Comparison of 2-arylnaphtho[2,3- b ]phospholes and 2-arylbenzo[ b ]phospholes: Effects of 2-Aryl groups and fused arene moieties on their optical and photophysical properties

Article abstract of DOI:10.1021/acs.joc.5b00541

Suzuki-Miyaura cross-coupling reactions were used in the divergent synthesis of a series of 2-arylnaphtho[2,3-b]phosphole P-oxides and their benzo[b]phosphole counterparts. We elucidated the electronic and steric effects of the 2-aryl groups and fused are

Full text of DOI:10.1021/acs.joc.5b00541

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pubs.acs.org/joc
Comparison of 2‑Arylnaphtho[2,3‑b]phospholes and
2‑Arylbenzo[b]phospholes: Effects of 2‑Aryl Groups and Fused Arene
Moieties on Their Optical and Photophysical Properties
Yoshihiro Matano,*,† Yuta Motegi,† Shinsuke Kawatsu,† and Yoshifumi Kimura‡
†Department of Chemistry, Faculty of Science, Niigata University, Nishi-ku, Niigata 950-2181, Japan
‡Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, Kyotanabe
610-0394, Japan
S
* Supporting Information
ABSTRACT: Suzuki−Miyaura cross-coupling reactions were used in
the divergent synthesis of a series of 2-arylnaphtho[2,3-b]phosphole P-
oxides and their benzo[b]phosphole counterparts. We elucidated the
electronic and steric effects of the 2-aryl groups and fused arene
moieties on the optical and photophysical properties of these two types
of phosphole-based π-systems.
i-conjugated phosphole derivatives are receiving attention
as new phosphorus-containing materials for use in organic
phosphole derivatives for the synthesis of phosphorus-
embedded [6]helicene structures.14 We envisioned that
naphtho[2,3-b]phosphole (Chart 1) would be a promising π-
extended framework for the development of new phosphole-
based fluorophores and semiconductors. Here, we report the
first divergent synthesis of a series of 2-arylnaphtho[2,3-
b]phosphole P-oxides and their benzo[b]phosphole counter-
parts using Suzuki−Miyaura cross-coupling reactions of the
corresponding 2-bromoareno[b]phosphole P-oxides with ar-
ylboronic acids. The electronic and steric effects of the 2-aryl
groups and fused-arene moieties on the optical and photo-
physical properties of these two types of π-systems will be
compared.15
P
electronics.1 2-Aryl- and 2,3-diaryl-benzo[b]phospholes (Chart
1) have been extensively investigated because of their light-
Chart 1. Benzo[b]phospholes (Left) and Naphtho[2,3-
a
b]phospholes (Right)
a
R2 = aryl; R3 = H or aryl; E = O, S, lone pair, etc.
We have recently reported the syntheses of 2-heteroaryl-, 2-
alkenyl-, and 2-alkynyl-benzo[b]phosphole π-systems,11 using
Stille, Heck, and Sonogashira reactions, respectively, of 2-
bromobenzo[b]phosphole P-oxide.16 2-Bromonaphtho[2,3-b]-
phosphole P-oxide 4 was chosen as a common precursor to use
the same cross-coupling strategy for the synthesis of 2-
arylnaphtho[2,3-b]phosphole derivatives. The precursor was
prepared from 2-bromo-3-(trimethylsilylethynyl)naphthalene
117 (Scheme 1). Treatment of 1 with diisobutylaluminum
hydride (DIBAL-H) in THF followed by addition of N-
bromosuccinimide (NBS) gave 2-bromo-3-[2-bromo-2-
(trimethylsilyl)vinyl]naphthalene 2 as an inseparable mixture
with 2-bromo-3-[2-(trimethylsilyl)vinyl]naphthalene. Lithiation
of crude 2 with ca. 2 equiv of nBuLi, followed by sequential
treatments with dichloro(phenyl)phosphine and hydrogen
peroxide, afforded 2-(trimethylsilyl)naphtho[2,3-b]phosphole
P-oxide 3. Bromolysis of the C(sp2)−Si bond of 3 with NBS
produced bromide 4 as a colorless solid.
emitting and electron-transporting properties.2−11 These
intrinsic features of π-conjugated benzo[b]phospholes originate
from rigid and coplanar π-frameworks bridged by a phosphorus
atom. Furthermore, the fundamental properties of benzo[b]-
phospholes can be finely tuned, like other phosphole-based π-
systems, by chemical functionalizations at the phosphole ring
carbons and phosphorus center. Several research groups have
independently developed efficient methods for the introduction
of aryl substituents at the 2- and 3-positions of a phosphole
ring, using intramolecular cyclizations of 2-(arylethynyl)-
phenylphosphine derivatives,2−7 intermolecular cycloadditions
of disubstituted acetylenes with phosphine derivatives,8−10 and
cross-coupling reactions of 2- or 3-bromobenzo[b]phosphole
P-oxides.7,11 Yoshikai et al. also established a highly modular
approach that allowed for the regioselective functionalization of
the fused benzene ring (benzo moiety) of the benzo[b]-
phosphole skeleton.10 However, to the best of our knowledge,
little attention has been paid to replacing the benzo moiety by a
polycyclic aromatic hydrocarbon (PAH).12−14 Recently,
Marinetti and co-workers reported photochemical and nickel-
catalyzed annulation reactions of 5,6-substituted benzo[b]-
Received: March 11, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.5b00541
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para-substituted phenylboronic acids 5b−f (Scheme 2). In all
cases, C−C bond formation was complete within 1−2 h,
affording the corresponding 2-arylnaphtho[2,3-b]phosphole P-
oxides 6b−f in 64−87% yields. The same catalyst also
promoted Suzuki−Miyaura cross-coupling reactions of 2-
bromobenzo[b]phosphole P-oxide 7 with arylboronic acids
5a−e,g,h, affording 2-arylbenzo[b]phosphole P-oxides 8a−e,g,h
in 62−90% yields (Scheme 2).18 A synthetic advantage of the
present cross-coupling protocol is its high functional group
tolerance; ethoxycarbonyl, cyano, and formyl groups were
delivered from 5b,c,h to final products 6b,c and 8b,c,h.
Compounds 6 and 8 were characterized using conventional
spectroscopic techniques. The 31P NMR peaks of 6 and 8
appeared at δP 37.4−37.8 and 38.7−39.6 ppm, respectively. In
the IR spectra of 6 and 8 in KBr pellets, the PO stretching
vibration bands were observed at 1192−1197 and 1182−1201
cm−1, respectively. The structures of 6d and 8c were
unambiguously elucidated by X-ray crystallography. As shown
in Figure 1, the naphtho[2,3-b]phosphole and p-anisyl rings in
Scheme 1. Synthesis of Bromide 4
We first screened the reaction conditions for Suzuki−
Miyaura cross-coupling of 4 with phenylboronic acid 5a and
found that the use of Pd(OAc)2, 2-(dicyclohexylphosphino)-
biphenyl [CyJohnPhos, denoted here by P(bp)Cy2], and a
mixed solvent system was effective for the desired C−C bond
formation. The reaction of 4 with 5a in the presence of catalytic
amounts of Pd(OAc)2 (10 mol %) and P(bp)Cy2 (20 mol %)
in acetonitrile−toluene−water (2:2:1 v/v/v) at 90 °C (bath
temperature) for 1 h gave 2-phenylnaphtho[2,3-b]phosphole P-
oxide 6a in 84% isolated yield after silica-gel column
chromatography (Scheme 2). Other bulky phosphine ligands
Scheme 2. Synthesis of 2-Arylnaphtho[2,3-b]phosphole P-
Oxides 6 and 2-Arylbenzo[b]phosphole P-Oxides 8
Figure 1. Crystal structure of 6d (50% ellipsoids). Top view (left) and
front view (right). Selected bond lengths (Å): P−C1, 1.814(3); P−C4,
1.819(2); P−O1, 1.487(2); C1−C2, 1.341(3); C2−C3, 1.466(3);
C3−C4, 1.429(4); C3−C8, 1.370(3); C4−C5, 1.356(4); C5−C6,
1.439(3); C6−C7, 1.436(4); C7−C8, 1.426(3).
6d are almost coplanar (dihedral angle between the two mean
planes = 10.0°), indicating that they are effectively π-
conjugated. Benzo[b]phosphole 8c also has a highly flat
structure (Figure S1, Supporting Information) with a narrow
dihedral angle of 7.4°. There are clear differences among the
C−C bond lengths of the fused benzene ring of 6d. The C3−
C4/C5−C6/C6−C7/C7−C8 bond lengths [1.426(3)−
1.439(3) Å] are appreciably longer than the C4−C5/C3−C8
bond lengths [1.356(4)−1.370(3) Å]. The average difference
between the six contiguous C−C bond lengths of 6d (0.05 Å)
is greater than that of 8c (0.02 Å), implying that the fused-
arene moieties of 6 and 8 keep the intrinsic nature of the
naphthalene and benzene rings, respectively.
We obtained UV/vis absorption and fluorescence spectra of
6 and 8 in CH2Cl2 to compare the electronic effects of the 2-
aryl substituents on the optical properties of the naphtho[2,3-
b]phosphole and benzo[b]phosphole P-oxides. Selected spectra
are shown in Figure 2, and the absorption/emission maxima
(λabs/λem) and fluorescence quantum yields (ΦF) are
summarized in Table 1.
As shown in Figure 2a, the absorption and fluorescence
spectra of 6a−c showed vibrational progressions derived from
their rigid π-frameworks. In each series of 6 and 8, electron-
withdrawing substituents (CO2Et, CN, CF3, CHO) had small
or negligible impacts on the spectral features, whereas electron-
such as DavePhos and XPhos (see Experimental Section for
definitions) showed similar efficiencies in terms of the reaction
time (1 h) and product yield (86−87%). When PPh3 was used
instead of P(bp)Cy2, however, the reaction rate was slower, and
6a was obtained in ca. 65% NMR yield after heating for 3 h.
With the Pd(OAc)2/P(bp)Cy2 catalyst in hand, we
performed Suzuki−Miyaura cross-coupling reactions of 4 with
B
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To compare the CT properties of these π-systems
quantitatively, we measured the solvatochromism of 6e and
8e (Figure S2, Supporting Information) and analyzed the
results using the Lippert−Mataga plots.20 The λabs/λem values of
6e varied from 412/478 nm (in toluene) to 404/561 nm (in
acetonitrile), and the Stokes shifts (Δν = νabs − νem) of 6e
greatly increased with increasing orientation polarizability (Δf)
of the solvent. The same trend was observed for 8e. As shown
in Figure S3 in the Supporting Information, the Lippert−
Mataga analyses gave linear solvation energy relationships
(LSERs) versus the Δf values (R = 0.97 in each case). The
LSERs of 6e (Δν/Δf = 1.15 × 104 cm−1) and 8e (Δν/Δf =
1.20 × 104 cm−1) are comparable, indicating that the highly
electron-donating para substituent enhances the CT properties
of the 2-arylnaphtho[2,3-b]phosphole and 2-arylbenzo[b]-
phosphole π-systems to the same degree.
The first oxidation potentials of 6a and 6e in CH2Cl2 (with
Bu4NPF6 as the supporting electrolyte) were determined to be
Epa = +1.34 and +0.49 V (vs ferrocene/ferrocenium),
respectively (Figure S4, Supporting Information). The para
substitution with the NPh2 group induced a large cathodic shift
of Epa, reflecting its high electron-donating ability. To gain
further insight into the electronic effects of the para
substituents on the HOMO and LUMO characteristics of the
2-arylnaphtho[2,3-b]phosphole π-system, we performed den-
sity functional theory (DFT) calculations for 6a,e at the
B3LYP/6-31G* level. As shown in Figure S5 in the Supporting
Information, the HOMO of 6a is delocalized over the
conjugated π-system, whereas that of 6e is localized on the
triphenylamine unit. The HOMO of 6e is higher than that of
6a, which qualitatively supports the observed result. In contrast,
the LUMOs of 6a and 6e reside mainly on the naphtho[2,3-
b]phosphole ring. These orbital characteristics imply that the
HOMO-to-LUMO transition of 6e has an intrinsic CT
character.
Most of the naphtho[2,3-b]phosphole derivatives (6a−d,f)
are moderately fluorescent, whereas 6e and most of the
benzo[b]phosphole derivatives (8a−e,g) are highly fluorescent.
To compare the photophysical properties of these two fused π-
systems, we measured the fluorescence lifetimes (τF) of 6a−f
and 8a−e,g in CH2Cl2 at room temperature. The τF values of
6a−f (2.5−4.7 ns) are appreciably shorter than those of 8a−e,g
(4.8−7.2 ns). The radiative and nonradiative decay rate
constants (kr and knr) calculated from the observed τF and
ΦF values are summarized in Table 1. In a series of the
naphtho[2,3-b]phosphole π-systems, the knr value of 6e is
significantly smaller than those of the other derivatives,
indicating that the exceptionally high ΦF value (0.85) of 6e
stems from the relatively small knr value. It is apparent that the
nonradiative dynamics of the excited CT state of 6e is
essentially different from that of the locally excited state of 6a.
The effects of the fused-arene moieties are also worth noting.
The kr values of 6a−d (1.1−1.9 × 108 s−1) and 8a−d (1.2−1.8
× 108 s−1) are comparable, whereas the knr values of 6a−d
(1.4−1.8 × 108 s−1) are considerably larger than those of 8a−d
(2.1−3.6 × 107 s−1). Furthermore, we tried to measure
phosphorescence spectra of 6a and 8a in toluene at 77 K.
Under these conditions, 6a showed phosphorescence peaks at
λmax = 618 and 682 nm (Figure S6, Supporting Information),
but 8a did not. In these less or slightly polarized rigid π-
systems, internal conversion from the excited singlet state to
the ground state is probably slower than intersystem crossing
(ISC) to the triplet state, i.e., the relatively large knr values of
Figure 2. UV/vis absorption (solid line) and fluorescence spectra
(dotted line, excited at the absorption maxima) of (a) 6a−e and (b)
8a−e in CH2Cl2.
Table 1. Optical and Photophysical Data of 6 and 8−10 in
CH2Cl2
a
λem/nm
τF/
c
b
6/8
λabs/nm (log ε)
(ΦF
)
ns
kr/s−1
knr/s−1
d
6a
6b
6c
6d
6e
6f
331 (4.44), 387
338 (4.48), 390
339 (4.49), 391
340 (4.46), 395
414 (4.49)
428 (0.37)
432 (0.54)
434 (0.54)
448 (0.46)
533 (0.85)
425 (0.42)
423 (0.85)
425 (0.82)
426 (0.87)
454 (0.82)
544 (0.81)
536 (0.81)
427 (0.056)
429 (0.035)
425 (<0.01)
3.5
2.8
2.5
3.8
4.7
3.0
7.2
5.1
4.8
6.4
6.0
6.1
1.1 × 108
1.9 × 108
1.8 × 108
1.2 × 108
1.8 × 108
1.4 × 108
1.2 × 108
1.6 × 108
1.8 × 108
1.3 × 108
1.3 × 108
1.3 × 108
1.8 × 108
1.6 × 108
1.8 × 108
1.4 × 108
3.2 × 107
1.9 × 108
2.1 × 107
3.6 × 107
2.7 × 107
2.8 × 107
3.2 × 107
3.1 × 107
d
d
d
d
332 (4.45), 387
350 (4.04)
e
8a
8b
8c
353 (4.12)
350 (4.19)
e
8d
365 (4.09)
8e
8g
8h
9
415 (4.29)
413 (4.29)
357 (4.21)
d
d
344 (4.53), 378
10
323 (4.52), 387
a
b
c
Excited at λabs
.
Absolute fluorescence quantum yields. Excitation
d
wavelengths are given in the Experimental Section. Absorption
maxima at the longest wavelength. The optical data for 8a and 8d in
e
THF were independently reported by Sanji et al. and Yamaguchi et al.
in refs 6 and 7a, respectively.
donating substituents (OMe, NPh2, NMe2) caused moderate or
large bathochromic shifts of the λabs and λem values relative to
those of the para-unsubstituted references 6a and 8a. It is
worth noting that the Ph2N- and Me2N-substituted derivatives
6e and 8e,g showed considerably broadened, structureless
absorption and emission bands in the visible region. These
spectral features suggest that 6e and 8e,g have large
intramolecular charge transfer (CT) from the donor (Ph2N
or Me2N) to the acceptor (arene-fused phosphole P-oxide)
units.19
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mL) was added diisobutylalminum hydride (DIBAL-H) (1 M, 9 mL, 9
mmol) at 0 °C, and the mixture was stirred for 18 h at room
temperature. N-Bromosuccinimide (NBS) (2.0 g, 11 mmol) was then
added at 0 °C, and the resulting mixture was stirred for 1 h at room
temperature. After quenching with water at 0 °C, the mixture was
passed through a Celite bed and the filtrate was separated. The
aqueous layer was extracted with hexane, and the combined organic
extracts were washed with brine, dried over Na2SO4, and evaporated
under reduced pressure to leave an oily residue, which was subjected
to silica-gel column chromatography (hexane/CH2Cl2 = 100:1). The
fraction of Rf = 0.76 (hexane/CH2Cl2 = 100:1) was collected and
evaporated to give an inseparable mixture of 2-bromo-3-[2-bromo-2-
(trimethylsilyl)vinyl]naphthalene (2) (ca. 1.4 g, ca. 3.6 mmol, ca. 50%
based on 1H NMR) and (2-(3-bromonaphthalen-2-yl)vinyl)-
trimethylsilane (ca. 1.4 mmol, ca. 19%). Compound 2 was
6a−d may indicate high efficiencies of the ISC processes of
6a−d compared with those of 8a−d.
Finally, we examined chemical functionalizations at the
phosphorus center of 6a (Scheme 3). Treatment of 6a with an
Scheme 3. Chemical Functionalizations of 6a
1
1
characterized by only H NMR spectroscopy. H NMR (400 MHz,
CD2Cl2) δ 0.34 (s, 9H), 7.44 (s, 1H), 7.48−7.52 (m, 2H), 7.72−7.86
(m, 2H), 8.10 (s, 1H), 8.23 (s, 1H).
excess of HSiCl3 in refluxing toluene gave the σ3-phosphorus
derivative 9, which further reacted with S8 in toluene to give P-
sulfide 10. Deoxygenation at the phosphorus center (from 6a to
9) shifts the longest λabs value hypsochromically, whereas
replacement with a thioxo function (from 6a to 10) does not
affect this value (Table 1). These chemical modifications
significantly reduce the ΦF values, although the reason for this
is not clearly understood.
In summary, we have established a convenient method for
the divergent synthesis of 2-arylnaphtho[2,3-b]phosphole P-
oxides and their benzo[b]phosphole counterparts using
Suzuki−Miyaura cross-coupling reactions of the corresponding
2-bromoareno[b]phosphole P-oxides. We have also shown that
the optical and photophysical properties of the naphtho[2,3-b]-
and benzo[b]phosphole π-systems can be finely tuned by
changing the 2-aryl groups. It is worth noting that the para-
R2N-substituted derivatives (R = Ph, Me) behave as polarity-
sensitive fluorophores because of the intrinsic CT character of
their excited states. The large solvatochromism and high
fluorescence quantum yields observed for these derivatives
show that donor−acceptor naphtho[2,3-b]phospholes and
benzo[b]phospholes would be promising π-frameworks for
constructing medium-sensitivity fluorescent probes and sen-
sors.19 The construction of different types of PAH-fused
phosphole derivatives for developing new phosphole-based
optical and semiconducting materials is now in progress.
Synthesis of 3. To a solution of crude 2 (ca. 1.4 g, ca. 3.6 mmol)
in Et2O (30 mL) was added n-BuLi (1.65 M, 7.25 mL, 12 mmol) at 0
°C, and the mixture was stirred for 2 h at room temperature, followed
by addition of PhPCl2 (0.80 mL, 5.9 mmol) at 0 °C. The resulting
mixture was stirred for 14 h at room temperature, and an excess of
aqueous H2O2 solution was then added to the mixture. After stirring
for 30 min, a saturated aq. NaHCO3 solution was added, and the
separated aqueous layer was extracted with EtOAc, and the combined
organic extracts were washed with brine, dried over Na2SO4, and
evaporated under reduced pressure. The residue was subjected to silica
gel column chromatography (CH2Cl2/acetone/Et3N = 100:10:1). The
violet fluorescent fraction of Rf = 0.54 (CH2Cl2/acetone = 10:1) was
collected, evaporated, and reprecipitated from hexane to give 2-
(trimethylsilyl)-1-phenylnaphtho[2,3-b]phosphole 1-oxide (3) as a
1
pale yellow solid (1.1 g, 3.2 mmol, 87%). mp 177−179 °C; H NMR
(700 MHz, CDCl3) δ 0.13 (s, 9H), 7.38−7.41 (m, 2H), 7.47−7.51 (m,
2H), 7.54−7.57 (m, 1H), 7.68 (d, 1H, JHP = 44.1 Hz), 7.67−7.70 (m,
2H), 7.73 (d, 1H, JHP = 2.8 Hz), 7.79 (d, 1H, J = 7.7 Hz), 7.86 (d, 1H,
J = 8.4 Hz) 8.07 (d, 1H, JHP = 9.8 Hz); 13C{1H} NMR (100 MHz,
CDCl3) δ −1.1 (d, JCP = 1.5 Hz), 123.4 (d, JCP = 9.7 Hz), 127.3, 128.3,
128.5 (d, JCP = 11.9 Hz), 128.8, 129.3, 130.5 (d, JCP = 9.7 Hz), 130.9
(d, JCP = 11.1 Hz), 131.1 (d, JCP = 98.2 Hz), 131.8 (d, JCP = 2.9 Hz),
132.6 (d, JCP = 102.7 Hz), 133.5 (d, JCP = 11.1 Hz), 135.4 (d, JCP = 2.2
Hz), 139.5 (d, JCP = 37.9 Hz), 142.4 (d, JCP = 59.5 Hz), 152.2 (d, JCP
=
6.7 Hz); 31P{1H} NMR (162 MHz, CDCl3) δ 47.2; IR (neat) ν 1191
(PO) cm−1; HRMS (ESI) m/z: [M + H]+ calcd for C21H22OPSi,
349.1172; found, 349.1168.
Synthesis of 4. To a solution of 3 (1.1 g, 3.2 mmol) in MeCN (30
mL) was added NBS (1.1 g, 6.1 mmol) at 0 °C, and the mixture was
stirred for 15 h at room temperature. Water was then added to the
mixture, the separated aqueous layer was extracted with CH2Cl2, and
the combined organic extracts were washed with brine, dried over
Na2SO4, and evaporated under reduced pressure. The residue was
reprecipitated from acetone to give 2-bromo-1-phenylnaphtho[2,3-
b]phosphole 1-oxide 4 as a colorless solid (0.89 g, 2.5 mmol, 80%). mp
EXPERIMENTAL SECTION
General Remarks. All melting points were recorded on a micro
melting point apparatus and are uncorrected. The identity and purity
of prepared compounds were established by H (400 or 700 MHz),
■
1
13C (100 or 175 MHz), and 31P (162 MHz) NMR spectroscopy and
high-resolution mass (HRMS) spectrometry (electron spray−quadru-
pole). The chemical shifts are reported in ppm as relative values vs
tetramethylsilane (1H, 13C) or H3PO4 (31P). IR spectra were obtained
using KBr pellets or neat films. UV/vis absorption, fluorescence, and
phosphorescence spectra and absolute fluorescence quantum yields
were obtained on the respective spectrometers. Electrochemical
measurements were performed using a glassy carbon working
electrode, a platinum wire counter electrode, and an Ag/Ag+ [0.01
M AgNO3, 0.1 M Bu4NPF6 (MeCN)] reference electrode. The
potentials were calibrated with ferrocene/ferrocenium (Fc/Fc+).
Compounds 117b and 711a were prepared according to reported
procedures. Other chemicals and solvents were of reagent grade and
used without further purification unless otherwise noted. Thin-layer
chromatography was performed with Kieselgel 60 F254, and
preparative column chromatography was performed using Silica Gel
60 (spherical, neutrality). All reactions were performed under an argon
atmosphere.
1
284−286 °C; H NMR (700 MHz, CDCl3) δ 7.44−7.49 (m, 2H),
7.52−7.62 (m, 3H), 7.64 (d, 1H, JHP = 28.7 Hz), 7.71 (d, 1H, JHP = 3.5
Hz), 7.73−7.78 (m, 2H), 7.82 (d, 1H, J = 7.7 Hz), 7.87 (d, 1H, J = 7.7
Hz), 8.12 (d, 1H, JHP = 11.9 Hz); 13C{1H} NMR (175 MHz, CDCl3)
δ 122.4 (d, JCP = 99.9 Hz), 123.3 (d, JCP = 9.3 Hz), 127.6, 127.7 (d, JCP
= 108.0 Hz), 128.4 (d, JCP = 107.8 Hz), 128.7, 128.9 (d, JCP = 13.0
Hz), 129.1, 129.4, 131.4 (d, JCP = 11.0 Hz), 132.0 (d, JCP = 10.0 Hz),
132.88 (d, JCP = 12.4 Hz), 132.94 (d, JCP = 2.6 Hz), 135.4 (d, JCP = 1.2
Hz), 137.5 (d, JCP = 24.8 Hz), 144.1 (d, JCP = 21.5 Hz); 31P{1H} NMR
(162 MHz, CDCl3) δ 33.2; IR (neat) ν 1207 (PO) cm−1; HRMS
(ESI) m/z: [M + H]+ calcd for C18H13BrOP, 354.9882; found,
354.9868.
General Procedure for the Synthesis of 6. A mixture of 4 (41
mg, 0.12 mmol), phenylboronic acid 5 (0.28 mmol), (2-biphenyl)-
dicyclohexylphosphine [CyJohnPhos] (8.6 mg, 24 μmol), Pd(OAc)2
(2.7 mg, 12 μmol), K2CO3 (52 mg, 0.38 mmol), MeCN (2 mL),
toluene (2 mL), and H2O (1 mL) was heated at 90 °C (bath
Synthesis of 2. To
a solution of 2-bromo-3-
(trimethylsilylethynyl)naphthalene 1 (2.2 g, 7.3 mmol) in THF (12
D
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temperature) for 2 h. The mixture was diluted with water, and the
aqueous layer was separated and then extracted with CH2Cl2. The
combined organic extracts were washed with brine, dried over Na2SO4,
and evaporated under reduced pressure. The residue was subjected to
silica-gel column chromatography (CH2Cl2/acetone/Et3N =
100:10:1). The fluorescent fraction was collected and reprecipitated
from hexane to give 6 as a solid. Other bulky phosphine ligands such
as DavePhos (2-dimethylamino-2′-dicyclohexylphosphinobiphenyl)
and XPhos (2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl)
were also effective for the present Suzuki−Miyaura cross-coupling
reactions.
JCP = 94.1 Hz), 160.1; 31P{1H} NMR (162 MHz, CDCl3) δ 37.8; IR
(KBr) ν 1195 (PO) cm−1; HRMS (ESI) m/z: [M + H]+ calcd for
C25H20O2P, 383.1195; found, 383.1188.
2-(4-(Diphenylamino)phenyl)-1-phenylnaphtho[2,3-b]phosphole
1-Oxide (6e). Rf = 0.65 (CH2Cl2/acetone = 10:1); mp 147 °C (dec.);
1H NMR (700 MHz, CDCl3) δ 6.97 (d, 2H, J = 8.4 Hz), 7.05 (t, 2H, J
= 7.7 Hz), 7.07−7.09 (m, 4H), 7.24−7.26 (m, 4H), 7.39−7.42 (m,
2H), 7.45−7.51 (m, 2H), 7.53−7.57 (m, 3H), 7.65 (d, 1H, JHP = 35.7
Hz), 7.73 (d, 1H, JHP = 3.5 Hz), 7.79 (d, 1H, J = 11.2 Hz), 7.80−7.83
(m, 2H), 7.84 (d, 1H, J = 7.7 Hz), 8.06 (d, 1H, JHP = 11.2 Hz);
13C{1H} NMR (175 MHz, CDCl3) δ 122.5, 123.0 (d, JCP = 8.6 Hz),
123.6, 125.0, 125.8 (d, JCP = 10.5 Hz), 126.9, 127.6 (d, JCP = 6.5 Hz),
128.4 (d, JCP = 14.3 Hz), 128.9 (d, JCP = 12.4 Hz), 129.30, 129.33,
1,2-Diphenylnaphtho[2,3-b]phosphole 1-Oxide (6a). Rf = 0.74
1
(CH2Cl2/acetone = 10:1); mp 267−268 °C; H NMR (700 MHz,
CDCl3) δ 7.29 (t, 1H, J = 7.7 Hz), 7.34 (t, 2H, J = 7.7 Hz), 7.38−7.40
(m, 2H), 7.46−7.51 (m, 2H), 7.56−7.59 (m, 1H), 7.75 (d, 2H, J = 7.7
Hz), 7.78−7.80 (m, 2H), 7.78 (d, 1H, JHP = 35.0 Hz), 7.81 (d, 2H, J =
7.0 Hz), 7.86 (d, 1H, J = 7.7 Hz), 8.11 (d, 1H, JHP = 11.2 Hz);
13C{1H} NMR (175 MHz, CDCl3) δ 123.7 (d, JCP = 9.3 Hz), 126.6 (d,
JCP = 6.5 Hz), 127.2, 128.6 (d, JCP = 1.9 Hz), 128.86 (d, JCP = 12.4
130.86 (d, JCP = 109.2 Hz), 130.88 (d, JCP = 9.8 Hz), 130.90 (d, JCP
=
99.4 Hz), 130.90, 131.0, 132.1 (d, JCP = 2.6 Hz), 133.0 (d, JCP = 11.7
Hz), 134.9 (d, JCP = 18.2 Hz), 135.8 (d, JCP = 1.2 Hz), 138.1 (d, JCP
=
28.7 Hz), 139.0 (d, JCP = 94.1 Hz), 147.1, 148.4; 31P{1H} NMR (162
MHz, CDCl3) δ 37.6; IR (KBr) ν 1194 (PO) cm−1; HRMS (ESI)
m/z: [M + H]+ calcd for C36H27NOP, 520.1825; found, 520.1805.
2-(4-(Trifluoro)phenyl)-1-phenylnaphtho[2,3-b]phosphole 1-
Oxide (6f). Rf = 0.72 (CH2Cl2/acetone = 10:1); mp 255−257 °C;
1H NMR (700 MHz, CDCl3) δ 7.39−7.42 (m, 2H), 7.49−7.54 (m,
Hz), 128.87, 128.94, 129.3, 130.6 (d, JCP = 99.4 Hz), 130.86 (d, JCP
109.2 Hz), 130.87, 130.93, 131.1 (d, JCP = 10.3 Hz), 132.2 (d, JCP = 2.6
Hz), 132.7 (d, JCP = 9.8 Hz), 133.2 (d, JCP = 11.9 Hz), 135.7 (d, JCP
=
=
1.2 Hz), 137.5 (d, JCP = 18.4 Hz), 137.7 (d, JCP = 28.2 Hz), 139.4 (d,
JCP = 94.3 Hz); 31P{1H} NMR (162 MHz, CDCl3) δ 37.7; IR (KBr) ν
1195 (PO) cm−1; HRMS (ESI) m/z: [M + H]+ calcd for
C24H18OP, 353.1090; found, 353.1079.
2-(4-Ethoxycarbonylphenyl)-1-phenylnaphtho[2,3-b]phosphole
1-Oxide (6b). Rf = 0.64 (CH2Cl2/acetone = 10:1); mp 248−250 °C;
1H NMR (700 MHz, CDCl3) δ 1.37 (t, 3H, J = 7.7 Hz), 4.33−4.37
2H), 7.58−7.61 (m, 3H), 7.76−7.79 (m, 2H), 7.83 (d, 1H, J = 7.7
Hz), 7.85 (d, 1H, JHP = 35.0 Hz), 7.85−7.87 (m, 3H), 7.89 (d, 1H, J =
9.1 Hz), 8.14 (d, 1H, JHP = 11.2 Hz); 13C{1H} NMR (175 MHz,
CDCl3) δ 123.9 (quart, JCF = 270.7 Hz), 124.5 (d, JCP = 9.3 Hz), 125.9
(quart, JCF = 3.9 Hz), 126.8 (d, JCP = 6.0 Hz), 127.6, 128.7, 128.8,
129.0 (d, JCP = 12.4 Hz), 129.4, 129.9 (d, JCP = 85.7 Hz), 130.4 (quart,
JCF = 32.0 Hz), 130.5 (d, JCP = 94.8 Hz), 130.9 (d, JCP = 11.0 Hz),
131.3 (d, JCP = 10.3 Hz), 132.5 (d, JCP = 2.1 Hz), 133.5 (d, JCP = 12.4
(m, 2H), 7.38−7.41 (m, 2H), 7.47−7.50 (m, 1H), 7.52 (t, 1H, J = 7.7
Hz), 7.59 (t, 1H, J = 7.7 Hz), 7.76−7.80 (m, 2H), 7.82 (d, 1H, J = 8.4
Hz), 135.6 (d, JCP = 1.4 Hz), 136.2 (d, JCP = 9.3 Hz), 137.2 (d, JCP
=
28.0 Hz), 138.1 (d, JCP = 95.5 Hz), 139.6 (d, JCP = 17.7 Hz); 31P{1H}
NMR (162 MHz, CDCl3) δ 37.4; IR (KBr) ν 1192 (PO) cm−1;
HRMS (ESI) m/z: [M + H]+ calcd for C25H17F3OP, 421.0964; found,
421.0941.
Hz), 7.83−7.85 (m, 2H), 7.84 (d, 1H, J = 3.5 Hz), 7.86 (d, 1H, JHP
=
35.0 Hz), 7.89 (d, 1H, J = 8.4 Hz), 8.00 (d, 2H, J = 8.4 Hz), 8.13 (d,
1H, JHP = 11.2 Hz); 13C{1H} NMR (100 MHz, CDCl3) δ 14.3, 61.1,
124.4 (d, JCP = 8.4 Hz), 126.4 (d, JCP = 5.8 Hz), 127.5, 128.7 (d, JCP
3.3 Hz), 128.9 (d, JCP = 13.5 Hz), 129.4, 130.11 (d, JCP = 100.1 Hz),
130.12, 130.4, 130.6 (d, JCP = 109.2 Hz), 130.8, 130.9, 131.2 (d, JCP
=
General Procedure for the Synthesis of 8. A mixture of 7 (0.11
g, 0.36 mmol), phenylboronic acid 5a (92 mg, 0.59 mmol), (2-
biphenyl)dicyclohexylphosphine (26 mg, 75 μmol), Pd(OAc)2 (8.1
mg, 36 μmol), K2CO3 (0.21 g, 1.5 mmol), MeCN (3 mL), and H2O (3
mL) was heated at 90 °C (bath temperature) for 1−3 h. The mixture
was diluted with water, and the aqueous layer was separated and then
extracted with EtOAc. The combined organic extracts were washed
with brine, dried over Na2SO4, and evaporated under reduced
pressure. The residue was subjected to silica-gel column chromatog-
raphy (CH2Cl2/acetone = 20:1). The fluorescent fraction was
collected and reprecipitated from hexane to give 8 as a solid.
1,2-Diphenylbenzo[b]phosphole 1-oxide (8a).6,7a,10 Rf = 0.42
=
10.5 Hz), 132.4 (d, JCP = 2.6 Hz), 133.4 (d, JCP = 11.7 Hz), 135.6 (d,
JCP = 1.2 Hz), 137.0 (d, JCP = 9.8 Hz), 137.3 (d, JCP = 28.0 Hz), 138.6
(d, JCP = 94.9 Hz), 139.3 (d, JCP = 17.8 Hz), 166.1; 31P{1H} NMR
(162 MHz, CDCl3) δ 37.5; IR (KBr) ν 1709 (CO), 1194 (PO)
cm−1; HRMS (ESI) m/z: [M + H]+ calcd for C27H22O3P, 425.1301;
found, 425.1293.
2-(4-Cyanophenyl)-1-phenylnaphtho[2,3-b]phosphole 1-Oxide
1
(6c). Rf = 0.58 (CH2Cl2/acetone = 10:1); mp > 300 °C; H NMR
(700 MHz, CDCl3) δ 7.39−7.42 (m, 2H), 7.49−7.52 (m, 1H), 7.53−
7.56 (m, 1H), 7.59−7.62 (m, 2H), 7.62 (d, 1H, J = 8.4 Hz), 7.74−7.78
(m, 2H), 7.83−7.86 (m, 3H), 7.87 (d, 1H, JHP = 2.8 Hz), 7.87 (d, 1H,
JHP = 32.9 Hz), 7.90 (d, 1H, J = 8.4 Hz), 8.14 (d, 1H, JH−P = 11.2 Hz);
13C{1H} NMR (100 MHz, CDCl3) δ 111.9, 118.9, 124.9 (d, JCP = 8.9
Hz), 127.0 (d, JCP = 6.7 Hz), 127.8, 128.8, 128.9, 129.0 (d, JCP = 12.6
Hz), 129.4, 129.7 (d, JCP = 101.2 Hz), 130.3 (d, JCP = 110.1 Hz), 130.8
(d, JCP = 11.1 Hz), 131.4 (d, JCP = 10.4 Hz), 132.6 (d, JCP = 3.0 Hz),
132.7, 133.5 (d, JCP = 11.9 Hz), 135.6, 136.9 (d, JCP = 28.3 Hz), 137.2
(d, JCP = 10.4 Hz), 137.7 (d, JCP = 94.5 Hz), 140.3 (d, JCP = 17.9 Hz);
31P{1H} NMR (162 MHz, CDCl3) δ 37.3; IR (KBr) ν 2227 (CN),
1
(CH2Cl2/acetone =20:1); mp 173−175 °C (dec.); H NMR (400
MHz, CDCl3) δ 7.27−7.44 (m, 7H), 7.45−7.54 (m, 2H), 7.60 (d, 1H,
JHP = 35.6 Hz), 7.60−7.65 (m, 1H), 7.68−7.71 (m, 2H), 7.73−7.79
(m, 2H); 31P{1H} NMR (162 MHz, CDCl3) δ 39.1; IR (neat) ν 1201
(PO) cm−1; HRMS (ESI) m/z: [M + H]+ calcd for C20H16OP,
303.0933; found, 303.0919.
2-(4-Ethoxycarbonylphenyl)-1-phenylbenzo[b]phosphole 1-
Oxide (8b). Rf = 0.30 (CH2Cl2/acetone = 20:1); mp 161−163 °C
1
(dec.); H NMR (400 MHz, CDCl3) δ 1.36 (t, 3H, J = 7.2 Hz), 4.34
1193 (PO) cm−1; HRMS (ESI) m/z: [M + H]+ calcd for
(q, 2H, J = 7.2 Hz), 7.35−7.56 (m, 6H), 7.62−7.67 (m, 1H), 7.70 (d,
1H, JHP = 36.0 Hz), 7.70−7.78 (m, 4H), 7.98 (d, 2H, J = 8.0 Hz);
13C{1H} NMR (100 MHz, CDCl3) δ 14.3, 61.0, 125.0 (d, JCP = 8.9
C25H17NOP, 378.1042; found, 378.1031.
2-(4-Methoxyphenyl)-1-phenylnaphtho[2,3-b]phosphole 1-Oxide
(6d). Rf = 0.58 (CH2Cl2/acetone = 10:1); mp 288−289 °C; 1H NMR
(400 MHz, CDCl3) δ 3.79 (s, 3H), 6.86 (d, 2H, J = 8.4 Hz), 7.36−
7.41 (m, 2H), 7.45−7.50 (m, 2H), 7.53−7.58 (m, 1H), 7.65 (d, 1H,
JHP = 35.6 Hz), 7.69−7.71 (m, 2H), 7.74 (d, 1H, JHP = 3.2 Hz), 7.76−
7.82 (m, 3H), 7.84 (d, 1H, J = 8.4 Hz), 8.08 (d, 1H, JHP = 10.8 Hz);
13C{1H} NMR (175 MHz, CDCl3) δ 55.3, 114.4, 123.0 (d, JCP = 8.4
Hz), 125.3 (d, JCP = 10.5 Hz), 126.9, 128.1 (d, JCP = 6.5 Hz), 128.4 (d,
JCP = 9.8 Hz), 128.8 (d, JCP = 12.4 Hz), 129.3, 130.75 (d, JCP = 99.4
Hz), 130.77 (d, JCP = 109.2 Hz), 130.8, 130.89 (d, JCP = 9.8 Hz),
130.90, 132.1 (d, JCP = 2.6 Hz), 133.0 (d, JCP = 11.7 Hz), 135.2 (d, JCP
= 19.1 Hz), 135.8 (d, JCP = 1.9 Hz), 138.0 (d, JCP = 28.7 Hz), 138.9 (d,
Hz), 126.4 (d, JCP = 6.0 Hz), 129.0 (d, JCP = 12.6 Hz), 129.2 (d, JCP
=
10.4 Hz), 129.6 (d, JCP = 10.4 Hz), 130.1, 130.31 (d, JCP = 83.3 Hz),
130.33, 130.6, 132.4 (d, JCP = 3.0 Hz), 132.7 (d, JCP = 108.6 Hz), 133.3
(d, JCP = 2.2 Hz), 136.7 (d, JCP = 10.4 Hz), 138.3 (d, JCP = 94.5 Hz),
138.4 (d, JCP = 19.3 Hz), 141.2 (d, JCP = 27.6 Hz), 166.0; 31P{1H}
NMR (162 MHz, CDCl3): δ 38.9; IR (neat) ν 1713 (CO), 1203
(PO) cm−1; HRMS (ESI) m/z: [M + H]+ calcd for C23H20O3P,
375.1145; found, 375.1128.
2-(4-Cyanophenyl)-1-phenylbenzo[b]phosphole 1-Oxide (8c). Rf
1
= 0.58 (CH2Cl2/acetone = 10:1); mp 231−232 °C; H NMR (700
MHz, CDCl3) δ 7.40−7.43 (m, 3H), 7.47 (dd, 1H, J = 3.5, 7.7 Hz),
E
DOI: 10.1021/acs.joc.5b00541
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
7.51 (dd, 1H, J = 1.4 Hz, 7.7 Hz), 7.56 (t, 1H, J = 7.7 Hz), 7.61 (d, 2H,
J = 8.4 Hz), 7.64−7.67 (m, 1H), 7.70 (d, 1H, JHP = 34.3 Hz), 7.70−
7.74 (m, 2H), 7.80 (d, 2H, J = 8.4 Hz); 13C{1H} NMR (175 MHz,
CDCl3) δ 112.0, 118.5, 125.3 (d, JCP = 9.8 Hz), 126.9 (d, JCP = 6.0
Hz), 129.0 (d, JCP = 98.7 Hz), 129.07, 129.14, 129.3 (d, JCP = 10.5
4H), 7.34 (t, 2H, J = 7.6 Hz), 7.39−7.50 (m, 4H), 7.69 (d, 2H, J = 8.4
Hz), 7.73 (d, 1H, JHP = 9.2 Hz), 7.77 (d, 1H, J = 8.4 Hz), 7.87 (d, 1H,
J = 8.0 Hz), 8.00 (s, 1H), 8.06 (d, 1H, JHP = 5.6 Hz); 13C{1H} NMR
(75 MHz, CDCl3) δ 122.2, 125.7, 126.3, 127.1 (d, JCP = 9.3 Hz), 127.9
(d, JCP = 3.8 Hz), 128.0 (d, JCP = 29.0 Hz), 128.1, 128.70 (d, JCP = 5.8
Hz), 128.71, 128.73, 129.3 (d, JCP = 22.2 Hz), 129.5 (d, JCP = 1.2 Hz),
Hz), 130.0 (d, JCP = 10.5 Hz), 130.7 (d, JCP = 11.0 Hz), 132.6 (d, JCP
=
133.2 (d, JCP = 4.5 Hz), 133.3 (d, JCP = 20.3 Hz), 133.7, 134.5 (d, JCP
=
2.5 Hz), 132.7 (d, JCP = 108.5 Hz), 133.5 (d, JCP = 1.9 Hz), 137.0 (d,
JCP = 3.1 Hz), 137.3 (d, JCP = 87.0 Hz), 139.4 (d, JCP = 19.6 Hz), 140.9
(d, JCP = 27.5 Hz); 31P{1H} NMR (162 MHz, CDCl3) δ 38.7; IR
(neat) ν 2226 (CN), 1196 (PO) cm−1; HRMS (ESI) m/z: [M +
H]+ calcd for C21H15NOP, 328.0886; found, 328.0876.
17.7 Hz), 136.3 (d, JCP = 17.0 Hz), 141.4, 144.3 (d, JCP = 3.1 Hz),
149.9 (d, JCP = 7.9 Hz); 31P NMR (161 MHz, CDCl3) δ −3.5; HRMS
(ESI) m/z: [M + H]+ calcd for C24H18P, 337.1141; found, 337.1131.
Synthesis of 10. Crude 9 (57 mg) was treated with elemental
sulfur (116 mg, 3.63 mmol) in refluxing toluene. After 9 was
consumed completely, the reaction mixture was evaporated under
reduced pressure. The residue was subjected to silica-gel column
chromatography (toluene/CH2Cl2 = 10:1), and the violet fluorescent
fraction of Rf = 0.28 (hexane/EtOAc = 10:1) was collected and
reprecipitated from MeOH to give 1,2-diphenylnaphtho[2,3-b]-
phosphole 1-sulfide (10) (30 mg, 0.082 mmol, 48%) as a pale pink
solid. mp 209−211 °C; 1H NMR (700 MHz, CDCl3) δ 7.28−7.30 (m,
1H), 7.33 (t, 2H, J = 7.0 Hz), 7.38−7.41 (m, 2H), 7.45−7.48 (m, 1H),
7.50 (t, 1H, J = 7.7 Hz), 7.57 (t, 1H, J = 7.0 Hz), 7.76 (d, 2H, J = 7.7
Hz), 7.81 (d, 1H, JHP = 35.0 Hz), 7.82 (d, 1H, J = 7.7 Hz), 7.88−7.93
(m, 4H), 8.09 (d, 1H, JHP = 11.9 Hz); 13C{1H} NMR (175 MHz,
CDCl3) δ 123.9 (d, JCP = 7.9 Hz), 127.0 (d, JCP = 7.2 Hz), 127.1, 128.4
(d, JCP = 28.2 Hz), 128.81, 128.82 (d, JCP = 12.4 Hz), 128.9, 129.1,
130.0 (d, JCP = 77.9 Hz), 130.2 (d, JCP = 11.7 Hz), 130.9 (d, JCP = 12.4
2-(4-Methoxyphenyl)-1-phenylbenzo[b]phosphole 1-Oxide (8d).6
Rf = 0.36 (CH2Cl2/acetone = 20:1); mp 155−157 °C; 1H NMR (700
MHz, CDCl3) δ 3.78 (s, 3H), 6.85 (d, 2H, J = 8.4 Hz), 7.28−7.31 (m,
1H), 7.36−7.41 (m, 3H), 7.46−7.50 (m, 2H), 7.47 (d, 1H, JHP = 36.4
Hz), 7.59−7.62 (m, 1H), 7.66 (d, 2H, J = 8.4 Hz), 7.74−7.77 (m,
2H); 31P{1H} NMR (162 MHz, CDCl3) δ 39.3; IR (neat) ν 1182
(PO) cm−1; HRMS (ESI) m/z: [M + H]+ calcd for C21H18O2P,
333.1039; found, 333.1025.
2-(4-(Diphenylamino)phenyl)-1-phenylbenzo[b]phosphole 1-
Oxide (8e). Rf = 0.66 (CH2Cl2/acetone = 10:1); mp 107−109 °C
(dec.); 1H NMR (700 MHz, CDCl3) δ 6.96 (d, 2H, J = 9.1 Hz), 7.03−
7.05 (m, 2H), 7.06−7.08 (m, 4H), 7.23−7.26 (m, 4H), 7.27−7.30 (m,
1H), 7.35−7.37 (m, 1H), 7.39−7.42 (m, 2H), 7.46 (d, 1H, JHP = 36.4
Hz), 7.48−7.51 (m, 4H), 7.57−7.60 (m, 1H), 7.76−7.79 (m, 2H);
13C{1H} NMR (100 MHz, CDCl3) δ 122.4, 123,6, 124.1 (d, JCP = 17.0
Hz), 132.0 (d, JCP = 3.1 Hz), 132.3 (d, JCP = 11.0 Hz), 133.3 (d, JCP
=
Hz), 125.0, 125.7 (d, JCP = 13.4 Hz), 127.5 (d, JCP = 6.7 Hz), 128.5 (d,
JCP = 10.5 Hz), 128.89 (d, JCP = 12.6 Hz), 128.95 (d, JCP = 10.4 Hz),
129.3, 130.3 (d, JCP = 97.4 Hz), 130.7, 130.8, 132.1 (d, JCP = 3.0 Hz),
132.5 (d, JCP = 108.6 Hz), 133.1 (d, JCP = 1.5 Hz), 133.9 (d, JCP = 20.1
Hz), 138.3 (d, JCP = 93.7 Hz), 147.0, 148.4; 31P{1H} NMR (162 MHz,
CDCl3) δ 39.1; IR (neat) ν 1197 (PO) cm−1; HRMS (ESI) m/z:
[M]+ calcd for C32H24NOP, 469.1590; found, 469.1580.
2-(4-(Dimethylamino)phenyl)-1-phenylbenzo[b]phosphole 1-
Oxide (8g). Rf = 0.34 (CH2Cl2/acetone = 20:1); mp 180−181 °C;
1H NMR (400 MHz, CDCl3) δ 2.95 (s, 6H), 6.63 (d, 2H, J = 8.8 Hz),
7.21−7.25 (m, 1H), 7.30−7.33 (m, 1H), 7.35−7.48 (m, 4H), 7.37 (d,
1H, JHP = 37.6 Hz), 7.55−7.62 (m, 3H), 7.74−7.80 (m, 2H); 13C{1H}
NMR (175 MHz, CDCl3) δ 40.1, 112.1, 120.4 (d, JCP = 10.5 Hz),
123.7 (d, JCP = 9.1 Hz), 127.81 (d, JCP = 7.2 Hz), 127.83 (d, JCP = 10.5
Hz), 128.77 (d, JCP = 11.7 Hz), 128.82 (d, JCP = 10.5 Hz), 130.70 (d,
JCP = 96.8 Hz), 130.72 (d, JCP = 10.5 Hz), 131.2 (d, JCP = 20.3 Hz),
131.9 (d, JCP = 2.6 Hz), 132.3 (d, JCP = 108.0 Hz), 133.0 (d, JCP = 1.9
Hz), 138.6 (d, JCP = 93.4 Hz), 142.6 (d, JCP = 28.9 Hz), 150.5;
31P{1H} NMR (162 MHz, CDCl3) δ 39.6; IR (neat) ν 1189 (PO)
cm−1; HRMS (ESI) m/z: [M + H]+ calcd for C22H21NOP, 346.1355;
found, 346.1343.
12.4 Hz), 134.4, 135.1 (d, JCP = 72.6 Hz), 135.3, 136.4 (d, JCP = 15.7
Hz), 138.2 (d, JCP = 24.9 Hz), 140.4 (d, JCP = 77.9 Hz); 31P NMR
(161 MHz, CDCl3) δ 45.18; HRMS (ESI) m/z: [M + H]+ calcd for
C24H18PS, 369.0861; found, 369.0863.
X-ray Crystallographic Data. 6d (CCDC 1048750): C25H19O2P,
MW = 382.37, 0.36 × 0.094 × 0.090 mm3, monoclinic, P21/n, a =
12.2059(5) Å, b = 6.2367(2) Å, c = 13.0601(5) Å, β = 108.2880(10)°,
V = 943.98(6) Å3, Z = 2, ρ = 1.345 g cm−3, μ = 1.64 cm−1, collected
6413, independent 3004, parameters 254, Rw = 0.0741, R = 0.0311 (I >
2σ(I)), GOF = 1.341. 8c (CCDC 1048751): C21H14NOP, MW =
327.30, 0.36 × 0.22 × 0.20 mm3, monoclinic, P21, a = 12.0467(6) Å, b
= 6.5161(3) Å, c = 12.2531(5) Å, β = 117.784(2)°, V = 850.95(7) Å3,
Z = 2, ρ = 1.277 g cm−3, μ = 1.67 cm−1, collected 7077, independent
3681, parameters 218, Rw = 0.0956, R = 0.0446 (I > 2σ(I)), GOF =
1.197.
Fluorescence Lifetime Measurements. The fluorescence life-
times of 6 and 8 were measured in CH2Cl2 using a streak camera as a
fluorescence detector. The excitation wavelengths were chosen
depending on the sample absorptions (6a−d, 385 nm; 6e,f, 330 nm;
8a,d, 360 nm; 8b, 360 nm; 8c, 380 nm; 8e, 420 nm). The excitation
pulse was generated by taking the second harmonic pulse (from 330 to
420 nm) of the output of an optical parametric amplifier (from 660 to
840 nm) operated by an amplified Ti:sapphire laser system.
DFT Calculations. The geometry optimization was performed by
B3LYP method21 with basis sets of 6-31G* for all atoms.22 All
calculations were carried out with the Gaussian 09 package.23
2-(4-Formylphenyl)-1-phenylbenzo[b]phosphole 1-Oxide (8h). Rf
1
= 0.33 (CH2Cl2/acetone = 20:1); mp 84−87 °C (dec.); H NMR
(400 MHz, CDCl3) δ 7.39−7.79 (m, 10H), 7.82−7.88 (m, 4H), 9.96
(s, 1H); 13C{1H} NMR (100 MHz, CDCl3): δ 125.2 (d, JCP = 9.7 Hz),
127.0 (d, JCP = 3.4 Hz), 129.0 (d, JCP = 11.9 Hz), 129.19 (d, JCP = 10.4
Hz), 129.20 (d, JCP = 98.2 Hz), 129.8, 130.2, 130.6 (d, JCP = 11.1 Hz),
132.5 (d, JCP = 3.0 Hz), 132.8 (d, JCP = 108.6 Hz), 133.4 (d, JCP = 1.4
Hz), 135.9, 137.7 (d, JCP = 94.5 Hz), 138.3 (d, JCP = 10.4 Hz), 139.2
(d, JCP = 19.3 Hz), 141.1 (d, JCP = 26.8 Hz), 191.5; 31P{1H} NMR
(162 MHz, CDCl3) δ 38.8; IR (neat) ν 1697 (CO), 1195 (PO)
cm−1; HRMS (ESI) m/z: [M + H]+ calcd for C21H16O2P, 331.0882;
found, 331.0874.
ASSOCIATED CONTENT
■
S
* Supporting Information
Complete ref 23, crystal structure of 8c, spectral data for 6e and
8e, cyclic voltammograms, results of DFT calculations, NMR
spectra for new compounds, and CIFs of 6d and 8c. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.joc.5b00541.
Synthesis of 9. A mixture of 6a (102 mg, 0.29 mmol),
trichlorosilane (60 μL, 0.59 mmol), and toluene (10 mL) was
refluxed, and progress of the reaction was monitored by TLC. After 6
h, aqueous NaOH solution (2M) was added, and the organic phase
was separated, dried over Na2SO4, and evaporated under reduced
pressure to give a colorless solid (104 mg). A part of the solid (47 mg)
was immediately subjected to silica-gel column chromatography
(CH2Cl2). The fraction of Rf = 0.18 (hexane) was collected and
reprecipitated from MeOH to give 1,2-diphenylnaphtho[2,3-b]-
phosphole (9) (33 mg, 0.99 μmol, 75%) as a colorless solid. mp
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: matano@chem.sc.niigata-u.ac.jp
Notes
1
250−252 °C (dec.); H NMR (400 MHz, CDCl3) δ 7.18−7.25 (m,
The authors declare no competing financial interest.
F
DOI: 10.1021/acs.joc.5b00541
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
(b) Uchiyama, M.; Furuyama, T.; Yoshida, K. Patent JP 2010202616,
2010.
(18) Yamaguchi et al. used Suzuki−Miyaura cross-coupling reactions
of 3-bromo-2-arylbenzo[b]phosphole P-oxides for the synthesis of 2,3-
diarylbenzo[b]phospholes. See ref 7.
(19) Quite recently, Yamaguchi et al. developed a polarity-sensitive
benzophosphole oxide-based fluorescent probe (R2 = p-Ph2NC6H4; R3
= Ph; E = O, Chart 1) with a high fluorescence quantum yield (ΦF =
0.90 in CH2Cl2). See ref 7c.
ACKNOWLEDGMENTS
■
We thank Dr. Hirohiko Watanabe (Hamamatsu Photonics
K.K.) for ΦF value measurements and Prof. Yasuhiko Yukawa
(Niigata University), Prof. Ko Furukawa (Niigata University),
and Dr. Kenji Yoza (Bruker Japan Co. Ltd.) for X-ray structure
analyses. This work was supported by JSPS KAKENHI grant
no. 25288020 and the Sasaki Foundation.
(20) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.;
Springer: Berlin, 2006.
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Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
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Wallingford, CT, 2009.
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DOI: 10.1021/acs.joc.5b00541
J. Org. Chem. XXXX, XXX, XXX−XXX