Sulfinyl- and sulfonyl-substituted 2-benzylbenzoxazoles and 2-benzylbenzothiazoles as potential photochromic compounds

Article abstract of DOI:10.1055/s-2003-39178

Some novel 2-benzylbenzoxazoles and 2-benzylbenzothiazoles, substituted at the 2′ position by electron-withdrawing groups, were synthesized via the lithiation of the benzoxazole or benzothiazole ring. The expected reversible photoinduced protontransfer reaction of such compounds was studied.

Full text of DOI:10.1055/s-2003-39178

1112
PAPER
Sulfinyl- and Sulfonyl-Substituted 2-Benzylbenzoxazoles and 2-Benzylbenzo-
thiazoles as Potential Photochromic Compounds
S
ubstituted 2-Benz
r
ylbenzo
n
xazoles and 2
a
-Benzylbe
u
nzothiazoles
l
a
s
Pote
t
ntial Photoch
H
romic
C
ompound
e
s
ynderickx,a Robert Guglielmetti,a Roger Dubest,b Jean Aubard,b André Samat*a
a
Université de la Méditerranée, Faculté des Sciences de Luminy, UMR 6114 CNRS Case 901, 13288 Marseille Cedex 9, France
Fax +33(491)829301; E-mail: samat@luminy.univ-mrs.fr.
b
Université de Paris 7, UMR CNRS 7086, 1 rue Guy de la Brosse, 75005 Paris, France
Received 22 November 2002; revised 11 March 2003
the lifetime of the metastable form1a and a best under-
standing of the PIPT mechanism.
Abstract: Some novel 2-benzylbenzoxazoles and 2-benzylben-
zothiazoles, substituted at the 2 position by electron-withdrawing
groups, were synthesized via the lithiation of the benzoxazole or
benzothiazole ring. The expected reversible photoinduced proton-
transfer reaction of such compounds was studied.
The major inconvenience of these PIPT system is the
degradation2 of the material after several cycles of color-
ation–fading.
Key words: benzylation, heterocycles, metalations, sulfones, pho-
tochemistry
As part of our effort to bypass the fatigue resistance of
such compounds, we decided to investigate the PIPT of
new benzyl heterocycles substituted by electron with-
drawing groups other than the o-nitro group.
The increasingly fast development in new technologies
associated with optoelectronics, molecular switches or
optical data storage require the design and synthesis of
novel materials. A promising system is the photoinduced
tautomerism of 2,4-dinitrotoluene derivatives and, in par-
ticular, the photoinduced proton transfer (PIPT) process
occurring in 2-(2 ,4 -dinitrobenzyl)pyridine ( -DNBP)
and in some of its derivatives (Scheme 1).
Recently, we have reported that 2-(2 ,4 -diphenylsulfo-
nylbenzyl)pyridine underwent a reversible PIPT reaction
in the crystalline phase as well as in ethanolic solution at
ambient temperature (Scheme 2).3
SO2Ph
SO2Ph
UV
O
CH2
SO2Ph
CH
SO2Ph
N
N
O
O
∆
N
N
H
"NH" colored form
CH
Scheme 2
N
HO
Going on with the synthesis of products having potential
photochromic behaviour, we report here the preparation
of novel 2-benzylbenzoxazoles and 2-benzylbenzothiaz-
oles 9–15 substituted by sulfoxide or sulfone groups
(Figure 1).
D
hn1
O
D; hn2
hn3
O
O
O
O
N
N
N
N
O
O
hn1
D
N
CH2
O
CH
CH2
SOnR1
N
N
X
H
"NH" Form
R2
Scheme 1
n= 1 or 2 ; X= O, S ; R1= Et, Ph ; R2= H, NO2, SO2Ph
These compounds have drawn much attention due to their
potential applications as optically bistable systems.1
Therefore a lot of effort has been focused on the optimiza-
Figure 1
tion of the efficiency of the photoreaction, the increase of Indeed, such PIPT systems containing a nitro group, at the
2 position, have been studied so far.4
The synthesis of 2-benzylbenzoxazoles and 2-benzylben-
zothiazoles substituted at the 2 position either by a sul-
Synthesis 2003, No. 7, Print: 20 05 2003.
Art Id.1437-210X,E;2003,0,07,1112,1116,ftx,en;Z14702SS.pdf.
foxide or a sulfone group (Scheme 3, Table 1) has been
approached by metalation of benzoxazole5 and
© Georg Thieme Verlag Stuttgart · New York

PAPER
Substituted 2-Benzylbenzoxazoles and 2-Benzylbenzothiazoles as Potential Photochromic Compounds
1113
OH
CH
N
N
N
X
ii
i
SR1
CH2
SR1
H
X
X
5-8
1-4
X= O, S
R2
R 1= Et, Ph
R2
R2 = H, SPh
Scheme 3 Reagents and conditions: (i) BuLi, –70 °C, then substituted benzaldehydes, then aq HCl–EtOH–THF; (ii) SOCl2, CHCl3, 0 to
20 °C, then Zn, HOAc, reflux.
Table 1 Synthesis of 2-Benzylbenzoxazoles and 2-Benzylbenzothiazoles Substituted Either by an Ethylthio Group or a Phenylthio Group
Product
X
O
O
S
R1
R2
Yield (%)
Product
Yield (%)
1
2
3
4
SEt
SPh
SEt
SPh
H
77
70
95
90
5
6
7
8
75
67
70
83
SPh
H
S
SPh
benzothiazole6 ring, followed by treatment with 2-(eth- compounds 9 and 13 was accomplished at the 4 position
ylthio)benzaldehyde and 2,4-di(phenylthio)benzalde- as illustrated in Scheme 5.
hyde.3 The isolated -hydroxybenzyl heterocycles 1–4
were converted by reaction with thionyl chloride to their
N
N
CH2
SO2Et
CH2
SO2Et
chloromethylene derivatives. The reduction of the crude
product was carried out by heating with zinc powder in
acetic acid7 to afford 2-(2 -ethylthiobenzyl)benzoxazole
(5), 2-(2 ,4 -diphenylthiobenzyl)benzoxazole (6), and
their benzothiazoles analogs 7 and 8 in good yield.
i
X
X
14, 15
X= O, S 9, 13
NO2
Scheme 5 Reagents and conditions: (i) HNO3 and H2SO4 at –5 °C.
Selective oxidation of the thioether group to a sulfoxide or
sulfone group was obtained by reaction with m-chloroper-
benzoic acid in chloroform (Scheme 4).
Different solutions of compounds 9–15 (Table 2) in etha-
nol, toluene or acetonitrile, at different temperatures (5–
25 °C) were submitted to UV–visible continuous irradia-
tion with a xenon lamp. Unfortunately, we have not ob-
served a stable colored form.
N
CH2
SOnR1
i
5 - 8
X
9-13
UV flash photolysis 8 of a toluene solution (10–3 M) of 2-
[2 -(ethylsulfonyl)-4 -nitrobenzyl]benzothiazole 15 gave
rise to photoinduced absorption in the visible region with
R2
Scheme 4 Reagents and conditions: (i) MCPBA in CHCl3 at 0 °C.
2 bands:
= 445 nm, colorability A1 = 0.3; and
max
max = 590 nm, colorability A2 = 0.19. We observed two
With a view to tracking the impact of a nitro substituent rate constants for the reverse decoloration of the metasta-
on the PIPT reaction in such structures, the nitration of ble form of about 15 s–1and 0.16 s–1 (Figure 2).
Table 2 Oxidation of the Thioether Group and Nitration of Compounds 9 and 13
Oxidation
Product
Nitration
Product
X
O
O
S
n
2
2
1
2
2
R1
Et
Ph
Et
Ph
Et
R2
Yield (%)
Yield (%)
60
9
10
11
12
13
H
65
85
87
80
92
14
15
SO2Ph
H
S
SO2Ph
H
S
45
Synthesis 2003, No. 7, 1112–1116 ISSN 1234-567-89 © Thieme Stuttgart · New York

1114
A. Heynderickx et al.
PAPER
Figure 2 UV/Vis absorption spectra change of 15 (10–3 M in toluene) induced by UV flash photolysis and decoloration spectra measured at
450 nm.
1H NMR (CDCl3): = 1.10 (t, 3 H, J = 7.3 Hz), 2.80 (q, 2 H, J = 7.3
In these photolyse conditions, the compound 15 was the
Hz), 5.51 (s, 1 H, OH), 6.58 (s, 1 H), 6.58–7.19 (m, 4 H), 7.29–7.38
only one to present a photochromic behavior.
(m, 2 H), 7.46–7.54 (m, 2 H).
13C NMR (CDCl3): = 14.4, 29.4, 67.9, 110.9, 120.1, 124.5, 125.2,
127.2, 127.9, 129.1, 131.4, 135.2, 139.7, 140.3, 150.9, 167.0.
Further studies dealing with functionalization of the 2 po-
sition of the benzyl are currently in progress and will be
the subject of a future report.
MS: m/z = 285 (molecular ion).
Anal. Calcd for C16H15NO2S (285.36): C, 63.34; H, 5.30; N, 4.91.
Mps were determined on a Büchi 510 apparatus in capillary tubes
Found: C, 63.28; H, 5.10; N, 4.82.
1
and are uncorrected. The H NMR and 13C NMR spectra were re-
corded in deuterochloroform on a Brücker BM 250 spectrometer
(250 and 62.5 MHz, respectively) using tetramethylsilane as the in-
2-[ -Hydroxy-2 ,4 -di(phenylthio)benzyl]benzoxazole (2)
This compound was prepared from 2,4-diphenylthiobenzaldehyde
ternal standard. Column liquid chromatography was carried out on
(13.12 g). The crude product was purified by column chromatogra-
silica gel Merck 60 (70–230 mesh). The IR data were recorded on
phy (silica gel; pentane–Et2O, 5:3) to afford 2.
an Avatar 320 spectrometer and were performed in potassium bro-
Yield: 11.40 g (70% overall); yellow oil.
1H NMR (CDCl3): = 5.23 (s, 1 H, OH), 6.51 (s, 1 H), 6.96–7.35
(m, 15 H), 7.42–7.53 (m, 2 H).
mide pellets. The electron impact MS were obtained on a Shimadzu
QP-5000 spectrometer. Microanalyses were performed by the Mi-
croanalytical Centre of the University of Aix-Marseille III.
Photoirradiation was carried out by using a xenon lamp (150 W,
flux 1000 W/m2) or a mercury lamp (500 W). UV flash photolysis
was performed with a xenon lamp (82 J) by the Institute of Topolo-
gy and Dynamics of Systems (ITODYS, Paris-Jussieu)
Anal. Calcd for C26H19NO2S2 (441.57): C, 70.72; H, 4.34; N, 3.17.
Found: C, 70.68; H, 4.21; N, 3.09.
Substituted 2-( -Hydroxybenzyl)benzothiazoles 3,4; General
Procedure
Solvents (SDS Company, France) were used without further purifi-
cation and were dried over sieves if necessary.
To a solution of 2-lithiobenzothiazole (36.9 mmol), prepared ac-
cording to the procedure reported in the literature, 6 in anhyd THF
(100 mL), at –78 °C under N2 atmosphere was slowly added a solu-
tion of substituted benzaldehyde (40.7 mmoles) in anhyd THF (50
mL), with the temperature of the reaction mixture being maintained
at –78 °C. After complete addition, the mixture was stirred
at –78 °C for 2 h and then allowed to warm to –20 °C for 1 h. After
quenching with a mixture of aq HCl (35%; 4 mL), EtOH (4 mL) and
THF (16 mL), the solution was gently warmed to r.t., made slightly
basic with sat. NaHCO3 and evaporated under vacuum nearly to
dryness. The residue was extracted with CH2Cl2 (4 × 40 mL). The
combined organic extracts were dried (MgSO4) and evaporated to
dryness.
THF was distilled under nitrogen from sodium benzophenone ketyl
and used immediately. Metalations were performed under an argon
atmosphere and reagents were handled with syringes through septa.
Substituted 2-( -Hydroxybenzyl)benzoxazole 1,2; General Pro-
cedure
To a solution of 2-lithiobenzoxazole (36.9 mmol), prepared accord-
ing to the procedure reported in the literature,5 in anhyd THF (100
mL), at –78 °C under a N2 atmosphere, was slowly added a solution
of substituted benzaldehyde (40.7 mmol) in anhyd THF (50 mL),
with the temperature of the reaction mixture being maintained at
–78 °C. The resulting mixture was allowed to warm to r.t. and
stirred overnight. After quenching with a mixture of aq HCl (35%;
4 mL), EtOH (4 mL) and THF (16 mL), the solution was made
slightly basic with sat. aq NaHCO3 and evaporated under vacuum
nearly to dryness. The residue was extracted with CH2Cl2 (4 × 40
mL). The combined organic extracts were dried (MgSO4), filtered
and evaporated to dryness.
2-[ -Hydroxy-2 -(ethylthio)benzyl]benzothiazole (3)
This compound was prepared from 2-ethylthiobenzaldehyde (6.76
g). The crude product was purified by column chromatography (sil-
ica gel; eluted by pentane–Et2O, 5:2) to afford 3.
Yield: 10.56 g (95% overall); white solid; mp 102 °C.
1H NMR (CDCl3): = 1.18 (t, 3 H, J = 7.4 Hz), 2.85 (q, 2 H, J = 7.4
Hz), 4.85 (s, 1 H, OH), 6.52 (s, 1 H, CH), 7.10–7.44 (m, 5 H), 7.51
(dd, 1 H, J = 2.0, 7.0 Hz), 7.72 (d, 1 H, J = 7.9 Hz), 7.90 (d, 1 H,
J = 7.9 Hz).
13C NMR (CDCl3): = 14.4, 29.3, 71.5, 121.7, 123.1, 125.1, 126.0,
127.1, 127.9, 129.0, 131.0, 134.8, 135.4, 141.7, 152.6, 174.9.
2-[ -Hydroxy-2 -(ethylthio)benzyl]benzoxazole (1)
This compound was prepared from 2-ethylthiobenzaldehyde (6.76
g). The crude product was purified by column chromatography (sil-
ica gel; pentane–Et2O, 5:3) to afford 1.
Yield: 8.11 g (77% overall); green solid; mp 102 °C.
MS: m/z = 301 (molecular ion).
Synthesis 2003, No. 7, 1112–1116 ISSN 1234-567-89 © Thieme Stuttgart · New York

PAPER
Substituted 2-Benzylbenzoxazoles and 2-Benzylbenzothiazoles as Potential Photochromic Compounds
1115
Anal. Calcd for C16H15NOS2 (301.43): C, 63.75; H, 5.02; N, 4.65.
Found: C, 63.68; H, 4.95; N, 4.62.
Anal. Calcd for C16H15NS2 (285.43): C, 67.33; H, 5.30; N, 4.91.
Found: C, 67.41; H, 5.35; N, 4.93.
2-[ -Hydroxy-2 ,4 -di(phenylthio)benzyl]benzothiazole (4)
This compound was prepared from 2,4-diphenylthiobenzaldehyde
(13.12 g). The crude product was purified by column chromatogra-
phy (silica gel; CH2Cl2) to afford 4.
2-[2 ,4 -Di(phenylthio)benzyl]benzothiazole (8)
The title product was prepared from 4 (5.49 g). Purification by chro-
matography (silica gel; pentane–Et2O, 7:1) afforded 8.
Yield: 4.40 g (9.96 mmol, 83%); yellow oil.
Yield: 15.20 g (90% overall); yellow oil.
1H NMR (CDCl3): = 4.45 (s, 2 H), 6.90–7.42 (m, 15 H), 7.65 (d,
1 H, J = 8 Hz), 7.84 (d, 1 H, J = 7.9 Hz).
1H NMR (CDCl3): = 4.90 (s, 1 H, OH), 6.62 (s, 1 H), 7.05–7.45
(m, 14 H), 7.49 (d, 1 H, J = 8.0 Hz), 7.74 (dd, 1 H, J = 1.1, 7.5 Hz),
7.90 (d, 1 H, J = 7.6 Hz).
Anal. Calcd for C26H19NS3 (441.63): C, 70.71; H, 4.34; N, 3.17.
Found: C, 70.65; H, 4.42; N, 3.20.
Anal. Calcd for C26H19NOS3 (457.63): C, 68.24; H, 4.18; N, 3.06.
Found: C, 68.14; H, 4.11; N, 3.00.
Oxidation of Sulfides to Sulfoxides 11 and Sulfones 9–10, 12, 13
and 26; General Procedure
Reduction of Alcohols to Substituted 2-Benzyl Heterocycles 5–
8;7 General Procedure
To a stirred solution of sulfide (20 mmol) in CHCl3 (100 mL) at
0 °C was added a solution of MCPBA (1.1, 2.1, or 4.1 equiv) in
CHCl3 (50 mL). The mixture was maintained at T °C for t h (see be-
low). At r.t., the resulting solid was separated by filtration, and the
filtrate poured into H2O (30 mL). The resulting solution was made
slightly basic with NaCO3. The layers were separated and the aq
layer extracted with CH2Cl2 (2 × 15 mL). The combined organic
layers were dried (MgSO4), filtered, and evaporated under reduce
pressure to afford crude sulfoxide, or sulfone.
To a stirred, cooled solution (5 °C) of substituted 2-( -hydroxyben-
zyl) heterocycle (12 mmol) in CHCl3 (30 mL) was added dropwise
thionyl chloride (2.2 g, 18 mmoles) at such a rate that the tempera-
ture did not exceed 20 °C. The red mixture was then stirred for 3 h
at r.t. After cooling at 5 °C, H2O (15 mL) was poured slowly into
the reaction mixture and adjusted to pH 8 with aq NaCO3. The lay-
ers were separated and the aq layer extracted with CH2Cl2 (2 × 10
mL). The combined organic layers were dried (MgSO4), filtered,
and concentrated in vacuo to give 2-( -chlorobenzyl) heterocycle.
This product was used without further purification, dissolved in gla-
cial HOAc (30 mL) and refluxed with stirring. Zinc dust (3.9 g, 60
mmol) was added over the period of 1 h. The heating was main-
tained for 6 h, then the insoluble material was filtered and the HOAc
removed in vacuo. The residue was treated with a mixture of
CH2Cl2 (20 mL) and H2O (20 mL). The resulting solution was ad-
justed to pH 8 with K2CO3. The layers were separated and the aq
layer extracted with CH2Cl2 (2 × 10 mL). The combined organic
layers were washed with brine (10 mL), dried (MgSO4), filtered,
and concentrated in vacuo to give the reduced product.
2-[2 -(Ethylsulfonyl)benzyl]benzoxazole (9)
Prepared by oxidation of 5 (5.39 g) with MCPBA (7.24 g, 2.1
equiv), T = 20 °C and t = 20 h. Purification by column chromatog-
raphy (silica gel; CH2Cl2–Et2O, 9:1) gave 9.
Yield: 3.92 g (13 mmol, 65%); yellow oil.
IR (KBr): 1320, 1160 cm–1 (SO2).
1H NMR (CDCl3): = 1.24 (t, 3 H, J = 7.4 Hz), 3.21 (q, 2 H, J = 7.4
Hz), 4.81 (s, 2 H), 7.12–7.67 (m, 7 H), 7.85 (d, 1 H, J = 7.8 Hz).
Anal. Calcd for C16H15NO3S (301.36): C, 63.77; H, 5.02; N, 4.65.
Found: C, 63.82; H, 5.10; N, 4.80.
2-[2 -(Ethylthio)benzyl]benzoxazole (5)
The title product was prepared from 1 (3.42 g). Purification by chro-
matography (silica gel; CH2Cl2) afforded 5.
2-[2 ,4 -Di(phenylsulfonyl)benzyl]benzoxazole (10)
Prepared by oxidation of 6 (8.51 g) with MCPBA (14.15 g, 4.1
equiv), T = 20 °C and t = 16 h. Purification by column chromatog-
raphy (silica gel; CH2Cl2–Et2O–EtOAc, 7:3:0.5) followed by a re-
crystallization from EtOH provided 10.
Yield: 2.42 g (9 mmoles, 75%); yellow oil.
1H NMR (CDCl3): = 1.19 (t, 3 H, J = 7.4 Hz), 2.82 (q, 2 H, J = 7.4
Hz), 4.40 (s, 2 H), 7.01–7.50 (m, 7 H), 7.61 (m, 1 H).
Yield: 8.32 g (17 mmol, 85%); colorless crystals; mp 177 °C.
IR (KBr): 1330, 1160 cm–1 (SO2).
1H NMR (CDCl3): = 4.60 (s, 2 H), 7.05–7.27 (m, 6 H), 7.34–7.54
(m, 5 H), 7.65 (m, 2 H), 7.88 (m, 2 H), 8.01 (dd, 1 H, J = 2, 8 Hz),
8.77 (d, 1 H, J = 2 Hz).
13C NMR (CDCl3): = 31.7, 110.4, 119.8, 124.4, 125.1, 127.7,
128.0, 129.2, 129.2, 129.7, 132.5, 133.6, 133.9, 134.0, 139.4, 139.8,
140.3, 140.8, 141.0, 142.2, 150.6, 162.2.
Anal. Calcd for C16H15NOS (269.09): C, 71.34; H, 5.61; N, 5.20.
Found: C, 71.31; H, 5.68; N, 5.15.
2-[2 ,4 -Di(phenylthio)benzyl]benzoxazole (6)
The title product was prepared from 2 (5.30 g). Purification by chro-
matography (silica gel; pentane–Et2O, 3:1) afforded 6.
Yield: 3.42 g (8 mmoles, 67%); as a yellow oil.
1H NMR (CDCl3): = 4.33 (s, 2 H), 6.93–7.42 (m, 16 H), 7.57 (m,
1 H).
MS: m/z = 489 (molecular ion).
Anal. Calcd for C26H19NO5S2 (489.56): C, 63.79; H, 3.91; N, 2.86.
Found: C, 63.77; H, 3.95; N, 2.81.
Anal. Calcd for C26H19NOS2 (425.57): C, 73.38; H, 4.50; N, 3.29.
Found: C, 73.30; H, 4.52; N, 3.16.
2-[2 -(Ethylsulfinyl)benzyl]benzothiazole (11)
2-[2 -(Ethylthio)benzyl]benzothiazole (7)
The title product was prepared from 3 (3.62 g). Purification by chro-
matography (silica gel; CH2Cl2) afforded 7.
Prepared by oxidation of 7 (5.71 g) with MCPBA (3.80 g, 1.1
equiv), T = 20 °C and t = 2 h. Purification by column chromatogra-
phy (silica gel; CH2Cl2–Et2O, 5:3) provided 11.
Yield: 2.40 g (8.4 mmol, 70%); yellow oil.
Yield: 5.24 g (17.4 mmol, 87%); solid; mp 59 °C.
IR (KBr): 1060, 1040, 1020 cm–1 (S=O).
1H NMR (CDCl3): = 1.12 (t, 3 H, J = 7.4 Hz, CH3), 2.72 (m, 2 H,
CH2), 4.40 (d, 1 H, Hb, Jab = 16 Hz, CH2 benzylic), 4.52 (d, 1 H, Ha,
1H NMR (CDCl3): = 1.19 (t, 3 H, J = 7.4 Hz), 2.84 (q, 2 H, J = 7.4
Hz), 4.54 (s, 2 H), 7.01–7.42 (m, 6 H), 7.67 (d, 1 H, J = 7.9 Hz),
7.91 (d, 1 H, J = 7.9 Hz).
13C NMR (CDCl3): = 14.4, 28.44, 38.8, 121.6, 122.8, 124.8,
126.0, 126.6, 128.3, 130.0, 130.7, 135.8, 136.5, 137.5, 153.4, 171.1.
Synthesis 2003, No. 7, 1112–1116 ISSN 1234-567-89 © Thieme Stuttgart · New York

1116
A. Heynderickx et al.
PAPER
Jab = 16 Hz, CH2 benzylic), 7.16–7.48 (m, 5 H), 7.69 (dd, 1 H,
J = 0.5, 7.8 Hz), 7.86 (m, 2 H).
13C NMR (CDCl3): = 6.5, 36.3, 46.6, 121.5, 122.7, 125.0, 125.1,
126.1, 128.7, 130.7, 131.3, 134.2, 135.2, 142.5, 152.9, 168.8.
1H NMR (CDCl3): = 1.2 (t, 3 H, J = 7.5 Hz), 3.19 (q, 2 H, J = 7.5
Hz), 4.84 (s, 2 H), 7.49–7.59 (m, 3 H), 7.68 (d, 1 H, J = 8.8 Hz),
8.02 (d, 1 H, J = 8 Hz), 8.20 (dd, 1 H, J = 2.0, 8.8 Hz), 8.34 (1 H, d,
J = 2.0 Hz).
13C NMR (CDCl3): = 7.00, 32.2, 51.0, 107.2, 119.8, 120.4, 128.7,
131.3, 132.9, 133.5, 134.2, 137.0, 145.1, 146.3, 149.9, 169.4.
Anal. Calcd for C16H15NOS2 (301.43): C, 63.75; H, 5.02; N, 4.65.
Found: C, 63.69; H, 4.94; N, 4.42.
MS: m/z = 346 (molecular ion).
2-[2 ,4 -Di(phenylsulfonyl)benzyl]benzothiazole (12)
Prepared by oxidation of 8 (8.3 g) with MCPBA (14.15 g, 4.1
equiv), T = 20 °C and t = 4 h. Purification by column chromatogra-
phy (silica gel; Et2O–EtOAc, gradient) followed by a recrystalliza-
tion from EtOH provided 13.
Anal. Calcd for C16H14N2O5S (346.36): C, 55.48; H, 4.07; N, 8.09.
Found: C, 55.51; H, 4.12; N, 8.07.
2-[2 -(Ethylsulfonyl)-4 -nitrobenzyl]benzothiazole (15)
Prepared from 13 (4.85 g). The crude product was recrystallized
from EtOH to afford 15.
Yield: (8.09 g, 9.2 mmol, 80%); solid, mp 160 °C.
IR (KBr): 1340,1170 cm–1 (SO2).
Yield: 2.49 g (6.9 mmol, 45% overall); solid; mp 155 °C.
1H NMR (CDCl3): = 4.75 (s, 2 H), 7.16–7.57 (m, 9 H), 7.67 (d, 1
H, J = 8 Hz), 7.72–7.80 (m, 3 H), 7.90 (m, 2 H), 8.00 (dd, 1 H,
J = 1.9, 8.1 Hz), 8.76 (d, 1 H, J = 1.9 Hz).
13C NMR (CDCl3): = 36.5, 121.7, 123.0, 125.4, 126.3, 127.9,
128.1, 129.3, 129.6, 129.8, 132.5, 133.9, 134.1, 134.1, 135.7, 140.1,
140.5, 140.9, 142.0, 142.1, 152.9, 166.9.
1H NMR (CDCl3): = 1.31 (t, 3 H, J = 7.4 Hz, CH3), 3.22 (q, 2 H,
J = 7.4 Hz, CH2), 5.04 (s, 2 H, CH2 benzylic), 7.52–7.71 (m, 3 H),
8.05 (d, 1 H, J = 9 Hz), 8.11 (d, 1 H, J = 8 Hz), 8.35 (dd, 1 H,
J = 2.2, 9 Hz), 8.77 (d, 1 H, J = 2.2 Hz).
13C NMR (CDCl3): = 7.1, 37.3, 51.1, 118.1, 121.5, 123.0, 126.1,
128.5, 131.2, 133.1, 134.1, 135.9, 136.8, 144.8, 156.7, 175.7.
Anal. Calcd for C26H19NO4S3 (505.63): C, 61.76; H, 3.79; N, 2.77.
Found: C, 61.79; H, 3.85; N, 2.71.
MS: m/z = 362.1 (molecular ion).
Anal. Calcd for C16H14N2O4S2 (362.43): C, 53.02; H, 3.89; N, 7.73;
Found: C, 53.20; H, 3.90; N, 7.73.
2-[2 -(Ethylsulfonyl)benzyl]benzothiazole (13)
Prepared by oxidation of 7 (5.71 g) with MCPBA (7.24 g, 2.1
equiv), T = 20 °C and t = 12 h. Purification by column chromatog-
raphy (silica gel; CH2Cl2–Et2O, 5:3, gradient) provided 12.
Acknowledgement
This work has received the support of the CNRS in the frame of the
GDR 2466 ‘Photochromism: Molecules, Mechanisms, Materials.’
Yield: 5.84 g (18.4 mmol, 92%); yellow oil.
IR (KBr): 1310, 1150 cm–1 (SO2).
1H NMR (CDCl3): = 1.13 (t, 3 H, J = 7.4 Hz), 3.1 (q, 2 H, J = 7.4
Hz), 4.86 (s, 2 H), 7.19–7.51 (m, 5 H), 7.68 (dd, 1 H, J = 0.8, 8.0
Hz), 7.82 (d, 1 H, J = 7.9 Hz), 7.95 (d, 1 H, J = 7.8 Hz).
13C NMR (CDCl3): = 7.2, 36.7, 51.0, 121.6, 122.8, 125.1, 126.1,
128.0, 131.1, 133.0, 134.1, 135.6, 136.7, 137.1, 153.1, 169.2.
References
(1) (a) Eichen, Y.; Lehn, J. M.; Scherl, M.; Haarer, D.;
Caselegno, R.; Corval, A.; Kuldova, K.; Trommsdorff, H. P.
J. Chem. Soc., Chem. Commun. 1995, 713. (b) Frank, I.;
Grimme, S.; Peyerimhoff, S. D. J. Phys. Chem. 1996, 100,
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(3) Heynderickx, A.; Samat, A.; Guglielmetti, R. J. Heterocycl.
Chem. 2001, 38, 737.
MS: m/z = 317 (molecular ion).
Anal. Calcd for C16H15NO2S2 (317.43): C, 60.54; H, 4.76; N, 4.41.
Found: C, 60.49; H, 4.99, N, 4.24
Nitration of Compounds 9 and 13; General Procedure
To a cooled (–5 °C) and well-stirred concd sulfuric acid (96%) (12
mL) was added gradually 9 or 13 (15.3 mmol). Then red fuming ni-
tric acid (density = 1.5, 0.7 mL, 16.8 mmol) was added dropwise
over a period of about 10 min. After complete addition, the mixture
was stirred at –5 °C for 3 h, and then poured onto ice (about 100 g).
The resulting solution was basified (pH 10) by adding sat. aq
NaOH, and extracted with Et2O (3 × 50 mL). The combined ethe-
real extracts were dried (MgSO4), filtered, and concentrated in vac-
uo.
(4) Organic Photochromes; El’tsov, A. V., Ed.; Plenum Press:
New York, 1990, 178–228.
(5) Nutaitis, C. F.; Obaza-Nutaitis, J. Org. Prep. Proceed. Int.
1997, 29, 315.
(6) (a) Gilman, H.; Beel, J. A. J. Am. Chem. Soc. 1949, 71,
2328. (b) Chikashita, H.; Ishibaba, M.; Ori, K.; Itoh, K. Bull.
Chem. Soc. Jpn. 1988, 61, 3637.
(7) Sperber, N.; Papa, D.; Schwenk, E.; Sherlock, M. J. Am.
Chem. Soc. 1951, 73, 3856.
2-[2 -(Ethylsulfonyl)-4 -nitrobenzyl]benzoxazole (14)
Prepared from 9 (4.61 g). The crude product was purified by column
chromatography (silica gel; CH2Cl2–pentane–Et2O, 6:4:0.5) and re-
crystallized from EtOH, to afford 14.
Yield: 3.18 g (9.2 mmol, 60% overall); yellow solid; mp 127 °C.
(8) Meyer, J. J.; Levoir, P.; Dubest, R. Analyst 1995, 120, 447.
Synthesis 2003, No. 7, 1112–1116 ISSN 1234-567-89 © Thieme Stuttgart · New York