A New Member of the BN-Phenanthrene Family: Understanding the Role of the B - N Bond Position

Article abstract of DOI:10.1021/acs.joc.9b00800

3,4-Dihydro-4-aza-3-boraphenanthrene, which shows the highest fluorescence quantum yield of all nonsubstituted BN-phenanthrenes reported to date (φ_F = 0.61), has been synthesized in only three steps (76% overall yield) from easily accessible 1-bromo-2-vinylnaphthalene, along with several substituted derivatives. The reactivity of these previously unknown BN-aromatic compounds toward organolithium compounds and bromine has been studied. This latter reaction affords bromo-substituted compounds that are suitable for further functionalization via Suzuki and Sonogashira couplings, with complete regioselectivity. The optical properties and excited state deactivation mechanisms of selected compounds were studied using computational methods.

Full text of DOI:10.1021/acs.joc.9b00800

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Article
A new member of the BN-phenanthrene family:
understanding the role of the B-N bond position
Alberto Abengozar, David Sucunza, Patricia García-García,
Diego Sampedro, Adrian Perez-Redondo, and Juan J. Vaquero
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00800 • Publication Date (Web): 12 May 2019
Downloaded from http://pubs.acs.org on May 17, 2019
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A new member of the BN-phenanthrene family: understanding the
role of the BN bond position
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Alberto Abengózar,† David Sucunza,†,* Patricia García-García,† Diego Sampedro,‡ Adrián Pérez-
Redondo† and Juan J. Vaquero†,*
† Departamento de Química Orgánica y Química Inorgánica, Instituto de Investigación Química “Andrés M. del
Río” (IQAR), Universidad de Alcalá, 28805-Alcalá de Henares, Spain
‡ Departamento de Química, Centro de Investigación en Síntesis Química (CISQ), Universidad de La Rioja, Madre
de Dios 53, 26006-Logroño, Spain
R1
R2
B
N
scalable synthesis
reactivity
optical properties
fluorescence quantum yields up to F = 0.72

ABSTRACT: 3,4-Dihydro-4-aza-3-boraphenanthrene, which shows the highest fluorescence quantum yield of all non-
substituted BN-phenanthrenes reported to date (ϕF = 0.61), has been synthesized in only three steps (76% overall yield)
from easily accessible 1-bromo-2-vinylnaphthalene, along with several substituted derivatives. The reactivity of these
previously unknown BN-aromatic compounds towards organolithium compounds and bromine has been studied. This
latter reaction affords bromo-substituted compounds that are suitable for further functionalization via Suzuki and
Sonogashira couplings, with complete regioselectivity. The optical properties and excited state deactivation mechanisms
of
selected
compounds
were
studied
using
computational
methods.
INTRODUCTION
C=C bond by a B–N bond have on the properties of BN-
aromatic compounds are still not fully understood and,
consequently, at times are difficult to predict. As such,
the information obtained from the simplest systems is
still highly valuable.
BN-polycyclic aromatic hydrocarbons (BN-PAHs)1 have
emerged as good candidates for the development of novel
materials.2 The replacement of a C=C bond in an aromatic
ring by an isoelectronic B−N bond leads to these new
compounds, which retain aromaticity and are structurally
analogous to their all-carbon counterparts but have
different properties as a result of the presence of a dipole
in the molecule. Thus, the azaborine unit has been
explored in the design of promising components for
enhanced optoelectronic devices,3 as well as in the search
for new ligands for transition metal-based catalysis.4
Moreover, the possibilities of BN-aromatic compounds as
isosteres of phenyl and naphthyl groups in medicinal
chemistry has also been reported.5
With regard to the above, a comparison of different BN
isosteres of naphthalene has been published recently.8
BN-isosteres 2,9 3,9a 4,10 511 and 612 of the simple polycyclic
aromatic hydrocarbon phenanthrene (1) have been
described and their optical properties studied, as has the
reactivity of 5 and 6 with activated electrophiles and
organolithium compounds.11a,12,13 This study showed that
fluorescence emission maxima and quantum efficiencies
are strongly affected by the position of the B−N bond
(Figure 1). However, as the reasons for these experimental
findings remain unclear, a systematic study into how this
structural difference influences the reactivity and optical
properties of these BN-phenanthrene analogs would be
worthwhile. Unfortunately, the lack of available synthetic
methods to access various permutations of this
Although BN-PAHs have received great interest in
recent years,6 this field is still limited by the lack of
general and mild synthetic methodologies for
synthesizing these compounds in sufficiently large
quantities.7 In addition, the effects that replacement of a
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substitution pattern currently precludes a study of this
nature.
subsequent treatment with two equivalents of
methylmagnesium bromide.19
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7
8
In this context, herein we describe an efficient synthesis
of a previously unknown BN-phenanthrene, namely 3,4-
dihydro-4-aza-3-boraphenanthrene (7), and several
substituted derivatives thereof, as well as an examination
of their reactivity. Moreover, we report an experimental
and theoretical investigation of their main optical
properties in comparison with those of phenanthrene and
other known isomers of BN-phenanthrene.
Scheme 1. Synthesis of BN-phenanthrenes 7a-7e
Br
H
H
B
N
8
9
R1 = H R1 = Ph
Pd[P(o-tol)3]2 Pd2(dba)3
CyPF-t-Bu SPhos
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7a
(81%)
Et2O
30 to 25 ºC
18 h
1
t-BuONa, (NH4)2SO4 PhNH2,t-BuONa
Dioxane Dioxane
R1 = H
LiAlH4
100 ºC, 12 h 100 ºC, 24 h
Cl
R1HN
R1
B


em = 347 nm
F = 0.09
N
BCl3
Toluene
2
3
4
30 to 110 ºC
1
9a
9b
(R = H, 94%)
B
18 h
N
B
N
1
(R = Ph, 99%)
BH
THF
30 to 25 ºC
18 h
R1 = Ph
MeMgBr
N
R
H
1:1 Toluene/CPME R2-BF3K
SiCl4, Et3N


em = 327 nm
F = 0.61
em = 450 nm
F = 0.53

em = 493-524 nm
F = 0.16-1.00
80110 ºC, 24 h
R2
Me
R1
B
R2
Ph
B
N
N
R1
B
BH
NH
5
6
7
N
N
B
1
2
7b
7c
7d
7e
(R = H, R = Me, 80%)
7e
(52%)
1
2
em = 356 nm
F = 0.01

em = 364 nm
F = 0.30
(R = H, R = vinyl, 65%)
this work
1
2
(R = H, R = Ph, 66%)
1
2
(R = Ph, R = Me, 5%)
Figure 1. Previously reported BN-phenanthrenes and their
fluorescence properties.
Scheme 2. Synthesis of BN-phenanthrenes 7f and 10
RESULTS AND DISCUSSION
Cl
The parent BN-phenanthrene compound 7a was prepared
from easily accessible 1-bromo-2-vinylnaphthalene (8)14 in
an overall yield of 76% (Scheme 1). The three steps
involved were: a Buchwald–Hartwig amination using
ammonium sulfate as an ammonia surrogate and Pd[P(o-
tol)3]2 and CyPF-tBu as catalytic system,15 treatment of
PhHN
Ph
B
N
BCl3
Toluene
30 to 110 ºC
18 h
9b
THF
30 to 25 ºC
PhMgBr
(X equiv)
intermediate 9a with boron trichloride to force
a
borylative cyclization, and subsequent treatment with
lithium aluminium hydride.16 Naphthalenamine (9a) was
used to synthesize boron-substituted derivatives 7b-7d by
way of an efficient annulation/aromatization process
using potassium organotrifluoroborates.17
18 h
Ph
B
Ph Ph
H
Ph
B
Ph
N
N
Synthesis of the nitrogen-substituted derivatives proved
more arduous. The first step again involved a Buchwald–
Hartwig amination, this time using aniline, Pd2(dba)3 and
SPhos,18 to prepare naphthalenamine 9b in excellent
yield. However, treatment of this intermediate with
potassium methyltrifluoroborate, SiCl4 and Et3N yielded
BN-phenanthrene 7e in a maximum yield of only 5%,
therefore this compound had to be synthesized via a two-
step sequence: addition of boron trichloride and
7f
7f
10
10
(77%) X = 1
()
(39%)
10
X-Ray of
(4%)
X = 2
The same synthetic methodology was followed with
phenylmagnesium bromide to give the expected
compound 7f in good yield when one equivalent of this
Grignard reagent was added to the previously formed
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chloro-substituted intermediate (Scheme 2). When two functionalization of BN-aromatic compounds. As such,
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4
5
6
7
8
equivalents were added, the main product of the reaction
was the zwitterionic derivative 10, with 7f being isolated
in very poor yield. The crystal structure of 10 was
determined by X-ray diffraction analysis (Figure S1),20
thus confirming this double addition to the boron atom,
which has been previously reported in similar BN-
aromatic compounds by Dewar et al.21
the bromination of four different 3,4-dihydro-4-aza-3-
boraphenanthrenes (7a, 7b, 7d and 7e) by treatment with
bromine in CH2Cl2 or N-bromosuccinimide (NBS) in the
presence of AlCl3 was studied (Scheme 4). All reactions
occurred with complete regioselectivity at C2 under both
conditions, as confirmed by X-ray diffraction analysis of a
single crystal of 11d (Figure S2).20 This result was expected
as this position next to the boron has been reported to be
the most reactive in related BN-aromatics for electrophilic
attacks.11a,23d However, compounds 11a-11c were isolated in
better yields when bromine was used as electrophile, and
11d after addition of NBS and AlCl3. The comparatively
low yield of 11a is due to the instability of 7a under these
reaction conditions and the difficulty of purifying it.
Indeed, the hydrogen connected to the boron was
replaced by a hydroxy group during this process.
9
Scheme 3. Reactivity with organolithium compounds
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H
B
R
B
MeLi
or
n-BuLi
H
H
N
N
THF
78 ºC, 18 h
7a
7b
7g
(R = Me 92%)
(R = Bu, 91%)
As these bromo-substituted derivatives can be used for
further functionalization, various palladium-catalyzed
cross-coupling reactions were tested with 11b and 11c
(Scheme 5). In this manner, 12a and 12b were formed in
good yields under standard Suzuki coupling conditions,
and alkynyl-BN-phenanthrene 13 isolated in moderate
yield after the Sonogashira coupling of 11c. Nevertheless,
the Buchwald–Hartwig reaction did not work under any
of the reaction conditions tested.
In order to gain a more in-depth understanding of the
properties of this new family of BN-phenanthrenes, and
to extend the possibilities for obtaining functionalized
derivatives, their reactivity was investigated. We started
by exploring the addition of organolithium compounds to
BN-phenanthrene 7a (Scheme 3) and found that addition
of two equivalents of MeLi or nBuLi afforded the
formation of 7b or 7g in excellent yields via a nucleophilic
aromatic substitution in which the hydride on boron acts
as a leaving group.19
Scheme 5. Cross-coupling reactions
R
PhB(OH)2
Pd(PPh3)4
Na2CO3
H
B
Ph
N
Scheme 4. Regioselective bromination of 7a, 7b, 7d,
7e
toluene/MeOH
70 ºC
R
B
R2
B
R2
B
Br2, CH2Cl2
12a
12b
(R = Me, 62%)
(R = Ph, 75%)
H
Br
A)
B)
R1
R1
Br
N
0 to 25 ºC, 1 h
or
N
N
H
Ph
Ph
Ph
NBS, AlCl3
PdCl2(PPh3)2
CuI, Et3N
H
B
N
CH2Cl2, 35 ºC, 2 h
11b 11c
,
7a 7b 7d 7e
,
,
,
DMF, 80 ºC
OH
Me
B
H
B
Br
H
Br
13
N
(47%)
N
To explore the photophysics of these previously
unknown BN-phenanthrenes, the UV and fluorescence
spectra of the parent compound 7a and some of its
substituted derivatives (7b-7f, 12b and 13) were measured
(Table 1, Figure 2). When compared with phenanthrene
(λem = 347 nm, ϕF = 0.09), the emission spectrum of 7a
underwent a slight bathochromic shift (λem = 371 nm),
along with a substantial increase in the quantum yield (ϕF
= 0.61). It is worth noting that this new BN-phenanthrene,
together with the previously known isomer 2, shows the
highest fluorescence quantum yield of all non-substituted
BN isosteres of phenanthrene reported to date.9a,10,11a,12
11a
11b
(A, 37%; B, 0%)
Ph
(A, 99%)
Me
H
B
Br
Ph
B
N
Br
N
11c
11d
(A, 46%; B, 75%)
(A, 94%)
Electrophilic aromatic substitution22 and, in particular,
halogenation, generally followed by cross-coupling
reactions,11a,23 has proven to be a useful tool for the
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non-nitrogen substituted species 7b-7d displayed
Page 4 of 13
a
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similar value to that of the parent compound (7a), the
quantum yield of nitrogen-substituted derivatives 7e and
7f was notably lower. Interestingly, in addition to the
common emission at around 400 nm found for other
derivatives, 7f shows another emission band located at ca.
560 nm. This additional band could be explained by
computational means (see SI). The steric hindrance
caused by the two neighboring aromatic rings allows for
the presence of two different minima of comparable
energy in the excited state. Emission from one of them
(more planar and analog to other compounds) implies the
emission at 397 nm, while the other minimum (more
distorted) implies the emission at 498 nm. These low
quantum yields could be due to excimer formation, as it
has been reported for related compounds.24 This was
checked by measuring the fluorescence dependence on
concentration of 7f (see SI), but no significant differences
were found. As an alternative deactivation channel, the
phenyl rings placed on the nitrogen atom could rotate
through the single bond to allow the excited state decay.
Finally, 12b and 13, which contain an additional phenyl or
alkynyl group at C2, maintained a high quantum yield but
showed a larger bathochromic shift (λem for 13 of 416 nm).
Table 1. UV/Vis and fluorescence data for BN-
phenanthrenes 7a-7f, 12b and 13[a]
[b]
compound
ε
λabs max
(exc) (nm)
λem
ϕF
(M-1cm-1)
(nm)
7a
7b
7c
9149
6995
9746
10685
5454
6200
15049
7294
351 (335)
352 (335)
355 (339)
360 (343)
359 (342)
364 (347)
365 (348)
387 (368)
371
373
387
383
387
392
396
416
0.61
0.70
0.42
0.57
0.04
0.04
0.51
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7d
7e
7f
12b
13
0.72
[a] All experiments were performed using cyclohexane
solutions. [b] Quantum yields reported relative to 9,10-
diphenylanthracene (ϕF = 0.93)
7a
7d
7f
12b
1,0
0,8
13
0,6
0,4
0,2
0,0
260
280
300
320
340
360
380
400
420
 (nm)
7a
7d
7f
12b
13
1,0
0,8
0,6
0,4
0,2
0,0
360
400
440
480
 (nm)
520
560
600
640
Figure 2. UV/Vis absorption (top) and emission (bottom)
spectra for selected BN-phenanthrenes 7a, 7d, 7f, 12b and 13
in cyclohexane
Figure 3. Computed critical points along the potential
energy surface for 6 (top) and 7a
The alkyl- and aryl-substituted derivatives 7b-7f
exhibited similar slightly red-shifted emission maxima
with respect to phenanthrene but diverged significantly
as regards the fluorescence quantum yield. Thus, while
A computational study was carried out to gain a deeper
insight into the photophysics of these BN-phenanthrenes,
with 7a being selected as the core structure for this new
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family of compounds. For the sake of comparison, we also
performed calculations for 6. We first computed the
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5
6
7
8
CONCLUSIONS
absorption spectra for both compounds using the
qualitative TD-DFT methodology (see Computational
Details). A good agreement between the experimental
and computational data was obtained when using the
B3LYP functional together with the 6-31+G** basis set;
cyclohexane was included as solvent using the PCM
method. For 6, S1 was found to be a bright state (325 nm, f
= 0.24), with an emission from the excited state at 356
nm. For 7a, an absorption with maximum at 326 nm (f =
0.12) and an emission at 331 nm were computed. The
HOMO-LUMO transition is mainly responsible for the
absorption in both compounds (see SI).
An efficient preparation of the previously unknown BN-
phenanthrene 7a (three steps from 2-bromo-1-
vinylnaphthalene 8; overall yield: 76%), along with several
substituted derivatives, has been reported. This
methodology could potentially be used to synthesise
more complex BN-PAHs by careful selection of the
starting materials. Moreover, the reactivity of this new
family of BN-aromatic species with organolithium
compounds and bromine has been evaluated. This latter
reaction afforded bromo-substituted compounds with
complete regioselectivity at C2, which are appropriate for
further functionalization via Suzuki and Sonogashira
couplings. A study of the photophysics of these new BN-
phenanthrenes confirmed the previously observed
dramatic effect of the B–N unit. Indeed, the parent
compound 7a underwent a slight bathochromic shift
along with a substantial increase in the quantum yield (ϕF
= 0.61) when compared with phenanthrene. The optical
properties of these compounds were rationalized by
means of theoretical calculations. Competitive radiative
and non-radiative deactivation mechanisms account for
the experimental data. In addition, a planar minimum in
the excited state is responsible for the emission, whereas
a kink in any of the non-substituted rings allows for the
non-emissive deactivation. This discovery suggests new
possibilities for obtaining functionalized BN-aromatics
with modulated properties, thus providing a further
option for tuning the emissive properties of
phenanthrene-based materials.
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The radiationless deactivation of the excited state
requires the presence of an accessible funnel to the
ground state, such as a conical intersection (CI) point.
Indeed, several CIs were found for 6 and 7a using CASSCF
(see SI). While structurally related to phenanthrene, the
presence of the B-N moiety implies an asymmetry in the
chromophore. As such, the different CIs found feature
the typical kink found in PAHs located in different parts
of the structure.25 In any case, the B-N bond does not take
part in the geometrical deformation. In this sense,
substitution of the carbon atoms also results in a
modification of the deactivation mechanisms in addition
to the optical properties.
To obtain
a more quantitative overview of the
properties of 6 and 7a, the critical points along the
potential energy surface (PES) were computed for both
compounds at the CASPT2//CASSCF level of theory using
a (14,13) active space and the ANO-L-VDZ basis set (see
Computational Details). The results are shown in Figure
3.
EXPERIMENTAL SECTION
General Methods. Reagents were acquired from
commercial sources and used without further
purification. When required, solvents were dried using an
MBRAUN MB-SPS-800 apparatus. In general, reactions
were carried out under an argon atmosphere using oven-
dried glassware with magnetic stirring and dry solvents.
Reactions were monitored using analytical TLC plates
(Merck; silica gel 60 F254, 0.25 mm), and compounds
were visualized with UV radiation. Silica gel grade 60
(70230 mesh, Merck) was used for column
chromatography. All melting points were determined in
open capillary tubes using a Stuart Scientific SMP3
melting point apparatus (uncorrected). IR spectra were
obtained using a Perkin-Elmer FTIR spectrum 2000
Both 6 and 7a share a similar shape of the PES, with a
planar minimum in the first excited state, which accounts
for the emission and the relatively small Stokes shift (see
Table 1). In both cases, the lower energy conical
intersection point is located well above the energy of the
S1 minimum. This allows for a radiative deactivation of
the excited state, in agreement with the relatively high
fluorescence quantum yields measured. If the energy
barrier in S1 is exceeded, the ground state could be
recovered by a competitive non-radiative mechanism. A
detailed analysis of the CIs is provided in the SI.
The energy profile for 6a and 7 is very similar to the one
already described in related BN-PAHs (see Figure 1).11a The
inclusion of the B-N moiety in the hydrocarbon backbone
modifies not only the absorption but also the availability
of competing deactivation channels. When a CI point of
low energy is available (as in 5,11a Figure 1), these
compounds will feature an emission of low intensity. In
contrast, high-energy CIs are related with strongly
emissive compounds (as in 2,11a 6 and 7a). This allows for
the rationalization of the optical properties of the BN-
phenanthrenes in which the BN moiety is located in
different positions. In turn, this should help in the design
of new BN-PAHs with controlled properties.
spectrophotometer. H, 13C{1H} and 11B{1H} NMR spectra
1
were recorded using either a Varian Mercury VX-300,
Varian Unity 300 or Varian Unity 500 MHz spectrometer
at room temperature. Chemical shifts are given in ppm ()
downfield from TMS, with calibration with respect to the
residual protonated solvent used (H = 7.24 ppm and C =
77.0 ppm for CDCl3). 11B{1H} NMR spectra were referenced
externally to BF3·OEt2 (B = 0 ppm). Coupling constants
(J) are in Hertz (Hz) and signals are described as follows:
s, singlet; d, doublet; t, triplet; q, quadruplet; m,
multiplet; br, broad; ap, apparent. High-resolution
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1
analysis (HRMS) was performed using an Agilent 6210
time of-flight LC/MS. Absorption spectra were recorded
1084, 989, 902, 800, 743. H NMR (500 MHz, CDCl3)
 (ppm) 7.827.79 (m, 1H, H-8), 7.787.76 (m, 1H, H-5),
7.47 (d, J = 8.6 Hz, 1H, H-3), 7.467.43 (m, 2H, H-6, H-7),
1
2
3
using
a
Uvikon 941 (Kontron Instruments) UV-Vis
Steady-state fluorescence
spectrophotometer.
7.30 (d, J = 8.6 Hz, 1H, H-4), 6.97 (dd, Jtrans = 17.4 Hz, Jcis
=
4
5
6
7
8
9
measurements were carried out using a PTI Quanta
Master spectrofluorimeter equipped with a Xenon flash
11.1 Hz, 1H, H-9), 5.73 (dd, Jtrans = 17.4 Hz, Jgem = 1.3 Hz, 1H,
H-10), 5.41 (dd, Jcis = 11.1 Hz, Jgem = 1.3 Hz, 1H, H-10), 4.33
(br s, 1H, NH2). 13C{1H} NMR (125 MHz, CDCl3)  (ppm)
138.7 (C-1), 133.8 (C-4a), 132.7 (C-9), 128.5 (C-5), 125.8 (C-
6), 125.2 (C-7), 125.0 (C-3), 123.7 (C-8a), 120.8 (C-8), 118.7
(C-4), 117.8 (C-2), 115.4 (C-10). HRMS (APCI) m/z
calculated for C12H12N [M+H]+: 170.0964. Found [M+H]+:
170.0973.
lamp as
a
light source, single concave grating
monochromators and Glan-Thompson polarizers in the
excitation and emission paths. Detection was allowed by a
photomultiplier cooled by a Peltier system. Slit widths
were selected at 6 nm for both excitation and emission
paths and polarizers were fixed at the “magic angle”
condition. Right angle geometry and rectangular 10 mm
path cells were used for the fluorescence measurements.
The starting material 1-Bromo-2-naphthaldehyde was
purchased from Sigma-Aldrich and was used without
further purification.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
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39
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46
47
48
49
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56
57
58
59
60
N-Phenyl-2-vinylnaphthalen-1-amine (9b). An oven-
dried Biotage microwave vial equipped with a stir bar was
charged with Pd2(dba)3·CHCl3 (31 mg, 0.030 mmol, 2.0
mol%), SPhos (30 mg, 0.072 mmol, 4.8 mol%), sodium
tert-butoxide (223 mg, 2.25 mmol, 1.5 equiv.) and aryl
bromide 8 (350 mg, 1.50 mmol, 1.0 equiv.). The vial was
sealed with a cap lined with a disposable Teflon septum,
evacuated under vacuum, and purged with argon three
times. Dioxane (15 mL) was added, followed by aniline (171
L, 1.80 mmol, 1.2 equiv.). The reaction mixture was
stirred at 100 ºC for 24 h, then diluted with Et2O (15 mL)
and filtered through a pad of Celite. The filtrate was
removed under reduced pressure and the remaining
residue was purified by flash column chromatography (5%
EtOAc/Hexane) to give 9b (366 mg, 1.49 mmol, 99%) as a
white solid. M.p.: 8688 ºC. IR (KBr) ῦmax (cm-1) 3392
(NH), 3061, 3038, 1602, 1498, 1416, 1377, 1308, 1254, 922,
820, 747, 691. 1H NMR (500 MHz, CDCl3)  (ppm)
8.068.04 (m, 1H, H-8), 7.91 (dd, J = 8.1, 1.4 Hz, 1H, H-5),
7.84 (d, J = 8.7 Hz, 1H, H-3), 7.81 (d, J = 8.7 Hz, 1H, H-4),
7.52 (ddd, J = 8.1, 6.8, 1.3 Hz, 1H, H-6), 7.47 (ddd, J = 8.2,
6.8, 1.4 Hz, 1H, H-7), 7.247.21 (m, 2H, H-11, H-13), 7.20
(dd, Jtrans = 17.6 Hz, Jcis = 11.1 Hz, 1H, H-15), 6.85 (tt, J = 7.4,
1.1 Hz, 1H, H-12), 6.656.62 (m, 2H, H-10, H-14), 5.92 (dd,
Jtrans = 17.6 Hz, Jgem = 1.1 Hz, 1H, H-16), 5.59 (br s, 1H, NH),
1-Bromo-2-vinylnaphthalene (8). MePPh3Br (1.93 g, 5.30
mmol, 1.3 equiv.) and tBuOK (701 mg, 6.12 mmol, 1.5
equiv.) were dissolved in THF (20 mL), and the resulting
yellow suspension was stirred at room temperature for 2
h. The reaction mixture was then cooled to 0 ºC and a
solution of 1-bromo-2-naphthaldehyde (1.00 g, 4.08 mmol,
1.0 equiv.) in THF (2 mL) added dropwise. After removing
the cooling bath, the mixture was stirred at room
temperature for 3 h. Silica gel was then added and the
solvents removed under reduced pressure. Purification by
flash column chromatography (Hexane) gave 8 (869 mg,
3.73 mmol, 91%) as a colorless oil, which solidified upon
1
cooling. H NMR (300 MHz, CDCl3)  (ppm) 8.34 (dd, J =
8.4, 1.2 Hz, 1H, H-8), 7.807.76 (m, 1H, H-5), 7.75 (d, J =
8.6 Hz, 1H, H-4) 7.65 (d, J = 8.6 Hz, 1H, H-3), 7.57 (ddd, J =
8.4, 6.9, 1.4 Hz, 1H, H-7), 7.48 (ddd, J = 8.0, 6.9, 1.2 Hz, 1H,
H-6), 7.38 (dd, Jtrans = 17.5 Hz, Jcis = 11.0 Hz, 1H, H-9), 5.82
(dd, Jtrans = 17.5 Hz, Jgem = 0.8 Hz, 1H, H-10), 5.47 (dd, Jcis
=
11.0 Hz, Jgem = 0.8 Hz, 1H, H-10). 13C{1H} NMR (75 MHz,
CDCl3)  (ppm) 136.8 (C-9), 134.9 (C-2), 134.0 (C-8a), 132.5
(C-4a), 128.0 (C-5), 127.74 (C-4), 127.70 (C-7), 127.5 (C-8),
126.6 (C-6), 123.9 (C-3), 123.7 (C-1), 117.4 (C-10). Spectral
data were in accordance with those in literature.14
13
5.41 (dd, Jcis = 11.1 Hz, Jgem = 1.1 Hz, 1H, H-16). C{1H} NMR
(125 MHz, CDCl3)  (ppm) 147.2 (C-9), 134.2 (C-4a), 133.8
(C-1), 133.0 (C-15), 132.1 (C-2), 131.5 (C-8a), 129.2 (2C, C-11,
C-13), 128.1 (C-5), 126.48 (C-4), 126.47 (C-7), 126.1 (C-6),
123.9 (C-8), 123.4 (C-3), 118.4 (C-12), 115.8 (C-16), 113.8 (2C,
C-10, C-14). HRMS (APCI) m/z calculated for C18H16N
[M+H]+: 246.1277. Found [M+H]+: 246.1270.
2-Vinylnaphthalen-1-amine (9a). Pd[P(o-tol)3]2 (18.2
mg, 0.025 mmol, 5.0 mol%) and CyPF-tBu (14.3 mg, 0.025
mmol, 5.0 mol%) were dissolved in dioxane (1 mL) in a
Schlenk flask and mixed for 5 min. An oven-dried Biotage
microwave vial equipped with a stir bar was charged with
aryl halide 8 (117 mg, 0.50 mmol, 1.0 equiv.), ammonium
sulfate (100 mg, 0.75 mmol, 1.5 equiv.) and sodium tert-
butoxide (223 mg, 2.25 mmol, 4.5 equiv.). The vial was
sealed with a cap lined with a disposable Teflon septum,
evacuated under vacuum and purged with argon three
times. Dioxane (5 mL) was added, followed by the
solution of the catalyst. The reaction was stirred at 100 ºC
for 12 h, then the reaction mixture was diluted with
EtOAc (10 mL) and filtered through a pad of Celite. The
filtrate was concentrated under reduced pressure and the
General procedure for borylative cyclization with
boron trichloride. The corresponding amine (1.0 equiv.)
was dissolved in anhydrous toluene (0.05 M) in a Schlenk
flask, and the resulting solution was cooled to 30 ºC.
Cold boron trichloride solution (1.0 M in hexanes; 2.0
equiv.) was added dropwise to the vigorously stirring cold
solution of amine in toluene using a syringe. Upon
conclusion of the addition, the reaction mixture was
allowed to warm to room temperature over one hour,
then heated at reflux for 18 hours. At the end of the
reaction, the mixture was concentrated under reduced
pressure to afford the corresponding BCl intermediate as
an air- and moisture-sensitive solid, which was used in
the next step without further purification.
remaining
residue
purified
by
flash
column
chromatography (10% EtOAc/Hexane) to give 9a (79 mg,
0.47 mmol, 94%) as an orange solid. M.p.: 5658 ºC. IR
(KBr) ῦmax (cm-1) 3350 (NH2), 3059, 1622, 1565, 1510, 1400,
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Page 7 of 13
The Journal of Organic Chemistry
3-Chloro-3,4-dihydro-4-aza-3-boraphenanthrene.
126.7 (C-8), 126.0 (C-9), 124.0 (C-10a), 121.8 (C-4a), 121.5 (C-
6), 119.7 (C-10). *Carbon not observed in 13C{1H} NMR,
assigned by gHSQC. 11B{1H} NMR (160 MHz, CDCl3)
 (ppm) 31.95. HRMS (APCI) m/z calculated for C12H11BN
[M+H]+: 180.0979. Found [M+H]+: 180.0977.
1
2
3
4
5
6
7
8
Following the general procedure, amine 9a (470 mg, 2.78
mmol) was dissolved in toluene (56 mL) followed by
addition of boron trichloride solution (5.6 mL, 5.55 mmol)
to give 3-chloro-3,4-dihydro-4-aza-3-boraphenanthrene
1
(589 mg, 2.76 mmol, 99%) as a red solid. H NMR (500
General procedure for borylative cyclization with
potassium organotrifluoroborates. An oven-dried
Biotage microwave vial equipped with a stir bar was
MHz, CDCl3)  (ppm) 8.81 (br s, 1H, NH), 8.18 (d, J = 8.3
Hz, 1H, H-10), 8.15 (d, J = 11.6 Hz, 1H, H-4), 7.91 (d, J = 7.7
Hz, 1H, H-7), 7.657.62 (m, 1H, H-9), 7.62 (d, J = 8.8 Hz,
1H, H-5), 7.617.58 (m, 1H, H-8), 7.58 (d, J = 8.8 Hz, 1H, H-
6), 6.89 (dd, J = 11.6, 1.9 Hz, 1H, H-3). 13C{1H} NMR (125
MHz, CDCl3)  (ppm) 148.0 (C-4), 135.7 (C-10b), 133.6 (C-
6a), 128.9 (C-7), 127.2 (C-5), 127.1 (C-8), 127.0 (C-3*), 126.3
(C-9), 123.3 (C-10a), 121.9 (C-6), 120.7 (C-4a), 119.6 (C-10).
*Carbon not observed in 13C{1H} NMR, assigned by
gHSQC. 11B{1H} NMR (160 MHz, CDCl3)  (ppm) 32.70.
charged
with
the
corresponding
potassium
9
organotrifluoroborate (1.0 equiv.). The vial was sealed
with a cap lined with a disposable Teflon septum,
evacuated under vacuum, and purged with argon three
times. CMPE (0.5 M) and toluene (0.5 M) were then
added, followed by the corresponding amine (1.2 equiv.),
SiCl4 (1.0 equiv.) and Et3N (1.5 equiv.) under argon. The
reaction mixture was stirred at 80 or 110 ºC for 24 h, then
at the end of the reaction, the mixture was cooled to
room temperature, diluted with Et2O and filtered through
a silica gel plug. The filtrate was concentrated under
reduced pressure and the remaining residue was purified
by flash column chromatography (using the eluent
indicated in each case) to afford the corresponding 3,4-
dihydro-4-aza-3-boraphenanthrenes.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
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48
49
50
51
52
53
54
55
56
57
58
59
60
3-Chloro-4-phenyl-3,4-dihydro-4-aza-3-boraphenanthrene.
Following the general procedure, amine 9b (491 mg, 2.00
mmol) was dissolved in toluene (40 mL) followed by
addition of boron trichloride solution (4.0 mL, 4.00
mmol) to give 3-chloro-4-phenyl-3,4-dihydro-4-aza-3-
boraphenanthrene (573 mg, 1.98 mmol, 99%) as a pale-
1
green solid. H NMR (500 MHz, CDCl3)  (ppm) 8.14 (d, J
= 11.5 Hz, 1H, H-4), 7.81 (dd, J = 8.0, 1.5 Hz, 1H, H-7), 7.65
(ap s, 2H, H-5, H-6), 7.497.42 (m, 3H, H-13, H-14, H-15),
7.35 (ddd, J = 8.0, 6.8, 1.0 Hz, 1H, H-8), 7.297.25 (m, 3H,
H-10, H-12, H-16), 7.01 (d, J = 11.5 Hz, 1H, H-3), 6.99 (ddd, J
= 9.0, 6.8, 1.5 Hz, 1H, H-9). 13C{1H} NMR (125 MHz, CDCl3)
 (ppm) 148.1 (C-4), 146.0 (C-11), 138.7 (C-10b), 135.5 (C-6a),
129.3 (2C, C-13, C-15), 128.8 (2C, C-12, C-16), 128.6 (C-7),
128.5 (C-3*), 127.8 (C-5), 127.2 (C-14), 126.2 (C-10), 125.9 (C-
8), 125.4 (C-10a), 124.4 (C-9), 124.0 (C-6), 123.9 (C-4a).
*Carbon not observed in 13C{1H} NMR, assigned by
gHSQC. 11B{1H} NMR (160 MHz, CDCl3)  (ppm) 34.41.
3-Methyl-3,4-dihydro-4-aza-3-boraphenanthrene
Following the general procedure,
(7b).
potassium
methyltrifluoroborate (122 mg, 1.00 mmol) was dissolved
in CPME (2.0 mL) and toluene (2.0 mL), followed by
addition of amine 9a (203 mg, 1.20 mmol), SiCl4 (116 L,
1.00 mmol) and Et3N (209 L, 1.50 mmol). After heating at
80 ºC, purification by flash column chromatography (5%
EtOAc/Hexane) gave 7b (154 mg, 0.80 mmol, 80%) as a
white solid. M.p.: 8486 ºC. IR (KBr) ῦmax (cm-1) 3400
(NH), 3011, 2927, 1591, 1561, 1449, 1128, 883, 833, 794, 745,
1
679. H NMR (500 MHz, CDCl3)  (ppm) 8.69 (br s, 1H,
NH), 8.23 (d, J = 8.5 Hz, 1H, H-10), 8.08 (d, J = 11.3 Hz, 1H,
H-4), 7.927.91 (m, 1H, H-7), 7.64 (d, J = 8.5 Hz, 1H, H-5),
7.61 (ddd, J = 8.5, 7.0, 1.7 Hz, 1H, H-9), 7.597.56 (m, 1H,
H-8), 7.54 (d, J = 8.5 Hz, 1H, H-6), 6.98 (dd, J = 11.3, 1.8 Hz,
1H, H-3), 0.92 (s, 3H, H-11). 13C{1H} NMR (125 MHz, CDCl3)
 (ppm) 144.8 (C-4), 135.9 (C-10b), 133.3 (C-6a), 131.0 (C-
3*), 128.8 (C-7), 127.6 (C-5), 126.3 (C-8), 125.7 (C-9), 123.7
(C-10a), 120.7 (C-4a), 120.6 (C-6), 119.6 (C-10), 2.7 (C-11*).
*Carbon not observed in 13C{1H} NMR, assigned by
gHSQC. 11B{1H} NMR (160 MHz, CDCl3)  (ppm) 37.55.
HRMS (APCI) m/z calculated for C13H13BN [M+H]+:
194.1136. Found [M+H]+: 194.1130.
3,4-Dihydro-4-aza-3-boraphenanthrene (7a). In
Schlenk flask, 3-chloro-3,4-dihydro-4-aza-3-
a
boraphenanthrene (589 mg, 2.76 mmol, 1.0 equiv.) was
dissolved in anhydrous Et2O (55 mL), and the resulting
solution cooled to 30 ºC. Cold lithium aluminum hydride
solution (1.0 M in Et2O; 5.5 mL, 5.52 mmol, 2.0 equiv.) was
added dropwise using a syringe, and the reaction mixture
was allowed to warm to room temperature and stirred for
18 hours. A hydrochloric acid solution (2.0 M in Et2O; 3.0
mL, 6.07 mmol, 2.2 equiv.) was then added and the
resulting mixture filtered through a silica gel plug. The
filtrate was concentrated under reduced pressure to
afford parental BN-phenanthrene 7a (404 mg, 2.26 mmol,
81%) as a pale-red solid without further purification. M.p.:
7880 ºC. IR (KBr) ῦmax (cm-1) 3410 (NH), 2963, 2541, 2470
(BH), 1586, 1562, 1442, 1428, 1261, 1100, 884, 796, 771, 666.
1H NMR (500 MHz, CDCl3)  (ppm) 9.28 (br s, 1H, NH),
8.27 (dd, J = 8.4, 1.2 Hz, 1H, H-10), 8.21 (dd, J = 11.3, 1.2 Hz,
1H, H-4), 7.937.91 (m, 1H, H-7), 7.67 (d, J = 8.6 Hz, 1H, H-
5), 7.64 (ddd, J = 8.4, 6.9, 1.5 Hz, 1H, H-9), 7.59 (d, J = 8.6
Hz, 1H, H-6), 7.59 (ddd, J = 8.0, 6.9, 1.2 Hz, 1H, H-8), 7.16
(ddd, J = 11.3, 2.5, 1.7 Hz, 1H, H-3), 5.734.78 (br s, 1H, BH).
13C{1H} NMR (125 MHz, CDCl3)  (ppm) 145.7 (C-4), 135.9
(C-10b), 133.4 (C-6a), 130.9 (C-3*), 128.9 (C-7), 127.7 (C-5),
3-Vinyl-3,4-dihydro-4-aza-3-boraphenanthrene
Following the general procedure,
(7c).
potassium
vinyltrifluoroborate (56 mg, 0.40 mmol) was dissolved in
CPME (0.8 mL) and toluene (0.8 mL), followed by
addition of amine 9a (81 mg, 0.48 mmol), SiCl4 (46 L,
0.40 mmol) and Et3N (84 L, 0.60 mmol). After heating at
80 ºC, purification by flash column chromatography (5%
EtOAc/Hexane) gave 7c (53 mg, 0.26 mmol, 65%) as a
white solid. M.p.: 9294 ºC. IR (KBr) ῦmax (cm-1) 3399
(NH), 3064, 2977, 1590, 1451, 1133, 1014, 944, 836, 754, 717,
1
643. H NMR (500 MHz, CDCl3)  (ppm) 8.80 (br s, 1H,
NH), 8.25 (d, J = 8.3 Hz, 1H, H-10), 8.16 (d, J = 11.4 Hz, 1H,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 13
13, C-15), 128.5 (C-7), 128.3 (2C, C-12, C-16), 128.1 (C-5),
H-4), 7.927.90 (m, 1H, H-7), 7.64 (d, J = 8.5 Hz, 1H, H-5),
7.62 (ddd, J = 8.3, 6.9, 1.5 Hz, 1H, H-9), 7.57 (ddd, J = 7.8,
6.9, 1.3 Hz, 1H, H-8), 7.55 (d, J = 8.5 Hz, 1H, H-6), 7.20 (dd,
J = 11.4, 1.8 Hz, 1H, H-3), 6.64 (dd, Jtrans = 19.6 Hz, Jcis = 13.3
Hz, 1H, H-11), 6.31 (dd, Jtrans = 19.6 Hz, Jgem = 3.5 Hz, 1H, H-
1
2
3
4
5
6
7
8
126.43 (C-14), 126.38 (C-8), 125.6 (C-10a), 125.3 (C-10), 123.9
(C-4a), 123.8 (C-9), 122.8 (C-6), 5.1 (C-17*). *Carbon not
observed in 13C{1H} NMR, assigned by gHSQC. 11B{1H}
NMR (160 MHz, CDCl3)  (ppm) 39.66. HRMS (APCI) m/z
calculated for C19H17BN [M+H]+: 270.1449. Found [M+H]+:
270.1439.
13
12), 6.10 (dd, Jcis = 13.3 Hz, Jgem = 3.5 Hz, 1H, H-12). C{1H}
NMR (125 MHz, CDCl3)  (ppm) 145.7 (C-4), 137.9 (C-11*),
135.7 (C-10b), 133.5 (C-6a), 132.0 (C-12), 128.9 (C-7), 128.0
(C-3*), 127.5 (C-5), 126.5 (C-8), 125.8 (C-9), 123.9 (C-10a),
121.5 (C-4a), 121.1 (C-6), 119.6 (C-10). *Carbon not observed
in 13C{1H} NMR, assigned by gHSQC. 11B{1H} NMR (160
MHz, CDCl3)  (ppm) 32.62. HRMS (APCI) m/z calculated
for C14H13BN [M+H]+: 206.1136. Found [M+H]+: 206.1128.
General procedure for the Grignard Reaction. In a
Schlenk flask, 3-chloro-4-phenyl-3,4-dihydro-4-aza-3-
boraphenanthrene (58 mg, 0.20 mmol, 1.0 equiv.) was
dissolved in anhydrous THF (4.0 mL), and the resulting
solution was cooled to 30 ºC. The corresponding
organomagnesium bromide solution (1.0 or 2.0 equiv.)
was added dropwise using a syringe, then the reaction
mixture was allowed to warm to room temperature and
stirred for 18 hours. At the end of the reaction, the
mixture was concentrated under reduced pressure and
the remaining residue was purified by flash column
chromatography (010% CH2Cl2/Hexane) to afford the
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3-Phenyl-3,4-dihydro-4-aza-3-boraphenanthrene
Following the general procedure,
(7d).
potassium
phenyltrifluoroborate (572 mg, 2.95 mmol) was dissolved
in CPME (5.9 mL) and toluene (5.9 mL), followed by
addition of amine 9a (600 mg, 3.55 mmol), SiCl4 (341 L,
2.95 mmol) and Et3N (617 L, 4.43 mmol). After heating at
80 ºC, purification by flash column chromatography (5%
EtOAc/Hexane) gave 7d (500 mg, 1.96 mmol, 66%) as a
white solid. M.p.: 9496 ºC. IR (KBr) ῦmax (cm-1) 3415 (NH),
corresponding
3-substituted-3,4-dihydro-4-aza-3-
boraphenanthrenes.
3-Methyl-4-phenyl-3,4-dihydro-4-aza-3-boraphenanthrene
(7e). Following the general procedure, 3-chloro-4-phenyl-
3,4-dihydro-4-aza-3-boraphenanthrene (58 mg, 0.20
mmol) and methylmagnesium bromide solution (1.0 M in
DBE; 400 L, 0.40 mmol) gave 7e (28 mg, 0.104 mmol,
52%) as a white solid.
1
2917, 1591, 1560, 1446, 1428, 1225, 1149, 791. H NMR (500
MHz, CDCl3)  (ppm) 9.21 (br s, 1H, NH), 8.34 (d, J = 8.3
Hz, 1H, H-10), 8.27 (d, J = 11.4 Hz, 1H, H-4), 8.038.01 (m,
2H, H-12, H-16), 7.957.93 (m, 1H, H-7), 7.70 (d, J = 8.7 Hz,
1H, H-5), 7.66 (ddd, J = 8.3, 6.9, 1.4 Hz, 1H, H-9), 7.60
(ddd, J = 8.0, 6.9, 1.2 Hz, 1H, H-8), 7.59 (d, J = 8.7 Hz, 1H,
H-6), 7.567.48 (m, 3H, H-13, H-14, H-15), 7.42 (dd, J = 11.4,
1.9 Hz, 1H, H-3). 13C{1H} NMR (125 MHz, CDCl3)  (ppm)
146.3 (C-4), 138.4 (C-11**), 135.9 (C-10b), 133.6 (C-6a), 132.6
(2C, C-12, C-16), 129.6 (C-14), 129.0 (C-7), 128.7 (C-3*), 128.3
(2C, C-13, C-15), 127.5 (C-5), 126.6 (C-8), 126.0 (C-9), 124.0
(C-10a), 121.5 (C-4a), 121.3 (C-6), 119.5 (C-10). *Carbon not
observed in 13C{1H} NMR, assigned by gHSQC. **Carbon
3,4-Diphenyl-3,4-dihydro-4-aza-3-boraphenanthrene (7f).
Following the general procedure, 3-chloro-4-phenyl-3,4-
dihydro-4-aza-3-boraphenanthrene (58 mg, 0.20 mmol)
and phenylmagnesium bromide solution (1.0 M in THF;
200 L, 0.20 mmol) gave 7f (51 mg, 0.154 mmol, 77%) as a
white solid. M.p.: 181183 ºC. IR (KBr) ῦmax (cm-1) 3051,
1
2918, 1584, 1490, 1431, 1328, 1276, 1246, 831, 737. H NMR
(500 MHz, CDCl3)  (ppm) 8.21 (d, J = 11.2 Hz, 1H, H-4),
7.827.81 (m, 1H, H-7), 7.70 (d, J = 8.5 Hz, 1H, H-5), 7.65
(d, J = 8.5 Hz, 1H, H-6), 7.33 (ddd, J = 8.0, 6.8, 1.0 Hz, 1H,
H-8), 7.327.29 (m, 1H, H-10), 7.267.22 (m, 3H, H-13, H-
14, H-15), 7.177.12 (m, 4H, H-3, H-19, H-20, H-21),
7.087.06 (m, 2H, H-12, H-16), 7.057.03 (m, 2H, H-18, H-
13
11
not observed in C{1H} NMR, assigned by gHMBC. B{1H}
NMR (160 MHz, CDCl3)  (ppm) 34.07. HRMS (APCI) m/z
calculated for C18H15BN [M+H]+: 256.1292. Found [M+H]+:
256.1284.
3-Methyl-4-phenyl-3,4-dihydro-4-aza-3-boraphenanthrene
(7e). Following the general procedure, potassium
methyltrifluoroborate (120 mg, 0.98 mmol) was dissolved
in CPME (2.0 mL) and toluene (2.0 mL), followed by
addition of amine 9b (288 mg, 1.18 mmol), SiCl4 (113 L,
0.98 mmol) and Et3N (205 L, 1.47 mmol). After heating at
110 ºC, purification by flash column chromatography
(Hexane) gave 7e (13 mg, 0.049 mmol, 5%) as a white
solid. M.p.: 9496 ºC. IR (KBr) ῦmax (cm-1) 3004, 2924, 1588,
13
22), 6.94 (ddd, J = 8.9, 6.8, 1.5 Hz, 1H, H-9). C{1H} NMR
(125 MHz, CDCl3)  (ppm) 147.2 (C-11), 146.2 (C-4), 142.3
(C-17**), 137.9 (C-10b), 135.6 (C-6a), 133.0 (2C, C-18, C-22),
132.7 (C-3*), 129.1 (2C, C-12, C-16), 129.0 (2C, C-13, C-15),
128.5 (C-7), 127.9 (C-5), 126.92 (2C, C-19, C-21), 126.87 (C-
10), 126.8 (C-8), 126.5 (C-14), 125.6 (C-10a), 125.5 (C-20),
124.5 (C-4a), 123.8 (C-9), 123.6 (C-6). *Carbon not
observed in 13C{1H} NMR, assigned by gHSQC. **Carbon
1
13
11
not observed in C{1H} NMR, assigned by gHMBC. B{1H}
NMR (160 MHz, CDCl3)  (ppm) 36.66. HRMS (EI) m/z
calculated for C24H18BN [M]+: 331.1527. Found [M]+:
331.1533.
1489, 1428, 1330, 1308, 1228, 1133, 827, 732, 698, 689. H
NMR (500 MHz, CDCl3)  (ppm) 8.05 (d, J = 11.2 Hz, 1H,
H-4), 7.78 (dd, J = 8.2, 1.5 Hz, 1H, H-7), 7.64 (d, J = 8.4 Hz,
1H, H-5), 7.57 (d, J = 8.4 Hz, 1H, H-6), 7.457.41 (m, 2H, H-
13, H-15), 7.37 (tt, J = 7.4, 1.3 Hz, 1H, H-14), 7.327.30 (m,
1H, H-10), 7.30 (ddd, J = 8.2, 6.8, 0.9 Hz, 1H, H-8),
7.207.17 (m, 2H, H-12, H-16), 7.00 (d, J = 11.2 Hz, 1H, H-3),
6.94 (ddd, J = 8.5, 6.8, 1.5 Hz, 1H, H-9), 0.60 (s, 3H, H-17).
13C{1H} NMR (125 MHz, CDCl3)  (ppm) 148.4 (C-11), 145.3
(C-4), 138.6 (C-10b), 135.3 (C-6a), 131.3 (C-3*), 129.4 (2C, C-
3,3,4-Triphenyl-4H-3,4-dihydro-4-aza-3-boraphenanthrene
(10). Following the general procedure, 3-chloro-4-phenyl-
3,4-dihydro-4-aza-3-boraphenanthrene (58 mg, 0.20
mmol) and phenylmagnesium bromide solution (1.0 M in
THF; 400 L, 0.40 mmol) gave 7f (3.0 mg, 0.009 mmol,
4%) and 10 (32 mg, 0.078 mmol, 39%) as a white solid.
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The Journal of Organic Chemistry
M.p.: 174176 ºC. IR (KBr) ῦmax (cm-1) 3045, 2998, 1495,
1431, 1371, 1274, 1190, 1149, 836, 732, 702. H NMR (500
flash column chromatography (Hexane) gave 7g (32 mg,
0.14 mmol, 91%) as a light-yellow oil. IR (NaCl) ῦmax (cm-1)
3411 (NH), 2955, 2923, 1592, 1559, 1447, 1329, 1123, 827, 736.
1H NMR (500 MHz, CDCl3)  (ppm) 8.70 (br s, 1H, NH),
8.25 (d, J = 8.4 Hz, 1H, H-10), 8.07 (d, J = 11.4 Hz, 1H, H-4),
7.90 (dd, J = 8.0, 0.8 Hz, 1H, H-7), 7.62 (d, J = 8.5 Hz, 1H,
H-5), 7.627.60 (m, 1H, H-9), 7.56 (ddd, J = 8.0, 6.9, 1.1 Hz,
1H, H-8), 7.52 (d, J = 8.5 Hz, 1H, H-6), 6.96 (dd, J = 11.4, 1.8
Hz, 1H, H-3), 1.701.64 (m, 2H, H-12), 1.491.41 (m, 2H, H-
13), 1.39 (t, J = 8.0 Hz, 2H, H-11), 0.97 (t, J = 7.3 Hz, 3H, H-
14). 13C{1H} NMR (125 MHz, CDCl3)  (ppm) 144.9 (C-4),
135.9 (C-10b), 133.4 (C-6a), 130.2 (C-3*), 128.9 (C-7), 127.6
(C-5), 126.4 (C-8), 125.8 (C-9), 123.8 (C-10a), 120.9 (C-4a),
120.7 (C-6), 119.6 (C-10), 28.4 (C-12), 25.8 (C-13), 18.8 (C-
11*), 14.2 (C-14). *Carbon not observed in 13C{1H} NMR,
assigned by gHSQC. 11B{1H} NMR (160 MHz, CDCl3)
 (ppm) 38.19. HRMS (APCI) m/z calculated for C16H19BN
[M+H]+: 236.1605. Found [M+H]+: 236.1600.
1
1
2
3
4
5
6
7
8
MHz, CDCl3)  (ppm) 7.81 (dd, J = 8.3, 0.7 Hz 1H, H-10),
7.787.76 (m, 1H, H-6, H-7), 7.54 (br s, 1H, NH), 7.52 (ddd,
J = 8.3, 7.1, 1.0 Hz, 1H, H-9), 7.427.39 (m, 2H, H-5, H-8),
7.307.22 (m, 2H, H-18, H-18’)†, 7.20 (d, J = 12.3 Hz, 1H, H-
3), 7.06 (d, J = 12.3 Hz, 1H, H-4), 7.066.96 (m, 8H, H-16,
H-16’, H-17, H-17’)†, 6.966.95 (m, 3H, H-13, H-14),
6.836.79 (m, 2H, H-12). †Proton signal appears as a broad
singlet probably due to restricted rotation of these phenyl
rings. 13C{1H} NMR (125 MHz, CDCl3)  (ppm) 151.4 (2C, C-
15**, C-15’**), 141.2 (C-11), 133.4 (C-6a), 133.0 (C-4a), 130.2
(C-3*), 129.9 (C-4), 129.3 (C-7), 129.2 (C-6), 128.8 (C-10b),
128.4 (2C, C-13), 128.0 (C-9), 127.5 (C-10a), 127.1 (C-5), 126.4
(C-14), 125.4 (C-8), 122.2 (2C, C-12), 118.8 (C-10). *Carbon
not observed in 13C{1H} NMR, assigned by gHSQC.
**Carbon not observed in 13C{1H} NMR, assigned by
gHMBC. C-16, C-16’, C-17, C-17’, C-18 and C-18’ are not
observed in 13C{1H} NMR probably due to broadening of
the signal caused by restricted rotation of these rings; no
cross peaks were observed in the gHSQC or gHMBC
spectra. 11B{1H} NMR (160 MHz, CDCl3)  (ppm) 1.44.
HRMS (EI) m/z calculated for C30H24BN [M]+: 409.2002.
Found [M]+: 409.2016.
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General procedure for the bromination of 3,4-
dihydro-4-aza-3-boraphenanthrenes. Method A: the
corresponding 3,4-dihydro-4-aza-3-boraphenanthrene (1.0
equiv.) was loaded into a Schlenk flask under argon.
Anhydrous CH2Cl2 (0.1 M) was then added, and the
resulting solution was cooled to 0 ºC. A recently prepared
bromine solution (0.2 M in CH2Cl2; 1.1 equiv.) was added
under argon at a rate of 1.1 mmol/h. After addition, the
reaction mixture was slowly warmed to room
temperature. The reaction was monitored by TLC and,
when complete (usually after stirring at r.t. for 1 hour),
the mixture was concentrated under reduced pressure.
The remaining residue was purified by flash column
chromatography (using the eluent indicated in each case)
to provide the desired 2-bromo-3,4-dihydro-4-aza-3-
boraphenanthrene. Method B: aluminum chloride (1.5
equiv.) and N-bromosuccinimide (1.5 equiv.) were loaded
into a Schlenk flask under argon. Anhydrous CH2Cl2 (0.02
M) was added, and the resulting suspension was stirred at
r.t. for 30 min. The mixture was then cooled to 35 ºC and
treated with a solution of the corresponding 3,4-dihydro-
4-aza-3-boraphenanthrene (1.0 equiv.) in CH2Cl2. This
reaction mixture was stirred at 35 ºC for 2 h. After
solvent removal, hexane was added, and the mixture was
filtered to remove any solids. The filtrate was further
concentrated under reduced pressure and the remaining
residue purified by flash column chromatography (using
the eluent indicated in each case) to provide the desired
2-bromo-3,4-dihydro-4-aza-3-boraphenanthrene.
General
procedure
for
the
reaction
with
organolithium compounds. In a Schlenk flask, 3,4-
dihydro-4-aza-3-boraphenanthrene 7a (1.0 equiv.) was
dissolved in anhydrous THF (0.1 M), and the resulting
solution was cooled to 78 ºC. At this temperature the
solution was treated with the corresponding
organolithium compound (2.0 equiv.). The reaction
mixture was stirred at low temperature for 2 h, then cold
hydrochloric acid (2.0 M in Et2O; 2.0 equiv.) was slowly
added to the reaction mixture at 78 ºC. The mixture was
allowed to stand at 78 ºC for 1 h, then warmed to room
temperature and allowed to stir for 12 hours. At the
conclusion of the reaction, the mixture was quenched
with saturated NH4Cl solution, and the aqueous layer was
extracted with Et2O. The combined organic layers were
dried over anhydrous Na2SO4, filtered and evaporated
under reduced pressure. The remaining residue was
purified by flash column chromatography (using the
eluent indicated in each case) to afford the corresponding
B-substituted products.
3-Methyl-3,4-dihydro-4-aza-3-boraphenanthrene
(7b).
Following the general procedure, compound 7a (54 mg,
0.30 mmol) was dissolved in THF (3.0 mL). The solution
was treated with methyllithium solution (1.6 M in Et2O;
375 L, 0.60 mmol) followed by addition of hydrochloric
acid (300 L, 0.60 mmol). Purification by flash column
chromatography (5% EtOAc/Hexane) gave 7b (53 mg,
0.27 mmol, 92%) as a white solid.
2-Bromo-3-hydroxy-3,4-dihydro-4-aza-3-boraphenanthrene
(11a). Following general procedure A, compound 7a (18
mg, 0.10 mmol) was dissolved in CH2Cl2 (1.0 mL), followed
by addition of bromine solution (550 L, 0.11 mmol).
Purification by flash column chromatography (20%
EtOAc/Hexane) gave 11a (10 mg, 0.037 mmol, 37%) as a
white solid. M.p.: 248250 ºC. IR (KBr) ῦmax (cm-1) 3584
(OH), 3400 (NH), 2918, 1590, 1560, 1456, 895, 797, 735,
688. 1H NMR (500 MHz, CDCl3)  (ppm) 8.24 (s, 1H, H-4),
8.07 (dd, J = 8.1, 1.5 Hz, 1H, H-10), 7.95 (br s, 1H, NH),
7.877.85 (m, 1H, H-7), 7.58 (ddd, J = 8.1, 6.9, 1.7 Hz, 1H,
H-9), 7.56 (ddd, J = 7.7, 6.9, 1.5 Hz, 1H, H-8), 7.46 (ap s,
3-Butyl-3,4-dihydro-4-aza-3-boraphenanthrene
(7g).
Following the general procedure, compound 7a (27 mg,
0.15 mmol) was dissolved in THF (1.5 mL). The solution
was treated with n-butyllithium solution (1.6 M in
hexanes; 188 L, 0.30 mmol) followed by addition of
hydrochloric acid (150 L, 0.30 mmol). Purification by
ACS Paragon Plus Environment

The Journal of Organic Chemistry
2H, H-5, H-6), 4.53 (s, 1H, OH). 13C{1H} NMR (125 MHz,
Page 10 of 13
chromatography (Hexane) gave 11d (26 mg, 0.075 mmol,
75%) as a white solid. M.p.: 134136 ºC. IR (KBr) ῦmax (cm-1)
1
2
3
4
5
6
7
8
CDCl3)  (ppm) 147.1 (C-4), 135.8 (C-10b), 133.6 (C-6a),
128.9 (C-7), 126.8 (C-8), 126.4 (C-5), 126.1 (C-9), 123.4 (C-
10a), 120.7 (C-6), 120.3 (C-3**), 119.7 (C-10), 118.4 (C-4a).
**Carbon not observed in 13C{1H} NMR, assigned by
gHMBC. 11B{1H} NMR (160 MHz, CDCl3)  (ppm) 27.31.
HRMS (APCI) m/z calculated for C12H10BBrNO [M+H]+:
274.0033. Found [M+H]+: 274.0030.
1
3053, 2919, 1582, 1489, 1401, 1328, 1231, 916, 747, 691. H
NMR (500 MHz, CDCl3)  (ppm) 8.36 (s, 1H, H-4), 7.77
(dd, J = 8.1, 1.5 Hz, 1H, H-7), 7.58 (d, J = 8.5 Hz, 1H, H-6),
7.54 (d, J = 8.5 Hz, 1H, H-5), 7.467.42 (m, 2H, H-13, H-15),
7.40 (tt, J = 7.3, 1.2 Hz, 1H, H-14), 7.32 (ddd, J = 8.1, 6.9, 0.7
Hz, 1H, H-8), 7.20 (d, J = 8.7 Hz, 1H, H-10), 7.187.15 (m,
2H, H-12, H-16), 6.93 (ddd, J = 8.7, 6.9, 1.5 Hz, 1H, H-9),
2-Bromo-3-methyl-3,4-dihydro-4-aza-3-boraphenanthrene
(11b). Following general procedure A, compound 7b (19
mg, 0.10 mmol) was dissolved in CH2Cl2 (1.0 mL), followed
by addition of bromine solution (550 L, 0.11 mmol).
Purification by flash column chromatography (2%
EtOAc/Hexane) gave 11b (27 mg, 0.099 mmol, 99%) as a
white solid. M.p.: 108110 ºC. IR (KBr) ῦmax (cm-1) 3400
(NH), 2917, 1588, 1558, 1454, 1426, 1144, 1009, 911, 797, 737,
0.72 (s, 3H, H-17). C{1H} NMR (125 MHz, CDCl3)  (ppm)
13
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
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60
148.2 (C-11), 145.9 (C-4), 137.9 (C-10b), 135.3 (C-6a), 130.5
(C-3**), 129.6 (2C, C-13, C-15), 128.7 (C-7), 128.3 (2C, C-12,
C-16), 127.2 (C-5), 127.0 (C-14), 126.1 (C-10), 125.7 (C-8),
125.4 (C-10a), 124.3 (C-9), 123.8 (C-6), 123.3 (C-4a), 4.9 (C-
17*). *Carbon not observed in 13C{1H} NMR, assigned by
gHSQC. **Carbon not observed in C{1H} NMR, assigned
13
by gHMBC. 11B{1H} NMR (160 MHz, CDCl3)  (ppm) 39.44.
HRMS (EI) m/z calculated for C19H15BBrN [M]+: 347.0475.
Found [M]+: 347.0471.
1
688. H NMR (500 MHz, CDCl3)  (ppm) 8.71 (br s, 1H,
NH), 8.31 (s, 1H, H-4), 8.20 (d, J = 8.3 Hz, 1H, H-10), 7.89
(dd, J = 7.9, 1.6 Hz, 1H, H-7), 7.62 (ddd, J = 8.3, 6.9, 1.6 Hz,
1H, H-9), 7.58 (ddd, J = 7.9, 6.9, 1.2 Hz, 1H, H-8), 7.53 (d, J
= 8.7 Hz, 1H, H-6), 7.51 (d, J = 8.7 Hz, 1H, H-5), 0.96 (s, 3H,
General procedure for the Suzuki reaction. In an
oven-dried Biotage microwave vial equipped with a stir
bar, the corresponding aryl bromide (0.15 mmol, 1.0
equiv.) and phenylboronic acid (27 mg, 0.21 mmol, 1.4
equiv.) were dissolved in toluene (0.6 mL) and methanol
(0.2 mL). The resulting solution was treated with a
suspension of sodium carbonate (375 mg) in distilled
water (1.5 mL) before addition of Pd(PPh3)4 (8.8 mg,
0.0075 mmol, 5.0 mol%). The vial was sealed with a cap
lined with a disposable Teflon septum and the reaction
mixture stirred at 70 ºC for 12 hours. At the end of the
reaction, the mixture was quenched with saturated NaCl
solution (5 mL) and the aqueous layer extracted with
EtOAc (3 x 5 mL). The combined organic layers were
dried over anhydrous Na2SO4, filtered and evaporated
under reduced pressure. The remaining residue was
purified by flash column chromatography (25%
EtOAc/Hexane) to afford the corresponding coupled
products.
13
H-11). C{1H} NMR (125 MHz, CDCl3)  (ppm) 145.1 (C-4),
135.1 (C-10b), 133.3 (C-6a), 130.3 (C-3**), 129.0 (C-7), 126.8
(C-8), 126.5 (C-5), 126.2 (C-9), 123.5 (C-10a), 121.7 (C-6),
120.8 (C-4a), 119.5 (C-10), 2.6 (C-11*). *Carbon not
observed in 13C{1H} NMR, assigned by gHSQC. **Carbon
13
11
not observed in C{1H} NMR, assigned by gHMBC. B{1H}
NMR (160 MHz, CDCl3)  (ppm) 37.16. HRMS (EI) m/z
calculated for C13H11BBrN [M]+: 271.0162. Found [M]+:
271.0172.
2-Bromo-3-phenyl-3,4-dihydro-4-aza-3-boraphenanthrene
(11c). Following general procedure A, compound 7d (255
mg, 1.00 mmol) was dissolved in CH2Cl2 (10 mL), followed
by addition of bromine solution (5.5 mL, 1.10 mmol).
Purification by flash column chromatography (5%
EtOAc/Hexane) gave 11c (315 mg, 0.94 mmol, 94%) as a
white solid. M.p.: 9395 ºC. IR (KBr) ῦmax (cm-1) 3402
(NH), 3049, 1586, 1558, 1425, 1409, 1226, 1022, 847, 805,
1
3-Methyl-2-phenyl-3,4-dihydro-4-aza-3-boraphenanthrene
(12a). Following the general procedure, aryl bromide 11b
(41 mg, 0.15 mmol) gave 12a (25 mg, 0.093 mmol, 62%) as
a white solid. M.p.: 126128 ºC. IR (KBr) ῦmax (cm-1) 3414
(NH), 2930, 1590, 1564, 1452, 1418, 1308, 1205, 1121, 807, 730,
739, 701. H NMR (500 MHz, CDCl3)  (ppm) 9.04 (br s,
1H, NH), 8.55 (s, 1H, H-4), 8.248.22 (m, 1H, H-10),
7.997.98 (m, 2H, H-12, H-16), 7.937.91 (m, 1H, H-7), 7.64
(ddd, J = 8.1, 6.9, 1.6 Hz, 1H, H-9), 7.637.60 (m, 1H, H-8),
7.60 (ap s, 2H, H-5, H-6), 7.547.49 (m, 3H, H-13, H-14, H-
15). 13C{1H} NMR (125 MHz, CDCl3)  (ppm) 147.6 (C-4),
138.1 (C-11**), 135.3 (C-10b), 133.5 (C-6a), 133.3 (2C, C-12, C-
16), 129.4 (C-14), 129.1 (C-7), 128.0 (2C, C-13, C-15), 127.8 (C-
3**), 127.1 (C-8), 126.5 (C-9), 126.4 (C-5), 123.6 (C-10a),
122.4 (C-6), 121.2 (C-4a), 119.5 (C-10). **Carbon not
observed in 13C{1H} NMR, assigned by gHMBC. 11B{1H}
NMR (160 MHz, CDCl3)  (ppm) 33.60. HRMS (EI) m/z
calculated for C18H13BBrN [M]+: 333.0319. Found [M]+:
333.0329.
1
703. H NMR (500 MHz, CDCl3)  (ppm) 8.80 (br s, 1H,
NH), 8.27 (d, J = 8.3 Hz, 1H, H-10), 8.01 (s, 1H, H-4), 7.91
(d, J = 8.0 Hz, 1H, H-7), 7.67 (d, J = 8.5 Hz, 1H, H-5),
7.657.62 (m, 1H, H-9), 7.597.55 (m, 2H, H-6, H-8),
7.507.48 (m, 2H, H-13, H-17), 7.457.42 (m, 2H, H-14, H-
16), 7.327.29 (m, 1H, H-15), 0.97 (s, 3H, H-11). 13C{1H}
NMR (125 MHz, CDCl3)  (ppm) 144.8 (C-12), 144.1 (C-3**),
142.3 (C-4), 135.3 (C-10b), 133.4 (C-6a), 128.9 (C-7), 128.24
(2C, C-14, C-16), 128.23 (2C, C-13, C-17), 127.7 (C-5), 126.4
(C-8), 126.0 (C-15), 125.9 (C-9), 123.5 (C-10a), 121.1 (C-6),
120.8 (C-4a), 119.7 (C-10), 2.9 (C-11*). *Carbon not
observed in 13C{1H} NMR, assigned by gHSQC. **Carbon
2-Bromo-3-methyl-4-phenyl-3,4-dihydro-4-aza-3-
boraphenanthrene (11d). Following general procedure B,
AlCl3 (20 mg, 0.15 mmol) and NBS (27 mg, 0.15 mmol)
were dissolved in CH2Cl2 (5 mL). The resulting suspension
was treated with a solution of compound 7e (27 mg, 0.10
mmol) in CH2Cl2 (2 mL). Purification by flash column
13
11
not observed in C{1H} NMR, assigned by gHMBC. B{1H}
NMR (160 MHz, CDCl3)  (ppm) 38.03. HRMS (EI) m/z
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calculated for C19H16BN [M]+: 269.1370. Found [M]+:
269.1376.
HRMS (EI) m/z calculated for C26H18BN [M]+: 355.1527.
Found [M]+: 355.1537.
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2
3
4
5
6
7
8
2,3-Diphenyl-3,4-dihydro-4-aza-3-boraphenanthrene (12b).
Following the general procedure, aryl bromide 11c (50 mg,
0.15 mmol) gave 12b (37 mg, 0.11 mmol, 75%) as a white
solid. M.p.: 172174 ºC. IR (KBr) ῦmax (cm-1) 3408 (NH),
Computational details. The ground state minima of 6
and 7a were computed at the DFT level of theory and the
vertical transitions at the TD-DFT level of theory. The
solvent (cyclohexane) effect was taken into account using
the polarizable continuum model (PCM).26 CAM-B3LYP27
and B3LYP28 functionals were tested using the 6-31+G**
basis set. The excitation and emission energies calculated
using the B3LYP functional are closer to the experimental
values.
1
3051, 3021, 1585, 1563, 1443, 1417, 809, 738, 700. H NMR
(500 MHz, CDCl3)  (ppm) 9.08 (br s, 1H, NH), 8.29 (d, J =
8.2 Hz, 1H, H-10), 8.18 (s, 1H, H-4), 7.94 (d, J = 7.9 Hz, 1H,
H-7), 7.74 (d, J = 8.6 Hz, 1H, H-5), 7.667.63 (m, 1H, H-9),
7.62 (d, J = 8.6 Hz, 1H, H-6), 7.617.58 (m, 1H, H-8), 7.58
(dd, J = 7.8, 1.8 Hz, 2H, H-12, H-16), 7.407.35 (m, 5H, H-
13, H-14, H-15, H-18, H-22), 7.337.30 (m, 2H, H-19, H-21),
7.287.24 (m, 1H, H-20). 13C{1H} NMR (125 MHz, CDCl3)
 (ppm) 144.4 (C-4), 144.1 (C-17), 143.2 (C-3**), 140.2 (C-
11**), 135.4 (C-10b), 133.5 (C-6a), 133.3 (2C, C-12, C-16), 129.0
(C-7), 128.8 (2C, C-18, C-22), 128.6 (C-14), 128.1 (2C, C-19,
C-21), 127.9 (2C, C-13, C-15), 127.6 (C-5), 126.7 (C-8), 126.13
(C-20), 126.08 (C-9), 123.7 (C-10a), 121.8 (C-6), 121.3 (C-4a),
119.7 (C-10). **Carbon not observed in 13C{1H} NMR,
assigned by gHMBC. 11B{1H} NMR (160 MHz, CDCl3)
 (ppm) 35.05. HRMS (EI) m/z calculated for C24H18BN
[M]+: 331.1527. Found [M]+: 331.1517.
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The computational photochemical study was performed
using the Multi-State Complete Active Space Perturbation
to Second Order with a Complete Active Space Self
Consistent
Field
reference
wavefunction
(MS-
CASPT2//SA-CASSCF) methodology.29 In this case, the
State Averaged-Complete Active Space Self Consistent
Field (SA-CASSCF) method was used to compute the
critical points along the potential energy surface. For both
6 and 7a, the active space chosen includes the complete
set of π and π* orbitals and the nitrogen atom lone pair
(14 electrons in 13 orbitals). The minima in S1 were
calculated from the Franck‒Condon structure by using
the steepest descent algorithm. The electronic states
crossings were optimized at the CASSCF level and the two
non-adiabatic coupling vectors defining the branching
plane (gradient difference and derivative coupling) were
computed. The dynamic correlation for the critical points
was included at the MS-CASPT2 level of theory. CASSCF
calculations were performed using the Gaussian 16
software30 while MOLCAS 8.2 was used to calculate the
CASPT2 single point energy corrections.31 Both CASSCF
and CASPT2 calculations were performed with the ANO-
L-VDZ basis set.
3-Phenyl-2-(phenylethynyl)-3,4-dihydro-4-aza-3-
boraphenanthrene (13). An oven-dried Biotage
microwave vial equipped with a stir bar was charged with
PdCl2(PPh3)2 (5.3 mg, 0.0075 mmol, 5.0 mol%), CuI (1.4
mg, 0.0075 mmol, 5.0 mol%) and aryl bromide 11c (50 mg,
0.15 mmol, 1.0 equiv.). The vial was sealed with a cap lined
with
a disposable Teflon septum, evacuated under
vacuum, and purged with argon three times. Anhydrous
DMF (1.5 mL) was added, followed by phenylacetylene (50
L, 0.45 mmol, 3.0 equiv.) and Et3N (63 L, 0.45 mmol, 3.0
equiv.) under argon. The reaction mixture was then
stirred at 80 ºC for 24 h. At the end of the reaction, the
mixture was quenched with saturated NaCl solution (10
mL) and the aqueous layer extracted with EtOAc (3 x 10
mL). The combined organic layers were dried over
anhydrous Na2SO4, filtered and evaporated under reduced
pressure. The remaining residue was purified by flash
column chromatography (20% CH2Cl2/Hexane) to afford
13 (25 mg, 0.070 mmol, 47%) as a brown solid. M.p.:
131133 ºC. IR (KBr) ῦmax (cm-1) 3408 (NH), 2914, 2850, 2185
ASSOCIATED CONTENT
Supporting Information
Computational data, X-ray crystallographic data for 10 and
11d, UV/Vis absorption and emission spectra and NMR
spectra for all new compounds (PDF).
The Supporting Information is available free of charge on the
ACS Publications website.
1
(CC), 1559, 1488, 1418, 1222, 803, 755, 703, 671. H NMR
(500 MHz, CDCl3)  (ppm) 9.20 (br s, 1H, NH), 8.48 (s, 1H,
H-4), 8.29 (d, J = 8.3 Hz, 1H, H-10), 8.248.22 (m, 2H, H-
12, H-16), 7.93 (d, J = 7.9 Hz, 1H, H-7), 7.687.65 (m, 2H,
H-5, H-9), 7.637.60 (m, 2H, H-6, H-8), 7.577.54 (m, 2H,
H-13, H-15), 7.537.50 (m, 3H, H-14, H-20, H-24), 7.357.32
AUTHOR INFORMATION
Corresponding Author
* david.sucunza@uah.es; juanjose.vaquero@uah.es
ACKNOWLEDGMENT
13
(m, 2H, H-21, H-23), 7.317.27 (m, 1H, H-22). C{1H} NMR
We are grateful to the Ministerio de Ciencia, Innovación y
Universidades (MICINN), AEI and FEDER (projects
CTQ2017-85263-R and CTQ2017-87372-P, FPU predoctoral
grant for A.A. and ‘‘Ramón y Cajal’’ contract for P.G.G.),
Instituto de Salud Carlos III (FEDER funds, ISCIII RETIC
REDINREN RD16/0009/0015), and University of Alcalá
(projects CCG2018/EXP-005 and CCG2018/EXP-008) for
financial support. The fluorescent picture of the graphical
abstract was performed by the Department of drawing and
(125 MHz, CDCl3)  (ppm) 149.6 (C-4), 138.3 (C-11**), 135.9
(C-10b), 133.9 (C-6a), 133.4 (2C, C-12, C-16), 131.4 (2C, C-20,
C-24), 129.5 (C-14), 129.1 (C-7), 128.3 (2C, C-21, C-23), 128.1
(2C, C-13, C-15), 127.7 (C-22), 127.2 (C-5), 127.1 (C-8), 126.4
(C-9), 124.4 (C-19), 123.7 (C-10a), 122.4 (C-3**), 122.1 (C-6),
120.9 (C-4a), 119.8 (C-10), 94.5 (C-18), 93.2 (C-17).
**Carbon not observed in 13C{1H} NMR, assigned by
gHMBC. 11B{1H} NMR (160 MHz, CDCl3)  (ppm) 34.53.
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J. Synthesis, Optical Properties, and Regioselective
Functionalization of 4a-Aza-10a-boraphenanthrene. Org. Lett.
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(13) Abengózar, A.; Fernández-González, M. A.; Sucunza, D.;
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