MCM-41@Schiff base-Co(OAc)2 as an efficient catalyst for the synthesis of pyran derivatives

Article abstract of DOI:10.1007/s11164-019-04038-1

Heterogeneous ordered mesoporous silica materials catalyst, MCM-41@Schiff base-Co(AcO)₂, reveals high catalytic performance within the synthesis of pyran derivatives using the multicomponent reaction of aldehydes, malononitrile and 2-naphthol (

Full text of DOI:10.1007/s11164-019-04038-1

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-04038-1
MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst
for the synthesis of pyran derivatives
Shiwei Pan1 · Puhui Li1 · Guihua Xu1 · Jingchang Guo1 · Libin Ke1 ·
Canquan Xie1 · Zhoucai Zhang1 · Yonghai Hui1
Received: 19 July 2019 / Accepted: 4 November 2019
© Springer Nature B.V. 2019
Abstract
Heterogeneous ordered mesoporous silica materials catalyst, MCM-41@Schif base-
Co(AcO)2, reveals high catalytic performance within the synthesis of pyran deriva-
tives using the multicomponent reaction of aldehydes, malononitrile and 2-naphthol
(or cyclohexane-1,3-dione) in water. The reactions aforded the desired products in
high yields (up to 97% and 95%). The substantial feature is that the mesoporous-
complex catalyst could be easily separated from the reaction mixture by centrifuga-
tion and reused at least 6 times with more than 80% yield in activity. The gram-scale
experiments were achieved with good yields and implied that the catalytic method
was efective and convenient for heterocyclic synthesis. What is more, the synthe-
sized catalyst was characterized using various spectroscopic techniques to obtain
the structural and functional features. The analysis results confrmed that the Co-
Schif base complex immobilized on the surface of mesoporous materials MCM-41.
Finally, a plausible reaction mechanism was proposed.
Keywords MCM-41 · Schif base · Heterogeneous · Pyran · Catalysis
Introduction
Pyran is an important structural units of six-membered oxygen heterocyclic com-
pounds, which can build various active structures of biopharmacological molecules
and natural products [1], such as antiproliferative activity of pyranoxanthone [2],
antibacterial agents [3, 4] and apoptosis-inducing agents [5, 6]. With the further
Shiwei Pan and Puhui Li contributed equally to this work.
* Yonghai Hui
hyhai97@126.com
1
College of Chemistry and Chemical Engineering, Key Laboratory of Clean Energy
Materials Chemistry of Guangdong Higher Education Institute, Lingnan Normal University,
Zhanjiang 524048, China
Vol.:(0123456789)
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S. Pan et al.
study of these compounds, pyran derivatives can be widely applied not only in
medicine and biochemistry, but also in these felds of dyes [7, 8], pH sensitizers
[9], semiconductors [10, 11] and materials [12, 13]. Therefore, due to their wide
application value, they have attracted much attention. The new synthetic methods of
pyran derivatives using diferent catalysts have been reported, for instance Brønsted
acid [14], BINOL based [15], Lewis acids [16], ionic liquids [17], nanomaterials
[18–20], etc. And good results were obtained. But the development of simply, envi-
ronment and convenient procedures for the synthesis of pyran or xanthene deriva-
tives continues to be a challenging endeavor in organic catalytic.
In recent years, following the increasing consciousness of “green chemistry,”
remarkable studies have been focused on fnding environmental, atomic economy,
recycling and reuse technology, etc., in the feld of organic synthesis. The ordered
mesoporous silica materials, as heterogeneous catalysts, have attracted particular
attention due to their environmentally friendly nature, low cost, recovery and recy-
clability [21]. This kind of materials has been applied in various felds such as drug
delivery, gas absorption, energy storage, catalysis [22, 23]. We previously reported
some studies with the aim of designing functional MCM-41, as classic heterogene-
ous catalysts, that can be used to the organic catalysis [24]. And among them, Schif
base-supported MCM-41 shows good catalytic activity [25]. In view of the great
potential of MCM-41, we have designed a new heterogeneous MCM-41@Schif
base-Co(AcO)2 catalytic system. In continuance, further investigation was carried
out by using catalyzing the reactions of aldehyde and malononitrile with 2-naphthol
(or cyclohexane-1,3-dione) to confrm the catalytic activity and reusablity. MCM-
41@Schif base-Co(AcO)2 has shown high catalytic performance in this reaction in
water and with high yields (up to 97% and 95%) (Scheme 1).
Experimental
All chemicals and MCM-41 were obtained from Adamas-Beta and used without
further purifcation. The samples were analyzed using FTIR spectroscopy (using a
Bruker equinx 55 in KBr matrix in the range of 4000–400 cm−1). Scanning elec-
tron microscope (SEM) images were recorded on LEO1430VP. Transmission
electron microscope (TEM) images were obtained from a Hitachi H-600 instru-
1
ment. H and 13C NMR spectra were recorded on an INOVA 400 MHz in CDCl3
as solvent and TMS as internal reference (chemical shifts, in ppm). Purifcation
Scheme 1 Synthesis of ligands
1 3

MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
of reaction products was carried out by column chromatography using Qingdao
silica gel (300–400 mesh). Analytical thin-layer chromatography (TLC) was per-
formed on silica gel GF254 (Qingdao, China) with ethyl acetate and petroleum ether
(60–90 °C). Melting points were determined on an elemental digital melting points
apparatus and were uncorrected.
Preparation of L2 and L4
In a typical procedure, 1 g of calcined MCM-41 was added to free three-necked bot-
tle, and then, 50 mL ethanol and 3 mL 3-aminopropyltriethoxysilane were injected
slowly under nitrogen protection. Afterward, refuxing lasted for 12 h and the mix-
ture was recovered by centrifugation. It was washed carefully with diethyl ether and
dichloromethane. The Schif base ligand L4 was synthesized from the reaction with
1 mmol modifcation of MCM-41 (L2) and 1 mmol aldehyde in 40 mL toluene, in
the presence of nitrogen under refux for 12 h. The mixture was cooled to room tem-
perature and fltered to give the corresponding crude product. The pure product was
washed by dichloromethane and petroleum ether.
General procedure for synthesis of pyran derivatives
Aldehyde 1a (0.2 mmol, 28.1 mg), malonitrile 2a (0.2 mmol, 13.2 mg), 2-naph-
thol 3 (0.2 mmol, 28.8 mg) (or 5,5-dimethylcyclohexane-1,3-dione 5a (0.2 mmol,
28.0 mg)) and L4 (0.01 g)-Co(OAc)2 (10 mol%) were added in water (1.0 mL) and
stirred at 100 °C for 3 h until completion (monitored by TLC). Then, the reaction
mixture was extracted with ethyl acetate (5 mL×3). The combined organic was
dried with anhydrous Na2SO4. After fltration and concentration, the residue was
purifed by column chromatography to give the corresponding adducts 4a and 6c.
Physical and spectroscopic data for 4a–4q and 6a–6v
3‑Amino‑1‑(4‑chlorophenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4a) White solid,
yield: 69.90 mg (97%); m.p: 210–211 °C (lit. [26] 207–209 °C); 1H NMR
(400 MHz, DMSO) δ 7.96–7.91 (m, 2H), 7.82–7.80 (m, 1H), 7.47–7.41 (m, 2H),
7.35–7.30 (m, 3H), 7.24–7.18 (m, 2H), 7.00 (s, 2H), 5.36 (s, 1H).
3‑Amino‑1‑(4‑fuorophenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4b) White solid,
yield: 64.74 mg (94%); m.p: 230–231 °C (lit. [26] 226–228 °C); 1H NMR
(400 MHz, DMSO) δ 7.96–7.91 (m, 2H), 7.84–7.82 (m, 1H), 7.48–7.40 (m, 2H),
7.31 (d, J=9.0 Hz, 1H), 7.25–7.19 (m, 2H), 7.15–7.09 (m, 2H), 6.99 (s, 2H), 5.35
(s, 1H).
3‑Amino‑1‑(4‑nitrophenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4c) White solid,
yield: 66.84 mg (90%); m.p: 168–170 °C (lit. [26] 168–170 °C); 1H NMR
(400 MHz, DMSO) δ 8.18–8.12 (m, 2H), 8.01–7.97 (m, 1H), 7.95–7.92 (m, 1H),
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S. Pan et al.
7.81–7.78 (m, 1H), 7.49–7.43 (m, 4H), 7.37 (d, J=8.6 Hz, 1H), 7.12 (s, 2H), 5.55
(s, 1H).
3‑Amino‑1‑(4‑methoxyphenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4d) White solid,
yield: 66.23 mg (93%); m.p: 193–195 °C (lit. [26] 195–197 °C); 1H NMR (400 MHz,
DMSO) δ 7.94–7.90 (m, 2H), 7.85 (d, J=7.7 Hz, 1H), 7.46–7.40 (m, 2H), 7.32 (d,
J=9.0 Hz, 1H), 7.10 (d, J=8.7 Hz, 2H), 6.89 (s, 2H), 6.81 (d, J–8.6 Hz, 2H), 5.24 (s,
1H), 3.67 (s, 3H).
3‑Amino‑1‑(2‑chlorophenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4e) White solid,
yield: 67.83 mg (94%); m.p: 255–256 °C (lit. [26] 265–267 °C); 1H NMR
(400 MHz, DMSO) δ 7.99–7.90 (m, 2H), 7.66–7.62 (m, 1H), 7.51–7.40 (m, 3H),
7.37–7.32 (m, 1H), 7.22–7.15 (m, 2H), 7.06–6.96 (m, 3H), 5.72 (s, 1H).
3‑Amino‑1‑(2‑bromophenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4f) White solid,
yield: 68.08 mg (84%); m.p: 245–246 °C (lit. [26] 229–231 °C); 1H NMR
(400 MHz, DMSO) δ 7.98–7.91 (m, 2H), 7.66–7.62 (m, 2H), 7.50–7.40 (m, 2H),
7.35 (d, J=8.9 Hz, 1H), 7.20 (td, J=7.6, 1.2 Hz, 1H), 7.13–7.03 (m, 3H), 6.92 (d,
J=7.5 Hz, 1H), 5.68 (s, 1H).
3‑Amino‑1‑(2‑methoxyphenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4g) White solid,
yield: 65.57 mg (92%); m.p: 224–225 °C (lit. [26] 222–224 °C); 1H NMR (400 MHz,
DMSO) δ 7.94–7.85 (m, 2H), 7.74 (d, J=8.1 Hz, 1H), 7.46–7.38 (m, 2H), 7.33–7.29
(m, 1H), 7.17–7.07 (m, 1H), 7.05–7.01 (m, 1H), 6.88–6.75 (m, 4H), 5.60 (s, 1H), 3.89
(s, 3H).
3‑Amino‑1‑(3‑chlorophenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4h) White solid,
yield: 66.39 mg (92%); m.p: 230–231 °C (lit. [26] 234–236 °C); 1H NMR
(400 MHz, DMSO) δ 8.02 (d, J=8.4 Hz, 1H), 7.9–7.88 (m, 2H), 7.73 (d, J=5.3 Hz,
2H), 7.53–7.48 (m, J=8.4, 1H), 7.44–7.36 (m, 2H), 7.36–7.33 (m, 1H), 7.20–7.17
(m, 2H), 7.13–7.10 (m, 1H), 5.54 (s, 1H).
3‑Amino‑1‑(2,4‑dichlorophenyl)‑1H‑benzo[f]chromene‑2‑carbonitrile(4i) Whitesolid,
yield 72.72 mg (92%); m.p: 211–212 °C (lit. [27] 214–216 °C); 1H NMR (400 MHz,
DMSO) δ 8.02–7.89 (m, 2H), 7.76–7.54 (m, 2H), 7.52–7.40 (m, 2H), 7.34 (d,
J=8.9 Hz, 1H), 7.30–7.24 (m, 1H), 7.08 (s, 2H), 7.02 (d, J=8.4 Hz, 1H), 5.70 (s, 1H).
3‑Amino‑1‑(naphthalen‑2‑yl)‑1H‑benzo[f]chromene‑2‑carbonitrile (4j) White solid,
yield: 69.26 mg (92%); m.p: 230–231 °C (lit. [28] 210–214 °C); 1H NMR
(400 MHz, DMSO) δ 7.99–7.76 (m, 7H), 7.49–7.35 (m, 5H), 7.24 (dd, J=8.5,
1.7 Hz, 1H), 7.04 (s, 2H), 5.49 (s, 1H).
Ethyl 3‑amino‑1‑(4‑chlorophenyl)‑1H‑benzo[f]chromene‑2‑carboxylate (4k) White
solid, yield: 72.17 mg (95%); m.p: 190–192 °C (lit. [29] 193 °C); 1H NMR
(400 MHz, DMSO) δ 7.99 (d, J=8.3 Hz, 1H), 7.93–7.87 (m, 2H), 7.67 (s, 2H),
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MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
7.52–7.46 (m, 1H), 7.44–7.35 (m, 2H), 7.30–7.21 (m, 4H), 5.52 (s, 1H), 4.16–4.03
(m, 2H), 1.25 (t, J=7.1 Hz, 3H).
Ethyl 3‑amino‑1‑(4‑bromophenyl)‑1H‑benzo[f]chromene‑2‑carboxylate (4l) White
solid, yield: 76.37 mg (90%); m.p: 234–235 °C (lit. [29] 231–232 °C); 1H NMR
(400 MHz, DMSO) δ 7.98 (d, J=8.5 Hz, 1H), 7.89 (dd, J=8.5, 3.0 Hz, 2H), 7.69
(s, 2H), 7.52–7.45 (m, 1H), 7.43–7.33 (m, 4H), 7.23 (t, J=5.4 Hz, 2H), 5.52 (s, 1H),
4.22–3.96 (m, 2H), 1.25 (t, J=7.1 Hz, 3H).
Ethyl 3‑amino‑1‑(4‑nitrophenyl)‑1H‑benzo[f]chromene‑2‑carboxylate (4m) White
solid, yield: 69.49 mg (89%); m.p: 226–227 oC (lit. [29] 233–234 °C); 1H NMR
(400 MHz, DMSO) δ 8.07–8.97 (m, 3H), 7.95–7.88 (m, 2H), 7.77 (s, 2H), 7.58–7.46
(m, 3H), 7.45–7.38 (m, 2H), 5.66 (s, 1H), 4.19–4.00 (m, 2H), 1.26 (t, J=7.1 Hz,
3H).
Ethyl 3‑amino‑1‑(4‑methoxyphenyl)‑1H‑benzo[f]chromene‑2‑carboxylate (4n) White
solid, yield: 69.08 mg (92%); m.p: 150–152 °C (lit. [29] 145–146 °C); 1H NMR
(400 MHz, DMSO) δ 8.01 (d, J=8.5 Hz, 1H), 7.91–7.81 (m, 2H), 7.56 (s, 2H), 7.53–
7.48 (m, 1H), 7.42 (t, J=7.5 Hz, 1H), 7.36 (d, J=8.9 Hz, 1H), 7.18–7.14 (m, 2H),
6.76–6.71 (m, 2H), 5.46 (s, 1H), 4.14–4.07 (m, 2H), 3.63 (s, 3H), 1.27 (t, J=7.1 Hz,
3H).
Ethyl 3‑amino‑1‑(2‑chlorophenyl)‑1H‑benzo[f]chromene‑2‑carboxylate (4o) White
solid, yield: 71.41 mg (94%); m.p: 170–172 °C (lit. [30] 170–172 °C); 1H NMR
(400 MHz, DMSO) δ 8.22 (d, J=8.5 Hz, 1H), 7.90 (d, J=8.7 Hz, 2H), 7.76 (s, 2H),
7.54–7.48 (m, 1H), 7.45–7.39 (m, 1H), 7.38–7.26 (m, 3H), 7.18–7.04 (m, 2H), 5.85
(s, 1H), 4.14–4.04 (m, 2H), 1.18 (t, J=7.1 Hz, 3H).
Ethyl 3‑amino‑1‑(2‑nitrophenyl)‑1H‑benzo[f]chromene‑2‑carboxylate (4p) White
solid, yield: 71.05 mg (91%); m.p: 240–241 °C (lit. [29] 248–250 °C); 1H NMR
(400 MHz, DMSO) δ 8.56 (d, J=8.3 Hz, 1H), 8.02–7.85 (m, 3H), 7.78 (s, 2H),
7.56–7.39 (m, 4H), 7.37–7.30 (m, 1H), 7.11–7.07 (dd, J=7.9, 1.3 Hz, 1H), 6.33 (s,
1H), 4.19–4.12 (m, 1H), 3.90–3.83 (m, 1H), 1.15 (t, J=7.0 Hz, 3H).
Ethyl3‑amino‑1‑(2,4‑dichlorophenyl)‑1H‑benzo[f]chromene‑2‑carboxylate(4q) White
solid, yield: 76.23 mg (92%); m.p: 200–201 °C (lit. [29] 196 °C); 1H NMR (400 MHz,
DMSO) δ 8.13 (d, J=8.4 Hz, 1H), 7.88 (dd, J=8.2, 3.2 Hz, 2H), 7.81 (s, 2H), 7.53–
7.46 (m, 1H), 7.43–7.38 (m, 2H), 7.34 (d, J=8.9 Hz, 1H), 7.29 (d, J=8.5 Hz, 1H),
7.20 (dd, J=8.5, 2.2 Hz, 1H), 5.81 (s, 1H), 4.08 (q, J=7.1 Hz, 2H), 1.18 (t, J=9.2,
3H).
2‑Amino‑7,7‑dimethyl‑5‑oxo‑4‑phenyl‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑carbon‑
itrile (6a) White solid, yield: 55.34 mg (94%); m.p: 220–222 °C (lit. [31] 229–
230 °C); 1H NMR (400 MHz, DMSO) δ 7.29 (t, J=7.4 Hz, 2H), 7.21–7.11 (m, 3H),
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S. Pan et al.
6.97 (s, 2H), 4.17 (s, 1H), 2.51 (dd, J=4.9, 3.0 Hz, 2H), 2.18 (dd, J=59.1, 16.1 Hz,
2H), 1.04 (s, 3H), 0.96 (s, 3H).
2‑Amino‑4‑(4‑fuorophenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6b) White solid, yield: 56.22 mg (90%); m.p: 232–234 °C (lit. [32]
230–232 °C); 1H NMR (400 MHz, DMSO) δ 7.20–7.15 (m, 2H), 7.10 (t, J=8.6 Hz,
2H), 6.95 (s, 2H), 4.21 (s, 1H), 2.60–2.45 (m, 2H), 2.18 (dd, J=54.1, 16.1 Hz, 2H),
1.04 (s, 3H), 0.96 (s, 3H).
2‑Amino‑4‑(4‑chlorophenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6c) White solid, yield: 61.16 mg (93%); m.p: 210–211 °C (lit. [32]
1
213–215 °C); H NMR (400 MHz, DMSO) δ 7.37–7.32 (m, 2H), 7.20–7.15 (m,
2H), 7.04 (s, 2H), 4.20 (s, 1H), 2.51–2.47 (m, 2H), 2.18 (dd, J=57.2, 16.1 Hz, 2H),
1.04 (s, 3H), 0.95 (s, 3H).
2‑Amino‑4‑(4‑bromophenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6d) White solid, yield: 66.44 mg (89%); m.p: 206–208 °C (lit. [31]
1
195–197 °C); H NMR (400 MHz, DMSO) δ 7.50–7.46 (m, 2H), 7.13–7.08 (m,
2H), 7.04 (s, 2H), 4.18 (s, 1H), 2.18 (dd, J=57.7, 15.9 Hz, 2H), 1.24 (s, 2H), 1.04
(s, 3H), 0.95 (s, 3H).
2‑Amino‑7,7‑dimethyl‑4‑(4‑nitrophenyl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6e) White solid, yield: 61.08 mg (90%); m.p: 186–188 °C (lit. [31]
1
180–182 °C); H NMR (400 MHz, DMSO) δ 8.20–8.13 (m, 2H), 7.47–7.42 (m,
2H), 7.16 (s, 2H), 4.35 (d, J=18.7 Hz, 1H), 2.54 (s, 2H), 2.19 (dd, J=59.5, 16.1 Hz,
2H), 1.05 (s, 3H), 0.96 (s, 3H).
2‑Amino‑4‑(4‑methoxyphenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6f) White solid, yield: 59.04 mg (91%); m.p: 200–202 °C (lit. [31]
200–203 °C); 1H NMR (400 MHz, DMSO) δ 7.09–7.02 (m, 2H), 6.92 (s, 2H), 6.85–
6.82 (m, 2H), 4.12 (s, 1H), 3.72 (s, 3H), 2.51 (d, J=1.8 Hz, 2H), 2.17 (dd, J=60.4,
16.1 Hz, 2H), 1.04 (s, 3H), 0.95 (s, 3H).
2‑Amino‑7,7‑dimethyl‑5‑oxo‑4‑(p‑tolyl)‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑car‑
bonitrile (16g) White solid, yield: 57.98 mg (94%); m.p: 212–214 °C (lit. [31] 208–
210 °C); H NMR (400 MHz, DMSO) δ 7.05 (dd, J=25.9, 8.0 Hz, 4H), 6.93 (s,
2H), 4.13 (s, 1H), 2.50 (s, 3H), 2.28–2.22 (m, 4H), 1.04 (s, 3H), 0.95 (s, 3H).
2‑Amino‑4‑(3‑chlorophenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6h) White solid, yield: 60.50 mg (92%); m.p: 211–213 °C (lit. [31]
1
210–212 °C); H NMR (400 MHz, DMSO) δ 7.35–7.31 (m, 1H), 7.27–7.25 (m,
1H), 7.17–7.16 (m, 1H), 7.14–7.11 (m, 1H), 7.07 (s, 2H), 4.22 (s, 1H), 2.55–2.49
(m, 2H), 2.28–2.11 (m, 2H), 1.04 (s, 3H), 0.96 (s, 3H).
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MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
2‑Amino‑7,7‑dimethyl‑5‑oxo‑4‑(m‑tolyl)‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑car‑
bonitrile (6i) White solid, yield: 56.13 mg (91%); m.p: 220–222 °C (lit. [26] 204–
206 °C); 1H NMR (400 MHz, DMSO) δ 7.17 (t, J=7.5 Hz, 1H), 7.00 (d, J=7.5 Hz,
1H), 6.96–6.91 (m, 4H), 4.13 (s, 1H), 2.52 (s, 2H), 2.27 (s, 3H), 2.24–2.09 (m, 2H),
1.04 (s, 3H), 0.97 (s, 3H).
2‑Amino‑4‑(2‑chlorophenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6j) White solid, yield: 61.81 mg (94%); m.p: 215–216 °C (lit. [31]
1
190–192 °C); H NMR (400 MHz, DMSO) δ 7.36 (dd, J=7.8, 1.3 Hz, 1H), 7.27
(td, J=7.4, 1.4 Hz, 1H), 2.23–7.16 (m, 2H), 7.00 (s, 2H), 4.70 (s, 1H), 2.52–2.49
(m, 2H), 2.17 (dd, J=67.8, 16.0 Hz, 2H), 1.05 (s, 3H), 0.99 (s, 3H).
2‑Amino‑4‑(2‑bromophenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6k) White solid, yield: 67.19 mg (90%); m.p: 151–152 °C (lit. [33]
150–152 °C); 1H NMR (400 MHz, DMSO) δ 7.55–7.51 (m, 1H), 7.31 (dd, J=10.9,
4.2 Hz, 1H), 7.12 (ddd, J=12.9, 6.8, 2.8 Hz, 2H), 7.00 (s, 2H), 4.71 (s, 1H), 2.53 (d,
J=3.5 Hz, 2H), 2.16 (dd, J=66.6, 16.0 Hz, 2H), 1.05 (s, 3H), 0.99 (s, 3H).
2‑Amino‑7,7‑dimethyl‑4‑(2‑nitrophenyl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6l) White solid, yield: 62.44 mg (92%); m.p: 222–224 °C (lit. [31]
230–232 °C); 1H NMR (400 MHz, DMSO) δ 7.82 (dd, J=8.1, 1.3 Hz, 1H), 7.66
(td, J=7.7, 1.3 Hz, 1H), 7.46–7.39 (m, 1H), 7.36 (dd, J=7.9, 1.4 Hz, 1H), 7.16
(s, 2H), 4.94 (s, 1H), 2.56 (d, J=1.5 Hz, 1H), 2.46 (d, J=17.6 Hz, 1H), 2.11 (dd,
J=73.5, 16.2 Hz, 2H), 1.02 (s, 3H), 0.89 (s, 3H).
2‑Amino‑4‑(2‑methoxyphenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6m) White solid, yield: 60.33 mg (93%); m.p: 202–204 °C (lit. [31]
1
190–194 °C); H NMR (400 MHz, DMSO) δ 7.18–7.13 (m, 1H), 7.00–7.93 (m,
2H), 6.85 (td, J=7.4, 1.1 Hz, 1H), 6.79 (s, 2H), 4.48 (s, 1H), 3.75 (s, 3H), 2.55 (d,
J=17.5, 1H), 2.45 (d, J=17.6 Hz, 1H), 2.27–2.04 (m, 2H), 1.05 (s, 3H), 0.97 (s,
3H).
2‑Amino‑4‑(2,4‑dichlorophenyl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitri1le (6n) White solid, yield: 69.02 mg (95%); m.p: 200–201 °C (lit. [31] 200–
202 °C); H NMR (400 MHz, DMSO) δ 7.52 (d, J=2.2 Hz, 1H), 7.36 (dd, J=8.4,
2.2 Hz, 1H), 7.21 (d, J=8.4 Hz, 1H), 7.07 (s, 2H), 4.68 (s, 1H), 2.51–2.50 (m, 2H),
2.17 (dd, J=65.0, 16.0 Hz, 2H), 1.04 (s, 3H), 0.98 (s, 3H).
2‑Amino‑7,7‑dimethyl‑4‑(naphthalen‑1‑yl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑
carbonitrile (6o) White solid, yield: 60.62 mg (88%); m.p: 230–232 °C (lit. [34]
1
232–233 °C); H NMR (400 MHz, DMSO) δ 8.37 (d, J=8.6 Hz, 1H), 7.94–7.89
(m, 1H), 7.77 (d, J=8.2 Hz, 1H), 7.59–7.50 (m, 2H), 7.48–7.42 (m, 1H), 7.24 (d,
J=6.6 Hz, 1H), 6.94 (s, 2H), 5.14 (s, 1H), 2.60 (s, 2H), 2.16 (dd, J=68.7, 16.1 Hz,
2H), 1.07 (s, 3H), 1.00 (s, 3H).
1 3

S. Pan et al.
2‑Amino‑4‑(furan‑2‑yl)‑7,7‑dimethyl‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑car‑
bonitrile (6p) White solid, yield: 51.18 mg (90%); m.p: 222–224 °C (lit. [34] 219–
221 °C); 1H NMR (400 MHz, DMSO) δ 7.49–7.46 (m, 1H), 7.05 (s, 2H), 6.32 (dd,
J=3.2, 1.9 Hz, 1H), 6.07–6.03 (m, 1H), 4.33 (s, 1H), 2.53 (d, J=14.5 Hz, 1H), 2.45
(d, J=17.7 Hz, 1H), 2.23 (dd, J=46.5, 16.1 Hz, 2H), 1.05 (s, 3H), 0.99 (s, 3H).
2‑Amino‑5‑oxo‑4‑phenyl‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑carbonitrile (6q) White
1
solid, yield: 49.53 mg (93%); m.p: 215–217 °C (lit. [35] 211–212 °C); H NMR
(400 MHz, DMSO) δ 7.28 (dd, J=10.4, 4.3 Hz, 2H), 7.21–7.18 (m, 1H), 7.16 (d,
J=1.4 Hz, 1H), 7.15 (s, 1H), 6.96 (s, 2H), 4.18 (s, 1H), 2.65–2.60 (m, 2H), 2.32–
2.24 (m, 2H), 2.00–1.92 (m, 2H).
2‑Amino‑4‑(4‑fuorophenyl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑carbonitrile
(6r) White solid, yield: 53.45 mg (94%); m.p: 190–191 °C (lit. [35] 209–210 °C);
1H NMR (400 MHz, DMSO) δ 7.22–7.16 (m, 2H), 7.13–7.07 (m, 2H), 7.00 (s, 2H),
4.21 (s, 1H), 2.63–2.58 (m, 2H), 2.34–2.23 (m, 2H), 1.99–1.86 (m, 2H).
2‑Amino‑4‑(4‑chlorophenyl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑carbonitrile
(6s) White solid, yield: 55.34 mg (92%); m.p: 223–224 °C (lit. [26] 224–226 °C);
1H NMR (400 MHz, DMSO) δ 7.34 (dd, J=8.7, 2.1 Hz, 2H), 7.20–7.17 (m, 2H),
7.03 (s, 2H), 4.20 (s, 1H), 2.64–2.59 (m, 2H), 2.32–2.23 (m, 2H), 1.97–1.87 (m,
2H).
2‑Amino‑4‑(4‑methoxyphenyl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑carbon‑
itrile (6t) White solid, yield: 53.34 mg (90%); m.p: 190–192 °C (lit. [26] 190–
192 °C); 1H NMR (400 MHz, DMSO) δ 7.09–7.04 (m, 2H), 6.92 (s, 2H), 6.86–6.81
(m, 2H), 4.14 (s, 1H), 3.72 (s, 3H), 2.64–2.55 (m, 2H), 2.33–2.22 (m, 2H), 2.00–
1.85 (m, 2H).
2‑Amino‑4‑(3‑chlorophenyl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑carbonitr1ile
(6u) White solid, yield: 57.14 mg (95%); m.p: 253–255 °C (lit. [26] 254 °C); H
NMR (400 MHz, DMSO) δ 7.33 (t, J=7.8 Hz, 1H), 7.27–7.24 (m, 1H), 7.18 (t,
J=1.9 Hz, 1H), 7.14 (dd, J=7.5, 1.2 Hz, 1H), 7.06 (s, 2H), 4.22 (s, 1H), 2.69–2.57
(m, 2H), 2.23–2.24 (m, 2H), 1.98–1.86 (m, 2H).
2‑Amino‑4‑(2‑chlorophenyl)‑5‑oxo‑5,6,7,8‑tetrahydro‑4H‑chromene‑3‑carbonitrile
(6v) White solid, yield: 54.13 mg (90%); m.p: 212–214 °C (lit. [31] 212–214 °C);
1H NMR (400 MHz, DMSO) δ 7.38–7.34 (m, 1H), 7.29–7.24 (m, 1H), 7.22–7.17
(m, 2H), 6.99 (s, 2H), 4.71 (s, 1H), 2.66–2.59 (m, 2H), 2.34–2.20 (m, 2H), 1.99–
1.87 (m, 2H).
1 3

MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
Results and discussion
The FTIR spectra of MCM-41 (L1), amine-functionalized MCM-41 (L2), MCM-
41@Schif base (L4) and MCM-41@Schif base-M (L4-Co(OAc)2) are shown in
Fig. 1. The FTIR spectrum of mesoporous materials catalysts exhibited characteris-
tic peaks at 1085 cm−1 and 799 cm−1 corresponding to Si–O–Si band. A new weak
adsorption peak around 2950 cm−1 was corresponding to vibration of N–H band
of amine-functionalized MCM-41. In the FTIR spectrum of L4, the presence of
the C=N group was confrmed at 1670 cm−1. The C=N band absorption shifts to
lower frequency of the spectrum of L4/M (Co(OAc)2) compared with the spectrum
of L4, which indicates that C=N coordinates with cobalt successfully. XRD spectra
of L1–L4/M are shown in Fig. 2. In the range of 15°–30°, the basic pore structure
was kept. In the spectrum of L4/M, a signifcant decrease in intensity was observed
because of placing Schif base group and metal salt into the MCM-41 pores that
change the internal structure of the mesoporous [36, 37]. SEM (Fig. 3) and TEM
(Fig. 4) of the diferent catalysts indicated that the nanoparticles showed uniform
Fig. 1 IR patterns of MCM-41 L1, amine-functionalized MCM-41 L2, L4, L4/M and L4/M (recycled)
catalyst)
Fig. 2 XRD patterns of MCM-
41 L1, amine-functionalized
MCM-41 L2, L4 and L4/M
1 3

S. Pan et al.
Fig. 3 SEM patterns of MCM-41 L1, amine-functionalized MCM-41 L2 and L4
Fig. 4 TEM patterns of MCM-41 L1, amine-functionalized MCM-41 L2 and L4
spherical shape. And the TEM image showed the hierarchical hollow mesoporous
structure of material.
The binding energies of the catalyst L4/M were 284.8 eV which were shown in
the deconvoluted XPS spectra in Fig. 5. In C 1s XPS spectra, there are three peaks
around 284.8, 286.4 and 288.0 eV which represented the C=C, C=N and C–Cl
groups, respectively [38]. In N 1s XPS spectra, there is a signal around 402.68 eV
which confrmed the C=N group of Schif base formation involves the condensation
of 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde and amine-functional-
ized MCM-41 L2. In O 1s XPS spectra, there is a peak at 532.28 eV that is Si–O–C
group. And, there is a peak around 399.48 eV that is the electron pair efect of nitro-
gen atoms and cobalt ions. The satellite peak of Co 2p 1/2 and Co 2p 3/2 spectra of
the catalyst complex shows two typical bands at 797.48 and 781.28 eV confrmed
the binding energy of Cobalt atom with Co2+ ion and the coordination of cobalt
metal with the C=N of Schif base and heterocycle groups. There is a satellite peak
around 797.48 eV, i.e., Co 2p 3/2, which confrmed the electrostatic interaction with
the L4 and Co(OAc)2. Furthermore, the wide survey of XPS spectra confrms that
there were C, O, N, Co and Si atoms on the synthesized catalyst.
In our initial study, we screened various catalysts to the reaction of 4-chlo-
robenzaldehyde 1a and malononitrile 2a with 2-naphthol 3. First, the catalytic
1 3

MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
Fig. 5 XPS analysis of L4/M with a C 1s scan, b N 1s scan, c O 1 s scan, d Co 2p scan, and e elemental
survey
activity of SiO2, MCM-41 and MCM-41@Schif bases in the multicomponent
reaction was tested. MCM-41 and MCM-41@Schif bases exhibited better cata-
lytic activity than SiO2, and L4 was found to be the most suitable for the reaction
and gave the highest reactivity (Table 1, entries 2–7). Comparative results indi-
cated that the pores indeed facilitated the reaction.
Following, the catalytic activity of a series of Lewis acids such as Zn(OAc)2,
Ni(OAc)2, Cu(OAc)2 and Co(OAc)2 was examined. L4-Co(OAc)2 gave the best
result, 95% yield (Table 1, entries 8–11). However, only 37% yield was achieved
1 3

S. Pan et al.
Table 1 Optimization of the
Entry Catalyst
Solvent Time (h) Temp (°C) Yield (%)a
reaction conditions
1
2
3
4
5
6
7
8
None
SiO2
L1
Water
Water
Water
Water
Water
Water
Water
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
100
100
100
100
100
100
100
100
100
100
100
100
90
80
50
100
100
100
100
–
–
20
31
32
60
41
36
45
35
95
37
79
75
68
30/54/94
97
L2
L3
L4
L5
L4/Zn(OAc)2 Water
L4/Ni(OAc)2 Water
L4/Cu(OAc)2 Water
L4/Co(OAc)2 Water
9
10
11
12
13
14
15
16
17b
18c
19d
Co(OAc)2
Water
L4/Co(OAc)2 Water
L4/Co(OAc)2 Water
L4/Co(OAc)2 Water
L4/Co(OAc)2 Water
L4/Co(OAc)2 water
L4/Co(OAc)2 Water
L4/Co(OAc)2 Water
1/2/5
3
3
90
90/80
3
Reaction conditions (unless noted otherwise): All the reactions were
performed with 4-chlorobenzaldehyde (0.20 mmol), malononitrile
(0.20 mmol), 2-naphthol (0.20 mmol), L (0.01 g) and Co(OAc)2
(10 mol%) in water (1 mL) at 100 °C for 3 h
aIsolated yield
b1a:2a:3=1:1.2:1
c1a:2a:3=1.1:1:1
dUse 5 mol% and 2.5 mol% Co(OAc)2
Scheme 2 Synthesis of 2-amino benzo[H] chromene with 2-naphthol
when the catalyst was Co(OAc)2 (Table 1, entry 12). Finally, some parameters
were considered to obtain higher yield. The efect of temperature, time, substrate
ratio and the catalyst loading was examined (Table 1, entries 13–18). It is note-
worthy when the substrate ratio was 1:1.2:1, 97% yield was achieved (Table 1,
1 3

MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
Table 2 Synthesis of 2-amino
Entry
R1
R2
Product
Yield(%)a
benzo[h] chromenes 4 from
2-naphthol
1
4-Cl–C6H4
CN
CN
CN
CN
CN
CN
CN
CN
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
97
94
90
93
94
84
92
92
92
92
95
90
89
92
94
91
92
2
4-F–C6H4
3
4
5
4-NO2–C6H4
4-CH3O–C6H4
2-Cl–C6H4
6
7
8
2-Br–C6H4
2-CH3O–C6H4
3-Cl–C6H4
9
2,4-Cl–C6H3
2-Naphthyl
4-Cl–C6H4
4-Br–C6H4
4-NO2–C6H4
4-CH3O–C6H4
2-Cl–C6H4
CN
CN
10
11
12
13
14
15
16
17
COOEt
COOEt
COOEt
COOEt
COOEt
COOEt
COOEt
2-NO2–C6H4
2,4-Cl–C6H3
Reaction conditions (unless noted otherwise): All the reactions were
performed with 1 (0.20 mmol), 2 (0.24 mmol), 3 (0.20 mmol), L4
(0.01 g) and Co(OAc)2 (10 mol%) in water (1 mL) at 100 °C for 3 h
aIsolated yield
entry 17). Extensive screening showed that the optimized conditions were 1a
(0.20 mmol), 2a (0.24 mmol), 3 (0.20 mmol), L4 (0.01 g)/Co(OAc)2 (10 mol%)
in water (1 mL) at 100 °C for 3 h (Scheme 2).
Under the optimized conditions, the substrate scope of the aromatic aldehyde and
malononitrile (or ethyl cyanoacetate) was investigated, and the corresponding prod-
ucts were obtained in good yields. As shown in Table 2, whether R2 was CN or
COOEt, the electronic nature and the position of the diferent substituents on the
aromatic ring had little infuence on yields. Moreover, fused-ring and multisubsti-
tuted aldehydes were also suitable substrates for the reaction (Table 2, entries 9, 10
and 17) (Scheme 3).
Scheme 3 Synthesis of 2-amino benzo[H] chromene derivatives
1 3

S. Pan et al.
Scheme 4 Synthesis of 2-amino-4H-pyran derivatives
Table 3 Synthesis of 2-amino-
Entry
R1
R3
Product
Yield (%)a
4H-pyrans 6 from cyclohexane-
1,3-dione
1
C6H4
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
6r
6s
94
90
93
89
90
91
94
92
91
94
90
92
93
95
88
90
93
94
92
90
95
90
2
4-F–C6H5
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
4-Cl–C6H4
4-Br–C6H4
4-NO2–C6H4
4-CH3O–C6H4
4-CH3–C6H4
3-Cl–C6H4
3-CH3–C6H4
2-Cl–C6H4
2-Br–C6H4
2-NO2–C6H4
2-CH3O–C6H4
2,4-Cl–C6H3
2-Naphthyl
2-Furyl
C6H5
4-F–C6H5
4-Cl–C6H4
4-CH3O–C6H4
3-Cl–C6H4
2-Cl–C6H4
H
H
H
H
6t
6u
6v
H
Reaction conditions (unless noted otherwise): All the reactions were
performed with 1 (0.20 mmol), 2 (0.24 mmol), 5 (0.20 mmol), L4
(0.01 g) and Co(OAc)2 (10 mol%) in water (1 mL) at 50 °C for 3 h
aIsolated yield
To expand the application of the present synthetic strategy, catalytic xanthene
of cyclohexane-1,3-dione was performed, and the corresponding products were
obtained with 88–95 yields. Similarly, fused-ring, multisubstituted and heteroar-
omatic-substituted aldehydes were also suitable substrates for the reaction of xan-
thenes. Furthermore, a scale-up version of the catalytic xanthenes of 2-naphthol 3
or cyclohexane-1,3-dione 5 was also performed to test the synthetic potential. As
1 3

MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
1 3

S. Pan et al.
Scheme 5 Synthesis of xanthene derivatives on a gram scale
shown in Scheme 5, by treatment of 20 mmol of 4-chlorobenzaldehyde under the
optimal reaction conditions, the desired synthesis of 4a or 6c was accomplished
in 85% or 80% yield using L4(0.1 g)/Co(OAc)2 (10 mol%) complex catalyst
(Scheme 4, Table 3).
As pyran is an important heterocyclic unit, many heterogeneous catalyst systems
have been developed to catalyze the synthesis of pyran derivatives. Table 4 shows
the catalytic data reported in the literature and this work. The present method using
MCM-41@Schif base-Co(OAc)2 as catalyst ofers several advantages, such as
greener conditions, simple procedure, excellent yields and ideal recyclable catalyst
(Scheme 5).
Out of the advantages of the organic mesoporous materials is its ability to func-
tion as a recyclable catalyst, recyclability of L4-Co(OAc)2 was investigated under
97
100
80
60
40
20
0
95
97
93
92
91
90
89
89
85
83
83
80
1
2
3
4
5
6
Fig. 6 Catalyst recycling studies
1 3

MCM‑41@Schif base‑Co(OAc)2 as an efcient catalyst for…
Scheme 6 Proposed catalytic mechanism
the optimized conditions (Fig. 6). After six cycles of reaction, 4a and 6c were still
aforded with 83% and 80% yields. The heterogeneity of L4-Co(OAc)2 in these two
reactions was confrmed by the “hot fltration” test. After a reaction run, the solid
and water were separated and separately used as catalyst for the reactions. Compared
with the previous catalytic activity, a slightly lower yield was gained in the solid,
and a small amount of products were observed for the water. This “hot fltration” test
indicated the dissolved cobalt salt leads to the slight decrease in the activity. And
the FTIR of catalyst after recycling of it for six times showed the intensity of C=N
adsorption peak decreased, which confrmed the loss of active components. So, in
the recycling experiments, the mixture of solid and water was stirred and dried and
used as catalyst for the next reaction run.
The formation of 4 and 6 could be explained by a possible mechanism shown in
Scheme 6. Firstly, the complex L4/Co(OAc)2 catalyzed the Knoevenagel condensa-
tion of aldehyde (1) and malononitrile (or ethyl cyanoacetate) (2) to give the inter-
mediate I [42]. And then, 2-naphthol (3) or cyclohexane-1,3-dione (5) attacked I to
provide intermediate II or II’. Tautomerism of II or II’ followed by intramolecular
nucleophilic addition of oxygen to the cyano group and protonation provides III or
III’, fnally, which undergoes isomerization to give the xanthenes of 4 and 6.
1 3

S. Pan et al.
Conclusion
In summary, a novel, green and efcient catalytic system has been developed for
the direct one-spot synthesis of xanthenes via MCM-41@Schif base-Co(OAc)2-
mediated three-component reaction of 2-naphthol (or cyclohexane-1,3-dione) with
aromatic aldehyde and malononitrile (or ethyl cyanoacetate). The corresponding
products were obtained in high yields (up to 97% and 95%) in water. Compared with
the methods described in the literature, the heterogeneous catalyst showed good lev-
els of recyclability and reusability, and it could be recovered at least six cycles still
maintained the yields at more than 80%. Further applications of MCM-41@Schif
base catalysts to other reactions are underway.
Acknowledgements We appreciate the fnancial support from the Special Fund for Outstanding Talented
Young and Middle-aged Persons of Lingnan Normal University (Grant No. ZL1908) and National Col-
lege Students Innovation and Entrepreneurship Training Program (Grant No. 201910579871).
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