Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca2N]+?e- in an Alcoholic Solvent: An Analogue of Solvated Electrons

Article abstract of DOI:10.1021/acs.joc.8b02094

Birch reduction of aromatic systems by solvated electrons in alkali metal-ammonia solutions is widely recognized as a key reaction that functionalizes highly stable π-conjugated organic systems. In spite of recent advances in Birch reduction with regard to reducing agent and reaction conditions, there remains an ongoing challenge to develop a simple and efficient Birch reaction under mild conditions. Here, we demonstrate that the inorganic electride [Ca₂N]^+?e^- promotes the Birch reduction of polycyclic aromatic hydrocarbons (PAHs) and naphthalene under alcoholic solvent in the vicinity of room temperature as a solid-type analogy to solvated electrons in alkali metal ammonia solutions. The anionic electrons from electride [Ca₂N]^+?e^- are transferred to PAHs and naphthalene via alcoholysis in a polar cosolvent medium. It is noteworthy that a high conversion yield to the hydrogenated products is ascribed to the extremely high electron transfer efficiency of 98%. This simple protocol utilizing an inorganic electride offers a direct and practical strategy for the reduction of aromatic compounds and provides an outstanding reducing agent for synthetic chemistry.

Full text of DOI:10.1021/acs.joc.8b02094

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Article
Birch Reduction of Aromatic Compounds by Inorganic Electride
2
+
-
[CaN]·e in Alcoholic Solvent; An Analogue of Solvated Electrons
Byung Il Yoo, Ye Ji Kim, Youngmin You, Jung Woon Yang, and Sung Wng Kim
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b02094 • Publication Date (Web): 23 Oct 2018
Downloaded from http://pubs.acs.org on October 24, 2018
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The Journal of Organic Chemistry
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,
, ,
† ‡ ∇
,*
†
†
∇
∥
†
Byung Il Yoo , Ye Ji Kim , YoungMin You , Jung Woon Yang and Sung Wng Kim
† Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea
‡
Center for Integrated Nanostructure Physics, Institute for Basic Science(IBS), Sungkyunkwan University, Suwon
440-746, Republic of Korea
Division of Chemical Engineering and Materials Science, Ewha Womans University, Seoul 120-750, Republic of
∥
Korea
KEYWORDS : Inorganic Electride, Birch Reduction, Electron Transfer, Solvated Electron
ABSTRACT: Birch reduction of aromatic systems by solvated electrons in alkali metal-ammonia solutions is widely rec-
ognized as a key reaction that functionalizes highly stable π-conjugated organic systems. In spite of recent advances in
Birch reduction with regards to reducing agent and reaction conditions, there remains an ongoing challenge to develop a
simple and efficient Birch reaction under mild conditions. Here, we demonstrate that the inorganic electride [Ca N] •e
promotes the Birch reduction of polycyclic aromatic hydrocarbons (PAHs) and naphthalene under alcoholic solvent in
the vicinity of room temperature as a solid-type analogy to solvated electrons in alkali metal-ammonia solutions. The ani-
+

2
+

onic electrons from electride [Ca N] •e are transferred to PAHs and naphthalene via alcoholysis in a polar co-solvent me-
2
dium. It is noteworthy that a high conversion yield to the hydrogenated products is ascribed to the extremely high elec-
tron transfer efficiency of 98%. This simple protocol utilizing an inorganic electride offers a direct and practical strategy
for the reduction of aromatic compounds and provides an outstanding reducing agent for synthetic chemistry.
7-9
■
INTRODUCTION
duction reactions. The reduction of naphthalene is re-
garded as one of the most representative Birch reductions
Since the venerated discovery of solvated electrons in
alkali metal-ammonia solutions, a variety of organic syn-
theses and pulse-radiolysis have been widely investigated
utilizing the solvated electrons found in diverse solvents
such as water and alcohols. Furthermore, the solvated
electrons have attracted much attention as a prototype
electronic conductor and an intriguing liquid, showing
metal-insulator transition and liquid-liquid phase separa-
1
0
in organic chemistry. Besides organic synthetic reactions,
the Birch reduction is utilized to functionalize materials.
For example, a highly hydrogenated graphene was suc-
cessfully fabricated by reducing graphite oxide or graphite
via Birch reduction using sodium-methanol or lithium-
ethanol solution to impart diverse physical properties to
the graphene, such as band gap tuning or ferromag-
1
,2
11,12
3
netism. After the early Birch reduction of naphthalene
tion. In synthetic organic chemistry, the solvated elec-
and benzene, various attempts were made to simplify the
reaction procedures and enhance the reduction perfor-
mance by supplementation with additional reducing
agents, proton source additives, photochemical activation,
tron, which is the smallest anionic electron and is trapped
within surrounding molecules of solvent, is recognized as
the most powerful reducing agent that allowed diverse
reduction reactions such as Birch and Bouveault-Blanc
1
3-21
4,5
and temperature control.
reactions due to its high redox potential.
As widely recognized, there is an urgent need to ad-
dress the many impediments for practical uses of the
Birch reduction. These include extreme reaction condi-
tions (alkali metals induce violent reaction, low tempera-
ture: −78 C), toxicity of reagents, high pressure H gas
environment, expensive noble metal catalysts, violent
quenching processes, and occurrence of side reactions
such as amination due to the nucleophilicity of ammo-
Thus, we are herein proposing that inorganic
electride, a solidified crystal of solvated electrons, can
From the 1940s, solvated electrons in sodium-ammonia
solution have been applied to the reduction of aromatic
compounds. In this process, the solvated electrons are
transferred to the aromatic rings to form radical anions
16
o
6
that are subsequently protonated or hydrogenated. This
2
is the basic mechanism of the pioneering Birch reduction
in synthetic organic chemistry, followed by the applica-
tion of solvated electron systems (such as alkali metal-
ammonia, -amine and -alcohol solutions) for various re-
6
, 17-22
nia.
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provide a powerful new reducing agent for simple and Table 1. Optimization of the reaction conditions for
Page 2 of 8
23
+

a
1
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mild Birch reduction. It is expected to provide high elec-
tron transfer efficiency and environmentally benign pro-
cesses in universal solvents such as alcohols.
the Birch reduction utilizing [Ca N] ·e electride
2
Electrides are ionic crystals with anionic electrons
trapped in the cavity spaces of crystallographic interstitial
sites. Similar to solvated electrons, electrides have provid-
ed a rich area for theoretical studies of quantum confine-
ment systems and high pressure elements as well as a
wide range of applications in synthetic chemistry and
GC
Yield
(%)
Electride
Equiv.
Time
(h)
Temp
#
Solvent
o
( C)
24-25
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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0
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0
electronic devices.
tride Cs (18-crown-6) •e was synthesized using solvated
electrons of cesium-amine solution as precursors. Alt-
hough the chemical and thermal instability of early or-
ganic electrides at room temperature hampered practical
The first crystalline organic elec-
+

1
1
1
HMPA
HMPA
24
24
rt
N.D.
N.D.
2
26
2
65
HMPA : iPrOH
3
4
5
1
1
24
24
48
24
48
24
48
24
24
24
24
rt
N.D.
40
(
1:1)
HMPA : iPrOH
1:1)
applications,
room
temperature
stable
organic
+
Na (TriPip222)•e and inorganic mayenite electrides
opened a new epoch in synthetic chemistry. In particu-
lar, the first room temperature stable inorganic electride
65
65
65
65
65
65
65
65
65
2
7
(
HMPA : iPrOH
(1:1)
4
+

1
42
[Ca Al O ] •4e , which has three-dimensionally con-
24
28 64
nected cages, was demonstrated to be a powerful reduc-
2
8-32
HMPA : iPrOH
ing reagent for organic reactions.
However, using the
6
7
1.5
1.5
2
68
(
1:1)
electrons trapped in the closed cage structure of
4
+

[
Ca Al O ] •4e has several limitations such as insuffi-
HMPA : iPrOH
(1:1)
24
28 64
71
cient scalability, electron transfer efficiency and yield. In
these regards, we have applied newly discovered inorgan-
HMPA : iPrOH
98
+

ic two-dimensional (2D) electride [Ca N] •e to develop a
8
9
10
11
2
b
(
1:1)
HMPA : iPrOH
1:1)
HMPA : MeOH
1:1)
Toluene : iPrOH
1:1)
Toluene : iPrOH
1:1)
(89)
simple and efficient organic synthetic reaction.
+

The inorganic electride [Ca N] •e consists of anionic
2
2
96
(
2D electron gas (2DEG) layer and cationic framework
+
[Ca N] layer. Compared to the closed-cage structure of
2
4
+

21
3
2
93
63
82
92
[Ca Al O ] •4e (electron concentration 2.33 x 10 cm ),
24
28 64
+
(

the [Ca N] •e has an open 2D layer structure and higher
2
22
3
electron concentration (1.37 x 10 cm ). This structural
advantage, together with extremely high electron mobility
(520 cm V s ) and low work function (2.6 eV), allows
efficient electron transfer to physically or chemically ad-
sorbed substances. Furthermore, diverse organic reac-
tions such as pinacol coupling and trifluoromethylation
have been successfully developed utilizing [Ca N] •e .
2
(
2
1 1
12
3
(
3
3
THF : iPrOH
13
2
65
+
 23, 34-
(1:1)
2
3
6
a
+
–
Here, we report a simple and efficient Birch reduction
of PAHs and naphthalene using the electride [Ca N] •e in
General conditions: 1a (0.5 mmol), [Ca N] •e (02 equiv.),
Solvent (co-solvent : 2 mL, alcoholic solvent : 2 mL), Isolat-
ed yield
2
+

b
2
alcoholic solvents, which is analogous to solvated elec-
trons in alkali-ammonia solutions. The alcoholysis of
ature. This indicates that the iPrOH activates the alco-
holysis of the [Ca N] •e at 65 °C, where the solubility of
anthracene in iPrOH increases to produce a reduced
product. Thus, we used co-solvent system (HMPA:iPrOH
= 1:1, v/v). Although no reaction occurred at room tem-
perature (3), a distinct reaction was observed at 65 °C.
This is ascribed to sufficient decomposition of the
[Ca N] •e via alcoholysis (6) and increased solubility of
anthracene. Considering the present results and the re-
ported hydrodehalogenation of organic halides by the
+

[
Ca N] •e effectively initiates an electron transfer to aro-
+

2
2
matic substrates, forming radical anions.
■ RESULTS AND DISCUSSION
Initial investigations into Birch reduction using
+

[
Ca N] •e were conducted with anthracene (Table 1). We
2
utilized the hexamethylphosphoramide (HMPA) solvent
as an electron transfer media which is known for dissolv-
+

2
3
7-38
ing alkali metals, generating solvated electrons.
First,
the reducing reaction of the anthracene was examined in
HMPA or co-solvent (HMPA-iPrOH) at different
+

[Ca N] •e in iPrOH at room temperature, it is supposed
2
that the reduction potential difference between electride
as an electron donor and the reactant as an electron ac-
ceptor needs to be controlled by managing reaction con-
ditions such as temperature or acidity of the solvent me
reaction temperatures (Table 1, entries 1-4). We observed
no reaction using HMPA solvent due to that the
+

[
Ca N] •e was hardly decomposed. However, in iPrOH
2
solvent, the reaction was preceded by increase of tempera
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2
3
+

dia. Therefore, to enhance the alcoholysis of [Ca N] •e
Table 2. Reaction scope of PAHs and naphthalenes
2
+

a
1
2
3
4
5
6
7
8
9
for the reduction of anthracene, the solvent temperature
was fixed at 65 °C. Although the increase in reaction time
is less effective to obtain a higher yield, the higher equiva-
for the Birch reduction utilizing [Ca N] ·e electride
2
+

lent of [Ca N] •e leads to more efficient reaction (6-9).
2
The GC yield of product gradually increased as the
equivalents of electride increased, reaching 98%.
Furthermore, we examined the solvent effect by con-
trolling the acidity of the alcoholic solvent and the polari-
ty of the co-solvent (10-13). The increase in the acidity of
alcoholic solvent alcohols [pKa; isopropanol (17.1), meth-
anol (15.5)] was not a critical factor 6 and 10. However,
when the co-solvent of toluene and iPrOH was used, the
reaction was hampered, rendering a lower yield (63%)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+

when we used the same 2 equivalent of [Ca N] •e (11).
2
+

Thus, we optimized the yield by the increase of [Ca N] •e
2
electride equivalents. The yield was increased to 82%
+

when 3 equiv. of [Ca N] •e electride was used (12). Fu-
2
thermore, the use of THF and iPrOH co-solvent produced
a moderately high yield (13). These results indicate that
the polarity of solvent media is an important factor for an
efficient electron transfer, leading to a high yield of 98%.
Thus, it is concluded that the solvation and transfer of
anionic electrons was facilitated in the aprotic solvent
media. Compared with the Birch reduction by solvated
electrons in alkali metal-ammonia solution, it is also no-
+

table that the Birch reduction with electride [Ca N] •e
2
occurs smoothly without any side reactions and quench-
ing processes.
For the expansion of reaction scope, we applied the co-
solvent systems of THF:iPrOH and HMPA:iPrOH. With
+

the established optimal condition [2 equiv. of [Ca N] •e ,
2
THF:iPrOH = 1:1 or HMPA:iPrOH = 1:1, v/v), 65 °C], we
examined the Birch reduction of various PAHs and two
naphthalene derivatives (Table 2) (See the supporting
Information). We confirmed the feasibility of the
+

[
Ca N] •e for the Birch reduction with tricyclic aromatic
2
hydrocarbons (2a-2c). The yield for electron-withdrawing
group (EWG) (2d) was higher than that for electron-
donating groups (EDG) (2e-2f). This result is probably
attributed to the stabilization of carbanion by the induc-
3
9
tive effect. In the case of 9-chloromethylanthracene and
-bromoanthracene (2c-2d), hydrodehalogenation and
a
+
–
9
General conditions : 1a (0.5 mmol), [Ca
N] •e (2 equiv.),
2
dearomatization reactions occurred simultaneously. In
sequence, we explored the Birch reduction of tetracyclic
aromatic hydrocarbons (2g-2h). Two different isomeric
neutral tetracyclic aromatic hydrocarbons (tetracene and
tetraphene) were well transformed into the partially hy-
drogenated products with high yields.y
solvent [THF : 2 mL, iPrOH : 2mL, (0.125 M)], 24 h; 2a, 2b, 2l,
2m (0.5 mmol), [Ca
iPrOH : 2mL, (0.125 M)], 24 h; 2c, 2g, 2h, 2k (0.5 mmol),
+
–
N] •e (3 equiv.), solvent [THF : 2 mL,
2
+
–
[
Ca N] •e (4 equiv.), solvent [THF : 2 mL, iPrOH : 2mL,
2
+ –
(
0.125 M)], 24 h; 2d, 2e, 2f (0.5 mmol), [Ca N] •e (5 equiv.),
2
solvent [THF : 2 mL, iPrOH : 2mL, (0.125 M)], 24 h; 2i, 2j (0.5
+
–
mmol), [Ca N] •e (10 equiv.), solvent [HMPA : 2 mL, iPrOH :
2mL, (0.125 M)], 24 h. Determined by NMR spectroscopy.
2
On the other hand, it is generally acknowledged that
the Birch reduction of naphthalene has been limited due
to the instability of naphthalene radical anions. Thus, the
Birch reduction of naphthalene could only be induced by
a high electron concentration system that is represented
by solvated electrons of alkali metal-ammonia solutions.
For example, the Birch reduction of naphthalene was
b
the optimal condition (1a), the Birch reduction of naph-
thalene derivatives rarely proceeded due to the low elec-
tron concentration (0.25 M). To expedite the formation of
naphthalene radical anions, we increased the electron
concentration from 0.25 M to 1.25 M by adding extra
equivalents of electride (2i-2j), allowing the reduction of
naphthalene and 1-fluoronaphthalene with the yield of 49%
and 99%, respectively. In addition, we also examined the
1
conducted with conducted with 2.6 M (2.6 mol L ) of
3
solvated electrons in sodium-ammonia solution. Under
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+

Scheme 1. Schematic illustration of a plausible mechanism for the Birch reduction of anthracene by [Ca N] •e
2
electride as the electron transfer agent
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
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0
1
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3
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0
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2
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0
1
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9
0
Birch-type reduction of alkyne and alkenes (2k-2m), also
producing corresponding alkanes with a high yield. How-
ever, the Birch reductions of both anisole and toluene
have not been accomplished under the present optimized
condition, requiring a further study for the reductions of
monocyclic aromatic hydrocarbons.
Figure 1 compares the electron transfer efficiency for
the Birch reduction of anthracene and naphthalene utiliz-
+

ing [Ca N] •e electride to those for previously reported
2
Birch reductions utilizing various reducing agents in
terms of electron concentration. The electron transfer
efficiency and concentration were calculated using the
ratio of provided and participated electrons (%) and the
To verify the validity of electron transfer via alcoholysis
1
+

amount of electrons per volume of solvent (M, mol L ),
respectively. (See the Supporting Information) For the
reduction of anthracene, the present Birch reduction
showed the highest electron transfer efficiency and com-
pleted the reaction with minimal use of the electride rea-
gent; it indicates that this protocol is an economical and
practical methodology. Meanwhile, for the reduction of
naphthalene, the present electride mediated Birch reduc-
tion showed moderately high electron transfer efficiency
when compared to that of the Birch reduction using
SmI /H O. However, in spite of the sufficient reduction
of the [Ca N] •e , we carried out experimental mechanisit-
2
ic studies. The reaction of anthracene was conducted with
the existence of radical scavengers under optimized con-
dition to elucidate the radical reaction that facilitates
+

electron transfer from the [Ca N] •e electride via the sin-
2
gle electron transfer process. (See the supporting Infor-
mation) With the presence of radical scavengers such as
TEMPO and 1,4-dinitrobenzene, the yields of entry 8 (ta-
ble 1) was decreased to a level corresponding to the
amount of radical scavengers. Also, the alcoholysis of
+

2
2
[
Ca N] •e electride was proved by the formation of calci-
2
ability of solvated electrons in alkali metal-ammonia solu-
tions, their practical use is impeded by the harsh reaction
um alkoxide and ammonia through the X-ray diffraction
3
2
and ion chromatography. Based on the these results, we
propose a plausible mechanism for the present Birch re-
duction as illustrated in scheme 1. In our process, iPrOH
plays vital role of both an activator for anionic electron
o
conditions such as low reaction temperature (< −30 C)
and violent reactions.
+

transfer from [Ca N] •e and a hydrogen source for proto-
2
nation of the reduced anthracene. The iPrOH is responsi-
+

ble for the alcoholysis of [Ca N] •e to produce calcium
2
isopropoxide (Ca(iPrO)2) and ammonia (NH ). The
3

Ca(iPrO) and NH was formed by the reaction of 2 iPrO
2
3
2
+
+

+
from iPrOH and Ca from [Ca N] •e , and reaction of H
from iPrOH and N of [Ca N] •e , respectively. Conse-
quently, the decomposition of [Ca N] •e via alcoholysis
2
+

3
2
+

2
released the anionic electrons that are supposed to be
solvated in co-solvent media like solvated electrons in
alkali metal ammonia solution. Afterward, the released
anionic electrons are transferred to anthracene, leading to
the formation of radical anions. The radical anions are
continuously protonated by proton abstraction from
iPrOH. An iterative series of anionic electron transfer,
radical anion formation, and protonation completes the
Birch reduction of anthracene.
Figure 1. Comparison of electron transfer efficiency and elec-
tron concentration in the reduction of anthracene and naph-
+

thalene using typical electron transfer agents and [Ca N] •e
2
electride.
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In contrast, it is noted that the Birch reduction utiliz-
4. Characterization Data for Products
+

1
2
3
4
5
6
7
8
9
ing [Ca N] •e electride was realized in the vicinity of
2
9,10-dihydroanthracene (1a’) According to General
Procedure of GP-1 with 1a (0.05 mmol) and [Ca N] •e (94
mg, 1 mmol, 2.0 equiv), compound 1a’ (83 mg, 92%) was
+

room temperature and in alcoholic solvents, although the
optimization for a high transfer efficiency beyond alkali
metal-ammonia solutions is further needed.
2
obtained. / According to revised General Procedure of
+

■
CONCLUSIONS
GP-1 with 2d (0.05 mmol) and [Ca N] •e (235 mg, 2.5
2
mmol, 5.0 equiv), compound 1a’ (76 mg, 87%) was ob-
In conclusion, we have demonstrated a simple, efficient
and mild Birch reduction of PAHs and naphthalene utiliz-
1
tained. H NMR (500 MHz, CDCl ); 7.29-7.27(m, 4H), 7.19-
3
13
1
+

7
1
.17(m, 4H), 3.93(s, 4H) ; C{ H} NMR (125 MHz, CDCl ) δ:
ing 2D inorganic electride [Ca N] •e in alcoholic solvents.
3
2
36.7, 127.4, 126.1, 36.2 ppm. The physical and spectral data
This protocol can provide a direct and pragmatic synthet-
ic root for the reduction of aromatic compounds. It also
can provide a powerful alternative reducing agent for syn-
thetic chemistry as an analogue of solvated electrons in
alkali metal-ammonia or amine solutions. Finally, we sus-
pect that, because the electride in alcoholic solvents
shows high electron transfer efficiency, it might also be
used for electro-catalytic reactions.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
were identical to those previously reported for this com-
4
0
pound.
9,10-dihydrophenanthrene (2a’) According to revised
General Procedure of GP-1 with 2a (0.05 mmol) and
+

[Ca N] •e (141 mg, 1.5 mmol, 3.0 equiv), compound 2a’
2
1
(80 mg, 89%) was obtained. H NMR (500 MHz, CDCl );
3
7.75(d, J = 10 Hz, 2H), 7.30-7.27(m, 2H), 7.23-7.20(m, 4H),
1
3
1
2
.86(s, 4H) ; C{ H} NMR (125 MHz, CDCl ) δ: 137.4, 134.5,
■
EXPERIMENTAL SECTION
3
1
128.2, 127.4, 127.0, 123.8, 29.1 ppm. The physical and spec-
tral data were identical to those previously reported for
1. General Methods. H NMR spectra were recorded at
room temperature on a Bruker at 500 MHz in CDCl (δ
41
3
1
3
this compound.
7
.26 ppm), C NMR spectral measurements were per-
9-methyl-9,10-dihydroanthracene (2b’) According to
formed at 125 MHz using CDCl (δ 77.16 ppm). All report-
3
revised General Procedure of GP-1 with 2b (0.05 mmol)
ed NMR values are given in parts per million (ppm). The
terms m, s, d, t, q, quint., and sept. represent multiplet,
singlet, doublet, triplet, quadruplet, quintuplet, and sep-
tet, respectively, and the term br means a broad signal.
+

and [Ca N] •e (141 mg, 1.5 mmol, 3.0 equiv), compound
2
2
b’ (83 mg, 86%) was obtained. / According to revised
General Procedure of GP-1 with 2c (0.05 mmol) and
+

+

[Ca
N] •e (188 mg, 2.0 mmol, 4.0 equiv), compound 2b’
2
1
2
. Synthesis of dicalcium nitride [Ca N] ∙e elec-
2
+

(84 mg, 87%) was obtained. H NMR (500 MHz, CDCl );
.30-7.26(m, 4H), 7.22-7.16(m, 4H), 4.11(d, J = 20 Hz, 1H),
3
tride. A stoichiometric polycrystalline [Ca N] •e elec-
2
7
4
3
tride was synthesized by the solid-state reaction of Ca N
3
2
.03(q, J=5 Hz, 1H), 3.87(d, J = 15 Hz, 1H), 1.42(d, J = 5 Hz,
powders and Ca metal chips. Mixture of Ca N powders
3
2
13
1
H) f; C{ H} NMR (125 MHz, CDCl ) δ: 141.6, 135.9, 127.8,
3
and Ca chips at a molar ratio of 1:1 were pressed into a
pellet form under pressure (20~30 MPa). The pellet was
fully covered with molybdenum foil and annealed at 800
127.0, 126.5, 126.1, 41.2, 35.2, 23.6 ppm. The physical and
spectral data were identical to those previously reported
4
0
o
3
for this compound.
-ethyl-9,10-dihydroanthracene (2e’) According to
revised General Procedure of GP-1 with 2e (0.05 mmol)
C for 48 hrs under vacuum (~10 Pa). Then, the sample
9
was quenched into water. To improve homogeneity of
+

[
Ca N] •e electride, the synthesized sample was ground
2
+

and [Ca N] •e (235 mg, 2.5 mmol, 5.0 equiv), compound
into a powder in an agate mortar in argon-filled glovebox
and re-annealed under the same conditions. The synthe-
2
1
2
e’ (40 mg, 38%) was obtained. H NMR (500 MHz,
+

CDCl ); 7.28-7.20(m, 4H), 7.20-7.18(m, 4H), 4.13-4.09(d,
3
sized [Ca N] •e electride is single phase without impuri-
2
+

1H), 3.87-3.79(m, 2H), 1.68-1.65(t, 2H), 0.89-0.86(t, 3H) ;
ties. The structure of synthesized [Ca N] •e electride was
2
1
3
1
C{ H} NMR (125 MHz, CDCl ) δ: 140.5, 136.1, 128.1, 127.7,
3
identified by X-ray diffractometer.
126.0, 125.9, 48.9, 35.3, 30.6, 12.1 ppm. The physical and
spectral data were identical to those previously reported
3
. General procedures for Birch reduction of Poly-
cyclic aromatic hydrocarbons (PAH) (GP-1) and of
42
for this compound.
+

naphthalene (GP-2). [Ca N] •e electride (94 mg, 1 mmol)
2
9,10-diphenyl-9,10-dihydroanthracene (2f’) Accord-
was added to a suspension of PAH (0.5 mmol) and naph-
thalene (0.5 mmol) in 4 ml of dry (THF or HMPA) and
ing to revised General Procedure of GP-1 with 2f (0.05
+

o
+

mmol) and [Ca N] •e (235 mg, 2.5 mmol, 5.0 equiv),
2
iPrOH in 1:1 mixture at 65 C. Because the [Ca N] •e elec-
2
1
compound 2f’ (83 mg, 50%) was obtained. H NMR (500
tride is oxidized even in the solvents under ambient at-
mosphere, the reactions were conducted in inert Ar gas
environment until the complete alcoholysis of electride
MHz, CDCl ); 7.31-7.28(q, 4H), 7.25-7.22(m, 3H), 7.16-
3
1
3
1
7.10(m, 12H), 5.23(s, 2H) ; C{ H} NMR (125 MHz, CDCl ) δ:
3
+

143.7, 139.3, 129.3, 128.6, 128.4, 126.5, 126.4, 50.3 ppm. The
physical and spectral data were identical to those previ-
that was observable by the color change of [Ca N] •e
2
electride from black to white. The reaction mixture was
quenched with 5% HCl concentrated aqueous solution
4
0
ously reported for this compound.
,12-dihydrotetracene (2g’) According to revised Gen-
eral Procedure of GP-1 with 2g (0.05 mmol) and
5
and then, extracted with Et O or n-haxane (20 mL×3). The
2
THF and HMPA were removed by washing with DI water.
+

The combined organic layers were dried over MgSO and
[Ca
N] •e (141 mg, 1.5 mmol, 3.0 equiv), compound 2g’
2
1
4
(
94 mg, 82%) was obtained. H NMR (500 MHz, CDCl );
concentrated in vacuo.
3
7.79-7.77(m, 2H), 7.75(s, 2H), 7.42-7.40(m, 2H), 7.34-
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 8
1
3
1
13
1
7
.32(m, 2H), 7.21-7.20(m, 2H), 4.18(s, 4H) ; C{ H} NMR
6H), 2.92(s, 4H) ; C{ H} NMR (125 MHz, CDCl ) δ: 141.8,
3
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
125 MHz, CDCl ) δ: 137.1, 135.7, 132.4, 127.3, 127.2, 126.3,
128.4, 128.3, 126.0, 37.9 ppm. The physical and spectral
data were identical to those previously reported for this
compound.
3
125.3, 125.2, 36.8 ppm. The physical and spectral data were
identical to those previously reported for this com-
pound.
,12-dihydrotetraphene (2h’) According to revised
General Procedure of GP-1 with 2h (0.05 mmol) and
4
0
4
0
7
+

[Ca N] •e (188 mg, 1.0 mmol, 2.0 equiv), compound 2h’
Supporting Information
2
1
1
13
(97 mg, 85%) was obtained. H NMR (500 MHz, CDCl );
H NMR and C NMR Spectra of the Products
3
8
.15(d, J = 10 Hz, 1H), 7.85(d, J = 5 Hz, 1H), 7.72(d, J = 5 Hz,
Reaction scope of PAHs and naphthalenes for the Birch re-
duction using HMPA
Mechanistic Study
Electron transferring Efficiency Calculation and Electron
Concentration
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
H), 7.56-7.54(m, 1H), 7.48-7.45(m, 1H), 7.42-7.39(m, 2H),
7
.34-7.32(m, 1H), 7.25-7.22(m,2H), 4.41(s, 2H), 4.18(s, 2H);
1
3
1
C{ H} NMR (125 MHz, CDCl ) δ: 135.3, 135.2, 132.7, 132.4,
3
131.5, 130.2, 128.7, 128.2, 127.7, 126.8, 126.5, 126.2, 126.2, 126.1,
125.0, 122.9, 35.8, 31.0 ppm. The physical and spectral data
were identical to those previously reported for this com-
4
3
pound.
1
,2,3,4-Tetrahydronaphthalene (2i’) According to
* kimsungwng@skku.edu
+

General Procedure of GP-2 with [Ca N] •e (470 mg, 5
mmol, 10.0 equiv), compound 2i’ (32 mg, 49%) was ob-
tained. / According to revised General Procedure of GP-2
with 2j (0.05 mmol) and [Ca N] •e (470 mg, 5 mmol, 10.0
equiv), compound 2i’ (51%) was obtained. The product
was mixture of 2i, 2j’ and 2i’. The product was mixture of
2i, 2j’ and 2i’. H NMR (500 MHz, CDCl ): δ = 7.09–7.05
(m, 4H), 2.78–2.76 (m, 4H), 1.81–1.78 (m, 4H) ppm. C{ H}
NMR (125 MHz, CDCl ) δ: 134.9, 120.6, 29.2, 22.7 ppm. The
2
∇ B. I. Y. and Y. J. K. equally contributed to this work.
+

2
This research was supported by Creative Materials Discovery
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Science and ICT (NRF-
2015M3D1A1070639)
1
3
1
3
1
3
physical and spectral data were identical to those previ-
ously reported for this compound.
4
5
(1) Hart, E. J.; Boag, J. W. Absorption Spectrum of the Hydrat-
ed Electron in Water and in Aqueous Solutions. J. Am. Chem. Soc.
Naphthalene (2i) According to revised General Proce-
+

dure of GP-2 with 2j (0.05 mmol) and [Ca N] •e (470 mg,
2
1962, 84, 4090−4095.
5 mmol, 10.0 equiv), compound 2f’ (18%, determined by
1
(2) Sauer, M. C.; Arai, S.; Dorfman, L. M. Pulse Radiolysis
H NMR spectroscopy) was obtained. The product was
Studies. VII. The Absorption Spectra and Radiation Chemical
Yields of the Solvated Electron in the Aliphatic Alcohols. J. Chem.
Phys. 1965, 42, 708−712.
(3) Wagner, M. J.; Dye, J. L. Alkalides, Electrides, and Expand-
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1
mixture of 2i, 2j’ and 2i’. H NMR (500 MHz, CDCl ): δ =
7.85–7.83 (m, 4H), 7.48–7.46 (m, 4H) ppm. C{ H} NMR
(125 MHz, CDCl ) δ: 133.5, 129.1, 125.4 ppm. The physical
and spectral data were identical to those previously re-
3
1
3
1
3
20
ported for this compound.
1,4-Dihydronaphthalene (2j’) According to revised
General Procedure of GP-2 with 2j (0.05 mmol) and
[Ca N] •e (470 mg, 5 mmol, 10.0 equiv), compound 2i’
(30%, determined by H NMR spectroscopy) was obtained.
The product was mixture of 2i, 2j’ and 2i’. H NMR (500
MHz, CDCl ): δ = 7.07–7.01 (m, 4H), 5.92–5.91 (m, 2H),
3.45–3.38 (m, 4H) ppm. C{ H} NMR (125 MHz, CDCl ) δ:
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tral data were identical to those previously reported for
this compound.
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
2
1
1
(7) Schultz, A. G.; Pettus, L. Desymmetrization of Benzoic Ac-
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1
3
1
id in the Context of the Asymmetric Birch Reduction-Alkylation
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3
(-)-Aspidospermidine. J. Org. Chem. 1997, 62, 6855−6861.
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1,2-diphenylethane (2k’) According to revised General
+

Procedure of GP-1 with 2k (0.05 mmol) and [Ca N] •e
(188 mg, 2.0 mmol, 4.0 equiv), compound 2k’ (79 mg, 87%)
was obtained. / According to revised General Procedure
of GP-1 with 2l (0.05 mmol) and [Ca N] •e (141 mg, 1.5
mmol, 3.0 equiv), compound 2k’ (62 mg, 68%) was ob-
tained. / According to revised General Procedure of GP-1
with 2m (0.05 mmol) and [Ca N] •e (141 mg, 1.5 mmol, 3.0
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2
(
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
2
(
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