Eco-friendly mono-1,4-hydrocyanation of diarenyl ketones using potassium hexacyanoferrate(II) as a cyanide source

Article abstract of DOI:10.3184/174751915X14197812950625

A selective mono-1,4-hydrocyanation of 10 diarenyl ketones using potassium hexacyanoferrate(II) as an eco-friendly cyanide source, potassium hydroxide as a catalyst, and benzoyl chloride as a promoter has been achieved. This protocol has the advantages of a non-toxic cyanide source, a heavy metal-free catalyst, selectivity, very good yields and a simple work-up procedure.

Full text of DOI:10.3184/174751915X14197812950625

44 RESEARCH PAPER
VOL. 39 JANUARY, 44–47
JOURNAL OF CHEMICAL RESEARCH 2015
Eco-friendly mono-1,4-hydrocyanation of diarenyl ketones using potassium
hexacyanoferrate(II) as a cyanide source
Xiao-Ning Hua, Chen-Hui Liub and Zheng Lib*
aGansu Provincial Center for Disease Control and Prevention, Lanzhou, Gansu, 730000, P.R. China
bCollege of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu, 730070, P.R. China
A selective mono-1,4-hydrocyanation of 10 diarenyl ketones using potassium hexacyanoferrate(II) as an eco-friendly cyanide
source, potassium hydroxide as a catalyst, and benzoyl chloride as a promoter has been achieved. This protocol has the advantages
of a non-toxic cyanide source, a heavy metal-free catalyst, selectivity, very good yields and a simple work-up procedure.
Keywords: mono-1,4-hydrocyanation, diarenyl ketone, potassium hexacyanoferrate(II), in situ HCN generation
The conjugate hydrocyanation of α,β-unsaturated ketones
is an important C–C bond forming reaction in synthetic
organic chemistry, which can produce significant β-cyano
ketones. β-Cyano ketones are valuable synthons for synthetic
organic chemistry.1,2 Therefore many different methods for the
conjugate hydrocyanation of α,β-unsaturated ketones have been
reported, which mainly use HCN,3 KCN,4 and Et2AlCN5 as
cyanide sources. However, these cyanide sources are strongly
toxic chemicals. Recently it has been reported that conjugate
hydrocyanation of α,β-unsaturated ketones could be conducted
using trimethylsilyl cyanide6–8 and acetone cyanohydrin9,10
as cyanide sources. However, trimethylsilyl cyanide is very
sensitive to moisture, and acetone cyanohydrin is unstable and
both can easily release toxic hydrogen cyanide when heated.
Therefore, there is a need to explore eco-friendly cyanating
agents for hydrocyanation reactions.
Potassium hexacyanoferrate(II), K4[Fe(CN)6], is non-
toxic and is used in the food industry for metal precipitation.
In addition, it has been described as an anti-agglutinating
auxiliary for table salt. K4[Fe(CN)6] is a by-product of the coal
chemical industry and is commercially available on a ton scale,
and is even cheaper than KCN. Recently, K4[Fe(CN)6] has
been used as a cyanide source for some substitution reactions
to synthesise benzonitriles,11–13 aroyl cyanides,14 benzyl
cyanides,15 and arylsulfonyl cyanides.16 Our current research
focused on the cyanation of unsaturated compounds including
C=O,17–20 C=N21–26 and/or C=C27–29 by nucleophilic addition
reactions using K4[Fe(CN)6] as an eco-friendly cyanide source.
As an extension of this work, we here report an efficient method
for the selective (conjugate) mono-1,4-hydrocyanation of
unsaturated compounds bearing one C=O and two C=C bonds,
a series of diarenyl ketones, using K4[Fe(CN)6] as a selective
1,4-nucleophilic addition reagent and an eco-friendly cyanide
source. To the best of our knowledge, no previous reports of
conjugate mono-1,4-hydrocyanation of diarenyl ketones have
been made.
Results and discussion
For the optimisation of the mono-1,4-hydrocyanation of
diarenyl ketones using K4[Fe(CN)6] as an eco-friendly cyanide
source we used as model substrate, 1,5-diphenylpenta-1,4-dien-
3-one 1a (Scheme 1, R=H). Because K4[Fe(CN)6] is a very
stable complex, it is difficult to release cyanide ions in general
conditions. In our previous work, it was found that benzoyl
chloride is an efficient promoter to activate cyanide ions
through the formation of benzoyl cyanide as an intermediate,
which could be isolated and identified from the reaction
system.20 Therefore, the hydrocyanation of 1a with K4[Fe(CN)6]
was attempted using benzoyl chloride as a promoter, in the
expectation that the reaction might afford the mono-1,4-
hydrocyanation product 2a (Scheme 1, R=H) in the presence
of appropriate catalysts and solvents. Indeed, this was the
case, and it was also found that only 0.2 equiv. of K4[Fe(CN)6]
was required for 1 equiv. of 1a, which indicated that six
CN– of K4[Fe(CN)6] could be fully utilised in this reaction.
In addition, no other side reactions such as 1,2-addition or
di-1,4-hydrocyanation were observed, even using an excess of
K4[Fe(CN)6], which indicated the high chemoselectivity of the
reaction.
Inaddition, itwasalsofoundthatcatalystsplayedacriticalrole
in the reaction. Various bases were used as catalysts to examine
the reaction of 1a with K4[Fe(CN)6] using benzoyl chloride as
a promoter and the results are shown in Table 1. No reactions
were observed using sodium carbonate or potassium carbonate
as catalysts, even after 24 h, but N,N-dimethylaminopyridine
(DMAP), 1,4-diazabicyclooctane (DABCO) or Et3N as
catalysts gave the product in low yield after heating at 60 °C
for 12 h (entries 1–3). However, the reaction proceeded in very
good yield under the same conditions in the presence of NaOH
or KOH, the latter giving the mono-1,4-hydrocyanation product
in slightly higher yield (entries 4 and 5).
The solvent also has a significant effect on the reaction, as
shown in Table 2. For example, although there was no reaction
O
CN
O
(i) K4[Fe(CN)6] / PhCOCl / 160 oC / 3h
(ii) KOH / MeCN / 60 oC / 11-16 h
R
R
R
R
2a–j
1a–j
Scheme 1 Mono-1,4-hydrocyanation of diarenyl ketones 1a–j using K4[Fe(CN)6] as a cyanide source.
* Correspondent. E-mail: lizheng@nwnu.edu.cn

JOURNAL OF CHEMICAL RESEARCH 2015 45
Table 1 The effect of various bases on the yield of mono-1,4-cyanation of
1,5-diphenylpenta-1,4-dien-3-one 1a using K4[Fe(CN)6] as a cyanide source
(Scheme 1)a
Table 3 Yields/reaction times of the mono-1,4-hydrocyanation of
1,5-diarylpenta-1,4-dien-3-ones 1a–j using K4[Fe(CN)6] as a cyanide
source (Scheme 1)a
Entry
Catalyst
Yield/%b
Entry
Compd
R
Reaction time/h
Yield/%b
1
2
3
4
5
DMAP
DABCO
Et3N
NaOH
KOH
12
25
36
81
84
1
2
3
4
5
6
7
8
9
2a
2b
2c
2d
2e
2f
2g
2h
2i
H
2-Me
4-Me
4-MeO
2,3-OCH2O
2-Cl
4-Cl
4-Br
12
12
13
16
11
13
13
12
15
13
84
83
81
76
73
70
81
76
70
78
aReaction conditions: (i) K4[Fe(CN)6] (0.4 mmol)/PhCOCl (2 mmol)/
160 °C/3 h; (ii) cooled, then 1a (1.5 mmol) and base (0.4 mmol) in MeCN
(5 mL) were added and stirred at 60 °C for 12 h.
bIsolated yield.
4-NO2
2-furylc
10
2j
aReaction conditions: (i) K4[Fe(CN)6] (0.4 mmol)/PhCOCl (2 mmol)/
160 °C/3 h; (ii) cooled, then 1a–j (1.5 mmol) and KOH (0.4 mmol) in MeCN
(5 mL) were added and stirred at 60 °C for 11–16 h.
bIsolated yield.
Table 2 The effect of solvents on the yield of mono-1,4-hydrocyanation of
1,5-diphenylpenta-1,4-dien-3-one 1a using K4[Fe(CN)6] as a cyanide source
(Scheme 1)a
Entry
Solvent
Yield/%b
cThis substituent replaces RC6H4.
1
2
3
4
5
6
CH2Cl2
THF
DMF
MeOH
EtOH
MeCN
33
42
45
68
74
84
ketone also gave a monohydrocyanation product in good (78%)
yield.
A plausible mechanism for the mono-1,4-hydrocyanation of
diarenyl ketones 1a–j with K4[Fe(CN)6] is shown in Scheme 2.
K4[Fe(CN)6] first reacts with benzoyl chloride to form benzoyl
cyanide. Then benzoyl cyanide is attacked by water in undried
MeCN to produce hydrogen cyanide in situ, which is converted
into cyanide ion in the presence of potassium hydroxide. The
cyanide ion then reacts with the diarenyl ketone by 1,4-addition
to form an intermediate enolate A, which is quenched by water
to produce the final monohydrocyanation products 2a–j.
aReaction conditions: (i) K4[Fe(CN)6] (0.4 mmol)/PhCOCl (2 mmol)/
160 °C/3 h; (ii) cooled, then 1a (1.5 mmol) and KOH (0.4 mmol) in solvent
(5 mL) were added and stirred at reflux or at 60 °C for 12 h.
bIsolated yield.
in toluene, in CH2Cl2, THF or DMF low yields were obtained
(entries 1–3). However, reaction in MeOH, EtOH or MeCN
gave the desired product in good to high yield (entries 4–6), the
latter giving the best yield.
Experimental
IR spectra were recorded using KBr pellets on an Alpha Centauri
FTIR spectrophotometer. NMR spectra were obtained on a Mercury-
400BB spectrometer (1H NMR at 400 MHz, 13C NMR at 100 MHz)
in CDCl3 using Me4Si as internal standard. Elemental analyses were
performed on a Vario El Elemental Analysis instrument. Melting
points were determined in an electrothermal melting point apparatus.
Potassium hexacyanoferrate(II) was dried at 80 °C under vacuum for
24 h and finely powdered prior to use. Diarenyl ketones were prepared
according to literature method.30
Mono-1,4-hydrocyanations of various diarenyl ketones with
K4[Fe(CN)6] were then examined using benzoyl chloride as a
promoter and potassium hydroxide as a catalyst in MeCN the
results are shown in Table 3. Diarenyl ketones bearing electron-
donating groups on their aromatic rings, such as methyl and
methoxy, or electron-withdrawing groups, such as chloro,
bromo or nitro, all gave 1,4-addition products smoothly in high
yield. The substitutents on the diarenyl ketones clearly have no
obvious effect on the yield of products. Di(furan-2-ylethenyl)
O
OH-
H2O
Ph
Cl
O
HCN
CN-
K4[Fe(CN)6]
Ph
CN
H
2O
KCl, FeCl2
O
Ph
OH
O
R
R
1a–j
O-
H2O
CN
O
CN
R
R
R
R
A
2a–j
OH-
Scheme 2 The proposed mechanism for mono-1,4-hydrocyanation of diarenyl ketones with K4[Fe(CN)6]/PhCOCl.

46 JOURNAL OF CHEMICAL RESEARCH 2015
Mono-1,4-hydrocyanation of diarenyl ketones 1a–j; general
procedure
194.7. Anal. calcd for C18H13Cl2NO: C, 65.47; H, 3.97; N, 4.24; found:
C, 65.56; H, 3.96; N, 4.25%.
A mixture of potassium hexacyanoferrate(II) (0.4 mmol) and benzoyl
chloride (2 mmol) was heated at 160°C for 3 h. Then the reaction
system was cooled to room temperature and diarenyl ketone 1a–j
(1.5 mmol), potassium hydroxide (0.4 mmol) and acetonitrile (5 mL)
were added. The mixture was stirred at 60°C for the appropriate time
indicated in Table 3. After completion of the reaction (monitored
by TLC), the resulting mixture was filtered and the filtrate was
concentrated and subjected to column chromatography using
petroleum ether and ethyl acetate (V/V=10:1) as eluent to give pure
product.
(E)-2,6-Bis(4-chlorophenyl)-4-oxohex-5-enenitrile (2g): White
solid, m.p. 104−106 °C (EtOAc); IR (νmax): 1656 (C=O), 2235 (CN)
1
cm–1; H NMR: δ 3.00 (dd, J=6.0 16.0 Hz, 1H, CHCHaHCO), 3.21
(dd, J=6.0, 16.0 Hz, 1H, CHCHbHCO), 4.29 (dd, J=7.6, 8.0 Hz, 1H,
ArCHCH2), 6.50 (d, J=16.0 Hz, 1H, COCH=CHAr), 7.047.32 (m,
8H, ArH), 7.36 (d, J=16.0 Hz, 1H, COCH=CHAr); 13C NMR: δ 31.5,
44.2, 120.3, 124.8, 127.2, 127.8, 128.1, 128.5, 128.9, 133.6, 134.9, 135.3,
145.1, 194.3. Anal. calcd for C18H13Cl2NO: C, 65.47; H, 3.97; N, 4.24;
found: C, 65.39; H, 3.97; N, 4.23%.
(E)-2,6-Bis(4-bromophenyl)-4-oxohex-5-enenitrile
(2h):
Oil;
IR (νmax): 1653 (C=O), 2231 (CN) cm–1; 1H NMR: δ 2.98 (dd,
J=6.0 16.0 Hz, 1H, CHCHaHCO), 3.19 (dd, J=6.0, 16.0 Hz, 1H,
CHCHbHCO), 4.28 (dd, J=7.6, 8.0 Hz, 1H, ArCHCH2), 6.49 (d,
J=16.0 Hz, 1H, COCH=CHAr), 7.02−7.30 (m, 8H, ArH), 7.33 (d,
J=16.0 Hz, 1H, COCH=CHAr); 13C NMR: δ 31.3, 44.1, 120.1, 124.5,
127.0, 127.5, 127.9, 128.2, 128.6, 133.2, 134.5, 135.1, 145.0, 194.2.
Anal. calcd for C18H13Br2NO: C, 51.58; H, 3.13; N, 3.34; found: C,
51.66; H, 3.12; N, 3.35%.
(E)-4-Oxo-2,6-diphenylhex-5-enenitrile (2a): White solid; m.p.
120−122 °C (EtOAc); IR (νmax): 1680 (C=O), 2244 (CN) cm–1;
1H NMR: δ 3.14 (dd, J=6.4, 17.6 Hz, 1H, CHCHaHCO), 3.35 (dd,
J=7.6, 17.6 Hz, 1H, CHCHHbCO), 4.43 (dd, J=6.4, 7.6 Hz, 1H,
ArCHCH2), 6.64 (d, J=16.0 Hz, 1H, COCH=CHAr), 7.19−7.36
(m, 8H, ArH), 7.44−7.46 (m, 2H, ArH), 7.50 (d, J=16.0 Hz, 1H,
COCH=CHAr); 13C NMR: δ 31.7, 46.0, 120.5, 124.9, 127.4, 128.3,
128.4, 128.9, 129.2, 130.9, 133.8, 135.2, 144.2, 194.4. Anal. calcd
for C18H15NO: C, 82.73; H, 5.79; N, 5.36; found: C, 82.67; H, 5.81; N,
5.35%.
(E)-2,6-Bis(4-nitrophenyl)-4-oxohex-5-enenitrile (2i): Oil; IR (νmax):
1
1658 (C=O), 2251 (CN) cm–1; H NMR: δ 3.05 (dd, J=7.6, 16.0 Hz,
1H, CHCHaHCO), 3.36 (dd, J=7.6, 16.0 Hz, 1H, CHCHbHCO),
4.33 (dd, J=7.6, 8.0 Hz, 1H, ArCHCH2), 6.58 (d, J=16.0 Hz, 1H,
COCH=CHAr), 7.37−7.40 (m, 2H, ArH), 7.42 (d, J=16.0 Hz, 1H,
COCH=CHAr), 8.01−8.26 (m, 6H, ArH); 13C NMR: δ 31.8, 44.6, 120.7,
125.1, 127.6, 127.9, 128.3, 128.8, 128.9, 133.8, 135.0, 135.8, 150.7,
194.6. Anal. calcd for C18H13N3O5: C, 61.54; H, 3.73; N, 11.96; found: C,
61.60; H, 3.72; N, 11.92%.
(E)-4-Oxo-2,6-di(2-tolyl)hex-5-enenitrile (2b): White solid, m.p.
1
8688 °C (EtOAc); IR (νmax): 1658 (C=O), 2237 (CN) cm–1; H NMR:
δ 2.33 (s, 3H, CH3), 2.36 (s, 3H, CH3), 3.05 (dd, J=8.8, 17.6 Hz,
1H, CHCHaHCO), 3.34 (dd, J=8.8, 17.6 Hz, 1H, CHCHbHCO),
4.55 (dd, J=4.8, 9.6 Hz, 1H, ArCHCH2), 6.59 (d, J=16.0 Hz, 1H,
COCH=CHAr), 7.13−7.24 (m, 6H, ArH), 7.39−7.48 (m, 2H, ArH),
7.83 (d, J=16.0 Hz, 1H, COCH=CHAr); 13C NMR: δ 19.2, 19.8, 28.6,
44.9, 120.7, 125.6, 126.4, 126.5, 126.9, 127.4, 128.4, 130.7, 130.9, 131.2,
132.8, 133.3, 135.3, 138.3, 141.7, 194.5. Anal. calcd for C20H19NO: C,
83.01; H, 6.62; N, 4.84; found: C, 82.95; H, 6.61; N, 4.86%.
(E)-4-Oxo-2,6-di(4-tolyl)hex-5-enenitrile (2c): White solid, m.p.
140−142 °C (EtOAc); IR (νmax): 1680 (C=O), 2244 (CN) cm–1; 1H NMR:
δ 2.28 (s, 3H, CH3), 2.31 (s, 3H, CH3), 3.11 (dd, J=6.4, 17.2 Hz, 1H,
CHCHaHCO), 3.32 (dd, J=8.0, 17.6 Hz, 1H, CHCHbHCO), 4.39 (dd,
J=6.8, 7.6 Hz, ArCHCH2), 6.60 (d, J=16.4 Hz, 1H, COCH=CHAr),
7.19−7.36 (m, 8H, ArH), 7.47 (d, J=16.4, 1H, COCH=CHAr);
13C NMR: δ 21.1, 21.5, 31.4, 46.0, 120.8, 124.0, 127.3, 128.5, 129.7,
129.8, 131.1, 132.2, 138.2, 141.7, 144.3, 194.5. Anal. calcd for
C20H19NO: C, 83.01; H, 6.62; N, 4.84; found: C, 83.09; H, 6.64; N,
4.83%.
(E)-2,6-Bis(furan-2-yl)-4-oxohex-5-enenitrile (2j): Oil; IR (νmax):
1
1678 (C=O), 2247 (CN) cm–1; H NMR: δ 3.17 (dd, J=6.4, 17.6 Hz,
1H, CHCHaHCO), 3.36 (dd, J=7.6, 17.6 Hz, 1H, CHCHHbCO), 4.46
(dd, J=6.4, 7.6 Hz, 1H, ArCHCH2), 6.34−6.81 (m, 3H, FuH), 6.68
(d, J=16.0 Hz, 1H, COCH=CHFu), 7.45−7.62 (m, 2H, FuH), 7.53
(d, J=16.0 Hz, 1H, COCH=CHFu), 8.13 (d, J=6.8 Hz, 1H, FuH);
13C NMR: δ 31.9, 46.4, 106.3, 109.8, 110.2, 112.9, 113.2, 120.4, 129.5,
132.2, 141.5, 143.2, 154.6, 194.9. Anal. calcd for C14H11NO3: C, 69.70;
H, 4.60; N, 5.81; found: C, 69.64; H, 4.61; N, 5.83%.
The authors thank the National Natural Science Foundation of
China (21162024, 21462038) for the financial support of this
work.
(E)-2,6-Bis(4-methoxyphenyl)-4-oxohex-5-enenitrile (2d): Oil;
IR (νmax): 1683 (C=O), 2246 (CN) cm–1; 1H NMR: δ 3.16 (dd,
J=6.4, 17.2 Hz, 1H, CHCHaHCO), 3.37 (dd, J=8.0, 17.6 Hz, 1H,
CHCHbHCO), 3.76 (s, 3H, OCH3), 3.79 (s, 3H, OCH3), 4.45 (dd, J=6.8,
7.6 Hz, ArCHCH2), 6.66 (d, J=16.4 Hz, 1H, COCH=CHAr), 7.21−7.38
(m, 8H, ArH), 7.54 (d, J=16.4, 1H, COCH=CHAr); 13C NMR: δ 31.6,
46.3, 55.6, 55.9, 120.9, 124.2, 127.5, 128.7, 129.8, 129.9, 131.2, 132.4,
138.3, 141.9, 144.4, 194.6. Anal. calcd for C20H19NO3: C, 74.75; H, 5.96;
N, 4.36; found: C, 74.81; H, 5.95; N, 4.35%.
Received 10 November 2014; accepted 19 December 2014
Paper 1403011 doi: 10.3184/174751915X14197812950625
Published: 9 January 2015
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