An oxy-Michael addition: 2,5-Dihydroxy-1,4-benzoquinone-assisted synthesis of 1-[ethoxy(phenyl)methyl]-2-naphthol and 5-[ethoxy(phenyl)methyl]-6- hydroxyquinoline derivatives

Article abstract of DOI:10.1007/s11164-012-0951-9

The 2,5-dihydroxy-1,4-benzoquinone-assisted oxy-Michael addition reaction between an aromatic aldehyde, EtOH and 2-naphthol or 6-hydroxyquinoline in the presence of HCl to afford the 1-[ethoxy(aryl)methyl]-2-naphthol and 5-[ethoxy(phenyl)methyl]-6-hydroxy

Full text of DOI:10.1007/s11164-012-0951-9

Res Chem Intermed
DOI 10.1007/s11164-012-0951-9
An oxy-Michael addition: 2,5-dihydroxy-
1,4-benzoquinone-assisted synthesis of
1-[ethoxy(phenyl)methyl]-2-naphthol and
5-[ethoxy(phenyl)methyl]-6-hydroxyquinoline
derivatives
•
Sajjad Keshipour Ahmad Shaabani
•
•
Milad Pedarpour Afshin Sarvary
Received: 16 September 2012 / Accepted: 22 November 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract The 2,5-dihydroxy-1,4-benzoquinone-assisted oxy-Michael addition reac-
tion between an aromatic aldehyde, EtOH and 2-naphthol or 6-hydroxyquinoline in the
presence of HCl to afford the 1-[ethoxy(aryl)methyl]-2-naphthol and 5-[eth-
oxy(phenyl)methyl]-6-hydroxyquinoline derivatives at room temperature is described.
Keywords Oxy-Michael addition Á o-Naphthoquinone methide Á
Multi-component reactions Á 2-Naphthol Á 6-Hydroxyquinoline
Introduction
Naphthalene and quinoline nucleus are commonly found in pharmaceutical and
agricultural agents [1–6]. For example, hydroxyquinoline and styrylquinoline
derivatives have been reported as potential HIV-1 integrase inhibitors [7] and
antifungal agents [8]. Also, some of them have herbicidal and antineoplastic
activities [9]. These compounds showed a good antifungal activity similar to some
novel compounds. So, hydroxyl-functionalized derivatives such as 2-naphthols are
one of the interesting scaffolds with bactericide and antioxidant activity [10].
o-Quinone methides (oQMs) are reactive a,b-unsaturated ketones and important
intermediates in many chemical and biological processes [11–13]. These interme-
diates are efficient dDNA alkylating and cross-linking agents [14, 15], and are
believed to be responsible for the cytotoxicity of antitumor antibiotics of the
mitomycin C and anthracycline families [16, 17]. These reactive species are
generated by photochemical dehydration of o-hydroxybenzyl alcohols and its
analogues [18–20]. High electrophilicity of the methide C- atom and also the Diels–
Alder reaction with electron-rich alkenes to oQMs are two of their important
S. Keshipour Á A. Shaabani (&) Á M. Pedarpour Á A. Sarvary
Department of Chemistry, Shahid Beheshti University G. C, P. O. Box 19396-4716, Tehran, Iran
e-mail: a-shaabani@sbu.ac.ir
123

S. Keshipour et al.
Fig. 1 Structures of oQM and
oNQMs
Scheme 1 Expected (4) and observed (5, 6) reaction products
synthetic features [18–22]. Recently, the photochemical generation and the
reactivity of o-naphthoquinone methides (oNQMs) were studied [23]. Irradiation
of 3-hydroxy-2-naphthalenemethanol and 2-hydroxy-1-naphthalenemethanol fol-
lowed by efficient dehydration led to the formation of isomeric oNQMs (Fig. 1).
b-Alkoxy ketones are valuable building blocks in a variety of natural products
[24]. These compounds are usually prepared by the aldol reaction and the
subsequent alkylation of the resulting hydroxyl group [25, 26]. The oxy-Michael
addition of the O-nucleophiles to electron-deficient a,b-unsaturated ketones has
been a significant challenge in organic synthesis, owing to the low reactivity
coupled with the reversibility of the reaction [27–33]. Some of the electron-deficient
olefins could undergo conjugate addition of the O-nucleophiles in the presence of
various acids and amines [30, 34–36].
In continuation of our study on multi-component reactions [37–40], 2,5-
dihydroxy-1,4-benzoquinone [41], and Michael additions [42], we investigated the
reaction of 2-naphthol (1a) or 6-hydroxyquinoline (1b), aromatic aldehydes 2, and
2,5-dihydroxy-1,4-benzoquinone (3) in the mixture of HCl (37 %) and ethanol (1:1)
at ambient temperature. In the event, the desired product 4 was not obtained, instead
the reaction afforded the corresponding products 5a–j in good to moderate yields
assisted with 2,5-dihydroxy-1,4-benzoquinone (3). The xanthene 6 is produced in
traces as a by-product (Scheme 1).
Results and discussion
In a pilot experiment, 2-naphthol (1a) (1 mmol), 2-nitrobenzaldehyde (2c)
(1 mmol), and 3 (1 mmol) were stirred in EtOH/HCl (1:1) for 24 h at room
temperature. On completion, the reaction mixture was filtered, and the precipitate
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An oxy-Michael addition
Scheme 2 The reaction of 2-naphthol (1a) and 3-methoxybenzaldehyde (2f) in the absence of
2,5-dihydroxy-1,4-benzoquinone (3)
washed with H2O/EtOH (1:2). The crude product (5c) was purified by recrystal-
lization from CH2Cl2/n-hexane (1:2) and was obtained in 82 % yield.
To illustrate the role of 3, the reaction of 1a and 3-methoxybenzaldehyde (2f)
was studied in the absence of 3. However, 14-phenyl-14H-dibenzo[a,j]xanthene (6)
was produced instead of the expected product 5 via a condensation reaction of 2f
with two molecules of 1a (Scheme 2) [44].
As indicated in Table 1, the optimum amount of 3 in the reaction of 2-naphthol
(1a) and 3-nitrozaldehyde (2a) was examined in EtOH/HCl (37 %) (1:1) at room
temperature for 24 h. The highest yield of 5a was obtained with 100 % of 3. A
further increase in the amount of 3 up to 150 % did not have significant effects on
the product yield.
To explore the scope and limitations of the reaction, we extended our studies to
various aldehydes and 6-hydroxyquinoline (1b) instead of 2-naphthol (1a). As
indicated in Fig. 2, aromatic aldehydes 2 containing electron-donating or electron-
withdrawing groups, and 1a or 1b in EtOH in the presence of 3 undergo a smooth
1:1:1 addition reaction at room temperature to produce 1-[ethoxy(aryl)methyl]-2-
naphthol and 5-[ethoxy(phenyl)methyl]-6-hydroxyquinoline derivatives 5a–j in
good to moderate yields.
The structure of compounds 5a–j was deduced from their IR, 1H NMR, 13C NMR
data, and elemental analyses. The 1H NMR spectrum of 5c consisted of a triplet for
3
the Me group (0.96 ppm, JHH = 7.0 Hz), two multiplets for CH2O (3.23 and
3
3.30 ppm, JHH = 7.0 Hz), a singlet for CH (3.98 ppm), a multiplet for aromatic
H-atoms (6.71–7.96 ppm), and a broad singlet for the OH group (10.12 ppm). The
1H decoupled 13C NMR spectrum of 5c showed 19 distinct resonances; partial
assignment of these resonances is given in the experimental section.
Table 1 Optimization of the amounts of 2,5-dihydroxy-1,4-benzoquinone (3)
Entry
1
2
3
4
5
6
Catalyst 3 (mol%)
Yield (%)a
5
25
21
50
42
75
63
100
86
150
87
Trace
Reaction conditions: 2-naphthol (1a) (1 mmol), 4-nitrobenzaldehyde (2a) (1 mmol), EtOH/HCl (37 %)
(1:1) (10 mL), room temperature, 24 h
a
Isolated yield
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S. Keshipour et al.
Fig. 2 Structures of products 5a–j
Further investigations into the scope, mechanism, and synthetic applications of
this reaction are now in progress.
Conclusions
A simple and efficient one-pot multi-component reaction for the synthesis of
1-[ethoxy(phenyl)methyl]-2-naphthol and 5-[ethoxy(phenyl)methyl]-6-hydroxy-
quinoline derivatives via an oxy-Michael addition reaction has been elaborated.
We developed a new route for oNQM generating and trapping it via ethoxy group
nucleophilic addition. To the best of our knowledge, this is the first reaction
promoted by 2,5-dihydroxy-1,4-benzoquinone as the auxiliary.
Experimental
Melting points were measured on an Electrothermal 9100 apparatus and are
uncorrected. IR spectra were recorded in KBr on a Shimadzu IR-470 spectrometer.
1H NMR Spectra were recorded on a Bruker DRX-300 Avance spectrometer at
300.13 MHz. The 13C NMR spectra were recorded at 75.47 MHz; for all NMR
spectra data, chemical shifts (d scale) are reported in parts per million (ppm). The
elemental analyses were performed with an Elementar Analysensysteme VarioEL.
The chemicals used in this work were purchased from Merck and Fluka Chemical.
Typical procedure for preparation of 1-[Ethoxy(4-nitrophenyl)methyl]-2-
naphthol (5a)
To a magnetically stirred solution of 2-naphthol (1a, 0.14 g, 1.0 mmol) in EtOH/
HCl (37 %) (1:1) (10 ml), 2,5-dihydroxy-1,4-benzoquinone (3, 0.14 g, 1 mmol) and
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An oxy-Michael addition
4-nitrobenzaldehyde (2a, 0.15 g, 1.0 mmol) was added, respectively. The reaction
mixture was stirred for 24 h at room temperature. After completion of the reaction
(monitored by TLC method), the residue was filtered off and crystallized from
CH2Cl2/n-hexane (1:2) and the product 5a was obtained as a brown powder.
1-[Ethoxy(4-nitrophenyl)methyl]-2-naphthol (5a)
Brown powder (0.28 g, yield 86 %). Mp [ 300 °C. IR: 3,272, 3,123, 2,911, 2,850,
1,637, 1,601, 1,571, 1,337 cm-1
.
1H NMR (300 MHz, DMSO) d: 0.94
3
(t, JHH = 6.9, 3H, CH3), 3.19-3.21 (m, 1H, OCH2), 3.27-3.30 (m, 1H, OCH2),
3.94 (s, 1H, CH), 6.69–7.94 (m, 10H, Ar), 10.25 (br s, 1H, OH). 13C NMR
(75 MHz, DMSO) d: 15.1 (CH3), 61.3 (CH2), 69.7 (CH), 113.9, 118.2, 123.0, 125.1,
125.3, 126.3, 128.7, 129.0, 129.4, 129.7, 131.3, 133.1, 133.4, 134.7, 150.1, 154.9.
Anal. Calcd. for C19H17NO4: C, 70.58; H, 5.30; N, 4.33; Found: C, 70.64; H, 5.39;
N, 4.23.
1-[Ethoxy(3-nitrophenyl)methyl]-2-naphthol (5b)
Brown powder (0.26 g, yield 82 %). Mp 292–293 °C. IR: 3,235, 3,097, 2,951,
2,869, 1,643, 1,611, 1,543, 1,347 cm-1
.
1H NMR (300 MHz, CDCl3) d: 1.18
3
(t, JHH = 7.0, 3H, CH3), 3.42–3.44 (m, 1H, OCH2), 3.54–3.57 (m, 1H, OCH2),
4.00 (s, 1H, CH), 7.20–8.32 (m, 10H, Ar), 10.20 (br s, 1H, OH). 13C NMR
(75 MHz, CDCl3) d: 15.7 (CH3), 64.2 (CH2), 74.1 (CH), 117.0, 118.3, 120.5, 122.1,
124.6, 126.5, 129.2, 129.5, 130.2, 130.6, 130.7, 132.3, 132.6, 145.9, 148.2, 154.4.
Anal. Calcd. for C19H17NO4: C, 70.58; H, 5.30; N, 4.33; Found: C, 70.59; H, 5.37;
N, 4.21.
1-[Ethoxy(2-nitrophenyl)methyl]-2-naphthol (5c)
Brown powder (0.26 g, yield 82 %). Mp [ 300 °C. IR: 3,357, 3,111, 2,925, 2,847,
1,648, 1,627, 1,545, 1,350 cm-1
.
1H NMR (300 MHz, DMSO) d: 0.96
3
(t, JHH = 6.9, 3H, CH3), 3.21–3.24 (m, 1H, OCH2), 3.29–3.31 (m, 1H, OCH2),
3.98 (s, 1H, CH), 6.71–7.96 (m, 10H, Ar), 10.12 (br s, 1H, OH). 13C NMR
(75 MHz, DMSO) d: 15.1 (CH3), 65.0 (CH2), 72.9 (CH), 113.8, 118.2, 123.0, 124.4,
125.3, 126.3, 128.9, 129.0, 129.2, 129.3, 131.0, 132.1, 133.1, 134.4, 150.7, 155.2.
Anal. Calcd. for C19H17NO4: C, 70.58; H, 5.30; N, 4.33; Found: C, 70.57; H, 5.35;
N, 4.27.
1-[Ethoxy(p-tolyl)methyl]-2-naphthol (5d)
Brown powder (0.23 g, yield 79 %). Mp [ 300 °C. IR: v 3,239, 3,009, 2,987, 2,911,
1,673, 1,605, 1,587 cm-1. 1H NMR (300 MHz, DMSO) d: 1.15 (t, 3JHH = 6.5, 3H,
CH2CH3), 1.96 (s, 3H, CH3), 4.00–4.04 (m, 3H, OCH2 and CH), 7.21–8.03 (m, 10H,
Ar), 9.98 (br s, 1H, OH). 13C NMR (75 MHz, DMSO) d: 15.1 (CH3), 34.9 (CH3),
55.3 (CH2), 78.1 (CH), 117.2, 119.1, 119.8, 122.2, 123.3, 125.1, 126.1, 126.7, 127.1,
123

S. Keshipour et al.
127.7, 128.0, 128.7, 129.5, 143.3, 146.9, 152.8. Anal. Calcd. for C20H20O2: C,
82.16; H, 6.89; Found: C, 81.07; H, 6.93.
1-[(4-(Benzyloxy)phenyl)(ethoxy)methyl]-2-naphthol (5e)
Brown powder (0.31 g, yield 81 %). Mp [ 300 °C. IR: 3,330, 3,067, 2,931, 1,659,
1,621, 1,537 cm-1. 1H NMR (300 MHz, DMSO) d: 1.17 (t, 3JHH = 6.8, 3H, CH3);
3.40–3.43 (m, 2H, OCH2Ph); 3.49 (br, 3H, CH and OCH2CH3); 7.18–8.20 (m, 15H,
Ar); 10.27 (br s, 1H, OH). 13C NMR (75 MHz, DMSO) d: 15.6 (CH3), 64.2, 64.3,
72.9 (CH), 117.0, 118.3, 120.5, 122.0, 122.9, 123.0, 124.4, 124.5, 126.4, 128.9,
129.2, 130.2, 130.7, 132.3, 132.6, 145.9, 148.2, 154.4. Anal. Calcd. for C26H24O3:
C, 81.22; H, 6.29; Found: C, 81.29; H, 6.17.
1-[Ethoxy(4-methoxyphenyl)methyl]-2-naphthol (5f)
Brown powder (0.19 g, yield 63 %). Mp [ 300 °C. IR: 3,231, 3,123, 2,917, 2,833,
1,641, 1,539, 1,537 cm-1. 1H NMR (300 MHz, DMSO) d: 1.20 (br, 3H, CH3), 3.61
(br, 3H, CH and OCH2), 3.67 (s, 3H, OCH3), 6.74–8.11 (m, 10H, Ar), 9.62 (br s, 1H, OH).
13C NMR (75 MHz, DMSO) d: 31.1 (CH3), 55.3, 56.1, 70.1 (CH), 113.4, 113.5,
113.6, 119.4, 121.0, 122.5, 124.4, 126.2, 128.8, 129.1, 129.5, 130.0, 134.6, 136.1,
153.1, 157.7. Anal. Calcd. for C20H20O3: C, 77.90; H, 6.54; Found: C, 77.79; H,
6.57.
1-[Ethoxy(naphthalen-2-yl)methyl]-2-naphthol (5g)
Brown powder (0.20 g, yield 61 %). Mp [ 300 °C. IR: 3,267, 3,019, 2,857, 1,639,
1,603, 1,531 cm-1. 1H NMR (300 MHz, DMSO) d: 1.05 (t, 3JHH = 7.0, 3H, CH3),
3.43–3.46 (m, 1H, OCH2), 3.90–3.94 (m, 2H, OCH2 and CH), 7.19–8.05 (m, 13H, Ar),
10.13 (br s, 1H, OH). Anal. Calcd. for C23H20O2: C, 84.12; H, 6.14; Found: C,
84.23; H, 6.09.
5-[(4-Bromophenyl)(ethoxy)methyl]-6-hydroxyquinoline (5h)
Dark yellow powder (0.26 g, yield 73 %). Mp 260–263 °C. IR: 3,233, 3,037, 2,928,
1,641, 1,601, 1,573 cm-1. 1H NMR (300 MHz, CDCl3) d: 1.30 (br, 3H, CH3), 3.86
(s, 1H, CH), 3.95–3.98 (m, 2H, OCH2), 6.74–7.88 (m, 9H, Ar), 9.87 (br s, 1H, OH).
13C NMR (75 MHz, CDCl3) d: 36.2 (CH3), 54.5 (CH2), 56.2 (CH), 112.5, 114.3,
114.4, 114.5, 115.8, 116.0, 128.5, 130.0, 130.1, 130.5, 130.6, 133.0, 157.7. Anal.
Calcd. for C18H16BrNO2: C, 60.35; H, 4.50; N, 3.91; Found: C, 60.53; H, 4.56; N,
3.79.
5-[Ethoxy(phenyl)methyl]-6-hydroxyquinoline (5i)
Gray powder (0.20 g, yield 71 %). Mp 230–233 °C. IR: 3,209, 3,102, 2,937, 1,631,
1
1,607, 1,551, 1,403 cm-1. H NMR (300 MHz, CDCl3) d: 1.31 (br, 3H, CH3),
3.98–4.01 (m, 2H, OCH2), 4.48 (s, 1H, CH), 7.10–7.84 (m, 9H, Ar), 9.99 (br s, 1H, OH).
123

An oxy-Michael addition
13C NMR (75 MHz, CDCl3) d: 14.9 (CH3), 57.3 (CH2), 73.9 (CH), 118.4, 119.1,
119.3, 122.2, 123.3, 125.2, 127.1, 127.8, 128.1, 128.7, 128.9, 143.3, 150.9, 156.1.
Anal. Calcd. for C18H17NO2: C, 77.40; H, 6.13; N, 5.01; Found: C, 77.46; H, 6.23;
N, 4.89.
5-[Ethoxy(4-methoxyphenyl)methyl]-quinolin-6-ol (5j)
Gray powder (0.21 g, yield 72 %). Mp 270–272 °C. IR: 3,321, 3,152, 3,019, 2,956,
1
1,672, 1,615, 1,532, 1,471 cm-1. H NMR (300 MHz, CDCl3) d: 1.29 (br, 3H,
CH3), 3.86 (s, 3H, OCH3), 3.96–3.99 (m, 2H, OCH2), 4.31 (s, 1H, CH), 7.12–7.93
(m, 10H, Ar), 10.02 (br s, 1H, OH). Anal. Calcd. for C19H19NO3: C, 73.77; H, 6.19;
N, 4.53; Found: C, 73.83; H, 6.21; N, 4.47.
14-(4-Methoxyphenyl)-14H-dibenzo[a,j]xanthene (6) [43]
1
White powder (0.28 g, yield 73 %). Mp 242–245 °C. H NMR (300 MHz, CDCl3)
d: 3.76 (s, 3H, CH3), 6.83 (s, 1H, CH), 6.87–8.00 (m, 16H, Ar). 13C NMR (75 MHz,
CDCl3) d: 41.7 (CH), 55.2 (CH3), 114.5, 119.2, 119.8, 122.6, 123.1, 127.1, 128.9,
129.3, 129.5, 129.6, 132.8, 133.9, 153.1, 158.4.
Acknowledgment We gratefully acknowledge financial support from the Research Council of the
Shahid Beheshti University.
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