Metal-Free Synthesis of N-Aryl-Substituted Azacycles from Cyclic Ethers Using POCl3

Article abstract of DOI:10.1021/acs.joc.9b00377

A facile method for the synthesis of N-aryl-substituted azacycles from arylamines and cyclic ethers has been developed. In this study, arylamines were treated with cyclic ethers in the presence of POCl₃ and DBU to provide five- A nd six-membered azacycles. Using this method, various azacycloalkanes, isoindolines, and tetrahydroisoquinolines were prepared in high yields. This synthetic method offers an efficient approach to the production of azacycles from cyclic ethers.

Full text of DOI:10.1021/acs.joc.9b00377

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Article
Metal-Free Synthesis of N-Aryl-Substituted
3
Azacycles from Cyclic Ethers using POCl
Minh Thanh La, Soosung Kang, and Hee-Kwon Kim
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00377 • Publication Date (Web): 30 Apr 2019
Downloaded from http://pubs.acs.org on May 1, 2019
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Metal-Free Synthesis of N-Aryl-Substituted Azacycles from
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Cyclic Ethers using POCl3
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,†,‡
Minh Thanh La†, Soosung Kang§, and Hee-Kwon Kim*
†Department of Nuclear Medicine, Molecular Imaging & Therapeutic Medicine Research Center,
Chonbuk National University Medical School and Hospital, Jeonju, 54907, Republic of Korea
‡Research Institute of Clinical Medicine of Chonbuk National University-Biomedical Research
Institute of Chonbuk National University Hospital, Jeonju, 54907, Republic of Korea
§College of Pharmacy and Graduate School of Pharmaceutical Sciences, Ewha Womans
University, Seoul 03760, Republic of Korea
Corresponding author: Hee-Kwon Kim.
* Corresponding author.
Tel: +82 63 250 2768; Fax: +82 63 255 1172.
E-mail address: hkkim717@jbnu.ac.kr (H-K Kim).
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GRAPHICAL ABSTRACT
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ABSTRACT
A facile method for the synthesis of N-aryl substituted azacycles from arylamines and cyclic
ethers has been developed. In this study, arylamines were treated with cyclic ethers in the
presence of POCl3 and DBU to provide five- and six-membered azacycles. Using this method,
various azacycloalkanes, isoindolines, and tetrahydroisoquinolines were prepared in high yields.
This synthetic method offers an efficient approach to the production of azacycles from cyclic
ethers.
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INTRODUCTION
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The development of novel synthetic methods for N-substituted azacycles is an important topic
in organic and medicinal chemistry; this is because these motifs possess valuable properties as
building blocks for structures of complex biomolecules, and N-substituted azacycles are present
in many pharmaceuticals as well as organic materials.1 Thus, azacycle structures have received
much attention in the drug discovery and materials industries. In particular, it was reported that
several novel drugs recently approved by the FDA contain an N-substituted azacycle moiety
(Figure 1).2.
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F
F
H2N
N
O
H
N
C
N
O
N
O
N
NH
Cl
O
N
N
N
N
NH
O
N
O
N
F
Gilteritinib (approved in 2018)
Ivosidenib (approved in 2018)
Figure 1. FDA approved drugs containing azacycles
Due to a variety of applications involving azacycle structures, several synthetic methods were
reported to prepare N-substituted azacycle compounds: the reaction of primary arylamines with
dihalides or diols,3 reduction of tertiary lactams or azacyclodienes formed by cyclocondensation
between dicarbonyl compounds and an amine,4 and a cross-coupling reaction of N-unsubstituted
azacycles and aryl halides.5 An intramolecular C(sp3)-N coupling reaction was also reported to
prepare N-substituted azacycles.6 The reaction of a primary amine with cyclic ethers to prepare
azacycles is an attractive method, as water is the co-product formed during condensation. Several
protocols using arylamines and cyclic ethers have been described; the first method to synthesize
N-phenylpyrollidine was the reaction of tetrahydrofuran and aniline, using activated alumina at
400 °C.7 Other metal-based approaches have been utilized for the synthesis of N-substituted
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azacycles, including Al2O3, AlCl3, TiCl4 or AlMe3.8 Recently, several methods were developed
using non-metal catalysts. Zhang and co-workers employed B(C6F5)3 and pTSA.H2O to
synthesize N-substituted azacycles via a frustrated Lewis pairs pathway.9 Other metal-free
protocols using HI or BF3.Et2O were also developed.10 However, these methods employ acid or
Lewis acid catalysts that may be incompatible with acid-sensitive functional groups. To
overcome the issues of previously reported azacycle syntheses, herein we report a metal-free and
efficient base-mediated synthesis of five- or six-membered ring azacycle compounds (Scheme
1).
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Previous studies:
- N,N-dialkylation of arylamine using dihalides or diol
NH2
N
n
X-(CH2)n-X
+
X = Cl, Br, I, OH
- Metal-based N-hetero-cyclization of arylamine
R2
NH2
metal-based reagents
R1
metal-based reagents = Al2O3, AlCl3, TiO2, TiCl4, AlMe3
R2
O
N
+
R1
n
n
- Metal-free N-hetero-cyclization of arylamine in acidic condition
R2
NH2
reagents
R2
O
N
+
R1
n
R1
n
reagents = B(C6F5)3 in pTSA.H2O, HI
This work:
R2
Metal-free N-hetero-cyclization of arylamine
NH2
POCl3
DBU
N
R2
O
n
+
R1
R1
n
Scheme 1. Synthesis of N-substituted azacycles.
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RESULTS AND DISCUSSION
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Synthetic chemistry of target products utilizing metal-free methods is a highly desirable green
methodology. For the development of a novel metal-free reaction, phosphoramidates can be
attractive intermediates for the preparation of target products since they are known precursors
that have been practically used to synthesize amines, imines, and heterocycles such as
aziridines.11 Thus, we envisioned that a synthesis of azacycles utilizing phosphoramidic
dichloride intermediates starting from amines would be realizable, and we hypothesized that
reactions of amines with POCl3 could be employed for in situ generation of phosphoramidic
dichloride, which are active intermediates leading to azacycles. Such utilization of this base
reaction system could be a novel approach to prepare N-unsubstituted azacycles. To test our
hypothesis, aniline was selected as a model substrate in the initial study. Reaction with
tetrahydrofuran (THF) was performed in xylene at 110 °C for 15 h, and the yield of the
corresponding azacycle was investigated. First, reactions with a series of Lewis acids including
CuCl2, FeCl3, ZnCl2, ZrCl4, and BiCl2 were surveyed. However, the product was not obtained in
most of the experiments (Table 1). When SnCl2 was employed, the product was obtained in low
yield. In addition, treatment with CaI2, or CaBr2 did not produce the azacycle. In this study,
POCl3 were employed for the synthesis of N-aryl substituted azacycle, and it was found that the
reaction with POCl3 provided the target azacycle with an improved yield (35%). Next, we
investigated the base effect on the synthesis of N-substituted azacycles. Employment of K2CO3,
NaHCO3, triethylamine, 4-dimethylaminopyridine (DMAP), KOH, and NaOH resulted in low
yields of azacycles. When Cs2CO3 was used as a base, the yield of azacycle increased to 70%,
but was still unsatisfactory. However, when DBU was used in the reaction, the desired azacycle
was prepared in significantly increased yield (95%). Screening of solvents was also performed to
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further optimize the reaction conditions. Reactions in MeCN, DMF, and DCE resulted in no
reaction. When toluene and PhCF3 were used as the reaction solvent, the yield of the azacycle
was enhanced to 44% and 45%, respectively. When xylene was employed in the reaction, the
yield of the corresponding azacycle increased significantly (95%).
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Table 1. Screening of reaction conditions for the preparation of azacyclesa.
NH2
Reagents,
Base
O
N
+
Solvent
110 oC, 15 h
1a
2a
3a
Entry
1
Reagents
CuCl2
FeCl3
ZnCl2
ZrCl4
Base
Solvent
Yieldb (%)
NRc
NRc
NRc
NRc
NRc
NRc
24
-
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
xylene
2
-
3
-
4
-
5
BiCl2
-
6
MnCl2
SnCl2
CaI2
-
7
-
8
-
NRc
NRc
35
9
CaBr2
POCl3
POCl3
POCl3
POCl3
POCl3
-
10
11
12
13
14
-
K2CO3
CsCO3
NaHCO3
Et3N
44
70
41
42
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24d
25e
POCl3
POCl3
POCl3
POCl3
POCl3
POCl3
POCl3
POCl3
POCl3
POCl3
POCl3
DMAP
KOH
NaOH
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
xylene
xylene
xylene
xylene
toluene
PhCF3
MeCN
DMF
NRc
23
22
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95
44
45
NRc
NRc
NRc
91
DCE
xylene
xylene
88
a Reaction conditions: compound 1a (1 mmol), THF 2a (20 mmol), reagents (1.5 mmol), Base (2
o
b
mmol), solvent (3 mL), 110 C, 15 h; Isolated yield after purification of flash column
c
d
chromatography; No reaction; compound 1a (1 mmol), THF 2a (10 mmol), POCl3 (1.5
o
e
mmol), DBU (2 mmol), xylene (3 mL), 110 C, 15 h; compound 1a (1 mmol), THF 2a (5
mmol), POCl3 (1.5 mmol), DBU (2 mmol), xylene (3 mL), 110 oC, 15 h
To better understand the effect of reagents and base on the reaction, reactions of aniline with a
series of equivalents of POCl3 and DBU were performed to produce the desired azacycle (see
Table S1 in supporting information). The reaction results indicated that the highest yield of
azacycle was observed in the presence of 1.5 equiv. of POCl3 and 2.0 equiv. of DBU (95%), but
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further addition of POCl3 and DBU did not enhance the yield. In addition, we further investigated
the use of different amounts of THF in the synthesis of azacycle. The yield of azacycle product
increased in proportion to the amount of reagent (88% for 5 equiv. of THF and 91% for 10 equiv.
of THF). In particular, employment of 20 equiv. of THF produced the target azacycle in high
yield, although there was no significant difference in yield between employment of 20 equiv., 30
equiv., and 40 equiv. of THF.
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With optimized reaction conditions in hand, the scope of this protocol for the synthesis of
azacycles from arylamines and cyclic ethers was explored (Scheme 2). Most of the target
azacycles were prepared in high yields via treatment of various arylamines with cyclic ethers.
The synthesis of azacycles from arylamines and cyclic ethers was not significantly influenced by
the electronic properties of substituents on the aromatic ring. Arylamines bearing electron-
donating groups (methyl-, methoxyl-) and electron-withdrawing groups (nitro-, chloro-, fluoro-)
reacted well with cyclic ethers under the optimal reaction conditions, yielding the desired N-aryl-
substituted azacycles in high yields (Scheme 2, 3b-j). Naphthylamine, 3,4-
(methylenedioxy)amine, and 1,4-benzodioxan-6-amine were also employed with
tetrahydrofuran, affording the corresponding azacycles in 92%, 82%, and 80% yield,
respectively (Scheme 2, 3k-m). Besides, N,N-dimethyl-p-phenylenediamine bearing a nitrogen
and 2-aminopyridine, a hetrocyclic amine, were used with tetrahydrofuran, yielding the
corresponding azacycles in 76%, and 55% yield, respectively (Scheme 2, 3n-o). It was
noteworthy that mono-substitution of the aniline such as p-t-Bu-substituted arylamine did not
result in a big difference from that of aniline in the reaction. However, the reaction of 3,5- and
2,6-disubstituted anilines provided the desired products in lower yields (Scheme 2, 3e-f). The
tolerance of different cyclic ethers was also explored. Even though 2-methyltetrahydrofuran is
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more sterically hindered than THF, it successfully reacted with various aryl amines (such as
aniline, amines containing electron-donating and electron-withdrawing groups, and
naphthylamine) to yield the corresponding products in high yields (Scheme 2, 3p-s). In addition,
tetrahydropyran, a six-membered cyclic ether, and oxepane, a seven-membered cyclic ether,
were employed for the synthesis of azacycles, and the yields were somewhat lower (Scheme 2,
3t-u). 1,4-Dioxane, a heterocyclic compounds, was also used to react with tetrahydrofuran,
giving the corresponding azacycles in 57% yield (Scheme 2, 3v).
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Scheme 2. Scope of synthesis of azacycloalkanesa
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9
R2
POCl3
DBU
NH2
N
R2
O
R1
n
+
R1
110 oC, 15 h
n
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n = 1, 2, 3
3
2
1
N
N
N
MeO
N
N
3b, 91%
3c, 90%
3a, 95%
3d, 93%
3e, 78%
F
N
N
N
Cl
N
N
O2N
F
F
3j, 90%
3i, 92%
3g, 84%
3h, 91%
3f, 63%
N
O
O
N
N
N
N
O
O
N
N
3k, 92%
3o, 55%
3l, 82%
3m, 80%
3n, 76%
N
N
N
N
N
Cl
3q, 90%
3p, 93%
3t, 65%
3r, 85%
3s, 83%
O
N
N
3u, 63%
3v, 57%
a
Reaction conditions: compound 1 (1 mmol), cyclic ethers 2 (20 mmol), POCl3 (1.5 mmol),
DBU (2 mmol), xylene (3 mL), 110 °C, 15 h
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From these positive synthesis results, the scope of utilizing POCl3 was extended to the synthesis
of nitrogen-containing fused heterocyclic ring materials from arylamines. In particular,
tetrahydroisoquinolines and isoindolines are important azacycle motifs in many biological active
pharmaceuticals and natural products.12 The treatment of aniline with phthalan readily resulted in
successful synthesis of the corresponding azacycle in 93% yield (Scheme 3, 5a). Furthermore,
the electronic effect of substituents on the aryl amine was not significantly different from those
shown in Scheme 3. The reaction of various arylamines bearing electron-donating groups or
electron-withdrawing groups with phthalan also produced the corresponding isoindolines in
satisfactory yields (Scheme 3, 5b-e). In addition, the reaction of arylamines with isochroman
under the same reaction conditions produced tetrahydroisoquinolines in high yields (Scheme 3,
5f-i). These results suggest that POCl3 and DBU could serve as an important reagent combination
for the efficient conversion of arylamines to N-aryl substituted five- and six-membered
azacycles.
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Scheme 3. Scope of synthesis of isoindolines and tetrahydroisoquinolinesa
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8
9
POCl3
NH2
R1
DBU
N
O
R1
+
110 oC, 15 h
n
n
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n = 1, 2
5
1
4
N
Cl
N
N
5a, 93%
5c, 93%
5b, 94%
O2N
N
N
N
5d, 92%
5f, 65%
5e, 83%
Cl
F
F
N
N
N
5g, 88%
5h, 85%
5i, 83%
a
Reaction conditions: compound 1 (1 mmol), cyclic ethers 4 (1.5 mmol), POCl3 (1.5 mmol),
DBU (2 mmol), xylene (3 mL), 110 °C, 15 h
To gain a mechanistic insight into this method, control experiments were performed. When
POCl3 and DBU were employed, the reaction successfully produced phosphoramidic dichloride
6, while employment of POCl3 alone or employment of DBU alone did not yield the
phosphoramidic dichloride. Besides, the controlled experiment using the prepared
phosphoramidic dichloride was performed. It was found that the reaction of the prepared
phosphoramidic dichloride 6 with THF under the same condition produced the corresponding
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product successfully. Thus, a plausible reaction pathway based on our results can be proposed, as
shown in Scheme 4. The initial addition of POCl3 and DBU to arylamine 1 probably affords
phosphoramidic dichloride 6. Then, THF reacts with phosphoramidic dichloride 6 to provide 7.
Intramolecular attack of the nitrogen on the carbon near phosphorus atom gives the desired
product, 1-phenyl-pyrrolidine 3a.
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O
P
H
N
H
NH2
Cl
Cl
O
POCl3
N
P
O
Cl
Cl
O
DBU
DBU HCl
7
1a
6
Cl
Cl
P
O
H
N
N
O
3a
8
Scheme 4. Proposed reaction mechanism for N-heterocyclization from arylamine.
CONCLUSION
In summary, a novel metal-free method for the synthesis of N‑aryl-substituted azacycles from
arylamines and cyclic ethers has been developed. In the present study, the combination of POCl3
and DBU is crucial to produce the desired products. Using this method, N-aryl substituted five-
and six-membered azacycles were prepared in high yields. Moreover, the reaction protocol is
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simple and efficient. We expect that this novel method will be useful for the synthesis of a
variety of five- and six-membered azacycles from cyclic ethers.
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Experimental section
General Information
All reactions were performed in 20-mL vials with Teflon caps. Commercial chemicals and
solvents were used without any purification. Reaction progress was analyzed by thin-layer
chromatography (TLC) using silica gel 60 F254 pre-coated aluminum plate from Merck and
TLC spots were observed under UV light (254nm) exposure. Flash chromatography was carried
out using 230–400 mesh silica gel and analytical grade solvents. Stuart SMP10 Melting Point
Apparatus was used to record melting points of products. Structure elucidation by NMR (1H and
13C NMR) was performed on Bruker Avance 400 MHz spectrometer. The chemical shifts were
reported in δ units (ppm) relative to the residual protonated solvent resonance, the coupling
constants (J) quoted in Hz, and multiplicity of signals was abbreviated as follows: singlet (s);
doublet (d); doublet of doublet (dd); triplet (t); multiplet (m). The high resolution mass spectra
(HRMS) were analyzed on 6200 series TOF/6500 series Q-TOF B.08.00.
General procedure of the synthesis of azacyles 3a-3r
To a 20 mL vial containing a stirring mixture of aniline (1a) (0.093 g, 1.00 mmol) and DBU
(0.304 g, 2.00 mmol) in xylene (3 mL) was added dropwise POCl3 (0.230 g, 1.50 mmol) at room
temperature. The mixture was then heated at 90 °C for 15 min. Tetrahydrofuran (1.6 mL, 20
mmol) were added to the reaction mixture and the vial was closed tightly with Teflon cap. The
reaction mixture was allowed to heat at 110 °C for 15 h. The reaction was cooled down to the
ambient temperature, then saturated aqueous NaHCO3 (10 mL) and brine (10mL) were added to
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the mixture. The aqueous mixture was extracted with Et2O and the organic layer was dried over
anhydrous sodium sulfate and subsequently concentrated under reduced pressure. The crude
product was then purified by flash column chromatography on silica gel with 2% diethyl ether in
n-hexane as eluent to afford the desired product 3a (0.140 g, 95% yield).
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1-phenylpyrrolidine (3a).8e Light yellow oil (0.140 g, 95% yield); 1H NMR (400 MHz, CDCl3) δ
7.29 (t, J = 7.2 Hz, 2H), 6.72 (t, J = 7.2 Hz, 1H), 6.63 (d, J = 8.0 Hz, 2H), 3.39-3.29 (m, 4H),
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2.11-2.00 (m, 4H); C NMR (100 MHz, CDCl3) δ 148.0, 129.1 (2C), 115.4, 111.7 (2C), 47.6
(2C), 25.5 (2C); HRMS (ESI) m/z (M+H)+ calcd for C10H14N = 148.1126; found 148.1129..
1-p-tolylpyrrolidine (3b).8e White solid (0.147 g, 91% yield); m.p. 41-43 °C; 1H NMR (400 MHz,
CDCl3) δ 7.09 (d, J = 8.0 Hz, 2H), 6.56 (d, J = 8.0 Hz, 2H), 3.35-3.25 (m, 4H), 2.31 (s, 3H),
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2.10-2.00 (m, 4H); C NMR (100 MHz, CDCl3) δ 146.1, 129.6 (2C), 124.5, 111.8 (2C), 47.9
(2C), 25.4 (2C), 20.3; HRMS (ESI) m/z (M+H)+ calcd for C11H16N = 162.1283; found 162.1285.
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1-(3-methoxyphenyl)pyrrolidine (3c).8e Colorless oil (0.160 g, 90% yield); H NMR (400 MHz,
CDCl3) δ 7.17 (t, J = 8.0 Hz, 1H), 6.27 (dd, J = 8.0 Hz, 2.0 Hz, 1H), 6.24 (dd, J = 8.0 Hz, 2.0 Hz,
1H), 6.16 (t, J = 2.0 Hz, 1H), 3.84 (s, 3H), 3.35-3.26 (m, 4H), 2.07-2.00 (m, 4H); 13C NMR (100
MHz, CDCl3) δ 160.7, 149.3, 129.8, 104.9, 100.5, 97.9, 55.1, 47.7 (2C), 25.5 (2C); HRMS (ESI)
m/z (M+H)+ calcd for C11H16NO = 178.1232; found 178.1237.
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1-(4-tert-butylphenyl)pyrrolidine (3d).9 White solid (0.189 g, 93% yield); m.p. 40-42 °C; H
NMR (400 MHz, CDCl3) δ 7.30 (d, J = 8.8 Hz, 2H), 6.58 (d, J = 8.8 Hz, 2H), 3.35-3.27 (m, 4H),
2.05-2.00 (m, 4H), 1.34 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 145.9, 137.9, 125.9 (2C), 111.3
(2C), 47.7 (2C), 33.7, 31.6 (3C), 25.5 (2C); HRMS (ESI) m/z (M+H)+ calcd for C14H22N =
204.1752; found 204.1751..
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1-(3,5-dimethylphenyl)pyrrolidine (3e).13 Colorless oil (0.137 g, 78% yield); 1H NMR (400 MHz,
CDCl3) δ 6.38 (s, 1H), 6.26 (s, 2H), 3.35-3.29 (m, 4H), 2.32 (s, 6H), 2.05-1.97 (m, 4H); 13C
NMR (100 MHz, CDCl3) δ 148.2, 138.7 (2C), 117.5, 109.7 (2C), 47.6 (2C), 25.5 (2C), 21.7 (2C);
HRMS (ESI) m/z (M+H)+ calcd for C12H18N = 176.1439; found 176.1441..
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1-(2,6-diisopropylphenyl)pyrrolidine (3f).9 Colorless oil (0.146 g, 63% yield); H NMR (400
MHz, CDCl3) δ 7.23 (t, J = 7.2 Hz, 1H), 7.15 (d, J = 7.2 Hz, 2H), 3.36-3.20 (m, 6H), 2.11-2.00
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(m, 4H), 1.25 (d, J = 6.0 Hz, 12H); C NMR (100 MHz, CDCl3) δ 150.1, 142.9, 126.3 (2C),
123.9 (2C), 52.8 (2C), 28.0 (2C), 26.6 (2C), 24.5 (4C); HRMS (ESI) m/z (M+H)+ calcd for
C16H26N = 232.2065; found 232.2067.
1-(4-nitrophenyl)pyrrolidine (3g).9 Yellow solid (0.162 g, 84% yield); m.p. 167-169 °C; H
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NMR (400 MHz, CDCl3) δ 8.13 (d, J = 9.2 Hz, 2H), 6.49 (d, J = 9.2 Hz, 2H), 3.37-3.29 (m, 4H),
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2.15-2.05 (m, 4H); C NMR (100 MHz, CDCl3) δ 151.9, 136.6, 126.3 (2C), 110.4 (2C), 47.9
(2C), 25.4 (2C); HRMS (ESI) m/z (M+H)+ calcd for C10H13N2O2 = 193.0977; found 193.0978..
1-(3-chlorophenyl)pyrrolidine (3h).9 Colorless oil (0.165 g, 91% yield); H NMR (400 MHz,
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CDCl3) δ 7.14 (t, J = 8.0 Hz, 1H), 6.64 (dd, J = 7.6 Hz, 1.2 Hz, 1H), 6.55 (t, J = 2.0 Hz, 1H),
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6.45 (dd, J = 8.4 Hz, 2.0 Hz, 1H), 3.32-3.25 (m, 4H), 2.07-2.00 (m, 4H); C NMR (100 MHz,
CDCl3) δ 148.8, 134.9, 130.0, 115.1, 111.4, 109.8, 47.6 (2C), 25.4 (2C); HRMS (ESI) m/z
(M+H)+ calcd for C10H13ClN = 182.0737; found 182.0736.
1-(4-fluorophenyl)pyrrolidine (3i).8e Colorless oil (0.153 g, 92% yield); H NMR (400 MHz,
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CDCl3) δ 7.03-6.93 (m, 2H), 6.55-6.47 (m, 2H), 3.33-3.20 (m, 4H), 2.10-2.00 (m, 4H); 13C NMR
(100 MHz, CDCl3) δ 156.0&153.6 (d, 1JC-F = 231.8 Hz, 1C), 144.8, 115.5&115.3 (d, 2JC-F = 21.9
Hz, 2C), 112.1&112.0 (d, 3JC-F = 4.6 Hz, 2C), 48.1 (2C), 25.5 (2C); HRMS (ESI) m/z (M+H)+
calcd for C10H13FN = 166.1032; found 166.1037.
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1-(2,4-difluorophenyl)pyrrolidine (3j).8e Colorless oil (0.166 g, 90% yield); 1H NMR (400 MHz,
CDCl3) δ 6.85-6.72 (m, 2H), 6.70-6.59 (m, 1H), 3.30-3.20 (m, 4H), 2.07-1.90 (m, 4H); 13C NMR
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(100 MHz, CDCl3) δ 156.0-153.5 (dd, JC-F = 238.3 Hz, 3JC-F = 12.4 Hz, 1C), 153.1-150.5 (dd,
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1JC-F = 243.4 Hz, 3JC-F = 10.9 Hz, 1C), 134.3, 115.2, 110.5&110.3 (d, 2JC-F = 18.2 Hz, 1C), 104.7-
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104.2 (t, JC-F = 25.5 Hz, 1C), 50.0 (2C), 25.0 (2C); HRMS (ESI) m/z (M+H)+ calcd for
C10H12F2N = 184.0938; found 184.0940.
1-(naphthalen-1-yl)pyrrolidine (3k).8e Light yellow oil (0.182 g, 92% yield); 1H NMR (400 MHz,
CDCl3) δ 8.29-8.22 (m, 1H), 7.88-7.82 (m, 1H), 7.52-7.45 (m, 3H), 7.40 (t, J = 7.6 Hz, 1H), 7.01
(d, J = 7.6 Hz, 1H), 3.48-3.38 (m, 4H), 2.12-2.02 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 147.7,
135.0, 128.3, 128.2, 125.9, 125.5, 124.8, 124.3, 121.3, 111.4, 52.7 (2C), 24.8 (2C); HRMS (ESI)
m/z (M+H)+ calcd for C14H16N = 198.1283; found 198.1284.
1-(benzo[d][1,3]dioxol-5-yl)pyrrolidine (3l).14 Light yellow solid (0.157 g, 82% yield); m.p. 68-
70 °C; 1H NMR (400 MHz, CDCl3) δ 6.74 (d, J = 8.4 Hz, 1H), 6.25 (d, J = 1.6 Hz, 1H), 5.99 (d,
J = 7.2 Hz, 1H), 5.87 (s, 2H), 3.30-3.20 (m, 4H), 2.07-1.97 (m, 4H); 13C NMR (100 MHz, CDCl3)
δ 148.3, 144.5, 138.1, 108.7, 103.0, 100.4, 94.5, 48.4 (2C), 25.4 (2C); HRMS (ESI) m/z (M+H)+
calcd for C11H14NO2 = 192.1025; found 192.1028.
1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)pyrrolidine (3m).15 Yellowish oil (0.165 g, 80% yield);
1H NMR (400 MHz, CDCl3) δ 6.79 (dd, J = 9.2 Hz, J = 3.2 Hz, 1H), 6.14 (d, J = 6.8 Hz, 2H),
4.28 – 4.20 (m, 4H), 3.22(t, J = 6.8 Hz, 4H), 2.01 -1.96 (m, 4H); 13C NMR (100 MHz, CDCl3) δ
143.94, 143.73, 117.51, 105.42, 105.23, 100.36, 64.86, 64.24, 48.14 (2C), 25.38 (2C); HRMS
(ESI) m/z (M+H)+ calcd for C12H16NO2 = 206.1181; found 206.1182.
N,N-dimethyl-4-(pyrrolidin-1-yl)aniline (3n).16 White solid (0.145 g, 76% yield); m.p. 68-70 °C
1H NMR (400 MHz, (CD3)2CO) δ 6.73 (d, J = 8.8 Hz, 2H), 6.49 (d, J = 8.5 Hz, 2H), 3.30-3.00
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(m, 4H), 2.75 (s, 6H), 1.97-1.91 (m, 4H); 13C NMR (100 MHz, (CD3)2CO) δ 142.84, 141.74,
115.69 (2C), 112.71 (2C), 47.85 (2C), 41.50 (2C), 24.95 (2C); HRMS (ESI) m/z (M+H)+ calcd
for C12H19N2 = 191.1548; found 191.1547.
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2-(pyrrolidin-1-yl)pyridine (3o).17 Yellow oil (0.082 g, 55% yield); 1H NMR (400 MHz, CDCl3)
δ 8.17 (d, J = 4.8 Hz, 1H), 7.48-7.41 (m, 1H), 6.52 (t, J = 6.0 Hz, 1H), 6.36 (d, J = 8.4 Hz, 1H),
3.50-3.40 (m, 4H), 2.09-2.00 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 157.2, 148.1, 136.9, 111.0,
106.5, 46.6 (2C), 25.5 (2C); HRMS (ESI) m/z (M+H)+ calcd for C9H13N2 = 149.1079; found
149.1080.
2-methyl-1-phenylpyrrolidine (3p).8e Light yellow oil (0.151 g, 93% yield); 1H NMR (400 MHz,
CDCl3) δ 7.30-7.23 (m, 2H), 6.84 (t, J = 8.8 Hz, 1H), 6.63 (d, J = 8.0 Hz, 2H), 3.96-3.87 (m, 1H),
3.51-3.43 (m, 1H), 3.25-3.16 (m, 1H), 2.19-1.97 (m, 3H), 1.79-1.70 (m, 1H), 1.22 (d, J = 6.4 Hz,
3H); 13C NMR (100 MHz, CDCl3) δ 147.2, 129.2 (2C), 115.1, 111.8 (2C), 53.6, 48.2, 33.1, 23.3,
19.4; HRMS (ESI) m/z (M+H)+ calcd for C11H16N = 162.1283; found 162.1285.
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2-methyl-1-p-tolylpyrrolidine (3q).8e Colorless oil (0.159 g, 90% yield); H NMR (400 MHz,
CDCl3) δ 7.06 (d, J = 6.4 Hz, 2H), 6.55 (d, J = 6.0 Hz, 2H), 3.90-3.80 (m, 1H), 3.47-3.38 (m,
1H), 3.23-3.10 (m, 1H), 2.28 (s, 3H), 2.15-1.95 (m, 3H), 1.75-1.65 (m, 1H), 1.20 (d, J = 5.6 Hz,
3H); 13C NMR (100 MHz, CDCl3) δ 145.3, 129.7 (2C), 124.2, 111.9 (2C), 53.7, 48.5, 33.2, 23.4,
20.3, 19.5; HRMS (ESI) m/z (M+H)+ calcd for C12H18N = 176.1439; found 176.1438.
1-(4-chlorophenyl)-2-methylpyrrolidine (3r).9 White solid (0.167 g, 85% yield); m.p. 41-43 °C;
1H NMR (400 MHz, CDCl3) δ 7.15 (d, J = 8.8 Hz, 2H), 6.51 (t, J = 6.0 Hz, 2H), 3.90-3.80 (m,
1H), 3.47-3.38 (m, 1H), 3.23-3.10 (m, 1H), 2.28 (s, 3H), 2.15-1.95 (m, 3H), 1.75-1.65 (m, 1H),
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1.20 (d, J = 5.6 Hz, 3H); C NMR (100 MHz, CDCl3) δ 145.7, 128.9 (2C), 119.9, 112.8 (2C),
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53.8, 48.3, 33.1, 23.3, 19.1; HRMS (ESI) m/z (M+H)+ calcd for C11H15ClN = 196.0893; found
196.0894.
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2-methyl-1-(naphthalen-1-yl)pyrrolidine (3s).18 Light yellow oil (0.176 g, 83% yield); H NMR
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(400 MHz, CDCl3) δ 8.30-8.25 (m, 1H), 7.88-7.82 (m, 1H), 7.55-7.40 (m, 4H), 7.07 (t, J = 7.6
Hz, 1H), 3.92-3.75 (m, 2H), 3.00-2.90 (m, 1H), 2.32-2.13 (m, 1H), 2.10-2.00 (m, 1H), 1.95-1.82
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(m, 1H), 1.80-1.70 (m, 1H), 1.11 (d, J = 5.6 Hz, 3H); C NMR (100 MHz, CDCl3) δ 146.9,
134.8, 130.1, 128.1, 125.8, 125.6, 124.7, 124.5, 122.0, 114.1, 55.7, 55.4, 33.6, 23.5, 18.7; HRMS
(ESI) m/z (M+H)+ calcd for C15H18N = 212.1439; found 212.1437.
1-phenylpiperidine (3t).9 Colorless oil (0.105 g, 65% yield); 1H NMR (400 MHz, CDCl3) δ 7.33-
7.24 (m, 2H), 6.98 (d, J = 7.6 Hz, 2H), 6.86 (t, J = 7.2 Hz, 1H), 3.30-3.15 (m, 4H), 1.85-1.72 (m,
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4H), 1.68-1.55 (m, 2H); C NMR (100 MHz, CDCl3) δ 152.3, 129.0 (2C), 119.2, 116.6 (2C),
50.7 (2C), 25.9 (2C), 24.3; HRMS (ESI) m/z (M+H)+ calcd for C11H16N = 162.1283; found
162.1283.
1-phenylazepane (3u).19 Light yellow oil (0.111 g, 63% yield); 1H NMR (400 MHz, CDCl3) δ
7.28-7.20 (m, 2H), 6.72 (d, J = 8.0 Hz, 2H), 6.64 (t, J = 7.2 Hz, 1H), 3.47 (t, J = 9.2 Hz, 4H),
1.85- 1.75 (m, 4H), 1.59 -1.55 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 148.86, 129.24 (2C),
115.08, 111.17 (2C), 49.04 (2C), 27.79 (2C), 27.17 (2C); HRMS (ESI) m/z (M+H)+ calcd for
C12H18N = 176.1439; found 176.1440.
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4-phenylmorpholine (3v).20 Light brown solid (0.093 g, 57% yield); m.p. 52-54 °C; H NMR
(400 MHz, CDCl3) δ 7.38-7.28 (m, 2H), 7.03-6.90 (m, 3H), 3.90 (t, J = 4.4 Hz, 4H), 3.19 (t, J =
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4.8 Hz, 4H); C NMR (100 MHz, CDCl3) δ 151.2, 129.2 (2C), 120.1, 115.7 (2C), 67.0 (2C),
49.4 (2C); HRMS (ESI) m/z (M+H)+ calcd for C10H14NO = 164.1075; found 164.1078.
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General procedure of the synthesis of azacyles 5a-5e
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To a 20 mL vial containing a stirring mixture of aniline (1a) (0.093 g, 1.00 mmol) and DBU
(0.304 g, 2.00 mmol) in xylene (3 mL) was added dropwise POCl3 (0.230 g, 1.50 mmol) at room
temperature. The mixture was then heated at 90 °C for 15 min. Phthalan (0.180 g, 1.50 mmol)
was added to the reaction mixture and the vial was closed tightly with Teflon cap. The reaction
mixture was allowed to heat at 110 °C for 15 h. The reaction was cooled down to the ambient
temperature, then saturated aqueous NaHCO3 (10 mL) and brine (10mL) were added to the
mixture. The aqueous mixture was extracted with Et2O and the organic layer was dried over
anhydrous sodium sulfate and subsequently concentrated under reduced pressure. The crude
product was then purified by flash column chromatography on silica gel with 2% diethyl ether in
n-hexane as eluent to afford the desired product 5a (0.181 g, 93% yield).
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2-phenylisoindoline (5a).8e White solid (0.181 g, 93% yield); m.p. 171-173 °C; H NMR (400
MHz, CDCl3) δ 7.43-7.32 (m, 6H), 6.80 (t, J = 7.2 Hz, 1H), 6.73 (d, J = 8.0 Hz, 2H), 4.70 (s, 4H);
13C NMR (100 MHz, CDCl3) δ 147.1, 137.9 (2C), 129.4 (2C), 127.2 (2C), 122.6 (2C), 116.2,
111.4 (2C), 53.8 (2C); HRMS (ESI) m/z (M+H)+ calcd for C14H14N = 196.1126; found 196.1129.
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2-p-tolylisoindoline (5b).21 White solid (0.197 g, 94% yield); m.p. 196-198 °C; H NMR (400
MHz, CDCl3) δ 7.41-7.30 (m, 4H), 7.16 (d, J = 8.4 Hz, 2H), 6.66 (d, J = 8.4 Hz, 2H), 4.67 (s,
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4H), 2.34 (s, 3H); C NMR (100 MHz, CDCl3) δ 145.2, 138.1 (2C), 129.9 (2C), 127.1 (2C),
125.3, 122.6 (2C), 111.7 (2C), 54.0 (2C), 20.3; HRMS (ESI) m/z (M+H)+ calcd for C15H16N =
210.1283; found 210.1285.
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2-(4-chlorophenyl)isoindoline (5c).8e White solid (0.214 g, 93% yield); m.p. 170-172 °C; H
NMR (400 MHz, CDCl3) δ 7.40-7.30 (m, 4H), 7.26 (d, J = 9.2 Hz, 2H), 6.61 (d, J = 8.8 Hz, 2H),
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(2C), 121.1, 112.6 (2C), 53.9 (2C); HRMS (ESI) m/z (M+H)+ calcd for C14H13ClN = 230.0737;
found 230.0738.
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2-(4-nitrophenyl)isoindoline (5d).22 Yellow solid (0.222 g, 92% yield); m.p. 266-268 °C; H
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NMR (400 MHz, CDCl3) δ 8.23 (d, J = 9.2 Hz, 2H), 7.43-7.35 (m, 4H), 6.64 (d, J = 9.2 Hz, 2H),
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4.80 (s, 4H); C NMR (100 MHz, CDCl3) δ 151.3, 137.5, 136.3 (2C), 127.8 (2C), 126.4 (2C),
122.7 (2C), 110.5 (2C), 54.0 (2C); HRMS (ESI) m/z (M+H)+ calcd for C14H13N2O2 = 241.0977;
found 241.0975.
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2-(2,6-dimethylphenyl)isoindoline (5e).23 White solid (0.186 g, 83% yield); m.p. 60-62 °C; H
NMR (400 MHz, CDCl3) δ 7.40-7.30 (m, 4H), 7.15-7.05 (m, 3H), 4.69 (s, 4H), 2.32 (s, 6H); 13C
NMR (100 MHz, CDCl3) δ 145.1, 140.1 (2C), 138.9 (2C), 128.7 (2C), 126.7 (2C), 126.9, 122.5
(2C), 57.2 (2C), 18.7 (2C); HRMS (ESI) m/z (M+H)+ calcd for C16H18N = 224.1439; found
224.1438.
General procedure of the synthesis of azacyles 5f-5i
To a 20 mL vial containing a stirring mixture of aniline (1a) (0.093 g, 1.00 mmol) and DBU
(0.304 g, 2.00 mmol) in xylene (3 mL) was added dropwise POCl3 (0.230 g, 1.50 mmol) at room
temperature. The mixture was then heated at 90 °C for 15 min. Isochroman (0.201 g, 1.50 mmol)
was added to the reaction mixture and the vial was closed tightly with Teflon cap. The reaction
mixture was allowed to heat at 110 °C for 15 h. The reaction was cooled down to the ambient
temperature, then saturated aqueous NaHCO3 (10 mL) and brine (10mL) were added to the
mixture. The aqueous mixture was extracted with Et2O and the organic layer was dried over
anhydrous sodium sulfate and subsequently concentrated under reduced pressure. The crude
product was then purified by flash column chromatography on silica gel with 2% diethyl ether in
n-hexane as eluent to afford the desired product 5f(0.136 g, 65% yield).
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2-phenyl-1,2,3,4-tetrahydroisoquinoline (5f).8e White solid (0.136 g, 65% yield); m.p. 45-47 °C;
1H NMR (400 MHz, CDCl3) δ 7.37-7.31 (m, 2H), 7.26-7.18 (m, 4H), 7.03 (d, J = 8.0 Hz, 2H),
6.89 (t, J = 7.6 Hz, 1H), 4.46 (s, 2H), 3.61 (t, J = 6.0 Hz, 2H), 3.03 (t, J = 5.6 Hz, 2H); 13C NMR
(100 MHz, CDCl3) δ 150.5, 134.9, 134.4, 129.2 (2C), 128.5, 126.5, 126.3, 126.0, 118.7, 115.2
(2C), 50.8, 46.6, 29.1; HRMS (ESI) m/z (M+H)+ calcd for C15H16N = 210.1283; found 210.1284.
2-(4-chlorophenyl)-1,2,3,4-tetrahydroisoquinoline (5g).8e White solid (0.215 g, 88% yield); m.p.
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69-71 °C; H NMR (400 MHz, CDCl3) δ 7.30-7.25 (m, 6H), 6.91 (d, J = 9.2 Hz, 2H), 4.41 (s,
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2H), 3.56 (t, J = 6.0 Hz, 2H), 3.01 (t, J = 6.0 Hz, 2H); C NMR (100 MHz, CDCl3) δ 149.0,
134.7, 134.0, 129.0 (2C), 128.5, 126.5 (2C), 126.1, 123.4, 116.2 (2C), 50.7, 46.5, 28.9; HRMS
(ESI) m/z (M+H)+ calcd for C15H15ClN = 244.0893; found 244.0895..
2-(2,4-difluorophenyl)-1,2,3,4-tetrahydroisoquinoline (5h).8e White solid (0.209 g, 85% yield);
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m.p. 85-87 °C; H NMR (400 MHz, CDCl3) δ 7.25-7.15 (m, 3H), 7.15-7.10 (m, 1H), 7.05-6.96
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(m, 1H), 6.92-6.78 (m, 2H), 4.29 (s, 2H), 3.42 (t, J = 5.6 Hz, 2H), 3.02 (t, J = 6.0 Hz, 2H); C
NMR (100 MHz, CDCl3) δ 159.1-156.9 (dd, 1JC-F = 211.4 Hz, 3JC-F = 11.6 Hz, 1C), 156.8-154.4
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(dd, JC-F = 217.3 Hz, 3JC-F = 11.7 Hz, 1C), 136.4&136.3 (d, 3JC-F = 8.8 Hz, 1C), 134.2 (2C),
128.9, 126.4, 126.3, 125.9, 120.1&120.0 (d, 3JC-F = 5.1 Hz, 1C), 110.8-110.5 (dd, 2JC-F = 21.1 Hz,
4JC-F = 3.6 Hz, 1C), 105.0-104.5 (t, 2JC-F = 25.5 Hz, 1C), 53.1, 49.3 (d, 4JC-F = 3.7 Hz, 1C), 28.8;
HRMS (ESI) m/z (M+H)+ calcd for C15H14F2N = 246.1094; found 246.1097.
2-(3,5-dimethylphenyl)-1,2,3,4-tetrahydroisoquinoline (5i).24 White solid (0.197 g, 83% yield);
m.p. 49-51 °C; 1H NMR (400 MHz, CDCl3) δ 7.25-7.15 (m, 4H), 6.67 (s, 2H), 6.55 (s, 1H), 4.43
13
(s, 2H), 3.57 (t, J = 5.6 Hz, 2H), 3.02 (t, J = 6.0 Hz, 2H), 2.35 (s, 6H); C NMR (100 MHz,
CDCl3) δ 150.8, 138.7 (2C), 134.9, 134.6, 128.5, 126.5, 126.3, 126.0, 120.8, 113.2 (2C), 51.0,
46.7, 29.3, 21.8 (2C); HRMS (ESI) m/z (M+H)+ calcd for C17H20N = 238.1596; found 238.1597.
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Phenylphosphoramidic dichloride (6).25 To a 20 mL vial containing a stirring mixture of aniline
(1a) (0.093 g, 1.00 mmol) and DBU (0.304 g, 2.00 mmol) in xylene (3 mL) was added dropwise
POCl3 (0.230 g, 1.50 mmol) at room temperature. The mixture was then stirred at 90 °C for 30
min, quenched with saturated ammonium chloride, and extracted with CH2Cl2 (2 × 10 mL). The
organic layer was dried over sodium sulfate and concentrated under reduced pressure. The
resulting residue was then purified by flash column chromatography on silica gel with hexane-
EtOAc as eluent to afford the desired product 6 (0.178 g, 85%). White solid (0.178 g, 85% yield);
m.p. 80-82 °C; 1H NMR (400 MHz, CDCl3) δ 7.39 (t, J = 8.4 Hz, 2H), 7.27-7.20 (m, 3H), 7.11-
7.00 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 136.3, 129.7 (2C), 125.2, 121.1 (2C); 31P NMR
(CDCl3) δ 8.43; HRMS (ESI) m/z (M+H)+ calcd for C6H7Cl2NOP = 209.9642; found 209.9645.
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:
1H and 13C NMR spectra of compounds 3a-3v, 5a-5i, and 6. Screening of reaction conditions for
the preparation of azacycles the products (PDF)
AUTHOR INFORMATION
Corresponding Author
* E-mail address: hkkim717@jbnu.ac.kr (H-K Kim).
ORCID
Minh Thanh La: 0000-0001-9280-1769
Soosung Kang: 0000-0001-7016-2417
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Hee-Kwon Kim: 0000-0001-7612-7049
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Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENT
This research was supported by Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Education (2018R1D1A1B07047572).
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