Ring-Opening Reaction of Imidazo[1,2-a]pyridines Using (Diacetoxyiodo)benzene and NaN3: The Synthesis of α-Iminonitriles

Article abstract of DOI:10.1002/ejoc.201601480

The reaction of imidazo[1,2-a]pyridine with NaN₃ in the presence of (diacetoxyiodo)benzene as an oxidant resulted in the unusual formation of α-iminonitriles in good yields under mild conditions. This method provides access to α-iminonitriles under cyanide-free and metal-free reaction conditions.

Full text of DOI:10.1002/ejoc.201601480

A Journal of
Accepted Article
Title: Ring opening Reaction of Imidazo[1,2-a]pyridines Using
(Diacetoxyiodo)benzene and NaN3: New Entry to the Synthesis
of ꢀ-Iminonitriles
Authors: Nandkishor N. Karade, Amit K. Kalbandhe, and Ashish C.
Kavale
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201601480
Link to VoR: http://dx.doi.org/10.1002/ejoc.201601480
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10.1002/ejoc.201601480
European Journal of Organic Chemistry
COMMUNICATION
Ring opening Reaction of Imidazo[1,2-a]pyridines Using
(Diacetoxyiodo)benzene and NaN3: New Entry to the Synthesis of
-Iminonitriles
Amit H. Kalbandhe, Ashish C. Kavale, Nandkishor N. Karade*
Dedicated to the memories of our mentor, motivator and a great teacher late Prof. Ram B. Kharat.
with amberlite IRA 400 [CN-] (Scheme 1).[12] Recently, the
Abstract: The reaction of imidazo[1,2,a]pyridine with NaN3 in
presence of (diacetoxyiodo)benzene (DIB) as oxidant resulted in an
unusual formation of -iminonitriles in good yields under mild
conditions. This methodology is a new tool to synthesize -
iminonitriles under cyanide- as well as metal-free reaction conditions.
oxidative Strecker three-component reaction of aldehyde,
amines, and Me3SiCN using the combination of oxone or IBX
with Bu4NBr has been reported for the synthesis of -
iminonitriles.[13] The modern method of -iminonitriles has been
accomplished from aryl halide via palladium-catalyzed double
isocyanide insertion and elimination reaction.[14] This literature
survey indicates that the methods of -iminonitrile synthesis are
not straightforward and generally involves use of highly toxic
NaCN, CuCN, BrCN, Hg(CN)2, Me3SiCN, and Bu3SnCN.
Therefore, the development of an efficient and cyanide-free
expedient method for the synthesis of -iminonitriles is
necessary.
Keywords: hypervalent iodine
imidazo[1,2,a]pyridine • nitrene
• -iminonitriles • azidation
Introduction
The -iminonitriles are versatile intermediates in organic
synthesis due to its bifunctional nature.[1] It has close structural
resemblance with Strecker -aminonitriles and can be viewed as
masked form of -amino acids.[2] The presence of an sp2-
prochiral center (a C=N bond) in -iminonitriles would serve a
latent possibility to furnish optically active -amino acid
derivatives. -Iminonitriles have been also used as precursor for
the synthesis of other useful building blocks such as -ketoacids,
amides, amidines, N-alkylketene-imines and cyanoenamides.[3]
It has been employed in the nuclear cyanation of arenes[4] as
well as in the synthesis of nitrogen containing heterocycles
through the cycloaddition reaction of nitrile group.[5] Owing to its
enormous synthetic utility, the various methods for the synthesis
of -iminonitriles are developed which include (a) nucleophilic
addition of NaCN to the Schiff base of aromatic aldehyde, with
the subsequent oxidation with air[6] (b) the manganese dioxide
oxidation of -aminonitriles[7] (c) the reaction of cyanogen
bromide with Schiff bases[8] (d) the reaction of nitrosoarene with
phenylacetonitriles[9] (e) the Beckmann rearrangement of oxime
sulfonates using Me3SiCN-Et2AlCl[10] (f) the reaction of imidoyl
chloride with aqueous KCN[11] and (g) the reaction of nitrones
On the other hand, imidazo[1,2-a]pyridines represent
an important class of fused heterocyclic motif exhibiting a
plethora of biological activities such as antitumor, antiprotozoal,
antiviral, antimicrobial, antiherpes, anticancer, anticonvulsant
and others.[15] Many of the clinically used drugs such as alpidem,
necopidem,
saripidem
(anxiolytic),
mosapramine
(antipsychotics), miroprofen (analgesics), olprinone (cardiac
stimulant), and zolimidine (gastroprotective) are found to contain
imidazo[1,2-a]pyridine as a key unit in their pharmacophores. [16]
Due to this remarkable pharmacological profile, there is a
growing interest in the synthesis and structural decoration of
imidazo[1,2-a]pyridines to obtain new scaffolds with modified
biological activities. The functionalization at C3 position is one of
the most common strategy to form structurally diverse
imidazo[1,2-a]pyridines. The fluorination,[17] thiocynation,[18]
sulfenylation,[19]
selenylation,[20]
nitrosylation,[21]
phosphonation,[22] arylation,[23] alkenylation,[24] carbonylation,[25]
formylation[26] and trifluoromethylation[27] are the recently
developed methodologies for the functionalization at C3 position
of imidazo[1,2-a]pyridines. The introduction of such a variety of
functional groups at C3 position of imidazo[1,2-a]pyridines have
been accomplished by employing oxidants such as CuI,
Cu(OAc)2, Mn(OAc)3, K2S2O8, molecular iodine and N-
chlorosuccinimide. It is important to note that the direct azidation
at C3 position of imidazo[1,2-a]pyridines has not been explored
so far. Therefore, we decided to examine the azidation of
[a]
A. H. Kalbandhe, A. W. Kawale, N. N. Karade*
Department of Chemistry,
Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur
Nagpur India-440033
E-mail: nnkarade@gmail.com
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejoc.201601480
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COMMUNICATION
Scheme 1. Various methods of preparation of -iminonitriles
imidazo[1,2-a]pyridines with subsequent click chemistry to
synthesize “drug-like” molecules.[28] The direct introduction of
azide using NaN3 at C3 position of imidazo[1,2-a]pyridines
requires screening of appropriate oxidizing agents. Hypervalent
iodine reagents are preferred as “metal-free” oxidizing agents in
modern organic chemistry due to mild conditions, ready
availability and benign environmental character.[29] The
hypervalent iodine(III) reagents such as (diacetoxyiodo)benzene
Results and Discussion
The reaction of NaN3 with 2-phenylimidazo[1,2-a]pyridine 1a
using DIB as an oxidant was selected for the model experiment.
The optimization reactions were carried out using different
amounts of DIB in various solvents (Table 1). Water was also
used in combination with other solvents to improve the solubility
of NaN3 in various experiments. The initial attempts to employ
(DIB),
[bis(trifluoroacetoxy)iodo]benzene
(BTI)
and
Table 1. Screening of reaction conditions
[(hydroxy)tosyloxyiodo]benzene (HTIB) in combination with
NaN3 and TMSN3 are known for the nuclear azidation of
activated arenes and other related transformations.[30] Therefore,
we envisaged that the azidation of imidazo[1,2-a]pyridines could
be carried out using NaN3 in combination with hypervalent
iodine(III) reagents as oxidants. However, it is observed that the
five-membered skeleton of imidazo[1,2-a]pyridines undergo ring
opening reaction with PhI(OAc)2/NaN3 to form -iminonitriles in
good yields. This transformation of imidazo[1,2-a]pyridines
involving ring opening of imidazole type skeleton is a rare and
unintended result leading to the formation of valuable synthetic
intermediate -iminonitriles.
Entry
Oxidants and conditionsa
PhI(OAc)2 (1.1 equiv)
PhI(OAc)2 (1.1 equiv)
PhI(OAc)2 (1.1 equiv)
PhI(OAc)2 (1.5 equiv)
PhI(OAc)2 (1.5 equiv)
PhI(OAc)2 (2.0 equiv)
PhI(OAc)2 (1.1 equiv)
PhI(OAc)2 (1.5 equiv)
PhI(OAc)2 (1.1 equiv)
PhI (0.1 equiv),
Solvent
Time (h)
24
Yield (%)
20
1
2
3
4
5
6
7
8
9
10
CH2Cl2
CH2Cl2 /H2O
CH3CN
10
34
24
42
CH3CN
24
44
CH3CN /H2O
CH3CN/H2O
CH3OH
10
60
3
84
24
12
CH3OH
24
19
THF
24
00
CH3CN
24
00
MCPBA (1.5 equiv)
PhI (0.5 equiv),
11
CH3CN
24
00
MCPBA (1.5 equiv)
aReaction conditions: 2-Phenylimidazo[1,2-a]pyridine 1a (1 mmol), NaN3 (3
mmol), oxidants and solvent at room temperature stirring for the specified time.
All listed yields are isolated ones.
Scheme 2.
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COMMUNICATION
CH2Cl2 as solvent resulted in poor yield of 2a at room
temperature (entry 1). When CH2Cl2/water combination (9:1)
was used as solvent, the yield of 2a was slightly improved (entry
2). The use of CH3CN as solvent resulted in increased yield 2a
(entry 3). To our delight, the product yields were improved
remarkably by increasing the quantity of DIB as well as using
CH3CN/water as solvent system for the reaction (entries 4-5).
The maximum yield of 2a was achieved using 2.0 equivalents of
DIB in CH3CN/water (9:1) solvent system (entry 6). Other
solvents such as MeOH and THF were found to be inferior for
the formation of 2a in satisfactory yields (entries 7-9). The in situ
generated hypervalent iodine(III) reagent from the reaction of
catalytic iodobenzene with terminal oxidant such as MCPBA was
also carried out for the reaction between NaN3 and 1a (entry 10-
11). However in these cases, we couldn’t get corresponding 2a.
Thus, the optimal reaction condition was reached by using 1a (1
equiv), NaN3 (3 equiv) and DIB (2 equiv) in CH3CN/H2O (9:1) as
solvent for getting the maximum yield of -iminonitrile 2a (entry
6).
hindrance was also not observed as imidazo[1,2,a]pyridines
bearing methyl groups at different positions reacted efficiently
with DIB/NaN3 to form the respective -iminonitriles in good
yields (Table 2, entries 2b, 2c, 2g, 2h, 2k, 2n, 2o, 2p and 2q).
The imidazo[1,2,a]pyridines with –OMe, –Cl, –Br and –CF3
substituents also resulted in good yields of -iminonitriles. This
methodology is also compatible for the synthesis of -
iminonitriles bearing pyrimidine and naphthalene moiety (Table 2,
entries 2t and 2u) in 82% and 81% yields respectively. All the
products of the reactions were characterized by IR, NMR (1H
and 13C), and HRMS analysis. The IR spectra of -iminonitriles
displayed strong bands at 1500 and 1540 cm-1 and a weak
absorption at 2220 cm-1 which are indicative of imino (C=N) and
a nitrile groups respectively. The 1H NMR spectra of the
products 2a-t indicates disappearance of C3 proton comapred to
the precursor imidazo[1,2,a]pyridines. A detail examination of
13C NMR of -imino nitriles showed characteristic signal around
δ 149 and δ 111 due to imino and nitrile carbon respectively.
A
plausible mechanism for the formation of -
With these results in hand, we sought to examine the
scope and generality of the method by employing a wide range
of imidazo[1,2,a]pyridines under the optimized reaction
conditions. As shown in Table 2, this methodology is compatible
iminonitriles from imidazo[1,2-a]pyridines has been presented in
Scheme 2. The ligand exchange reaction between PhI(OAc)2
and NaN3 forms PhI(OAc)N3. The imidazo[1,2-a]pyridines
attacks on electrophilic PhI(OAc)N3 through C3 position to form
the intermediate 3. Thus, the hypervalent iodine(III) has
assembled two reacting ligands around its coordination sphere.
The propensity of intermediate 3 for reductive elimination of
with
a variety of imidazo[1,2,a]pyridines bearing electron-
donating and -withdrawing groups either at aryl or pyridine type
ring. The yields of the reactions were not found to be dependent
on electronic effect of the substituents. The effect of steric
Scheme 3. Plausible mechanism for the formation of -iminonitrile from imidazo[1,2-a]pyridine
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Table 2. Synthesis of -iminonitriles from imidazo[1,2,a]pyridine using NaN3 and DIBa
Reaction conditions: Imidazo[1,2,a]pyridine 1 (1 mmol), NaN3 (3 mmol) and DIB ( 2 mmol) in CH3CN/H2O (9:1) at rt stirring. Yields are of
isolated pure products.
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reaction was monitored by TLC. After completion, water was added to
quench the reaction and the aqueous phase was extracted with CH2Cl2.
The combined organic extracts were dried over Na2SO4, filtered, and
concentrated under reduced pressure to afford the crude residue. The
crude product was purified by flash column chromatography using
petroleum ether (40-60 oC) and ethyl acetate to afford corresponding (Z)-
N-(pyridin-2-yl)benzimidoyl cyanide 2 in good yields.
iodobenzene introduces azide group at C3 position of
imidazo[1,2-a]pyridines to form σ-complex 4 which undergoes
aromatization to furnish 3-azido imidazo[1,2-a]pyridines 5. The
aryl azides are well known for the thermal decomposition to form
nitrene as an intermediate.[31] Therefore, 5 can undergo thermal
decomposition to form nitrene
6
which is trapped
intramolecularly to form strained azirine 7. Finally, 7 undergoes
ring opening of azirine unit with concomitant cleavage of five
member ring to form -iminonitrile 2. It is important to mention
that there is only one related example in the literature for the ring
opening reaction of 3-nitroso-2-phenylimidazo[1,2-a]pyridine
with triethyl phosphate to form -iminonitrile.[32]
(Z)-N-(Pyridin-2-yl)benzimidoyl cyanide (2a): Yellow solid (173.9 mg,
84% yield); mp 62-64 oC; 1H NMR (400 MHz, CDCl3) δ (ppm) 7.39 (dd, J
= 7.9, 3.5 Hz, 1H), 7.41 (dd, J = 4.0, 1.6 Hz ,1H), 7.63 (td, J = 6.6, 7.16
Hz, 2H), 7.69 (dd, J = 6.1, 1.1 Hz, 2H), 7.98 (td, J = 5.9, 1.8 Hz, 1H), 8.17
(dd, J = 5.5, 1.8 Hz, 2H), 8.58 (dd, J = 3.96, 0.8 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ (ppm) 111.5, 118.4, 122.9, 128.7, 129.0, 133.3, 133.6,
138.3, 141.1, 148.9, 159.1; IR(cm-1): 2919, 2315, 1573, 1521, 1450,
+
1208, 989, 770, 677; HRMS-ESI: MS calculated for C13H9N3[M+1]
208.0867, found [M+1]+ 208.0869.
Conclusions
(Z)-N-(3-Methylpyridin-2-yl)benzimidoyl cyanide (2b): Yellow solid
(180.5 mg, 81% yield); mp 58-60 oC; 1H NMR (400 MHz, CDCl3) δ (ppm)
2.33 (s, 3H, CH3), 7.24 (dd, J = 4.7, 2.7 Hz, 1H), 7.55 (td, J = 6.2, 5.4 Hz,
2H), 7.64-7.60 (m, 1H), 7.69 (dd, J = 6.9, 0.72 Hz, 1H), 8.14 (dd, J = 5.6,
1.6 Hz, 2H), 8.33 (dd, J = 3.4, 1.2 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
(ppm) 17.3, 111.8, 123.3, 128.0, 128.6, 129.0, 133.1, 133.8, 139.1,
140.2, 146.1, 157.5; IR (cm-1): 2922, 2218, 1572, 1451, 1221, 992, 774,
686; HRMS-ESI: MS calculated for C14H12N3 [M+1]+ 222.1022, found
[M+1]+ 222.1026.
In summary, the present methodology is an unintended
synthesis of -iminonitriles from imidazo[1,2-a]pyridines using
NaN3 and hypervalent iodine(III) reagent, DIB. It is a metal-free
and cyanide-free synthesis of -iminonitriles which is a valuable
synthetic intermediate in organic synthesis. The reaction
conditions are exceptionally mild with excellent yields of -
iminonitriles. The ring opening reaction of imidazo[1,2-
a]pyridines with the simultaneous cleavage of C-C and C-N
bonds in a single transformation are still rare in the literature.
(Z)-N-(4-Methylpyridin-2-yl)benzimidoyl cyanide (2c): Yellow solid
1
(176.5 mg,79% yield); mp 56-58 oC; H NMR (400 MHz, CDCl3) δ (ppm)
2.43 (s, 3H, CH3), 7.10-7.08 (m, 2H), 7.54 (td, J = 7.1, 5.0 Hz, 2H), 7.59
(dd, J = 5.9, 1.32 Hz, 1H), 8.22 (dd, J = 3.8, 1.7 Hz, 2H), 8.45 (d, J = 5.0
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ (ppm) 21.0, 111.5, 118.8, 124.0,
128.6, 129.0, 133.2, 133.6, 141.0, 148.5, 149.7, 159.3; IR (cm-1): 2922,
2217, 1597, 1521, 1447, 1410, 1273, 1012, 770, 685; HRMS-ESI: MS
calculated for C14H12N3 [M+1]+ 222.1022, found [M+1]+ 222.1026.
(Z)-N-(3-Chloro-5-(trifluoromethyl)pyridin-2-yl)benzimidoyl cyanide
(2d): Yellow solid (198.7 mg, 64% yield), mp: 58-60 oC; 1H NMR (400
MHz, CDCl3) δ (ppm) 7.58 (t, J = 7.9, 1.6 Hz, 2H), 7.69 (td, J = 4.6, 1.5
Hz,1H), 8.08 (d, J = 1.7 Hz, 1H), 8.28 (dd, J = 7.4, 1.3 Hz, 2H), 8.73 (d, J
= 1.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ (ppm) 110.6, 121.2, 123.9,
125.4, 126.2, 126.5, 129.3, 134.5, 135.8, 143.9, 144.0, 158.8; IR (cm-1):
2927, 2136, 1564, 1448, 1322, 1263, 1123, 1006, 912, 777, 689; HRMS-
ESI: MS calculated for C14H8N3ClF3 [M+1]+ 310.0352, found [M+1]+
310.0353.
Experimental Section
General Information. 1H NMR (400 MHz) and 13C NMR (100 MHz)
spectra were measured in CDCl3 as the solvent with tetramethylsilane
(TMS) as the internal standard at room temperature. All chemical shifts
(δ) are given in parts per million (ppm) and J values are given in hertz
(Hz). High-resolution mass spectra were recorded on QTOF mass
analyzer. IR spectra were recorded using ATR mode. Melting points were
determined in
a capillary tube and are uncorrected. Thin-layer
chromatography (TLC) was carried out on SiO2 (silica gel 60 F254), and
the spots were located with ultraviolet (UV) light. Flash chromatography
was carried out on SiO2 (silica gel 60, 100 to 200-mesh size). Drying of
organic extracts after workup of reactions was performed over anhydrous
Na2SO4. All reagents and solvents were purchased and used without
further purification. Imidazo[1,2-a]pyridines were prepared according to
the literature procedures.[33]
(Z)-N-(5-Bromopyridin-2-yl)benzimidoyl cyanide (2e): Yellow solid
(248.3 mg, 86% yield), mp 88-90 oC; 1H NMR (400 MHz, CDCl3) δ (ppm)
7.20 (d, J = 8.4 Hz, 1H), 7.54 (td, J = 5.2, 1.3 Hz, 2H), 7.62 (td, J = 5.2,
2.0 Hz, 1H), 7.95 (dd, J = 5.9, 2.4 Hz, 1H), 8.21 (dd, J = 5.2, 2.0 Hz, 2H),
8.65 (d, J = 2.2 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ (ppm) 111.4,
119.6, 120.1, 128.8, 129.1, 133.5, 133.6, 140.9, 141.3, 149.9, 157.5; IR
(cm-1): 2213, 1592, 1565, 1449, 1366, 1237, 1091, 1006, 844, 770, 680;
HR-MS ESI: MS calculated for C13H9N3Br [M+1]+ 285.9977, found
[M+1]+ 285.9974.
General Procedure for Synthesis of corresponding (Z)-N-(pyridin-2-
yl)benzimidoyl cyanide: To
a stirred solution of substituted 2-
arylimidazo[1,2-a]pyridine (1 mmol) 1 in CH3CN (9 mL), and water (1
mL), (diacetoxyiodo)benzene (2.0 mmol) and NaN3 (3.0 mmol) were
sequentially added into a 50 mL round bottom flask. The reaction
mixture was stirred at room temperature for 3 h. The progress of the
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COMMUNICATION
(Z)-4-Methoxy-N-(pyridin-2-yl)benzimidoyl cyanide (2f): Yellow solid
(189.7 mg, 80 % yield), mp 74-76 oC; 1H NMR (400 MHz, CDCl3) δ (ppm)
3.90 (s, 3H, OCH3), 7.02 (dd, J = 4.9, 2.0 Hz, 2H), 7.26-7.21 (m, 2H),
7.81 (td, J = 5.9, 1.8 Hz, 1H), 8.18 (dd, J = 4.9, 2.0 Hz, 2H), 8.58 (dd, J =
3.8, 0.8 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ (ppm) 55.6, 111.6, 114.4,
118.1, 122.4, 126.6, 130.8, 138.2, 140.4, 159.5, 163.9; IR (cm-1): 2922,
2317, 1546, 1457, 1425, 1257, 1168, 1021, 837, 794, 739; HR-MS ESI:
MS calculated for C14H11N3O [M+1]+ 238.0970, found [M+1]+ 238.0975.
(Z)-4-Methoxy-N-(3-methylpyridin-2-yl)benzimidoyl cyanide (2g):
Yellow solid (198.4 mg, 79% yield), mp 80-82 oC; 1H NMR (400 MHz,
CDCl3) δ (ppm) 2.35 (s, 3H, CH3), 3.91 (s, 3H, OCH3), 7.03 (dd, J = 5.0,
2.8 Hz, 2H), 7.17 (td, J = 4.6, 2.6 Hz, 1H) 7.61 (d, J = 7.2 Hz, 1H), 8.20
(dd, J = 5.0, 2.8 Hz, 2H), 8.39 (dd, J = 3.6, 1.0 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ (ppm) 17.3, 55.6, 111.9, 114.4, 122.8, 126.9, 127.7,
130.6, 139.0, 139.5, 146.0, 157.8, 163.7; IR (cm-1): 2912, 2313, 1583,
1442, 1281, 1254, 1161, 1021, 836, 771; HR-MS ESI : MS calculated for
C15H14 N3O [M+1]+ 252.1127, found [M+1]+ 252.1131.
(Z)-N-(5-Bromopyridin-2-yl)-4-methylbenzimidoyl cyanide (2l): Yellow
o
1
solid (243.6 mg, 81% yield), mp 104-106 C; H NMR (400 MHz, CDCl3)
δ (ppm) 2.46 (s, 3H, CH3), 7.17 (d, J = 8.4 Hz, 1H), 7.35 (d, J = 8.1 Hz,
2H), 7.94 (dd, J = 6.0, 2.4 Hz, 1H), 8.11 (d, J = 8.3 Hz, 2H), 8.64 (d, J =
2.3 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ (ppm) 21.7, 111.4, 119.3,
119.9, 128.8, 129.8, 131.0, 140.8, 141.3, 144.8, 149.9, 157.7; IR (cm-1):
2921, 2215, 1587, 1558, 1445, 1364, 1287, 1213, 1179, 1087, 1005,
831; HR-MS ESI: MS calculated for C14H13N3Br [M+1]+ 302.0283, found
[M+1]+ 302.0287.
(Z)-4-Chloro-N-(pyridin-2-yl)benzimidoyl cyanide (2m): Yellow solid
(201.5 mg, 83% yield), mp 110-112 oC; 1H NMR (400 MHz, CDCl3) δ
(ppm) 7.32-7.27 (m, 2H), 7.53 (dd, J = 4.8, 2.5 Hz, 2H), 7.85 (td, J = 5.9,
1.8 Hz, 1H), 8.18 (dd, J = 4.8, 2.5 Hz, 2H), 8.61 (dd, J = 2.3, 1.0 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ (ppm) 111.4, 118.8, 123.2, 129.4, 129.9,
132.2, 138.3, 139.7, 139.8, 148.9, 158.7; IR (cm-1): 2211, 1580, 1429,
1403, 1215, 1093, 1003, 837, 796, 744; HR-MS ESI: MS calculated for
C13H9N3Cl [M+1]+ 242.0479, found [M+1]+ 242.0480.
(Z)-4-Methoxy-N-(4-methylpyridin-2-yl)benzimidoyl cyanide (2h):
Yellow solid (196.5 mg, 78% yield), mp 82-84 oC; 1H NMR (400 MHz,
CDCl3) δ (ppm) 2.42 (s, 3H, CH3), 3.90 (s, 3H, OCH3),7.07-7.00 (m, 4H),
8.17 (dd, J = 4.9, 2.0 Hz, 1H) 8.43 (d, J = 5.0 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ (ppm) 21.0, 55.6, 111.6, 114.4, 118.5, 123.5, 125.5,
129.0, 129.5, 130.7, 140.3, 148.5, 149.6, 159.7, 163.8; IR (cm-1): 2918,
2313, 1587, 1458, 1248, 1159, 1021, 830, 772; HR-MS ESI : MS
calculated for C15H14 N3O [M+1]+ 252.1127, found [M+1]+ 252.1131.
(Z)-N-(5-Bromopyridin-2-yl)-4-methoxybenzimidoyl cyanide (2i):
(Z)-4-Chloro-N-(3-methylpyridin-2-yl)benzimidoyl
cyanide
(2n):
Yellow solid (199.4 mg, 78%), mp 84-86 oC; 1H NMR (400 MHz, CDCl3) δ
(ppm) 2.38 (s, 3H, CH3), 7.22 (dd, J = 4.8, 2.7 Hz, 1H), 7.52 (d, J = 4.8,
2.5 Hz, 2H), 7.64 (dd, J = 6.8, 0.8 Hz, 1H), 8.19 (dd, J = 4.8, 2.5 Hz, 2H),
8.41 (d, J = 3.6, 1.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ (ppm) 17.2,
111.6, 123.6, 128.4, 129.3, 129.8, 132.4, 139.2, 139.6, 146.1, 157.0; IR
(cm-1): 2921, 2209, 2116, 1588, 1552, 1485, 1400, 1229, 1090, 1005,
832, 800; HR-MS ESI: MS calculated for C14H11N3Cl [M+1]+ 256.0637,
found [M+1]+ 256.0636.
o
1
Yellow solid (256.2 mg, 81% yield), mp 114-116 C; H NMR (400 MHz,
CDCl3) δ (ppm) 3.91 (s, 3H, OCH3), 7.03 (dd, J = 4.9, 2.0 Hz, 2H), 7.15
(d, J = 8.4 Hz, 1H), 7.93 (dd, J = 6.0, 2.4 Hz, 1H), 8.17 (dd, J = 4.9, 2.0
Hz, 2H), 8.63 (d, J = 2.2 Hz, 1H), 13C NMR (100 MHz, CDCl3) δ (ppm)
55.6, 111.5, 114.5, 119.0, 119.8, 126.4, 130.9, 140.5, 140.8, 149.8,
157.9, 164.1 ; IR (cm-1): 2919, 2124, 1580, 1446, 1217, 1172, 1008, 835;
HR-MS ESI : MS calculated for C14H10 BrN3O [M+1]+ 316.0077, found
[M+1]+ 316.0080.
(Z)-4-Chloro-N-(4-methylpyridin-2-yl)benzimidoyl
cyanide
(2o):
Yellow viscous solid (190.6 mg, 74%); 1H NMR (400 MHz, CDCl3) δ
(ppm) 2.37 (s, 3H, CH3), 7.05-7.03 (m, 2H), 7.45 (dd, J = 4.8, 2.4 Hz,
2H), 8.09 (dd, J = 4.8, 2.4 Hz, 2H), 8.38 (d, J = 4.8 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ (ppm) 21.0, 111.4, 119.2, 124.3, 129.3, 129.8,
132.2, 139.6, 148.5, 149.5, 149.8, 158.9, 161.6; IR (cm-1): 2923, 2214,
1586, 1545, 1463, 1400, 1246, 1151, 1086, 1004, 831, 715; HR-MS
ESI : MS calculated for C14H11N3Cl [M+1]+ 256.0637, found [M+1]+
256.0636.
(Z)-4-Methyl-N-(pyridin-2-yl)benzimidoyl cyanide (2j): Yellow solid
(186.2 mg, 84% yield), mp 92-94 oC; 1H NMR (400 MHz, CDCl3) δ (ppm)
2.46 (s, 3H, CH3), 7.28-7.23 (m, 2H), 7.35 (d, J = 8.2 Hz, 2H), 7.83 (td, J
= 5.9, 1.8 Hz, 1H), 8.12 (d, J = 8.2 Hz, 2H), 8.59 (dd, J = 3.9, 0.8 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ (ppm) 21.7, 111.5, 118.1, 122.7, 128.7,
129.9, 131.1, 138.2, 141.1, 144.4, 148.9, 159.4; IR (cm-1): 2920, 2214,
1574, 1551, 1427, 1214, 1180, 1009, 821, 800, 742; HR-MS ESI: MS
calculated for C14H12N3 [M+1]+ 222.1026, found [M+1]+ 222.1026.
(Z)-4-Bromo-N-(3-methylpyridin-2-yl)benzimidoyl
cyanide
(2p):
o
1
Yellow solid (239.7 mg, 80% yield), mp 106-108 C; H NMR (400 MHz,
CDCl3) δ (ppm) 2.38 (s, 3H, CH3), 7.22 (dd, J = 4.8, 2.7 Hz, 1H), 7.64
(dd, J = 5.9, 0.8 Hz,1H), 7.67 (dd, J = 4.8, 2.4 Hz, 2H), 8.11 (dd, J = 4.8,
2.4 Hz, 2H), 8.41 (dd, J = 3.0, 1.1 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
(ppm) 17.2, 111.6, 123.7, 128.2, 128.5, 129.9, 132.3, 132.9, 138.9,
139.2, 146.1, 157.0; IR (cm-1): 2922, 2209, 2115, 1581, 1554, 1482,
1397, 1232, 1115, 1070, 1003, 829, 801; HR-MS ESI: MS calculated for
C14H11N3Br [M+1]+ 300.0134, found [M+1]+ 300.0131.
(Z)-4-Methyl-N-(4-methylpyridin-2-yl)benzimidoyl
cyanide
(2k):
Yellow solid (178.5 mg, 76% yield), mp: 96-98 oC; 1H NMR (400 MHz,
CDCl3) δ (ppm) 2.36 (s, 3H, CH3), 2.45 (s, 3H, CH3), 7.18 (dd, J = 4.8,
2.7 Hz, 1H), 7.34 (d, J = 8.1 Hz, 2H), 7.62 (dd, J = 6.8, 0.6 Hz, 1H), 8.13
(d, J = 8.3 Hz, 2H), 8.40 (dd, J = 3.5, 1.2 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ (ppm) 17.2, 21.7, 111.8, 123.1, 127.8, 128.6, 129.7, 131.4,
139.0, 140.2, 144.1, 146.1, 157.7; IR (cm-1): 2922, 2202, 2113, 1593,
1549, 1416, 1232, 1172, 1114, 1002, 824, 795; HR-MS ESI: MS
calculated for C15H14N3 [M+1]+ 236.1180, found [M+1]+ 236.1182.
(Z)-4-Bromo-N-(4-methylpyridin-2-yl)benzimidoyl
cyanide
(2q):
o
1
Yellow solid (241.5 mg, 80% yield), mp 102-104 C; H NMR (400 MHz,
CDCl3) δ (ppm) 2.43 (s, 3H, CH3), 7.12-7.10 (m, 2H), 7.68 (dd, J = 4.8,
2.4 Hz,2H), 8.08 (dd, J = 4.8, 2.4 Hz, 2H), 8.45 (d, J = 4.9Hz, 1H); 13C
NMR (100 MHz, CDCl3) δ (ppm) 21.0, 111.4, 119.3, 124.3, 129.9, 132.3,
132.7, 139.7, 148.5, 149.8, 158.8; IR (cm-1): 2919, 2207, 1578, 1537,
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10.1002/ejoc.201601480
European Journal of Organic Chemistry
COMMUNICATION
1480, 1397, 1244, 1147, 1071, 1005, 840, 825, 716; HR-MS ESI: MS
calculated for C14H11N3Br [M+1]+ 300.0133, found [M+1]+ 300.0131.
(Z)-4-Bromo-N-(4-bromopyridin-2-yl)benzimidoyl cyanide (2r): Yellow
University Grants Commission [No. F. 540/19/DRS-I/2016 (SAP
DRS-I)] for the financial support. The authors are also grateful to
SAIF, Punjab University, Chandigarh, India, for recording the
NMR spectra.
1
solid (329.4 mg, 90% yield), mp 146-148 oC; H NMR (400 MHz, CDCl3)
δ (ppm) 7.21 (d, J = 8.4 Hz, 1H), 7.69 (dd, J = 4.9, 2.3 Hz, 2H), 7.96 (dd,
J = 6.0, 2.4 Hz, 1H), 8.09 (dd, J = 4.8, 2.3 Hz, 2H), 8.65 (d, J = 2.2 Hz,
1H); 13C NMR (100 MHz, CDCl3) δ (ppm) 111.2, 120.2, 120.6, 128.0,
130.1, 132.4, 132.5, 140.0, 140.9, 149.9, 157.0; IR (cm-1): 2210, 1579,
1482, 1396, 1236, 1079, 1003, 834; HR-MS ESI: MS calculated for
C13H8N3Br2 [M+1]+ 363.9083, found [M+1]+ 363.9079.
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(Z)-2-methyl-N-(pyridin-2-yl)benzimidoyl cyanide (2s): Yellow liquid
(128.8 mg, 58% yield); 1H NMR (400 MHz, CDCl3) δ (ppm) 7.21 (d, J =
8.0, Hz, 1H), 7.29-7.27 (m,1H), 7.40-7.33 (m, 2H), 7.46 (td, J = 6.2, 1.2
Hz, 1H), 7..84 (td, J = 5.9, 1.8 Hz, 1H), 8.00 (dd, J = 6.7, 1.0 Hz, 1H) ;
13C NMR (100 MHz, CDCl3) δ (ppm) 22.1, 112.0, 117.6, 122.7, 126.4,
131.5, 132.0, 132.4, 132.5, 130.3, 138.3, 139.3, 142.6, 148.9, 159.5 ;
IR(cm-1): 2925, 2114, 1579, 1558, 1458, 1425, 1210, 1036, 799, 742,
719 ; GCMS-: MS calculated for C14H11N3 [M] 221 found [M + 23]+ 244
(Z)-N-(Pyrimidin-2-yl)benzimidoyl cyanide (2t): Yellow solid (172.0 mg,
82% yield), mp 84-86 oC; 1H NMR (400 MHz, CDCl3) δ (ppm) 7.27 (t, J =
4.8 Hz, 1H), 7.56 (td, J = 5.7, 1.4 Hz, 2H), 7.66 (td, J = 4.3, 1.9 Hz, 1H),
8.28 (dd, J = 5.3, 1.4 Hz, 2H), 8.86 (d, J = 4.8 Hz, 2H); 13C NMR (100
MHz, CDCl3) δ (ppm) 118.7, 119.0, 129.1, 129.2, 132.3, 134.2, 144.3,
158.8, 165.3; IR (cm-1): 2314, 1549, 1394, 1237, 1173, 1004, 822, 771,
681; HR-MS ESI: MS calculated for C12H9N4 [M+1]+ 209.0820 , found
[M+1]+ 209.0822.
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(Z)-N-(Pyridin-2-yl)-2-naphthimidoyl cyanide (2u): Yellow solid (209.0
mg, 81% yield), mp 98-100 oC; 1H NMR (400 MHz, CDCl3) δ (ppm) 7.32-
7.28 (m, 2H), 7.66-7.58 (m, 2H), 7.86 (td, J = 5.9, 1.8 Hz, 1H), 7.96-7.90
(m, 2H), 8.03 (d, J = 7.9, 1.0 Hz, 1H), 8.33 (dd, J = 6.8, 1.8 Hz, 1H), 8.63
(dd, J = 2.4, 0.8 Hz, 1H), 8.70 (d, J = 1.2 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ (ppm) 111.6, 118.5, 122.9, 123.1, 127.2, 127.9, 128.9, 129.0,
131.4, 131.9, 132.7, 135.7, 138.3, 141.0, 148.9, 159.2; IR (cm-1): 2218,
1577, 1555, 1459, 1430, 1281, 1192, 1125, 943, 821, 742; HR-MS ESI:
MS calculated for C17H12N3 [M+1]+ 258.1026, found [M+1]+ 258.1026.
(Z)-2,2,2-trifluoro-N-(pyridin-2-yl)acetimidoyl cyanide (2v): Yellow
liquid (103.9 mg, 52% yield); 1H NMR (400 MHz, CDCl3) δ (ppm) 7.07 (td,
J = 5.9, 1.0 Hz, 1H), 7.39 (td, J = 5.6, 1.2 Hz ,1H), 7.70 (dd, J = 8.2, 0.9
Hz, 1H), 8.20 (dd, J = 4.9, 1.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
(ppm) 114.7, 118.9, 124.3, 126.7, 145.8, 148.8, 157.0; IR (cm-1): 2928,
2114, 1545, 1380, 1274, 1112, 1014, 748, 725
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European Journal of Organic Chemistry
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Key Topic* Hypervalent iodine
Amit H. Kalbandhe, Ashish C. Kavale,
Nandkishor N. Karade*
Page No. – Page No.
Ring
opening
Reaction
of
Imidazo[1,2-a]pyridines
Using
(Diacetoxyiodo)benzene and NaN3:
New Entry to the Synthesis of -
Iminonitriles
Imidazo[1,2-a]pyridines undergo unusual ring opening reaction to form -
iminonitriles using (diacetoxyiodo)benzene and NaN3 under mild conditions.
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