Iron(III) chloride-promoted direct conversion of aryl/alkyl cyanides to esters

Article abstract of DOI:10.1080/00397910600770722

Aryl/alkyl cyanides were quickly converted into the corresponding esters in the presence of iron(III) chloride in refluxing alcohols with very good yields. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910600770722

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Iron(III) Chloride–Promoted Direct Conversion
of Aryl/Alkyl Cyanides to Esters
R. Srinivasan a , K. Srinivasa Rao a , G. Jayachitra a & Samuel L. Ralte a
a Fine Chemicals Laboratory, Division of Organic Chemistry III, Indian
Institute of Chemical Technology, Hyderabad, India
Published online: 16 Feb 2007.
To cite this article: R. Srinivasan , K. Srinivasa Rao , G. Jayachitra & Samuel L. Ralte (2006): Iron(III)
Chloride–Promoted Direct Conversion of Aryl/Alkyl Cyanides to Esters, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:19, 2883-2886
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Synthetic Communicationsw, 36: 2883–2886, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600770722
Iron(III) Chloride–Promoted Direct
Conversion of Aryl/Alkyl Cyanides to Esters
R. Srinivasan, K. Srinivasa Rao, G. Jayachitra, and
Samuel L. Ralte
Fine Chemicals Laboratory, Division of Organic Chemistry III, Indian
Institute of Chemical Technology, Hyderabad, India
Abstract: Aryl/alkyl cyanides were quickly converted into the corresponding esters in
the presence of iron(III) chloride in refluxing alcohols with very good yields.
Keywords: Alcohols, cyanides, esters, iron(III) chloride, one-pot conversion
FeCl3 is a versatile reagent in areas of synthetic chemistry such as conversion
of epoxides to chlorohydrins,[1] benzylations of arenes,[2] poly condensation
between citric acid and polyethylene glycol,[3] Friedel–Crafts sulfonyl-
ation reactions of aromatics,[4] cationic polymerization,[5] debenzylation of
complex oligosaccharides,[6] catalytic deprotection of benzylic esters,[7]
selective t-BuOH esterification with Ac2O using Si-MCM-41,[8] and Friedel–
Crafts acetylation of benzene in ionic liquids.[9] Surprisingly, there is no
report on conversion of cyanides to esters using FeCl3.
We have been recently engaged with functional group transformations in
the presence of Lewis acids, which play key roles in many organic syntheses.
During this course of study, we reported the usage of borontrifluoride etherate
complex in the direct conversion of aryl/alkyl cyanides to esters.[10]
In this report, we highlight our new findings based on the reactions
between benzonitrile or malononitrile and alcohols, which were converted
into the corresponding esters in the presence of FeCl3. The alcohols were
used as a reactant and solvent (Scheme 1).
Received in India February 28, 2006
Address correspondence to R. Srinivasan, Fine Chemicals Laboratory, Division of
Organic Chemistry III, Indian Institute of Chemical Technology, Hyderabad 500 007,
India. E-mail: rajsrini@yahoo.com
2883

2884
R. Srinivasan et al.
Scheme 1.
Table 1. FeCl3-catalysed ester formation from cyanides with different alcohols
Substrate (S)
[Solvent]
Time
(h)
Yielda
(%)
Molar ratio
S:FeCl3
S. no.
Product
1
2
3
4
5
6
7
8
[CH3OH]
[C2H5OH]
R ¼ CH3
25
12
4
36.0[10]
74.8[10]
70.0[11]
92.6[11]
90.8[11]
63.3[11]
47.5[11]
90.0[11]
1:5
1:5
1:5
1:5
1:3
1:1
1:0.5
1:5
R ¼ C2H5
R ¼ C3H7
R ¼ C4H9
R ¼ C4H9
R ¼ C4H9
R ¼ C4H9
R ¼ C5H11
[n-C3H7OH]
[n-C4H9OH]
[n-C4H9OH]
[n-C4H9OH]
[n-C4H9OH]
[n-C5H11OH]
2
1
2
4
1
9
10
[n-C4H9OH]
[n-C5H11OH]
R ¼ C4H9
R ¼ C5H11
4
1
64.7[13]
60.7
1:3
1:5
11
12
13
14
[CH3OH]
R ¼ CH3
32
21
24
6
61.3[10]
63.3[10]
60.0[14]
54.0[14]
1:3
1:3
1:3
1:5
[C2H5OH]
[i-C3H7OH]
[i-C3H7OH]
R ¼ C2H5
R ¼ i-C3H7
R ¼ i-C3H7
15
16
17
18
19
[CH3OH]
R ¼ CH3
32
21
10
6
59.0[10]
65.0[10]
75.7[10]
63.0[10]
81.6[15]
1:3
1:3
1:3
1:5
1:5
[C2H5OH]
[i-C3H7OH]
[i-C3H7OH]
[n-C4H9OH]
NCCH2CN
[CH3OH]
R ¼ C2H5
R ¼ i-C3H7
R ¼ i-C3H7
R ¼ i-C4H9
NCCH2CO2R
R ¼ CH3
2
20
21
1
1
71
76
1:5
1:3
[C2H5OH]
R ¼ C2H5
aIsolated yield.

Conversion of Aryl/Alkyl Cyanides to Esters
2885
Scheme 2.
Several experiments were conducted utilizing the substituted aromatic
and heteroaromatic cyanides and aliphatic alcohols such as methanol,
ethanol, n- or i-propanol, n-butanol, and n-pentanol, and the results are
tabulated (Table 1). The substrate-to-catalyst ratio was also optimized by con-
ducting various experiments as mentioned in Table 1.
Malononitrile was heated in a refluxing alcohol in the presence of FeCl3
for 1 h. Surprisingly, we found the formation of alkyl cyanoacetate
1
(monoester) exclusively, which was confirmed by the H NMR spectrum.
The selectivity of monoester formation was higher in FeCl3-catalyzed conver-
.
sion than in BF3 OEt2-catalyzed conversion in methanol as well as in
ethanol[10] (Scheme 2).
In conclusion, FeCl3-promoted direct conversion of nitriles to the
corresponding esters (alkyl/aryl–alkyl) had been successful.
EXPERIMENTAL
Procedure for a Selected Example
FeCl3 (7.87 g, 48.55 mmol) was added to a solution of benzonitrile (1 g,
9.71 mmol) and alcohol (15 mL) under N2 portionwise and stirred for
15 min at room temperature. Then the reaction mixture was refluxed for an
appropriate time (Table 1). It was filtered through a Celite pad and concen-
trated; saturated NaHCO3 solution was introduced and extracted with
CH2Cl2 (3 Â 50 mL). The combined organic layer was washed with water
and brine, dried (Na2SO4), and concentrated. The residue was purified on
silica gel using ethyl acetate–light petroleum.
1H NMR (400 MHz, CDCl3/TMS): d 0.89–0.97 (m, 3H); 1.25–1.50
(m, 4H); 1.75–1.85 (m, 2H); 4.31 (t, J ¼ 6.6 Hz, 2H); 7.28 (dt, J ¼ 7.6,
1.6 Hz 1H); 7.40–7.50 (m, 2H); 7.78 (dd, J ¼ 7.6, 1.6 Hz, 1H).
ACKNOWLEDGMENTS
The authors thank Indian Institute of Chemical Technology (IICT) and
Council of Scientific and Industrial Research (CSIR), New Delhi, India, for
financial support.
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