Use of magnesium (turnings) as a powerful catalyst for the o-acylative cleavage of tetrahydrofuran

Article abstract of DOI:10.1080/00397911.2010.502992

In a short reaction time, acyl chlorides and dry tetrahydrofuran react in the presence of a catalytic amount of magnesium turnings (Mg) at 25 °C to give 4-chlorobutyl esters in excellent yields. Copyright

Full text of DOI:10.1080/00397911.2010.502992

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Use of Magnesium (Turnings) as a
Powerful Catalyst for the O-Acylative
Cleavage of Tetrahydrofuran
a
a
M. A. Pasha & Krishnappa Manjula
a
Department of Studies in Chemistry, Bangalore University,
Bangalore, India
Version of record first published: 25 May 2011.
To cite this article: M. A. Pasha & Krishnappa Manjula (2011): Use of Magnesium (Turnings) as a
Powerful Catalyst for the O-Acylative Cleavage of Tetrahydrofuran, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 41:15, 2309-2314
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1
Synthetic Communications , 41: 2309–2314, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.502992
USE OF MAGNESIUM (TURNINGS) AS A POWERFUL
CATALYST FOR THE O-ACYLATIVE CLEAVAGE OF
TETRAHYDROFURAN
M. A. Pasha and Krishnappa Manjula
Department of Studies in Chemistry, Bangalore University, Bangalore, India
GRAPHICAL ABSTRACT
Abstract In a short reaction time, acyl chlorides and dry tetrahydrofuran react in the pres-
ꢀ
ence of a catalytic amount of magnesium turnings (Mg) at 25 C to give 4-chlorobutyl
esters in excellent yields.
Keywords Acyl chlorides; 4-chlorobutylesters; magnesium turnings; tetrahydrofuran
INTRODUCTION
The cleavage of tetrahydrofuran (THF) with acyl chlorides to give 4-chlorobu-
tyl esters is a useful reaction, particularly in the synthesis of natural products and
[
1]
polyfunctional molecules where a four-carbon chain is required to be added.
Syntheses of 4-chlorobutyl esters from THF and acid chloride in the presence of
[
ZnCl2, FeCl3, Mo(CO)6, MoCl5, SmI2, PdCl (PPh ) , CoCl2, NaI,
2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
2
[12]
3 2
[10]
[11]
[13]
lanthanide salts,
[
graphite,
H O, have been reported.
aluminum complexes,
InBr3,
and La(NO3)3 ꢁ
14]
6
2
Many of these procedures suffer from one or other limitations such as use of
expensive reagents, longer reaction times, and high temperatures. In some cases,
the yields are poor to moderate, environmentally toxic catalysts are used, and cum-
bersome methodologies are employed. Therefore, there is a need for versatile, simple,
and environmentally friendly processes for the synthesis of 4-chlorbutyl esters.
Studies on the use of the nontoxic and inexpensive environmentally benign
metal magnesium have greatly expanded all around the world, and a search for
application of magnesium and magnesium compounds has pulled up numerous
[
15]
records. Cleavage of the THF ring by triphenylmethylmagnesium bromide to give
5
[16]
,5,5-triphenylpentan-1-ol,
the use of magnesium bromide for the acylation of
Received February 19, 2010.
Address correspondence to M. A. Pasha, Department of Studies in Chemistry, Central College
Campus, Bangalore University, Bangalore 560 001, India. E-mail: m_af_pasha@ymail.com
2
309

2310
M. A. PASHA AND K. MANJULA
[17]
alcohols, and the use of magnesium alkoxides in the synthesis of benzoheterocyc-
[18]
lic compounds have been investigated recently.
In this paper, we describe our successful use of magnesium as a catalyst for
ꢀ
the O-acylative cleavage of THF in the presence of acyl chlorides at 25 C to get
4
-chlorobutyl esters.
RESULTS AND DISCUSSION
Earlier reports from our laboratory described the synthesis of 4-chlorobutyl
[
19a]
esters from THF and acyl chlorides in the presence of zinc dust under sonication.
To avoid the use of sonication, we studied the reaction under normal condition with
[
9b]
a catalytic amount of molecular iodine to get 4-chlorobutyl esters. In continuation
with our work on the synthesis of 4-chlorobutyl esters using simpler reagents and
catalysts, we are reporting a simple and efficient method of synthesis of 4-chlorobu-
tyl esters from THF and acyl chlorides using a catalytic amount of magnesium turn-
ꢀ
ings in the absence of any additional solvent at 25 C (Scheme 1) in less than 10 min
with excellent yields.
To standardize the reaction conditions, different amounts of magnesium turn-
ings were used to get 4-chlorobutyl benzoate from THF and benzoyl chloride; the
results are summarized in Table 1. From Table 1 it is clear that the reaction can
be carried out in the presence of a catalytic amount of magnesium turnings, and
the yield of the product is maximum (94% with 0.024 g). It is not possible without
magnesium turnings (entries 5 and 6).
To extend the reaction of THF with different acyl chlorides in the presence of
catalytic magnesium, the reactions of THF with alkyl, aryl, and allyl, substituted
acyl chlorides were taken up. The reactions were carried out under normal condition,
and the results are summarized in Table 2. From this table, it is clear that aroyl
Scheme 1. Mg metal-catalyzed O-acylative cleavage of tetrahydrofuran.
ꢀ
Table 1. Reaction of THF and benzoyl chloride in the presence=absence of Mg turnings at 25 C
Entry
Amount of Mg (g)
Time (min)
Yield (%)
1
2
3
4
5
6
0.24
0.18
0.12
0.06
0.024
Nil
30
30
78
80
30
30
80
87
94
05
24 (hours)
No reaction

O-ACYLATIVE CLEAVAGE OF TETRAHYDROFURAN
2311
a
Table 2. Reaction of acyl chlorides with THF in presence of magnesium turnings at 25 C
ꢀ
b
Product (3)
Entry
Acid chloride (2)
Time (min)
Yield (%)
95
a
03
b
c
05
05
94
92
d
e
f
05
05
90
94
06
08
90
92
g
a
0
.024 g of Mg.
b 1
Products are characterized by IR, H NMR, and LC–mass spectral analysis.
chlorides containing both electron-withdrawing and electron-donating groups react
equally efficiently to give 4-chlorobutylesters in excellent yield in less than 10 min.
EXPERIMENTAL
[
20]
Different acyl chlorides were prepared by standard procedures and purified
before use. All reagents were commercial products, solids were used without further
purification, and liquids were distilled before use. Reactions were monitored on TLC
[
19a,b]
by comparison with the samples prepared by known methods.
Yields refer to
the isolated yields of the products and are based on 10 mmol of starting acid chlor-
ide. A Nicolet 400D Fourier transform–infrared (FT-IR) spectrophotometer was
1
used for IR spectral analysis. H NMR spectra were recorded on a 400-MHz Bruker
instrument and liquid chromatography (LC)–mass analysis was performed on an
Agilent Technologies 1200 series instrument.

2312
M. A. PASHA AND K. MANJULA
General Experimental Procedure for the Preparation of
4-Chlorobutyl Esters
Acyl chloride (10 mmol) and THF (10 ml) were taken in a 25-ml
round-bottomed flask. To this, magnesium turnings (0.024 g) were added and stirred
ꢀ
at 25 C. The progress of the reaction was monitored by thin-layer chromatography
(TLC); after completion of the reaction, the contents were filtered and washed with
ether (25 ml), and the organic layer was washed successively with saturated
NaHCO (10 ml), followed by water (3 ꢂ 10 ml), dried over anhydrous Na SO ,
3
2
4
concentrated, and purified by silica-gel column chromatography (5% ethyl acetate–
1
petroleum ether) to afford pure 4-chlorobutyl esters. The IR, H NMR, and LC-MS
spectral data of 4-chlorobutyl esters prepared by this procedure are presented.
Spectroscopic Data of the Products
ꢃ1
1
CH CO (CH ) Cl (3a). IR (neat) n ¼ 1739, 725 cm ; H NMR (400 MHz,
3
2
2 4
CDCl ) d: 1.78–1.87 (m, 4H), 2.04 (s, 3H), 3.55–3.58 (t, 2H, J ¼ 6 Hz), 4.06–4.11
3
þ
(
t, 2H, J ¼ 6 Hz); MS: m=z ¼ 151.0 (M ).
ꢃ1
1
C H CO (CH ) Cl (3b). IR (neat) n ¼ 1716, 711 cm ; H NMR (400 MHz,
6
5
2
2 4
CDCl ) d: 1.97 (m, 4H), 3.59 (t, 2H, J ¼ 4 Hz), 4.35 (t, 2H, J ¼ 4 Hz), 7.44 (d, 2H,
3
þ
J ¼ 8 Hz), 7.61 (t, 1H, J ¼ 8 Hz), 8.01 (d, 2H, J ¼ 8 Hz); MS: m=z ¼ 212 (M ).
ꢃ1
1
ClCH CO (CH ) Cl (3c). IR (neat) n ¼ 1751, 752 cm ; H NMR (400 MHz,
2
2
2 4
CDCl ) d: 1.65–1.93 (m, 4H), 2.07 (s, 2H), 3.61 (t, 2H, J¼ 6 Hz), 4.15 (t, 2H,
3
þ
J ¼ 6 Hz); MS: m=z ¼ 184 (M ).
ꢃ1
1
ClC H CO (CH ) Cl (3d). IR (neat) n ¼ 1720, 745 cm ; H NMR (400 MHz,
6
4
2
2 4
CDCl ) d: 1.93 (m, 4H), 3.65 (m, 2H), 4.38 (m, 2H), 7.67 (d, 2H, J ¼ 8 Hz) 7.89 (d,
3
þ
2
H, J ¼ 8 Hz); MS: m=z ¼ 246 (M ).
ꢃ1
1
BrC H CO (CH ) Cl (3e). IR (neat) n ¼ 1725, 743 cm ; H NMR (400 MHz,
6
4
2
2 4
CDCl ) d: 1.93 (m, 4H), 3.55 (m, 2H), 4.38 (m, 2H), 7.63 (d, 2H, J ¼ 8.4 Hz), 7.88 (d,
3
þ
2
H, J ¼ 8.5 Hz); MS: m=z ¼ 292 (M ).
ꢃ1
1
NO C H CO (CH ) Cl (3f). IR (neat) n ¼ 1745, 725 cm
;
H NMR
2
6
4
2
2 4
(
400 MHz, CDCl ) d: 1.92 (m, 4H), 3.65 (m, 2H), 4.36 (m, 2H), 7.52 (d, 2H,
3
þ
J ¼ 8 Hz), 7.96 (d, 2H, J ¼ 8 Hz); MS: m=z ¼ 257 (M ).
ꢃ1
1
C H CH=CHCO (CH ) Cl (3g). IR (neat) n ¼ 1768, 768 cm
;
H NMR
6
5
2
2 4
(
400 MHz, CDCl ) d: 1.93 (m, 4H), 3.65 (m, 2H), 4.38 (m, 2H), 6.42 (d, 1H,
3
J ¼ 16 Hz), 7.74 (d, 1H, J ¼ 16 Hz), 7.50 (d, 2H, J ¼ 8 Hz), 7.49 (t, 1H, J ¼ 8 Hz),
þ
7
.61 (d, 2H, J ¼ 8 Hz); MS: m=z ¼ 238 (M ).
CONCLUSION
In conclusion, we have presented a simple, efficient, economically viable, and
solvent-free protocol for the preparation of 4-chlorobutyl esters from THF and acyl
chlorides in the presence of catalytic amounts of nontoxic, readily available, and
inexpensive magnesium turnings. The advantageous of our method include a simple

O-ACYLATIVE CLEAVAGE OF TETRAHYDROFURAN
2313
reaction setup not requiring specialized equipment, room temperature conditions,
excellent product yields, short time, and elimination of solvents. The present method
[
19a,b]
is as efficient as our previous methods of synthesis of 4-chlorobutyl esters.
ACKNOWLEDGMENT
Krishnappa Manjula is thankful to V. P. Jayashankara for his timely help and
encouragement.
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