Microwave-assisted reduction of α,β-unsaturated carbonyl compounds in solid state using sodium borohydide supported on magnesium sulfate (NaBH4/MgSO4-7H2O)

Article abstract of DOI:10.1080/00397910802149097

Reduction of varieties of carbonyl compounds such as ketones and α,β-unsaturated cyclic ketones were carried out quickly and efficiently by NaBH4/MgSO4-7H2O under microwave irradiation. The corresponding products were obtained in high to excellent yields. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910802149097

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Microwave-Assisted Reduction
of α,β-Unsaturated Carbonyl
Compounds in Solid State Using
Sodium Borohydide Supported
on Magnesium Sulfate (NaBH4/
MgSO4-7H2O)
Hossein Abbastabar Ahangar a b , Katayoun Marjani a
& Gholam Hossein Mahdavinia c
a Faculty of Chemistry, Teacher Training University ,
Tehran, Iran
b Young Researcher Club of Iran
c Department of Chemistry , Islamic Azad
University—Marvdasht Branch , Marvdasht, Iran
Published online: 30 Sep 2008.
To cite this article: Hossein Abbastabar Ahangar , Katayoun Marjani & Gholam
Hossein Mahdavinia (2008) Microwave-Assisted Reduction of α,β-Unsaturated
Carbonyl Compounds in Solid State Using Sodium Borohydide Supported on Magnesium
Sulfate (NaBH4/MgSO4-7H2O), Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 38:20, 3414-3421, DOI:
10.1080/00397910802149097
To link to this article: http://dx.doi.org/10.1080/00397910802149097

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Synthetic Communications1, 38: 3414–3421, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802149097
Microwave-Assisted Reduction of a,b-
Unsaturated Carbonyl Compounds in Solid State
Using Sodium Borohydide Supported on
Magnesium Sulfate (NaBH4/MgSO4-7H2O)
Hossein Abbastabar Ahangar,1,2 Katayoun Marjani,1 and
Gholam Hossein Mahdavinia3
1Faculty of Chemistry, Teacher Training University, Tehran, Iran
2Young Researcher Club of Iran
3Department of Chemistry, Islamic Azad University—Marvdasht Branch,
Marvdasht, Iran
Abstract: Reduction of varieties of carbonyl compounds such as ketones and
a,b-unsaturated cyclic ketones were carried out quickly and efficiently by
NaBH4=MgSO4-7H2O under microwave irradiation. The corresponding products
were obtained in high to excellent yields.
Keywords: Microwave, NaBH4, reduction, a,b-unsaturated carbonyl compounds
INTRODUCTION
Organic reactions carried out in dry media have received attention in
recent years.[1] They have many advantages over reactions carried out
in solution, such as greater selectivity, enhanced reaction rates, cleaner
products, and manipulative simplicity. Reduction is one of the frequently
used reactions in organic synthesis, and a vast variety of reducing agents
have been introduced.[2–4] Among the powerful reducing agents that have
been developed for the reduction of functional groups, LiAlH4 and
Received January 14, 2008.
Address correspondence to Hossein Abbastabar Ahangar, Faculty of
Chemistry, Teacher Training University, PO Box 15614, Tehran, Iran. E-mail:
abbastabar@gmail.com
3414

Reduction of a,b-Unsaturated Carbonyl Compounds
3415
NaBH4 are the commonly used reagents in synthetic organic laboratories.
Lithium aluminum hydride is an exceedingly powerful reducing agent cap-
able of reducing all organic functional groups. However, it is quite difficult
to use this reagent for the selective reduction of multifunctional molecules.
On the other hand, sodium borohydride is a relatively mild reducing agent,
which is primarily used for the reduction of reactive functional groups in
protic solvents. As the result, the rate of reductions is sometimes slow,
and a relatively low chemoselectivity accompanies the reactions.
A literature review shows that though the reduction of carbonyl
compounds as an important synthetic methodology was usually achieved
with NaBH4 in protic solvents, this transformation under solvent-free
conditions has been rarely investigated (e.g., the solid-state reduction of
ketones has been achieved by mixing with sodium borohydride and stor-
ing the mixture in a dry box for 5 days). The major shortcoming of this
method is that it takes a long time for any practical application. In addi-
tion, the need for large amounts of NaBH4 is a serious limitation of this
method.[5] Reduction of aldehydes and ketones with NaBH4 impregnated
on neutral Al2O3 under microwave irradiation has also been reported.
Though the reported method is fast and suitable for reduction of alde-
hydes, in the case of ketones the need for large amounts of NaBH4 (eight-
fold) and moderate yields of products are major limitations.[6] In another
report, microwave-assisted reduction of acetophenone and ethyl phenyl
ketone with NaBH4 in the presence of celite, SiO2, MgSO4, and cellulose
under solvent-free condition was investigated.[7] Also, in recent years,
reduction of carbonyl compounds with NaBH4=SiO2 and NaBH4 in
water were reported.[8,9] Therefore, to develop the strategies mentioned
previously and to find efficient and environmentally friendly catalysts
for organic reactions, here we report a mild, convenient, and simple
method for fast and efficient reduction of carbonyl compounds to their
corresponding alcohols with NaBH4=MgSO4-7H2O under solvent-free
conditions (Scheme 1).
In a preliminary test, we used an excess amount of NaBH4 without
any support to reduce 4-hydroxy-3,4-diphenylcyclopent-2-enone and
found a 30% conversion under microwave irradiation (Table 1, entry 1).
Scheme 1. Showing 3,4-diphenylcyclopent-2-en-1,4-diol in stereochemical form.

3416
H. A. Ahangar et al.
Table 1. Solid-state reduction of 4-hydroxy-3,4-diphenylcyclopent-2-enone with
NaBH4 under microwave irradiation
Entry
Support
Ketone=NaBH4 (equiv)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
None
Clay
SiO2
Al2O3
MgSO4-7H2O
MgSO4-7H2O
MgSO4-7H2O
MgSO4-7H2O
1:10
1:10
1:10
1:10
1:10
1:5
10
5
8
7
8
8
8
8
30
nil
35
40
90
90
90
70
1:2
1:1
We deduced that the powder of excess NaBH4 dispersed the aggregation
of ketones and subsequently made a useful contact to provide an efficient
reaction. To test this hypothesis, we used clay, SiO2, Al2O3, and MgSO4-
7H2O as a support for the reduction of 4-hydroxy-3,4-diphenylcyclopent-
2-enone under microwave irradiation. This reaction was more facile and
proceeded to give the highest yield with NaBH4=MgSO4-7H2O under sol-
vent-free conditions (Table 1, entry 7). For further investigation of the
usefulness of the microwave irradiation protocol, various carbonyl com-
pounds were used in the reaction. Results are shown in Table 2. All the
compounds in Table 2 (entries 1–5) have a phenyl group in the position
arbitrarily designated 4 a and one at position 3. The shielding of the 5 a
hydrogens relative to 5 b is readily explained if we assume that the plane
of the 4 a-phenyl group is nearly normal to that of the cyclopentene ring,
because of steric interference with the 3-phenyl ring. The 5 a-hydrogen
then lies above the plane of 4 a-phenyl ring, and we deduced that two
hydroxyl groups can be trans according their coupling constant with
5 a and 5 b hydrogens.
In conclusion, we have developed a mild, simple, cost-effective, and
green procedure for the reduction of carbonyl compounds using
NaBH4=MgSO4-7H2O. Moreover, the mild reaction conditions, high
yield of products, easy workup, and ready availability of the catalyst will
make the present method a useful and convenient methodology for the
reduction of carbonyl compounds.
EXPERIMENTAL
The microwave oven used for this work was an ETHOS-MR (800 W,
180ꢀC) operating at 2450 MHz. Melting points were determined on an
Electrothermal 9100 instrument and are uncorrected. Infrared (IR)

Table 2. Solid-state reduction of carbonyl compounds with NaBH4=MgSO4-7H2O under microwave irradiation
Mp (ꢀC)
Reported
Entry
1
Carbonyl compound
Time (min)
8
Product
Yield (%)a
90
Found
1a
148–150
149–151[10]
2
3
7
8
1b
1c
95
90
175–178
190–192
—
200–202[10]
4
5
9
8
1d
1e
80
172–174
142–144
172–174[10]
95b
140–142[10]
(Continued )

Table 2. Continued
Mp (ꢀC)
Reported
Entry
6
Carbonyl compound
Time (min)
8
Product
Yield (%)a
82
Found
1f
158–160
159[11]
7
8
5
5
1g
1h
96
95
94–96
64–66
97[12]
67–68[13]
9
10
1i
82
287–290
258–270[14]
aIsolated yield.
bWith methanol as a solvent.

Reduction of a,b-Unsaturated Carbonyl Compounds
3419
spectra were recorded on a Perkin-Elmer 843 spectrophotometer (KBr).
1H NMR spectra were recorded on a Varian 500-MHz spectrometer in
acetone-d6 using TMS as an internal reference. Products were identified
by comparison of melting points and spectroscopic data with those
reported.
Typical Procedure for Reduction of Carbonyl Compound
with NaBH4/MgSO4-7H2O
To a mixture of NaBH4 (4 mmol) and MgSO4-7H2O (1.5 g), carbonyl
compound (2 mmol) was added and the mixture was well ground with
a pestle and irradiated in a microwave oven (800 W) for an appropriate
time (Table 2). After completion of the reaction (monitored by thin-layer
chromectography, TLC), the reaction mixture was diluted with water.
The resulting solid product was collected by filtration and recrystallized
from toluene.
Data
Compound 1a
1
IR (KBr): vmax=cmꢁ1 3382, 1578, 1501, 1262, 1285, 774, 701 cmꢁ1; H
3
2
NMR (acetone-d6) d 2.18 (1H, dd, J ¼ 4.5, J ¼ 14 Hz), 2.78 (1H, dd,
3J ¼ 7.08, 2J ¼ 14 Hz), 4.1 (OH, d, 3J ¼ 5.6 Hz), 4.7 (OH, s), 5.15
3
(1H, m), 6.41 (1H, d, J ¼ 2.25 Hz), 7.09–7.56 (10H, m).
Compound 1b
IR (KBr): vmax=cmꢁ1 3370, 3327, 1498, 1452, 1075, 998, 760, 698 cmꢁ1
;
1H NMR (acetone-d6) d 1.68 (3H, d, 4J ¼ 0.67 Hz), 2.19 (1H, dd,
3J ¼ 5, 2J ¼ 13.5 Hz), 2.70 (1H, dd, 3J ¼ 7, 2J ¼ 13.5 Hz), 4.2 (OH, d,
3J ¼ 6.56 Hz), 4.31 (OH, s), 4.74 (1H, m), 7.12–7.36 (10H, m). Anal.
calcd. for C18H18O2: C, 81.17; H, 6.81. Found: C, 81.00; H, 6.81.
Compound 1c
1
IR (KBr): vmax=cmꢁ1 3328, 3259, 1490, 1444, 1011, 768, 693 cmꢁ1; H
3
3
NMR (acetone-d6) d 1.1 (3H, d, J ¼ 7 Hz), 2.10 (1H, qui, J ¼ 7 Hz),
4.13 (OH, d, 3J ¼ 6.71 Hz), 4.24 (OH, s), 4.68 (1H, td, 3J ¼ 1.78,
3
3J ¼ 6.74 Hz), 6.41 (1H, d, J ¼ 1.8 Hz), 7.08–7.43 (10H, m).

3420
H. A. Ahangar et al.
Compound 1d
1
IR (KBr): vmax=cmꢁ1 3330, 1486, 1442, 1350, 1061, 1031, 690 cmꢁ1; H
2
3
NMR (acetone-d6) d 2.44 (1H, dd, J ¼ 14.25, J ¼ 3.75 Hz), 2.86 (1H,
2
3
3
dd, J ¼ 14.25, J ¼ 7.25 Hz), 4.28 (OH, d, J ¼ 5.74 Hz), 4.55 (OH, s),
3
3
4.68 (1H, td, J ¼ 1.78, J ¼ 6.74 Hz), 5.44 (1H, m), 6.95–7.9 (15H, m).
Compound 1e
1
IR (KBr): vmax=cmꢁ1 3461, 1486, 1444, 1373, 1150, 1064, 694 cmꢁ1; H
NMR (acetone-d6) d 1.07 (3H, d, 3J ¼ 7.50 Hz), 1.90 (3H, d, 4J ¼ 1.0 Hz),
3
2.10 (1H, m), 4.03 (OH, s), 4.12 (OH, d, J ¼ 7.25 Hz), 4.49 (1H, m),
7.09–7.39 (10H, m).
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Reduction of a,b-Unsaturated Carbonyl Compounds
3421
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