One-pot synthesis of nitronaphthalenes from Morita-Baylis-Hillman acetates and primary nitroalkanes via sequential SN2′-intramolecular oxidative nucleophilic substitution of hydrogen-E2 elimination

Full text of DOI:10.1002/bkcs.10774

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DOI: 10.1002/bkcs.10774
BULLETIN OF THE
S. Y. Kim et al.
KOREAN CHEMICAL SOCIETY
One-Pot Synthesis of Nitronaphthalenes from Morita–Baylis–Hillman
Acetates and Primary Nitroalkanes via Sequential SN20-Intramolecular
Oxidative Nucleophilic Substitution of Hydrogen-E2 Elimination
*
Su Yeon Kim, Ko Hoon Kim, Beom Kyu Min, Jimin Kim, and Jae Nyoung Kim
Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-
757, Korea. *E-mail: kimjn@chonnam.ac.kr
Received February 2, 2016, Accepted February 24, 2016, Published online May 19, 2016
Keywords: Nitronaphthalenes, Morita–Baylis–Hillman acetates, Primary nitroalkanes, Intramolecular
oxidative nucleophilic substitution of hydrogen
Morita–Baylis–Hillman (MBH) adducts have been used
extensively for the synthesis of various cyclic compounds.1
Among them, the synthesis of poly-substituted naphtha-
lenes from MBH adducts has been studied extensively by
us2a–e and other groups.2f–i Very recently, Basavaiah and
Reddy reported an interesting synthesis of naphthalenes by
using sodium nitrite-mediated intramolecular Friedel-Crafts
(IMFC) cyclization of secondary nitro compounds derived
from MBH acetates (Eq. (1)), as shown in Scheme 1.3
Although various aryl moieties including m-methoxyphenyl
group have been successfully employed in the IMFC reac-
tion, nitroaryl groups failed to give the corresponding
naphthalenes. As shown in Eq. (2), we reasoned out that
the synthesis of 7-nitronaphthalene could be feasible by
inverting the electrophilic and nucleophilic centers.
An oxidative nucleophilic substitution of hydrogen
(ONSH) pathway for the C C bond formation between
electron-deficient arenes such as nitroarenes and nucleo-
philes in the presence of an oxidant has been studied exten-
sively.4,5 Recently, an aerobic oxidation of the intermediate
σH-adduct has emerged as economic and safe alternatives
of external oxidants such as KMnO4 or AgNO3.6 Very
recently, we also reported the synthesis of 2,3-diarylindoles
and 5-aryluracils by an aerobic ONSH reaction in high
yields.7
addition, an intramolecular ONSH reaction has also been
known although the example is rather limited.9 In these
contexts, we decided to examine the reaction between
MBH acetate of m-nitrobenzaldehyde 1a and nitroethane,
as shown in Scheme 2.
At the outset of our experiment, the reaction of 1a and
nitroethane (2.0 equiv) was carried out in DMSO in the
presence of Cs2CO3 (3.0 equiv) under O2 balloon atmos-
phere.7 To our delight, 7-nitronaphthalene 2a was obtained
in moderate yield (48%) after a short period of time (1 h)
at room temperature. The yield was quite reasonable con-
sidering the low yield reported for the intermolecular
ONSH reaction between nitroarene and nitroalkane.8 It is
interesting to note that the formation of the regioisomeric
5-nitronaphthalene, linked to the ortho-position of nitro
group, was not observed. Such para-selectivity has been
reported in many articles.6,7 The use of DMF as solvent
and/or K2CO3 as base was less effective, as already
observed by others6 and us7 in a similar ONSH reaction.
The use of lesser amount of nitroethane or Cs2CO3
decreased the yield of 2a.10
The formations of 1:1 adduct I and dihydronaphthalene
IV were not observed during the reaction of 1a and
nitroethane. Thus, we examined the preparation of I in
other ways from 1a and nitroethane. Among the examined
conditions the reaction in aqueous THF at room tempera-
ture afforded I in good yield (85%, E/Z = 6:1) along with a
trace amount of 2a (3%).11 With this 1:1 adduct I in our
The ONSH reaction between nitroarenes and nitroalkanes
has been reported in some articles,8 although the yield of
coupled product was low to moderate (24–60%). In
MeO
COOMe
MeO
COOMe
NO2
MeO
COOMe
NaNO2
IMFC
(1)
(2)
ꢁ-
+
ꢁ
H3C
O
CH3
1
CH3
N
N
O
O
7
O2N
COOMe
O2N
COOMe
N
COOMe
ꢁ- NO2
CH3
O2
Cs2CO3
O
ONSH
4
CH3
5
ꢁ+
H
H3C NO2
ꢀH-adduct
Scheme 1. Comparison between Basavaiah (Eq. (1)) and our approaches (Eq. (2)).
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hand, the synthesis of 2a was examined. The reaction of
I in DMSO in the presence of Cs2CO3 (2.0 equiv) under
O2 balloon atmosphere afforded 2a in good yield (59%).
The result stated that the yield of two-pot reaction (50%)
was similar to that of the one-pot reaction (48%).
and 1-nitropropane gave 2k in a similar yield (49%). In
addition, the reaction of MBH acetate 1d, bearing an acetyl
moiety, and ethyl nitroacetate also gave 2l in moderate
yield (50%).
It is interesting to note that the reaction of 1c and ethyl
nitroacetate afforded 7-chloronaphthalene 2m in low yield
(32%) along with de-nitrated naphthalene 2m0 (22%). A plau-
sible mechanism for the formation of 2m0 was suggested in
Scheme 3. A protonation of the σH-adduct and two-fold elim-
ination of HNO2 could form 2m0. Thus we examined the
reaction in the presence of an excess amount of Cs2CO3 (4.0
equiv) in order to reduce the possibility of protonation. The
yield of 2m increased up to 44% as expected, and the yield
of 2m0 decreased to 9%.13 In other entries, we did not
observe the formation of similar de-nitrated product.
Thus, we carried out the synthesis of 6- or 7-
nitronaphthalenes from MBH acetates 1a–1d and primary
nitroalkanes under the influence of Cs2CO3 in DMSO at
room temperature by following the one-pot procedure. The
results are summarized in Table 1. The reactions of 1a
and 1-nitropropane, 1-nitrobutane, methyl 4-nitrobutyrate,
1-phenyl-2-nitroethane, 2-(2-nitroethyl)thiophene, and phe-
nylnitromethane afforded the corresponding naphthalenes
2b–2g in moderate yields (46–50%). The reaction of ethyl
nitroacetate afforded 2h in higher yield (58%) than other
nitroalkanes. The reactions of methoxy derivative 1b with
1-nitropropane or ethyl nitroacetate afforded 2i (49%) and
2j (61%), respectively. For the preparation of 2j, a slight
The reaction mechanism could be proposed, with 2a as
an example, as shown in Scheme 4. The SN20 reaction of 1a
o
warming (50 C, 3 h) of the reaction mixture was required
NO2
for the completion.12 The reaction of chloro derivative 1c
O2N
COOMe
O2N
Cl
COOMe
H
H
COOEt
1c
Cl
H
H
EtOOC NO2
EtOOC NO2
OAc
O2N
COOMe
NO2
CH3CH2NO2
- HNO2
O2N
COOMe
Cs2CO3, DMSO
H
H
COOMe
1 h, O2 balloon
H
typical
H
room temperature
CH3
1:1 adduct I
ONSH
pathway
SN2'
MBH acetate 1a
Cl
O2
EtOOC NO2
- HNO2
ONSH
O2N
COOMe
O2N
COOMe
- HNO2
O2N
Cl
COOMe
+
COOMe
E2
CH3
H3C NO2
Cl
2a (48%)
IV
COOEt
2m (32%)
COOEt
2m' (22%)
Scheme 2. One-pot synthesis of 7-nitronaphthalene 2a via sequen-
Scheme 3. Unexpected formation of 2m0.
tial SN20, intramolecular ONSH, and elimination of nitrous acid.
Table 1. Synthesis of naphthalenes using intramolecular ONSH process.
OAc
1a: X= H, EWG = COOMe
1b: X= OMe, EWG = COOMe
1c: X= Cl, EWG = COOMe
1d: X= H, EWG = COMe
O2N
EWG
O2N
X
EWG R-CH2NO2
Conditionsa
X
1a-1d
R
R = Me, Et, n-Pr, CH2CH2COOMe, CH2Ph, CH2-(2-thienyl), Ph, COOEt
O2N
O2N
COOMe
O2N
COOMe
O2N
O2N
COOMe
O2N
O2N
COOMe
CH2CH2CH3
CH3
2a (48%)
CH2CH3
CH2CH2COOMe
2c (50%)
2b (49%)
2d (47%)
COOMe
COOMe
COOMe
COOMe
O2N
COOMe
COOMe
COOEt
2h (58%)
Ph
2g (48%)
CH2Ph
2e (49%)
S
2f (46%)
O
O2N
O2N
COOMe
O2N
O2N
Cl
CH3
MeO
MeO
CH2CH3
2i (49%)
COOEt
2j (61%)b
CH2CH3
2k (49%)
COOEt
2l (50%)
a
b
Conditions: MBH acetate 1 (1.0 mmol), nitroalkane (2.0 equiv), Cs2CO3 (3.0 equiv), DMSO, room temperature, 1 h, O2 balloon.
Room temperature (1 h) and then 50 ꢀC (3 h).
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O2N
COOMe
O2N
COOMe
O2N
COOMe
O2N
COOMe
NO2
Cs2CO3
O2
- HOO
ONSH
H
(path a)
H
HOO
H3C NO2
H
H3C NO2
H3C NO2
CH3
I
ꢀH-adduct II
IV
III
- HNO2
2a
CH3CH2NO2
SN2'
O2N
H+
COOMe
O2N
COOMe
- HNO2
VNS
(path b)
O2
1a
H
VI
CH3
CH3
V
Scheme 4. Proposed mechanism for the formation of 2a.
o
and nitroethane would form an intermediate I, which could
be converted to the σH-adduct II in the presence of Cs2CO3.
The σH-adduct II might be converted to the hydroperoxide
III in the presence of molecular oxygen,6,7 and III was
changed to dihydronaphthalene IV by liberation of hydro-
peroxide.6,7 Final elimination of nitrous acid furnished 2a
(path a).14 The intermediate II is a tertiary nitroalkane, thus
dihydronaphthalene VI might be formed by elimination of
Compound 2b: 49%; pale yellow solid, mp 164–166 C;
IR (KBr) 1723, 1531, 1347, 1279, 1249 cm−1; H NMR
1
(CDCl3, 600 MHz) δ 1.42 (t, J = 7.8 Hz, 3H), 3.18
(q, J = 7.8 Hz, 2H), 4.01 (s, 3H), 8.12 (s, 1H), 8.20
(d, J = 9.0 Hz, 1H), 8.35 (dd, J = 9.0, 2.4 Hz, 1H), 8.62
(s, 1H), 8.89 (d, J = 2.4 Hz, 1H); 13C NMR (CDCl3,
125 MHz) δ 14.76, 25.95, 52.55, 121.16, 125.63, 126.44,
127.81, 129.27, 130.98, 131.91, 136.38, 141.45, 145.61,
166.47; ESIMS m/z 260 [M++H]. Anal. calcd for
C14H13NO4: C, 64.86; H, 5.05; N, 5.40. Found: C,
64.77; H, 5.32; N, 5.21.
15
HNO2 and a following protonation (path b) according to
vicarious nucleophilic substitution (VNS)4 of hydrogen
pathway. A subsequent aerobic oxidation of VI could pro-
vide 2a.16 Thus, the mechanism involving VNS pathway
could not be excluded completely at this stage.
o
Compound 2h: 58%; pale yellow solid, mp 184–186 C;
IR (KBr) 1720, 1707, 1530, 1335, 1231 cm−1; H NMR
1
In summary, various poly-substituted naphthalenes bear-
ing a nitro group at 6- or 7-positions were synthesized from
MBH acetates and primary nitroalkanes17 in moderate
yields in one-pot procedure. The reaction involved three
consecutive processes: an introduction of nitroalkane in
SN20 fashion, an intramolecular aerobic ONSH reaction,
and a final E2 elimination of HNO2.
(CDCl3, 500 MHz) δ 1.51 (t, J = 7.0 Hz, 3H), 4.06
(s, 3H), 4.54 (q, J = 7.0 Hz, 2H), 8.45 (dd, J = 9.5,
2.5 Hz, 1H), 8.91 (d, J = 1.5 Hz, 1H), 8.92 (d, J = 2.5 Hz,
1H), 8.93 (d, J = 1.5 Hz, 1H), 9.20 (d, J = 9.5 Hz, 1H);
13C NMR (CDCl3, 125 MHz) δ 14.33, 52.83, 61.92,
122.84, 125.85, 128.21, 128.37, 128.58, 132.25, 132.69,
135.71, 136.88, 145.94, 165.44, 165.95; ESIMS m/z
304 [M+ + H]. Anal. calcd for C15H13NO6: C, 59.41; H,
4.32; N, 4.62. Found: C, 59.70; H, 4.26; N, 4.54.
Experimental
Acknowledgments. This work was supported by the
National Research Foundation of Korea (NRF) grant
funded by the Korea government (MSIP) (NRF-
2015R1A4A1041036). Spectroscopic data were obtained
from the Korea Basic Science Institute, Gwangju branch.
Typical Procedure for the Synthesis of 2a. To a stirred
solution of MBH acetate 1a (279 mg, 1.0 mmol) and
nitroethane (150 mg, 2.0 mmol) in DMSO (4.0 mL) was
added Cs2CO3 (978 mg, 3.0 mmol) at room temperature,
and the reaction mixture was stirred for 1 h under O2 bal-
loon atmosphere. After the usual aqueous extractive workup
with EtOAc and column chromatographic purification proc-
ess (hexanes/CH2Cl2/EtOAc, 15:2:1), compound 2a was
obtained as a pale yellow solid, 118 mg (48%). Selected
spectroscopic data of 2a, 2b and 2h are as follows.
Supporting Information. Additional supporting informa-
tion is available in the online version of this article.
References
o
Compound 2a: 48%; pale yellow solid, mp 218–220 C;
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Bull. Korean Chem. Soc. 2016, Vol. 37, 946–949
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by both the presence of an electron-donating methoxy group
and an electron-delocalization of the anionic ethyl nitroacetate
moiety.
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the formation of many intractable side products was observed.
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in their case proceeds even under argon atmosphere, and they
suggested the involvement of DMSO as an oxidant.6b
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Bull. Korean Chem. Soc. 2016, Vol. 37, 946–949
© 2016 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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