Selective Borylation of [4]Helicene

Article abstract of DOI:10.1002/ejoc.201600979

The Ir-catalyzed borylation of [4]helicene under different reaction conditions was studied for the first time. The results indicate that monoborylation proceeds to give a mixture of 2- and 3-borylated products in good yields (up to 74 % isolated yield). It was possible to shift the selectivity in favor of the 3-borylated product by using sterically demanding ligands. The monoborylated [4]helicenes were further arylated by using a Suzuki–Miyaura cross-coupling or oxidized to the corresponding phenols in very good yields.

Full text of DOI:10.1002/ejoc.201600979

A Journal of
Accepted Article
Title: Selective Borylation of [4]Helicene
ˇ
ˇ
Authors: David Necas; Reinhard P. Kaiser; Jan Ulc
This manuscript has been accepted after peer review and the authors have elected
to post their Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by using the Digital
Object Identifier (DOI) given below. The VoR will be published online in Early View as
soon as possible and may be different to this Accepted Article as a result of editing.
Readers should obtain the VoR from the journal website shown below when it is pu-
blished to ensure accuracy of information. The authors are responsible for the content
of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201600979
Link to VoR: http://dx.doi.org/10.1002/ejoc.201600979
Supported by

European Journal of Organic Chemistry
10.1002/ejoc.201600979
FULL PAPER
Selective Borylation of [4]Helicene
David Nečas,* [a] Reinhard P. Kaiser,[a] and Jan Ulč [a]
Abstract: Ir-catalyzed borylation of [4]helicene under different
reaction conditions was studied for the first time. The obtained
results indicate that monoborylation proceeded to give a mixture of
2- and 3-borylated product in good yields (up to 74% isolated yield).
It was possible to shift selectivity in favor of the 3-borylated product
by using sterically demanding ligands. The monoborylated
[4]helicenes were further arylated by using Suzuki-Miyaura cross-
coupling or oxidized to the corresponding phenols in very good
yields.
Results and Discussion
Since the bay-region torsion-angle in phenanthrene (the shortest
[n]helicene) is close to 0°, we chose benzo[c]phenanthrene
([4]helicene, the shortest [n]helicene that is non-planar in its
lowest energy conformation, torsion-angle 19°,[1] Figure 1) as a
substrate to prove the aforementioned idea.
Introduction
Helicenes represent a unique class of polycyclic aromatic
hydrocarbons where the benzene rings are ortho-fused, fully
conjugated, and with a non-planar topology. They have attracted
much interest owing to their unrivalled structural features[1–3] and
have also been shown to be effective in the development of
materials with chiroptical properties, which are useful for
molecular-based electronic applications.[4–6] Of importance,
these properties can be addressed by introducing the
substituents at the periphery of the helical core. From the
synthetic point of view such modifications are not trivial,
therefore the selectively substituted helicenes are usually made
from pre-functionalized substrates.[1,2] These methods are
usually not general enough to produce a large library of
congeners. This can be explained by the lack of compatibility of
some functional groups or their deactivation effects on the key
Figure 1. Molecular structure of [4]helicene.
Based on the preceding studies of iridium-catalyzed
borylation of arenes[10–15] and fused polyarenes[9,16–26] we
subjected [4]helicene 1 to mild borylation conditions. Equimolar
quantities of the substrate and B2pin2 and a catalytic amount of
[Ir(OMe)(cod)]2 (5 mol% Ir) and dtbpy (10 mol%) were reacted in
cyclohexane at 23 °C for 18 h. Removal of the volatiles and
subsequent column chromatography on silica gel (hexane/DCM
from 100:0 to 0:100) resulted in three colorless fractions,
unreacted 1 (39%), a mixture of monoborylated [4]helicenes
(51%) and the last small fraction containing a mixture of
bisborylated [4]helicenes (<8%). The subsequent separation of
the second fraction by non-aqueous reverse phase
chromatography (NARP) afforded two regioisomers, 2-borylated
[4]helicene 2a (27%) and 3-borylated [4]helicene 2b (22%). The
structure of the products 2a and 2b was unequivocally confirmed
reaction for producing helicenes. Although
a
post-
functionalization of helicenes appears attractive and would
greatly accelerate the development of new functional molecules
it has been underdeveloped in the history of helicene
chemistry.[7,8]
We speculated that helicenes could be selectively
functionalized by an iridium catalyzed, sterically driven C-H
activation/borylation process. According to the best of our
knowledge such an endeavor, i.e. borylation of helical
polyaromatics, has not been reported yet.[9] Because of the
avoidance of borylation of C-H bonds ortho to ring junction we
speculated that, by using standard conditions, helicenes would
be nearly equally borylated at the accessible positions 2 and 3.
Since the position 3 is more distant from the other end of the
molecule and thus less sterically hindered, the appropriate
choice of catalytic system and the third dimension (nonplanarity)
of the molecule would contrive additional level of regioselectivity
to distinguish between these two positions.
by
a single-crystal X-ray diffraction analysis (Figure 2).
Separation of the third fraction provided two analytically pure
compounds showing that the second borylation could take place
on the other terminal ring of [4]helicene in positions 10 and 11
giving rise to symmetrical 3,10-bisborylated [4]helicene 2d and
unsymmetrical 2,10-bisborylated [4]helicene 2c. Formation of
symetrically bisborylated 2,11-bisborylated [4]helicene was not
observed.
[a]
Department of Organic Chemistry, Faculty of Science,
Charles University in Prague
Albertov 6, 128 43 Praha 2, Czech Republic
E-mail: david.necas@natur.cuni.cz
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600979
FULL PAPER
This positive result prompted us to look for conditions that
enable to control regioselectvity of borylation as well as to
increase yields of mono-borylated products. Easy recovery and
recycling of the unreacted helicene allowed us to use 2
equivalents of 1 to reduce the amount of the formed bisborylated
products 2c and 2d when screening the reaction conditions
(Table 1). Excess of 1, temperature increased to 50 °C, and a
shorter reaction time resulted in the same conversion of 1 with a
slightly better yield of the 2a and 2b (Entry 1). Additional
increase of the reaction temperature to 80 °C gave 56:44
mixture of 2a and 2b in 74% isolated yield (based on 1 eq. of 1)
in 3 hours (Entry 2). The reaction did not proceed at 23 °C in
polar solvents such as 1,4-dioxane, THF or ethyl acetate
(Entries 3-5). When a less polar MTBE was used at 23 °C the
reaction took place with a low conversion of 13% (Entry 6).
Increasing the reaction temperature to 80 °C did not bring any
considerable improvement in the yield (entry 7), and the use of
microwave conditions[27,28] resulted in lower selectivity affording
a complex mixture of products in which the presence of tri-
borylated [4]helicenes was observed by EI/MS (entry 8). Change
of the ligand to 3,4,7,8-tetramethyl-1,10-phenanthroline, which
often overperforms dtbpy,[29] did not provide any improvement
and resulted in a low conversion at 80 °C either MTBE or
cyclohexane (entries 9, 10). (See the SI for the complete list of
conditions tested.)
Scheme 1. Ir-catalyzed borylation of [4]helicene.
Figure 2. ORTEP drawings of 2a (left) and 2b (right) with 30% thermal
ellipsoids.
Table 1. Ir-catalyzed borylation of 1 under various conditions.
Entry
Ligand[a]
dtbpy
Solvent[b]
cyclohexane
cyclohexane
dioxane
THF
Temp. [°C]
Time [h]
Conversion[c]
Yield 2a + 2b[d]
1
2
3
4
5
6
7
8
9
10
50
80
23
23
23
23
80
80[e]
80
80
12
3
59
82
0
54
74
0
dtbpy
dtbpy
18
18
18
18
3
dtbpy
0
0
dtbpy
EtOAc
0
0
dtbpy
MTBE
13
20
50
3
13
18
n.d.
n.d.
n.d.
dtbpy
MTBE
dtbpy
MTBE
1
tmphen
cyclohexane
MTBE
3
tmphen
3
30
[a] dtbpy - 4,4´-Di-tert-butyl-2,2´-dipyridyl; tmphen - 3,4,7,8-Tetramethyl-1,10-phenanthroline. [b] MTBE – Methyl tert-butyl ether. [c] Conversion based on 1 eq. of 1.
[d] Isolated combined yield of 2a+2b based on 1 eq. of 1 (ratio 2a/2b 1/0.8). [e] Microwave irradiation.
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600979
FULL PAPER
In order to take advantage of the shape of the molecule 1
and affect the regioisomer ratio we followed the idea of Itami and
coworkers for para-substitution of benzene derivatives, based on
the steric difference of active catalysts possessing bipyridyl or
bisphosphine type ligands.[30] The ratio of products 2a and 2b
ranged from 1:1 to 1:3 depending on the ligand used (Table 2).
Whereas the standard dtbpy ligand afforded 2a and 2b in almost
1:1 ratio, more rigid and sterically demanding ligands preferred
position 3, which is sterically less shielded by the other terminal
benzene ring of the molecule. Bipyridine type ligands such as
2,9-di-iso-butyl-1,10-phenanthroline L2 and neocuproine L1
combined with [Ir(cod)OH]2 afforded the products 2a and 2b in
1:1.3 and 1:1.6 ratio, respectively (Entries 1 and 2). A sterically
demanding diphosphine ligand, DM-MeO-BIPHEP L3, reported
as the best one for para-substitution provided 1:1.9 mixture of 2a
and 2b in 48% combined yield (Entry 3). By further screening of
other ligands, we found that DM-Segphos L10 (Entry 10) or DM-
Garphos L6 (Entry 6) provided the products in a good combined
isolated yields of 65% and 52% and better regioselectivity with
the 2a:2b ratios of 1:2.8 and 1:2.7, respectively.
To demonstrate the synthetic utility of the products 2a and
2b, Suzuki-Miyaura cross-coupling reactions of both isomers
with selected aryl iodides were carried out (Scheme 2). Both
monoborylated helicenes showed a good reactivity and the
respective arylated products 3a-3d and 4a-4d were obtained in
good isolated yields (80-92%)
Table 2. Effect of the ligand on the regioselectivity of Ir-catalyzed C-H
borylation of [4]helicene 1.
Entry
Ligand
L1
Yield 2a + 2b [%][a]
Ratio 2a/2b[b]
1/1.6
1
2
42
34
L2
1/1.3
3
L3
48
31
51
52
34
31
23
65
54
1/1.9
1/2.1
1/2.4
1/2.7
1/2.4
1/1.9
1/1.9
1/2.8
1/2.3
4
L4
5
L5
Scheme 2. Pd-catalyzed coupling reactions of 2a and 2b
6
L6
7
L7
In addition, transformation of the prepared boronates 2 to
the corresponding phenols 5 was attempted.[31] Gratifyingly, the
reactions of boronates 2a and 2b with N,N-dimethyl-4-toluidine
N-oxide in DCM proceeded uneventfully giving rise to the
corresponding hydroxy derivatives 5a and 5b in 83% and 89%
isolated yields, respectively (Scheme 3).
8
L8
9
L9
10
11
L10
L11
[a] Isolated combined yield of 2a+2b based on 1 eq. of 1. [b] Ratio determined
by 1H NMR.
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600979
FULL PAPER
the vessel was crimp-sealed with a septum cap under the flow of argon.
Afterwards, the reaction mixture was stirred at 23 °C for 18 h. DCM (2
mL) was added and the solution was filtered through a short pad of silica
gel (washed with DCM 5 mL). Volatiles were removed under reduced
pressure and column chromatography of the residue (hexane/DCM from
100/0 to 0/100) afforded recovered [4]helicene (the first fraction, 9 mg,
39%), a mixture of 2a and 2b (the second fraction, 18.1 mg, 51%), and a
mixture of 2c and 2d (the third fraction, 3.7 mg, <8%). The second and
third fractions were subsequently separated by preparative nonaqueous
reversed-phase HPLC (NARP). Separation of the second fraction
(MeOH/DCM 99/1) afforded 9.6 mg of 2a (27%) and 7.8 mg of 2b (22%).
Separation of the third fraction (MeOH/DCM 97/3) afforded 2c (~1.5 mg,
~3%) and 2d (~1.5 mg, ~3%).
Scheme 3. Hydroxylations of boronate esters 2a and 2b.
Conclusions
In summary, we have shown that [4]helicene could be
selectively monoborylated by using Ir-catalyzed borylation
process to produce, predominantly, two regioisomers of
[4]helicene-mono(boronate) esters. In addition, by using different
ligands the regioselectivity of the monoborylation could be
improved. Both prepared Bpin helicenes show good stability and
reactivity for Suzuki-Miyaura coupling reactions. Application of
this chemistry and extension for higher helicenes are underway
in our laboratory.
General procedure for the Table 1 and Table SI-1: A flame dried 10 ml
thick-wallet crimp reaction vial was charged with [Ir(OMe)cod]2 (3.3 mg,
0.005 mmol), ligand (0.01 mmol), B2pin2 (25 mg, 0.1 mmol), and
[4]helicene (46 mg, 0.2 mmol). Then cyclohexane (0.8 mL) was added
and argon was bubbled through the reaction mixture to remove O2 and
reduce the volume to 0.5 mL and the vessel was crimp-sealed with a
septum cap under the flow of argon. Afterwards, the reaction mixture was
stirred and heated (optional) in an aluminum heating block at appropriate
temperature for desired time. (Entry 8, microwave reactor was used).
After cooling (optional), DCM (2 mL) was added and the solution was
filtered through a short pad of silica gel (washed with DCM 5 mL).
Volatiles were removed under reduced pressure and column
chromatography of the residue (hexane/DCM 2:1) afforded recovered
[4]helicene (the first fraction) and a mixture of 2a and 2b (the second
fraction). The ratio of 2a:2b was calculated by integration of aromatic
region of 1H NMR spectra of second fraction, solitary singlet at  = 9.63
ppm belongs to 2a and solitary singlet at  = 8.54 ppm belongs to 2b.
(See the Supporting Information file for a detailed discussion about the
determination of regioisomers ratios.)
Experimental Section
General methods: Catalysts, reagents and solvents were obtained from
commercial suppliers (Aldrich, TCI, Alfa Aesar, Strem Chemicals, Penta)
and were used without further purification. Solvents for column
chromatography were distilled prior to use. Argon was used as an inert
gas. Silica gel 60 (0.035–0.070 mm) (Acros Organics) was used for
column chromatography. TLC was performed on aluminum sheets with
layer of Silica gel 60 F254 purchased from MERCK. Spots on TLC plates
were detected by using UV lamp (λ = 254 nm) or basic permanganate
solution. PTLC was performed on glass sheets with layer of Silica gel GF
(Analtech). NMR spectra were recorded on Varian VNMRS 300 (ν(1H) =
299.94 MHz, ν(13C) = 75.43 MHz), on Bruker Avance III (400 MHz) (ν(1H)
= 400.13 MHz, ν(13C) = 100.61 MHz), or on Bruker Avance III (600 MHz)
(ν(1H) = 600.17 MHz, ν(13C) = 150.04 MHz) in deuterated solvents and
referenced to residual solvent peak (CDCl3 1H: 7.26 ppm, 13C: 77 ppm).
Chemical shifts are given in δ-scale, coupling constants J are given in Hz.
Mass spectra were recorded on VG-Analytical ZAB-SEQ. Infrared
spectra were recorded in KBr and measured on spectrometer Thermo
Nicolet AVATAR 370 FT-IR. All melting points are uncorrected and were
determined on Kofler apparatus. HPLC separations were performed on a
Gilson 321 H2 pumps with 25x250 mm preparative column (Labio, Czech
Republic), filled with BIOSPHER PSI 120 C18 sorbent (7μm mesh).
[Ir(OH)cod]2 was prepared according to the reported procedure[32]
[4]Helicene was prepared according to the reported procedure,[33] and
recrystallized before use.
General procedure for the Table 2: A flame dried 10 ml thick-wallet
crimp reaction vial was charged with [Ir(OH)cod]2 (3.2 mg, 0.005 mmol),
ligand (0.01 mmol), B2pin2 (25 mg, 0.1 mmol), and [4]helicene (46 mg,
0.2 mmol). Then cyclohexane (0.8 mL) was added and argon was
bubbled through the reaction mixture to remove O2 and reduce the
volume to 0.5 mL and the vessel was crimp-sealed with a septum cap
under the flow of argon. Afterwards, the reaction mixture was stirred and
heated in an aluminum heating block at 80 °C for 16 h. After cooling,
DCM (2 mL) was added and the solution was filtered through a short pad
of silica gel (washed with DCM 5 mL). Volatiles were removed under
reduced pressure and column chromatography of the residue
(hexane/DCM 2:1) afforded recovered [4]helicene (first fraction) and
mixture of 2a and 2b (second fraction). The ratio of 2a:2b was calculated
by integration of aromatic region of 1H NMR spectra of second fraction,
solitary singlet at  = 9.63 ppm belongs to 2a and solitary singlet at  =
8.54 ppm belongs to 2b. (See the Supporting Information file for a
detailed discussion about the determination of regioisomers ratios.)
2-(Benzo[c]phenanthren-2-yl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (2a). Colorless crystals: m.p. 161.2 °C (DCM/MeOH); H
1
CCDC 1487957 (2a) and CCDC 1487958 (2b) contain the
supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
NMR (600 MHz, Chloroform-d) δ 9.63 (s, 1H), 9.20 (d, J = 8.5 Hz, 1H),
8.05 – 8.02 (m, 3H), 7.92 – 7.82 (m, 4H), 7.76 (ddd, J = 8.4, 6.9, 1.5 Hz,
1H), 7.65 (ddd, J = 7.9, 6.8, 1.1 Hz, 1H), 1.42 (s, 12H); 13C NMR (151
MHz, Chloroform-d) δ 135.61, 135.26, 133.55, 130.92, 130.87, 130.30,
129.65, 128.40, 128.29, 127.92, 127.84, 127.60, 127.42, 127.26, 126.69,
126.30, 125.85, 83.91 (2C), 24.95 (4C); IR (DRIFT, KBr) 2977, 1608,
1388, 1338, 1304, 1139, 860, 756, 661 cm-1; EI-MS m/z (%) 354 (100),
269 (10), 254 (88); HRMS (ESI) calcd for C24H24O2B 355.18639, found
355.18655.
Borylation of [4]helicene (First experiment and separation of
products): A flame dried 10 ml thick-wallet crimp reaction vial was
charged with [Ir(OMe)cod]2 (3.3 mg, 0.005 mmol), dtbpy (2.7 mg, 0.01
mmol), B2pin2 (25 mg, 0.1 mmol), and [4]helicene (23 mg, 0.1 mmol).
Then cyclohexane (0.8 mL) was added and argon was bubbled through
the reaction mixture to remove O2 and reduce the volume to 0.5 mL and
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600979
FULL PAPER
2-(Benzo[c]phenanthren-3-yl)-4,4,5,5-tetramethyl-1,3,2-
138.62, 137.19, 133.53, 132.46, 131.29, 130.62, 130.37, 129.71 (2C),
128.93, 128.59, 127.81, 127.54, 127.51, 127.40 (2C), 127.10, 126.87,
126.78, 126.24, 125.97, 125.83, 125.24, 21.15; IR (DRIFT, KBr) 3039,
1602, 1499, 845, 829, 815, 787, 746, 676 cm-1; EI-MS m/z (%) 318 (100),
302 (10), 226 (60), 92 (33); HRMS (EI) calcd for C25H18 318.1409, found
318.1405.
1
dioxaborolane (2b). Colorless crystals: m.p. 168.6 °C (DCM/MeOH); H
NMR (600 MHz, Chloroform-d) δ 9.17 – 9.10 (m, 2H), 8.54 (s, 1H), 8.07
(dd, J = 8.4, 1.3 Hz, 1H), 8.03 (dd, J = 7.9, 1.4 Hz, 1H), 7.98 – 7.90 (m,
2H), 7.86 – 7.81 (m, 2H), 7.70 (ddd, J = 8.4, 6.9, 1.4 Hz, 1H), 7.66 – 7.60
(m, 1H), 1.44 (s, 12H); 13C NMR (151 MHz, Chloroform-d) δ 136.36,
133.43, 132.73, 132.14, 131.69, 131.12, 130.41, 128.52, 127.96, 127.89,
127.86, 127.16, 126.96, 126.80, 126.76, 126.22, 125.85, 84.01 (2C),
24.96 (4C); IR (DRIFT, KBr) 2980, 1606, 1457, 1366, 1308, 1139, 967,
850, 751, 695 cm-1; EI-MS m/z (%) 354 (100), 268 (17), 254 (30), 226
(16); HRMS (ESI) calcd for C24H24O2B 355.18639, found 355.18652.
2-(4-Methoxyphenyl)benzo[c]phenanthrene (3c). Yield 29.8 mg (89%);
a colorless amorphous solid: m.p. 116.2 °C; 1H NMR (600 MHz,
Chloroform-d) δ 9.31 (bs, 1H), 9.20 (d, J = 8.6 Hz, 1H), 8.07 (d, J = 8.2
Hz, 1H), 8.04 (dd, J = 8.0, 1.4 Hz, 1H), 7.93 – 7.91 (m, 2H), 7.88 – 7.80
(m, 3H), 7.76 – 7.68 (m, 3H), 7.64 (ddd, J = 7.9, 6.8, 1.1 Hz, 1H), 7.10 –
7.05 (m, 2H), 3.90 (s, 3H); 13C NMR (151 MHz, Chloroform-d) δ 159.25,
138.48, 133.97, 133.52, 132.24, 131.29, 130.64, 130.37, 128.92, 128.59,
128.56 (2C), 127.78, 127.51, 127.45, 127.10, 126.87, 126.64, 126.22,
125.80, 125.60, 125.07, 114.44 (2C), 55.40; IR (DRIFT, KBr) 3046, 3005,
2931, 2833, 1608, 1510, 1499, 1284, 1247, 1180, 1038, 1028, 847, 834,
791, 752 cm-1; EI-MS m/z (%) 334 (100), 319 (25), 289 (23), 276 (16),
263 (11), 226 (45), 108 (18); HRMS (APCI) calcd for C25H18O 334.13522,
found 334.13535.
2,2'-(Benzo[c]phenanthrene-2,10-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (2c). A colorless amorphous solid: m.p. 133.5 °C; 1H
NMR (400 MHz, Chloroform-d) δ 9.62 (s, 1H), 9.18 (d, J = 8.5 Hz, 1H),
8.54 (s, 1H), 8.12 (dd, J = 8.5, 1.2 Hz, 1H), 8.01 (s, 2H), 7.97 – 7.80 (m,
4H), 1.45 (s, 12H), 1.41 (s, 12H); 13C NMR (101 MHz, Chloroform-d) δ
136.27, 135.57, 135.20, 132.80, 132.17, 131.60, 131.21, 130.98, 129.74,
127.94, 127.89, 127.75, 127.65, 127.59, 127.44, 126.68, 84.04 (2C),
83.91 (2C), 24.97 (4C), 24.95 (4C); IR (DRIFT, KBr) 2978, 2929, 1609,
1444, 1386, 1364, 1344, 1302, 1143, 1099, 967, 850, 686, cm-1; EI-MS
m/z (%) 480 (100), 394 (5), 380 (6), 294 (8), 280 (17); HRMS (ESI) calcd
for C30H35O4B2 481.27160, found 481.27174.
2-(4-(Trifluoromethyl)phenyl)benzo[c]phenanthrene (3d). Yield 29.8
1
mg (80%); colorless crystals: m.p. 160.6 °C (DCM/MeOH); H NMR (600
MHz, Chloroform-d) δ 9.35 (s, 1H), 9.13 (d, J = 8.4 Hz, 1H), 8.12 (d, J =
8.3 Hz, 1H), 8.06 (d, J = 7.9 Hz, 1H), 7.94 (d, J = 8.5 Hz, 2H), 7.91 – 7.84
(m, 5H), 7.78 (d, J = 8.1 Hz, 2H), 7.71 (ddd, J = 8.4, 6.9, 1.4 Hz, 1H),
7.66 (ddd, J = 8.0, 6.8, 1.2 Hz, 1H); 13C NMR (151 MHz, Chloroform-d) δ
145.05, 137.28, 133.60, 133.03, 131.37, 130.55, 130.22, 129.37 (q, J =
30.4 Hz), 129.27, 128.71, 127.81, 127.77 (3C), 127.61, 127.50 (2C),
127.01, 126.83, 126.71, 126.41, 126.03, 125.91 (q, J = 3.7 Hz), 124.99,
124.32 (q, J = 271.9 Hz); IR (DRIFT, KBr) 3050, 1614, 1326, 1164, 1111,
1071, 847, 831, 787, 750 cm-1; EI-MS m/z (%) 372 (100), 331 (9), 302
(17), 226 (35), 145 (15); HRMS (EI) calcd for C25H15F3 372.1126, found
372.1123.
3,10-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)benzo[c]phenanthrene (2d). Colorless crystals: m.p. 273.5 °C
(DCM/MeOH); 1H NMR (400 MHz, Chloroform-d) δ 9.11 (d, J = 8.5 Hz,
2H), 8.52 (d, J = 1.0 Hz, 2H), 8.07 (dd, J = 8.5, 1.2 Hz, 2H), 7.96 (d, J =
8.5 Hz, 2H), 7.82 (d, J = 8.5 Hz, 2H), 1.43 (s, 24H).); 13C NMR (151 MHz,
Chloroform-d) δ 136.37 (2C), 132.75 (2C), 132.45 (2C), 132.32 (2C),
131.31 (2C), 128.46 (2C), 127.09 (2C), 127.05 (2C), 126.81 (2C), 84.09
(4C), 25.03 (8C); IR (DRIFT, KBr) 2978, 2932, 1612, 1449, 1367, 1320,
1302, 1145, 1092, 968, 845, 701, cm-1; EI-MS m/z (%) 480 (100), 394 (6),
381 (8), 294 (10), 280 (20); HRMS (ESI) calcd for C30H35O4B2 481.27160,
found 481.27178.
3-Phenylbenzo[c]phenanthrene (4a). Yield 25.9 mg (85%); colorless
crystals: m.p. 145.1 °C (DCM/MeOH) (Lit.[35] 138-139 °C, HOAc); 1H
NMR (400 MHz, Chloroform-d) δ 9.23 – 9.16 (m, 2H), 8.24 (d, J = 2.0 Hz,
1H), 8.04 (dd, J = 7.9, 1.4 Hz, 1H), 7.99 – 7.82 (m, 7H), 7.72 (ddd, J =
8.5, 6.9, 1.5 Hz, 1H), 7.65 (ddd, J = 7.5, 7.0, 1.2 Hz, 1H), 7.57 – 7.51 (m,
2H), 7.45 – 7.40 (m, 1H); 13C NMR (101 MHz, Chloroform-d) δ 140.61,
138.33, 133.86, 133.55, 131.07, 130.31, 129.48, 128.94 (2C), 128.58,
128.43, 127.85, 127.70, 127.50, 127.48, 127.36 (2C), 127.29, 127.27,
126.86, 126.34, 126.19, 125.92, 125.37; IR (DRIFT, KBr) 3050, 2923,
1597, 1486, 1422, 1230, 884, 835, 749, 696 cm-1; EI-MS m/z (%) 304
(100), 226 (19), 77 (20); HRMS (EI) calcd for C24H16 304.1252, found
304.1249.
Cross-coupling reactions of 2a or 2b with aryl iodides: To a solution
of 2a or 2b (35.4 mg, 0.1 mmol) in toluene/H2O (10/1, 2 mL) was added
XPhos-Pd-G3 (4.3 mg, 5 mol%), K3PO4 (42.5 mg, 200 mol%) and an aryl
iodide (0.12 mmol) and the reaction mixture was stirred at 23 °C for 6h.
All volatiles were evaporated, the residue redissolved in DCM and
separated by preparative TLC (hexane/DCM 10:1) to give the
corresponding product 3 or 4.
2-Phenylbenzo[c]phenanthrene (3a). Yield 26.2 mg (86%); colorless
1
crystals: m.p. 141.8 °C (DCM/MeOH); H NMR (600 MHz, Chloroform-d)
δ 9.36 (bs, 1H), 9.19 (d, J = 8.4 Hz, 1H), 8.10 (d, J = 8.2 Hz, 1H), 8.04 (d,
J = 7.5 Hz, 1H), 7.95 – 7.88 (m, 3H), 7.86 – 7.83 (m, 2H), 7.82 – 7.79 (m,
2H), 7.71 (ddd, J = 8.4, 7.0, 1.3 Hz, 1H), 7.66 – 7.62 (m, 1H), 7.56 – 7.51
(m, 2H), 7.44 – 7.40 (m, 1H); 13C NMR (151 MHz, Chloroform-d) δ 141.53,
138.88, 133.56, 132.61, 131.30, 130.61, 130.35, 128.99, 128.99 (2C),
128.61, 127.80, 127.60, 127.58 (2C), 127.55, 127.35, 127.10, 126.96,
126.86, 126.29 (2C), 125.88, 125.32; IR (DRIFT, KBr) 3093, 3052, 1599,
1485, 1447, 1226, 846, 763, 702, 679 cm-1; EI-MS m/z (%) 304 (100),
226 (55), 78 (28); HRMS (EI) calcd for C24H16 304.1252, found 304.1255.
The spectral characteristics of 3a were in agreement with the previously
published data.[34]
3-(p-Tolyl)benzo[c]phenanthrene (4b). Yield 28.3 mg (89%); colorless
1
crystals: m.p. 138.8 °C (DCM/MeOH); H NMR (400 MHz, Chloroform-d)
δ 9.22 – 9.14 (m, 2H), 8.22 (d, J = 2.0 Hz, 1H), 8.04 (dd, J = 7.9, 1.4 Hz,
1H), 7.98 – 7.83 (m, 5H), 7.75 – 7.69 (m, 3H), 7.64 (ddd, J = 7.9, 7.0, 1.1
Hz, 1H), 7.37 – 7.33 (m, 2H), 2.45 (s, 3H); 13C NMR (101 MHz, CDCl3) δ
138.27, 137.69, 137.34, 133.89, 133.55, 130.99, 130.31, 129.68 (2C),
129.31, 128.56, 128.38, 127.86, 127.69, 127.39, 127.29, 127.22, 127.18
(2C), 126.87, 126.15, 125.99, 125.88, 125.29, 21.18; IR (DRIFT, KBr)
3045, 2917, 2854 1514, 1497, 1487, 884, 833, 815, 789, 740, 677 cm-1;
EI-MS m/z (%) 318 (100), 302 (10), 226 (14), 91 (10); HRMS (EI) calcd
for C25H18 318.1409, found 318.1407.
2-(p-Tolyl)benzo[c]phenanthrene (3b). Yield 27.7 mg (87%); colorless
1
crystals: m.p. 139.7 °C (DCM/MeOH); H NMR (600 MHz, Chloroform-d)
δ 9.34 (s, 1H), 9.19 (d, J = 8.5 Hz, 1H), 8.09 (d, J = 8.3 Hz, 1H), 8.04 (dd,
J = 7.8, 0.7 Hz, 1H), 7.94 – 7.91 (m, 2H), 7.88 (dd, J = 8.3, 1.6 Hz, 1H),
7.86 – 7.82 (m, 2H), 7.72 – 7.68 (m, 3H), 7.66 – 7.62 (m, 1H), 7.40 –
7.31 (m, 2H), 2.46 (s, 3H); 13C NMR (151 MHz, Chloroform-d) δ 138.81,
3-(4-Methoxyphenyl)benzo[c]phenanthrene (4c). Yield 30.8 mg (92%);
colorless crystals: m.p. 151.2 °C (DCM/MeOH); 1H NMR (600 MHz,
Chloroform-d) δ 9.18 (d, J = 6.6 Hz, 1H), 9.17 (d, J = 7.0 Hz, 1H), 8.18 (d,
J = 2.1 Hz, 1H), 8.04 (dd, J = 8.0, 1.5 Hz, 1H), 7.96 – 7.90 (m, 3H), 7.85
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600979
FULL PAPER
(d, J = 6.3 Hz, 1H), 7.84 (d, J = 6.3 Hz, 1H), 7.78 – 7.75 (m, 2H), 7.71
(ddd, J = 8.5, 6.9, 1.5 Hz, 1H), 7.65 (ddd, J = 7.9, 6.8, 1.1 Hz, 1H), 7.09 –
7.06 (m, 2H), 3.90 (s, 3H); 13C NMR (151 MHz, Chloroform-d) δ 159.36,
137.93, 133.92, 133.54, 133.07, 130.92, 130.29, 129.07, 128.55, 128.38,
128.35 (2C), 127.85, 127.64, 127.32, 127.30, 127.22, 126.87, 126.12,
125.87, 125.60, 125.12, 114.40 (2C), 55.39; IR (DRIFT, KBr) 3046, 3003,
2837, 1606, 1510, 1500, 1286, 1252, 1233, 1024, 836, 819, 792, 757,
677, 644 cm-1; EI-MS m/z (%) 334 (100), 319 (27), 289 (31), 226 (16);
HRMS (APCI) calcd for C25H18O 334.13522, found 334.13524.
This work was supported by a grant from the Czech Science
Foundation (reg. No. 14-16391P). The authors would like to
thank Dr. Ivana Císařová (Department of Inorganic Chemistry,
Charles University in Prague) for the X-ray structure
determinations.
Keywords: Borylation • C-H activation • Helicene •
Homogeneous catalysis • Iridium
3-(4-(Trifluoromethyl)phenyl)benzo[c]phenanthrene (4d). Yield 30.5
mg (82%); colorless crystals: m.p. 178.4 °C (DCM/MeOH); H NMR (600
[1]
[2]
M. Gingras, Chem. Soc. Rev. 2013, 42, 968–1006.
M. Gingras, G. Félix, R. Peresutti, Chem. Soc. Rev. 2013, 42, 1007–
1050.
M. Gingras, Chem. Soc. Rev. 2013, 42, 1051–1095.
Y. Yang, R. C. da Costa, M. J. Fuchter, A. J. Campbell, Nat. Photonics
2013, 7, 634–638.
Y. Yang, R. C. da Costa, D.-M. Smilgies, A. J. Campbell, M. J. Fuchter,
Adv. Mater. 2013, 25, 2624–2628.
J. Storch, J. Zadny, T. Strasak, M. Kubala, J. Sykora, M. Dusek, V.
Cirkva, P. Matejka, M. Krbal, J. Vacek, Chem. – Eur. J. 2015, 21, 2343–
2347.
P. M. op den Brouw, W. H. Laarhoven, Recl. Trav. Chim. Pays-Bas
1978, 97, 265–268.
J. W. Diesveld, J. H. Borkent, W. H. Laarhoven, Recl. Trav. Chim. Pays-
Bas 1980, 99, 391–394.
G. Zhang, F. Rominger, M. Mastalerz, Chem. – Eur. J. 2016, 22, 3084–
3093.
1
MHz, Chloroform-d) δ 9.22 (d, J = 8.8 Hz, 1H), 9.15 (d, J = 8.4 Hz, 1H),
8.24 (d, J = 1.9 Hz, 1H), 8.05 (d, J = 7.9 Hz, 1H), 7.98 – 7.84 (m, 7H),
7.81 – 7.75 (m, 2H), 7.73 (ddd, J = 8.4, 7.0, 1.3 Hz, 1H), 7.69 – 7.64 (m,
1H); 13C NMR (151 MHz, Chloroform-d) δ 144.11, 136.71, 133.75, 133.58,
131.31, 130.24, 129.98, 129.47 (q, J = 32.5 Hz), 128.69, 128.65, 127.81,
127.75, 127.61 (2C), 127.57 (2C), 127.17, 126.81, 126.74, 126.32,
126.05, 125.86 (q, J = 3.7 Hz), 125.04, 124.33 (q, J = 271.9 Hz); IR
(DRIFT, KBr) 3047, 1614, 1412, 1330, 1157, 1128, 1110, 1071, 836 cm-
1; EI-MS m/z (%) 372 (100), 302 (10), 226 (26), 145 (12); HRMS (EI)
calcd for C25H15F3 372.1126, found 372.1121.
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Hydroxylation of 2a and 2b: Hydroxylation of boronate esters 2a and
2b was carried out according to the previously reported procedure.[31] To
a solution of N,N-dimethyl-4-toluidine N-oxide (22.6 mg, 0.15 mmol) in
DCM (1.5 mL) was added boronate ester 2 (35.4 mg, 0.1 mmol) and the
reaction mixture was stirred at 23 °C for 5h. All volatiles were evaporated
and the residue was purified by preparative TLC (ethyl acetate/hexane
1:4) to give the corresponding product 5.
[10] T. Ishiyama, Y. Nobuta, J. F. Hartwig, N. Miyaura, Chem. Commun.
2003, 2924–2925.
[11] T. Ishiyama, J. Takagi, K. Ishida, N. Miyaura, N. R. Anastasi, J. F.
Hartwig, J. Am. Chem. Soc. 2002, 124, 390–391.
[12] J.-Y. Cho, M. K. Tse, D. Holmes, R. E. Maleczka, M. R. Smith, Science
2002, 295, 305–308.
[13] J. F. Hartwig, Chem. Soc. Rev. 2011, 40, 1992–2002.
[14] I. A. I. Mkhalid, J. H. Barnard, T. B. Marder, J. M. Murphy, J. F. Hartwig,
Chem. Rev. 2010, 110, 890–931.
[15] T. Ishiyama, N. Miyaura, Pure Appl. Chem. 2006, 78, DOI
10.1351/pac200678071369.
[16] D. N. Coventry, A. S. Batsanov, A. E. Goeta, J. A. K. Howard, T. B.
Marder, R. N. Perutz, Chem. Commun. 2005, 2172–2174.
[17] R. Ozawa, K. Yoza, K. Kobayashi, Chem. Lett. 2011, 40, 941–943.
[18] T. Kimoto, K. Tanaka, Y. Sakai, A. Ohno, K. Yoza, K. Kobayashi, Org.
Lett. 2009, 11, 3658–3661.
[19] M. N. Eliseeva, L. T. Scott, J. Am. Chem. Soc. 2012, 134, 15169–15172.
[20] S. D. Ros, A. Linden, K. K. Baldridge, J. S. Siegel, Org. Chem. Front.
2015, 2, 626–633.
[21] A. G. Crawford, Z. Liu, I. A. I. Mkhalid, M.-H. Thibault, N. Schwarz, G.
Alcaraz, A. Steffen, J. C. Collings, A. S. Batsanov, J. A. K. Howard, et
al., Chem. – Eur. J. 2012, 18, 5022–5035.
Benzo[c]phenanthren-2-ol (5a). Yield 20.3 mg (83%); a yellowish
amorphous solid; 1H NMR (400 MHz, Chloroform-d) δ 9.13 (d, J = 8.5 Hz,
1H), 8.56 (d, J = 2.3 Hz, 1H), 8.01 (dd, J = 7.9, 1.6 Hz, 1H), 7.95 – 7.78
(m, 4H), 7.71 – 7.58 (m, 3H), 7.23 (dd, J = 8.7, 2.4 Hz, 1H), 5.16 (s, 1H);
13C NMR (151 MHz, Chloroform-d) δ 154.12, 133.29, 131.67, 131.58,
130.49, 130.36, 128.59, 128.56, 127.61, 127.23 (2C), 126.93, 126.25,
126.11, 125.67, 124.65, 116.29, 111.59; IR (DRIFT, KBr) 3333, 3048,
1604, 1524, 1506, 1203, 839, 750, 622, 538 cm-1; EI-MS m/z (%) 244
(100), 226 (16), 213 (26), 189 (39); HRMS (EI) calcd for C18H12O
244.0888, found 244.0889.
[22] Z. Liu, Y. Wang, Y. Chen, J. Liu, Q. Fang, C. Kleeberg, T. B. Marder, J.
Org. Chem. 2012, 77, 7124–7128.
[23] S. Hitosugi, Y. Nakamura, T. Matsuno, W. Nakanishi, H. Isobe,
Tetrahedron Lett. 2012, 53, 1180–1182.
Benzo[c]phenanthren-3-ol (5b). Yield 21.7 mg (89%); a yellowish
amorphous solid; 1H NMR (600 MHz, Chloroform-d) δ 9.06 (d, J = 8.4 Hz,
1H), 9.04 (d, J = 9.2 Hz, 1H), 8.01 (dd, J = 7.9, 1.5 Hz, 1H), 7.86 – 7.74
(m, 4H), 7.67 (ddd, J = 8.4, 6.8, 1.5 Hz, 1H), 7.62 (ddd, J = 8.0, 6.8, 1.2
Hz, 1H), 7.36 (d, J = 2.8 Hz, 1H), 7.27 (dd, J = 9.3, 2.8 Hz, 1H), 5.16 (s,
1H); 13C NMR (151 MHz, Chloroform-d) δ 153.34, 135.12, 133.59, 130.00,
129.84, 129.71, 128.51, 127.79, 127.63 (2C), 126.84, 126.54, 126.37,
125.96, 125.83, 125.16, 116.54, 111.23; IR (DRIFT, KBr) 3354, 3049,
1626, 1612, 1525, 1502, 1420, 1232, 866, 833, 749, 671, 572, 418 cm-1;
EI-MS m/z (%) 244 (100), 226 (12), 215 (45), 189 (36); HRMS (EI) calcd
for C18H12O 244.0888, found 244.0889. The spectral characteristics of 5b
were in agreement with the previously published data.[36]
[24] L. Ji, K. Fucke, S. K. Bose, T. B. Marder, J. Org. Chem. 2015, 80, 661–
665.
[25] H. Shinokubo, Proc. Jpn. Acad. Ser. B 2014, 90, 1–11.
[26] Y. Koyama, S. Hiroto, H. Shinokubo, Angew. Chem. Int. Ed. 2013, 52,
5740–5743.
[27] P. Harrisson, J. Morris, T. B. Marder, P. G. Steel, Org. Lett. 2009, 11,
3586–3589.
[28] L. Zeqing, L. Zhibin, W. Yuqiang, Y. Pei, Res. Chem. Intermed. 2012, 39,
1917–1926.
[29] S. M. Preshlock, B. Ghaffari, P. E. Maligres, S. W. Krska, R. E.
Maleczka, M. R. Smith, J. Am. Chem. Soc. 2013, 135, 7572–7582.
[30] Y. Saito, Y. Segawa, K. Itami, J. Am. Chem. Soc. 2015, 137, 5193–5198.
[31] C. Zhu, R. Wang, J. R. Falck, Org. Lett. 2012, 14, 3494–3497.
[32] L. M. Green, D. W. Meek, Organometallics 1989, 8, 659–666.
[33] M. Scholz, M. Mühlstädt, F. Dietz, Tetrahedron Lett. 1967, 8, 665–668.
[34] L. Peng, L. T. Scott, J. Am. Chem. Soc. 2005, 127, 16518–16521.
[35] J. Szmuszkovicz, E. J. Modest, J. Am. Chem. Soc. 1950, 72, 566–570.
[36] J. Carreras, M. Patil, W. Thiel, M. Alcarazo, J. Am. Chem. Soc. 2012,
134, 16753–16758.
Supporting Information (see footnote on the first page of this article):
1
Crystallographic data of compounds 2a and 2b, H and 13CNMR spectra
of all described compounds.
Acknowledgements
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600979
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Layout 2:
FULL PAPER
C-H Activation
D. Nečas*, R. P. Kaiser, J. Ulč
Page No. – Page No.
Selective Borylation of [4]Helicene
Ir-catalyzed borylation of [4]helicene has been studied. The results indicate that
monoborylation proceeded to give a mixture of 2- and 3-borylated product in good
yields. The use of sterically demanding ligands favored formation of the 3-borylated
product. The monoborylated [4]helicenes were further arylated by using Suzuki-
Miyaura cross-coupling or oxidized to the corresponding phenols in very good
yields.
This article is protected by copyright. All rights reserved