Solid-state synthesis of 4-[(indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-5- pyrazolones by catalysis of molecular iodine

Article abstract of DOI:10.1080/00397910600640388

4-[(Indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-5-pyrazolones could be smoothly and effectively obtained in good yields through the iodine-catalyzed reactions under solid-state conditions at room tempertaure. The three-component approach in a one-pot proced

Full text of DOI:10.1080/00397910600640388

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Solid‐State Synthesis of
4‐[(Indol‐3‐yl)‐arylmethyl]‐1‐phenyl‐3‐methyl‐5‐pyrazolone
by Catalysis of Molecular Iodine
Min Xia a & Yuedong Lu a
a Department of Chemistry , Zhejiang Science and Technology University , Hangzhou, China
Published online: 22 Sep 2006.
To cite this article: Min Xia & Yuedong Lu (2006) Solid‐State Synthesis of
4‐[(Indol‐3‐yl)‐arylmethyl]‐1‐phenyl‐3‐methyl‐5‐pyrazolones by Catalysis of Molecular Iodine, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:16, 2389-2399, DOI:
10.1080/00397910600640388
To link to this article: http://dx.doi.org/10.1080/00397910600640388
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Synthetic Communicationsw, 36: 2389–2399, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600640388
Solid-State Synthesis of 4-[(Indol-3-yl)-
arylmethyl]-1-phenyl-3-methyl-5-
pyrazolones by Catalysis of Molecular
Iodine
Min Xia and Yuedong Lu
Department of Chemistry, Zhejiang Science and Technology University,
Hangzhou, China
Abstract: 4-[(Indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-5-pyrazolones could be
smoothly and effectively obtained in good yields through the iodine-catalyzed
reactions under solid-state conditions at room tempertaure. The three-component
approach in a one-pot procedure was reported for the first time. A possible
mechanism was suggested to elucidate the remarkable reaction selectivities.
Keywords: Catalysis, iodine, one pot, solid state, three component
Recently, solid-state (solvent-free) reactions have increasingly attracted much
attention in the field of organic synthesis because of their inherent environ-
mental advantages.[1] Apart from the absence of organic solvents, solid-
state reactions are very different from traditional solution-phase reactions in
yields, reaction rates, and conditions,[2] In some cases, mechanisms and selec-
tivities can be dramatically distinguisheded,[3] because the limitation of
movements in solid-state molecules lead to different forms of interactions in
microenvironments. Moreover, the design of multicomponent reactions
(MCR) is an important research field in combinatorial chemistry,[4] and
therefore great efforts are being made to find and develop new multicompo-
nent reactions.[5] Because they are usually a one-pot reactions, MCRs
Received in R.O.C. January 10, 2006
Address correspondence to Min Xia, Department of Chemistry, Zhejiang Sci-Tech
University, Hangzhou 310018, China. E-mail: xiamin@zist.edu.cn
2389

2390
M. Xia and Y. Lu
generally afford good yields and ready operations and are fundamentally
different from two-component reactions in several aspects.[6]
Methane derivatives with aromatic and/or heterocyclic substituents are
utilized in various fields such as dyes, synthetic intermediates,[7] potential
medicines,[8] host molecules in inclusion complexes,[9] and so on. 4-[(Indol-
3-yl)-arylmethyl]-1-phenyl-3-methyl-5-pyrazolones are a species in which
two different heterocycles with remarkably important bioactivities and
pharmaceutical activities are arranged at the same carbon atom. Although
the two-component synthesis of them from the reactions of indole and
4-arylidene-3-methyl-1-phenyl-5-pyrazolones under solid-state conditions
was reported,[10] the lengthy procedure for the preparation of starting
materials and the moderate yields (41–67%) inhibited direct and effective
access to this kind of compound. Therefore, for synthetic efficiency, it is
necessary to further develop a straightforward and effective one-step
approach to them by the three-component reactions of aldehydes, indole,
and 1-phenyl-3-methyl-5-pyrazolones. To our best of knowledge, there has
been no such report in literature.
In recent years, molecular iodine has been widely applied as an inexpen-
sive and ready available catalyst in various transformations.[11] Because of its
moderate Lewis acidity, reactions catalyzed by iodine effectively take place in
neutral media under very mild conditions. Moreover, its water-tolerance
makes it an excellent candidate, superior to those water-sensitive metal
Lewis acids for reactions in which water would be generated in the process.
Herein, we described our case in which 4-[(indol-3-yl)-arylmethyl]-1-
phenyl-3-methyl-5-pyrazolones were smoothly offered in good yields by
iodine-catalyzed one-pot reactions of aldehydes, indole, and 1-phenyl-3-
methyl-5- pyrazolones under solvent-free conditions.
We selected the reaction of 4-chlorobenzaldehyde and indole with
1-phenyl-3-methyl-5-pyrazolone in the presence of iodine as the model
(Scheme 1). The three substrates (in a molar ratio of 1:1:1) and 10 mol%
iodine were mixed and ground well at room temperature in a mortar; the
resulting mixture was kept for 2 h. As expected, the target product of
4-[(indol-3-yl)-4-chlorophenylmethyl]-1-phenyl-3-methyl-5-pyrazolone 4c
could be provided in 91% yield, prolonged time would not improve the
yield even if the amount of iodine was raised from 10 mol% to 50 mol%. It
seemed that 10 mol% iodine was sufficient to drive the solid-state, three-
component reaction. Interestingly, a kind of white solid could also be
obtained in 21% yield within 2 h in the absence of iodine, and its amount
could be improved to 83% for overnight. However, its melting point and
spectral data were remarkably different from that of 4c. Compared with the
authentic sample prepared through the literature method,[12] it was
confirmed that the white solid offered without the catalyst of iodine shoud
be 4-chlorophenyl-bis(1-phenyl-3-methyl-5-pyrazolon-4-yl)methane 5.
Obviously, there was large distinction in reaction routes between our one-
pot, three-component reactions and the reported two-component ones. Based

Solid-State Synthesis
2391

2392
M. Xia and Y. Lu
on these facts and other literature,[10,12] a possible mechanism of the iodine-
catalyzed one-pot reactions was proposed to explain the remarkable reaction
selectivities: in the absence of iodine as a catalyst, the three-component
mixture could provide only the product 5 at room temperature, because it
was well known[13] that bis(indolyl)methane derivative 7 could not be
obtained without the presence of Lewis acids. Moreover, it was reported[14]
that bis(pyrazolonyl)methane derivatives would be formed smoothly at
room temperature in the absence of Lewis acids. With the catalysis of
iodine as an effective Lewis acid, however, the intermediate 6 was offered
in preference to the intermediate 8, because the latter was too unstable to
undergo the further transformation. Similarly, the formation of 6 was in
accordance with literature[14] that Lewis acids largely promoted the generation
of arylmethylenylpyrazolone derivatives at room temperature. The subsequent
Michael addition of indole with the intermediate 6 was successfully carried
out to afford the target compound 4a in excellent yields. Because of the
catalysis of iodine, the yield of 4a in our case was dramatically improved to
91%, compared with the yield of 56% in the reported two-component
reactions.[10] The evident difference in yields could be attributed to the mild
Lewis acidity of iodine, because there were some reports[15] that iodine was
an efficient catalyst in Michael addition of indole with a,b-unsaturated
carbonyl compounds (i.e., the intermediate 6, in our case).
According to the results of the model reaction, we extended the one-pot,
three-component synthesis of 4-[(indol-3-yl)-arylmethyl]-1-phenyl-3-methyl-
5-pyrazolones to other aldehydes (Scheme 2), and the results are indicated in
Table 1. Generally, the one-pot reactions could be carried out conveniently in
the catalysis of iodine to give expected products 4a–l in good yields.
Although aldehydes with electron-donating groups such as CH3- and CH3O-
efficiently provided the target compounds in good yields (Table 1, 4d and
4 g), the hydroxyl group seemed an exception because 4-hydroxybenzaldehyde
afforded quite low yield of a mixture with 4-hydroxyphenyl- bis(1-phenyl-3-
methyl-5-pyrazolon-4-yl) methane and 4-[(indol-3-yl)-4- hydroxyphenyl-
methyl]- 1-phenyl-3-methyl-5-pyrazolone. As for vanillin, only starting
materials could be recovered. The iodine-catalyzed three-component
reactions seemed to have steric effect also, because both 2,4-dichlorobenzal-
dehyde and 2,6-dichlorobenzaldehyde were unable to undergo the needed
Scheme 2.

Solid-State Synthesis
2393
Table 1. Solid-state synthesis of 4a–l by catalysis of iodine in a one-pot operation
Entry
ArCHO
Product
Yield (%)a
89
4a
4b
87
4c
91
4d
4e
4f
74
93
85
(continued)

2394
M. Xia and Y. Lu
Table 1. Continued
Entry
ArCHO
Product
Yield (%)a
77
4 g
4 h
89
4i
81
4j
88
72
79
4 k
4l
aReferred to isolated yields.

Solid-State Synthesis
2395
transformation. Surprisingly, however, 2-chlorobenzaldehyde was an
effective candidate for the one-pot procedure to supply the product 4i in
81%. Besides, heterocyclic aldehyde such as 2-furaldehyde (4l) could also
be selected as an active substrate for the iodine-catalyzed solvent-free
reaction, whereas a,b-unsaturated aldehydes such as cinnamaldehyde could
not be successfully utilized in our case. It was unfortunate to find that
aliphatic aldehydes could not efficiently undergo such solid-state three-
component reactions.
The spectral data supported that enolic hydroxyl groups instead of
carbonyl groups existed at 5-pyrazolonyl moieties in products 4. The IR
spectra showed bands at ca. 3200 and 1600 cm21 for O-H and C55C absorp-
tions respectively, whereas the absorption of carbonyl (ꢀ1650 cm21) in
3-methyl-1-phenyl-5-pyrazolone was not observed in compound 4.
1
Moreover, the signals of methine protons in H NMR spectra appeared as
broad singlet peaks instead of apparently doublet peaks, but the enolic
hydroxyl protons could not be detected in DMSO-d6 solution.
In conclusion, we herein described a novel and convenient approach to
4-[(indol-3-yl)-4-hydroxyphenyl-methyl]-1-phenyl-3-methyl-5-pyrazolones
in good yields through a solid-state procedure under iodine catalysis. The
straightforward route, environmentally-friendly operation, readily available
catalyst, and dramatically improved yields make our reactions one of the
most efficient methods to rapidly access this kind of species. The further
research on these compounds is in process.
EXPERIMENTAL
Melting points were determined on X4 mp apparatus, and the thermometer
was not corrected. 1H NMR spectra were obtained on a Bruker Avance
DMX 400-MHz instrument using TMS as internal standard in DMSO-d6.
FT-IR spectra were recorded on Nicolet Avatar spectrophotometer.
Elemental analysis was carried out on a Carlo-Ebbra instrument. All
reactions were carried out without dry media and inert gas protection.
Solid-State Preparation of 4-Chlorophenyl-bis(1-phenyl-3-methyl-
5-pyrazolon-4-yl)methane 5
At room temperature, aldehyde (1 mmol) and 1-phenyl-3-methyl-5-pyrazo-
lone (1 mmol, 0.16 g) were mixed and ground well in a mortar with a
pestle; the mixture was kept overnight and dissolved in EtOH (10 mL). The
concentrated residue was purified by silica-gel column chromatograhy
(ethyl acetate/petrolem ¼ 1:3) to provide products pure enough for spectral
analysis. The products utilized for elemental analysis were obtained by
further recrystallization from EtOH/CHCl3.

2396
M. Xia and Y. Lu
White solid; mp 207 ꢀ 2088C (lit.[12] 2108C); IR (KBr) 3060, 1604, 1499,
1
1408, 1297, 1194, 1070, 1021, 834, 745, 698 cm21; H NMR (400 MHz,
DMSO-d6): d 2.22 (s, 6H), 4.83 (s, 1H), 7.16–7.26 (m, 6H), 7.27–7.41
(m, 4H), 7.69 (d, J ¼ 8.0 Hz, 4H); anal. calcd. for C27H23N4O2: C, 74.48;
H, 5.29; N, 12.87. Found: C, 75.62; H, 5.19; N, 12.71%.
General Procedure for the Preparation of 4-[(Indol-3-yl)-
arylmethyl]-1-phenyl-3-methyl-5-pyrazolones 4 under I2-Catalyzed
Solid-State Conditions
At room temperature, aldehyde (1 mmol), indole (1 mmol, 0.107 g), 1-phenyl-
3-methyl-5-pyrazolone (1 mmol, 0.16 g) and iodine (0.1 mmol, 0.0254 g) were
mixed and ground well in a mortar with a pestle; the mixture was kept for 2 h
and dissolved in ethanol (10 mL). The resulting solution was treated with aq.
Na2S2O3 (5%, 10 mL) and extracted with ethyl acetate (3 Â 5 mL). The
combined organic layer was dried over anhydrous sodium sulphate, concen-
trated in vacuo, and purified by silica-gel column chromatograhy (ethyl
acetate/petrolem ¼ 2:1) to provide products pure enough for spectral
analysis. The products utilized for elemental analysis were obtained by
further recrystallization from EtOH/CHCl3.
Data
4a: white solid; mp 203 ꢀ 2058C (lit10 2078C); IR (KBr): 3413, 3227, 3060,
2921, 2868, 1604, 1569, 1503, 1457, 1221, 1094, 745 cm21 1H NMR
;
(DMSO-d6):
d
1.85(s, 3H), 5.50(s, br, 1H), 6.86 ꢀ 6.90(m, 2H),
7.05 ꢀ 7.12(m, 3H), 7.20(t, 2H, J ¼ 8.4 Hz), 7.31 ꢀ 7.37(m, 3H),
7.42(t, 2H, J ¼ 8.0 Hz), 7.75(d, 2H, J ¼ 8.0 Hz), 10.86(s, 1H); anal. calcd.
for C25H20N3OF: C, 75.56; H, 5.04; N, 10.58. Found: C, 75.72; H, 5.09; N,
10.51%
4b: white solid; mp 235–2368C (lit.10 2368C); IR (KBr): 3415, 3239,
3056, 2921, 2864, 1601, 1544, 1499, 1405, 739, 706 cm21 1H NMR
;
(DMSO-d6): d 1.83 (s, 3H), 5.52 (s, br, 1H), 6.83 (s, 1H), 6.89 (t, 1H,
J ¼ 7.6 Hz), 7.05 (t, 1H, J ¼ 7.6 Hz), 7.18–7.22 (m, 3H), 7.26–7.31
(m, 4H), 7.36 (d, 1H, J ¼ 8.0 Hz), 7.42 (t, 2H, J ¼ 8.0 Hz), 7.75 (d, 2H,
J ¼ 8.0 Hz), 10.84 (s, 1H); anal. calcd. for C25H21N3O: C, 79.15; H, 5.54;
N, 11.08. Found: C, 79.33; H, 5.61; N, 10.98%.
4c: white solid; mp 173–1758C (lit.10 1768C); IR (KBr): 3415, 3227, 3056,
2917, 1868, 1609, 1568, 1486, 1409, 1090, 1012, 743 cm21; 1H NMR (DMSO-
d6): d 1.86 (s, 3H), 5.50 (s, br, 1H), 6.88–6.92 (m, 2H), 7.05 (t, 1H, J ¼ 7.6 Hz),
7.20 (t, 2H, J ¼ 8.0 Hz), 7.32 ꢀ 7.37 (m, 5H), 7.42 (t, 2H, J ¼ 8.0 Hz), 7.74
(d, 2H, J ¼ 8.0 Hz), 10.88(s, 1H); anal. calcd. for C25H21N3OCl: C, 72.64; H,
4.84; N, 10.17. Found: C, 72.81; H, 4.91; N, 10.10%.

Solid-State Synthesis
2397
4d: white solid; mp 180–1828C (lit.10 1788C); IR (KBr): 3415, 3256,
3051, 2917, 2859, 1609, 1572, 1499, 1450, 1409, 1311, 1094, 743,
1
698 cm21; H NMR (DMSO-d6): d 1.82 (s, 3H), 2.26 (s, 3H), 5.47 (s, br,
1H), 6.82 (s, 1H), 6.88 (t, 1H, J ¼ 7.6 Hz), 7.03–7.09 (m, 3H), 7.16–7.20
(m, 4H), 7.35 (d, 1H, J ¼ 8.0 Hz), 7.42 (t, 2H, J ¼ 8.0 Hz), 7.75 (d, 2H,
J ¼ 8.0 Hz), 10.82(s, 1H); anal. calcd. for C26H23N3O: C, 79.39; H, 5.85;
N, 10.69. Found: C, 79.54; H, 5.94; N, 10.77%.
4e: yellowish solid; mp 184–1868C (lit.10 1848C); IR (KBr): 3415, 3223,
3056, 2921, 2864, 1597, 1519, 1413, 1348, 1111, 743 cm21 1H NMR
;
(DMSO-d6): d 1.92 (s, 3H), 5.65 (s, br, 1H), 6.93 (t, 1H, J ¼ 7.2 Hz), 6.97
(s, 1H), 7.07 (t, 1H, J ¼ 7.6 Hz), 7.19–7.25 (m, 2H), 7.27–7.45 (m, 3H),
7.56(d, 2H, J ¼ 8.4 Hz), 7.74 (d, 2H, J ¼ 8.0 Hz), 8.16 (d, 2H, J ¼ 8.4 Hz),
10.96 (s, 1H); anal. calcd. for C25H20N4O2: C, 70.75; H, 4.72; N, 11.32.
Found: C, 70.94; H, 4.81; N, 11.45%.
4f: pale red solid; mp 182–1848C (lit.10 1888C); IR (KBr): 3415, 3219,
3056, 2970, 2847, 2786, 1605, 1568, 1495, 1409, 1298, 1102, 1008,
1
747 cm21; H NMR (DMSO-d6): d 1.86 (s, 3H), 5.49 (s, br, 1H), 6.88–6.92
(m, 2H), 7.05 (t, 1H, J ¼ 7.6 Hz), 7.18–7.26 (m, 4H), 7.36 (d, 1H,
J ¼ 8.0 Hz), 7.40–7.47(m, 4H), 7.74(d, 2H, J ¼ 8.0 Hz), 10.88(s, 1H); anal.
calcd. for C25H20N3OBr: C, 65.64; H, 4.38; N, 9.19. Found: C, 65. 82; H,
4.41; N, 9.27%.
4g: white solid; mp 170–1718C (lit.10 1688C); IR (KBr): 3415, 3248,
3056, 2921, 1609, 1568, 1503, 1454, 1245, 1172, 1106, 1033, 743,
1
698 cm21; H NMR (DMSO-d6): d ¼ 1.82 (s, 3H), 3.72 (s, 3H), 5.45 (s, br,
1H), 6.82–6.90 (m, 4H), 7.04 (t, 1H, J ¼ 7.6 Hz), 7.16–7.21 (m, 4H), 7.35
(d, 1H, J ¼ 8.0 Hz), 7.42 (t, 2H, J ¼ 7.6 Hz), 7.75 (d, 2H, J ¼ 8.0 Hz),
10.82 (s, 1H); anal. calcd. for C26H23N3O2: C, 76.28; H, 5.62; N, 10.27.
Found: C, 76.44; H, 5.69; N, 10.21%.
4h: yellowish solid; mp 242–2448C (lit.10 2468C); IR (KBr): 3421, 3186,
1
3064, 2924, 2871, 1599, 1529, 1499, 1456, 1415, 1350, 714 cm21; H NMR
(DMSO-d6): d 1.96 (s, 3H), 5.66 (s, br, 1H), 6.91 (t, 1H, J ¼ 7.2 Hz), 6.99
(s, 1H), 7.07 (t, 1H, J ¼ 8.0 Hz), 7.19 (t, 1H, J ¼ 8.0 Hz), 7.26 (d, 1H,
J ¼ 7.6 Hz), 7.38 (d, 1H, J ¼ 8.0 Hz), 7.43 (t, 2H, J ¼ 7.6 Hz), 7.59 (t, 1H,
J ¼ 8.0 Hz), 7.74 (d, 2H, J ¼ 7.6 Hz), 7.80 (d, 1H, J ¼ 8.0 Hz), 8.08 (d, 1H,
J ¼ 8.0 Hz), 8.16 (s, 1H), 10.96 (s, 1H); anal. calcd. for C25H20N4O3: C,
70.75; H, 4.72; N, 11.32. Found: C, 70.98; H, 4.77; N, 11.23%.
4i: white solid; mp 161–1638C; IR (KBr): 3419, 3272, 3056, 2925, 2864,
1601, 1556, 1499, 1405, 1102, 1041, 739, 690 cm21; 1H NMR (DMSO-d6): d
1.81 (s, 3H), 5.75 (s, br, 1H), 6.81 (s, 1H), 6.89 (t, 1H, J ¼ 7.2 Hz), 7.05 (t, 1H,
J ¼ 7.6 Hz), 7.11 (d, 1H, J ¼ 7.6 Hz), 7.18–7.22 (m, 3H), 7.30 (d, 1H,

2398
M. Xia and Y. Lu
J ¼ 7.6 Hz), 7.36–7.43 (m, 4H), 7.74 (d, 2H, J ¼ 7.6 Hz), 10.88 (s, 1H); anal.
calcd. for C25H20N3OCl: C, 72.64; H, 4.84; N, 10.17. Found: C, 72.81; H,
4.91; N, 10.26%.
4j: white solid; mp 176–1788C; IR (KBr): 3414, 3254, 3061, 2921, 2868,
1617, 1570, 1498, 1457, 1416, 1325, 1164, 1124, 1068, 1017, 743, 703 cm21
;
1H NMR (DMSO-d6): d 1.89 (s, 3H), 5.60 (s, br, 1H), 6.91 (d, 2H, J ¼ 7.2 Hz),
7.06 (t, 1H, J ¼ 7.2 Hz), 7.18–7.24 (m, 2H), 7.37 (d, 1H, J ¼ 8.0 Hz), 7.42
(t, 2H, J ¼ 8.0 Hz), 7.51 (d, 2H, J ¼ 7.6 Hz), 7.64 (d, 2H, J ¼ 8.0 Hz), 7.74
(d, 2H, J ¼ 8.0 Hz), 10.92 (s, 1H); anal. calcd. for C26H20N3OF3: C, 70.75;
H, 4.53; N, 9.52. Found: C, 70.93; H, 4.58; N, 9.44%.
4k: white solid; mp 152–1548C; IR (KBr): 3415, 3256, 3060, 2884, 1609,
1568, 1482, 1229, 1041, 931, 747 cm21; 1H NMR (DMSO-d6): d 1.87 (s, 3H),
5.39 (s, br, 1H), 5.94 (s, 2H), 6.76–6.81 (m, 2H), 6.84–6.90 (m, 3H), 7.04
(t, 1H, J ¼ 7.2 Hz), 7.17–7.21 (m, 2H), 7.34 (d, 1H, J ¼ 8.0 Hz), 7.41
(t, 2H, J ¼ 8.0 Hz), 7.73 (d, 2H, J ¼ 7.6 Hz), 10.82 (s, 1H); anal. calcd. for
C26H21N3O3: C, 73.76; H, 4.99; N, 9.93. Found: C, 73.92; H, 5.03; N, 10.07%.
4l: pale solid; mp 191–1938C; IR (KBr): 3413, 3243, 3057, 2922, 1602,
1552, 1498, 1405, 1009, 738, 704 cm21; 1H NMR (DMSO-d6): d 1.88 (s, 3H),
5.56 (s, br, 1H), 6.05 (s, 1H), 6.39 (s, 1H), 6.90–6.94 (m, 2H), 7.06 (t, 1H,
J ¼ 7.6 Hz), 7.19 (t, 1H, J ¼ 7.2 Hz), 7.31 (d, 1H, J ¼ 8.0 Hz), 7.36 (d, 1H,
J ¼ 8.0 Hz), 7.43 (t, 2H, J ¼ 8.0 Hz), 7.58 (s, 1H), 7.75 (d, 2H, J ¼ 8.0 Hz),
10.89 (s, 1H); anal. calcd. for C23H19N3O2: C, 74.80; H, 5.15; N, 11.38.
Found: C, 74.93; H, 5.17; N, 11.27%.
ACKNOWLEDGMENT
We are grateful for the financial support from the Nature Science Foundation
of China (project number 20402013).
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2399
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