Facile synthesis of functionalized oligophenothiazines via one-pot bromine-lithium exchange-borylation-suzuki coupling (BLEBS)

Article abstract of DOI:10.1055/s-2008-1032118

The bromine-lithium exchange in bromophenothiazines followed by transmetalation with trimethyl borate and addition of palladium catalyst, 1.2 equivalents of a base, and an aryl halide yields the cross-coupling products in moderate to very good yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1032118

PAPER
1121
Facile Synthesis of Functionalized Oligophenothiazines via One-Pot Bromine–
Lithium Exchange–Borylation–Suzuki Coupling (BLEBS)
O
ne-Pot Synthesis
d
of
O
ligophe
a
nothiazinesm W. Franz, Thomas J. J. Müller*
Lehrstuhl für Organische Chemie, Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität Düsseldorf,
Universitätsstr. 1, 40225 Düsseldorf, Germany
Fax +49(211)8114324; E-mail: ThomasJJ.Mueller@uni-duesseldorf.de
Received 26 October 2007; revised 18 December 2007
ments of directly linked phenothiazinyl dyads and triads11
Abstract: The bromine–lithium exchange in bromophenothiazines
that can be regarded as models for polymers with elec-
followed by transmetalation with trimethyl borate and addition of
tronically coupled electrophores. Retrosynthetic analysis
palladium catalyst, 1.2 equivalents of a base, and an aryl halide
with fragmentations based upon Suzuki arylations12 sug-
yields the cross-coupling products in moderate to very good yields.
gested the use of boronates. Although several one-pot pro-
Key words: borylations, cross-coupling, heterocycles, metalation,
cedures with Negishi, Stille, and Kumada cross-coupling
reactions have been reported,13 practical one-pot prepara-
tions of boronates from electron-rich heterocycles by
halogen–lithium exchange followed by subsequent Suzu-
ki–Miyaura cross-coupling have remained largely unex-
plored. Here, we report a straightforward access to
functionalized arylated phenothiazines, phenothiazinyl
dyads and triads by a one-pot bromine–lithium exchange–
borylation–Suzuki (BLEBS) sequence.
oligomers, one-pot reactions
Phenothiazines constitute a pharmaceutically important
class of heterocycles1 with a broad spectrum of pharmaco-
logical activity.2 Most interestingly, phenothiazines are
also able to cleave DNA upon photochemical induction.3
As a consequence of the low oxidation potential, these tri-
cyclic nitrogen–sulfur heterocycles readily form stable
radical cations and their physiological activities can also
be attributed to this circumstance.4 Furthermore, the first
reversible oxidations1,5 are accompanied by characteristic,
deep colored radical cation absorptions. Thus, phenothi-
azine derivatives have become valuable spectroscopic
probes in molecular and supramolecular arrangements for
photoinduced electron transfer (PET) studies6 and as
functional motifs in materials science.7 The prospect of
incorporating highly redox active fragments like phe-
nothiazines into conjugated chains could constitute a so
far unknown class of redox addressable molecular wires,
and in particular, for redox manipulation of single mole-
cules with nanoscopic scanning techniques.8,9 Recently,
as part of our program to synthesize and investigate wire-
like oligophenothiazines,10 we communicated the synthe-
ses, structures, and first cyclic voltammetry measure-
In contrast to stepwise protocols which inevitably lead to
reduced yields during workup or chromatography, we set
out to develop a one-pot synthesis of arylphenothiazines
and oligophenothiazines by a BLEBS sequence. There-
fore, in the BLEBS reaction, a THF solution of a bro-
mophenothiazine 1 was cooled to –78 °C (dry ice/acetone
bath) and treated with n-butyllithium. Then, trimethyl bo-
rate was added and the reaction mixture was allowed to
come to room temperature. Finally, an aryl halide 2, cata-
lytic amounts of [Pd(PPh)3]4, and 1.2 equivalents of potas-
sium tert-butoxide were added and the mixture was heated
overnight affording the corresponding cross-coupling
products 3 in moderate to good yields (Scheme 1,
Table 1).
BLEBS sequence:
n-BuLi, –78 °C, THF
then: B(OMe)3, then r.t.
then: [Pd(PPh3)4], Ar-Hal (2)
KOt-Bu, reflux
Br
X
S
X
S
Ar
or
N
N
Two-step protocol:
n-C6H13
n-C6H13
1) n-BuLi, –78 °C, THF
then: B(OMe)3, then
pinacol, AcOH, r.t.
2) [Pd(PPh3)4], Ar-Hal (2)
K2CO3, DME, H2O, reflux
1a: X = phenothiazine
1b: X = H
3
BLEBS sequence: 54–83%
two-step protocol: 29–58%
Scheme 1 One-pot BLEBS sequence
SYNTHESIS 2008, No. 7, pp 1121–1125
x
x
.
x
x
.2
0
0
8
Advanced online publication: 06.03.2008
DOI: 10.1055/s-2008-1032118; Art ID: T16907SS
© Georg Thieme Verlag Stuttgart · New York

1122
A. W. Franz, T. J. J. Müller
PAPER
3a or 3e (traces)
or 2d only gave trace amounts of the desired products 3a
or 3e, respectively (Scheme 2). The major product in ei-
ther case was the pinacolyl boronate 4. Hence, the BLEBS
sequence appears to be superior with respect of efficiency
and practicability.
O
O
O
O
B
B
+
O
1a
S
N
B
O
[Pd(OAc)2, dppf]
KOAc (5 equiv), DMF, 60 °C, 16 h
then: 2a or 2d, 100 °C, 3 h
In conclusion, we have developed a one-pot approach to
functionalized (oligo)phenothiazines, starting from bro-
mophenothiazines. In comparison to the conventional
two-step protocol with intermediate workup and purifica-
tion, or even in comparison to a one-pot protocol with
bis(pinacolato)diboron as borylation source, the BLEBS
sequence always gives higher yields in shorter time. Fur-
thermore, THF is used as the sole solvent, which allows
maintaining water-free conditions. Finally, only one
equivalent of the base is needed. This makes the BLEBS
protocol generally suitable for coupling with base sensi-
tive aryl halides. Further studies with other heterocyclic
substrates and the extension of this one-pot methodology
are currently underway.
n-C6H13
4 (major product)
Scheme 2 Attempted one-pot palladium-catalyzed borylation–Su-
zuki coupling using bis(pinacolato)diboron
The conventional two step synthesis of the desired
arylphenothiazines and oligophenothiazines 3 requires the
preparation and isolation of the phenothiazine pinacolyl
boronate or boronic acid.14 Either the rather expensive tet-
ramethyl dioxoborolane is coupled by palladium catalysis
according to Masuda’s procedure15 with a suitable bro-
mophenothiazine 1, or, by bromine–lithium exchange of 1
followed by trapping with trialkyl borate and subsequent
transesterification with pinacol, the corresponding pinac-
olyl boronate is obtained in moderate yield.14 After purifi-
cation, Suzuki–Miyaura cross-coupling of borylated
phenothiazines works in many cases in very good yields
in a DME–H2O mixture and in the presence of an excess
of potassium carbonate.16 Yet, following the two-step pro-
tocol, with workup and chromatography after each step,
several days are required for the preparation of the desired
products 3 and the maximum yield is always limited by
the synthesis of the boronate. Most advantageously, the
BLEBS sequence circumvents the isolation of the bor-
onate and simultaneously reduces the amounts of added
base for the Suzuki step. Furthermore, THF can be suc-
cessfully used as the sole and common solvent in the reac-
tion mixture under water-free conditions. Only one
equivalent of base is finally needed since an ate-complex
is already formed by electrophilic trapping of the
lithiophenothiazine. This makes the BLEBS protocol
most suitable for aryl and heteroaryl halides bearing base-
sensitive functional groups (Table 1, entries 3 and 4).
Even aldehyde functionalities are carried through the se-
All reactions involving water-sensitive compounds were
carried out in flame-dried Schlenk glassware under N2 or
argon. Reagents and catalysts were purchased reagent
grade and used without further purification. Solvents were
dried and distilled according to standard procedures.22
The phenothiazine compounds 1a, 1b, 2a, and 2d were
synthesized according to literature procedures.11,16c Flash
column chromatography: silica gel 60, mesh 230–400,
Merck. TLC: silica gel plates (60 F254 Merck, Darmstadt).
1H, 13C, and DEPT spectra were recorded on
Bruker ARX 250, Bruker DRX 300 or Bruker DRX 500
spectrometer in CD2Cl2 or acetone-d6 as solvent, unless
otherwise stated. The assignments of quaternary C, CH,
CH2 and CH3 were made on the basis of DEPT spectra.
Mass spectra were recorded with JEOL JMS-700 und
Finnigan TSQ 700 spectrometers. Elemental analyses
were carried out in the microanalytical laboratory of the
Organisch-Chemisches Institut, Universität Heidelberg.
BLEBS Sequences on Bromophenothiazines 1; General Proce-
quence without formation of undesired side products (en- dure (GP)
To a well-stirred mixture of bromophenothiazine 1 (1 equiv) dis-
tries 5 and 6). The overall equimolarity of all reagents and
substrates used render the BLEBS protocol very econom-
ical and practical. Therefore, functionalized (oligo)phe-
nothiazines can be easily obtained in a one-pot reaction.
solved in anhyd THF and cooled down to –78 °C, was added drop-
wise a 1.6 M hexane solution of n-BuLi (1.1 equiv) via a syringe.
After stirring for 5 min at –78 °C, trimethyl borate (1.2 equiv) was
dropped slowly into the mixture and it was allowed to come to r.t.
Then, aryl halide 2 (1.2 equiv), Pd(PPh3)4 (4 mol%), and t-BuOK
(1.2 equiv) were added and the solution was stirred for 14 h at
67 °C. After cooling down to r.t., the mixture was diluted with
CH2Cl2 (150 mL) and aq sat. Na2SO3 (100 mL). The organic phase
was separated and the aqueous layer was extracted with CH2Cl2 (3
× 50 mL). The combined organic layers were dried (MgSO4) and the
solvents were removed under vacuum. The residue was purified
with flash chromatography yielding in the phenothiazines 3a–f as
yellow or orange oils or resins.
All products 3 were fully characterized by 1H, 13C NMR,
UV/Vis, and IR spectroscopy, mass spectrometry, and
correct combustion analysis. The obtained phenothiazines
and oligophenothiazines from the BLEBS sequence are
favorable building blocks in oligomer syntheses,16,17 and
starting materials for the design of phenothiazine-
fullerene dyads18 and phenothiazine functionalized sur-
faces.19 Therefore, an inexpensive and straightforward
preparation is highly desirable. An alternative could be
the Miyaura reaction using the rather expensive bis(pina-
colato)diboron.20 However, in our hands attempts to apply
a similar one-pot procedure21 to the coupling of 1a and 2a
7-Bromo-10,10¢-dihexyl-10H,10¢H-3,3¢-biphenothiazine (3a)
Prepared according to the GP and purified by flash chromatography
(hexane–acetone, 25:1); yield: 2.70 g (83%); yellow resin.
IR (KBr): 2952, 2925, 2853, 1600, 1575, 1457, 1250 cm–1.
Synthesis 2008, No. 7, 1121–1125 © Thieme Stuttgart · New York

PAPER
One-Pot Synthesis of Oligophenothiazines
1123
Table 1 One-Pot BLEBS Reactions
En- Bromophenothiazine 1
try
Aryl halide 2
Coupling product 3 (yield of BLEBS protocol, %)
Yield (%) of
the conven-
tional two-
step protocol
n-C6H13
N
I
S
Br
S
Br
S
1
2
4016c
S
Br
N
N
n-C6H13
n-C6H13
N
1a
2a
n-C6H13
3a (83)
n-C6H13
N
n-C6H13
N
5317
S
S
S
N
Br
2a
S
Br
S
N
N
n-C6H13
n-C6H13
n-C6H13
1b
1a
3b (77)
CO2Et
S
N
3
4
42
29
CO2Et
Br
2b
n-C6H13
3c (72)
Br
S
1a
1a
CO2Et
CO2Et
N
2c
n-C6H13
3d (54)
n-C6H13
N
Br
S
N
CHO
S
N
5
6
46
S
CHO
n-C6H13
2d
n-C6H13
3e (69)
n-C6H13
N
S
S
CHO
1b
2d
5818a
S
N
N
n-C6H13
n-C6H13
3f (62)
1H NMR (300 MHz, acetone-d6): d = 0.82–0.87 (m, 6 H), 1.27–1.29
(m, 8 H), 1.43–1.45 (m, 4 H), 1.71–1.83 (m, 4 H), 3.89 (t, J = 6.8
Hz, 2 H), 3.92 (t, J = 7.0 Hz, 2 H), 6.90–7.03 (m, 5 H), 7.13–7.22
(m, 2 H), 7.26–7.32 (m, 2 H), 7.35 (d, J = 2.2 Hz, 2 H), 7.39–7.44
(m, 2 H).
UV/Vis (CH2Cl2): lmax (e) = 268 (44000), 284 (320000), 326
(16400), 362 nm (11800).
Anal. Calcd for C36H39BrN2S2 (643.8): C, 67.17; H, 6.11; Br, 12.41;
N, 4.35; S, 9.96. Found: C, 67.13; H, 6.20; Br, 12.23; N, 4.35; S,
9.89.
13C NMR (75 MHz, acetone-d6): d = 14.2 (CH3), 23.2 (CH2), 27.1
(CH2), 27.1 (CH2), 27.4 (CH2), 27.5 (CH2), 32.1 (CH2), 32.2 (CH2),
47.8 (CH2), 47.9 (CH2), 114.7 (Cq), 116.6 (CH), 116.7 (CH), 117.0
(CH), 118.0 (CH), 123.2 (CH), 125.0 (Cq), 125.6 (CH), 126.0 (Cq),
126.1 (CH), 126.3 (CH), 127.6 (Cq) 128.0 (CH), 128.3 (CH), 130.0
(CH), 130.9 (CH), 134.7 (Cq), 135.3 (Cq), 144.7 (Cq), 145.3 (Cq),
145.4 (Cq), 146.0 (Cq).
7-Bromo-10,10¢-dihexyl-7¢-(10-hexyl-10H-phenothiazin-3-yl)-
10H,10¢H-3,3¢-biphenothiazine (3b)
Prepared according to the GP and purified by flash chromatography
(hexane–acetone, 25:1); yield: 1.11 g (77%); yellow resin.
IR (KBr): 2953, 2928, 2868, 2854, 1630, 1458, 1378, 1332, 1252,
1241, 807 cm–1.
MS (FAB+): m/z (%) = 644.2 (M+, 100), 599.1 (M+ – C6H13, 40),
474.0 (M+ – 2 C6H13, 35).
Synthesis 2008, No. 7, 1121–1125 © Thieme Stuttgart · New York

1124
A. W. Franz, T. J. J. Müller
PAPER
1H NMR (300 MHz, CD2Cl2): d = 0.85 (m, 9 H), 1.29 (m, 12 H),
1.46 (m, 6 H), 1.81 (m, 6 H), 3.95 (m, 6 H), 6.94 (m, 2 H), 7.04 (m,
4 H), 7.21 (m, 3 H), 7.33 (m, 2 H), 7.48 (m, 8 H), 7.39–7.44 (m, 2
H).
13C NMR (75 MHz, CD2Cl2): d = 14.2 (CH3), 23.0 (CH2), 23.0
(CH2), 26.9 (CH2), 27.0 (CH2), 27.1 (CH2), 27.2 (CH2), 27.2 (CH2),
31.8 (CH2), 31.9 (CH2), 47.9 (CH2), 47.9 (CH2), 48.0 (CH2), 114.6
(Cq), 115.8 (CH), 115.9 (CH), 116.0 (CH), 116.1 (CH), 117.0 (CH),
122.7 (CH), 124.7 (Cq), 124.8 (Cq), 125.0 (Cq), 125.0 (Cq), 125.2
(CH), 125.3 (CH), 125.3 (CH), 125.5 (CH), 125.5 (Cq), 125.6 (CH),
125.8 (CH), 127.1 (Cq), 127.7 (CH), 127.7 (CH), 129.8 (CH), 130.3
(CH), 134.3 (Cq), 134.4 (Cq), 134.5 (Cq), 134.8 (Cq), 144.2 (Cq),
144.4 (Cq), 144.5 (Cq), 144.7 (Cq), 144.8 (Cq), 145.5 (Cq).
MS (FAB+): m/z (%) = 431.3 (M+, 100), 386.3 (M+ – OCH2CH3,
14), 346.2 (M+ – C6H13, 15), 300.2 (M+ – C6H13 – OCH2CH3, 5),
273.2 (M+ – C6H13 – CO2CH2CH3, 2).
UV/Vis (CH2Cl2): lmax (e) = 246 (28700), 274 (35900), 304
(14400), 352 nm (10800).
Anal. Calcd for C27H29NO2S (431.6): C, 75.14; H, 6.77; N, 3.25; S,
7.43. Found: C, 75.02; H, 6.83; N, 3.44; S, 7.45.
10,10¢-Dihexyl-10H,10¢H-3,3¢-biphenothiazine-7-carbaldehyde
(3e)
Prepared according to the GP and purified by flash chromatography
(hexane–acetone, 20:1); yield: 0.41 g (69%); orange oil.
IR (KBr): 2953, 2926, 2854, 1685, 1602, 1579, 1461, 1415, 1377,
1335, 1310, 1279, 1244, 1198, 1144, 1104, 807, 747 cm–1.
MS (FAB+): m/z (%) = 925 (M+, 100), 840 (M+ – C6H13, 26), 755
(M+ – 2 C6H13, 10), 640 (M+ – 3 C6H13, 12).
1H NMR (300 MHz, CD2Cl2): d = 0.86–0.90 (m, 6 H), 1.28–1.35
(m, 8 H), 1.40–1.47 (m, 4 H), 1.75–1.86 (m, 4 H), 3.84 (t, J = 7.3
Hz, 2 H), 3.88 (t, J = 7.3 Hz, 2 H), 6.87–6.94 (m, 5 H), 7.13 (dd,
J = 7.8, 1.2 Hz, 1 H), 7.16–7.19 (m, 1 H), 7.28 (dd, J = 5.7, 2.1 Hz,
2 H), 7.31 (t, J = 2.3 Hz, 1 H), 7.34 (t, J = 2.3 Hz, 1 H), 7.56 (d,
J = 2.0 Hz, 1 H), 7.63 (dd, J = 8.4, 2.0 Hz, 1 H), 9.77 (s, 1 H).
UV/Vis (CH2Cl2): lmax (e) = 240 (4300), 272 (6600), 326 (2900),
364 nm (2300).
Anal. Calcd for C54H58BrN3S3 (925.2): C, 70.11; H, 6.32; Br, 8.64;
N, 4.54; S, 10.40. Found: C, 70.29; H, 6.32; Br, 8.37; N, 4.67; S,
10.57.
13C NMR (75 MHz, CD2Cl2): d = 14.32 (CH3), 14.33 (CH3), 23.17
(CH2), 23.19 (CH2), 27.0 (CH2), 27.1 (CH2), 27.2 (CH2), 27.4
(CH2), 32.0 (CH2), 32.1 (CH2), 48.0 (CH2), 48.6 (CH2), 115.4 (CH),
116.0 (CH), 116.2 (CH), 116.8 (CH), 122.9 (CH), 124.6 (Cq), 124.8
(Cq), 125.0 (Cq), 125.4 (CH), 125.5 (CH), 125.7 (CH), 125.8 (Cq),
125.9 (CH), 127.8 (CH), 127.9 (CH), 128.5 (CH), 130.7 (CH),
131.7 (Cq), 134.2 (Cq), 135.8 (Cq), 142.9 (Cq), 145.1 (Cq), 145.6
(Cq), 150.9 (Cq), 190.3 (CH).
Ethyl 4-(10-Hexyl-10H-phenothiazin-3-yl)benzoate (3c)
Prepared according to the GP and purified by flash chromatography
(hexane–acetone, 25:1); yield: 0.311 g (72%); yellow oil.
IR (film): 2956, 2928, 2855, 1713, 1605, 1575, 1463, 1366, 1334,
1273, 1182, 1106, 1019, 856, 772, 748, 485 cm–1.
1H NMR (300 MHz, acetone-d6): d = 0.85 (t, J = 7.1 Hz, 3 H), 1.30
(m, 4 H), 1.37 (t, J = 7.1 Hz, 3 H), 1.47 (m, 2 H), 1.81 (m, 2 H), 3.97
(t, J = 6.9 Hz, 2 H), 4.35 (q, J = 7.2 Hz, 2 H), 6.95 (dt, J = 1.2, 7.5
Hz, 1 H), 7.04 (d, J = 8.1 Hz, 1 H), 7.11 (d, J = 8.4 Hz, 1 H), 7.16
(m, 1 H), 7.21 (m, 1 H), 7.49 (d, J = 2.1 Hz, 1 H), 7.55 (dd, J = 2.1,
J = 8.7 Hz, 1 H), 7.74 (d, J = 8.7 Hz, 2 H), 8.04 (d, J = 8.7 Hz, 2 H).
EI MS (70 eV): m/z (%) = 594 (18), 593 (43), 592 (M+, 100), 507
(M+ – C6H13, 24), 422 (M+ – 2 C6H13, 25).
UV/Vis (CH2Cl2): lmax (e) = 270 (39400), 290 (57300), 326
(17800), 396 nm (14100).
13C NMR (75 MHz, acetone-d6): d = 14.2 (CH3), 14.6 (CH3), 23.3
(CH2), 27.1 (CH2), 27.5 (CH2), 32.1 (CH2), 47.9 (CH2), 61.4 (CH2),
116.7 (CH), 116.9 (CH), 123.5 (CH), 124.9 (Cq), 126.2 (Cq), 126.3
(CH), 127.0 (CH), 127.1 (CH), 128.0 (CH), 128.4 (CH), 129.8 (Cq),
130.7 (CH), 134.6 (Cq), 144.9 (Cq), 145.8 (Cq), 146.4 (Cq), 166.5
(Cq).
MS (FAB+): m/z (%) = 431.3 (M+, 100), 386.3 (M+ – OCH2CH3,
11), 346.2 (M+ – C6H13, 14), 300.2 (M+ – C6H13 – OCH2CH3, 4),
273.2 (M+ – C6H13 – CO2CH2CH3, 3).
Anal. Calcd for C37H40N2OS2 (592.9): C, 74.96; H, 6.80; N, 4.73; S,
10.82. Found: C, 75.12; H, 6.81; N, 4.85; S, 10.66.
10,10¢-Dihexyl-7¢-(10-hexyl-10H-phenothiazin-3-yl)-10H,10¢H-
3,3'-biphenothiazine-7-carbaldehyde (3f)
Prepared according to the GP and purified by flash chromatography
(hexane–acetone, 20:1); yield: 0.37 g (62%); orange resin.
IR (KBr): 2954, 2927, 2855, 1684, 1603, 1579, 1459, 1416, 1379,
1336, 1243, 1199, 1148, 1106, 1006, 874, 807, 747 cm–1.
UV/Vis (CH2Cl2): lmax (e) = 264 (31500), 320 nm (8200).
1H NMR (300 MHz, CD2Cl2): d = 0.86–0.91 (m, 9 H), 1.28–1.35
(m, 12 H), 1.39–1.49 (m, 6 H), 1.75–1.86 (m, 6 H), 3.82–3.91 (m, 6
H), 6.87–6.94 (m, 7 H), 7.11–7.19 (m, 2 H), 7.28–7.36 (m, 8 H),
7.56 (d, J = 1.9 Hz, 1 H), 7.63 (dd, J = 8.4, 1.9 Hz, 1 H), 9.71 (s, 1
H).
13C NMR (75 MHz, CD2Cl2): d = 14.32 (CH3), 14.34 (CH3), 14.35
(CH3), 23.17 (CH2), 23.20 (CH2), 23.21 (CH2), 27.0 (CH2), 27.20
(CH2), 27.22 (CH2), 27.36 (CH2), 27.37 (CH2), 27.4 (CH2), 32.0
(CH2), 32.1 (CH2), 48.0 (CH2), 48.1 (CH2), 48.6 (CH2), 115.3 (CH),
116.0 (CH), 116.09 (CH), 116.10 (CH), 116.14 (CH), 116.8 (CH),
122.9 (CH), 124.6 (Cq), 124.8 (Cq), 125.0 (Cq), 125.1 (Cq), 125.2
(Cq), 125.4 (CH), 125.42 (CH), 125.44 (CH), 125.47 (CH), 125.67
(Cq), 125.69 (CH), 125.76 (CH), 125.78 (CH), 125.9 (CH), 127.8
(CH), 127.9 (CH), 128.5 (CH), 130.7 (CH), 131.7 (Cq), 134.2 (Cq),
134.6 (Cq), 134.7 (Cq), 135.8 (Cq), 142.9 (Cq), 144.5 (Cq), 144.8
(Cq), 144.9 (Cq), 145.7 (Cq), 150.9 (Cq), 190.3 (CH).
Anal. Calcd for C27H29NO2S (431.7): C, 75.14; H, 6.77; N, 3.25; S,
7.43. Found: C, 74.95; H, 6.91; N, 3.15; S, 7.33.
Ethyl 2-(10-Hexyl-10H-phenothiazin-3-yl)benzoate (3d)
Prepared according to the GP and purified by flash chromatography
(hexane–acetone 25:1); yield: 0.231 g (54%); yellow oil.
IR (film): 2955, 2928, 2856, 1716, 1601, 1577, 1463, 1444, 1395,
1365, 1333, 1288, 1246, 1194, 1163, 1128, 1089, 762, 465 cm–1.
1H NMR (300 MHz, acetone-d6): d = 0.86 (t, J = 7.2 Hz, 3 H), 1.04
(t, J = 7.1 Hz, 3 H), 1.31 (m, 4 H), 1.48 (m, 2 H), 1.81 (m, 2 H), 3.97
(t, J = 7.1 Hz, 2 H), 4.10 (q, J = 7.2 Hz, 2 H), 6.94 (dt, J = 1.2, 7.5
Hz, 1 H), 7.05 (m, 2 H), 7.09 (m, 1 H), 7.12 (m, 1 H), 7.15 (m, 1 H),
7.21 (m, 1 H), 7.41 (m, 1 H), 7.45 (m, 1 H), 7.57 (dt, J = 1.5, 7.5 Hz,
1 H), 7.74 (dd, J = 1.8, 7.2 Hz, 1 H).
13C NMR (75 MHz, acetone-d6): d = 14.2 (CH3), 14.3 (CH3), 23.3
(CH2), 27.2 (CH2), 27.6 (CH2), 32.2 (CH2), 47.8 (CH2), 61.4 (CH2),
116.2 (CH), 116.7 (CH), 123.3 (CH), 125.2 (Cq), 125.3 (Cq), 127.8
(CH), 127.9 (CH), 128.1 (CH), 128.4 (CH), 128.5 (CH), 130.3
(CH), 131.1 (CH), 132.0 (CH), 132.6 (Cq), 136.4 (Cq), 141.7 (Cq),
145.5 (Cq), 146.2 (Cq), 169.2 (Cq).
MS (FAB+): m/z (%) = 876 (19), 875 (44), 874 (M + H+, 78), 873
(M+, 100), 872 (31), 802 (M+ – C5H11, 14), 790 (20), 789 (M+ + H –
C6H13, 32), 788 (M+ – C6H13, 24), 704 (M+ + H – C12H26, 12), 703
(M+ – C12H26, 9), 620 (12), 619 (M+ + H – C18H39, 19), 618 (M+ –
C18H39, 20).
Synthesis 2008, No. 7, 1121–1125 © Thieme Stuttgart · New York

PAPER
One-Pot Synthesis of Oligophenothiazines
1125
UV/Vis (CH2Cl2): lmax (e) = 264 (66300), 288 (101300), 368 nm
(8) (a) For applications of AFM and STM in chemistry, see
papers in the dedicated issue of Chem. Rev. 1997, 97, 1015–
1230; issue 4. (b) For applications in molecular electronics,
see, for example: Rabe, J. P. In An Introduction to Molecular
Electronics; Petty, M. C.; Bryce, M. R.; Bloor, D., Eds.;
Oxford University Press: New York, 1995, 261–278.
(c) For nanoscale materials, see papers in the dedicated issue
of Acc. Chem. Res. 1999, 32, 387–454; issue 5.
(9) For conductance of single molecules under STM conditions,
see, for example: (a) Bumm, L. A.; Arnold, J. J.; Cygan, M.
T.; Dunbar, T. D.; Burgin, T. P.; Jones, L. I. I.; Allara, D. L.;
Tour, J. M.; Weiss, P. S. Science 1996, 271, 1705.
(b) Davis, W. B.; Svec, W. A.; Ratner, M. A.; Wasielewski,
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(26800).
Anal. Calcd for C55H59N3OS3 (874.3): C, 75.56; H, 6.80; N, 4.81; S,
11.00. Found: C, 75.56; H, 6.83; N, 4.88; S, 11.10.
Acknowledgment
The support of this work by the Deutsche Forschungsgemeinschaft
(Graduate College 850, stipend for A.W.F.; SPP 1181) and by the
Fonds der Chemischen Industrie is gratefully acknowledged. The
authors also cordially thank Dr. Markus Sailer for valuable discus-
sions and the BASF AG for the generous donation of chemicals.
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Synthesis 2008, No. 7, 1121–1125 © Thieme Stuttgart · New York