Phosphonium salt-catalysed synthesis of nitriles from in situ activated oximes

Article abstract of DOI:10.1016/j.tet.2012.01.067

A metal-free catalytic method for the conversion of aromatic and aliphatic aldoximes to nitriles at room temperature using oxalyl chloride (1.2 equiv) in combination with 5 mol % of triphenylphosphine oxide is reported. Of the many potential pathways leading from oxime to nitrile a manifold involving chlorophosphonium salt-catalysed decomposition of oxime chlorooxalates formed in situ is shown to be operative.

Full text of DOI:10.1016/j.tet.2012.01.067

Tetrahedron 68 (2012) 2899e2905
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Phosphonium salt-catalysed synthesis of nitriles from in situ activated oximes
*
Ross M. Denton , Jie An, Petra Lindovska, William Lewis
School of Chemistry University of Nottingham, University Park, Nottingham NG7 2RD, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A metal-free catalytic method for the conversion of aromatic and aliphatic aldoximes to nitriles at room
temperature using oxalyl chloride (1.2 equiv) in combination with 5 mol % of triphenylphosphine oxide is
reported. Of the many potential pathways leading from oxime to nitrile a manifold involving chlor-
ophosphonium salt-catalysed decomposition of oxime chlorooxalates formed in situ is shown to be
operative.
Received 17 October 2011
Received in revised form 10 January 2012
Accepted 23 January 2012
Available online 30 January 2012
Ó 2012 Published by Elsevier Ltd.
Keywords:
Nitriles
Oximes
Catalysis
Phosphonium salts
Phosphine oxides
1. Introduction
reaction for the synthesis of alkyl halides from alcohols17 and
epoxides18 reported by us as well as by Rutjes and van Delft.19
The nitrile functional group is fundamental to organic chemis-
try1 and nitrile-containing molecules are also valuable end prod-
ucts in their own right.2 The laboratory-scale3 synthesis of aliphatic
nitriles is usually accomplished by nucleophilic substitution of alkyl
halides with inorganic cyanides,4 while the synthesis of aryl nitriles
can be achieved classically by direct cyanation of aryl halides using
copper(I) cyanide5 or more recently via palladium,6 copper7 or
nickel8 catalysis. An alternative method, applicable to the synthesis
of both aliphatic and aromatic substrates, involves dehydration of
primary amides or aldoximes. The latter can be achieved using
stoichiometric reagents or,9 more desirably, via catalysis.9u,10 Of the
documented stoichiometric methods the dehydration of aldoximes
using in situ generated halophosphonium salts is attractive as these
reactions take place at room temperature under mild conditions.
Specific examples include the PPh3/CCl4 system11 (Eq. 1) and the
use of PPh3/molecular halogen combinations.12 A disadvantage of
these methods is the production of phosphine oxides as stoichio-
metric by-products; however, recent work by others and us has
involved the development of catalytic versions of reactions that are
mediated by stoichiometric phosphorus(V) reagents.13 These in-
clude the phosphine oxide-catalysed aza-Wittig reactions de-
veloped by Marsden,14 the phosphine-catalysed Wittig reactions
developed by O’Brien,15 the phosphine-catalysed reduction of silyl
peroxides by Woerpel16 and the development of a catalytic Appel
At the outset of this study we reasoned, in analogy with our
previous work,17,18 that it might be possible to develop a catalytic
aldoxime dehydration process by combining the conversion of
aldoximes into nitriles (Eq. 1)6 with the oxalyl chloride-mediated
transformation of phosphine oxides into chlorophosphonium
salts (Eq. 2).20 In this way the phosphine oxide by-product derived
from the dehydration could be converted back into the active hal-
ophosphonium salt to achieve a process, that is, catalytic with
respect to the phosphorus component.
O
OH
P
Ph3P/CCl4
N
CHCl3
HCl
Ph
Ph
(1)
(2)
R
N
Ph
3
R
H
1
2
O
P
Cl
(COCl)2
C6H6
Cl
Ph
CO
CO2
P
Ph
Ph
Ph
Ph
3
Ph
4
2. Results and discussion
We began by confirming that chlorotriphenylphosphonium
chloride 4, formed from triphenylphosphine oxide and oxalyl
chloride, was effective for the stoichiometric dehydration of test
substrate benzaldehyde oxime 1a (Table 1, entry 1). The high yield
and short reaction time were encouraging and an initial trial of the
* Corresponding author. Tel.: þ44 115 951 4194; fax: þ44 115 951 3564; e-mail
address: ross.denton@nottingham.ac.uk (R.M. Denton).
0040-4020/$ e see front matter Ó 2012 Published by Elsevier Ltd.
doi:10.1016/j.tet.2012.01.067

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R.M. Denton et al. / Tetrahedron 68 (2012) 2899e2905
Table 1
Development of catalytic aldoxime dehydrationa
O
O
Cl
P
Cl
Ph
Ph
OH
H
N
Ph
3a 5 mol %
O
1.5 equiv.
Ph
N
Ph
CHCl3, 1 h, room temp.
1a
2a
Entry
Catalyst loading (mol %)
(COCl)2 (mol %)
Addition protocol
Time
Yield 2a %
1
2
3
4
5
6
100
5
5
5
2
100
100
100
120
120
120
1a added to (COCl)2 and 3 in one portion
1a and (COCl)2 added to 3 and (COCl)2 over 1 h
1a added to (COCl)2 and 3 over 0.5 h
1a added to (COCl)2 and 3 over 0.5 h
1a added to (COCl)2 and 3 over 0.5 h
1a added to (COCl)2 over 0.5 h
3 min
2 h
1 h
1 h
1 h
91b
73c
91b
99b
78b
0
0
1 h
a
1 mmol scale with respect to 1a.
b
c
Isolated yield.
Yield determined by 1H NMR using C2H2Cl4 as an internal standard.
catalytic reaction with 5 mol % triphenylphosphine oxide and
1 equiv of oxalyl chloride followed (entry 2). A 73% yield of product
was obtained with the remainder of the mass balance being the
mono oxime ester 5a derived from the reaction of the oxime with
oxalyl chloride.
which the chlorophosphonium salt reacts with the oxime to pro-
vide intermediate 9 that undergoes conversion to the nitrile
product. However, from the results presented in Table 1 it is ap-
parent that the highest yields are obtained when the oxime sub-
strate is added to a solution of 5 mol % triphenylphosphine oxide
and 1.2 equiv of oxalyl chloride. Under this addition protocol, in
which the oxime will be exposed to a large excess of oxalyl chloride,
it is very likely that activated oxime esters of type 5 (shown in cycle
2 of Scheme 2) are formed and, further, that they are implicated in
the formation of product through a second manifold (cycle 2,
In this reaction both the oxalyl chloride and the oxime were
added simultaneously (and separately) to a solution of 5 mol % of
chlorophosphonium salt 4a that had been preformed from tri-
phenylphosphine oxide and oxalyl chloride. This protocol was
adopted in an attempt to minimize the reaction between the oxime
and oxalyl chloride that would result in the formation of mono and
bis oxime esters 5a and 6a that we believed would be unreactive
by-products. We were therefore surprised to observe that, upon
addition of the oxime substrate to a solution of oxalyl chloride and
triphenylphosphine oxide, the nitrile product was obtained in an
improved 91% yield (entry 3). Increasing the amount of oxalyl
chloride to 1.2 equiv improved the yield still further (entry 4) while
decreasing the loading of triphenylphosphine oxide was detri-
mental (entry 5). Finally, no nitrile product was obtained in the
absence of triphenylphosphine oxide (entry 6). That an increased
yield was obtained using the addition protocol of entries 3e5
suggested a role for the oxime esters 5a and 6a in the formation of
the nitrile product; however, before investigating the reactivity of
5a and 6a in more detail we first conducted a study of substrate
scope using the optimal conditions from entry 4.
Table 2
Substrate scope for catalytic dehydration of aldoximesa
O
O
Cl
P
Cl
Ph
Ph
OH
H
N
Ph
3a catalyst
O
1.2 equiv.
R
N
R
CHCl3, 1 h, room temp.
1
2
CN
O
CN
Ph
Ph CN
CN
Ph
S
2d
2a
2b
2c
CN
CN
CN
Br
CN
O2N
Br
F3CO
HO
2e
2f
2g
2h
The results obtained show that the reaction is effective for
a range of aliphatic, aromatic and heteroaromatic substrates and
that good to excellent yields (73e99%) were obtained in all cases.
Substrates that have basic/nucleophilic heteroatoms, such as 1h
and 1i (entries 11 and 12) were also efficiently converted into ni-
triles; furthermore, nitro, ketone and trifluoromethoxy groups
were also tolerated.
We next applied the reaction to the synthesis of a naturally
occurring pyrrole from Angelas oroides.21 The synthesis began with
the double bromination of commercially available pyrrole 7. The
dibromide obtained after recrystallisation was then condensed
with hydroxylamine hydrochloride to afford the corresponding
oxime 1m. Dehydration of this substrate using the conditions
depicted in Table 2 afforded the natural product in 91% isolated
yield (Scheme 1).
CN
CN
7
CN
CN
N
2i
Me
Me
2j
2k
2l
Entry
Oxime
Solvent
Method
Product
Yield 2 %
1
2
3
4
5
6
7
8
1a
1a
1a
1b
1c
1d
1d
1e
1f
1g
1h
1i
1j
1k
1l
CHCl3
CHCl3
CHCl3
CHCl3
EtOAc
EtOAc
CHCl3
EtOAc
CHCl3
CHCl3
CHCl3
EtOAc
CHCl3
CHCl3
CHCl3
a
b
a
b
a
a
b
a
a
b
b
b
a
a
a
2a
2a
2a
2b
2c
2d
2d
2e
2f
2g
2h
2i
2j
2k
2l
99
76
94b
90
93
95
77
73
82
87
85
77
99
88
95
9
10
11
12
13
14
15
2.1. Mechanistic studies
Having examined the scope of the reaction we examined in
more detail the roles of the phosphine oxide and derived chloro-
phosphonium salt in the catalytic reaction. At the outset we en-
visaged a catalytic cycle of the type depicted as cycle 1 within
Scheme 2 (resulting from the combination of Eqns. 1 and 2) in
a
1 mmol scale with respect to 1; all yields isolated yields except for 2j (de-
termined by 1H NMR using C2H2Cl4 as an internal standard).
b
10 mmol scale with respect to 1. See Experimental section for details of methods
a and b.

R.M. Denton et al. / Tetrahedron 68 (2012) 2899e2905
2901
Fig. 1. Crystal structure of 6a.
With both mono and bis oxime esters synthesized and charac-
terized we investigated their reactivity with phosphine oxides and
phosphonium salts (Table 3). In the first instance the mixture of 5a
and 6a (74%:26%) obtained from the reaction depicted in entry 1
was treated with 5 mol % of triphenylphosphine oxide under the
conditions employed in the catalytic reactions (entry 1). Complete
conversion of 5a into the nitrile product was observed while the bis
ester present in the mixture remained unchanged. In an analogous
reaction with chlorophosphonium salt 4a (entry 2) we observed
complete conversion into benzonitrile.24 These results clearly in-
dicated that the pathway involving decomposition of activated
oximes of type 5 is feasible under the conditions of the catalytic
reactions.
Scheme 1. Reagents and conditions: (a) Br2, AcOH, CHCl3, 50 ꢀC, 16 h, 56%; (b)
NH2OH$HCl, NaOH, EtOH, 1.5 h, 87%; (c) (COCl)2 1.2 equiv, Ph3PO 5 mol %, CHCl3, rt, 1 h,
91%.
Scheme 2). In this pathway the activated oxime ester 5 may un-
dergo non-catalysed or catalysed decomposition to the nitrile as
shown.
To gain further information we monitored the catalytic de-
hydration of benzaldehyde oxime to benzonitrile via multinuclear
NMR. In this experiment the oxime was added to a solution of
oxalyl chloride (1.2 equiv) and triphenylphosphine oxide (5 mol %)
in one portion and 1H, 13C and 31P spectra were recorded approxi-
mately every 10 min. Inspection of the 13C NMR spectra recorded at
5 min (Fig. 2) revealed a mixture of mono ester 5a, bis ester 6a,
oxalyl chloride and benzonitrile; the major species being 5a. Sub-
sequent spectra showed a decay of the carbonyl resonances asso-
ciated with 5a and an increase of those associated with the
benzonitrile product while the peaks associated with the bis ester
6a remained constant throughout.
Scheme 2.
In order to explore the various possible pathways we prepared
and characterized the mono oxime ester22 5a by slow addition of the
relevantoximetooxalylchloride(Table 3). Inthisreactionthedesired
monoester5awasobtained with (26%)of thecorrespondingbis ester
6a. While the ester carbonyl carbon and azamethine 13C NMR reso-
nances associated with the mono ester were well resolved (CDCl3
100 MHz d 160.2 and 159.3 ppm, respectively) a single peak at 158.4
was observed for the bis ester indicating overlap of these two reso-
nances. Thiswasconfirmed by deliberate synthesisof thebisester6a,
X-ray crystallography23 (Fig. 1) and subsequent NMR analysis.
Table 3
Synthesis and reactivity of oxime estersa
Entry
Oxime
Catalyst (loading mol %)
Yield 2 %
1
2
3
4
5
1a
1a
1j
1j
1j
3a (5)
4a (5)
No cat.
3a (5)
4a (5)
74
71
32
97
97
a
Yield determined by 1H NMR using C2H2Cl4 as an internal standard.
Fig. 2. NMR study of catalytic reaction.

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R.M. Denton et al. / Tetrahedron 68 (2012) 2899e2905
Inspection of analogous 31P NMR spectra showed chloro-
at room temperature using inexpensive and readily available re-
agents. In contrast to our original design, which was based on de-
hydration under Appel conditions, the dehydration reaction takes
place via in situ activation of the oximewith oxalyl chloride followed
by chlorophosphonium salt-catalysed decomposition to product.
phosphonium salt 4a but no triphenylphosphine oxide. While the
conditions under, which the NMR data was acquired are not identical
to those employed in all of the catalytic reactions (method a involves
addition of the oxime to a solution of phosphine oxide and oxalyl
chloride over 30 min) the results of this study provide strong support
for catalysis occurring in cycle 2 of Scheme 2 and, specifically, for
chlorophosphonium salt 4a being responsible25 for conversion of the
activated oxime ester 5a into the product. This is consistent with the
results presented in Table 1, which showed that the highest yield of
benzonitrile was obtained under conditions that expose the both
oxime substrate and the phosphine oxide to an excess of oxalyl
chloride (entry 3, Table 1). Catalysis in cycle 1 may be occurring when
the oxime and oxalyl chloride are added simultaneously and sepa-
rately to a preformed solution of phosphonium salt 4a (entry 2, Table
1); however, it is clear that superior results are obtained from the
activated ester pathway. We then repeated this study with the ali-
phatic oxime 1j. In contrast to the above we noted, in this case, that
the mono oxime ester 5j undergoes slow conversion into the nitrile
product in the absence of catalyst (32% after 1 h, entry 3).26 A much-
improved 97% yield of nitrile product was obtained when the mono
ester was treated with 5 mol % of either triphenylphosphine oxide or
chlorotriphenylphosphonium chloride. These results indicate that
catalytic reactions with aliphatic substrates are also operating in
cycle 2 but that some of the product mayarise from direct conversion
of 5j to the product perhaps via a retro ene process in which oxalic
acid mono chloride is generated as a an initial by-product.
4. Experimental
4.1. General information
Glassware was dried in an oven overnight before use. Thin layer
chromatography was carried out on Polgram SIL G/UV254 silica-
aluminium plates and plates were visualised using ultra-violet light
(254 nm) and KMnO4 solution. For flash column chromatography
Fluorochem silica gel 60, 35e70 m was used. NMR data was collected
at either 270, or 400 MHz. Data was manipulated directly from the
spectrometer or via a networked PC with appropriate software. All
samples were analysed in CDCl3 unless otherwise stated. Reference
values for residual solvent were taken as
d
d
¼7.27 (CDCl3) for 1H NMR;
¼77.1 (CDCl3) for 13C NMR. Multiplicities for coupled signals we
designated using the following abbreviations: s¼singlet, d¼doublet,
t¼triplet, q¼quartet, quin¼quintet, sex¼sextet and br¼broad signal,
and coupling constants are given in hertz. Where appropriate, COSY,
HMQC and HMBC experiments were performed to aid assignment.
31P NMR was recorded with decoupling. Single crystal X-ray dif-
fraction was carried out by the X-ray crystallography department at
the University of Nottingham using a Bruker SMART 1000 CCD area
detector diffractometer. All solvents and reagents were obtained
from commercial sources and used as supplied.
Finally, we speculate on the role that the phosphine oxide and
chlorophosphonium salt play in the conversion of the activated
mono oxime ester 5 to nitrile (Scheme 3). In the case of the phos-
phine oxide activation of substrate 5 may occur via addition to the
acid chloride followed by elimination to afford 10. In the case of the
chlorophosphonium salt 4 one tentative possibility is a Lewis acid/
Lewis base interaction between the ester carbonyl oxygen and the
phosphonium salt25 resulting in the formation of a transient pen-
tacoordinate phosphorane, such as 11, which then decomposes to
product returning the phosphonium salt.
4.2. General procedure to determine the yield via 1H NMR
The crude reaction mixture was dissolved in CDCl3 and trans-
ferred to a volumetric flask (two washings of the original flask were
done after transfer) that was subsequently made up to the correct
volume with further CDCl3. To a 1 mL aliquot of this solution was
added
1,1,2,2-tetrachlorethane
(accurately
approximately
15e80 mg). The 1H NMR spectrum was recorded and the mass of
the product calculated according to the equation below:
ꢀ
ꢁ
massproduct
¼
areaproduct=areastandard
ꢀ
ꢁ
ꢁ
MWproduct=MWstandard ꢁ massstandard
ꢁ purity factorstandard ꢁ n ꢁ m
where n corrects for the amount of the crude reaction mixture used
and m corrects for the number of protons associated with the res-
onance used.
4.3. Synthesis of nitriles
4.3.1. Method a. To a solution of triphenylphosphine oxide (14 mg,
0.050 mmol) in either CHCl3, CDCl3 or EtOAc (2.0 mL) was added
oxalyl chloride (102 mL, 1.21 mmol) and the reaction mixture was
stirred for 5 min. The appropriate oxime (1.00 equiv) as solution in
either CHCl3, CDCl3 or EtOAc (1.0 mL) was then added over 0.5 h via
syringe pump at room temperature and the reaction mixture was
stirred for a further 0.5 h at room temperature after which the
solvent was removed in vacuo. Purification by flash chromatogra-
phy (silica, 10e100% Et2O/pet. ether) gave the pure nitriles.
Scheme 3.
3. Conclusions
4.3.2. Method b. To a solution of triphenylphosphine oxide (14 mg,
0.050 mmol) in either CHCl3, CDCl3 or EtOAc (3.0 mL) was added
In summary we have developed a metal-free catalytic method for
the dehydration of aromatic and aliphatic aldoximes that takes place
oxalyl chloride (102
stirred for 5 min. The appropriate oxime (1.00 equiv) was then
mL, 1.21 mmol) and the reaction mixture was

R.M. Denton et al. / Tetrahedron 68 (2012) 2899e2905
2903
added in one portion and the reaction mixture was stirred for 1.0 h
at room temperature after which the solvent was removed in vacuo.
Purification by flash chromatography (silica, 10e100% Et2O/pet.
ether) gave the pure nitriles.
Bromobenzaldoxime (200 mg, 1.00 mmol), oxalyl chloride
(102 L, 1.21 mmol), triphenylphosphine oxide (14 mg,
m
0.050 mmol) and EtOAc (3.0 mL). Purification by flash column
chromatography (silica, 50% Et2O/pet. ether) afforded 2e as a white
solid (133 mg, 73%). Mp 54 ꢀC; 1H NMR (400 MHz, CDCl3)
4.3.3. Benzonitrile 2a.27 The following reagents were combined in
the amounts indicated according to method a. (E)-benzaldehyde
d
7.73e7.65 (m, 2H, ArH), 7.51e7.41 (m, 2H, ArH); 13C NMR
(400 MHz, CDCl3)
d 134.3, 134.0, 133.2, 127.7, 125.3, 117.2, 115.8.
oxime (121 mg, 0.999 mmol), oxalyl chloride (102 mL, 1.21 mmol),
triphenylphosphine oxide (14 mg, 0.050 mmol) and CHCl3 (3.0 mL).
Purification by flash column chromatography (silica, 10% Et2O/pet.
ether) afforded 2a as a colourless oil (102 mg, 99%). Rf (17% Et2O/pet.
4.3.10. 4-(Trifluoromethoxy)benzonitrile 2f.32 The following re-
agents were combined in the amounts indicated according to
method a. 4-(Trifluoromethoxy)benzaldehyde oxime (103 mg,
ether) 0.57; 1H NMR (400 MHz, CDCl3)
d
7.69e7.58 (m, 3H, ArH),
0.502 mmol), oxalyl chloride (51 mL, 0.60 mmol), triphenylphos-
5.52e7.44 (m, 2H, ArH); 13C NMR (100 MHz, CDCl3)
d
132.7, 132.1,
phine oxide (7.0 mg, 0.025 mmol) and CHCl3 (1.5 mL). Purification by
flash column chromatography (silica, 17% Et2O/pet. ether) afforded
2f as a colourless oil (76 mg, 82%). 1H NMR (400 MHz, CDCl3)
129.1, 118.8, 112.3.
4.3.4. Benzonitrile 2a27 large-scale reaction. To a solution of tri-
phenylphosphineoxide(139mg, 0.499mmol)inCHCl3 (20.0mL)was
added oxalyl chloride (1.02 mL, 12.1 mmol) and the reaction mixture
was stirred for 5 min (E)-benzaldehyde oxime (1.21 g, 10.0 mmol) as
solution in CHCl3 (10.0 mL) was then added simultaneously over
45minviapressure equalizing dropping funnel atroomtemperature.
The reaction mixture was stirred for another 0.5 h at room temper-
ature. The solvent was then removed in vacuo. Purification by flash
column chromatography (silica, 10% Et2O/pet. ether) afforded 2a as
a colourless oil (965 mg, 94%). Rf (17% Et2O/pet. ether) 0.57.
d
7.76e7.70(m, 2H, ArH), 7.35e7.29 (m, 2H, ArH); 13C NMR (100 MHz,
CDCl3)
d
152.2, 134.2, 121.2, 120.2 (q, J¼258 Hz), 117.7, 110.9.
4.3.11. 4-Nitrobenzonitrile 2g.33 The following reagents were com-
bined in the amounts indicated according to method b. 4-Nitro-
benzaldehyde oxime (166 mg, 0.999 mmol), oxalyl chloride (102 mL,
1.21 mmol), triphenylphosphine oxide (14 mg, 0.050 mmol) and
CHCl3 (3.0 mL). Purification by flash column chromatography (silica,
100%Et2O)afforded2gasawhitesolid(129mg,87%). Mp146e147 ꢀC;
1HNMR(400MHz,CDCl3)
ArH); 13C NMR (100 MHz, CDCl3)
d
8.40e8.34(m, 2H, ArH), 7.93e7.87 (m, 2H,
150.0, 133.5, 124.3, 118.3, 116.8.
d
4.3.5. Cinnamonitrile 2b.28 The following reagents were combined
in the amounts indicated according to method b. (E/Z) cinnamy-
laldehyde oxime (147 mg, 0.999 mmol), oxalyl chloride (102 mL,
1.21 mmol), triphenylphosphine oxide (14 mg, 0.050 mmol) and
CHCl3 (3.0 mL). Purification by flash column chromatography (sil-
ica,100% Et2O) afforded 2b as a colourless oil (116 mg, 90%). 1H NMR
4.3.12. 3-Bromo-4-hydroxybenzonitrile 2h.34 The following re-
agents were combined in the amounts indicated according to
method b. 3-Bromo-4-hydroxybenzaldehyde oxime (216 mg,
1.00 mmol), oxalyl chloride (102
mL, 1.21 mmol), triphenylphos-
phine oxide (14 mg, 0.050 mmol) and CHCl3 (3.0 mL). Purification
by flash column chromatography (silica, 83% Et2O/pet. ether)
afforded 2h as a white solid (168 mg, 85%). Mp 156 ꢀC; 1H NMR
(400 MHz, CDCl3)
d
7.49e7.36 (m, 6H, 5ꢁ ArH and ArCH), 5.89 (d,
J¼16.7 Hz, 1H, CHCN); 13C NMR (100 MHz, CDCl3)
d 150.6, 133.5,
131.2, 129.1, 127.4, 118.2, 96.4.
(400 MHz, CDCl3)
d
7.81 (d, J¼2.0 Hz, 1H, ArH), 7.55 (dd, J¼8.4 Hz
and 2.0 Hz, 1H, ArH), 7.1 (d, J¼8.4 Hz, 1H, ArH), 6.07 (s, 1H, OH); 13C
4.3.6. Benzoyl cyanide 2c.29 The following reagents were
combined in the amounts indicated according to method a. 2-
Isonitrosoacetophenone (149 mg, 0.999 mmol), oxalyl chloride
NMR (100 MHz, CDCl3) d 156.3, 136.1, 133.5, 117.6, 117.0, 110.7, 105.6.
4.3.13. Nicotinonitrile 2i.30 To a solution of triphenylphosphine
(102
mL, 1.21 mmol), triphenylphosphine oxide (14 mg,
oxide (14 mg, 0.050 mmol) in EtOAc (3.0 mL) was added oxalyl
0.050 mmol) and EtOAc (3.0 mL). Purification by flash column
chromatography (silica, 100% Et2O) afforded 2c as a yellow oil
chloride (102 mL, 1.21 mmol) and the reaction mixture was stirred
for 5 min. 3-Pyridinealdoxime (122 mg, 0.999 mmol) was then
added in a single portion. The reaction mixture was stirred for 1.0 h
at room temperature before being quenched with water (5.0 mL)
and extracted with Et2O (5.0 mL). The aqueous phase was adjusted
to pH¼9 using NaOH (3 drops of a 50% aqueous solution) and
extracted with Et2O (2ꢁ5 mL). The combined organic phases were
dried over MgSO4 and the solvent was removed in vacuo. Purifi-
cation by flash chromatography (silica, 67% Et2O/pet. ether) affor-
ded 2i as a white solid (80 mg, 77%). Mp 50 ꢀC; 1H NMR (400 MHz,
(122 mg, 93%). 1H NMR (270 MHz, CDCl3)
d
8.18e8.13 (m, 2H, ArH),
7.83e7.77 (m, 1H, ArH), 7.65e7.59 (m, 2H, ArH); 13C NMR (68 MHz,
CDCl3) 167.9, 136.9, 133.3, 130.5, 129.5, 112.7.
d
4.3.7. Thiophene-2-carbonitrile 2d.30 The following reagents were
combined in the amounts indicated according to method b. Thio-
phene-2-carboxaldoxime (127 mg, 0.999 mmol), oxalyl chloride
(102
mL, 1.21 mmol), triphenylphosphine oxide (14 mg,
0.050 mmol) and CHCl3 (3.0 mL). Purification by flash column
chromatography (silica, 20% Et2O/pet. ether) afforded 2d as a col-
CDCl3)
(m, 1H, ArH), 7.47e7.41 (m, 1H, ArH); 13C NMR (100 MHz, CDCl3)
153.1, 152.6, 139.3, 123.7, 116.6, 110.2.
d 8.91e8.87 (m, 1H, ArH), 8.84e8.80 (m, 1H, ArH), 8.00e7.94
ourless oil (84 mg, 77%). 1H NMR (400 MHz, CDCl3)
d
7.66e7.60 (m,
2H, SCHCHCH); 7.16e7.11 (m, 1H, SCH); 13C NMR (100 MHz, CDCl3)
137.5, 132.6, 127.7, 114.3, 109.9.
d
d
4.3.14. Butyronitrile 2j.35 The following reagents were combined in
the amounts indicated according to method a. Butyraldoxime
4.3.8. Thiophene-2-carbonitrile 2d.28 The following reagents were
combined in the amounts indicated according to method a. Thio-
phene-2-carboxaldoxime (127 mg, 0.999 mmol), oxalyl chloride
(87 mg, 1.0 mmol), oxalyl chloride (102
phosphine oxide (14 mg, 0.050 mmol) and CDCl3 (3.0 mL) gave 2j
(68 mg, 99%) by1HNMR.1HNMR (400 MHz, CDCl3)
2.33 (t, J¼7.1 Hz,
2H, CH2CN),1.75e1.65 (m, 2H, CH2CH2CN),1.08 (t, J¼7.4 Hz, 3H, CH3);
13C NMR (100 MHz, CDCl3)
119.7, 19.2, 19.1, 13.4.
mL, 1.21 mmol), triphenyl-
d
(102
mL, 1.21 mmol), triphenylphosphine oxide (14 mg,
0.050 mmol) and EtOAc (3.0 mL). Purification by flash column
chromatography (silica, 20% Et2O/pet. ether) afforded 2d as a col-
ourless oil (104 mg, 95%).
d
4.3.15. Cyclohexanecarbonitrile 2k.31 The following reagents were
combined in the amounts indicated according to method a.
Cyclohexanecarboxaldehyde oxime (127 mg, 0.999 mmol), oxalyl
4.3.9. 2-Bromobenzonitrile 2e.31 The following reagents were
combined in the amounts indicated according to method a. 2-
chloride (102 mL, 1.21 mmol), triphenylphosphine oxide (14 mg,

2904
R.M. Denton et al. / Tetrahedron 68 (2012) 2899e2905
0.050 mmol) and CDCl3 (3 mL). Purification by flash column chro-
matography (silica, 33% Et2O/pet. ether) afforded 2k as a colourless
(121 mg, 0.999 mmol) as solution in CHCl3 (1.0 mL) over 0.5 h via
syringe pump at room temperature and the reaction mixture was
stirred for 0.5 h at room temperature. Gave (E)-2-(benzylidenea-
minooxy)-2-oxoacetyl chloride 5a (86%), bis ester 6a (14%), ben-
zonitrile 2a (0%) by 1H NMR. (E)-2-(Benzylideneaminooxy)-2-
oil (96 mg, 88%). 1H NMR (400 MHz, CDCl3)
d 2.67e2.58 (m, 1H,
CHCN), 1.91e1.36 (m, 10H, 5ꢁ CH2); 13C NMR (400 MHz, CDCl3)
d
122.7, 29.5, 28.0, 25.3, 24.1.
oxoacetyl chloride 5a.39 1H NMR (400 MHz, CDCl3)
d
8.53 (s, 1H,
ArCH), 7.77e7.72 (m, 2H, ArH), 7.58e7.52 (m, 1H, ArH), 7.50e7.45
(m, 2H, ArH); 13C NMR (100 MHz, CDCl3)
.160.2, 159.3, 154.1, 132.9,
129.2, 128.9, 128.6; bis ester 6a40 1H NMR (400 MHz, CDCl3)
8.56
4.3.16. Decanenitrile 2l.36 The following reagents were combined
in the amounts and method indicated according to method a.
d
Decanal aldoxime3 (171 mg, 0.998 mmol), oxalyl chloride (102
mL,
d
1.21 mmol), triphenylphosphine oxide (14 mg, 0.050 mmol) and
CHCl3 (3.0 mL). Purification by flash column chromatography (sil-
ica, 50% Et2O/pet. ether) afforded 2l as a colourless oil (146 mg,
(s, 2H, 2ꢁ ArCH), 7.78e7.73 (m, 4H, ArH), 7.57e7.51 (m, 2H, ArH),
7.50e7.43 (m, 4H, ArH); 13C NMR (100 MHz, CDCl3)
d 158.4 (2C),
132.6, 129.2, 129.1, 128.8.
95%). 1H NMR (400 MHz, CDCl3)
d
2.33 (t, J¼7.2 Hz, 2H, CH2CN),
1.70e1.60 (m, 2H, CH2CH2CN), 1.49e1.39 (m, 2H, CH2CH2CH2CN),
1.36e1.21 (m, 10H, CH3CH2CH2CH2CH2CH2), 0.88 (t, J¼7.1 Hz, 3H,
4.3.20.2. Table 3 entry 1. To a solution of triphenylphosphine
oxide (14 mg, 0.050 mmol) in CHCl3 (2.0 mL) was added (E)-2-
(benzylideneaminooxy)-2-oxoacetyl chloride 5a (212 mg,
1.00 mmol) as solution in CHCl3 (1.0 mL) over 0.5 h via syringe
pump at room temperature and the reaction mixture was stirred
for 0.5 h at room temperature. The solvent was removed in
vacuo. Purification by flash column chromatography (silica, 10%
Et2O/pet. ether) afforded benzonitrile 2a as a colourless oil
(76 mg, 74%).
CH3); 13C NMR (100 MHz, CDCl3)
d 119.9, 31.8, 29.3, 29.2, 28.8, 28.7,
25.4, 22.7, 17.1, 14.1.
4.3.17. 4,5-Dibromo-1H-pyrrole-2-carbaldehyde
8n.37 Pyrrole-2-
carboxaldehyde (951 mg, 10.0 mmol), was dissolved in chloro-
form (30 mL) and glacial acetic acid (4.5 mL). Bromine (1.02 mL,
19.9 mmol) was slowly added at room temperature to the resulting
cloudy solution and, once addition was complete, the reaction
mixture was heated at 50 ꢀC for 16 h. After cooling to room tem-
perature the reaction mixture was quenched with NaHCO3 (150 mL
4.3.20.3. Table 3 entry 2. To a solution of triphenylphosphine
oxide (14 mg, 0.050 mmol) and oxalyl chloride (17 mL, 0.20 mmol)
of
a
saturated aqueous solution) and extracted with Et2O
in CHCl3 (2.0 mL) was added (E)-2-(benzylideneaminooxy)-2-
oxoacetyl chloride 5a (212 mg, 1.00 mmol) as a solution in CHCl3
(1.0 mL) over 0.5 h via syringe pump at room temperature and the
reaction mixture was stirred for 0.5 h at room temperature. The
solvent was removed in vacuo. Purification by flash column chro-
matography (silica, 10% Et2O/pet. ether) afforded benzonitrile 2a as
a colourless oil (73 mg, 71%).
(50 mLꢁ4). The combined organic layer was dried over MgSO4,
filtered and the solvent was removed in vacuo. The crude product
crystallized (EtOAc/pet. ether) affording 8n as pale pink powder
(1.42 g, 56%). Mp 153e154 ꢀC; 1H NMR (400 MHz, CDCl3)
d 10.25 (br,
1H, NH), 9.36 (s, 1H, CHO), 6.89 (d, J¼2.6 Hz, 1H, NHC]CH); 13C
NMR (100 MHz, CDCl3)
d 177.7, 133.2, 123.0, 112.9, 101.9.
4.3.18. (Z)/(E)-4,5-Dibromo-1H-pyrrole-2-carbaldehyde
oxime
4.3.20.4. Table 3 entry 3. To a solution of oxalyl chloride (102 mL,
1m.38 A suspension of 4,5-dibromo-1H-pyrrole-2-carbaldehyde
(1.23 g, 4.86 mmol), NH2OH$HCl (677 mg, 9.74 mmol) and NaOH
(390 mg, 9.75 mmol) in EtOH (50 mL) was heated at 80 ꢀC for 1.5 h.
After cooling to room temperature H2O (50 mL) was added and the
reaction mixture was extracted with EtOAc (3ꢁ50 mL). The com-
bined organic layers were washed with brine (2ꢁ50 mL), dried over
MgSO4, filtered and the solvent was removed in vacuo. Purification
by flash column chromatography (silica, 33% EtOAc/pet. ether)
afforded 1m as a pale yellow powder (1.13 g, 87%). (Z)-isomer 1H
1.21 mmol) in CHCl3 (2.0 mL) was added butyraldoxime (87 mg,
1.0 mmol) as solution in CHCl3 (1.0 mL) over 0.5 h via syringe pump
at room temperature and the reaction mixture was stirred for 0.5 h
at room temperature. Gave butyronitrile 2j (32%) by 1H NMR.
4.3.20.5. Table 3 entry 4. To a solution of oxalyl chloride (102 mL,
1.21 mmol) in CHCl3 (2.0 mL) was added butyraldoxime (87 mg,
1.0 mmol) as a solution in CHCl3 (1.0 mL) over 0.5 h via syringe
pump at room temperature. Triphenylphosphine oxide 3a (14 mg,
0.050 mmol) was then added and the reaction mixture was stirred
for 1 h. Gave butyronitrile 2j (97%) by 1H NMR.
NMR (400 MHz, CD3CN)
d 10.55 (br, 1H), 9.35 (br, 1H), 7.81 (s, 1H,
CH]NOH), 6.61 (d, J¼2.3 Hz, 1H, NHC]CH); 13C NMR (100 MHz,
CD3CN)
d
141.0, 128.4, 117.5, 104.7, 100.4; (E)-isomer 1H NMR
(400 MHz, CD3CN)
d
10.12 (br, 1H), 8.75 (s, 1H), 7.14 (s, 1H, CH]
4.3.20.6. Table 3 entry 5. To a solution of oxalyl chloride (102 mL,
NOH), 6.40 (d, J¼2.9 Hz, 1H, NHC]CH); 13C NMR (100 MHz, CD3CN)
1.21 mmol) in CHCl3 (2.0 mL) was added butyraldoxime (87 mg,
1.0 mmol) as solution in CHCl3 (1.0 mL) over 0.5 h via syringe pump
at room temperature. Triphenylphosphine oxide 3a (14 mg,
d
137.3, 127.1, 115.0, 104.4, 100.0.
4.3.19. 2-Cyano-4,5-dibromopyrrole 2m.21 To a solution of triphe-
0.050 mmol) and oxalyl chloride (4 mL, 0.05 mmol) were then
nylphosphine oxide (3.5 mg, 0.13 mmol) in EtOAc (1.0 mL) was
added and the reaction mixture was stirred for 1 h. Gave butyr-
added oxalyl chloride (51
was stirred for
m
L, 0.60 mmol) and the reaction mixture
onitrile 2j (97%) by 1H NMR.
5
min (Z)/(E)-4,5-dibromo-1H-pyrrole-2-
carbaldehyde oxime (134 mg, 0.500) as solution in EtOAc
(0.5 mL) was then added over 0.5 h via syringe pump and the re-
action mixture was stirred for 0.5 h at room temperature after
which the solvent was removed in vacuo. Purification by flash
chromatography (silica, 17% EtOAc/pet. ether) gave 2m as a white
Acknowledgements
This work was supported by the University of Nottingham New
Researcher’s Fund NF5012 and The Nuffield Foundation Bursary to
P.L. We are grateful to Dr. Deborah Kays (University of Nottingham)
for the loan of a Young’s NMR tube.
solid (114 mg, 91%). Mp 176 ꢀC; 1H NMR (400 MHz, CDCl3)
d 9.26 (br,
1H, NH), 6.86 (d, J¼2.9 Hz, 1H, NHC]CH); 13C NMR (100 MHz,
CDCl3)
d 122.8, 112.3, 107.4, 103.2, 100.7.
Supplementary data
4.3.20. Control reactions.
4.3.20.1. Table 1 entry 7. To a solution of oxalyl chloride (102 mL,
1.21 mmol) in CHCl3 (2.0 mL) was added (E)-benzaldehyde oxime
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2012.01.067.

R.M. Denton et al. / Tetrahedron 68 (2012) 2899e2905
2905
50, 1717e1719; (k) See Ref 36. For catalytic dehydration using propylphos-
phonic anhydride, see; (l) See Ref. 9v. For an interesting approach to catalysis of
the Beckmann rearrangement, see; (m) Vanos, C. M.; Lambert, T. H. Chem. Sci.
2010, 1, 705e708.
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