NO2, –CN) and/or in the
4-positions of the 2- and 6-phenyl groups (–Br, –CN, –OMe, –CO–Ph, –COCF3, –CO2H) was pre-
pared and the influence of the substituents on their photocolouration was followed. The title com-
pounds were prepared by substitution reactions of the parent thiopyrans or by cyclization of suitably
substituted 1,3,3,5-tetraarylpentane-1,5-diones. The substances lacking the 3,5-substituents exhibited
blue or green UV-photocolouration while the 3- and/or 5-substituted species did not. Typical bleach-
ing process for a selected compound is analyzed in terms of dispersive first-order kinetics.
Key words: Thiopyrans; Cyanodebromination; Lithiodebromination; Photocolouration; Hypervalent
structures; Photochromism; Photochemistry.
The photocolouration of 2,4,4,6-tetraphenyl-4H-thiopyrans1 seems to be of general in-
terest because their hypervalent photoisomers are proposed2 to be formed during the
process. From the previous solid state investigations2 follows that the colouration
caused by UV/VIS-illumination is only occuring on surface crystal layers with little
molecular motion, the packing of the molecules has negligible effects and the observed
electronic absorption spectra can be satisfactory interpreted using the CNDO/S-CI
quantum chemical calculations of the isolated molecules2. Although the unusual photo-
chemical behaviour has been demonstrated on several examples1, a limited knowledge
on a preparative introduction of additional substituents and their effects on the 4H-thio-
pyran system may be extracted from the published experimental data3. It appears that
the heterocyclic system exhibits donating π-electron properties with the most reactive 3-
and 5-positions towards electrophilic agents like chlorine4, bromine4a and nitric acid4a
allowing to obtain appropriate 3,5-disubstituted products. On the other hand, no trans-
formations of the substances based on any various substituent displacements have yet
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthiopyrans
663
been reported. Hence, the aim of this paper is to investigate the preparation of some
2,4,4,6-tetraphenyl-4H-thiopyran derivatives substituted in the 3,5-positions of the
heterocyclic ring and/or in the para-positions of the 2- and 6-phenyl groups. The
strategy of the presented syntheses starting from the earlier described4a 3,5-dibromo-
2,4,4,6-tetraphenyl-4H-thiopyran (1) and 2,6-bis(4-bromophenyl)-4,4-diphenyl-4H-
thiopyran (2) is based on successive (i) bromodeprotonation with bromine, (ii)
cyanodebromination of the bromo derivatives with copper(I) cyanide and (iii) lithiode-
bromination with butyllithium and subsequent displacement of the metal substituents
by acyl groups. Attempts have been also made to convert the cyano groups to benzoyl
and carboxy functions.
Ph Ph
Ph Ph
3
5
X
X
4
6
2
S
S
Y
Y
X
X
1
3
5
8
9
10
2
6
15 16
17
18
30
X
Y
Br
H
H
H
CN Br Br CN
Br CN CN
X
Br CN Li COCF COPh CO H OMe
3
2
H
Ph Ph
Ph Ph
X
S
S
Y
Y
X
Y
4
13
7
23 24
25
26
27
X
Br NO
X
Y
Br Br
CN CONH COCF OMe
2 3
2
Y
H
Br
CN OMe OMe OMe
OMe
H
Ph Ph
Ph Ph
2
4
O N
2
NO
2
3
1
5
O
O
S
Y
X
X
Y
11 12 14
19 20 21
22
X
Y
Br CN Br
Br CN CN
X
Y
H
H
Br OMe Br
Br OMe OMe
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

664
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
The 3,5-dibromo derivative 1 was prepared from the parent 2,4,4,6-tetraphenyl-4H-
thiopyran (3) by a standard procedure4a using the Br2/3 ratio 2 : 1 in carbon disulfide
solution under mild conditions while intermediate 3-bromo-2,4,4,6-tetraphenyl-4H-thio-
pyran (4) was isolated when only the ratio Br2/3 1.3 : 1 in a more diluted solution was
used. Application of the standard method5 making use of copper(I) cyanide in DMF at
elevated temperature to 3,5-dibromo derivative 1 gave expected 3,5-dicyano-2,4,4,6-
tetraphenyl-4H-thiopyran (5) in 87% yield. The same procedure with 2,6-bis(4-bromo-
phenyl) derivative 2 led to a mixture of major (40%) 2,6-bis(4-cyanophenyl)-4,4-diphenyl-
4H-thiopyran (6) and minor (1.8%) asymmetrically disubstituted intermediate 7.
To obtain tetrasubstituted derivatives of the parent 4H-thiopyran 3, brominations of
dibromo derivative 2 and dicyano derivative 6 have been attempted. In fact, the ex-
pected 3,5-dibromo-2,6-bis(4-bromophenyl)-4,4-diphenyl-4H-thiopyran (8) and 3,5-di-
bromo-2,6-bis(4-cyanophenyl)-4,4-diphenyl-4H-thiopyran (9) were prepared in 78 and
84% yields, respectively. All attempts at the cyanodebromination of compounds 8 and 9
afforded complex reaction mixtures from which only low preparative yields (1.7 and
6.4%, respectively) of 3,5-dicyano-2,6-bis(4-cyanophenyl)-4,4-diphenyl-4H-thiopyran (10)
could be obtained.
An alternative approach to tetrasubstituted derivatives of the parent 4H-thiopyran 3
has utilized the 3,5-nitration4a of the heterocyclic system. Thus, 2,6-bis(4-bromophenyl)-
3,5-dinitro-4,4-diphenyl-4H-thiopyran (11) was prepared by the reaction of compound 2
with 100% HNO3 in chloroform. It may be noted that a change of the standard proce-
dure4a with compound 2 using a large excess of nitric acid–acetic anhydride reagent led
only to 3-mononitro derivative 13. Subsequent cyanodebromination of 3,5-dinitro deri-
vative 11 afforded a mixture from which major (42%) dicyano compound 12 and the
corresponding minor (4.5%) intermediate 14 were isolated.
An additional approach to attach carbonyl-like substituents to the 2,6-diphenyl
groups has been investigated. Thus, 2,6-bis(4-lithiophenyl)-4,4-diphenyl-4H-thiopyran (15)
was generated in situ from dibromo derivative 2 and butyllithium by the recommended6
procedure in tetrahydrofuran at –78 °C, and then converted with ethyl trifluoroacetate
to 4,4-diphenyl-2,6-bis(4-trifluoroacetylphenyl)-4H-thiopyran (16) which was then iso-
lated in 45% yield. Further experiments have been focused on functional transforma-
tions of the para-cyano groups in the substance 6. The reaction of the 4H-thiopyran 6
with phenyllithium yielded 56% of 2,6-bis(4-benzoylphenyl)-4,4-diphenyl-4H-thiopy-
ran (17) while dicarboxylic acid 18 was isolated in 65% yield after the reaction of 6
with potassium hydroxide in diethylene glycol followed by acidification of the reaction
mixture. The prepared compounds 16, 17 and 18 are the first examples of the sunlight
sensitive 2,4,4,6-tetraaryl-4H-thiopyrans containing carbonyl functionality.
It has been widely documented1c,7 that the reaction of sodium amide with any aceto-
phenone–benzophenone mixture leads to 1,3,3,5-tetraphenyl-1,5-pentadione (19)
(Scheme 1, X = Y = H) which can be easily heterocyclized to 4H-thiopyran 3 and
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthiopyrans
665
analogous procedure with 4-bromoacetophenone (X = Y = 4-Br) gave7a,7b correspond-
ing 2,6-bis(4-bromophenyl) derivative 2. Using a 1 : 1 ratio of 4-bromo- and 4-methoxy-
acetophenones (X = 4-Br, Y = 4-OMe) a complex mixture containing expected
1,5-diketones 20, 21 and 22 (1 : 1 : 2) was obtained, out of which the asymmetrically
substituted 1-(4-bromophenyl)-5-(4-methoxyphenyl)-3,3-diphenylpenta-1,5-dione (22)
was chromatographically isolated in 9% yield. Its heterocyclization with P4S10 in
xylene by the general procedure1c afforded the expected 2-(4-bromophenyl)-6-(4-
methoxyphenyl)-4,4-diphenyl-4H-thiopyran (23) in 73% yield. Subsequent cyanode-
bromination of thiopyran 23 with copper(I) cyanide led to the expected major
2-(4-cyanophenyl) derivative 24 (59%) in addition to minor carboxamide 25 (5%) after
a preparative column chromatography. Consequently, low yields of multiple-step
cyanodebrominations as well as adverse effects of prolonged reaction times might be
explained by the formation of analogous side products. Using the above-mentioned
reactions with butyllithium and ethyl trifluoroacetate for the preparation of 16, the
asymmetrically substituted 4H-thiopyran 23 was finally converted to expected 4-trifluoro-
acetyl derivative 26 accompanied by the by-product 27. It may be noted that all at-
tempts at an analogous reaction of diketone 20 (refs7a,7b) with copper(I) cyanide led to
complex mixtures of hardly isolable products.
The structure of all new compounds (Table I) was confirmed by standard IR and
NMR techniques. The presence of the 4H-thiopyran ring is associated with the occur-
rence of IR absorption bands in the region 1 583–1 614 cm–1, in addition to easily
identifiable functional group characteristic bands (Table I), for example two different
1
CN stretching modes 2 218 and 2 236 cm–1 of tetracyano derivative 10. H and 13C
NMR signals (Tables II and III) were assigned per analogia using tabulated increments
1
and considering available data1c,4a. In the H NMR spectra of asymmetrically substituted
derivatives 7 and 23–27 two doublets caused by about a 1.1 Hz meta-coupling were
observed and assigned to H-3 and H-5 protons. Similarly, para-substituted phenyl
moieties in the 2- and 6-positions were recognized by the presence of typical AA′BB′
1
spin patterns in the H NMR spectra of compounds 6–14, 16–18 and 22–27.
Mass spectra of compounds 7, 9–11, 16 and 24–27 were also investigated (Table IV).
The abundance of molecular ions (Table V) has been found to be strongly dependent on
the 3,5-substitution patterns. Thus, for 3,5-unsubstituted compounds 7, 16, 24–27 as
Ph Ph
O
Ph Ph
-
Me
Me
H O
2
O
O
O O
Y
X
Y
X
SCHEME 1
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

666
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthipyrans
667
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

668
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
TABLE II
1H NMR data of new 4H-thiopyrans
δ (multiplicity, intensity, J in Hz)
Compounda
H-3
H-5
H-2 (o)
H-6 (o)
H-2 (m)
H-6 (m)
H-4 (p)
CH3
H-4 (o)
H-4 (m)
4
5
6
7
6.22
s, 1 H
7.29–7.58b
m, 20 H, +H-2(p)
–
7.39–7.57b
m, 16 H, +H-2 (p)
7.63
m, 4 H
7.39–7.57b
6.37
s, 2 H
7.69c
m, 8 H
7.25–7.33b
m, 6 H
7.40
m, 4 H
6.23
7.51
7.45
7.28c
7.25c
7.37
d, 1 H, 1.3
6.34
d, 2 H, 8.5
d, 2 H, 8.5
m, 4 H
m, 2 H
m, 4 H
7.69c
7.67c
d, 1 H, 1.3
d, 2 H, 8.5
d, 2 H, 8.5
8
9
–
–
–
–
–
7.52c
d, 4 H, 8.4
7.25
d, 4 H, 8.4
7.74
m, 4 H
7.39
m, 2 H
7.47c
m, 4 H
7.71c
d, 4 H, 7.2
7.67c
d, 4 H, 7.2
7.36–7.52b
m, 10 H
10
11
12
13
7.80
d, 4 H, 8.2
7.72
d, 4 H, 8.2
7.42–7.57b
m, 10 H
7.60c
d, 4 H, 8.4
7.44
d, 4 H, 8.5
7.60c
m, 4 H
7.36–7.44b
m, 6 H
7.76
d, 4 H, 7.7
7.68c
d, 4 H, 7.7
7.57c
m, 4 H
7.27–7.44b
m, 6 H
6.60
s, 1 H
7.58
d, 2 H, 8.4
7.51
7.49
7.37c
m, 4 H
7.33
m, 2 H
7.42
m, 4 H
d, 2 H, 8.4
7.38c
d, 2 H, 8.4
d, 2 H, 8.4
14
–
7.62
d, 2 H, 8.6
7.76
7.42c
d, 2 H, 8.6
7.67
7.56
m, 4 H
7.38–7.43b,c
m, 6 H
d, 2 H, 8.5
d, 2 H, 8.5
16
6.44
s, 2 H
7.78
d, 4 H, 8.3
8.10
d, 4 H, 8.3
7.24–7.32b
m, 6 H
7.39
m, 4 H
17d
6.41
7.73
7.84c
7.33
7.28
7.39
s, 2 H
d, 4 H, 8.3
d, 4 H, 8.3
m, 4 H
m, 2 H
m, 4 H
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthiopyrans
669
TABLE II
(Continued)
δ (multiplicity, intensity, J in Hz)
Compounda
H-3
H-5
H-2 (o)
H-6 (o)
H-2 (m)
H-6 (m)
H-4 (p)
CH3
H-4 (o)
H-4 (m)
18e
23
6.61
s, 2 H
7.78
d, 4 H, 8.2
8.00
d, 4 H, 8.2
7.22–7.31b
m, 6 H
7.38
m, 4 H
6.26
d, 1 H, 1.6
6.33
7.62
d, 2 H, 8.8
7.55c
7.55c
m, 2 H
6.97
7.37–7.47b
m, 6 H
7.32
m, 4 H
3.86
s, 3 H
d, 1 H, 1.1
m, 2 H
d, 2 H, 8.8
24
25f
26
27
6.38
d, 1 H, 1.1
6.19
7.72
d, 2 H, 8.2
7.55
7.66
d, 2 H, 8.8
6.93
7.25–7.34b
m, 6 H
7.39
m, 4 H
3.84
s, 3 H
d, 1 H, 1.1
d, 2 H, 8.8
d, 2 H, 8.8
6.34
7.82
d, 2 H, 8.2
7.54
7.68
d, 2 H, 8.8
6.91
7.22–7.39b
m, 10 H
3.82
d, 1 H, 1.1
6.16c
d, 1 H, 1.1
d, 2 H, 8.8
d, 2 H, 8.8
s, 3 H
6.19
d, 1 H, 1.1
6.47
7.56
d, 2 H, 8.8
7.79
6.94
d, 2 H, 8.8
8.10
7.24–7.42b
m, 10 H
3.84
d, 1 H, 1.1
d, 2 H, 8.8
d, 2 H, 8.8
s, 3 H
6.30
d, 1 H, 1.1
6.21
7.59
d, 2 H, 8.8
7.65
6.94
d, 2 H, 8.8
7.39b
7.39b
m, 11 H
+H-6 (p)
7.28
m, 2 H
3.84
7.39b
d, 1 H, 1.1
m, 2 H
s, 3 H
a
b
In the symmetrical compounds (4–6, 8–12, 16–18) H-3, H-5 and/or H-2, H-6 protons are identical;
c
d
unresolved multiplet; overlapping signals; additional signals: 7.50 m, 4 H (Ph-m); 7.61 m, 2 H
(Ph-p); 7.81c m, 4 H (Ph-o); measured in (CD3)2SO, 13.09 bs, 2 H (COOH); 6.15c bs, 2 H (NH2).
e
f
well as for 3,5-dicyano derivative 10, intense signals corresponding to M+• ions were
observed. On the contrary, mass spectra of 3,5-dibromo derivative 9 exhibit very weak
signals of M+• ions and with 3,5-dinitro derivative 11 no molecular ions were observed
• +
at all. Also the abundance ratios (M – X•)+/(M – C6H5 ) are strongly affected by the
mentioned substituent patterns. For the 3,5-unsubstituted and 3,5-dicyano derivatives 7,
10, 16 and 24–27 the abundance ratios are substantially less than unity while for the
3,5-dibromo and 3,5-dinitro derivatives 9 and 11, the values of 2.5 and 7.0, respec-
tively, were observed. Such behaviour seems to be in agreement with previous find-
ings4a. Other important fragment ions are formed by the loss of PhX(Y) and/or
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

670
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthipyrans
671
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

672
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
C6H4X(Y) species from molecular ions of 7, 9–11, 16 and 24–27. Moreover, in the
mass spectra of 9 and 11 certain ions with composition of the mass [M – (X + HX)],
[M – (Ph + HX)], [M – (X + Ph + X)], [M – (X + PhH + HX)], [M – (X + X + C6H4Y)]
and [M – (X + HX + PhY)] are present. Several types of ions are characteristic also in
the low m/z region of the mass spectra, where ions X(Y)C6H4CS+ seem to be structu-
rally significant. The occurrence of ions m/z 165 and 166 most probably indicates the
presence of fluorene-like fragments in accordance with mass spectra of similar pre-
viously reported4a compounds. In the EI spectra of amide 25 the same ions predomi-
nated as they appeared in the EI spectrum of nitrile 24, but in the FAB mass spectra no
such ions were observed. This fact could be explained by the dehydration 25→24 tak-
ing place on heating of amide 25 in a direct-inlet probe during EI MS measurements.
Only 3,5-unsubstituted 4H-thiopyran derivatives 6, 7, 16–18 and 23–27 exhibit the
UV/VIS-induced photocolouration (Table V) while the 3,5-substituted ones 1, 4, 5 and
8–14 are inactive in the followed visible spectral region. It may be noted, that a photo-
colouration has been recently reported8 for 3,5-dimethyl-2,4,4,6-tetraphenyl-4H-thiopyran
TABLE IV
Mass spectra of selected 4H-thiopyrans
Compound
m/z (relative abundance, %)
DI temperature, °C
7
200
507 (M+•, 71), 505 (M+•, 67), 430 (100), 428 (97), 405 (5), 403 (5), 350 (13),
349 (10), 348 (10), 314 (6), 272 (7), 166 (14), 154 (19), 146 (10)
9
612 (M+•, 0.7), 610 (M+•, 1.4), 608 (M+•, 0.7), 535 (19), 533 (41), 531 (100), 529
235
(82), 453 (7), 451 (10), 450 (10), 449 (8), 373 (20), 371 (13), 165 (12), 146 (14)
10
275
502 (M+•, 71), 501 (18), 425 (100), 400 (7), 317 (13), 166 (46), 165 (19), 146 (34),
121 (6), 102 (5)
11
606 (M+•, 55), 604 (M+•, 100), 602 (M+•, 48), 575 (8), 573 (14), 558 (10), 557 (8),
250
479 (6), 401 (22), 399 (16), 345 (5), 321 (10), 265 (13), 201 (7), 199 (8), 165 (15)
594 (M+•, 65), 525 (6), 517 (100), 421 (16), 420 (17), 228 (3), 175 (5), 166 (7),
165 (9)
16
170
24
457 (M+•, 94), 380 (100), 337 (13), 272 (7), 228.5 (M2+, 4), 190 (5), 166 (11),
230
25a
165 (19), 151 (10), 146 (5), 121 (4)
476 ((M + H)+, 100), 475 (80), 398 (65)
26
528 (M+•, 100), 451 (100), 408 (8), 355 (12), 354 (10), 311 (6), 191 (7), 166 (12),
170
165 (18), 151 (9)
27
432(M+•, 84), 355 (100), 312 (13), 247 (6), 166 (7), 165 (13), 151 (7), 121 (8)
165
a
FAB ionization.
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthiopyrans
673
but not for analogous 3,5-diphenyl derivative. Hence, it may be suggested that the
photocolouration will be limited to the 4H-thiopyrans lacking at the 3- and 5-positions
electron withdrawing substituents hindering a formation of the 3,5-bridge in the pro-
posed2b photoisomers like 28 or 29 shown in the Scheme 2 and formed in surface layers
of their crystal matrix without significant changes of molecular shapes2a. However,
from the kinetic studies (see bellow) it follows that two types of coloured species have
been formed. A recent quantum chemical study9 on a more extended series of π-elec-
tron molecular systems containing the C=S=C moiety also supports the existence of
*
Ph
Ph
S
Ph Ph
Ph Ph
2
Ph
Ar
1
2
1
2
1
2
1
S
S
Ar
Ar
Ar
Ar
Ph
S
Ar
Ar
Ar
28
29
1
2
Ar and Ar : 4-X-phenyl or 4-Y-phenyl
SCHEME 2
such hypervalent species. Data in Table VI suggest that the substituents X and Y af-
fected to a certain degree the visible absorption of the coloured 28-like photoisomers.
It reveals that the strongly π-electron with-drawing groups like COCF3, COPh, CO2H,
and partly CN, shift the maximum of the visible absorption bands to longer wave-
TABLE V
High-resolution mass spectral elemental analysis of selected 4H-thiopyrans
Elemental
composition
Compound
Found
Calculated
Type of ion
7
9
505.0505
529.0373
502.1241
601.9432
594.1077
457.1508
475.1613
528.1362
432.1550
505.0500
529.0374
502.1252
601.9425
594.1088
457.1500
475.1606
528.1371
432.1548
C30H20NS79Br
C31H18N2S79Br
C33H18N4S
C29H18NO2S79Br2
C33H20O2SF6
C31H23NOS
M+•
(M – Br)+
M+•
(M – NO2)+
M+•
M+•
M+•
M+•
M+•
10
11
16
24
25
26
27
C31H25NO2S
C32H23O2SF3
C30H24OS
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

674
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
lengths in comparison to earlier observed1c maxima of 28 out of 4H-thiopyrans 2 (398
and 564 nm) and 30 (394 and 600 nm).
Basic characteristics of the absorption spectra of the active substances 6, 7, 16–18,
23, 24 and 26 in chloroform show (Table VI) that, generally, four absorption peaks at
wavelengths λ = 234 ÷ 242 nm, 252 ÷ 268 nm, 277 ÷ 298 nm and 312 ÷ 360 nm can be
observed. The first and third absorption bands are as a rule superimposed on the main
TABLE VI
UV-VIS absorption maxima of the compounds studied
Starting 4H-thiopyran (CHCl3)
28-like photoisomers (solid state)a
Compoundb
λmax, nmc,d
log εe
4-X
4-Y
λmax, nmd
3
6
250 (270 sh)
4.47
4.55
4.60
4.52
4.60
4.51
4.58
4.57
4.50
H
H
564 s, 381
647 s, 422
613 s, 410
667 m, 470
656 w, 407
642 s, 418
610 m, 392
621 s, 437
672 s, 467
260 (312 m, 242 s)
252 (320 w, 252 sh)
292 (342 m, 252 s)
258 (333 m, 285 s)
268 (318 m, 242 sh)
254 (277 sh)
CN
CN
7
Br
CN
16
17
18
23
24
26
COCF3
COPh
CO2H
Br
COCF3
COPh
CO2H
OMe
OMe
OMe
256 (326 w, 281 sh)
262 (360 w, 298 sh)
CN
COCF3
a Polycrystalline powder in MgO after 15 s irradiation with a high pressure 200 W mercury discharge
c
lamp with an appropriate filter 230 nm < λ ≤ 350 nm; b before UV-illumination; main maximum,
satelites are given in parentheses; d symbols: s strong, m medium, w weak, sh shoulder; e ε in dm3 mol–1 cm–1.
0.5
A
0.4
0.3
0.2
0.1
0.0
1
2
FIG. 1
UV-VIS absorption spectra of pow-
der 26 at room temperature: 1 before
UV irradiation, 2 photochromic
bands after UV exposure
200
400
600
800
1 000
λ, nm
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthiopyrans
675
peak and are usually observed as main peak shoulders. The absorption spectra of the
solid phase are shifted to the red (Fig. 1); the first absorption band is observed at λ = 320
÷ 380 nm. Immediately after the irradiation of the substances under study with the light
of λexc ≤ 350 nm at room temperature, a green or blue colour was observed. The typical
difussion-reflection spectrum for 4H-thiopyran 26 (X = 4-COCF3, Y = 4-OMe) is given
in Fig. 1; the maximum of the new absorption lies at 672 and ca 467 nm. As it follows
from Table VI, the new absorptions are shifted to the red for all substituted substances
in comparison with unsubstituted compound 3 in the solid phase. The photocolouration
was also observed in solutions by flash photolysis. Here, four transient absorption
bands were observed; e.g. for the substance 3, the bands 310, 370, 420 and (530 ± 10)
nm were detected. The ratios of absorbances of these peaks are 92 : 20 : 10 : 1. This
transient absorption represents short lived species, τ = 180 µs (monomolecular reac-
tion). Evidently, the coloured species are stabilized in the solid state where two absorp-
tion bands were detected for λ > 370 nm: λ1 = 381 nm, λ2 = 564 nm with the ratio of
absorbances 1 : 2. The alternation of the absorbance intensities for the band maxima at
381 and 564 nm (rigid phase) and 370 and 530 nm (solution) and the missing of the
band at 420 nm in the rigid phase suggests that at least two types of species like 28 and
29 are responsible for the colouration process. Moreover, the dispersitivity of the
bleaching process in the rigid phase, which time dependence can be expressed by a
stretched exponential function
[M(t)]/[M(0)] = exp [–(νt)α] ,
(1)
where 0 < α < 1 measures the deviation from the our exponential behaviour, ν is the
decay rate constant, [M(t)] and [M(0)] is the concentration of the coloured species at
the time t and time t = 0, respectively, can follow from several facts: (i) the superposi-
tion of several exponentials of several coloured species, (ii) the broad distribution of
0.43
A
0.41
FIG. 2
0.39
Thermal bleaching of 28-like
species (polycrystalline UV-irradi-
ated sample of 4H-thiopyran 26
0.37
mixed with MgO) at room tem-
0
10
20
30
40
50
60
perature
t, min
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

676
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
the relaxation times and (iii) statistical distribution of thermodynamic reaction par-
ameters, especially in polycrystalline materials.
Concerning the case (iii), the optical properties of disordered polycrystalline material
must be regarded as resulting from a set of individual processes of different rates,
weighted by the distribution of parameters. If the kinetics are first-order at each site, the
superposition of time independent rates will cause the overall rate of the process to be
time dependent. The corresponding decay low for these dispersive processes10a differs
from the pure exponential form and follows exp (–tα).
In irregular systems, such as in the polycrystalline material, activation energies and
entropies of the photochromic back reaction depend on the local geometry around the
reacting species, and, consequently, they are quantities with statistical variation. The
thermally induced back reaction is associated with the rate constant ν(E) according to
the relation
ν(E) = ν0 exp [–(Em – E)/kT] ,
(2)
where ν0 is the frequency factor and E is the energy. Since the difference between the
ground state energy E and the maximum Em of the energy barrier depends on a set of
conformational parameters, each varying statistically, the most probable distribution
function for Em – E was assumed10b to be a Gaussian function characterized by its width
σ. Therefore, the time dependence of the concentration of coloured species should be
the convolution of first-order decay functions reflecting the monomolecular nature of
the reaction and the distribution function for the reaction rates
[M(t)] = {[M(0)]/(2πσ2)1/2} ∫ exp {–(E0 – E)2/2σ2} exp {–ν(E)t} dE .
(3)
The experimental results in air for the substance 3 have given the following parameters
at T = 288 K: α = 0.64, σ = 0.033 eV, ν = 8.42 . 10–5 s–1. The decay process was
possible to describe with one stretched exponential function. The photocolouration pro-
cess was found to be reversible, i.e. colouration with UV irradiation and thermal
bleaching could be repeated many times. It could be pointed out that the bleaching in
the rigid phase is much slower, several hundreds microseconds in solution. The bleach-
ing process in the case of the substituted substances 6, 7, 16–18, 23, 24 and 26 (see
Table VI) was different. Here, it was impossible to make successful fits of the decay
curves by a single-stretched exponential function, but two functions had to be used. A
typical example of the course of the thermal bleaching for compounds 26 is given in
Fig. 2. The successful fit was obtained by two-stretched exponentials with α1 = 0.69 for
shorter times (t < 1.5 min) and α2 = 0.34 for longer times. It means that at least two
coloured species like 28 and 29 are responsible for the photocolouration process. The
substitution strongly but not lucidly influencies the speed of the thermal bleaching:
4H-thiopyrans 16, 24 and 26 bearing the groups COCF3 and OMe behave as the parent
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthiopyrans
677
4H-thiopyran 3, e.g. the bleaching is longer than 10 h, while the substituents Br, CN,
COPh, CO2H and OMe in the compounds 6, 7, 17, 18 and 23 make the bleaching
process shorter.
EXPERIMENTAL
Temperature data are uncorrected. Melting points were determined using a Boetius apparatus. NMR
spectra (δ, ppm; J, Hz) were measured on a GEMINI 300 HC instrument (deuteriochloroform solu-
tions, TMS as internal standard) at 298 K. Homocorrelated 2D NMR experiments COSY and
1
ROESY were used to resolve overlapping signals in H NMR spectra (Table II). IR spectra (ν, cm–1;
CHCl3) were taken on a FTIR spectrometer NICOLET 740. UV-VIS absorption spectra were
measured in chloroform using a Hewlett–Packard 8451A recording spectrophotometer. The diffuse
reflectance of polycrystalline powders were recorded by a Perkin–Elmer–Hitachi 340 instrument.
Electron ionization spectra were mesured on a VG-7070E mass spectrometer with double focusation
(EB geometry, ion source temperature 250 °C, ionizing electron current 50 µA, ionizing electron energy
70 eV, accelerating voltage 6 kV). Samples were introduced using a direct inlet probe and heated to
lowest temperature necessary to record spectra of desired quality. Accurate mass measurements were
performed by the peak matching technique at a resolving power of 7 000 (10% valley definition)
with perfluorokerosene as standard and HRMS data are given in Table V. Fast atom bombardment
(FAB) mass spectrum of compound 25 was recorded on the same instrument. A standard saddle field
FAB gun was operated at 8 kV and 2 mA. Xenon as bombarding gas and a matrix of 3-nitrobenzyl
alcohol were used. HPLC was performed on a Separon SGX C18 column (3 × 150 mm, particle size
5 µm, Tessek, Czech Republic) in the inversion phase (methanol–water 9 : 1, UV detection at 254 nm),
and TLC on Silufol UV254 (Kavalier, Czech Republic). Preparative column chromatography: silica
gel (Aldrich) and preparative TLC (plates 20 × 20 × 0.05 cm, silica gel Aldrich, 5–25 µm, UV de-
tection at 254 nm). Samples for elemental analysis were dried in vacuo (ca 150 Pa) over paraffine
and P4O10 at 110 °C or at room temperature.
3-Bromo-2,4,4,6-tetraphenyl-4H-thiopyran (4)
2,4,4,6-Tetraphenyl-4H-thiopyran1c 3 (7.00 g, 17.4 mmol) was added at 0 °C to a stirred solution of
bromine (3.46 g, 22.6 mmol) in carbon disulfide (910 ml). After stirring for 3 h at 0 °C and for 18 h at
room temperature the reaction mixture was decomposed with a saturated aqueous solution of sodium
sulfite, treated with dichloromethane and the collected organic extracts were dried with magnesium
sulfate. Evaporation of the solvent in vacuo and crystallization of the residue afforded 7.78 g (93%)
colourless crystals of monobromoderivative 4, see Tables I–III.
Preparation of Cyano Derivatives 5–7, 10, 12, 14 and 24. General Procedure
Dry DMF (13–30 ml) was added under argon and stirring to bromo derivative 1, 2, 8, 9, 11 or 23
(10–60 mmol) and copper(I) cyanide11 (2–25 equivalents) and the mixture was then stirred at 175–185 °C
until disappearance of the starting compound (7.5–15 h). After cooling the reaction mixture was
poured into saturated solution of ammonium chloride in aqueous ammonia. The resulting precipitate
was filtered off, washed with water and dissolved in dichloromethane. The extract was dried with
magnesium sulfate, evaporated and subjected to column chromatography (silica gel 100–250 g,
eluents, see below). Crude products were purified by crystallization, see Table I, and the following
yields of the products were achieved: 5 (87%, CHCl3–C6H6 1 : 1), 6 and 7 (40 and 1.8%, CH2Cl2 or
CHCl3), 10 (1.7 and 6.4% from compounds 8 and 9, respectively, CH2Cl2–AcOEt 1 : 1 and then
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

678
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
preparative TLC, PE–CH2Cl2–AcMe 12 : 8 : 1), 14 and 12 (4.5%, PE–CH2Cl2 1 : 1, 42%, PE–CH2Cl2
1 : 2 and then CH2Cl2), and 24 and 25 (59 and 5%, PE–CH2Cl2 1 : 1 and then preparative TLC,
CH2Cl2–AcOEt 1 : 1) Individual spectral characteristics are given in Tables I–V.
3,5-Dibromo-2,6-bis(4-bromophenyl)-4,4-diphenyl-4H-thiopyran (8)
Bromine (2.3 g, 14.4 mmol) was added dropwise at 0 °C and under stirring to a solution of thio-
pyran1c 2 (2.74 g, 4.87 mmol) in carbon disulfide (55 ml), the reaction was allowed to continue for
3 h at the same temperature and then let at room temperature overnight. The same work-up procedure
as in the case of 4 yielded 2.42 g (78%) of tetrabromo derivative 8 as brownish crystals, see Tables I–III.
3,5-Dibromo-2,6-bis(4-cyanophenyl)-4,4-diphenyl-4H-thiopyran (9)
A solution of bromine (0.94 g, 7.84 mmol) in carbon disulfide (20 ml) was added under stirring at 0 °C
to thiopyran 6 (0.886 g, 1.96 mmol) in CH2Cl2 (15 ml). The mixture was stirred at 0 °C for 3 h and
at room temperature for 18 h. Then after cooling to 0 °C an additional portion of dibromine (4.07 g,
34.0 mmol) was added and the mixture was finally stirred 5 h at 0 °C. An analogous work-up as in
the case of 4 led to colourless crystals (1.01 g, 84%) of 3,5-dibromo derivative 9, see Tables I–V.
2,6-Bis(4-bromophenyl)-3,5-dinitro-4,4-diphenyl-4H-thiopyran (11)
Fuming 100% HNO3 (2.43 ml, 53.4 mmol) was added at 0 °C to a stirred solution of thiopyran 2
(2.00 g, 3.57 mmol) in chloroform (15 ml) and the reaction mixture was stirred for 1 h at the same
temperature. The collected organic layers obtained after treatment with water to pH 7 and an addi-
tional extraction of the aqueous phase with dichloromethane were dried with magnesium sulfate and
evaporated. The reaction mixture did not contain mononitro derivative 13 and was separated by
loose-layer chromatography on silica gel (70 g, petroleum ether–chloroform 1 : 1). Crystallization of
the crude product afforded yellow crystals (0.724 g, 31%) of dinitrothiopyran 11, see Tables I–V.
2,6-Bis(4-bromophenyl)-3-nitro-4,4-diphenyl-4H-thiopyran (13)
A mixture of 63% nitric acid (12.12 g, 121 mmol), thiopyran 2 (0.5 g, 0.892 mmol) and dichloro-
methane (5 ml) was gradually added to stirred acetanhydride (54.19 g, 531 mmol) cooled with a salt-
ice bath (–15 °C). After 23 min the reaction was quenched by pouring the mixture on ice,
dichloromethane (30 ml) was added and the resulting two-phase system was worked up as in the case
of 11. Preparative TLC on silica gel (45 g, petroleum ether–dichloromethane 2 : 1) followed by crys-
tallization yielded yellow crystals (0.150 g, 28%) of mononitro derivative 13, see Tables I–III.
2,6-Bis(4-trifluoroacetylphenyl)-4,4-diphenyl-4H-thiopyran (16)
Thiopyran 2 (2 g, 3.56 mmol) was heated in a mild argon flow to ca 70 °C and after cooling to room
temperature, tetrahydrofuran (50 ml) was added under argon. The solution was cooled at –78 °C in
the inert atmosphere and butyllithium (4.7 ml, 8.51 mmol) in hexane (1.81 M solution) was added in
portions. The resulting yellow slurry precipitate of 15 stirred for 15 min at –78 °C and then ethyl
trifluoroacetate (2.12 ml, 2.53 g, 17.8 mmol) was added at once under vigorous stirring. The colour
of the reaction mixture was changed from blue (several seconds) to brown and the mixture was
allowed to reach room temperature (40 min). The solution was decomposed with saturated aqueous
ammonium chloride (200 ml) and shaken up with diluted hydrochloric acid, treated with diethyl ether
(2 × 50 ml), combined organic layers were washed with saturated aqueous sodium hydrogencarbonate
solution, dried with magnesium sulfate and evaporated. Column chromatography on silica gel (200 g,
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Some New Functionalized Tetraphenylthiopyrans
679
petroleum ether–dichloromethane 1 : 1) and repeated crystallization afforded colourless needles,
(0.957 g, 45%) of thiopyran 16, see Tables I–V.
2,6-Bis(4-benzoylphenyl)-4,4-diphenyl-4H-thiopyran (17)
The reaction of thiopyran 6 (0.485 g, 1.10 mmol) in diethyl ether (15 ml) with phenyllithium in diethyl
ether (1.18 M solution, 3.2 ml, 3.78 mmol) under vigorous stirring at 0 °C was performed in the same
manner as in the above-mentioned case but only for 1 h at 0 °C and the reaction mixture was allowed
to stand overnight at ambient temperature. The resulting solution was poured into aqueous 5% NaOH
(200 ml), extracted with dichloromethane, washed with water, dried with magnesium sulfate and
evaporated. Column chromatography on silica gel (50 g, benzene) and crystallization resulted in yellowish
crystals (0.373 g, 56%) of dibenzoyl derivative 17, see Tables I–III.
2,6-Bis(4-carboxyphenyl)-4,4-diphenyl-4H-thiopyran (18)
Thiopyran 6 (1 g, 2.21 mmol) and potassium hydroxide (0.75 g, 13.7 mmol) in diethylene glycol (20 ml)
were stirred and heated at 180 °C for 2 h. The resulting mixture was poured onto water (200 ml),
extracted with chloroform (50 ml) and diethyl ether (2 × 50 ml). The aqueous layer was then heated
to 50 °C to remove residual diethyl ether and acidified with diluted sulfuric acid. After recooling, the
precipitate of crude product was collected on a sintered-glass filter, thoroughly washed with water,
recrystallized and the crystals washed with a small amount of dichloromethane. Dicarboxylic acid 18
(0.704 g, 65%) was obtained as finely crystalline powder, see Tables I–III.
1-(4-Bromophenyl)-5-(4-methoxyphenyl)-3,3-diphenylpentane-1,5-dione (22)
A solution of benzophenone (22.5 g, 0.123 mol), 4-methoxyacetophenone (15 g, 0.1 mol) and 4-bromo-
acetophenone (20 g, 0.1 mol) in diethyl ether (50 ml) was added dropwise to a stirred suspension of
sodium amide (14.5 g, 0.35 mol) in diethyl ether (100 ml) cooled in ice-water bath. The reaction
mixture was stirred for 2 h at room temperature and allowed to stay overnight. After 1 h heating on
water bath it was carefully decomposed by water (200 ml) and extracted with benzene. Collected
organic layers were washed with water, diluted sulfuric acid, repeatedly with water and after drying
with magnesium sulfate evaporated in vacuo. The residue was subjected to water steam distillation (2 h),
extracted with benzene and organic extracts were worked up as above. The crude residue was sub-
jected to column chromatography on silica gel (600 g, 7 × 35 cm) with cyclohexane and then with
benzene. Fractions containing diketone 22 (TLC, RF = 0.4, benzene) were evaporated and let to crystallize
from methanol (3 ml) and acetonitrile (0.5 ml) under cooling. Recrystallization from ethanol–benzene
and then from xylene yielded colourless crystals (4.75 g, 9%) of diketone 22, m.p. 131–132 °C. For
C30H25O3Br (513.4) calculated: 70.18% C, 4.91% H, 15.56% Br; found: 69.92% C, 5.06% H,
1
15.33% Br. IR spectrum: 1 689 (C=O), 1 601, 1 585 (C=C arom.). H NMR spectrum: 3.81 s, 3 H
(OMe); 4.32 s, 2 H (H-2); 4.38 s, 2 H (H-4); 6.83 d, 2 H, J = 8.8 (m-C6H4OMe); 7.15 m, 2 H
(p-Ph3); 7.21–7.31 m, 8 H (o,m-Ph3); 7.49 d, 2 H, J = 8.8 (m-C6H4Br); 7.69 d, 2 H, J = 8.8 (o-C6H4Br);
7.82 d, 2 H, J = 9.3 (o-C6H4OMe). 13C NMR spectrum: 44.20 CH2 (C-4); 44.83 CH2 (C-2); 47.37 C
(C-3); 55.26 CH3 (OMe); 113.44 CH (m-C6H4OMe); 126.17 CH (p-Ph3); 127.52 CH (o-Ph3); 127.75 C
(p-C6H4Br); 128.07 CH (m-Ph3); 129.47 CH (o-C6H4Br); 130.19 CH (o-C6H4OMe); 131.29 C (i-C6H4OMe);
131.57 CH (m-C6H4Br); 136.84 C (i-C6H4Br); 147.87 C (i-Ph3); 163.27 C (p-C6H4OMe); 197.69 C (C-5);
198.25 C (C-1).
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

680
Kroulik, Chadim, Polasek, Nespurek, Kuthan:
2-(4-Bromophenyl)-6-(4-methoxyphenyl)-4,4-diphenyl-4H-thiopyran (23)
A mixture of diketone 22 (3 g, 5.84 mmol) and P4S10 (4 g, 9.0 mmol) in xylene (50 ml) was stirred
under nitrogen and heated at 135 °C and the conversion was monitored by HPLC. After 10 h another
portion of P4S10 (4 g, 9.0 mmol) was added and the reaction was finished after 17 h. The mixture was
filterred off, evaporated in vacuo and the crude product was purified by column chromatography on
silica gel (150 g, cyclohexane and then benzene). The product 23 was recrystallized to afford 2.19 g
(73%) of colourless needles, see Tables I–III.
2-(4-Methoxyphenyl-6-(4-trifluoroacetylphenyl)-4,4-diphenyl-4H-thiopyran (26)
and 2-(4-Methoxyphenyl)-4,4,6-triphenyl-4H-thiopyran (27)
Reaction of 4H-thiopyran 23 (0.5 g, 0.978 mmol) with a solution of butyllithium in hexane (0.65 ml,
1.173 mmol) and ethyl trifluoroacetate (0.35 ml, 2.933 mmol) was performed in the same manner as
in the case of 16. The crude reaction mixture was separated by column chromatography on silica gel
(50 g, petroleum ether–dichloromethane 1 : 1). First fractions afforded, after evaporation and crystal-
lization, white crystals of by-product 27 (71 mg, 17%) while the following fractions gave yellow
crystals of the expected product 26 (0.291 g, 56%), see Tables I–V.
The work was partly sponsored by the Grant Agency of the Academy of Sciences of the Czech
Republic (grants No. A4050603 and No. 12/96K). The authors thank Dr P. Sedmera, Institute of
Microbiology, Academy of Sciences of the Czech Republic, Prague, for much valuable discussion.
REFERENCES
1. a) Mori Y., Maeda K.: J. Chem. Soc., Perkin Trans. 2 1991, 2061; b) Pirelahi H., Parchamazad I.,
Abaii M. S., Sheikhebrahimi S.: Phosphorus, Sulfur Silicon Relat. Elem. 1991, 58, 545; c) Sebek P.,
Nespurek S., Hrabal R., Adamec M., Kuthan J.: J. Chem. Soc., Perkin Trans. 2 1992, 1301.
2. a) Bohm S., Sebek P., Nespurek S., Kuthan J.: Collect. Czech. Chem. Commun. 1994, 59, 1115;
b) Bohm S., Adamec M., Nespurek S., Kuthan J.: Collect. Czech. Chem. Commun. 1995, 60,
1621.
3. Kuthan J., Sebek P., Bohm S.: Adv. Heterocycl. Chem. 1994, 59, 179.
4. a) Schwarz M., Sebek P., Kuthan J.: Collect. Czech. Chem. Commun. 1992, 57, 546; b) Sebek P.,
Kroulik J., Sedmera P., Havlicek V., Kuthan J.: Collect. Czech. Chem. Commun. 1994, 59, 2269.
5. Ellis G. P., Romney-Alexander T. M.: Chem. Rev. 1987, 87, 779.
6. Creary X.: J. Org. Chem. 1987, 52, 5026.
7. a) Carvalho A. P.: Ann. Chim. (Paris) 1935, 4, 499; b) Kurfurst A., Zeleny J., Schwarz M.,
Kuthan J.: Chem. Papers 1987, 41, 623; c) Sebek P., Novotny J., Kratochvil B., Schwarz M.,
Kuthan J.: Collect. Czech. Chem. Commun. 1992, 57, 2383.
8. Pirelahi H., Rahmani H., Mouradzadegun A., Fathi A., Moudjoodi A.: J. Photochem. Photobiol., A
1996, 101, 33.
9. Fabian J., Hess B. A., Jr.: J. Org. Chem. 1997, 62, 1766.
10. a) Richert R.: Chem. Phys. Lett. 1985, 118, 534; b) Richert R., Bassler H.: Chem. Phys. Lett.
1985, 116, 302.
11. Furniss B. S., Hannaford A. J., Smith P. W. G., Tatchel A. R.: Vogel’s Textbook of Practical
Organic Chemistry, 5th ed.. Longman Group U.K. Ltd., London 1989.
Collect. Czech. Chem. Commun. (Vol. 63) (1998)