PMA-SiO2: A heterogenous catalyst for O-, S-, and N-nucleophilic substitution reactions of aryl propargyl alcohols

Article abstract of DOI:10.1080/00397910801914335

Aryl-propargylic alcohols undergo O-, S-, and N-nucleophilic substitution reactions in the presence of a catalytic amount of PMA-SiO2. Copyright Taylor & Francis Group, LLC.

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PMA‐SiO2: A Heterogenous Catalyst for O‐, S‐,
and N‐Nucleophilic Substitution Reactions of
Aryl Propargyl Alcohols
P. Srihari a , J. Shyam Sunder Reddy a , Dinesh C. Bhunia a , S. S. Mandal a &
J. S. Yadav a
a Organic Division I, Indian Institute of Chemical Technology, Hyderabad,
India
Version of record first published: 25 Apr 2008.
To cite this article: P. Srihari , J. Shyam Sunder Reddy , Dinesh C. Bhunia , S. S. Mandal & J. S. Yadav (2008):
PMA‐SiO2: A Heterogenous Catalyst for O‐, S‐, and N‐Nucleophilic Substitution Reactions of Aryl Propargyl
Alcohols, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 38:9, 1448-1455
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Synthetic Communicationsw, 38: 1448–1455, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801914335
PMA-SiO2: A Heterogenous Catalyst for
O-, S-, and N-Nucleophilic Substitution
Reactions of Aryl Propargyl Alcohols
P. Srihari, J. Shyam Sunder Reddy, Dinesh C. Bhunia,
S. S. Mandal, and J. S. Yadav
Organic Division I, Indian Institute of Chemical Technology,
Hyderabad, India
Abstract: Aryl-propargylic alcohols undergo O-, S-, and N-nucleophilic substitution
reactions in the presence of a catalytic amount of PMA-SiO2.
Keywords: Allylation, heteropolyacid, Nicholas reaction, propargyl alcohol,
propargylation
INTRODUCTION
The synthetic flexibility of allyl and alkynl moieties, which offer excellent
handles for transformations into various other functional group,[1] has
gained significant importance for allylic and propargylic systems. During
the past few years, the focus has been on substitution reactions of propargylic
alcohol derivatives with different nucleophiles. The Nicholas reaction[2] is an
effective tool for the propargylic substitution process, which is achieved by
using a stoichiometric amount of Co2(CO)8. Reports where rhenium,[3]
ruthenium,[4] and gold complexes[5] are utilized for nucleophilic substitution
reactions on propargylic alcohols, including both intramolecular and intermo-
lecular substitutions and also substitution reactions on propargylic esters,[6]
transformations with propargyl ethers,[7] and catalyzed by Lewis acids, are
well precedented. More recently, Zhan et al.[8] have reported BiCl3- and
Received in India October 27, 2007
Address correspondence to P. Srihari, Organic Division I, Indian Institute of
Chemical Technology, Hyderabad 500007, India. E-mail: srihari@iict.res.in
1448

PMA-SiO2
1449
FeCl3- catalyzed nucleophilic substitutions on propargyl acetates/alcohols
along with propargylation of aromatic compounds. However, many of these
reactions suffer because of the high cost of the reagents, large amounts of
reagent, or multistep process. A better reagent system that could catalyze
the reaction more efficiently involve fewer steps would be a welcome
addition to the existing repetoire.
During the past decade, considerable emphasis has been given to green
chemistry, which involves high atom efficiency, improvements in selectivity,
elimination of hazardous reagents, easy separation with recovery, and reuse of
reagents for environmentally clean synthesis.[9] One of the key principles
involved in green chemistry is to minimize the stoichiometric quantities of
reagents to catalytic amounts and to allow the process to run with high effi-
ciency. Heteropolyacids have a strongly acidic character and hence exhibit
higher catalytic activity than conventional catalysts such as mineral acids,
mixed oxides, and ion exchange resins. Their unique properties such as
ability to accept and release electrons, high proton mobility, easy filteration,
and minimal waste generation due to reuse and recycling of the catalyst
make them highly attractive as environmentally benign and economically
feasible solid catalysts.[10]
Recently, the heteropolyacid montmorillonite K-10 was used as a mild
acid for mediating the Nicholas reaction.[11] In the study of environmentally
benign catalytic reagent systems, we have shown that phosphomolybdic
acid supported on silica gel (PMA/SiO2) works as an excellent heterogenous
solid reagent system, catalyzing acetal deprotection and Ferrier rearrangement
reactions.[12] In continuation of the investigations with PMA-SiO2 as solid
Scheme 1.
Table 1. O-Nucleophilic substitution reactions of propargyl alcohols
Sl. no.
Catalyst (mol%)
Time (h)
Yield (%)
1
2
3
4
5
0.5
1.0
2.0
3.0
5.0
2.0
2.0
2.0
2.0
2.0
80
90
90
90
90

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P. Srihari et al.
Table 2. PMA-SiO2-catalyzed O-, S-, and N-nucleophilic substition reactions on aryl
propargylic alcohols
Propargyl
alcohol a
Nucleophile
b
Time
(h)
Yieldsb
(%)
Sl. no.
1
Producta c
2.0
2.0
2.0
90
83
91
2
3
4
3.0
78
5
6
7
2.0
2.0
3.0
88
84
72
8
9
3.0
2.0
75
75
10
11
12
2.0
2.0
3.0
85
83
68
13
14
3.0
2.0
75
85
15
16
0.5
90
no reaction
1
aAll the products are characterized by H and 13C NMR and mass spectroscopy.
bIsolated and unoptimized yields.

PMA-SiO2
1451
reagent system, we disclose herein O-, S-, and N-nucelophilic substitution
reactions of propargylic alcohols (see Scheme 1).
RESULTS AND DISCUSSION
Initially, ethanol was added to the mixture of 9a in acetonitrile in the presence
of 0.5 mol% of PMA-SiO2, and the reaction mixture was stirred for 2 h. Only
5% conversion to the product was observed. However, when the reaction
mixture was heated to reflux temperature, the reaction progressed well and
yielded 75% of ethyl ether 9c. To further increase the yields and optimize
the reaction conditions, investigations were made using different concen-
trations of the catalyst on 1,3-diphenyl-prop-2-yn-1-ol with allyl alcohol.
This study clearly shows that 1 mol% catalyst yields the best results with
respect to time (see Table 1).
Encouraged by this result, a few other alcohols such as allyl alcohol,
propargyl alcohol, and secondary alcohols were studied for the generality of
this substitution reaction and produced the expected products (see Table 2).
Having obtained successful results with O-nucleophiles, we applied this
protocol for sulfur and nitrogen nucleophilic substitution reactions and were
delighted to see that both the sulfur and nitrogen substitution reactions
worked well. Thiophenol gave the thio ether 3c exclusively without any
C-nucleophilic-substituted product. This may be attributed to the more
nucleophilic character of sulfur than of carbon. Surprisingly, simple alkane
thiols (ethane thiol) and mercaptobenzothiol gave very poor yields of the
expected products. Both primary as well as secondary amines 4b, 7b, and
8b responded well under this protocol to result in the corresponding pro-
pargylic amines 4c, 7c, and 8c. However, aniline, acetamide, and piperidine
did not give the expected product and always resulted in a mixture of
undesired spots. (The NMR spectra of the crude mixture showed no character-
istic protons of the desired product. No further attempts were made to isolate
and characterize the individual spots.) It is noteworthy to mention the present
protocol also worked well for C-nucleophilic substitution with allyl trimethyl
silane to get the product 14c. Also the aryl propargyl alcohol 15a with free
terminal acetylene moiety underwent the substitution reaction to afford the
corresponding product in good yield within half an hour. When the present
protocol was applied to propargyl alcohols without the aryl group, no
reaction was observed even after 12 h (serial no. 16).
CONCLUSION
In conclusion, the PMA–SiO2 reagent system works as an efficient heteroge-
nous catalyst for heteroatom-centered nucleophilic substitution reaction with
aryl-propargylic alcohols. The clean and operationally simple procedure with

1452
P. Srihari et al.
easy work up, involving simple filteration of the catalyst, makes this a more
attractive protocol than the existing procedures. Further work on exploration
of these substituted products is currently under way.
EXPERIMENTAL
General Experimental Procedure
PMA-SiO2 (1.0 mol%) was added to a solution of propargyl alcohol (1 mmol)
and nucleophile (1 mmol) in acetonitrile (5 mL). The mixture was stirred at
reflux temperature for the appropriate time. After the completion of the
reaction (monitored by thin-layer chromatography, TLC), the reaction mixture
was cooled, filtered, and washed with dichloromethane (DCM). The combined
organic filterates were evaporated to dryness in vacuo. The crude product was
purified by column chromatography (ethyl acetate and hexane as eluents).
Spectroscopic Data of New Compounds
(3-(Prop-2-ynyloxy)prop-1-yne-1,3-diyl)dibenzene (2c): Light yellow
1
liquid. IR (neat): 2923, 2854, 2223, 1589, 1489, 1061, 757, 693 cm21. H
NMR (CDCl3, 300 MHz): d 2.42 (t, J ¼ 2.2 Hz, 1H), 4.35 (dq, J ¼ 2.2,
15.8, 45.3 Hz, 2H), 5.60 (s, 1H), 7.28–7.39 (m, 6H), 7.45–7.49 (m, 2H),
7.54–7.57 (m, 2H). 13C NMR (CDCl3, 75 MHz: 55.47, 70.57, 74.91, 79.36,
85.96, 88.05, 122.35, 127.48, 127.71, 128.26, 128.53, 128.60, 131.81,
137.91. ESIMS: m/z: 269 (Mþ þ 23).
Compound 4c: Colorless solid. Mp 87 8C. IR (KBr): 3422, 2962, 2859, 2198,
1
1565, 1478, 1334, 1261, 1058, 799 cm21. H NMR (CDCl3, 200 MHz): d
1.35–1.84 (m, 8H), 3.64–3.73 (m,1H), 5.57 (s, 1H), 7.30–7.39 (m, 8H),
7.74–7.80 (m, 2H), 11.45–11.53 (m, 1H, NH). 13C NMR (CDCl3,
75 MHz): d 23.78, 34.63, 55.87, 92.96, 126.88, 127.56, 128.06, 128.37,
129.18, 130.47, 136.14, 140.30, 166.02, 187.90. ESIMS: m/z: 314 (Mþ þ 39).
1-(1-(Allyloxy)-3-phenylprop-2-ynyl)-4-fluorobenzene (5c): Yellow liquid.
IR (neat): 2927, 2199, 1721, 1696, 1508, 1274, 1231, 1155, 1063, 839,
1
759 cm21. H NMR (CDCl3, 200 MHz): d 4.14–4.23 (m, 2H), 5.12–5.37
(m, 3H), 5.85–6.05 (m, 1H), 7.00–7.56 (m, 9H). ESIMS: m/z: 289
(Mþ þ 23).
1-Fluoro-4-(3-phenyl-1-(prop-2-ynyloxy)prop-2-ynyl)benzene (6c): Yellow
liquid. IR (neat): 2925, 2371, 2200,1639, 1508, 1224, 1063, 759 cm21
.
1H NMR (CDCl3, 200 MHz): d 2.43 (t, J ¼ 2.3 Hz, 1H), 4.36 (dq, J ¼ 2.3,
15.6, 29.6, 2H), 5.58 (s, 1H), 7.05 (t, J ¼ 8.6 Hz, 2H), 7.24–7.33 (m, 3H),
7.43–7.58 (m, 4H). 13C NMR (CDCl3, 75 MHz): d 55.5, 69.86, 75.04, 79.23,

PMA-SiO2
1453
85.64, 88.33, 115.29, 128.33, 128.71, 128.77, 129.49, 129.60, 131.83, 161.24.
ESIMS: m/z: 287 (Mþ þ 23).
N-Benzyl-1-(4-fluorophenyl)-3-phenylprop-2-yn-1-amine (7c): Light
yellow solid, mp 75 8C. IR (KBr): 3446, 2924, 2854, 2232, 1589, 1564,
1481, 1327, 1220, 764 cm21
.
1H NMR (CDCl3, 300 MHz): d 4.40
(d, J ¼ 6.8 Hz, 2H), 5.72 (s, 1H), 7.03 (t, J ¼ 8.3 Hz, 2H), 7.18–7.42
(m, 10 H), 7.85–7.91 (m, 2H), 11.66 (brs, 1H, NH). 13C NMR (CDCl3,
75 MHz): d 48.4, 93.5, 114.9, 115.2, 126.8, 127.41, 127.7, 128.5, 128.7,
129.2, 129.4, 129.6, 135.4, 138.3, 166.8, 187.2. EIMS: m/z: 354 (Mþ þ 39).
HRMS calcd. for C22H18NKF: 354.1271; found 354.1266.
N-(1-(4-Fluorophenyl)-3-phenylprop-2-ynyl)cyclopentanamine (8c): Light
yellow solid. mp 74 8C. IR (KBr): 3437, 2958, 2863, 2196, 1665, 1589,
1
1564, 1482, 1332, 1220, 764 cm21. H NMR (CDCl3, 300 MHz): d 1.43–
1.67 (m, 4H), 1.80–1.91 (m, 4H), 3.70–3.80 (m, 1H), 5.57 (s, 1H), 7.02
(t, J ¼ 8.3 Hz, 2H), 7.37–7.44 (m, 5H), 7.81–7.87 (m, 2H), 11.50
(d, J ¼ 9.1 Hz, 1H, NH). 13C NMR (CDCl3, 75 MHz): d 23.82, 34.67, 55.97,
92.58, 114.85, 115.14, 127.56, 128.47, 129.08, 129.19, 129.31, 136.09,
166.19, 186.47. ESIMS: m/z: 311 (Mþ þ 18).
(3-Ethoxy-3-(4-methoxyphenyl)prop-1-ynyl)trimethylsilane (9c): Yellow
1
liquid. IR (neat): 2961, 2900, 2170, 1612, 1511, 1249, 1077, 845 cm21. H
NMR (CDCl3, 200 MHz): d 0.20 (s, 9H), 1.22 (t, J ¼ 6.9 Hz, 3H), 3.43–
3.72 (m, 2H), 3.79 (s, 3H), 5.03 (s, 1H), 6.83 (d, J ¼ 8.6 Hz, 2H), 7.36
(d, J ¼ 8.6 Hz, 2H). 13C NMR (CDCl3, 75 MHz): d 20.12, 15.14, 55.25,
63.47, 71.34, 91.91, 103.63, 113.76, 128.84, 130.98, 159.61. ESIMS: m/z:
285 (Mþ þ 23).
(3-(Allyloxy)-3-(4-methoxyphenyl)prop-1-ynyl)trimethylsilane (10c): Yellow
1
liquid. IR (neat): 2959, 2838, 2170, 1612, 1512, 1249, 1035, 846 cm21. H
NMR (CDCl3, 200 MHz): d 0.19 (s, 9H), 3.97 (s, 3H), 3.99–4.14 (m, 2H),
5.08–5.32 (m, 3H), 5.75–6.04 (m, 1H), 6.84 (d, J ¼ 7.4 Hz, 2H), 7.36
(d, J ¼ 8.8 Hz, 2H). ESIMS: m/z: 297 (Mþ þ 23).
(3-(4-Methoxyphenyl)-3-(prop-2-ynyloxy)prop-1-ynyl)trimethylsilane (11c):
Pale yellow liquid. IR (neat): 2957, 2857, 2171, 1611, 1512, 1461, 1248, 1033,
1
845 cm21. H NMR (CDCl3, 300 MHz): d 0.20 (s, 9H), 2.38 (t, J ¼ 2.3 Hz,
1H), 3.79 (s, 3H), 4.22 (dq, J ¼ 2.3, 15.8, 42.3 Hz, 2H), 5.29 (s, 1H), 6.82–
6.86 (m, 2H), 7.35–7.40 (m, 2H). 13C NMR (CDCl3, 75 MHz): d 20.2, 55.0,
55.3, 70.0, 74.7, 79.4, 93.0, 102.2, 113.8, 129.2, 128.9, 159.8. EIMS: m/z 295
(Mþ þ 23). HRMS calcd. for C16H20O2NaSi: 295.1130; found 295.1132.
(3-Isopropoxy-3-(4-methoxyphenyl)prop-1-ynyl)trimethylsilane
Yellow liquid. IR (neat): 2961, 2929, 2858, 2170, 1611, 1510, 1248, 1039,
(12c):
1
844 cm21. H NMR (CDCl3, 300 MHz): d 0.07 (s, 9H), 1.06–1.10 (m, 6H),
3.67 (s, 3H), 3.76–3.82 (m, 1H), 4.96 (s, 1H), 6.71 (d, J ¼ 8.3 Hz, 2H),
7.23 (d, J ¼ 8.3 Hz, 2H). 13C NMR, (CDCl3, 75 MHz): d 20.1, 21.7, 55.2,

1454
P. Srihari et al.
68.9, 69.5, 91.1, 104.5, 113.7, 128.7, 131.5, 159.5. EIMS: m/z 299 (Mþ þ 23).
HRMS calcd. for C16H24O2NaSi: 299.1443; found 299.1445.
1-Methoxy-4-(1-(prop-2-ynyloxy)oct-2-ynyl)benzene (13c): Yellow liquid.
IR (neat): 2929, 2857, 2197, 1608, 1511, 1461, 1249, 1057, 1034,
1
831 cm21. H NMR (CDCl3, 200 MHz): d 0.91 (t, J ¼ 7.0 Hz, 3H), 1.25–
1.61 (m, 6H), 2.23–2.38 (m, 2H), 3.79 (s, 3H), 4.22 (dq, J ¼ 2.3, 15.6,
32.0 Hz, 2H), 5.29 (s, 1H), 6.83 (d, J ¼ 8.6 Hz, 2H), 7.38 (d, J ¼ 8.6 Hz,
2H). 13C NMR (CDCl3, 75 MHz): d 13.87, 18.76, 22.08, 31.01, 31.33,
43.81, 54.83, 55.21, 69.87, 74.44, 79.62, 88.93, 128.73, 128.98, 130.71,
131.96. EIMS: m/z: 215 (Mþ-55).
1-(1-Allyloxy-prop-2-ynyl)-4-methoxy-benzene (15c): Yellow liquid. 1H
NMR (CDCl3, 400 MHz): d 2.47 (d, J ¼ 2.19 Hz, 1H), 3.73 (s, 3H), 4.02
(dd, J ¼ 5.4, 12.4 Hz, 2H), 5.03 (d, J ¼ 1.4 Hz, 1H), 5.12 (dd, J ¼ 1.4,
10.2 Hz, 1H), 5.23 (dd, J ¼ 2.1, 17.5 Hz, 1H), 5.78–5.89 (m, 1H), 6.78
(d, J ¼ 8.1 Hz, 2H), 7.31 (d, J ¼ 8.1 Hz, 2H). 13C NMR (CDCl3, 75 MHz):
d 55.80, 69.15, 70.37, 72.52, 81.97, 114.06, 117.92, 128.97, 130.56, 134.37,
159.95. EIMS: m/z: 225 (Mþ þ 23).
ACKNOWLEDGMENTS
Three of us (J. S. S. R., D. C. B., and S. S. M.) thank Council of Scientific and
Industrial Research (CSIR), New Delhi, for financial assistance.
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