A convergent, modular approach to functionalized 2,1-borazaronaphthalenes from 2-aminostyrenes and potassium organotrifluoroborates

Article abstract of DOI:10.1021/jo402616w

Azaborines are an important class of compounds with applications in both medicinal chemistry and materials science. The first borazaronaphthalene, 2-chloro-2,1-borazaronaphthalene, was reported in 1959; however, access to more highly functionalized substructures has been limited because of the harsh reaction conditions required to displace the chloride on boron. A convergent approach has been developed to synthesize disubstituted 2,1-borazaronaphthalenes from N-substituted 2-aminostyrenes and potassium organotrifluoroborates, where the potassium organotrifluoroborate is converted to the active R-BX₂ species (X = Cl or F) in situ by addition of a fluorophile. Starting from aryl-, heteroaryl-, alkynyl-, alkenyl-, and alkyltrifluoroborates, a library of highly functionalized 2,1-borazaronaphthalenes were synthesized in one step under mild, transition-metal-free conditions.

Full text of DOI:10.1021/jo402616w

Article
pubs.acs.org/joc
A Convergent, Modular Approach to Functionalized
2,1‑Borazaronaphthalenes from 2‑Aminostyrenes and Potassium
Organotrifluoroborates
Steven R. Wisniewski, Courtney L. Guenther, O. Andreea Argintaru, and Gary A. Molander*
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia,
Pennsylvania 19104-6323, United States
S
* Supporting Information
ABSTRACT: Azaborines are an important class of compounds with applications in both medicinal chemistry and materials
science. The first borazaronaphthalene, 2-chloro-2,1-borazaronaphthalene, was reported in 1959; however, access to more highly
functionalized substructures has been limited because of the harsh reaction conditions required to displace the chloride on boron.
A convergent approach has been developed to synthesize disubstituted 2,1-borazaronaphthalenes from N-substituted 2-
aminostyrenes and potassium organotrifluoroborates, where the potassium organotrifluoroborate is converted to the active R−
BX2 species (X = Cl or F) in situ by addition of a fluorophile. Starting from aryl-, heteroaryl-, alkynyl-, alkenyl-, and
alkyltrifluoroborates, a library of highly functionalized 2,1-borazaronaphthalenes were synthesized in one step under mild,
transition-metal-free conditions.
material, providing access to molecules with chemiluminescent
properties. Azaborines have been shown to function as organic
light-emitting diodes (OLEDs)6a and organic field-effect
transistors (OFETs).6c Therefore, the synthesis of function-
alized 1,2-azaborines could provide access to new classes of
chemiluminescent compounds as well.
INTRODUCTION
■
The isosteric replacement of CC with B−N within the
context of aromatic systems leads to azaborines, a class of
compounds whose synthesis and reactivity have attracted much
attention over the past few years.1 Theoretical calculations as
well as experimental data have shown that 1,2-azaborines are
stable aromatic molecules whose aromaticity and thermal
stability are slightly lower than those of the corresponding C
C aromatic systems.2
Isosteric replacement has become a powerful strategy in
many diverse areas, including the pharmaceutical and agro-
chemical fields,3 where there is increasing interest in the use of
1,2-azaborine substructures to increase structural diversity.4 For
example, Liu and Heider have demonstrated that the BN
isosteres of ethylbenzene can bind the hydrophobic pocket of
the L99A mutant of T4 lysozyme,4a and these azaborines also
act as inhibitors of the enzyme ethylbenzene dehydrogenase
(EbDH).4b Methods to access functionalized 1,2-azaborines in
a straightforward, efficient manner could have an impact on the
discovery of new bioactive compounds, leading to novel drug
candidates that might overcome the limited range of chemical
space in current sample collections.5
Currently there exist a limited number of approaches to 2,1-
borazaronaphthalenes. In 1959, Dewar and Dietz published the
synthesis of the first 2,1-borazaronaphthalene via an annulation
reaction between 2-aminostyrene and BCl3 (Scheme 1, I).7 It
was later shown that functionalization at nitrogen could be
achieved through deprotonation with MeLi and reaction with
an alkyl or acyl electrophile.8 Dewar expanded the scope of
these systems by showing that substitution on boron could be
achieved by refluxing in Et2O with an aryl Grignard reagent
(Scheme 1, III).3,9 Paetzold synthesized 2,1-borazaronaphtha-
lenes via a three-component reaction employing aniline, an
aryldichloroborane, and phenylacetylene (Scheme 1, IIA).10a As
mentioned above, in early syntheses of N-substituted 2,1-
borazaronaphthalenes, functionalization at nitrogen took place
subsequent to ring formation in a second process under
strongly basic reaction conditions.8 However, Paetzold
developed a different set of conditions for the synthesis of N-
substituted 2,1-borazaronaphthalenes (Scheme 1, IIB).10b An
In addition to their medicinal chemistry applications, 1,2-
azaborines have made a significant impact in materials science
because of their photophysical properties.6 Replacing one or
more of the carbon atoms in a polycyclic aromatic hydrocarbon
(PAH) with boron decreases the HOMO−LUMO gap of the
Received: November 25, 2013
© XXXX American Chemical Society
A
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There are currently no reported examples of the one-step
synthesis of 1,2-disubstituted 2,1-borazaronaphthalenes. Pre-
viously reported methods require further functionalization at
nitrogen and/or boron. The only reported examples of aryl
substitution on boron in monosubstituted 2,1-borazaronaph-
thalenes are phenyl,7 2-pyridinyl,6d or pentafluorophenyl10a
rings, where the desired products were synthesized in yields of
43−69%, 13%, and 78−89%, respectively.
Scheme 1. Synthesis and Functionalization of
2,1‑Borazaronaphthalenes
To alleviate these limitations, we sought to develop a
versatile, concise, metal-free synthesis of B- and N-substituted
2,1-borazaronaphthalenes under mild reaction conditions using
inexpensive materials. The approach is loosely based on the
original Dewar synthesis of 2-chloro-2,1-borazaronaphthalene.
A plausible mechanism for that approach to 2-chloro-2,1-
borazaronaphthalene from boron trichloride and 2-amino-
styrene is outlined in Scheme 2. The first step consists of a
Scheme 2. Plausible Mechanism for the Synthesis of
2‑Chloro-2,1-borazaronaphthalene
known reaction between a primary amine and BCl3, which
results in the formation of a N−B bond with loss of HCl to
form 2.12 Nucleophilic attack of the terminal alkene, stabilized
by resonance from the amine, results in cyclization with loss of
Cl− to form the iminium intermediate 3. Elimination of HCl
and aromatization of this complex provides 2-chloro-2,1-
borazaronaphthalene (4).
The potential versatility of this approach can be highlighted
by noting that one N−H bond remains intact throughout the
transformation. Thus, substitution on nitrogen could easily be
achieved by starting with a secondary amine derivative of 2-
aminostyrene, providing the corresponding N-substituted 2,1-
borazaronaphthalene in one step. Furthermore, two of the
chlorides in BCl3 are lost as HCl, with the third being
incorporated into the final product. Therefore, to synthesize B-
substituted 2,1-borazaronaphthalenes, one would utilize an R−
BX2 species (X = halide). Dewar confirmed this possibility by
employing commercially available phenyldichloroborane to
synthesize 2-phenyl-2,1-borazaronaphthalene.7 However, only
a limited number of organodichloroboranes (<10) are
commercially available. Furthermore, the conventional syn-
thesis of aryldihaloboranes, in particular, is an onerous process,
beginning with the conversion of a minimally functionalized
aryl halide to the corresponding aryl Grignard or aryllithium
reagent. This intermediate then undergoes transmetalation to
an arylstannane, which is quenched with BCl3 to form the
aryldihaloborane (Scheme 3, I).13 Aside from the excess waste
generated from the series of transmetalations, sensitive
functional groups cannot be tolerated because of the use of
highly reactive organometallic reagents. A second common
approach to aryldihaloboranes is the Friedel−Crafts-type
addition of BCl3 to arenes in the presence of AlCl3 (Scheme
3, II).14 However, the regioselectivity in the addition of boron
is difficult to control, and the high reactivity of these Lewis
acids again limits the functional group tolerance.
N-substituted aniline starting material was employed, which was
first reacted with boron trichloride. The resulting product was
then heated to reflux with phenylacetylene, purified, and heated
with ZnCl2. Finally, Liu recently published the Rh-catalyzed
synthesis of B-substituted 1,2-dihydro-1,2-azaborines by react-
ing 1,2-dihydro-1,2-(chloro)azaborine with trimethylarylstan-
nanes in THF at 100 °C.11 In a single example, Liu
demonstrated the reaction with 2-chloro-2,1-borazaronaphtha-
lene, providing the cross-coupled product in 71% yield
(Scheme 1, IV).
Although these methods are effective for synthesizing and
functionalizing 2,1-borazaronaphthalenes, they are not without
limitations. BCl3 is not an ideal reagent for the transformation
because of its strength as a Lewis acid and inherent reactivity.
The use of aryl Grignard or organolithium reagents involves
strongly nucleophilic reaction conditions that limit the
functional group tolerance. Paetzold’s method suffers from
the use of a superstoichiometric amount of ZnCl2 in addition to
the high temperature and long reaction times needed to
synthesize the desired product. Liu greatly improved the
substrate scope by coupling cyano- and carbonyl-containing
arylstannanes in yields of 41 to 81%.11 However, this method is
limited by the use of an expensive rhodium catalyst, toxic and
atom-inefficient arylstannane reagents, and a reaction temper-
ature much greater than the boiling point of the solvent.
B
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array of solvents was tested in reactions at 80 °C for 24 h. On
the basis of Matteson’s adaptation of the Vedejs protocol,17
SiCl4 was first used as a fluorophile to generate the required
PhBCl2. Any R−BX2 species (X = Br, Cl, F) should be
practicable in the reaction, and therefore, several other
fluorophiles were employed as well (entries 6−10). However,
SiCl4 provided the desired product in the highest yield. The
addition of cyclopentyl methyl ether (CPME), a coordinating
solvent, led to an increase in yield compared with toluene
(entries 1−5). A 1:1 toluene/CPME mixture was found to be
more effective than other solvent combinations. Therefore,
after optimization of the solvent and fluorophile, the best
conditions were found to be 1 equiv of SiCl4 in 1:1 toluene/
CPME at 80 °C for 24 h, which provided the desired product in
60% isolated yield (entry 5).
Scheme 3. Methods for Synthesizing Phenyldichloroborane
A more general, convenient approach to organodihalobor-
anes was first reported by Vedejs, who generated organo-
dichloroboranes in situ by the addition of fluorophiles to
potassium organotrifluoroborates (nearly 500 structurally
diverse samples of which are commercially available) in THF
or acetonitrile (Scheme 3, III).15 Adapting this protocol would
allow the use of air- and moisture-stable organotrifluoroborates
in the borazine synthesis,16 which was expected to expand the
range of functional groups and subunits that could be
incorporated. Thus, aryl- as well as alkyl-, alkenyl-, and
alkynyltrifluoroborate substrates were envisioned as suitable
precursors. Therefore, a mild synthesis of highly functionalized
2,1-borazaronaphthalenes utilizing N-substituted 2-aminostyr-
enes and potassium organotrifluoroborates was envisioned.
Reported herein is the Lewis acid-promoted annulation/
aromatization reaction of substituted 2-aminostyrenes and
potassium organotrifluoroborates to provide functionalized
2,1-borazaronaphthalenes. By formation of the required R−
BX2 species in situ via conversion of the organotrifluoroborate
with SiCl4, an array of 2,1-borazaronaphthalenes have been
prepared. The use of aryl-, heteroaryl-, alkynyl-, alkenyl-, and
alkyltrifluoroborates opens an effective and straightforward
route to novel 2,1-borazaronaphthalenes.
Final refinement of the reaction conditions required various
temperatures, concentrations, and ratios of reagents to be
examined (Table 2). At 80 °C, the reaction provided more
Table 2. Final Reaction Refinement of the Synthesis of
2,1‑Borazaronaphthalenes
entry amine:BF3K:SiCl4 (equiv) conc. (M) temp (°C), time yield (%)
1
2
3
4
5
6
7
8
9
1.0:1.0:1.0
1.0:1.0:1.0
1.0:1.0:1.0
1.0:1.0:1.0
1.0:1.0:1.0
1.5:1.0:1.0
1.0:2.0:1.0
1.0:1.0:0.75
1.5:1.0:1.0
0.1
0.25
0.5
1
80, 30 min
80, 30 min
80, 30 min
80, 30 min
60, 4 h
58
60
65
42
65
79
65
73
78
0.5
0.5
0.5
0.5
0.5
60, 4 h
60, 4 h
60, 4 h
40, 18 h
desired product when the concentration was increased to 0.5
M, but then the yield decreased at 1 M (entries 1−4).
Interestingly, the reaction was complete after 30 min at 80 °C,
and when the temperature was lowered to 60 °C, the desired
product was isolated in the same yield in 4 h (entry 5).
Increasing the amount of amine increased the yield by 20%
(entry 6); however, increasing the amount of phenyltrifluor-
oborate did not change the yield of the reaction (entry 7).
Decreasing the amount of SiCl4 to 0.75 equiv resulted in a
lower yield (entry 8). Employing the conditions from entry 6
but lowering the reaction temperature to 40 °C afforded the
desired product in 78% yield, but with a longer reaction time of
18 h (entry 9).
RESULTS AND DISCUSSION
■
N-Benzyl-2-aminostyrene (5) and potassium phenyltrifluoro-
borate were chosen as model substrates for the synthesis of 1-
benzyl-2-phenyl-2,1-borazaronaphthalene (6) (Table 1). An
Table 1. Initial Reaction Conditions for the Synthesis of
2,1‑Borazaronaphthalenes
In addition to the variation of these parameters, several
additives were screened in the reaction. Utilization of 1 or 2
equiv of K2CO3, which was added to quench the HCl generated
in the reaction, did not change the yield of the reaction.
Addition of 1 or 2 equiv of NaOt-Bu or NEt3 resulted in no
product formation. The use of KBr, which was added to form
the R−BBr2 species in situ, also did not change the yield of the
reaction.18 Therefore, the preferred conditions for the synthesis
of 1-benzyl-2-phenyl-2,1-borazaronaphthalene were determined
to be 1.5 equiv of amine, 1.0 equiv of organotrifluoroborate,
and 1.0 equiv of SiCl4 in a 1:1 toluene/CPME mixture at 60 °C
for 4 h.
entry
solvent
toluene
fluorophile (1 equiv)
yield (%)
1
2
SiCl4
58
36
18
16
60
47
42
41
0
1:1 toluene/DME
1:1 toluene/THF
1:1 toluene/TBME
1:1 toluene/CPME
1:1 toluene/CPME
1:1 toluene/CPME
1:1 toluene/CPME
1:1 toluene/CPME
1:1 toluene/CPME
SiCl4
3
SiCl4
4
SiCl4
5
SiCl4
6
(p-tol)SiCl3
SiBr4
7
8
TMSCI
BF3·OEt2
BF3·SMe2
9
10
5
C
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Table 3. Scope of the Reaction with Potassium (Hetero)aryltrifluoroborates
Reaction conditions (unless otherwise noted): 1.5 equiv of amine, 1.0 equiv of (hetero)aryltrifluoroborate, 1.0 equiv of SiCl4, 1:1 toluene/CPME, 60
a
b
°C, 4 h. Reaction completed on a 5 mmol scale. Reaction temperature of 40 °C, 18 h.
These standard conditions were applied to a variety of
functionalized potassium aryl- and heteroaryltrifluoroborates,
which reacted with 5 to provide the corresponding 1-benzyl-
2,1-borazaronaphthalenes in yields up to 79% (Table 3).
Sixteen different potassium aryl- and heteroaryltrifluoroborates
afforded the corresponding disubstituted 2,1-borazaronaphtha-
lenes in moderate to good yields. Electron-donating aryltri-
fluoroborates with para or meta substitution provided the
desired products in good yield (entries 2−5 and 7). When the
aryltrifluoroborates contained electron-withdrawing groups
substituted meta or para, or for disubstituted derivatives, the
corresponding 2,1-borazaronaphthalenes were synthesized in
yields up to 70% (entries 8−13). The mild conditions of this
method allowed ester, nitrile, and nitro functional groups on
the aryltrifluoroborate (entries 8−10), which would not be
possible in approaches using Grignard reagents. 3-Thienyl-, 4-
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dibenzofuranyl-, and 4-dibenzothienyltrifluoroborate provided
the desired products in moderate yields after the reaction
temperature was lowered to 40 °C (entries 14−16). Because of
steric factors imposed by substituting the 2,1-borazaronaph-
thalene at the 1 and 2 positions, sterically encumbered
organotrifluoroborates provided the corresponding products
in lower yields, as is evident in the use of 1- and 2-
naphthyltrifluoroborate, where the less sterically hindered 2-
naphthyltrifluoroborate results in a higher product yield of 69%
(entries 5 and 6). The scalability of the reaction conditions was
illustrated by conducting the reaction on a 5 mmol scale
without loss of yield (entry 1).
herein allows diverse, readily available primary and secondary
alkyltrifluoroborates to be employed in a direct, straightforward,
one-step synthesis of 2-alkyl-2,1-borazaronaphthalenes with
yields up to 58% (Table 5). For example, β,β,β-trifluoroethyl-
Table 5. Scope of the Reaction with Potassium
Alkyltrifluoroborates
After synthesizing aryl- and heteroaryl-containing 2,1-
borazaronaphthalenes, we sought to extend this method to
alkenyl- and alkynyltrifluoroborates, providing access to novel
systems (Table 4). There are no previously reported examples
Table 4. Scope of the Reaction with Potassium Alkenyl- and
Alkynyltrifluoroborates
Reaction conditions (unless otherwise noted): 1.5 equiv of amine, 1.0
Reaction conditions: 1.2 equiv of amine, 1.0 equiv of alkyltrifluor-
oborate, 1.0 equiv of SiCl4, 1:1 toluene/CPME, 40 °C, 18 h. A 95:5
cis:trans ratio of R−BF3K was employed in the reaction.
equiv of alkyltrifluoroborate, 1.0 equiv of SiCl4, 1:1 toluene/CPME, 40
a
a
°C, 18 h. Reaction completed on a 5 mmol scale.
trifluoroborate19 was effectively used in the reaction, affording
the corresponding product in 40% yield (entry 3). An acyclic
secondary trifluoroborate was successfully utilized, and the
desired product was obtained in 58% yield (entry 4). Cyclic
secondary trifluoroborates such as cyclopropyl, cyclobutyl, and
cyclohexyl derivatives provided the desired products in good
yields (entries 5−7). Scaling up the reaction with potassium
methyltrifluoroborate provided a similar yield on a 5 mmol
scale (entry 1).
After synthesizing an array of 2,1-borazaronaphthalenes with
varying groups on boron, the method was extended by reacting
diverse nitrogen-substituted 2-aminostyrenes with phenyl-
trifluoroborate to provide the corresponding 2-phenyl-2,1-
borazaronaphthalenes (Table 6). This convergent approach
allows disubstituted 2,1-borazaronaphthalenes to be easily
synthesized. The requisite starting materials for this method
were synthesized via a Buchwald−Hartwig amination of
commercially available 2-bromostyrene.20 Different groups
were installed on nitrogen, such as PMB and allyl, and the
of 2,1-borazaronaphthalenes with alkenyl or alkynyl substitu-
ents. With a decrease in the reaction temperature to 40 °C, four
different azaborines of this type were synthesized in yields up to
57%. It is important to note that both cis- and trans-
propenyltrifluoroborate were used in the reaction, and
complete retention of stereochemistry of the olefin was
achieved (entries 1 and 2). A phenyl-substituted alkenyltri-
fluoroborate provided the desired product in 51% yield (entry
3). A 2-alkynyl-substituted 2,1-borazaronaphthalene was
synthesized in good yield starting from 1-hexynyltrifluoroborate
(entry 4).
Previously reported B-alkyl-substituted 2,1-borazaronaphtha-
lenes have been limited to simple aliphatic derivatives, including
methyl, ethyl, isopropyl, and tert-butyl systems, which were
synthesized in yields of 43%, 54%, 8%, and 25%, respective-
ly.7,10b All of these materials were generated via addition of an
alkylmetallic reagent to the B−Cl derivative in a second step
after assembly of the aromatic core. The approach described
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onaphthalenes. To access the requisite substrates, substituted 2-
bromobenzaldehydes were converted in a two-step process via
Wittig olefination and Buchwald−Hartwig amination to provide
access to the requisite 2-aminostyrenes with substituents placed
at various positions about the arene.21 These aminostyrenes
provided the corresponding 2,1-borazaronaphthalenes in yields
up to 75% (Table 7). Electron-withdrawing substituents such as
Table 6. Scope of the Reaction with N-Substituted
2‑Aminostyrenes
Table 7. Scope of the Reaction with Substituted
2‑Aminostyrenes
Reaction conditions: 1.5 equiv of amine, 1.0 equiv of aryltrifluor-
oborate, 1.0 equiv of SiCl4, 1:1 toluene/CPME, 60 °C, 4 h.
fluorine and trifluoromethyl groups provided the desired
product in yields of 73% and 64%, respectively (entries 1 and
2). Substitution of electron-donating methyl and methoxy
groups about the aromatic ring gave the corresponding 2,1-
borazaronaphthalenes in good yields (entries 3 and 4). The
nature of the process ensures that complete control of the
regiochemistry can be achieved in the placement of substituents
about both rings, an advantage enjoyed over many syntheses of
substituted naphthalenes themselves.
One potential route to obtain monosubstituted N−H 2,1-
borazaronaphthalenes7,10a would employ the synthesis of an N-
protected azaborine that could later be deprotected. It was for
this reason that N-benzyl-2-aminostyrene was chosen for
optimization. However, because of the aromatic character of
the 2,1-borazaronaphthalene, the N−C bond of the benzyl
group acts more like a C−C bond. Attempts to remove this
protecting group, as well as the PMB and allyl protecting
groups, were unsuccessful, resulting in recovery of the starting
2,1-borazaronaphthalene in almost all cases, demonstrating the
stability of these azaborines. To achieve the synthesis of N−H
2,1-borazaronaphthalenes, the two-component annulation/
aromatization reactions were carried out with 2-aminostyrene.
After lowering the concentration of the standard reaction
conditions to 0.25 M, the monosubstituted 2,1-borazaronaph-
Reaction conditions (unless otherwise noted): 1.5 equiv of amine, 1.0
equiv of aryltrifluoroborate, 1.0 equiv of SiCl4, 1:1 toluene/CPME, 60
a
°C, 4 h. Reaction temperature of 40 °C, 18 h.
corresponding 2,1-borazaronaphthalenes were synthesized in
yields of 61% and 55%, respectively (entries 2 and 3). A
straight-chain alkylamine was also synthesized and employed in
the reaction to provide the desired product in 71% yield (entry
4).
As with the 1-naphthyltrifluoroborate, steric restrictions on
substitution of the azaborine at the 1 and 2 positions were
evident, as the yield decreased to 40% when an aryl group was
substituted on nitrogen (entry 5), and no desired product was
obtained when a diphenylmethyl group was substituted on
nitrogen (entry 6).
Having synthesized 1,2-disubstituted 2,1-borazaronaphtha-
lenes with various substituents on nitrogen and boron, we
sought to extend the method to aryl-substituted 2-amino-
styrenes, as aryl-functionalized 2-aminostyrenes have not
previously been employed in the synthesis of 2,1-borazar-
F
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thalenes were prepared in yields up to 66%. However, addition
of 1.5 equiv of NEt3, which served to quench the HCl formed
during the reaction, led to increased yields, providing the
desired products in yields up to 95% (Table 8). Cyclic and
demonstrate that the fourth complementary substitution
pattern was accessible, an aryl-substituted 2-aminostyrene was
reacted with potassium methyltrifluoroborate, providing access
to 1-aryl-2-alkyl-2,1-borazaronaphthalene 13 (eq 1).
Table 8. Scope of the Reaction with 2-Aminostyrene
The overall impact of this method can be demonstrated by
comparing the current synthesis of 2,1-borazaronaphthalenes
with those of the isosteric substituted naphthalenes. Whereas
the syntheses of 1-alkyl-2-aryl- and 1,2-dialkyl-2,1-borazaro-
naphthalenes (7a−p and 9a−g, respectively) proceed under
mild reaction conditions, the syntheses of the corresponding
disubstituted naphthalenes employ alkyl and aryl Grignard
reagents for substitution at the 2-position of the naphthalene
followed by a high temperature oxidation.22 The use of these
Grignard reagents severely restricts the types of functional
groups that can be incorporated. The synthesis of 1-alkyl-2-aryl-
and 1,2-diarylnaphthalenes requires a palladium-catalyzed
borylation and/or cross-coupling.23 Although effective in
providing a range of products with high functional group
tolerance, the synthesis of the electrophilic naphthalene in these
systems requires several steps and harsh reaction conditions. By
contrast, the synthesis of the 2,1-borazaronaphthalenes (7a−p
and 10d) is a transition-metal-free route that does not require a
multistep synthesis of starting materials. The synthesis of 1-aryl-
2-alkylnaphthalenes requires only one step;24 however, only a
few examples have been reported, and these are void of any
functional groups. In fact, only straight-chain alkyl substituents
were present on the alkyne in this gallium-catalyzed reaction.
The success in utilizing highly elaborated potassium alkyltri-
fluoroborates alleviates the problem of synthesizing function-
alized alkynes, and the corresponding 2,1-borazaronaphthalene
13 was synthesized in similar yield. The synthesis of 1-
substituted-2-alkynyl- and 1-substituted-2-alkenylnaphthalenes
can be envisioned to proceed through a cross-coupling similar
to that for the 1,2-diarylnaphthalenes.25 More importantly, in
comparison with 11a−d, there are only a few examples of the
synthesis of 1,2-disubstituted naphthalenes with further
substitution on the naphthyl ring. For example, there are no
reported examples of the naphthalenes analogous to the
fluorinated and trifluoromethylated 2,1-borazaronaphthalenes
11a and 11b.26 The corresponding 2,1-borazaronaphthalenes
are synthesized in a convergent manner by reacting an aryl- or
N-substituted 2-aminostyrene with an organotrifluoroborate to
provide access to highly functionalized products with complete
control of regioselectivity that would be virtually impossible to
replicate easily in the naphthalenes themselves.
Reaction conditions (unless otherwise noted): 1.2 equiv of amine, 1.0
equiv of organotrifluoroborate, 1.0 equiv of SiCl4, 1.5 equiv of NEt3,
a
1:1 toluene/CPME, 40 °C, 18 h. Without 1.5 equiv of NEt3.
acyclic alkyltrifluoroborates provided the desired products in
high yields (entries 1 and 2). The mild reaction conditions
allowed the installation of an alkyl iodide and bromide on the
2,1-borazaronaphthalene, providing the desired products in
69% and 80% yield, respectively (entries 3 and 4). Alkenyl and
alkynyltrifluoroborates could be employed, providing the
desired products in good yield (entries 5 and 6). Electron-
donating, electron-withdrawing, and electron-neutral aryltri-
fluoroborates were effective in the reaction, as the 2,1-
borazaronaphthalenes were synthesized in yields up to 95%
(entries 7−9). Three heterocyclic trifluoroborates were used in
the reaction, providing the desired products in yields up to 92%
(entries 10−12).
CONCLUSIONS
■
Forty-nine N- and B-substituted 2,1-borazaronaphthalenes were
synthesized via an annulation/aromatization reaction of
potassium organotrifluoroborates and substituted 2-amino-
styrenes. By utilization of the in situ conversion of organo-
trifluoroborates to the active organodihaloboranes with SiCl4,
the use of harsh reaction conditions was avoided, allowing the
synthesis of highly functionalized azaborines in a straightfor-
ward, efficient manner. Alkyl, alkenyl, aryl, and heteroaryl
substituents at the 2-position of 2,1-borazaronaphthalenes can
be prepared from the same synthetic precursor, allowing a
1-Alkyl-2-aryl-, 1,2-dialkyl, and 1,2-diaryl-2,1-borazaronaph-
thalenes have been synthesized in yields up to 95%. To
G
dx.doi.org/10.1021/jo402616w | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
4.28. 19F NMR (338.8 MHz, acetone-d6): δ −141.3. IR (neat): 3064,
2357, 1374, 959, 798, 748 cm−1. HRMS (ESI) m/z: calcd for
C12H7BF3S [M − K]− 251.0316, found 251.0314.
library of highly functionalized and substituted 2,1-borazar-
onaphthalenes to be synthesized easily. In fact, more diversity
has been introduced into the 2,1-borazaronaphthalene platform
as a result of this study than in all previous studies over the past
50+ years combined.
Furthermore, whereas the synthesis of the isosteric 1,2-
disubstituted naphthalenes requires the use of strongly
nucleophilic organometallic reagents that limit the types of
functional groups that can be tolerated, the synthesis of
disubstituted 2,1-borazaronaphthalenes described herein pro-
ceeds under mild reaction conditions. The reactions also
transpire without the need for preactivation of the rings or
expensive transition-metal catalysts in a convergent, modular
manner that permits complete control of the regioselectivity
and substituents about both aromatic rings. Investigations of
the reactivity of these compounds and applications of this
approach to other borazine cores are currently underway.
General Procedure for the Synthesis of 2-Aminostyrenes. To
an oven-dried Biotage microwave vial equipped with a stir bar were
added Pd(μ-Cl) dimer (0.02 mmol, 0.5 mol %), JohnPhos (0.04
mmol, 1 mol %), and NaOt-Bu (5.6 mmol, 1.4 equiv). The vial was
sealed with a cap lined with a disposable Teflon septum, evacuated
under vacuum, and purged with Ar three times. Toluene (8 mL) was
added, followed by 2-bromostyrene (4 mmol, 1 equiv) and the
corresponding amine (4.8 mmol, 1.2 equiv). The resulting mixture was
heated to 80 °C and stirred until full consumption of 2-bromostyrene
was observed by HPLC (∼24 h). The reaction mixture was cooled to
rt, diluted with Et2O (16 mL), and filtered over Celite. The solvent
was removed in vacuo, and the product was purified by flash column
chromatography on silica gel with an EtOAc/hexanes mixture as the
eluent. The eluent for most of the amines was hexanes to 2% EtOAc/
hexanes.
N-Benzyl-2-vinylaniline (7a-amine).28 The reaction was conducted
using 27 mmol of 2-bromostyrene, and the catalyst loading was
reduced to 0.25 mol % Pd(μ-Cl) dimer and 0.5 mol % JohnPhos. The
EXPERIMENTAL SECTION
■
1
General Considerations. JohnPhos, NaOt-Bu, 2-bromostyrene,
and SiCl4 were purchased and used as received. Amines were distilled
prior to use. Toluene and CPME were dried using a JC Meyer solvent
system. Standard benchtop techniques were employed to handle air-
sensitive reagents. Melting points (°C) are uncorrected. NMR spectra
were recorded on a 500 or 400 MHz spectrometer. 19F NMR chemical
shifts were referenced to external CFCl3 (0.0 ppm). 11B NMR spectra
were obtained on a spectrometer equipped with the appropriate
decoupling accessories. All 11B NMR chemical shifts were referenced
to external BF3·OEt2 (0.0 ppm), with a negative sign indicating an
upfield shift. Chemical shifts (δ) are given in parts per million.
Multiplicities are denoted as follows: s = singlet, d = doublet, t =
triplet, m = multiplet, br = broad. Coupling constants (J) are given in
hertz. 1H NMR data are presented as follows: chemical shift
(multiplicity, coupling constant, integration). Analytical thin-layer
chromatography (TLC) was performed on TLC silica gel plates (0.25
mm) precoated with a fluorescent indicator. Standard flash
chromatography procedures were followed using 32−63 μm silica
gel. Visualization was effected with UV light. HRMS data were
obtained by either ESI or CI using a TOF mass spectrometer.
Potassium β,β,β-Trifluoroethyltrifluoroborate.19 White solid.
product was obtained as a yellow oil (4.44 g, 78%). H NMR (500
MHz, CDCl3): δ 7.41−7.33 (m, 4H), 7.31−7.26 (m, 2H), 7.18−7.12
(m, 1H), 6.82−6.71 (m, 2H), 6.64 (d, J = 8.1 Hz, 1H), 5.62 (dd, J =
1.6, 17.3 Hz, 1H), 5.31 (dd, J = 1.6, 11.0 Hz, 1H), 4.36 (d, J = 5.3 Hz,
2H), 4.17 (br s, 1H). 13C NMR (125.8 MHz, CDCl3): δ 145.2, 139.4,
133.1, 129.1, 128.8, 127.6, 127.5, 127.4, 124.4, 117.7, 116.5, 111.1,
48.5.
N-(4-Methoxybenzyl)-2-vinylaniline (10a-amine). The reaction
was conducted using 7 mmol of 2-bromostyrene, and the catalyst
loading was reduced to 0.25 mol % Pd(μ-Cl) dimer and 0.5 mol %
JohnPhos. The product was obtained as a yellow oil (1.12 g, 69%). 1H
NMR (500 MHz, CDCl3): δ 7.33−7.26 (m, 3H), 7.19−7.12 (m, 1H),
6.92−6.86 (m, 2H), 6.80−6.70 (m, 2H), 6.65 (d, J = 8.2 Hz, 1H), 5.61
(dd, J = 1.6, 17.4 Hz, 1H), 5.29 (dd, J = 1.6, 11.0 Hz, 1H), 4.28 (s,
2H), 4.08 (br s, 1H), 3.81 (s, 3H). 13C NMR (125.8 MHz, CDCl3): δ
159.1, 145.3, 133.1, 131.4, 129.1, 129.0, 127.5, 124.4, 117.6, 116.4,
114.2, 111.1, 55.4, 48.0. IR (neat): 3436, 2840, 1602, 1509, 1246, 747
cm−1. HRMS (ESI) m/z: calcd for C16H18NO [M + H]+ 240.1388,
found 240.1378.
N-Allyl-2-vinylaniline (10b-amine). Obtained as a yellow oil (643
1
mg, 81%). H NMR (500 MHz, CDCl3): δ 7.31 (dd, J = 7.6 Hz, 1.0
Mp: >250 °C. 1H NMR (500 MHz, acetone-d6): δ 1.08 (br s, 2H). 13
C
Hz, 1H), 7.23−7.20 (m, 1H), 6.85−6.78 (m, 2H), 6.68 (d, J = 8.1 Hz,
1H), 6.07−5.99 (m, 1H), 5.66 (dd, J = 17.4 Hz, 1.7 Hz, 1H), 5.38−
5.32 (m, 2H), 5.23 (dd, J = 10.3 Hz, 1.2 Hz, 1H), 3.99 (br s, 1H),
3.85−3.83 (m, 2H). 13C NMR (125.8 MHz, CDCl3): δ 144.9, 135.3,
132.9, 128.8, 127.4, 124.3, 117.4, 116.3, 116.2, 111.0, 46.5. IR (neat):
3436, 3082, 1601, 1507, 131, 913, 746 cm−1. HRMS (ESI) m/z: calcd
for C11H14N [M + H]+ 160.1126, found 160.1131.
NMR (125.8 MHz, acetone-d6): δ 131.9 (J = 280 Hz), 25.2 (br). 11B
NMR (128.38 MHz, acetone-d6): δ 3.75. 19F NMR (338.8 MHz,
acetone-d6): δ −56.6, −139.6. IR (neat): 1322, 1260, 1056, 957, 794,
662 cm−1. HRMS (ESI) m/z: calcd for C2H2BF6 [M − K]− 151.0154,
found 151.0148.
Potassium 3-Bromopropyltrifluoroborate.27 White solid. Mp:
1
>250 °C. H NMR (500 MHz, acetone-d6): δ 3.41−3.36 (m, 2H),
N-Butyl-2-vinylaniline (10c-amine).29 Obtained as a yellow oil
1.82−1.77 (m, 2H), 0.24−0.21 (m, 2H). 13C NMR (125.8 MHz,
acetone-d6): δ 38.2, 29.8, 18.2 (br). 11B NMR (128.38 MHz, acetone-
d6): δ 6.03. 19F NMR (338.8 MHz, acetone-d6): δ −141.1. IR (neat):
2912, 1437, 1267, 1080, 1009, 920, 868, 832 cm−1. HRMS (ESI) m/z:
calcd for C3H6BF3Br [M − K]− 188.9698, found 188.9704.
Potassium 3-Iodopropyltrifluoroborate.27 White solid. Mp:
>250 °C. 1H NMR (500 MHz, acetone-d6): δ 3.20 (t, J = 7.6 Hz, 2H),
1.83−1.77 (m, 2H), 0.25−0.18 (m, 2H). 13C NMR (125.8 MHz,
acetone-d6): δ 30.9, 20.3 (br), 13.1. 11B NMR (128.38 MHz, acetone-
d6): δ 5.80. 19F NMR (338.8 MHz, acetone-d6): δ −141.0. IR (neat):
2918, 1267, 1215, 1084, 992, 918, 859 cm−1. HRMS (ESI) m/z: calcd
for C3H6BF3I [M − K]− 236.9559, found 236.9577. Anal. Calcd for
C3H6BF3IK: C, 13.06; H, 2.19; F, 20.66. Found: C, 12.78; H, 1.92; F,
20.06.
1
(502 mg, 72%). H NMR (500 MHz, CDCl3): δ 7.26−7.23 (m, 1H),
7.19−7.14 (m, 1H), 6.77−6.67 (m, 2H), 6.63 (d, J = 8.2 Hz, 1H), 5.60
(dd, J = 1.6, 17.3 Hz, 1H), 5.30 (dd, J = 1.6, 11.0 Hz, 1H), 3.74 (br s,
1H), 3.15−3.11 (m, 2H), 1.68−1.60 (m, 2H), 1.49−1.40 (m, 2H),
0.97 (t, J = 7.4 Hz, 3H). 13C NMR (125.8 MHz, CDCl3): δ 145.7,
133.2, 129.1, 127.6, 124.2, 117.1, 116.2, 110.7, 43.9, 31.8, 20.5, 14.1.
N-Phenyl-2-vinylaniline (10d-amine).30 Obtained as a yellow oil
(661 mg, 85%). 1H NMR (500 MHz, CDCl3): δ 7.48 (dd, J = 1.4, 7.7
Hz, 1H), 7.28−7.18 (m, 4H), 7.04−6.99 (m, 1H), 6.96−6.85 (m, 4H),
5.69 (dd, J = 1.4, 17.5 Hz, 1H), 5.53 (br s, 1H), 5.32 (dd, J = 1.4, 11.0
Hz, 1H). 13C NMR (125.8 MHz, CDCl3): δ 144.2, 140.2, 133.0, 130.2,
129.5, 128.7, 127.3, 122.7, 120.6, 120.2, 117.4, 116.4.
N-Benzhydryl-2-vinylaniline (10e-amine). Obtained as a yellow
solid (821 mg, 72%). Mp: 76−78 °C. 1H NMR (500 MHz, CDCl3): δ
7.41−7.35 (m, 8H), 7.32−7.27 (m, 3H), 7.09−7.05 (m, 1H), 6.84 (dd,
J = 17.4, 11.0 Hz, 1H), 6.76−6.72 (m, 1H), 6.48 (d, J = 7.8 Hz, 1H),
5.67 (d, J = 17.4 Hz, 1H), 5.58 (br s, 1H), 5.33 (dd, J = 10.9, 1.3 Hz,
1H), 4.41 (br s, 1H). 13C NMR (125.8 MHz, CDCl3): δ 144.1, 142.8,
136.6, 132.9, 128.7, 127.3, 127.2, 124.3, 117.6, 116.4, 112.1, 109.5,
Potassium Dibenzo[b,d]thiophen-4-yltrifluoroborate. White
1
solid. Mp: >250 °C. H NMR (500 MHz, acetone-d6): δ 8.20−8.16
(m, 1H), 8.03 (d, J = 7.6 Hz, 1H), 7.85−7.81 (m, 1H), 7.62 (d, J = 6.7
Hz, 1H), 7.39−7.36 (m, 2H), 7.31−7.27 (m, 1H). 13C NMR (125.8
MHz, acetone-d6): δ 142.9, 140.6, 136.0, 133.8, 130.3, 130.3, 125.7,
123.4, 122.2, 121.0, 119.3. 11B NMR (128.38 MHz, acetone-d6): δ
H
dx.doi.org/10.1021/jo402616w | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
62.8. IR (neat): 3423, 3062, 2844, 1735, 1500, 907, 742 cm−1. HRMS
(ESI) m/z: calcd for C21H20N [M + H]+ 286.1596, found 286.1597.
General Procedure for the Wittig Olefination and Buch-
wald−Hartwig Amination for the Synthesis of Substituted 2-
Aminostyrenes. To an oven-dried 25 mL round-bottom flask with a
stir bar was added MePh3PBr (6 mmol, 1.2 equiv). The flask was
sealed with a septum, evacuated, and purged three times with Ar. The
flask was cooled to −78 °C, and n-BuLi (1.6 M in hexanes, 6 mmol,
1.2 equiv) was added dropwise, keeping the reaction temperature
below −70 °C. The reaction mixture was stirred at −78 °C for 1 h and
allowed to warm to rt. The mixture was cooled to −78 °C, and the
corresponding aldehyde (4 mmol, 1 equiv) was added dropwise (or in
small portions if solid) over the course of 10 min. The reaction
mixture was allowed to warm slowly to rt and was stirred for 18 h. The
reaction was quenched at 0 °C by addition of sat. aq NH4Cl, and the
mixture was extracted with EtOAc, dried (MgSO4), and concentrated.
Ph3PO was removed by addition of Et2O, cooling to 0 °C, and filtering
over a small plug of silica. The crude product was taken directly to the
next step after the product was confirmed by NMR analysis. To an
oven-dried Biotage microwave vial equipped with a stir bar was added
Pd(μ-Cl) dimer (0.02 mmol, 0.5 mol %), JohnPhos (0.04 mmol, 1 mol
%), and NaOt-Bu (5.6 mmol, 1.4 equiv). The vial was sealed with a
cap lined with a disposable Teflon septum, evacuated under vacuum,
and purged with Ar three times. Toluene (8 mL) was added, followed
by the substituted-2-bromostyrene (4 mmol, 1 equiv) and benzyl-
amine (4.8 mmol, 1.2 equiv). The resulting mixture was heated to 80
°C and stirred until full consumption of 2-bromostyrene was observed
by HPLC (∼24 h). The reaction mixture was cooled to rt, diluted with
Et2O (16 mL), and filtered over Celite. The solvent was removed in
vacuo, and the product was purified by flash column chromatography
on silica gel with hexanes as the eluent.
(neat): 3430, 2921, 2851, 1612, 1515, 1218, 732 cm−1. HRMS (ESI)
m/z: calcd for C17H20NO2 [M + H]+ 270.1494, found 270.1488.
2-Aminostyrene (2-Vinylaniline, 12-amine). 2-Aminostyrene
was synthesized according to a literature procedure.31To a 100 mL
round-bottom flask with stir bar were added 2-aminophenethyl alcohol
(20 g, 146 mmol) and potassium hydroxide (8.2 g, 146 mmol). The
flask was connected to a vacuum distillation apparatus and heated to
180 °C under vacuum (0.05 Torr). The product was distilled over 4 h
1
and collected as a colorless oil (13.15 g, 75%). H NMR (500 MHz,
acetone-d6): δ 7.28 (d, J = 7.6 Hz, 1H), 7.00 (dd, J = 7.6, 7.6 Hz, 1H),
6.89 (dd, J = 17.4, 11.2 Hz, 1H), 6.72−6.69 (m, 1H), 6.64−6.57 (m,
1H), 5.59 (d, J = 17.4 Hz, 1H), 5.18 (d, J = 11.0 Hz, 1H), 4.60 (br s,
2H). 13C NMR (125.8 MHz, acetone-d6): δ 145.3, 133.0, 128.5, 126.2,
122.6, 117.2, 115.6, 112.9.
General Procedure for the Synthesis of 2,1-Borazaronaph-
thalenes. To an oven-dried Biotage microwave vial equipped with a
stir bar was added the potassium organotrifluoroborate (0.5 mmol, 1
equiv). The vial was sealed with a cap lined with a disposable Teflon
septum, evacuated under vacuum, and purged with Ar three times.
CPME (0.5 mL) and toluene (0.5 mL) were added, followed by the 2-
vinylaniline (0.75 mmol, 1.5 equiv or 0.60 mmol, 1.2 equiv), SiCl4 (0.5
mmol, 1 equiv), and NEt3 (0.75 equiv, if required) under Ar. The
resulting mixture was heated either to 60 °C for 4 h or to 40 °C for 18
h, depending on the substrate, and then cooled to rt and diluted with
hexanes (2 mL). The reaction mixture was filtered over a 2 in. plug of
silica and flushed with 20% CH2Cl2/hexanes (10 mL). The solvent
was removed in vacuo to provide the desired product. A few B-alkyl
2,1-borazaronaphthalenes required purification via flash column
chromatography with 30% CH2Cl2/hexanes as the eluent.
1-Benzyl-2-phenyl-2,1-borazaronaphthalene (7a). Obtained as a
tan solid (117 mg, 79%). Mp: 95−98 °C. 1H NMR (500 MHz,
CDCl3): δ 8.13 (d, J = 11.4 Hz, 1H), 7.70 (d, J = 7.6 Hz, 1H), 7.57−
7.48 (m, 2H), 7.36−7.27 (m, 7H), 7.24−7.17 (m, 2H), 7.13 (d, J = 7.1
Hz, 2H), 7.05 (d, J = 11.4 Hz, 1H), 5.44 (s, 2H). 13C NMR (125.8
MHz, CDCl3): δ 145.5, 141.3, 139.4, 132.7, 130.4, 128.9, 128.7, 128.1,
127.9, 127.5, 127.0, 125.9, 121.2, 117.2, 52.6. 11B NMR (128.38 MHz,
CDCl3): δ 37.04. IR (neat): 3026, 1609, 1548, 1241, 966, 814, 701
cm−1. HRMS (CI) m/z: calcd for C21H18BN [M]+ 295.1532, found
295.1521.
N-Benzyl-5-trifluoromethyl-2-vinylaniline (11a-amine). The re-
action was completed on a 2 mmol scale, and the product was
obtained as a yellow oil (160 mg, 29%). 1H NMR (500 MHz, CDCl3):
δ 7.51 (d, J = 1.5 Hz, 1H), 7.41−7.37 (m, 5H), 7.35−7.32 (m, 1H),
6.76 (dd, J = 17.4, 11.0 Hz, 1H), 6.65 (d, J = 8.6 Hz, 1H), 5.71 (dd, J =
17.1, 1.2 Hz, 1H), 5.44 (dd, J = 11.0, 1.2 Hz, 1H), 4.54 (br s, 1H), 4.43
(s, 2H). 13C NMR (125.8 MHz, CDCl3): δ 147.3, 138.2, 131.8, 128.8,
127.5, 127.3, 126.3 (q, J = 212 Hz), 125.9 (q, J = 3.7 Hz), 124.52 (q, J
= 3.7 Hz), 123.8, 119.0 (q, J = 32 Hz), 118.17, 109.9, 47.9. IR (neat):
3446, 3031, 2857, 1615, 1523, 1328, 1290, 1109 cm−1. HRMS (ESI)
m/z: calcd for C16H15NF3 [M + H]+ 278.1157, found 278.1165.
N-Benzyl-3-fluoro-2-vinylaniline (11b-amine). Obtained as a
1-Benzyl-2-(4-tert-butylphenyl)-2,1-borazaronaphthalene (7b).
1
Obtained as a tan solid (78 mg, 44%). Mp: 134−136 °C. H NMR
(500 MHz, CDCl3): δ 8.11 (d, J = 11.4 Hz, 1H), 7.69 (d, J = 7.6 Hz,
1H), 7.51 (d, J = 8.1 Hz, 2H), 7.36 (d, J = 8.2 Hz, 2H), 7.34−7.28 (m,
4H), 7.26−7.21 (m, 1H), 7.20−7.13 (m, 3H), 7.08 (d, J = 11.3 Hz,
1H), 5.48 (br s, 2H), 1.32 (s, 9H). 13C NMR (125.8 MHz, CDCl3): δ
151.1, 145.3, 141.4, 139.7, 132.9, 130.4, 128.9, 128.6, 127.5, 126.9,
125.9, 124.8, 121.1, 117.2, 52.7, 34.8, 31.5. 11B NMR (128.38 MHz,
CDCl3): δ 37.17. IR (neat): 2966, 1610, 1553, 1239, 805, 764 cm−1.
HRMS (CI) m/z: calcd for C25H26BN [M]+ 351.2158, found
351.2167.
1
yellow oil (390 mg, 43%). H NMR (500 MHz, CDCl3): δ 7.39−
7.35 (m, 4H), 7.31 (d, J = 4.2 Hz, 1H), 7.06−7.04 (m, 1H), 6.60 (dd, J
= 18.0, 11.6 Hz, 1H), 6.51−6.45 (m, 1H), 6.42 (d, J = 8.3 Hz, 1H),
5.74 (d, J = 18.1 Hz, 1H), 5.62 (d, J = 11.7 Hz, 1H), 4.58 (br s, 1H),
4.37−4.36 (m, 2H). 13C NMR (125.8 MHz, CDCl3): δ 161.1 (d, J =
244 Hz), 147.0 (d, J = 6.3 Hz), 139.0, 129.2 (d, J = 11.3 Hz), 128.9,
127.5, 127.4, 127.0 (d, J = 3.8 Hz), 120.7 (d, J = 3.8 Hz), 111.5 (d, J =
16.5 Hz), 106.5 (d, J = 3 Hz), 104.4 (d, J = 23 Hz), 48.52. IR (neat):
3428, 3029, 2917, 2849, 1470, 1120, 735, 698 cm−1. HRMS (ESI) m/
z: calcd for C16H18N [M + H]+ 224.1439, found 224.1442.
1-Benzyl-2-(3-methylphenyl)-2,1-borazaronaphthalene (7c). Ob-
tained as a yellow oil that crystallized in the refrigerator (89 mg, 57%).
Mp: 97−99 °C. 1H NMR (500 MHz, CDCl3): δ 8.10 (d, J = 11.4 Hz,
1H), 7.69 (d, J = 8.0 Hz, 1H), 7.38−7.25 (m, 6H), 7.23−7.09 (m,
6H), 7.04 (d, J = 11.4 Hz, 1H), 5.43 (s, 2H), 2.29 (s, 3H). 13C NMR
(125.8 MHz, CDCl3): δ 145.4, 141.3, 139.5, 137.1, 133.6, 130.4, 129.5,
128.9, 128.8, 128.7, 127.8, 127.5, 126.9, 125.9, 121.1, 117.2, 52.6, 21.7.
11B NMR (128.38 MHz, CDCl3): δ 37.38. IR (neat): 3026, 1610,
1549, 1412, 762 cm−1. HRMS (CI) m/z: calcd for C22H20BN [M]+
309.1689, found 309.1700.
N-Benzyl-5-methyl-2-vinylaniline (11c-amine). Obtained as a
1
yellow oil (473 mg, 53%). H NMR (500 MHz, CDCl3): δ 7.45−
7.39 (m, 4H), 7.36−7.33 (m, 1H), 7.24 (d, J = 7.8 Hz, 1H), 6.80 (dd, J
= 17.4, 11.5 Hz, 1H), 6.62 (d, J = 7.8 Hz, 1H), 6.54 (s, 1H), 5.64 (d, J
= 17.4 Hz, 1H), 5.30 (d, J = 11.0 Hz, 1H), 4.39 (s, 2H), 4.17 (br s,
1H), 2.33 (s, 3H). 13C NMR (125.8 MHz, CDCl3): δ 145.0, 139.3,
138.9, 132.7, 128.6, 127.6, 127.3, 127.2, 121.5, 118.4, 115.4, 111.6,
48.4, 21.7. IR (neat): 3435, 3027, 2858, 1611, 1514, 1453, 908, 806,
697 cm−1. HRMS (ESI) m/z: calcd for C16H18N [M + H]+ 224.1439,
found 224.1442.
1-Benzyl-2-(3-methoxyphenyl)-2,1-borazaronaphthalene (7d).
1
Obtained as a tan solid (105 mg, 64%). Mp: 97−100 °C. H NMR
(500 MHz, CDCl3): δ 8.11 (d, J = 11.4 Hz, 1H), 7.69 (d, J = 7.7 Hz,
1H), 7.36−7.31 (m, 2H), 7.30−7.23 (m, 3H), 7.22−7.15 (m, 2H),
7.13−7.09 (m, 3H), 7.07−7.01 (m, 2H), 6.88−6.84 (m, 1H), 5.42 (s,
2H), 3.57 (s, 3H). 13C NMR (125.8 MHz, CDCl3): δ 158.9, 145.6,
141.4, 139.5, 130.4, 129.1, 128.9, 128.8, 127.5, 126.9, 125.9, 125.0,
121.2, 117.2, 117.1, 114.2, 54.9, 52.7. 11B NMR (128.38 MHz,
CDCl3): δ 36.77. IR (neat): 3032, 1589, 1547, 1417, 1226, 764 cm−1.
N-Benzyl-4,5-dimethoxy-2-vinylaniline (11d-amine). Obtained as
1
a yellow oil (430 mg, 40%). H NMR (500 MHz, CDCl3): δ 7.43−
7.36 (m, 4H), 7.32−7.29 (m, 1H), 6.93 (s, 1H), 6.77 (dd, J = 17.1,
11.0 Hz, 1H), 6.29 (s, 1H), 5.56 (d, J = 17.4 Hz, 1H), 5.24 (d, J = 11.0
Hz, 1H), 4.36 (s, 2H), 4.01−3.65 (br s, 1H), 3.86 (s, 3H), 3.80 (s,
3H). 13C NMR (125.8 MHz, CDCl3): δ 150.0, 141.3, 140.1, 139.3,
132.1, 128.6, 127.5, 127.3, 115.8, 113.8, 111.6, 97.4, 56.7, 55.8, 49.2. IR
I
dx.doi.org/10.1021/jo402616w | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
HRMS (ESI) m/z: calcd for C22H21BNO [M + H]+ 326.1716, found
326.1721.
1-Benzyl-2-(3,5-bis(trifluoromethyl)phenyl)-2,1-borazaronaph-
thalene (7k). Obtained as a tan solid (109 mg, 50%). Mp: 88−92 °C.
1H NMR (500 MHz, CDCl3): δ 8.21 (d, J = 11.4 Hz, 1H), 7.90 (s,
1-Benzyl-2-(2-naphthyl)-2,1-borazaronaphthalene (7e). Ob-
1
tained as a tan solid (119 mg, 69%). Mp: 146−148 °C. H NMR
2H), 7.82 (s, 1H), 7.76 (d, J = 8.0 Hz, 1H), 7.46−7.41 (m, 2H), 7.33−
7.22 (m, 4H), 7.07 (d, J = 7.4 Hz, 2H), 7.01−6.97 (m, 1H), 5.34 (s,
2H). 13C NMR (125.8 MHz, CDCl3): δ 146.8, 141.2, 138.5, 132.5,
132.4, 130.8 (q, J = 46.3 Hz), 130.7, 129.4, 129.1, 127.5, 127.4, 125.6,
123.7 (q, J = 273.4 Hz), 121.9, 117.1, 52.7. 11B NMR (128.38 MHz,
CDCl3): δ 36.09. IR (neat): 2921, 1611, 1350, 1277, 1126, 764 cm−1.
HRMS (ESI) m/z: calcd for C23H16BF7N [M + F]− 450.1264, found
450.1265.
1-Benzyl-2-(4-fluorophenyl)-2,1-borazaronaphthalene (7l). Ob-
tained as a tan solid (110 mg, 70%). Mp: 112−114 °C. 1H NMR (500
MHz, CDCl3): δ 8.13 (d, J = 11.3 Hz, 1H), 7.73−7.69 (m, 1H), 7.52−
7.46 (m, 2H), 7.38−7.28 (m, 4H), 7.24−7.17 (m, 2H), 7.12 (d, J = 7.1
Hz, 2H), 7.05−6.99 (m, 3H), 5.41 (s, 2H). 13C NMR (125.8 MHz,
CDCl3): δ 163.2 (d, J = 252.5 Hz), 145.7, 141.3, 139.3, 134.6 (d, J =
8.2 Hz), 130.5, 129.0, 128.8, 127.5, 127.1, 125.8, 121.3, 117.2 (d, J =
20.0 Hz), 114.9, 52.6. 11B NMR (128.38 MHz, CDCl3): δ 35.99. IR
(neat): 2913, 1594, 1216, 812 cm−1. HRMS (ESI) m/z: calcd for
C22H20BFNO [M + OCH3]− 344.1622, found 344.1627.
(500 MHz, CDCl3): δ 8.16 (d, J = 11.4 Hz, 1H), 8.00 (s, 1H), 7.82−
7.77 (m, 2H), 7.75−7.70 (m, 2H), 7.62 (dd, J = 1.1, 8.2 Hz, 1H),
7.47−7.41 (m, 2H), 7.39−7.34 (m, 2H), 7.32−7.28 (m, 2H), 7.26−
7.19 (m, 2H), 7.16−7.10 (m, 3H), 5.48 (s, 2H). 13C NMR (125.8
MHz, CDCl3): δ 145.6, 141.4, 139.4, 133.2, 133.1, 132.8, 130.5, 129.9,
128.9, 128.8, 128.3, 127.8, 127.5, 127.0, 127.0, 126.1, 125.9, 125.9,
121.2, 117.2, 52.7. 11B NMR (128.38 MHz, CDCl3): δ 36.66. IR
(neat): 3051, 1608, 1546, 1227, 804 cm−1. HRMS (CI) m/z: calcd for
C25H20BN [M]+ 345.1689, found 345.1700.
1-Benzyl-2-(1-naphthyl)-2,1-borazaronaphthalene (7f). Obtained
as a yellow oil that crystallized in the refrigerator (26 mg, 15%). Mp:
1
144−146 °C. H NMR (500 MHz, CDCl3): δ 8.15 (d, J = 11.3 Hz,
1H), 7.86 (d, J = 7.9 Hz, 1H), 7.80 (d, J = 8.2 Hz, 1H), 7.77−7.74 (m,
2H), 7.49 (d, J = 6.6 Hz, 1H), 7.47−7.43 (m, 1H), 7.42−7.34 (m,
4H), 7.24−7.18 (m, 3H), 7.16−7.12 (m, 1H), 7.07−7.01 (m, 3H),
5.30 (s, 2H). 13C NMR (125.8 MHz, CDCl3): δ 145.2, 141.3, 139.0,
135.3, 133.3, 130.5, 129.4, 129.1, 128.9, 128.7, 128.6, 128.6, 127.8,
127.6, 126.8, 125.9, 125.6, 125.5, 121.3, 117.3, 52.9. 11B NMR (128.38
MHz, CDCl3): δ 30.03. IR (neat): 3026, 1592, 1549, 946, 762 cm−1.
HRMS (CI) m/z: calcd for C25H20BN [M]+ 345.1689, found
345.1689.
1-Benzyl-2-(2,4-difluorophenyl)-2,1-borazaronaphthalene (7m).
1
Obtained as a tan solid (22 mg, 13%). Mp: 107−110 °C. H NMR
(500 MHz, CDCl3): δ 8.13 (d, J = 11.3 Hz, 1H), 7.74−7.70 (m, 1H),
7.39−7.33 (m, 2H), 7.32−7.26 (m, 2H), 7.24−7.17 (m, 3H), 7.06 (d, J
= 7.2 Hz, 2H), 6.99 (d, J = 11.3 Hz, 1H), 6.86−6.77 (m, 2H), 5.35 (s,
2H). 13C NMR (125.8 MHz, CDCl3): δ 165.0 (dd, J = 115.3, 12.7
Hz), 163.1 (dd, J = 122.6, 10.9 Hz), 145.7, 141.1, 138.8, 134.6 (dd, J =
11.8, 9.1 Hz), 130.5, 128.8, 128.8, 127.7, 127.0, 125.9, 121.5, 117.3,
111.4 (dd, J = 20.0, 2.7 Hz), 103.6 (dd, J = 29.1, 24.5 Hz), 52.8. 11B
NMR (128.38 MHz, CDCl3): δ 35.50. IR (neat): 2923, 1606, 1241,
973, 808 cm−1. HRMS (ESI) m/z: calcd for C21H16BF3N [M + F]−
350.1328, found 350.1330.
1-Benzyl-2-(4-methylphenyl)-2,1-borazaronaphthalene (7g). Ob-
tained as a white solid (111 mg, 72%). Mp: 96−98 °C. 1H NMR (500
MHz, acetone-d6): δ 8.17 (d, J = 11.2 Hz, 1H), 7.76 (d, J = 7.6 Hz,
1H), 7.46−7.40 (m, 3H), 7.37−7.34 (m, 1H), 7.30−7.27 (m, 2H),
7.22−7.18 (m, 2H), 7.14 (d, J = 7.6 Hz, 4H), 7.01 (d, J = 11.2 Hz,
1H), 5.50 (s, 2H), 2.30 (s, 3H). 13C NMR (125.8 MHz, acetone-d6): δ
145.3, 141.1, 139.4, 137.4, 130.2, 132.5, 128.6, 128.5, 128.4, 127.3,
126.7, 125.6, 121.0, 117.0, 51.8, 20.4. 11B NMR (128.38 MHz,
acetone-d6): δ 37.99. IR (neat): 2919, 1606, 1410, 1243, 803, 767
cm−1. HRMS (CI) m/z: calcd for C22H20BN [M]+ 309.1689, found
309.1688.
1-Benzyl-2-(3-thienyl)-2,1-borazaronaphthalene (7n). Obtained
1
as an off-white solid (84 mg, 56%). Mp: 108−110 °C. H NMR (500
MHz, acetone-d6): δ 8.17 (d, J = 11.5 Hz, 1H), 7.76 (d, J = 7.8 Hz,
1H), 7.65 (s, 1H), 7.49 (dd, J = 4.6, 2.7 Hz, 1H), 7.43−7.37 (m, 1H),
7.35−7.31 (m, 4H), 7.30−7.20 (m, 4H), 7.11 (d, J = 11.2 Hz, 1H),
5.57 (s, 2H). 13C NMR (125.8 MHz, acetone-d6): δ 145.2, 141.3,
139.2, 131.7, 131.1, 130.1, 128.8, 128.5, 127.3, 126.8, 125.6, 125.3,
121.0, 116.8, 52.0. 11B NMR (128.38 MHz, acetone-d6): δ 35.47. IR
(neat): 2922, 1551, 2523, 1232, 764 cm−1. HRMS (CI) m/z: calcd for
C19H17BNS [M + H]+ 302.1175, found 302.1183.
Methyl-3-(2-benzyl-2,1-borazaronaphthyl)benzoate (7h). Ob-
1
tained as a tan solid (115 mg, 65%). Mp: 91−93 °C. H NMR (500
MHz, CDCl3): δ 8.26−8.21 (m, 1H), 8.15 (d, J = 11.4 Hz, 1H), 8.00
(td, J = 1.5, 7.9 Hz, 1H), 7.72 (d, J = 7.6 Hz, 1H), 7.68 (td, J = 1.3, 7.4
Hz, 1H), 7.41−7.35 (m, 3H), 7.32−7.27 (m, 2H), 7.26−7.19 (m, 2H),
7.11 (d, J = 7.1 Hz, 2H), 7.04 (d, J = 11.4 Hz, 1H), 5.40 (s, 2H), 3.85
(s, 3H). 13C NMR (125.8 MHz, CDCl3): δ 167.6, 145.9, 141.2, 139.1,
136.9, 134.0, 130.5, 129.5, 129.2, 128.9, 128.9, 127.9, 127.5, 127.0,
125.8, 121.4, 117.2, 52.6, 52.1. 11B NMR (128.38 MHz, CDCl3): δ
36.78. IR (neat): 3026, 1714, 1548, 1233, 1107, 752 cm−1. HRMS
(ESI) m/z: calcd for C23H21BNO2 [M + H]+ 354.1665, found
354.1657.
1-Benzyl-2-(4-dibenzofuryl)-2,1-borazaronaphthalene (7o). Ob-
1
tained as a white solid (89 mg, 46%). Mp: 106−107 °C. H NMR
(500 MHz, acetone-d6): δ 8.28 (d, J = 11.2 Hz, 1H), 8.11−8.07 (m,
2H), 7.85 (d, J = 7.8 Hz, 1H), 7.59 (d, J = 7.3 Hz, 1H), 7.55 (d, J = 8.6
Hz, 1H), 7.45−7.33 (m, 5H), 7.28−7.22 (m, 3H), 7.17−7.12 (m, 4H),
5.52 (s, 2H). 13C NMR (125.8 MHz, acetone-d6): δ 158.0, 155.9,
145.5, 143.9, 140.1, 138.9, 131.0, 130.3, 128.6, 128.3, 127.6, 127.0,
126.6, 125.8, 124.1, 122.8, 122.6, 121.3, 120.7, 120.6, 117.2, 111.4,
111.3, 52.4. 11B NMR (128.38 MHz, acetone-d6): δ 37.20. IR (neat):
3027, 2923, 1712, 1550, 1186, 757, 737 cm−1. HRMS (CI) m/z: calcd
for C27H20BNO [M]+ 385.1638, found 385.1626.
3-(2-Benzyl-2,1-borazaronaphthyl)benzonitrile (7i). Obtained as a
yellow oil that crystallized in the refrigerator (80 mg, 50%). Mp: 117−
1
119 °C. H NMR (500 MHz, CDCl3): δ 8.17 (d, J = 11.4 Hz, 1H),
7.79 (s, 1H), 7.75−7.71 (m, 1H), 7.69 (td, J = 1.3, 7.6 Hz, 1H), 7.60
(td, J = 1.4, 7.8 Hz, 1H), 7.41−7.35 (m, 3H), 7.32−7.28 (m, 2H),
7.26−7.21 (m, 2H), 7.08 (d, J = 7.2 Hz, 2H), 6.97 (d, J = 11.3 Hz,
1H), 5.35 (s, 2H). 13C NMR (125.8 MHz, CDCl3): δ 146.5, 141.1,
138.7, 136.6, 136.2, 131.6, 130.7, 129.2, 129.2, 128.5, 127.6, 127.4,
125.7, 121.7, 119.5, 117.2, 112.1, 52.6. 11B NMR (128.38 MHz,
CDCl3): δ 36.03. IR (neat): 3030, 2227, 1610, 1550, 1414, 763 cm−1.
HRMS (ESI) m/z: calcd for C22H17BFN2 [M + F]− 339.1469, found
339.1471.
1-Benzyl-2-(4-dibenzothienyl)-2,1-borazaronaphthalene (7p).
Obtained as a white solid (88 mg, 44%). Mp: 116−117 °C. 1H
NMR (500 MHz, acetone-d6): δ 8.30−8.28 (m, 2H), 8.24 (d, J = 8.1
Hz, 1H), 7.90−7.88 (m, 1H), 7.83 (d, J = 7.8 Hz, 1H), 7.57−7.55 (m,
2H), 7.49−7.39 (m, 4H), 7.25 (dd, J = 9.5, 7.3 Hz, 1H), 7.21−7.12
(m, 6H), 5.49 (s, 2H). 13C NMR (125.8 MHz, acetone-d6): δ 146.6,
143.4, 141.4, 139.8, 139.3, 136.1, 135.1, 130.9, 130.2, 129.1, 128.9,
128.1, 127.2, 127.1, 126.2, 124.8, 124.7, 123.0, 122.2, 121.9, 121.7,
117.8, 52.6. 11B NMR (128.38 MHz, acetone-d6): δ 37.20. IR (neat):
3028, 1711, 1548, 1371, 1220, 752 cm−1. HRMS (CI) m/z: calcd for
C27H21BNS [M + H]+ 402.1488, found 402.1477.
1-Benzyl-2-((E)-1-propen-1-yl)-2,1-borazaronaphthalene (8a).
Obtained as a yellow oil that crystallized in the refrigerator (70 mg,
54%). Mp: 70−72 °C. 1H NMR (500 MHz, acetone-d6): δ 8.02 (d, J =
11.5 Hz, 1H), 7.66−7.64 (m, 1H), 7.41 (d, J = 8.6 Hz, 1H), 7.33−7.27
(m, 3H), 7.23−7.16 (m, 3H), 7.13−7.08 (m, 2H), 6.87−6.82 (m, 1H),
1-Benzyl-2-(3-nitrophenyl)-2,1-borazaronaphthalene (7j). Ob-
1
tained as a tan solid (84 mg, 49%). Mp: 114−117 °C. H NMR
(500 MHz, CDCl3): δ 8.41−8.36 (m, 1H), 8.23−8.14 (m, 2H), 7.80−
7.73 (m, 2H), 7.49−7.45 (m, 1H), 7.41−7.38 (m, 2H), 7.34−7.28 (m,
2H), 7.27−7.22 (m, 2H), 7.09 (d, J = 7.2 Hz, 2H), 7.01 (d, J = 11.3
Hz, 1H), 5.38 (s, 2H). 13C NMR (125.8 MHz, CDCl3): δ 148.0, 146.5,
141.1, 138.6, 138.4, 130.7, 129.2, 129.1, 128.8, 127.5, 127.4, 127.3,
125.7, 123.0, 121.7, 117.2, 52.6. 11B NMR (128.38 MHz, CDCl3): δ
35.70. IR (neat): 3030, 1609, 1528, 1342, 808, 730 cm−1. HRMS (ESI)
m/z: calcd for C21H17BN2NaO2 [M + Na]+ 363.1281, found 363.1270.
J
dx.doi.org/10.1021/jo402616w | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
6.26 (d, J = 17.5 Hz, 1H), 5.42 (s, 2H), 1.92−1.89 (m, 3H). 13C NMR
(125.8 MHz, acetone-d6): δ 146.2, 144.3, 141.5, 139.0, 130.0, 128.5,
128.2, 127.0, 126.8, 125.8, 120.5, 116.0, 50.2, 21.5. 11B NMR (128.38
MHz, acetone-d6): δ 37.27. IR (neat): 3010, 1713, 1608, 1552, 1358,
1218, 982, 758 cm−1. HRMS (CI) m/z: calcd for C18H18BN [M]+
259.1532, found 259.1539.
1088, 1048, 762 cm−1. HRMS (CI) m/z: calcd for C17H15BNF3 [M]+
301.1250, found 301.1245.
1-Benzyl-2-isopropyl-2,1-borazaronaphthalene (9d). Obtained as
a yellow oil that crystallized upon standing (76 mg, 58%). Mp: 67−69
1
°C. H NMR (500 MHz, acetone-d6): δ 8.08 (d, J = 11.5 Hz, 1H),
7.67 (dd, J = 7.6, 1.5 Hz, 1H), 7.41−7.38 (m, 1H), 7.34−7.27 (m,
3H), 7.21 (d, J = 7.3 Hz, 1H), 7.16−7.12 (m, 3H), 6.99 (d, J = 11.7
Hz, 1H), 5.44 (s, 2H), 1.69−1.62 (m, 1H), 1.15−1.11 (m, 6H). 13C
NMR (125.8 MHz, acetone-d6): δ 145.2, 141.2, 139.1, 139.0, 128.5,
128.2, 126.8, 126.7, 125.6, 120.5, 116.4, 49.7, 20.0. 11B NMR (128.38
MHz, acetone-d6): δ 41.05. IR (neat): 2950, 2917, 1558, 1440, 1134,
764 cm−1. HRMS (CI) m/z: calcd for C18H20BN [M]+ 261.1689,
found 261.1688.
1-Benzyl-2-((Z)-1-propen-1-yl)-2,1-borazaronaphthalene (8b).
Obtained as a yellow oil that crystallized in the refrigerator overnight
1
(74 mg, 57%). Mp: 70−72 °C. H NMR (500 MHz, acetone-d6): δ
8.08 (d, J = 11.2 Hz, 1H), 7.70 (d, J = 7.8 Hz, 1H), 7.43 (d, J = 8.6 Hz,
1H), 7.35−7.31 (m, 1H), 7.29−7.25 (m, 2H), 7.21−7.13 (m, 4H),
7.02−6.99 (m, 1H), 6.33−6.27 (m, 1H), 6.08 (d, J = 13.7 Hz, 1H),
5.40 (s, 2H), 1.86 (d, J = 6.8 Hz, 3H). 13C NMR (125.8 MHz,
acetone-d6): δ 144.4, 141.4, 138.8, 138.7, 130.1, 128.5, 128.2, 127.0,
126.7, 125.8, 120.7, 116.2, 51.1, 17.7. 11B NMR (128.38 MHz,
acetone-d6): δ 36.46. IR (neat): 3010, 1713, 1608, 1218, 982, 807, 758
cm−1. HRMS (CI) m/z: calcd for C18H18BN [M]+ 259.1532, found
259.1527.
1-Benzyl-2-cyclopropyl-2,1-borazaronaphthalene (9e). Obtained
as a yellow oil that crystallized in the refrigerator (64 mg, 49%). Mp:
41−43 °C. 1H NMR (500 MHz, CDCl3): δ 7.90 (d, J = 11.6 Hz, 1H),
7.56 (d, J = 7.9 Hz, 1H), 7.32−7.26 (m, 4H), 7.25−7.19 (m, 3H),
7.12−7.06 (m, 1H), 6.41 (d, J = 11.6 Hz, 1H), 5.48 (s, 2H), 0.87−0.81
(m, 2H), 0.70−0.64 (m, 2H), 0.36−0.26 (m, 1H). 13C NMR (125.8
MHz, CDCl3): δ 145.0, 141.8, 139.1, 130.2, 128.8, 128.4, 127.0, 126.6,
126.2, 120.4, 115.8, 51.1, 6.4. 11B NMR (128.38 MHz, CDCl3): δ
38.54. IR (neat): 3000, 1610, 1416, 761 cm−1. HRMS (CI) m/z: calcd
for C18H18BN [M]+ 259.1532, found 259.1534.
1-Benzyl-2-cyclobutyl-2,1-borazaronaphthalene (9f). Obtained as
a yellow oil that crystallized in the refrigerator (69 mg, 51%). Mp: 44−
47 °C. 1H NMR (500 MHz, acetone-d6): δ 8.11 (d, J = 11.5 Hz, 1H),
7.68 (dd, J = 7.7, 1.3 Hz, 1H), 7.36−7.24 (m, 4H), 7.20−7.07 (m,
5H), 5.28 (s, 2H), 2.53−2.51 (m, 1H), 2.22−2.12 (m, 5H), 1.96−1.91
(m, 1H). 13C NMR (125.8 MHz, acetone-d6): δ 145.2, 141.4, 138.9,
130.0, 128.4, 128.2, 126.8, 126.6, 125.6, 120.4, 116.1, 50.1, 25.8, 22.0.
11B NMR (128.38 MHz, acetone-d6): δ 39.92. IR (neat): 3027, 2962,
2858, 1551, 1414, 1217, 760 cm−1. HRMS (CI) m/z: calcd for
C19H20BN [M]+ 273.1689, found 273.1692.
1-Benzyl-2-((E)-3-phenyl-1-propen-1-yl)-2,1-borazaronaphtha-
lene (8c). Obtained as a yellow oil that crystallized in the refrigerator
1
(85 mg, 51%). Mp: 75−77 °C. H NMR (500 MHz, acetone-d6): δ
8.02 (d, J = 11.5 Hz, 1H), 7.67−7.64 (m, 1H), 7.44 (d, J = 8.6 Hz,
1H), 7.35−7.10 (m, 13H), 6.94−6.88 (m, 1H), 6.37 (d, J = 17.4 Hz,
1H), 5.48 (s, 2H), 3.59 (d, J = 6.6 Hz, 2H). 13C NMR (125.8 MHz,
acetone-d6): δ 149.9, 144.9, 141.9, 139.4, 130.4, 129.2, 129.0, 128.9,
128.8, 128.7, 127.5, 127.2, 126.4, 126.3, 121.0, 116.5, 50.8, 43.0. 11B
NMR (128.38 MHz, acetone-d6): δ 35.32. IR (neat): 3026, 1608,
1416, 1218, 990, 763, 748, 700 cm−1. HRMS (CI) m/z: calcd for
C24H23BN [M + H]+ 336.1924, found 336.1926.
1-Benzyl-2-(1-butynyl)-2,1-borazaronaphthalene (8d). Obtained
as a yellow oil that crystallized upon standing (71 mg, 47%). Mp: 46−
47 °C. 1H NMR (500 MHz, acetone-d6): δ 8.53 (d, J = 11.2 Hz, 1H),
8.16 (d, J = 7.8 Hz, 1H), 7.93 (d, J = 8.6 Hz, 1H), 7.84−7.79 (m, 1H),
7.77−7.58 (m, 7H), 7.37 (d, J = 11.2 Hz, 1H), 6.15 (s, 2H), 2.83 (dd, J
= 8.5, 7.0 Hz, 2H), 1.98−1.93 (m, 2H), 1.87−1.82 (m, 2H), 1.32−1.27
(m, 2H). 13C NMR (125.8 MHz, acetone-d6): δ 145.5, 141.4, 139.3,
130.6, 129.0, 128.8, 127.3, 127.2, 126.6, 121.4, 116.9, 111.0, 53.3, 31.0,
21.0, 19.6, 13.3. 11B NMR (128.38 MHz, acetone-d6): δ 29.01. IR
(neat): 3029, 2956, 2930, 2185, 1549, 1412, 1228, 806, 762 cm−1.
HRMS (CI) m/z: calcd for C21H22BN [M]+ 299.1845, found
299.1841.
1-Benzyl-2-methyl-2,1-borazaronaphthalene (9a). Obtained as a
tan solid (56 mg, 48%). Mp: 56−60 °C. 1H NMR (500 MHz, CDCl3):
δ 7.93 (d, J = 11.4 Hz, 1H), 7.61 (d, J = 7.6 Hz, 1H), 7.30−7.25 (m,
4H), 7.23−7.18 (m, 1H), 7.13−7.08 (m, 3H), 6.87 (d, J = 11.4 Hz,
1H), 5.30 (s, 2H), 0.84 (s, 3H). 13C NMR (125.8 MHz, CDCl3): δ
144.3, 141.9, 138.7, 130.3, 128.8, 128.4, 127.0, 126.7, 126.0, 120.5,
116.0, 51.1. 11B NMR (128.38 MHz, CDCl3): δ 38.99. IR (neat):
2966, 1608, 1355, 1221, 761 cm−1. HRMS (CI) m/z: calcd for
C16H16BN [M]+ 233.1376, found 233.1374.
1-Benzyl-2-cyclohexyl-2,1-borazaronaphthalene (9g). Obtained
as a yellow oil that crystallized in the refrigerator (63 mg, 42%). Mp:
1
48−51 °C. H NMR (500 MHz, CDCl3): δ 8.03 (d, J = 11.60 Hz,
1H), 7.62 (d, J = 7.63 Hz, 1H), 7.33−7.27 (m, 4H), 7.25−7.21 (m,
1H), 7.15−7.11 (m, 3H), 7.05−7.00 (m, 1H), 5.39 (s, 2H), 1.82−1.69
(m, 5H), 1.60−1.23 (m, 6H). 13C NMR (125.8 MHz, CDCl3): δ
145.0, 139.0, 130.0, 128.6, 128.5, 128.1, 127.8, 126.2, 125.7, 120.4,
116.4, 50.3, 30.3, 27.8, 27.0. 11B NMR (128.38 MHz, CDCl3): δ 39.34.
IR (neat): 3029, 2917, 2846, 1552, 1418, 802, 761 cm−1. HRMS (CI)
m/z: calcd for C21H24BN [M]+ 301.2002, found 301.2008.
1-(4-Methoxybenzyl)-2-phenyl-2,1-borazaronaphthalene (10a).
Obtained as a white solid (100 mg, 61%). Mp: 134−136 °C. 1H
NMR (500 MHz, CDCl3): δ 8.11 (d, J = 11.3 Hz, 1H), 7.69 (d, J = 7.7
Hz, 1H), 7.56−7.51 (m, 2H), 7.36−7.30 (m, 5H), 7.20−7.15 (m, 1H),
7.06−7.01 (m, 3H), 6.82 (d, J = 8.6 Hz, 2H), 5.37 (s, 2H), 3.75 (s,
3H). 13C NMR (125.8 MHz, CDCl3): δ 158.6, 145.5, 141.3, 132.7,
131.4, 130.4, 128.7, 128.1, 127.8, 127.5, 126.9, 121.1, 117.2, 114.3,
55.3, 52.0. 11B NMR (128.38 MHz, CDCl3): δ 37.19. IR (neat): 2998,
1609, 1509, 1246, 759 cm−1. HRMS (ESI) m/z: calcd for
C22H20BNNaO [M + Na]+ 348.1536, found 348.1547.
1-Allyl-2-phenyl-2,1-borazaronaphthalene (10b). Obtained as a
yellow oil that crystallized in the refrigerator (325 mg, 55%). Mp: 44−
46 °C. 1H NMR (500 MHz, acetone-d6): δ 8.13 (d, J = 11.2 Hz, 1H),
7.77−7.74 (m, 1H), 7.64−7.60 (m, 3H), 7.54−7.51 (m, 1H), 7.42−
7.35 (m, 3H), 7.25 (dd, J = 8.5, 7.5 Hz, 1H), 6.91 (d, J = 11.2 Hz, 1H),
6.15−6.09 (m, 1H), 5.18 (dd, J = 10.6, 1.3 Hz, 1H), 4.95 (dd, J = 17.4,
1.2 Hz, 1H), 4.84−4.82 (m, 2H). 13C NMR (125.8 MHz, acetone-d6):
δ 145.2, 141.1, 136.0, 132.2, 130.2, 128.5, 127.8, 127.5, 127.1, 121.0,
116.7, 115.0, 50.2. 11B NMR (128.38 MHz, acetone-d6): δ 37.19. IR
(neat): 3029, 2917, 2846, 1552, 1418, 802, 761 cm−1. HRMS (CI) m/
z: calcd for C17H16BN [M]+ 245.1376, found 245.1382.
1-Benzyl-2-(4-penten-1-yl)-2,1-borazaronaphthalene (9b). Ob-
1
tained as a yellow oil (72 mg, 50%). H NMR (500 MHz, CDCl3):
δ 8.00−7.94 (m, 1H), 7.60 (d, J = 7.5 Hz, 1H), 7.29−7.22 (m, 4H),
7.21−7.16 (m, 1H), 7.12−7.05 (m, 3H), 6.95 (dd, J = 2.1, 11.5 Hz,
1H), 5.88−5.77 (m, 1H), 5.28 (s, 2H), 5.02−4.89 (m, 2H), 2.11 (q, J
= 7.0 Hz, 2H), 1.78−1.70 (m, 2H), 1.34−1.28 (m, 2H). 13C NMR
(125.8 MHz, CDCl3): δ 144.7, 141.7, 139.4, 138.7, 130.3, 128.8, 128.4,
127.0, 126.9, 125.9, 120.5, 116.1, 114.4, 50.6, 37.0, 26.0. 11B NMR
(128.38 MHz, CDCl3): δ 38.94. IR (neat): 2921, 1610, 1415, 759
cm−1. HRMS (CI) m/z: calcd for C20H22BN [M]+ 287.1845, found
287.1841.
2-Benzyl-1-trifluoroethyl-2,1-borazaronaphthalene (9c). Ob-
1
tained as an off-white solid (60 mg, 40%). Mp: 76−78 °C. H NMR
(500 MHz, CDCl3): δ 7.98 (d, J = 11.60 Hz, 1H), 7.57 (d, J = 7.63 Hz,
1H), 7.24 (d, J = 3.97 Hz, 2H), 7.21−7.15 (m, 2H), 7.13 (d, J = 7.02
Hz, 1H), 7.11−7.07 (m, 2H), 7.03−6.98 (m, 1H), 6.95 (d, J = 7.63
Hz, 1H), 5.17 (s, 2H), 2.20 (q, J = 13.4 Hz, 2H). 13C NMR (125.8
MHz, CDCl3): δ 145.9, 141.4, 137.5, 130.6, 129.1, 129.0, 128.9 (q, J =
274 Hz), 127.5, 127.2, 125.6, 121.6, 116.3, 50.1. 11B NMR (128.38
MHz, CDCl3): δ 38.94. IR (neat): 3033, 2956, 2924, 2853, 1249,
1-Butyl-2-phenyl-2,1-borazaronaphthalene (10c). Obtained as a
yellow oil (93 mg, 71%). 1H NMR (500 MHz, CDCl3): δ 8.02 (d, J =
11.3 Hz, 1H), 7.70 (dd, J = 7.7, 1.5 Hz, 1H), 7.63−7.59 (m, 1H),
7.57−7.51 (m, 3H), 7.45−7.40 (m, 2H), 7.39−7.34 (m, 1H), 7.26−
7.21 (m, 1H), 6.89 (d, J = 11.3 Hz, 1H), 4.18−4.12 (m, 2H), 1.82−
1.72 (m, 2H), 1.33−1.23 (m, 2H), 0.84 (t, J = 7.4 Hz, 3H). 13C NMR
K
dx.doi.org/10.1021/jo402616w | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(126 MHz, CDCl3): δ 144.8, 141.1, 132.4, 130.7, 128.6, 127.8, 127.5,
127.4, 120.8, 115.7, 47.8, 32.4, 20.3, 13.9. 11B NMR (128 MHz,
CDCl3): δ 36.35. IR (neat): 2957, 1609, 1551, 1411, 751 cm−1. HRMS
(CI) m/z: calcd for C18H20BN [M]+ 261.1689, found 261.1680.
1,2-Diphenyl-2,1-borazaronaphthalene (10d). Obtained as a tan
solid (56 mg, 40%). Mp: 111−115 °C. 1H NMR (500 MHz, CDCl3):
δ 8.19 (d, J = 11.4 Hz, 1H), 7.74 (dd, J = 1.4, 7.8 Hz, 1H), 7.45−7.40
(m, 2H), 7.39−7.31 (m, 2H), 7.26−7.23 (m, 3H), 7.22−7.14 (m, 6H),
6.97 (d, J = 8.5 Hz, 1H). 13C NMR (125.8 MHz, CDCl3): δ 145.4,
144.0, 142.9, 134.0, 129.9, 129.6, 129.5, 128.4, 127.7, 127.3, 127.2,
126.2, 121.3, 117.8. 11B NMR (128.38 MHz, CDCl3): δ 35.38. IR
(neat): 2921, 1595, 1293, 702 cm−1. HRMS (ESI) m/z: calcd for
C20H17BN [M + H]+ 282.1454, found 282.1455.
1-Benzyl-2-phenyl-6-trifluoromethyl-2,1-borazaronaphthalene
(11a). Obtained as a white solid (116 mg, 64%). Mp: 110−112 °C. 1H
NMR (500 MHz, CDCl3): δ 8.34 (d, J = 11.2 Hz, 1H), 8.18 (s, 1H),
7.69−7.64 (m, 2H), 7.57 (dd, J = 6.2, 3.1 Hz, 2H), 7.36−7.30 (m,
5H), 7.26−7.22 (m, 1H), 7.17−7.14 (m, 3H), 5.58 (s, 2H). 13C NMR
(125.8 MHz, acetone-d6): δ 145.2, 138.6, 132.2, 128.7, 128.2, 128.1,
127.7, 127.4 (q, J = 24 Hz), 127.0, 126.9, 126.5 (q, J = 251 Hz), 125.6,
125.5, 124.5 (q, J = 4 Hz), 118.1, 52.0. 11B NMR (128.38 MHz,
acetone-d6): δ 38.76. IR (neat): 3026, 2925, 2851, 1623, 1326, 1120,
902, 704 cm−1. HRMS (CI) m/z: calcd for C22H17BNF3 [M]+
363.1406, found 363.1397.
6.44 (d, J = 11.5 Hz, 1H), 0.80−0.75 (m, 2H), 0.57−0.55 (m, 2H),
0.32−0.28 (m, 1H). 13C NMR (125.8 MHz, acetone-d6): δ 144.3,
140.1, 128.9, 127.8, 125.0, 119.9, 117.7, 5.4. 11B NMR (128.38 MHz,
acetone-d6): δ 38.06. IR (neat): 3380, 3076, 2998, 1561, 1137, 748
cm−1. HRMS (CI) m/z: calcd for C11H12BN [M]+ 169.1063, found
169.1069.
2-(3-Bromopropyl)-2,1-borazaronaphthalene (12c). Obtained as
1
a white solid (99 mg, 80%). Mp: 65−67 °C. H NMR (500 MHz,
acetone-d6): δ 9.31 (br s, 1H), 8.01 (d, J = 11.5 Hz, 1H), 7.62 (d, J =
7.6 Hz, 1H), 7.50−7.47 (m, 1H), 7.41−7.37 (m, 1H), 7.14−7.10 (m,
1H), 6.8 (d, J = 11.7 Hz, 1H), 3.54−3.51 (m, 2H), 2.18−2.12 (m,
2H), 1.40−1.35 (m, 2H). 13C NMR (125.8 MHz, acetone-d6): δ 144.4,
140.8, 129.0, 127.9, 125.2, 120.3, 118.0, 36.7, 29.7. 11B NMR (128.38
MHz, acetone-d6): δ 37.91. IR (neat): 3362, 3006, 2958, 1559, 809,
760 cm−1. HRMS (CI) m/z: calcd for C11H13BNBr [M]+ 249.0324,
found 249.0317.
2-(3-Iodopropyl)-2,1-borazaronaphthalene (12d). Obtained as a
1
white solid (103 mg, 69%). Mp: 61−63 °C. H NMR (500 MHz,
acetone-d6): δ 9.3 (br s, 1H), 8.0 (d, J = 11.5 Hz, 1H), 7.62 (d, J = 7.8
Hz, 1H), 7.48 (d, J = 8.1 Hz, 1H), 7.41−7.37 (m, 1H), 7.14−7.10 (m,
1H), 6.79 (d, J = 11.5 Hz, 1H), 3.33 (dd, J = 8.0, 7.1 Hz, 2H), 2.15−
2.09 (m, 2H), 1.37−1.34 (m, 2H). 13C NMR (125.8 MHz, acetone-
d6): δ 144.4, 140.8, 129.0, 127.9, 125.2, 120.3, 118.0, 30.6, 10.6. 11B
NMR (128.38 MHz, acetone-d6): δ 37.78. IR (neat): 3363, 2950,
2917, 1558, 1440, 763 cm−1. HRMS (CI) m/z: calcd for C11H13BNI
[M]+ 297.0186, found 297.0174.
1-Benzyl-2-phenyl-5-fluoro-2,1-borazaronaphthalene (11b). Ob-
1
tained as a white solid (117 mg, 73%). Mp: 126−127 °C. H NMR
(500 MHz, acetone-d6): δ 8.43 (d, J = 11.5 Hz, 1H), 7.56 (dd, J = 6.5,
3.1 Hz, 2H), 7.38−7.33 (m, 4H), 7.31−7.26 (m, 3H), 7.23−7.20 (m,
1H), 7.15 (d, J = 7.6 Hz, 2H), 7.09 (d, J = 11.7 Hz, 1H), 6.98 (dd, J =
9.7, 8.2 Hz, 1H), 5.51 (s, 2H). 13C NMR (125.8 MHz, acetone-d6): δ
159.8 (d, J = 246 Hz), 142.3 (d, J = 6.3 Hz), 138.9, 136.0 (d, J = 7.5
Hz), 132.2, 128.7, 128.5 (d, J = 10 Hz), 128.1, 127.7, 126.9, 125.6,
116.4 (d, J = 16 Hz), 113.3 (d, J = 4 Hz), 106.3 (d, J = 21 Hz), 52.3.
11B NMR (128.38 MHz, acetone-d6): δ 38.00. IR (neat): 3016, 2926,
1590, 1405, 1234, 974, 783, 728 cm−1. HRMS (CI) m/z: calcd for
C21H17BNF [M]+ 313.1438, found 313.1431.
2-((E)-1-Propen-1-yl)-2,1-borazaronaphthalene (12e). Obtained
1
as a white solid (44 mg, 52%). Mp: 56−57 °C. H NMR (500 MHz,
acetone-d6): δ 9.23 (br s, 1H), 7.99 (d, J = 11.5 Hz, 1H), 7.59 (d, J =
7.6 Hz, 1H), 7.46−7.43 (m, 1H), 7.39−7.35 (m, 1H), 7.10 (dd, J =
8.3, 7.5 Hz, 1H), 6.98 (d, J = 11.6 Hz, 1H), 6.78−6.71 (m, 1H), 6.09
(d, J = 17.6 Hz, 1H), 1.91−1.90 (m, 3H). 13C NMR (125.8 MHz,
acetone-d6): δ 144.1, 143.6, 141.0, 129.0, 127.9, 125.5, 120.2, 118.0,
21.1. 11B NMR (128.38 MHz, acetone-d6): δ 32.98. IR (neat): 3370,
2846, 1612, 1438, 986, 816, 751 cm−1. HRMS (CI) m/z: calcd for
C11H13BN [M + H]+ 170.1141, found 170.1142.
2-(1-Butynyl)-2,1-borazaronaphthalene (12f). Obtained as a
1-Benzyl-2-phenyl-7-methyl-2,1-borazaronaphthalene (11c).
1
yellow oil that crystallized in the refrigerator (76 mg, 73%). Mp:
Obtained as a white solid (116 mg, 75%). Mp: 91−93 °C. H NMR
1
42−44 °C. H NMR (500 MHz, acetone-d6): δ 9.65 (br s, 1H), 8.05
(500 MHz, acetone-d6): δ 8.14 (d, J = 11.2 Hz, 1H), 7.64 (d, J = 7.8
Hz, 1H), 7.54 (dd, J = 6.5, 3.1 Hz, 2H), 7.32−7.27 (m, 6H), 7.22−
7.19 (m, 1H), 7.15 (d, J = 7.3 Hz, 2H), 7.04 (d, J = 7.8 Hz, 1H), 6.92
(d, J = 11.2 Hz, 1H), 5.47 (s, 2H), 2.28 (s, 3H). 13C NMR (125.8
MHz, acetone-d6): δ 145.2, 141.1, 139.4, 138.6, 132.2, 130.1, 128.6,
127.7, 127.6, 126.7, 125.6, 125.2, 122.4, 117.2, 51.7, 21.2. 11B NMR
(128.38 MHz, acetone-d6): δ 37.99. IR (neat): 3055, 3023, 3005, 2921,
1599, 1349, 963, 830, 699 cm−1. HRMS (CI) m/z: calcd for C22H20BN
[M]+ 309.1689, found 309.1675.
(d, J = 11.2 Hz, 1H), 7.64 (d, J = 7.8 Hz, 1H), 7.56 (d, J = 8.1 Hz,
1H), 7.43 (dd, J = 8.8, 7.7 Hz, 1H), 7.16 (dd, J = 8.0, 7.3 Hz, 1H), 6.79
(d, J = 11.5 Hz, 1H), 2.36 (dd, J = 10.0, 7.0 Hz, 2H), 1.57−1.53 (m,
2H), 1.52−1.44 (m, 2H), 0.94−0.87 (m, 3H). 13C NMR (125.8 MHz,
acetone-d6): δ 144.7, 140.6, 129.0, 128.3, 125.1, 120.8, 118.1, 30.7,
21.6, 19.1, 12.9. 11B NMR (128.38 MHz, acetone-d6): δ 26.72. IR
(neat): 3385, 2931, 2187, 1560, 1174, 808, 760 cm−1. HRMS (CI) m/
z: calcd for C14H17BN [M + H]+ 210.1454, found 210.1462.
2-Phenyl-2,1-borazaronaphthalene (12g).7a Obtained as a white
solid (96 mg, 95%). Mp: 136−138 °C. 1H NMR (500 MHz, acetone-
d6): δ 9.76 (br s, 1H), 8.18 (d, J = 11.7 Hz, 1H), 8.06 (d, J = 7.1 Hz,
2H), 7.70−7.66 (m, 2H), 7.47−7.41 (m, 4H), 7.30 (d, J = 11.6, 1H),
7.18 (dd, J = 10.8, 7.8 Hz, 1H). 13C NMR (125.8 MHz, acetone-d6): δ
145.4, 141.0, 133.0, 129.3, 129.1, 128.2, 127.9, 125.6, 120.7, 118.5. 11B
NMR (128.38 MHz, acetone-d6): δ 34.23. IR (neat): 3380, 2925,
1560, 1440, 1212, 815, 752 cm−1. HRMS (CI) m/z: calcd for
C14H12BN [M]+ 205.1063, found 205.1065.
1-Benzyl-2-phenyl-6,7-dimethoxy-2,1-borazaronaphthalene
(11d). Obtained as a white solid (104 mg, 59%). Mp: 112−115 °C. 1H
NMR (500 MHz, acetone-d6): δ 8.09 (d, J = 11.29 Hz, 1H), 7.60−7.51
(m, 2H), 7.38−7.28 (m, 6H), 7.25−7.17 (m, 3H), 6.95 (s, 1H), 6.83
(d, J = 11.29 Hz, 1H), 5.49 (s, 2H), 3.84 (s, 3H), 3.60 (m, 3H). 13C
NMR (125.8 MHz, acetone-d6): δ 150.9, 145.0, 144.8, 139.7, 136.3,
132.5, 128.8, 127.8, 127.7, 127.0, 126.1, 121.2, 111.5, 101.0, 55.5, 55.1,
52.4. 11B NMR (128.38 MHz, acetone-d6): δ 38.12. IR (neat): 3029,
3004, 2965, 2871, 1546, 1261, 1226, 762, 737 cm−1. HRMS (CI) m/z:
calcd for C23H23BNO2 [M]+ 356.1822, found 356.1820.
2-(4-Methylphenyl)-2,1-borazaronaphthalene (12h). Obtained as
a white solid (102 mg, 93%). Mp: 131−132 °C. 1H NMR (500 MHz,
acetone-d6): δ 9.69 (br s, 1H), 8.15 (d, J = 11.5 Hz, 1H), 7.95 (d, J =
7.8 Hz, 2H), 7.67 (dd, J = 8.8, 7.2 Hz, 2H), 7.45−7.42 (m, 1H), 7.29−
7.25 (m, 3H), 7.17 (dd, J = 8.8, 7.5 Hz, 1H), 2.36 (s, 3H). 13C NMR
(125.8 MHz, acetone-d6): δ 145.1, 141.0, 139.1, 133.1, 129.1, 128.6,
128.2, 125.6, 120.6, 118.5, 20.6. 11B NMR (128.38 MHz, acetone-d6):
δ 34.20. IR (neat): 3380, 3012, 1713, 1561, 1438, 802, 753 cm−1.
HRMS (CI) m/z: calcd for C15H15BN [M + H]+ 220.1298, found
220.1302.
2-Methyl-2,1-borazaronaphthalene (12a).9 Obtained as a white
solid (39 mg, 55%). Mp: 70−71 °C. 1H NMR (500 MHz, acetone-d6):
δ 9.26 (br s, 1H), 7.94 (d, J = 11.2 Hz, 1H), 7.60 (d, J = 7.8 Hz, 1H),
7.46−7.42 (m, 1H), 7.38−7.34 (m, 1H), 7.10 (dd, J = 7.3, 7.0 Hz,
1H), 6.74 (d, J = 11.5 Hz, 1H), 0.69 (s, 3H). 13C NMR (125.8 MHz,
acetone-d6): δ 143.8, 141.0, 128.9, 127.7, 125.0, 120.0, 117.8. 11B
NMR (128.38 MHz, acetone-d6): δ 37.72. IR (neat): 3363, 2931,
1560, 1438, 764, 752 cm−1. HRMS (CI) m/z: calcd for C9H10BN
[M]+ 143.0906, found 143.0895.
2-Cyclopropyl-2,1-borazaronaphthalene (12b). Obtained as a
white solid (41 mg, 52%). Mp: 67−68 °C. 1H NMR (500 MHz,
acetone-d6): δ 9.16 (br s, 1H), 7.91 (d, J = 11.5 Hz, 1H), 7.57−7.55
(m, 1H), 7.43−7.40 (m, 1H), 7.36−7.32 (m, 1H), 7.09−7.05 (m, 1H),
2-(4-Fluorophenyl)-2,1-borazaronaphthalene (12i). Obtained as a
1
white solid (96 mg, 86%). Mp: 131−132 °C. H NMR (500 MHz,
acetone-d6): δ 9.79 (br s, 1H), 8.18 (d, J = 11.5 Hz, 1H), 8.10−8.07
(m, 2H), 7.69 (d, J = 7.8 Hz, 1H), 7.65 (d, J = 8.3 Hz, 1H), 7.45 (dd, J
L
dx.doi.org/10.1021/jo402616w | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
= 8.8, 7.6 Hz, 1H), 7.27 (d, J = 11.5 Hz, 1H), 7.21−7.17 (m, 3H). 13
C
Kohli (University of Pennsylvania) is acknowledged for
obtaining HRMS data.
NMR (125.8 MHz, acetone-d6): δ 164.0 (d, J = 246 Hz), 145.5, 141.0,
135.2 (d, J = 7.5 Hz), 129.1, 128.3, 125.5, 120.7, 118.5, 114.65 (d, J =
20 Hz). 11B NMR (128.38 MHz, acetone-d6): δ 33.86. IR (neat):
3381, 3064, 2924, 1593, 1205, 813, 758 cm−1. HRMS (CI) m/z: calcd
for C14H12BFN [M + H]+ 224.1047, found 224.1050.
REFERENCES
■
(1) For recent reviews of azaborines, see: (a) Liu, Z.; Marder, T. B.
Angew. Chem., Int. Ed. 2008, 47, 242. (b) Campbell, P. G.; Marwitz, A.
J. V.; Liu, S.-Y. Angew. Chem., Int. Ed. 2012, 51, 6074. (c) Bosdet, M. J.
D.; Piers, W. E. Can. J. Chem. 2009, 87, 8.
2-(3-Thiophenyl)-2,1-borazaronaphthalene (12j). Obtained as a
1
white solid (97 mg, 92%). Mp: 154−155 °C. H NMR (500 MHz,
acetone-d6): δ 9.73 (br s, 1H), 8.16−8.12 (m, 2H), 7.75 (d, J = 4.6 Hz,
1H), 7.66 (d, J = 7.8 Hz, 1H), 7.58 (d, J = 8.3 Hz, 1H), 7.53 (dd, J =
4.4, 2.4 Hz, 1H), 7.43 (dd, J = 8.8, 7.3 Hz, 1H), 7.24 (d, J = 11.5 Hz,
1H), 7.16 (dd, J = 9.0, 7.5 Hz, 1H). 13C NMR (125.8 MHz, acetone-
d6): δ 145.2, 141.0, 132.6, 131.2, 129.1, 128.2, 125.5, 125.4, 120.6,
118.3. 11B NMR (128.38 MHz, acetone-d6): δ 31.77. IR (neat): 3379,
2925, 1563, 1058, 1031, 756 cm−1. HRMS (CI) m/z: calcd for
C12H11BNS [M + H]+ 212.0705, found 212.0710.
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2-(4-Dibenzofuryl)-2,1-borazaronaphthalene (12k). Obtained as a
white solid (126 mg, 82%). Mp: 144−146 °C. H NMR (500 MHz,
1
CDCl3): δ 9.53 (br s, 1H), 8.23 (d, J = 11.5 Hz, 1H), 8.16 (d, J = 7.1
Hz, 1H), 8.03 (dd, J = 14.9, 7.6 Hz, 2H), 7.73 (d, J = 7.8 Hz, 2H),
7.55−7.47 (m, 5H), 7.43−7.40 (m, 1H), 7.28−7.25 (m, 1H). 13C
NMR (125.8 MHz, CDCl3): δ 160.2, 155.8, 145.4, 140.2, 133.8, 129.4,
128.3, 127.0, 125.7, 124.0, 123.3, 123.0, 122.8, 122.2, 121.0, 120.7,
118.7, 115.5. 11B NMR (128.38 MHz, CDCl3): δ 33.59. IR (neat):
3392, 2923, 1561, 116, 754, 736, 721 cm−1. HRMS (CI) m/z: calcd for
C20H14BNO [M]+ 295.1168, found 295.1165.
2-(N-Toluenesulfonylpiperidin-4-yl)-2,1-borazaronaphthalene
1
(12l). Obtained as a white solid (31 mg, 17%). Mp: 72−73 °C. H
NMR (500 MHz, CDCl3): δ 8.00 (d, J = 11.5 Hz, 1H), 7.69 (d, J = 8.1
Hz, 1H), 7.66 (s, 1H), 7.60 (d, J = 7.8 Hz, 2H), 7.42−7.40 (m, 1H),
7.35 (d, J = 8.1 Hz, 2H), 7.26−7.24 (m, 1H), 7.17 (dd, J = 8.3, 7.5 Hz,
2H), 6.78 (d, J = 11.5 Hz, 1H), 3.87 (d, J = 11.2 Hz, 2H), 2.46 (s, 3H),
2.34 (dd, J = 12.3, 11.0 Hz, 2H), 1.98−1.90 (m, 2H), 1.79−1.70 (m,
2H), 1.24−1.17 (m, 1H). 13C NMR (125.8 MHz, acetone-d6): δ 145.1,
143.2, 139.7, 133.3, 129.5, 129.3, 128.2, 127.7, 125.3, 121.0, 117.9,
47.6, 28.2, 21.4. 11B NMR (128.38 MHz, acetone-d6): δ 36.96. IR
(neat): 3343, 2915, 1597, 1455, 1108, 1057, 1034, 613 cm−1. HRMS
(ESI) m/z: calcd for C20H24BN2O2S [M]+ 367.1652, found 367.1647.
1-Phenyl-2-methyl-2,1-borazaronaphthalene (13). Obtained as a
white solid (47 mg, 43%). Mp: 59−61 °C. 1H NMR (500 MHz,
CDCl3): δ 7.99 (d, J = 11.6 Hz, 1H), 7.65 (dd, J = 7.6, 1.2 Hz, 1H),
7.55−7.51 (m, 2H), 7.45−7.43 (m, 1H), 7.26−7.24 (m, 1H), 7.18−
7.14 (m, 3H), 6.90 (d, J = 11.3 Hz, 1H), 6.77 (d, J = 8.5 Hz, 1H), 0.48
(s, 3H). 13C NMR (125.8 MHz, acetone-d6): δ 144.3, 144.0, 143.0,
129.7, 129.5, 128.3, 127.9, 127.1, 125.6, 120.5, 116.8. 11B NMR
(128.38 MHz, acetone-d6): δ 36.21. IR (neat): 3002, 2929, 1592, 1490,
1307, 762 cm−1. HRMS (CI) m/z: calcd for C15H14BN [M]+
219.1219, found 219.1219.
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ASSOCIATED CONTENT
■
S
* Supporting Information
1
Copies of H, 13C, and 11B NMR spectra for all compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: gmolandr@sas.upenn.edu.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Dr. Lauren Monovich (Novartis Institutes for
Biomedical Research, Inc.) for providing the inspiration for this
research, which was supported by the NIGMS (R01 GM-
081376). Frontier Scientific is acknowledged for their generous
donation of potassium organotrifluoroborates. Dr. Rakesh
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