Direct transformation from arylamines to aryl naphthalene-1,8-diamino boronamides: A metal-free sandmeyer-type process

Article abstract of DOI:10.3390/molecules24030377

A direct metal-free transformation from arylamines to aryl naphthalene-1,8-diamino boronamides, a type of masked boronic acid, has been developed based on Sandmeyer-type reactions. A nonsymmetrical diboron reagent, B(pin)-B(dan), was utilized as the boryl

Full text of DOI:10.3390/molecules24030377

molecules
Communication
Direct Transformation from Arylamines to Aryl
Naphthalene-1,8-diamino Boronamides: A Metal-Free
Sandmeyer-Type Process
Siyi Ding , Qiang Ma, Min Zhu, Huaping Ren, Shaopeng Tian, Yuzhen Zhao and
Zongcheng Miao *
Key Laboratory of Organic Polymer Photoelectric Materials, School of Science, Xijing University,
Xi’an 710123, China; dingsiyi2009@163.com (S.D.); coobi@163.com (Q.M.); zhum_588@163.com (M.Z.);
hpren2034@163.com (H.R.); tspspirit@163.com (S.T.); zyz19870226@163.com (Y.Z.)
* Correspondence: miaozongcheng@xijing.edu.cn; Tel.: +86-189-9115-0632
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 21 December 2018; Accepted: 16 January 2019; Published: 22 January 2019
Abstract: A direct metal-free transformation from arylamines to aryl naphthalene-1,8-diamino
boronamides, a type of masked boronic acid, has been developed based on Sandmeyer-type reactions.
A nonsymmetrical diboron reagent, B(pin)-B(dan), was utilized as the borylating reagent, and the
B(dan) moiety was transferred to the aim products selectively. This conversion tolerated a series of
functional groups, including chloro, bromo, fluoro, ester, hydroxy, cyano and amide.
Keywords: boronamides; sandmeyer-type reaction; metal-free borylation
1. Introduction
Organoboron compounds, because of their increasing utilization in synthetic chemistry,
drug discovery and materials science, have attracted significant attention in recent years [
react with various functional groups to construct new carbon-carbon bonds or carbon-heteroatom
bonds, which can rapidly construct the complex structures of target molecules [ ]. Therefore,
much effort has been devoted to the exploration of synthesizing organoboron compounds [ ]. On the
other hand, to take best advantage of their diverse reactivity, chemists have also focused on adjusting
their reactivity by varying masking groups on the boron atoms [ ]. When naphthalene-1,8-diaminato
1]. They can
2,3
4–6
2
(dan) ligand is used as the masking group, which has two nitrogen atoms that may donate their
lone pair electrons to the vacant p-orbital of the boron atoms, the formed naphthalene-1,8-diamino
boronamide (Bdan) compounds are robust enough to avoid undesirable organic reactions, such as
Suzuki-Miyaura coupling reactions. Moreover, such compounds can be easily transformed to their
corresponding boronic acids by simple treatment under aqueous acidic conditions. These features
enable their wide application as modular synthetical building blocks [4,7,8], especially in the iterative
cross-coupling reactions [9–12] and the application of di-boron compounds [13–18].
When it comes to the synthesis of aryl B(dan) compounds, the most common strategy is
condensation between commercially available aryl boronic acids and 1,8-diaminonaphthalene in
refluxing toluene (Scheme 1, Path 1) [9]. If aryl halides are used as the starting materials, free boronic
acids can be initially obtained via the traditional reactions between aryl magnesium, or –lithium,
which derive from metal halogen exchanges, with trimethyl borate followed by hydrolytic workup
(Scheme 1, Path 2). Then, aryl B(dan) compounds are accessible via the condensation process (Scheme 1,
Path 1). The common products of Miyaura borylation reactions of aryl halides via the catalysis of
transition metal such as Pd [19
,20], Cu [21] and Ni [22,23] (Scheme 1, Path 3), aryl B(pin), can be
converted to their B(dan) derivatives in the presence of FeCl2 [24] (Scheme 1, Path 4). In addition
Molecules 2019, 24, 377; doi:10.3390/molecules24030377
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to these two indirect approaches, in 2015, Xu and Li reported a direct synthetical pathway of aryl
B(dan) from aryl halides [25], which utilized a Pd-catalyzed selective boronyl transfer process of
the non-symmetrical diboron reagent B(pin)-B(dan) (Scheme 1, Path 5). Later, similarly processed
catalyzed Cu was also proved to be feasible by the Yoshida group [26,27]. As mentioned above,
to the best of our knowledge, the synthesis of aryl B(dan) is largely dependent on the accessibility of
aryl halides. Moreover, these approaches suffer from sensitivity to air and moisture, in view of the
intermediation of aryl metallic compounds [28]. Such a situation inspired our exploration towards
metal-free synthesis of aryl B(dan) compounds.
Scheme 1. Different routes to synthesize aryl B(dan) derivatives.
Arylamines, as cheap and abundant organic feedstock, can go through Sandmeyer-type
reactions [29–32], being easily converted into various functional groups. Generally, two steps are
required to complete the transformation from arylamines to aryl boronic acids or their derivatives.
The amino groups can first be replaced by halides which are then utilized in the borylation reactions,
as indicated in Scheme 1. Recently, Wang and co-workers reported a novel metal-free borylation
method using arylamines as the starting materials [33
symmetrical B(pin)-B(pin) was utilized as the borylating reagent [37
–
36] (Scheme 1, Path 6). In this process,
39]. In order to obtain aryl
–
B(dan) from arylamines, an additional step is required to complete the conversion (Scheme 1, Path 4).
So far, no one has ever realized the conversion from arylamines into their aryl B(dan) derivatives. It was
envisaged that the nonsymmetrical B(pin)-B(dan) might be useful to achieve such a process [40–46].
Inspired by this idea, we sought to apply B(pin)-B(dan) in Sandmeyer-type reactions of arylamines.
2. Results
At the outset, we carried out the reactions under the reaction conditions that were similar to the
previously reported Sandmeyer-type borylation reactions [47–62], with MeCN as the solvent. We chose
4-methoxyl aniline as the starting material, and no target product could be observed under the classical
reaction conditions [t-BuONO, MeCN, room temperature]. However, by increasing the reaction
◦
temperature to 80 C, a low yield of 28% was obtained. As the Sandmeyer reaction was well known to
involve a radical mechanism, we added the radical initiator benzoyl peroxide (BPO) in subsequent
experiments. Consequently, 13% of compound 1a could be obtained at room temperature, compared
with 31% at 80 ◦C (Table 1, entries 1–4). In view that a base could accelerate the trans-borylation of
B2pin2, we expected that a base could also play the same role for B(pin)-B(dan). Then, our expectations
were met. After extensive variation of bases, the yield of reaction was significantly improved by the
addition of NaOAc (Table 1, entries 5 and 18–20). Further experiments were conducted to improve
the yield and it was noted that the addition of phase-transfer catalyst tetrabutylammonium iodide
(TBAI) could enhance the yield of 1a to 75% (Table 1, entry 9). Lowering the loading of aryl amines
was detrimental to this transformation, and 2.0 equivalent of 4-methoxyl aniline worked best in terms

Molecules 2019, 24, 377
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of reactivity (Table 1, entries 9, and 14–17). Finally, further assessment of the reaction temperature
effect indicated that decreasing or increasing the temperature led to dramatically lower yields (Table 1,
entries 9–13).
Table 1. Optimization of reaction conditions.
◦
Entry 1
ArNH2
Base
Additive
T ( C)
Yield 2 (%)
1
2
3
4
5
6
2.0 eq.
2.0 eq.
2.0 eq.
2.0 eq.
2.0 eq.
2.0 eq.
-
-
-
-
-
-
RT
80
RT
80
80
80
-
28
13
31
68
-
BPO (benzoyl peroxide) (0.1 eq.)
BPO (0.1eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
BPO (0.1 eq.)
-
BPO (0.1 eq.), TBAI
(tetrabutylammonium iodide) (0.1 eq.)
TBAI (0.1 eq.)
7
2.0 eq.
-
80
64
8
2.0 eq.
2.0 eq.
2.0 eq.
2.0 eq.
2.0 eq.
2.0 eq.
1.0 eq.
1.2 eq.
1.5 eq.
1.8 eq.
2.0 eq.
2.0 eq.
2.0 eq.
-
80
80
RT
50
100
120
80
80
80
80
80
22
75
10
35
50
20
33
41
52
58
29
trace
32
9 3
10
11
12
13
14
15
16
17
18
19
20
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
NaOAc (1.5 eq.)
t-BuOK (1.5 eq.)
CsCO3 (1.5 eq.)
NaOCH3 (1.5 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
BPO (0.1 eq.), TBAI (0.1 eq.)
80
80
1
Reaction conditions: aniline (0.2 mmol), t-BuONO (0.2 mmol), Bpin-B(dan) (0.1 mmol), MeCN (0.6 mL).
2
3
The reaction was stirred in N2 atmosphere for 6 h.
reaction conditions.
Isolated yield.
Entries in bold represent optimized
Having defined an appropriate set of reaction conditions, we briefly investigated the scope
of arylamines with various functional groups (Scheme 2). For most of the para-substituted
arylamines (compounds 1a–1f) and meta-substituted substrates (compounds 1g–1q), moderate
yields were obtained. Then, relatively low yields of compounds 1r or 1s were obtained, in which
ortho-methylphenylamine and ortho-(ethoxycarbonyl)aniline were used. These results hinted that this
reaction was sensitive to the steric hindrance. Compared with electron-rich arylamines, the anilines
with electron-withdrawing groups showed higher reactivity. This new strategy featured broad
functional-group tolerance. The anilines bearing functional groups, such as ester (compounds
1f
cyano (compound 1e) and amide (compound 1m) were compatible. Halogen atoms of arylamines,
such as bromo (compound 1b 1j), chloro (compound 1q) and fluoro (compound 1c 1i 1k and 1p
, 1l and 1s), were suitable substrates. Additionally, the moieties with hydroxy (compound 2d),
,
,
,
)
atoms, remained intact under the standard conditions, demonstrating the mild nature of the reaction
condition. In order to confirm the practicality and potential application of this metal-free borylation
process, the reaction was carried out on a 2.0 mmol scale under the standard reaction conditions for
selected substrates (ortho-, meta- and para-substituted compounds). The reactions provided the desired
derivatives in moderate yields.

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Scheme 2. Different routes to synthesize aryl B(dan) derivatives.
(a) Unless otherwise noted,
the reaction conditions are as follows: aryl amine (0.2 mmol, 2.0 eq.), B(pin)-B(dan) (0.1 mmol, 1.0 eq.),
t-BuONO (0.2 mmol, 2.0 eq.), TBAI (0.01 mmol, 0.1 eq.), NaOAc (0.15 mmol, 1.5 eq.), BPO (0.01 mmol,
◦
0.1 eq.), MeCN (0.6 mL), 80 C. (
b) Yield of isolated product. (
c) Large scale experiments, reaction
conditions: aryl amine (2 mmol, 2.0 eq.), B(pin)-B(dan) (1 mmol, 1.0 eq.), t-BuONO (2 mmol, 2.0 eq.),
◦
TBAI (0.1 mmol, 0.1 eq.), NaOAc (1.5 mmol, 1.5 eq.), BPO (0.1 mmol, 0.1 eq.), MeCN (6.0 mL), 80 C.
3. Discussion
Based on our previous work on the synthesis and application of differentiated di-boron
compounds [18], we applied this new strategy to the preparation of di-boron reagents containing the
B(dan) group. Taking the di-functionalized compound 1j as an example (Scheme 3), the potential
application of this product was checked (The details were shown in Supplementary). Firstly, in the
presence of Pd(II) catalyst, the Br atom could react with B2(pin)2 to synthesize the site-differentiated
diboron arene
masking groups for boronic acids on
reaction. The B(pin) group could be selectively transformed into the aryl while the B(dan) group
2. As anticipated [
9,
14], the reactivities of B(pin) and B(dan), with two effective
2, could be differentiated in the Suzuki-Miyaura coupling
remained intact. After the workup and purification process, the compound
yield. In agreement with previous experience, the B(dan) group on compound
3
3
was obtained in 81%
could be activated by
hydrolysis under aqueous condition to obtain its boronic acid, which can be used in the sequential
Suzuki-Miyaura cross-coupling reaction to form compound . Therefore, we have demonstrated the
4
usefulness of the naphthalene-1,8-diamino borylation in the facile preparation of boron-differentiated
di-boron compounds, which may serve as polyvalent nucleophiles for the modular construction of
multifunctionalized poly(hetero)arenes by consecutive cross coupling reactions.

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Scheme 3. Successive and selective Suzuki-Miyaura cross-coupling reaction using 3-bromophenyl
B(dan) 2j as the starting material.
4. Materials and Methods
4.1. Methods and Material
4.1.1. General Information
Unless otherwise noted, all reactions were carried out in a flame-dried, sealed Schlenk reaction
tube under an atmosphere of nitrogen. Analytical thin-layer chromatography (TLC) was performed on
glass plates coated with 0.25 mm 230–400 mesh silica gel containing a fluorescent indicator. Preparative
thin-layer chromatography (PTLC) was performed on pre-coated, glass-backed GF254 silica gel plates.
Visualization was accomplished by exposure to a UV lamp. All the products in this article are
compatible with standard silica gel chromatography. Column chromatography was performed on
silica gel (200–300 mesh) using standard methods.
4.1.2. Structural Analysis
NMR spectra were measured on a nuclear magnetic resonance apparatus (Avance III HD 400M,
1
Bruker, Germany) and chemical shifts (
δ
) are reported in parts per million (ppm). H-NMR spectra
were recorded at 400 MHz in NMR solvents and referenced internally to corresponding solvent
resonance, and 13C-NMR spectra were recorded at 100 MHz and referenced to corresponding solvent
resonance. Carbons bearing boron substituents were generally not observed due to quadrupolar
relaxation. Coupling constants are reported in Hz with multiplicities denoted as s (singlet), d (doublet),
t (triplet), q (quartet), m (multiplet) and br (broad). Infrared spectra were collected on a Thermo
Fisher Nicolet 6700 FT-IR spectrometer (Waltham, MA, USA) using ATR (Attenuated Total Reflectance)
method. Absorption maxima (ν
max) are reported in wavenumbers (cm−1). High resolution mass
spectra (HRMS) were acquired with an ESI source or APCI source (MTQ III q-TOP, Bruker, Germany).
4.1.3. Materials
Commercial reagents and solvent were purchased from J&K, Energy, Sigma-Aldrich, Alfa Aesar,
Acros Organics, Strem Chemicals, TCI and used as received unless otherwise stated.
4.2. General Procedure for the Direct Transformation from Arylamines to Aryl Naphthalene-1,8-
diamino Boronamides
In air, Bpin-B(dan) (0.1 mmol, 1.0 eq.), aryl amide (0.2 mmol, 2.0 eq.), TBAI (0.01 eq.),
NaOAc (0.15 eq.), and BPO (0.01 eq.) were sequentially weighed and added to a screw-capped
Schenk tube containing a magnetic stir bar. The vessel was evacuated and refilled with nitrogen for
three times. t-BuONO (0.2 eq.) and MeCN (0.6 mL) were added in turn under N2 atmosphere using
syringes through a septum which was temporarily used to replace the screw cap. The reaction mixture
◦
was then vigorously stirred at 80 C for the indicated time. The resulting mixture was filtered through

Molecules 2019, 24, 377
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a pad of Celite®, and the filter cake was washed with ethyl acetate (3 mL
was evaporated under vacuum to dryness and the residue was purified by column chromatography to
yield the desired product.
×
2). The combined filtrate
4.3. Analytical Data of Products 1a–1t
2-(4-methoxyphenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1a, CAS: 1159803-53-8) [25].
Yield: 20.6 mg (75%); white solid; m.p.: 163.2~165.6 ◦C; IR (cm−1): 3407, 1594, 1495, 1407, 1224, 1181,
1029; 1H-NMR (400 MHz, CDCl3)
δ
7.59 (d, J = 8.8 Hz, 2H), 7.15 (t, J = 8.0 Hz, 2H), 7.05 (d, J = 8.0 Hz,
2H), 6.98 (d, J = 8.4 Hz, 2H), 6.42 (d, J = 7.2 Hz, 2H), 6.00 (s, 2H), 3.86 (s, 3H); 13C-NMR (100 MHz,
CDCl3)
161.4, 141.2, 140.3, 136.4, 133.0, 127.6, 117.7, 113.9, 105.9, 55.2; 11B-NMR (128 MHz, CDCl3)
29.1; HRMS (APCI) m/z calcd for C17H14BN2O (M−): 273.1205, found: 273.1203.
δ
δ
2-(4-bromophenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1b) [
9
]. Yield: 20.0 mg (62%);
white solid; m.p.: 135.6~136.2 C; IR (cm−1): 3408.9, 2921.3, 2851.4, 2362.0, 2342.0, 1596.0, 1511.4, 1400.3,
1373.3, 817.5, 752.2, 690.0; 1H-NMR (400 MHz, CDCl3)
7.57 (d, J = 8.2 Hz, 2H), 7.48 (d, J = 8.2 Hz,
2H), 7.14 (t, J = 7.8 Hz, 2H), 7.06 (d, J = 8.0 Hz, 2H), 6.40 (d, J = 7.2 Hz, 2H), 5.96 (s, 2H); 13C-NMR
◦
δ
(100 MHz, CDCl3)
δ 140.8, 136.3, 133.0, 131.5, 127.7, 124.9, 119.9, 118.1, 106.2; HRMS (APCI) m/z calcd
for C16H12BBrN2 (M−): 322.0282, found: 322.0279.
2-(4-(trifluoromethyl)phenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1c) [25]. Yield:
◦
23.7 mg (76%); white solid; m.p.: 127.0~130.3 C; IR (cm−1): 3414.2, 2365.0, 2341.9, 1527.7, 1493.5,
1
1398.9, 1166.0, 1035.0, 826.8, 747.1; H-NMR (400 MHz, CDCl3)
δ 7.75 (d, J = 7.9 Hz, 2H), 7.69 (d,
J = 8.0 Hz, 2H), 7.13 (t, J =7.8 Hz, 2H), 7.09 (d, J = 7.8 Hz, 2H), 6.44 (dd, J = 7.2, 0.8 Hz, 2H), 6.01 (s, 2H);
13C-NMR (100 MHz, CDCl3)
δ
140.8, 136.5, 132.2 (q, J = 32 Hz), 131.9, 127.8, 125.1 (q, J = 4 Hz), 124.2
(q, J = 272 Hz), 120.1, 118.4, 103.8; 11B-NMR (128 MHz, CDCl3) 30.1; 19F-NMR (377 MHz, CDCl3)
δ δ
−62.88; HRMS (APCI) m/z calcd for C17H11BF3N2 (M−): 311.0973, found: 311.0974.
4-(1H-naphtho[1,8-de][1,3,2]diazaborinin-2(3H)-yl)phenol (1d) [25]. Yield: 13.5 mg (52%); white solid;
m.p.: 222.6~225.7 ◦C; IR (cm−1): 3441.0, 3414.9, 3028.7, 2361.5, 2343.2, 1582.3, 1487.1, 1404.1, 1200.2,
1177.8, 813.5, 753.2; 1H-NMR (400 MHz, CDCl3)
δ
7.55 (d, J = 8.2 Hz, 2H), 7.14 (t, J = 7.8 Hz, 2H), 7.05 (d,
J = 8.2 Hz, 2H), 6.91 (d, J = 8.3 Hz, 2H), 6.41 (d, J = 7.3 Hz, 2H), 5.98 (s, 2H), 4.90 (s, 1H); 13C-NMR
(100 MHz, CDCl3)
δ 157.4, 141.2, 136.3, 133.3, 127.6, 119.7, 117.7, 115.3, 105.9; HRMS (APCI) m/z calcd
for C16H12BN2O (M−): 259.1048, found: 259.1049.
4-(1H-naphtho[1,8-de][1,3,2]diazaborinin-2(3H)-yl)benzonitrile (1e) [25]. Yield: 13.7 mg (51%);
white solid; m.p.: 220.4~225.1 C; IR (cm−1): 3409.3, 3401.7, 3393.0, 3370.2, 2362.0, 2220.1, 1516.3,
◦
1
1593.4, 1405.2, 1082.6, 818.4; H-NMR (400 MHz, CDCl3)
δ 7.72 (dd, J = 8.0, 3.2 Hz, 4H), 7.14 (t,
J = 7.7 Hz, 2H), 7.09 (d, J = 8.0 Hz, 2H), 6.43 (d, J = 7.2 Hz, 2H), 5.99 (s, 2H); 13C-NMR (100 MHz,
CDCl3)
140.4, 136.3, 132.0, 131.7, 127.7, 120.0, 118.7, 118.5, 113.7, 106.4; 11B-NMR (128 MHz, CDCl3)
28.8; HRMS (ESI) m/z calcd for C17H12BN3Na (M+): 292.1022, found: 292.1014.
δ
δ
methyl 4-(1H-naphtho[1,8-de][◦1,3,2]diazaborinin-2(3H)-yl)benzoate (1f). Yield: 24.5 mg (81%);
white solid; m.p.: 202.2~203.6 C; IR (cm−1): 3387.9, 2920.4, 2849.8, 2364.4, 2342.4, 1705.0, 1592.7,
1397.3, 759.4, 704.7; 1H-NMR (400 MHz, CDCl3)
δ
8.09 (d, J = 8.0 Hz, 2H), 7.71 (d, J = 7.9 Hz, 2H), 7.15
(t, J = 7.8 Hz, 2H), 7.07 (d, J = 8.2 Hz, 2H), 6.43 (d, J = 7.2 Hz, 2H), 6.05 (s, 2H). 3.95 (s, 3H); 13C-NMR
(100 MHz, CDCl3) 167.0, 140.8, 136.4, 131.6, 131.5, 129.2, 127.6, 120.0, 118.2, 106.2, 52.3; HRMS (APCI)
m/z calcd for C18H15BN2O2 (M−): 302.1232, found: 302.1230.
δ

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2-(m-tolyl)-2,3-dihydro-1H-nap◦htho[1,8-de][1,3,2]diazaborinine (1g) [25]. Yield: 18.3 mg (71%);
white solid; m.p.: 103.8~106.3 C; IR (cm−1): 3409.1, 3050.8, 3029.9, 1593.0, 1581.1, 1326.2, 817.9,
762.0, 702.8; 1H-NMR (400 MHz, CDCl3)
δ 7.44 (d, J = 8.2 Hz, 2H), 7.34 (m, 2H), 7.14 (t, J = 7.8 Hz, 2H),
7.05 (d, J = 8.2 Hz, 2H), 6.41 (d, J = 7.3 Hz, 2H), 6.02 (s, 2H), 2.42 (s, 3H); 13C-NMR (100 MHz, CDCl3)
δ
141.2, 137.7, 136.4, 132.2, 131.1, 128.5, 128.2, 127.6, 119.9, 117.8, 106.0, 21.6; 11B NMR (128 MHz, CDCl3)
δ 30.4; HRMS (APCI) m/z calcd for C17H14BN2 (M−): 257.1256, found: 257.1257.
2-(3-methoxyphenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1h) [25]. Yield: 19.2 mg
(70%); white solid; m.p.: 113.7~116.4 C; IR (cm−1): 3452.9, 3409.8, 3049.7, 3032.7, 1593.0, 1515.4, 1478.6,
◦
1406.1, 1243.3, 693.5, 658.1; 1H-NMR (400 MHz, CDCl3)
δ 7.37 (t, J = 7.7 Hz, 1H), 7.21 (d, J = 7.2 Hz, 1H),
7.14 (m, 3H), 7.05 (d, J = 8.1 Hz, 2H), 7.00 (dd, J = 8.1, 2.0 Hz, 1H), 6.40 (d, J = 7.3 Hz, 2H), 6.00 (s, 2H),
3.86 (s, 3H); 13C-NMR (100 MHz, CDCl3)
δ
159.5, 141.1, 136.4, 129.6, 127.7, 123.9, 119.9, 117.9, 117.0,
30.1; HRMS (APCI) m/z calcd for C17H14BN2O (M−):
115.5, 106.1, 55.3; 11B-NMR (128 MHz, CDCl3)
δ
273.1205, found: 273.1207.
2-(3-(trifluoromethoxy)phenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1i).
21.3 mg (65%); brown oil; IR (cm−1): 3414.2, 2365.0, 2341.9, 1527.7, 1493.5, 1398.9, 1166.0, 1035.0,
826.8, 747.1; 1H-NMR (400 MHz, CDCl3)
7.56 (d, J = 7.4 Hz, 2H), 7.48 (m, 2H), 7.33 (d, J = 8.1 Hz, 1H),
7.16 (t, J = 7.7 Hz, 2H), 7.08 (d, J = 8.2 Hz, 2H), 6.43 (d, J = 7.2 Hz, 2H), 5.98 (s, 2H); 13C-NMR (100 MHz,
Yield:
δ
CDCl3) δ 149.4, 140.7, 136.3, 129.8, 127.7, 123.7, 122.7, 119.9, 118.2, 106.1; HRMS (APCI) m/z calcd for
C17H12BF3N2O (M−): 328.1000, found: 328.1002.
2-(3-bromophenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1j) [9]. Yield: 19.3 mg (60%);
white solid; m.p.: 86.6~87.9 ◦C; IR (cm−1): 3408.9, 2921.3, 2851.4, 2362.0, 2342.0, 1596.0, 1511.4, 1400.3,
1373.3, 817.5, 752.2, 690.0; 1H-NMR (400 MHz, CDCl3)
J = 7.4 Hz, 1H), 7.29 (t, J = 7.7 Hz, 1H), 7.13 (t, J = 7.8 Hz, 2H), 7.05 (d, J = 7.9 Hz, 2H), 6.39 (d, J = 7.2
δ 7.73 (s, 1H), 7.57 (d, J = 8.0 Hz, 1H), 7.51 (d,
Hz, 2H), 5.94 (s, 2H); 13C-NMR (100 MHz, CDCl3)
δ 140.7, 136.3, 134.4, 133.2, 130.1, 129.9, 127.7, 123.1,
119.9, 118.1, 106.3; HRMS (APCI) m/z calcd for C16H12BBrN2 (M−): 322.0282, found: 322.0280.
2-(3-fluorophenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1k). Yield: 16.8 mg (64%);
◦
yellow solid; m.p.: 103.3~104.6 C; IR (cm−1): 3442.7, 3435.4, 3032.2, 1595.8, 1520.5, 1371.4, 757.1, 749.4,
686.3; 1H-NMR (400 MHz, CDCl3)
δ
7.41 (m, 2H), 7.33 (dd, J = 2.4, 9.2 Hz, 1H), 7.14 (m, 3H), 7.06 (d,
162.9 (d, J = 246
J = 8.0 Hz, 2H), 6.41 (d, J = 7.3 Hz, 2H), 5.97 (s, 2H); 13C-NMR (100 MHz, CDCl3)
δ
Hz), 140.8, 136.3, 130.1 (d, J = 7 Hz), 127.7, 127.0 (d, J = 3 Hz), 119.9, 118.1, 118.0 (d, J = 23 Hz), 117.1 (d,
J = 20 Hz), 106.2; HRMS (APCI) m/z calcd for C16H12BFN2 (M−): 262.1083, found: 262.1080.
Methyl 3-(1H-naphtho[1,8-de][1,3,2]diazaborinin-2(3H)-yl)benzoate (1l). Yield: 23.6 mg (78%);
◦
pink solid; m.p.: 178.9~179.8 C; IR (cm−1): 3452.9, 3409.8, 2049.7, 1515.4, 1478.6, 1077.0, 816.1;
1H-NMR (400 MHz, CDCl3)
δ 8.33 (s, 1H), 8.13 (dt, J = 8.8, 1.4 Hz, 1H), 7.83 (d, J = 7.4 Hz, 1H), 7.52 (t,
J = 7.6 Hz, 1H), 7.15 (t, J = 7.8 Hz, 2H), 7.07 (d, J = 8.0 Hz, 2H), 6.45 (d, J = 7.2 Hz, 2H), 6.09 (s, 2H), 3.97
(s, 3H); 13C-NMR (100 MHz, CDCl3)
δ 167.2, 140.8, 136.3, 135.9, 132.6, 131.3, 130.0, 128.4, 127.7, 119.9,
118.1, 106.2, 52.3; HRMS (APCI) m/z calcd for C18H15BN2O2 (M−): 302.1232, found: 302.1228.
3-(1H-naphtho[1,8-de][1,3,2]diazaborinin-2(3H)-yl)benzamide (1m). Yield: 15.5 mg (54%); brown solid;
◦
m.p.: 168.4~169.5 C; IR (cm−1): 3382.8, 3101.1, 3048.7, 2341.2, 2366.2, 1599.3, 1568.7, 1506.6, 816.3,
758.5, 668.6; 1H-NMR (400 MHz, CDCl3)
(t, J = 7.7 Hz, 2H), 7.05 (d, J = 8.2 Hz, 2H), 6.39 (d, J = 7.0 Hz, 2H), 6.05 (s, 2H); 13C-NMR (100 MHz,
CDCl3) 168.6, 141.0, 137.8, 136.3, 129.0, 127.6, 127.5, 122.9, 121.7, 119.9, 117.8, 106.1; HRMS (APCI)
m/z calcd for C17H14BN3O (M−): 287.1235, found: 287.1233.
δ 7.85 (s, 1H), 7.49 (m, 1H), 7.36 (m, 3H), 7.30 (s, 1H), 7.13
δ

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2-(3,4-dimethoxyphenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1n). Yield: 18.8 mg
(62%); light pink solid; m.p.: 174.5~175.0 ◦C; IR (cm−1): 3407.2, 1594.4, 1495.9, 1407.7, 1224.1, 1181.2,
1029.0; 1H-NMR (400 MHz, CDCl3)
δ
7.24 (d, J = 7.9 Hz, 1H), 7.13 (m, 3H), 7.06 (d, J = 8.2 Hz, 2H), 6.96
(d, J = 7.9 Hz, 1H), 6.43 (d, J = 7.2 Hz, 2H), 5.99 (s, 2H), 3.97 (s, 3H), 3.93 (s, 3H); 13C-NMR (100 MHz,
CDCl3)
δ 150.9, 148.9, 141.1, 136.4, 127.6, 124.9, 119.7, 117.8, 113.8, 111.1, 106.0, 56.1, 55.8; HRMS (APCI)
m/z calcd for C18H17BN2O2 (M−): 304.1389, found: 304.1385.
2-(benzo[d][1,3]dioxol-5-yl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1o) [25]. Yield:
◦
19.9 mg (69%); white solid; m.p.: 173.5~175.8 C; IR (cm−1): 3399.2, 1594.3, 1478.2, 1402.7, 1232.1,
1034.0; 1H-NMR (400 MHz, CDCl3)
δ 7.15 (t, J = 7.4 Hz, 3H), 7.06 (t, J = 6.6 Hz, 3H), 6.91 (d, J = 7.6 Hz,
1H), 6.40 (d, J = 7.2 Hz, 2H), 6.00 (s, 2H), 5.94 (s, 2H); 13C-NMR (100 MHz, CDCl3)
δ 149.4, 147.8, 141.1,
136.3, 127.6, 125.8, 119.7, 117.8, 110.9, 108.8, 106.0, 101.0; HRMS (ESI) m/z calcd for C17H14BN2O2 (M+):
289.1148, found: 289.1147.
2-(3,5-difluorophenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1p). Yield: 17.9 mg (64%);
◦
yellow solid; m.p.: 113.2~114.6 C; IR (cm−1): 3414.2, 2365.0, 2341.9, 1398.8, 1317.8, 1105.6, 1082.3,
818.4; 1H-NMR (400 MHz, CDCl3)
δ 7.75 (d, J = 7.9 Hz, 2H), 7.68 (d, J = 8.0 Hz, 2H), 7.16 (t, J = 7.8 Hz,
2H), 7.08 (d, J = 7.8 Hz, 2H), 6.43 (dd, J = 7.2, 0.6 Hz, 2H), 6.01 (s, 2H); 13C-NMR (100 MHz, CDCl3)
δ
160.7 (dd, J = 249 Hz, 6 Hz), 137.9, 133.8, 125.1, 117.4, 115.8, 111.3 (dd, J = 17 Hz, 6 Hz), 103.8, 102.9
(t,J = 25 Hz); HRMS (APCI) m/z calcd for C16H11BN2F2 (M−): 280.0989, found: 280.0991.
2-(3,5-dichlorophenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1q) [63]. Yield: 20.6 mg
◦
(66%); green solid; m.p.: 164.2~165.8 C; IR (cm−1): 3381.9, 2946.7, 2364.1, 1559.7, 1507.0, 1266.1, 1068.1,
746.4; H-NMR (400 MHz, CDCl3)
1
δ 7.46 (dd, J = 8.3, 1.7 Hz, 3H), 7.15 (t, J = 8.0 Hz, 2H), 7.08 (d,
J = 8.0 Hz, 2H), 6.42 (d, J = 7.2 Hz, 2H), 5.94 (s, 2H); 13C-NMR (100 MHz, CDCl3)
δ 140.4, 136.3, 135.3,
130.1, 129.7, 127.7, 120.0, 118.4, 106.4; HRMS (APCI) m/z calcd for C16H11BN2Cl2 (M−): 312.0398,
found: 312.0395.
2-(o-tolyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (1r) [25]. Yield: 11.6 mg (45%);
◦
white solid; m.p.: 73.2~75.1 C; IR (cm−1): 3420.1, 3404.9, 2360.8, 2341.0, 1594.1, 1506.1, 1325.8,
1318.1, 1077.9, 818.4, 656.0; 1H-NMR (400 MHz, CDCl3)
δ 7.44 (d, J = 7.3 Hz, 1H), 7.31 (t, J = 7.5 Hz,
1H), 7.21 (m, 2H), 7.12 (t, J = 7.8 Hz, 2H), 7.05 (d, J = 8.5 Hz, 2H), 6.33 (d, J = 7.2 Hz, 2H), 5.80 (s, 2H),
2.49 (s, 3H); 13C-NMR (100 MHz, CDCl3)
δ
141.1, 140.7, 136.4, 132.3, 129.7, 129.3, 127.7, 125.3, 119.8,
30.0; HRMS (APCI) m/z calcd for C17H14BN2 (M−):
117.9, 105.9, 22.4; 11B NMR (128 MHz, CDCl3)
δ
257.1256, found: 257.1257.
Methyl 2-(1H-naphtho[1,8-de][1,3,2]diazaborinin-2(3H)-yl)benzoate (1s) [25]. Yield: 15.4 mg (51%);
◦
white solid; m.p.: 160.3~164.5 C; IR (cm−1): 3381.9, 2946.7, 2364.1, 1699.4, 1507.6, 1134.7, 1266.1,
1068.1, 816.3, 746.4; 1H-NMR (400 MHz, CDCl3)
8.04 (d, J = 7.8 Hz, 1H), 7.54 (m, 2H), 7.47 (m, 1H),
7.11 (t, J = 7.8 Hz, 2H), 7.04 (d, J = 7.8 Hz, 2H), 6.31 (d, J = 7.2 Hz, 2H), 5.73 (s, 2H), 3.86 (s, 3H);
δ
13C-NMR (100 MHz, CDCl3)
δ 168.3, 141.3, 136.4, 133.2, 132.7, 132.1, 129.6, 128.9, 127.6, 119.6, 117.6,
105.8, 52.4; 11B NMR (128 MHz, CDCl3)
301.1154, found: 301.1157.
δ
31.0; HRMS (APCI) m/z calcd for C18H14BN2O2 (M−):
2-(naphthalen-1-yl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine (2t) [25]. Yield: 14.1 mg (48%);
◦
white solid; m.p.: 140.2~143.6 C; IR (cm−1): 3420.2, 3402.4, 1594.6, 1508.8, 1498.6, 1315.5, 1167.3;
1H-NMR (400 MHz, CDCl3)
8.22 (dd, J = 6.4, 3.2 Hz, 1H), 7.91 (m, 2H), 7.70 (d, J = 6.4 Hz, 1H), 7.52
(m, 3H), 7.17 (t, J = 8.0 Hz, 2H), 7.11 (d, J = 8.0 Hz, 2H), 6.38 (d. J = 7.2 Hz, 2H), 6.02 (s, 2H); 13C-NMR
δ
(100 MHz, CDCl3)
δ 141.1, 136.4, 135.4, 133.3, 130.7, 129.6, 128.8, 127.9, 127.7, 126.3, 125.9, 125.4, 120.0,
118.0, 106.1; 11B-NMR (128 MHz, CDCl3)
found: 295.1399.
δ
30.7; HRMS (ESI) m/z calcd for C20H16BN2 (M+): 295.1407,

Molecules 2019, 24, 377
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5. Conclusions
In conclusion, by employing the non-symmetrical di-boron compound, B(pin)-B(dan), as the
borylating reagent, we have realized a metal-free Sandmeyer-type borylation reaction under relatively
mild conditions and afforded various aryl B(dan) compounds in moderate yields. The procedure
tolerates a series of functional groups, including chloro, bromo, fluoro, ester, hydroxy, cyano and
amide groups. Further studies on the mechanism are in progress in our laboratory (The proposed
mechanism was shown in the Supporting Information). We anticipate that this protocol described
herein could serve as an important supplement to the existing strategies for preparing the aryl-B(dan)
compounds and will then find wide application in organic synthesis and related fields.
Supplementary Materials: Experimental procedures and spectral data for the borylated products. This material
is available free of charge via the Internet.
Author Contributions: S.D. conceived and designed the experiment; Q.M. and M.Z. performed the experiments;
S.D. and H.R. analyzed the data; S.T. and Y.Z. contributed reagents/materials/analysis; S.D. and Z.M. wrote
the paper.
Funding: This research was funded by the Special Fund for Talent Research of Xijing University, Grant number
XJ17B01, Scientific Research Program Funded by Shaanxi Provincial Education Department (Program No.18JK1196)
and the National Natural Science Foundation of Shaanxi, Grant number 2017JQ2037.
Acknowledgments: We would like to thank Pengfei Li (Xi’an Jiaotong University) very much for his guidance
and advices during this work.
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds (1a–1t, 2, 3 and 4) are available from the authors.
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