Zinc-mediated tandem-one-pot facile synthesis of 1-(arylsulfonyl) aryl/heteryl methanes: A case of C-S bond formation

Article abstract of DOI:10.1080/00397911.2010.488310

Reaction of arylmethyl/heteryl methyl zinc chloride (generated in situ from aryl methyl and heteryl methyl chloride and zinc metal) with aryl sulfonyl chlorides in tetrahydrofuran (THF) under mild conditions (i.e., at room temperature) furnishes the corresponding 1-(aryl sulfonyl)aryl/heteryl methanes in good yields.

Full text of DOI:10.1080/00397911.2010.488310

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Zinc-Mediated Tandem-One-Pot Facile
Synthesis of 1-(Arylsulfonyl) Aryl/Heteryl
Methanes: A Case of C‒S Bond Formation
K. Srinivas a & P. K. Dubey a
a Department of Chemistry, College of Engineering, JNT University,
Hyderabad, India
Published online: 20 Apr 2011.
To cite this article: K. Srinivas & P. K. Dubey (2011) Zinc-Mediated Tandem-One-Pot Facile Synthesis
of 1-(Arylsulfonyl) Aryl/Heteryl Methanes: A Case of C‒S Bond Formation, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 41:11, 1584-1592,
DOI: 10.1080/00397911.2010.488310
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Synthetic Communications1, 41: 1584–1592, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.488310
ZINC-MEDIATED TANDEM-ONE-POT FACILE
SYNTHESIS OF 1-(ARYLSULFONYL) ARYL/HETERYL
METHANES: A CASE OF CꢀS BOND FORMATION
K. Srinivas and P. K. Dubey
Department of Chemistry, College of Engineering, JNT University,
Hyderabad, India
GRAPHICAL ABSTRACT
Abstract Reaction of arylmethyl/heteryl methyl zinc chloride (generated in situ from
aryl methyl and heteryl methyl chloride and zinc metal) with aryl sulfonyl chlorides in
tetrahydrofuran (THF) under mild conditions (i.e., at room temperature) furnishes the
corresponding 1-(aryl sulfonyl)aryl/heteryl methanes in good yields.
Keywords Aryl sulfonyl chloride; 2-(a-chloroalkyl)benzimidazoles; KI; one pot; zinc
INTRODUCTION
The aryl sulfones are common structures in valuable molecules in fields such
as pharmaceuticals, agrochemicals, and polymer sciences.[1] In particular, their
immense utilities in medicinal chemistry and their unique bioactivities have attracted
considerable attention. For example, diaryl sulfones have been reported to inhibit
HIV-1[2] reverse transcriptase, and diphenyl sulfone[3] is used as an intermediate
for the synthesis of 4,40-diamino-diphenyl sulfone (DAPSONE), which is effective
for leprosy treatment.[4] The aryl sulfones can be prepared from the transition
metal–catalyzed reactions using sulfonic acids or sulfonyl chloride,[5] but the
Received January 26, 2010.
Address correspondence to P. K. Dubey, Department of Chemistry, College of Engineering,
JNT University Hyderabad, Kukatpally, Hyderabad 500 085, A. P., India. E-mail: kummarisrinivas@
gmail.com
1584

CASE OF CꢀS BOND FORMATION
1585
prefunctionalizing such as metallization or halogenations of arenas are required. A
well-known process involving the formation of new CꢀS bonds from aromatic CꢀH
bonds is the Friedel–Crafts (FC) sulfonylation of various arenes, especially electron-
rich arenas.[6,7] Sulfonchlorides or sulfoanhydride are general substrates employed in
the FC sulfonylation. Organozinc reagents are some of the most useful organometal-
lic reagents for organic synthesis.[8] However, their applications in organic synthesis
were limited to very specific reactions because of their moderate reactivity. These
reagents were soon replaced by the more reactive organo magnesium and organo
lithium reagents, which found broad applications in organic synthesis. However, it
became clear that this high reactivity had some drawbacks, such as low chemoselec-
tivity, and only allowed R groups bearing relatively little functionality. When one
looks at the reductive potential of various metals, zinc stands out as a promising can-
didate. While zinc has a much more negative reductive potential (Eꢁ ¼ ꢀ1.216 ev),
pure zinc is not sensitive to air and water. It was noticed that organozinc reagents
could be easily prepared and have higher functional group compatibility in compari-
son with organo lithium and Grignard reagents. The easy of preparation and high
functional group compatibility of organozincs allow numerous applications in
synthetic chemistry. It is already used in the Reformatsky reaction,[9] Negishi
coupling,[10] Barbier-type reactions,[11] transformation of acid chloride or chlorofor-
mates to a wide range of functional groups, such as amides,[12] FC acylation,[13] and
recently in the synthesis of diarylmethanes.[14]
In continuation of our earlier work[15–17] on synthesis of new derivatives with
potential biological activity, we now report a simple, one-pot preparation of the title
compounds using zinc metal without isolating the sodium or potassium salts of
substituted benzenesulphonyl chlorides.
At first, we prepared activated zinc by treating commercially available zinc
with 2% hydrochloric acid and then with water, alcohol, acetone, and absolute ether.
The zinc was then warmed in a hot air oven at 100 ꢁC for a short time and used
immediately.
2-Chloromethyl benzimidazole was reacted with activated zinc in tetrahydro-
furan (THF) at room temperature (25–30 ꢁC) (slowly the temperature of reaction
mixture rose up to 40–45 ꢁC) and kept for about 1.5–2.0 h (allowing in situ generation
of the chloromethyl zinc benzimidazole), followed by the addition of p-methylben-
zene sulfonyl chloride slowly under stirring conditions for about 0.5 h. The formation
Scheme 1. 2-Chloromethyl benzimidazole with activated zinc followed by addition of p-methylbenzene
sulfonyl chloride.

1586
K. SRINIVAS AND P. K. DUBEY
Table 1. Comparison of yields at different temperatures
Temperature (ꢁC)
Time (h)
Zn (eq.)a
Yield (%)
28–30
10
65
3.0
8.0–8.5
3.0
1.2
1.2
1.2
72
56
63
aAll the reactions were performed in THF at the indicated tempera-
ture for the indicated time.
of the product was indicated by thin-layer chromatography (TLC), and later simple
workup resulted in the formation of the compound. The structure of the compound
was established by comparison of its spectral and analytical data with those of the
authentic sample[18] (Scheme 1).
To ascertain the optimum temperature, several reactions were carried out on
chloromethyl benzimidazole and p-methyl benzene sulfonyl chloride mediated by zinc,
and finally the best result was obtained at 30 ꢁC (room temperature only) (Table 1).
Having established the reaction temperature, various halo compounds and
sulfonyl chlorides were subjected to reactions that resulted in the formation of a
CꢀS bond in one pot.
In the presence of zinc powder, we observed a smooth insertion reaction in
which complete consumption of the starting materials was observed in 1.5–2.0 h at
ambient temperature (30 ꢁC), followed by reaction with sulfonyl chlorides, which
provided aryl=heteryl sulfone derivatives in average to good yields (Table 2).
Similarly, for all the entries except for 1e and 1f, the procedure is the same as
described. For reactions with 1e and 1f, halomethyl derivatives (10 mmol), zinc
(12 mmol), and a catalytic amount of KI were stirred for about 1.5 h and followed
by the addition of required sulfonyl chloride slowly under stirring. The formation
of the product was indicated by TLC. Later the reaction mixture filtered, and the
filtrate poured into ice cold water. A few drops of sulfuric acid were added and
extracted with ethyl acetate, resulting in the formation of the compound
(Schemes 3 and 4 respectively).
EXPERIMENTAL
General Procedure for Compounds 3a–3h
2-Chloromethyl benzimidazole (1.6 g, 10 mmol) was reacted with activated zinc
(0.78 g, 12 mmol) in tetrahydrofuran (THF) at room temperature (25–30 ꢁC) (slowly
the temperature of reaction mixture rose up to 40–45 ꢁC within 45–60 min) and kept
for about 1.5–2.0 h (allowing for generation of the in situ chloromethyl zinc benzimi-
dazole), followed by the addition of p-methylbenzene sulfonyl chloride (2.0 g,
10.5 mmol) slowly under stirring conditions for about 0.5 h. The formation of the
product was indicated by TLC. Later the reaction mixture was filtered, and the
filtrate was poured into ice cold water. A few drops of sulfuric acid were added
and extracted with ethyl acetate, resulting in the formation of the compound. The
structure of the compound was established as 3a by comparison of its spectral and
analytical data with those of the authentic sample.

CASE OF CꢀS BOND FORMATION
1587
Table 2. Synthesis of compound 3 from 1 and 2
Entry
Reagent
Product (3)
Time (h)
Yield (%)
1a
2a
2b
2a
3.0
4.5
4.5
72
1a
1b
71
68
1b
1c
2b
2a
4.5
4.5
70
70
1c
1d
1d
2b
2a
2b
4.0
4.5
4.0
71
72
69
1e#
2a
5.0
68
(Continued )

1588
K. SRINIVAS AND P. K. DUBEY
Table 2. Continued
Product (3)
Entry
Reagent
Time (h)
Yield (%)
1f#
2b
4.0
69
#We observed the formation of product in this case taking place in 3.0 h when KI
is used during the formation of zinc complex.
Data for Compounds 3a–3h
2-(Toluene-4-sulfonylmethyl)-1H-benzimidazole (3a): IR (KBr) cmꢀ1: 3000
1
(NH), 1308 (SO2); H NMR (DMSO-d6): d 2.4 (s, 3H, ꢀCH3), 4.95 (s, 2H, ꢀCH2),
Scheme 2. Scope of the reaction conditions.

CASE OF CꢀS BOND FORMATION
1589
Scheme 3. Synthesis of 3i using KI in catalytic amounts.
ꢂ
7.2–7.7 (m, 8H, Ar-H), 12.6 (bs, 1H, ꢀNH, D2O exchangeable); Mþ þ 1: 287. Anal.
calcd. for C15H14N2O2S requires C, 62.92; H, 4.93; N, 9.78%. Found: C, 62.86;
H, 4.87; N, 9.74%.
2-Benzenesulfonylmethyl-1H-benzimidazole (3b). IR (KBr) cmꢀ1: 3000
1
(NH), 1300 (SO2); H NMR (DMSO-d6): d 4.85 (s, 2H, ꢀCH2), 7.15–7.80 (m, 9H,
ꢂ
Ar-H), 12.65 (bs, 1H, -NH, D2O exchangeable); Mþ þ 1: 273. Anal. calcd. for
C14H12N2O2S requires C, 61.75; H, 4.44; N, 10.29%. Found: C, 61.70; H, 4.40; N,
10.26%.
2-[1-(Toluene-4-sulfonyl)-ethyl]-1H-benzimidazole (3c). IR (KBr) cmꢀ1
:
3000 (NH), 1298 (SO2); 1H NMR (DMSO-d6): d 1.84 (d, J ¼ 7.16 Hz, 3H,
ꢀCHꢀCH3), 2.36 [s, 3H, ꢀC6H4ꢀCH3-(p)], 4.68 (q, J ¼ 7.14 Hz, 1H, ꢀCHꢀCH3),
ꢂ
7.2–7.7 (m, 8H, Ar-H), 10.3 (bs, 1H, -NH-, D2O exchangeable); Mþ þ 1: 301. Anal.
calcd. for C16H16N2O2S requires C, 63.98; H, 5.37; N, 9.33%. Found: C, 63.94;
H, 5.35; N, 9.30%.
2-(1-Benzenesulfonyl-ethyl)-1H-benzimdazole (3d). IR (KBr) cmꢀ1
:
1
3000, 1308 (SO2); H NMR (DMSO-d6): d 1.9 (d, J ¼ 7.16 Hz, 3H, ꢀCHꢀCH3),
4.7 (q, J ¼ 7.12 Hz, 1H, ꢀCHꢀCH3), 7.2–7.7 (m, 9H, Ar-H), 10.3 (bs, 1H, ꢀNH,
ꢂ
D2O exchangeable); Mþ þ 1: 287. Anal. calcd. for C15H14N2O2S requires C,
62.92; H, 4.93; N, 9.78%. Found: C, 62.86; H, 4.91; N, 9.74%.
1-Methyl-2-(toluene-4-sulfonylmethyl)-1H-benzimidazole (3e). IR (KBr)
1
cmꢀ1: 1300 (SO2); H NMR (CDCl3): d 2.45 (s, 3H, ꢀCH3), 3.95 (s, 3H, ꢀNCH3),
ꢂ
4.75(s, 2H, ꢀCH2), 7.2–7.7(m, 8H, Ar-H);Mþ þ 1:301. Anal. calcd. forC16H16N2O2S
requires: C, 63.98; H, 5.37; N, 9.33%. Found: C, 63.94; H, 5.32; N, 9.28%.
Scheme 4. Synthesis of 3j using KI in catalytic amounts.

1590
K. SRINIVAS AND P. K. DUBEY
2-Benzenesulfonylmethyl-1-methyl-1H-benzimidazole (3g). 1H NMR
(CDCl3): d 1.85 (d, J ¼ 7.18 Hz, 3H, ꢀCH2ꢀCH3), 2.40 [s, 3H, ꢀC6H4ꢀCH3-(p)],
3.95 (s, 3H, ꢀNCH3), 4.70 (q, J ¼ 7.0 Hz, 1H, ꢀCHꢀCH3), 7.2–7.7 (m, 8H,
ꢂ
Ar-H); Mþ þ 1: 315. Anal. calcd. for C17H18N2O2S requires: C, 64.94; H, 5.77; N,
8.91%. Found: C, 64.90; H, 5.75; N, 8.86%.
1-Methyl-2-[1-toluene-4-sulfonyl)-ethyl]-1H-benzimidazole
1
(3h).
IR (KBr): H NMR (CDCl3): d 1.70 (d, J ¼ 7.18 Hz, 3H, ꢀCHꢀCH3), 3.85 (s,
3H, ꢀNCH3), 5.10 (q, J ¼ 7.0 Hz, 1H, ꢀCHꢀCH3), 7.2–7.87 (m, 9H, Ar-H);
ꢂ
Mþ þ 1: 301. Anal. calcd. for C16H16N2O2S requires C, 63.98; H, 5.37; N, 9.33%.
Found: C, 63.95; H, 5.33; N, 9.29%.
General Procedure for Reactions with Entries 1e and 1f
Halo methyl derivatives 1e and 1f (10 mmol), zinc (12 mmol), and a catalytic
amount of KI were stirring for about 1.5 h followed by the addition of required
sulfonyl chloride slowly under stirring. The formation of the product was indicated
by TLC. Later the reaction mixture was filtered, and the filtrate was poured into
ice-cold water. A few drops of sulfuric acid were added and extracted with ethyl
acetate, resulting in the formation of the compound.
1-Methyl-4-phenylmethanesulfonyl-benzene (3i). IR (KBr) cmꢀ1: 1312
1
(SO2); H NMR (CDCl3): d 2.38 (s, 3H, ꢀCH3), 4.61 (s, 2H, ꢀCH2), 7.11–7.57
ꢂ
(m, 9H, aromatic protons); Mþ þ 1: 247.
CONCLUSION
These reactions are not only of interest from an economical point of view; in
many cases, they also offer considerable synthetic advantages in terms of yield,
selectivity, and simplicity of the reaction procedure. To our delight, a complete
switchover of expedient outcome was realized in this reaction.
ACKNOWLEDGMENTS
The authors are highly indebted to the Council of Scientific and Industrial
Research, government of India, New Delhi, for financial support (senior research fel-
lowship to Mr. K. Srinivas). They are also thankful to the authorities of Jawaharlal
Nehru Technological University Hyderabad for providing laboratory facilities.
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