Acceptorless dehydrogenative construction of CN and CC bonds through catalytic aza-Wittig and Wittig reactions in the presence of an air-stable ruthenium pincer complex

Article abstract of DOI:10.1039/c8dt04725a

The construction of CN bonds was achieved by the dehydrogenative coupling of alcohol and azide via aza-Wittig type reaction. The reaction is catalyzed by an acridine-derived ruthenium pincer complex and does not use any oxidant. The present protocol offers a wide substrate scope, including aliphatic, aryl or heteroaryl alcohol/azides. This expeditious protocol was successfully applied to construct a CC bond directly from alcohol via dehydrogenative Wittig reaction. Furthermore, the synthesis of structurally important pyrrolo[1,4]benzodiazepine derivatives was also achieved by this methodology.

Full text of DOI:10.1039/c8dt04725a

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Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
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DOI: 10.1039/C8DT04725A
Journal Name
Paper
Acceptorless Dehydrogenative Construction of C=N and C=C bond
through Catalytic Aza-Wittig and Wittig Reaction in the Presence
of Air-stable Ruthenium Pincer Complex
Received 00th January 20xx,
Accepted 00th January 20xx
Nandita Biswas,a Kalicharan Das,a Bitan Sardar a and Dipankar Srimani*a
DOI: 10.1039/x0xx00000x
The construction of C=N bond has been achieved by the dehydrogenative coupling of alcohol and azide via aza-Wittig type
reaction. The reaction is catalyzed by acridine derived ruthenium pincer complex and it does not use any oxidant. The
present protocol offers a wide range of substrate scope including aliphatic, aryl or heteroaryl alcohol/azide. This expeditious
protocol has also been successfully applied to construct a C=C bond directly from alcohol via dehydrogenative Wittig
reaction. Furthermore, the synthesis of structurally important Pyrrolo[1,4]benzodiazepines derivatives has also been
achieved by the use of this methodology.
www.rsc.org/
blocks.10-14 Most of these highly active metal complexes involve
pyridine,11 bipyridine,12 acridine13 and diethyl amino14 based
phosphine pincer ligands. Although these phosphine based
Introduction
Though Staudinger and Meyers first reported the synthesis of
phosphazines,1 it was only after the work of Wittig,2 the
phosphazines have been applied in the construction of C=N
bonds and become popular as aza-Wittig reagents. Since then,
the Wittig and aza-Wittig reactions have experienced
remarkable development and have become a powerful tool for
the construction of nitrogen-containing heterocycles.3 An
effective ‘borrowing hydrogen’ method to synthesize alkane
directly from alcohol, through indirect Wittig reaction catalysed
by iridium or ruthenium complex, was first developed by
William and co-workers.4 Recently, Milstein and co-workers
have shown the selective synthesis of alkene5a directly from
alcohol through catalytic oxidant-free Wittig reaction5 or Julia
olefination6 in presence of phosphine based-ruthenium pincer
complex. A few years ago, William and co-worker7 developed a
method to convert alcohols into N-alkyl anilines via aza-Wittig
type reaction8 in presence of iridium catalyst. However, the
selective formation of C=N bond9 and C=C bond directly from
alcohol through catalytic aza-Wittig and Wittig reaction is highly
important and would be a significant advance if this could be
performed by air stable pincer complexes.
pincer ligands have shown significant applications in the area of
homogeneous catalysis, they have encountered well-known
drawbacks associated with their air and moisture sensitivities
and cost-effectiveness. Thus, the search for new air-stable
pincer ligands and their applicability in the catalysis have
attracted much attention in the recent time.15,16,17 In this
18
regard, N-heterocyclic carbenes (NHC) based ligand is found
to be one of the best alternatives and even can exhibit a
different type of catalytic applicability compared to the
phosphine analogue.16 Very recently, Gusev and co-workers
showed the superior activity of HN(C2H4SEt)2 ligand over the
phosphine analog.17 Herein we have synthesized new air and
moisture stable NNS- and SNS-ruthenium pincer complexes (Fig.
1) and investigated their catalytic applicability towards
dehydrogenative aza-Wittig and Wittig-reaction for the
construction of C=N and C=C bond.
Results and discussion
First, the acridine-based SNS ligand was prepared by
nucleophilic
substitution
reaction
of
4,5-
Recently pincer based ruthenium complexes have attracted
much attention due to their tremendous application towards
the development of environmentally benign, atom-economical
sustainable methodologies for the synthesis of useful building
bis(bromomethyl)acridine with the corresponding thiolate.19
H
H
N
N
S
Cl
Ru
N
S
N
S
Cl
Ru
Cl
a. Department of Chemistry, Indian Institute of Technology Guwahati, Assam, India,
781039 Fax: (+91)-361-258-2349; Phone: (+91)-361-258-3312; E-mail:
dsrimani@iitg.ernet.in.
S
Cl
Ru
PPh3
S
Cl
Cl
PPh3
PPh3
2
1
3
1
† Electronic Supplementary Information (ESI) available: copies of H NMR and 13C
NMR spectra of all the compounds. CCDC 1847040, 1865785 and 1865803. For ESI
and crystallographic data in CIF or other electronic format see DOI: See
DOI: 10.1039/x0xx00000x
Fig. 1 Ruthenium pincer complexes
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J. Name., 2013, 00, 1-3 | 1
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ARTICLE
Journal Name
Ph
P
View Article Online
Ph
Ph
Cat 1 (1mol%)
OH
+
DOI: 10.1039/C8DT04725A
N
N
KOH (5 mol%)
6a
Dioxane 120 o
24 h
C
4a
35%
5
Scheme 1 Catalytic oxidant free aza-Wittig reaction in presence of acridine SNS
based ruthenium pincer complex.
36% (E)-N-benzylidene-1-phenylmethanamine was obtained
after 24 h and 64% benzyl alcohol remained unreacted (Table 1,
entry 1). As the reaction showed similar activity, we decided to
proceed further through the protocol with in situ generated
phosphazine. Thus, when toluene was used as a solvent, 46%
desired imine was formed only after 18 h (Table 1, entry 2).
Upon increasing the reaction temperature (bath temperature
135 °C), the yield of the desired (E)-N-benzylidene-1-
phenylmethanamine was improved to 91% with the complete
consumption of benzyl alcohol as indicated by NMR. Pure imine
was obtained (87%) after column chromatography. Under the
similar reaction conditions, complex 2 or 3 gave an inferior yield
of the desired imine (Table 1, entries 4 and 5). However, when
0.05 mol% of catalyst 1 was used, keeping other conditions
unaltered, only 70% desired imine was obtained after 36 h. The
effect of the base has been studied and KOH is found more
1
2
3
Fig. 2. Molecular structure of complex 1 (thermal ellipsoid 50% probability level),
2 and 3 (thermal ellipsoid 30% probability level).
t
effective than BuOK or K2CO3 (Table 1, entries 7 and 8). The
catalyst failed to give any desired imine without a catalytic
amount of base. The reaction under air gave 83% yield of the
desired imine after 24 h, which was slightly lower compared to
the inert reaction condition (Table 1, entry 15).
The complex 1 was synthesized by stirring RuCl2(PPh3)3 with the
ligand in CH2Cl2 for 12 h. The brown colored single crystal
suitable for X-ray diffraction was developed by layering the
solution of the complex 1 in mixture of dichloromethane and
acetonitrile with diethyl ether under air. Crystal structure (Fig.
2) showed the geometry of the Ru center to be pseudo-
octahedral type with an elongated Ru-N bond (2.56 Å). This
bond length is slightly longer than the one observed in case of
acridine PNP based ruthenium pincer complex reported by
Table 1 Optimization of the reaction condition for the catalytic aza-Wittig reaction.a
Cat (1 mol%)
base (5 mol%)
N3
N
OH
+
PPh3
6a
Milstein (Ru-N: 2.479 Å) [13c] or Hofmann (Ru-N: 2.488 Å) [13d]
.
4a
Entry
7a
Yieldb
[%]
Bath
temperature (oC)
The complexes 2 and 3 were prepared by refluxing the
RuCl2(PPh3)3 with the corresponding tridentate ligand in THF.
1H- and 31P{1H}-NMR spectral analysis reveals that the complex
2 exists as one pure isomer in solution whereas complex 3 exists
in solution as an isomeric mixture (60:40) at room temperature.
The complex 2 and 3 were crystallized by layering their solution
in CHCl3 with diethyl ether and hexane respectively at ambient
temperature. The solid-state structure of both 2 and 3 was
found to be trans-(meri-) dichloride complex (Fig. 2).
Initially, the catalytic activity of the complexes towards the
synthesis of imines directly from alcohol and phosphazines was
investigated. To explore the feasibility of the catalytic aza-Wittig
reaction, a dioxane solution containing benzyl alcohol (1 mmol)
and PhCH2N=PPh3 (1 mmol) was refluxed at 120 °C (bath
temperature) for 24 h in presences of 0.01 mmol of complex 1
and 0.05 mmol of KOH under argon atmosphere. 35% (E)-N-
benzylidene-1-phenylmethanamine was isolated (Scheme 1).
Encouraged by the initial attempt, we thought to prepare the
aza-Wittig reagent in situ. Thus a mixture of benzyl alcohol (1
mmol), benzyl azide (1 mmol) and triphenyl phosphine (1 mmol)
in dioxane (5 mL) was refluxed (Bath temperature 120 °C) in
presence of 0.01 mmol of complex 1 and 0.05 mmol of KOH.
Time
(h)
Cat.
Solvent
Base
KOH
KOH
KOH
Dioxane
Toluene
Toluene
120
120
135
135
24
18
18
1
1
1
1
2
3
4
36
46
91
2
KOH
KOH
-
18
18
18
Toluene
Toluene
Toluene
30
60
5
6
135
135
3
1
trace
tBuOK
K2CO3
135
135
52
43
1
1
Toluene
Toluene
18
18
7
8
KOH
KOH
9
1
1
76
55
24
24
10
THF
10
Et2O
5
11
1
1
Toluene
Toluene
52
70
27
30
83
KOH
KOH
4
135
135
12c
36
24
24
24
[(p-Cymene)
RuCl2]2
KOH
Toluene
135
13
14
RuCl2(PPh3)3
KOH
KOH
Toluene
Toluene
135
135
15d
1
a
Reaction conditions: Benzyl alcohol (1 mmol), benzyl azide (1 mmol), PPh3
(1mmol), solvent (5 mL). b NMR yield using dioxane or CH3CN as internal standard.
c 0.5 mol% catalyst loading. d under air
2 | J. Name., 2012, 00, 1-3
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ARTICLE
Table 2 Catalytic Aza-Wittig type reaction directly from alcohol and azide.a
Under the similar condition, [(p-Cymene)RuCl2]2 or RuCl2(PPh3)3
View Article Online
gave substantially lower yield of the desDirOeId: 1p0r.1o0d39u/cCt8(DTTa0b4l7e251A,
entries 13-14).
R2
Cat (1mol%)
R2 N3
7
R1
N
R1
OH
To study the scope of the reaction with respect to aromatic
azides, the optimized reaction conditions were applied to the
reaction of benzyl alcohol and phenyl azide. 85% yield of the
desired (E)-N-benzylidenebenzenamine was obtained after 18 h
(Table 2, entry 2). Encouraged by this result, we wanted to
expand the scope of the reaction. Thus, the reactions of
differentially substituted benzyl alcohol with variously
substituted aromatic or benzyl azide were studied. It has been
observed that both electron-withdrawing and electron-
donating substituents in the aromatic ring gave excellent yield
in this catalytic dehydrogenative aza-Wittig reaction
methodology. Exploring the scope of the reaction with regard
to secondary alcohol, 1-Phenylethanol was reacted with phenyl
azide. The yield of the desired imine was 65% (Table 2, entry 14)
even after 48 h, which is probably due to the lower reactivity of
ketones towards the aza-Wittig reaction. In this reaction, 35%
of acetophenone was also observed. Secondary azide, reacting
with benzyl alcohol also gave moderate yield (54%).
Delightfully, no dehalogenation reaction was observed when 4-
chlorobenzyl alcohol or 4-bromobenzyl alcohol was used as
substrates. It is interesting to note that 75% of (E)-N-(2-
aminobenzylidene)benzenamine were achieved when 2-amino
benzyl alcohol was reacted with 2 equivalent of phenyl azide
and triphenyl phosphine (Table 2, entry 16). 2-
Nitrobenzylzlcohol and phenyl azide gave (E)-N-(2-
nitrobenzylidene) benzenamine in 74% yield. A small amount
(15%) of (E)-N-(2-aminobenzylidene) benzenamine was also
obtained due to the reduction of the nitro group under the
reaction condition (Table 2, entry 17). The reaction
methodology was successfully extended to heterocyclic
alcohols; both 2-thiophenemethanol and 2-pyridinemethanol
gave moderate to good yields of the desired imine under the
optimized reaction conditions. To expand the scope of the
reaction with regard to aliphatic alcohols or aliphatic azide, the
optimized reaction conditions were applied to the reaction of
hexanol with hexyl azide. An excellent yield (83%) of the desired
imine was obtained only after 24 h (Table 2, entry 22). Similarly,
octanol reacted smoothly with benzyl azide to give a mixture of
(E)-N-octyl-1-phenylmethanimine (71%) and (E)-N-benzyloctan-
1-imine (14%). Here the initially formed (E)-N-benzyloctan-1-
imine was isomerized to form the more stable (E)-N-octyl-1-
phenylmethanimine under the reaction conditions and has
been isolated (65%).
KOH (5 mol%)
PPh3, Toluene, 135 o
6
4
C
18 h
R1, R2= alkyl,aryl,aliphatic, heteroaryl
Yieldb
(%)
Entry
Alcohol
Azide
Product
OH
N
N3
1
91(87)
85(80)
90(85)
6a
N3
OH
OH
2
3
N
6b
N
N3
Cl
Cl
6c
N3
OH
OH
N
87(80)
87(84)
4
6d
F
F
N3
N3
N
5
6e
MeO
MeO
N
OH
OH
(86)
6
7
6f
N
N3
(84)
(80)
6g
N3
OH
8
N
Br
Br
Br
6h
N3
(82)
(85)
OH
OH
9
N
6i
Br
Br
OMe
Br
N3
10
N
6j
MeO
MeO
MeO
OH
N
N3
11
(90)
6k
N3
N3
OH
OH
N
12
13
(88)
91
6l
N
PhO
6m
PhO
N3
OH
c
N
65(55)
(54)
14
15
6n
OH
OH
N3
N
6o
N3
N3
N3
16d
17
N
(75)
(74)
NH2
6p
NH2
OH
NO2
N
6q
NO2
OH
18
(80)
N
6r
OH
S
OH
N3
OH
19
N
(79)
(60)
S
6s
To understand whether the reaction is going through the aza-
Wittig type reaction pathway or through the in situ formation
of amine 20 by hydrogen auto-transfer reaction, we performed
the reaction of 4-methoxy benzyl alcohol and benzyl azide in the
absence of PPh3. Only 40 % desired imine was observed
together with 56% of (E)-N-benzylidene-1-phenylmethanamine
(Scheme 2). Next, we treated the benzyl azide with the catalyst
and base, under the same conditions and we observed the
formation of (E)-N-benzylidene-1-phenylmethanamine (54%).21
N3
20
21
N
OH
N
N
N
N
N
N
6t
N3
N
(65)
OH
OH
6u
22e
23
H3
C
H3
C
CH3
4
83(68)
(65)
H3
C
N
4
4
N3
4
6v
N3
H3
C
N
OH
5
6
6w
a
Reaction conditions: Alcohol (1 mmol), benzyl azide (1 mmol), PPh3 (1mmol),
Toluene (5 mL), Cat 1 (1 mol%), KOH (5 mol%). NMR yield, the yield in the
parenthesis-isolated yield. c 48 h. d Phenyl azide (2 mmol), PPh3 (2 mmol). e 24 h.
b
In
sharp
contrast,
the
reaction
of
(benzylimino)triphenylphosphorane with 4-methoxybenzyl
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Table 3 Catalytic Wittig type reaction directly from alcohol and Wittig salt.
alcohol under the optimized reaction condition gave an
excellent yield (96%) of the desired imine.
View Article Online
DOI: 10.1039/C8DT04725A
Cat 1 (1 mol%)
tBuOK (1.3 eq)
PPh3
PPh3
R2
R1
OH
R2
PPh3 Br
R1
P
Cat 1 (1 mol%)
+
OH
Dioxane, 135 o
24 h
C
N
N
PPh3
+
KOH (5 mol%)
Toluene, 135 oC, 18 h
MeO
8
OMe
4
9
96%
R1, R2= aryl, alkyl, heteroaryl
Yield (%)b
Product
N
Entry
Alcohol Wittig Salt
OH
56%
Cat 1 (1mol%)
N3
+
+
MeO
KOH (5 mol%)
Toluene, 135 oC, 18 h
N
PPh3 Br
OH
75
86
1
2
40%
OMe
9a
Cat 1 (1mol%)
OH
OH
PPh3 Br
PPh3 Br
N3
N
KOH (5 mol%)
9b
9c
MeO
MeO
Br
Toluene, 135 oC, 18 h
54%
88
90
Scheme 2. Control experiments
3
4
Br
Br
Thus, we can conclude that the reaction was proceeding mainly
through the aza-Wittig type reaction pathway via the rapid in
situ formation of the aza-Wittig reagent.
OH
PPh3 Br
PPh3 Cl
9c
Br
It was of interest to us to expand the catalytic activity of the Ru-
complex towards the oxidant-free Wittig reactions of alcohols
for the construction of C=C bond. Table 3 summarizes the
ruthenium catalysed olefination reaction between alcohol and
Wittig-salt. The reaction works well with different benzylic or
heteroaryl alcohols and in most of the cases the E isomer is the
major product together with a very small amount of Z product
(1-2 %). The reaction is slower and moderate yield was obtained
when aliphatic alcohol or aliphatic phosphonium salt was used
80
83
OH
5
6
9d
9e
Br
Br
OH
PPh3 Cl
OH
OH
7
8
81
76
PPh3 Br
PPh3 Br
9f
1
Br
as substrates (Table 3, entries 11 and 12). H NMR analysis of
the
crude
mixture
of
the
reaction
between
O
butyltriphenylphosphonium bromide with benzyl alcohol and 1-
phenyl ethanol showed that E:Z isomers were formed in 30:70
ratio.
O
9g
9h
9i
60
40
9
N
PPh3 Cl
PPh3 Br
OH
OH
N
N
N
Finally, we tried to apply our methodology to synthesize
structurally important heterocyclic compounds. There is a wide
range of biologically important compounds having
pyrrolo[1,4]benzodiazepines (PBDs) as a core structural unit.22
Thus, we wanted to apply our methodology to synthesize PBDs.
Therefore we have synthesized (S)-(2-azidophenyl)(2-
(hydroxymethyl) pyrrolidin-1-yl)methanone 12 by the reaction
of 2-azidobenzoyl chloride and L-prolinol. When a toluene
solution containing 1:1 mixture of (S)-(2-azidophenyl)(2-
10c
OH
11d
12e
54
45
PPh3 Br
PPh3 Br
9j
OH
OH
5
5
9k
(hydroxymethyl)
triphenylphosphine was refluxed in the presence of 1 mol% cat
1, mol% KOH, (S)-1,2,3,10,11,11a-hexahydro-5H-
pyrrolidin-1-yl)methanone
and
PPh3 Br
13f
75
5
NH2
NH2
9l
benzo[e]pyrrolo[1,2-a][1,4]diazepin-5-one was obtained after
20 h (Scheme 2). Interestingly no racemization was observed as
the reaction was performed under almost neutral reaction
condition. The imine formed was hydrogenated in situ to the
corresponding amine 13. Thus to obtain (S)-1,2,3,11a-
tetrahydro-5H-benzo[e]pyrrolo[1,2-a][1,4]diazepin-5-one, 14
a Reaction conditions: Alcohol (1 mmol), phosphonium salt (1.2 mmol), dioxane (5
mL), Cat 1 (1 mol%), tBuOK (1.3 mmol). b Isolated yield, cE/Z 54:46, acetophenone
left (35%). d E/Z 30:70, e 48 h, f Wittig salt (2 mmol).
we
have
treated
(S)-(2-azidophenyl)(2-
(hydroxymethyl)pyrrolidin-1-yl) methanone, 12 with equimolar
amount of triphenylphosphine in the presence of 0.01 mmol of
KOH and diphenyl acetylene as H2 acceptor. Gratifyingly, good
yield of the desired product was obtained.
4 | J. Name., 2012, 00, 1-3
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H
N
handled under proper safety precautions such as i) chlorinated
solvent should not be used as reaction media ii) organic azides
should not be distilled iii) azides should be kept in dark at low
temperature. 24
H
H
View Article Online
DOI: 10.1039/C8DT04725A
Cat 1 (1mol%)
OH
H
OH
H
N3
N
KOH (5 mol%)
N3
K2CO3
+
PPh3, Toluene, 135 oC
O
13
Cl HN
CH2Cl2/H2
rt, 20 h
O
85%
N
N
O
Cat 1 (1mol%)
KOH (5 mol%)
O
10
11
12
N
PPh3
,
Ph
Ph
Synthesis of 4,5-bis(ethylthiomethyl)acridine: NaOH (0.47g, 12
mmol) was taken in 5 mL of water and the resulting NaOH
solution was added dropwise to a solution of ethanethiol
(0.62g, 10 mmol) in ethanol (50 mL). Then the resulting mixture
was refluxed for 30 min and then 4,5-bis(bromomethyl)acridine
(1.8 g, 5 mmol) in tetrahydrofuran (10 mL), was added to it.
After that, the reaction mixture was refluxed for another 2 h.
After cooling to room temperature, the reaction mixture was
poured into distilled water (100 mL) and extracted with 80 mL
of chloroform. The extract was washed with water (3 × 25 mL)
and dried over anhydrous sodium sulfate. The solvent was
evaporated under reduced pressure on a rotary evaporator and
the crude mixture was purified by silica gel column
chromatography using hexane: ethyl acetate (9.5:0.5) to afford
the pure ligand as a yellow solid (Yield: 1.3 g, 80%. 1H NMR (600
MHz, CDCl3): δ (ppm) 8.71 (s, 1H), 7.89 (dd, J = 8.5, 1.4 Hz, 2H),
7.76 (dd, J = 6.9, 1.3 Hz, 2H), 7.48 (dd, J = 8.4, 6.7 Hz, 2H), 4.60
(s, 4H), 2.60 (q, J = 7.4 Hz, 4H), 1.31 (t, J = 7.4 Hz, 6H); 13C{1H}
NMR (150 MHz, CDCl3): δ (ppm) 146.52, 137.76, 136.42, 129.40,
127.33, 126.89, 125.54, 31.80, 26.55, 14.76. HRMS (ESI) calcd
for C19H21NS2 [M + H ]+ 328.1194, Found 328.1192.
O
Toluene, 135 oC
14
76%
Scheme 3 Application of catalytic aza-Wittig reaction to synthesize benzodiazepines
derivatives.
Conclusions
In conclusion, we have developed a catalytic route for the
formation of C=N bond directly from alcohol and azide. The
reaction strategy involves in situ preparation of aza-Wittig
reagent and dehydrogenative coupling of aza-Wittig reagent
with alcohol in presence of acridine derived air stable
ruthenium pincer complex. This reaction showed a wide range
of substrate scope. This efficient method has also been applied
to the olefination reaction of alcohol and phosphonium salt. As
a highlight, we successfully applied our protocol devising the
synthesis
benzodiazepines.
of
structurally
important
Pyrrolo[1,4]
Experimental section
Synthesis of (2-(ethylthio)-N-(pyridin-2-ylmethyl)aniline:
Pyridine-2-carboxaldehyde (0.721 g, 6.7 mmol) and 2-
(ethylthio)aniline (1.0 g, 6.5 mmol) were dissolved in dry MeOH
(25 mL) and the resulting mixture was refluxed for 24 h. After
cooling the reaction, NaBH4 (1.228 g, 32.5 mmol) was added
portion wise in stirring condition at 0 °C and the stirring was
continued for 6 hours at room temperature. Then the solvent
was evaporated and 25 ml water was added and neutralized by
acetic acid. After that, it was extracted by CH2Cl2 (40 mL×3) and
the combined organic phase was dried over Na2SO4. Then, the
solvent was evaporated to get the crude product, which was
purified further by silica gel column chromatography using 10-
30 % ethyl acetate in hexane. Brown liquid (Yield 1.308 g, 82%).
1H NMR (600 MHz, CDCl3) δ 8.62-8.58 (m, 1H), 7.63 (td, J = 7.7,
1.8 Hz, 1H), 7.43 (dd, J = 7.6, 1.6 Hz, 1H), 7.30 (d, J = 7.8 Hz, 1H),
7.20-7.10 (m, 2H), 6.64 (td, J = 7.5, 1.3 Hz, 1H), 6.54 (dd, J = 8.2,
1.3 Hz, 1H), 6.02 (brs, 1H), 4.54 (s, 2H), 2.79 (q, J = 7.4 Hz, 2H),
1.25 (t, J = 7.4 Hz, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 158.89,
149.43, 148.87, 136.78, 136.23, 130.01, 122.15, 121.23, 117.88,
117.09, 110.54, 49.44, 29.18, 15.05. HRMS (ESI) calcd for
C14H16N2S [M + H ]+: 245.1112; found, 245.1119.
General Informations: Unless otherwise mentioned, all the
chemicals were purchased from common commercial sources
and used as received. RuCl2(PPh3)3 was purchased from Sigma-
Aldrich. All solvents were dried by using standard procedure.23
Solvent such as toluene were predried using CaH2 and dried
over Na with benzophenone indicator. The preparation of
catalyst was carried out under argon atmosphere with freshly
distilled dry THF or dichloromethane. All catalytic reactions
were carried out under argon atmosphere using dried glassware
and standard syringe/septa techniques. DRX-400 Varian
spectrometer and Bruker Avance III 600 and 400 spectrometers
were used to record 1H, 13C NMR and 31P NMR. Chemical shifts
(δ) are reported in ppm downfield from tetramethylsilane;
spin−spin coupling constant (J) are expressed in Hz, and other
data are reported as follows: s = singlet, d = doublet, t = triplet,
m = multiplet, q = quartet, and br s = broad singlet. IR spectra
were recorded on Perkin Elmer Instrument at room
temperature making KBr pellet. MS (ESI-HRMS): Mass spectra
were recorded on an Agilent Accurate-Mass Q-TOF LC/MS 6520.
X-ray crystallographic data were collected using Agilent Super
Nova (Single source at offset, Eos) diffractometer and Bruker
Nonius SMART APEX CCD diffractometer equipped with a
graphite monochromator. Data refinement and cell reduction
were carried out by CrysAlisPro. Structures were solved by
direct methods using SHELXS-97 and refined by full-matrix least-
squares on F2 using SHELXL-97. All of the non-H atoms were
refined anisotropically. SQUEEZE was used to reduce
contribution of solvent molecule (diethylether/ acetonitrile) to
the overall electron density. Column chromatography was done
with SRL Silica gel 100-200 mesh. Organic azides should be
Synthesis of 2-(ethylthio)-N-(2-(ethylthio)benzyl)ethan-1-
amine: A solution of 2-(ethylthio)benzaldehyde (2.127g, 12.79
mmol) and 2-(ethylthio)ethan-1-amine compound (1.282 g,
12.18 mmol) in 45 mL dry MeOH was refluxed for overnight.
Then, the reaction mixture was cooled to room temperature
and NaBH4 (1.154 g, 30.5 mmol) was added portion wise in
°
stirring condition at 0 C and the stirring was continued for 6
hours at room temperature. Then the solvent was evaporated
and 60 ml water was added and neutralized by acetic acid. The
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aqueous layer was then extracted with CH2Cl2 (80 mL
) and taken in 3 mL dry THF and was added dropwise to the solution
View Article Online
DOI: 10.1039/C8DT04725A
the combined organic phase was dried over Na2SO4. Then the of [RuCl2(PPh3)3] (0.181g, 0.18 mmol) in 5 mL degassed dry THF.
solvent was evaporated to get the crude product, which was Then, it was refluxed for 6 hours under argon atmosphere. After
purified further by silica gel column chromatography using 10- cooling it down to the room temperature, the solvent was
30 % ethyl acetate in hexane. White solid. (Yield 2.958 g, 95%). evaporated to obtain the residue, which was thoroughly
1H NMR (600 MHz, CDCl3) δ 7.75 (dd, J = 7.7, 2.2 Hz, 1H), 7.45- washed with diethyl ether and dried under vacuum to get
7.42 (m, 1H), 7.36 (ddt, J = 9.3, 7.7, 1.5 Hz, 1H), 7.32-7.27 (m, yellow solid (Yield 0.103g, 81%). The single crystal was grown by
1H), 4.37 (s, 2H), 3.52-3.43 (m, 1H), 3.08 (t, J = 7.3 Hz, 2H), 3.03- slow diffusion of hexane in the CHCl3 solution of the complex.
2.93 (m, 4H), 2.48 (q, J = 7.4 Hz, 2H), 1.33 (td, J = 7.3, 1.5 Hz, 3H), 1H NMR (400 MHz, CDCl3): δ (ppm) 1st dias. (Cis-isomer) (60%)
1.22 (td, J = 7.4, 0.9 Hz, 3H). 13C{1H} NMR (150 MHz, CDCl3) δ 7.77-7.19 (m, 19H), 5.10 (t, J = 10.7 Hz, 1H), 3.94 (t, J = 11.8 Hz,
137.03, 131.87, 131.08, 130.65, 130.26, 127.39, 48.39, 45.60, 1H), 3.67-2.10 (m, 7H), 1.5-0.8 (m, 5H), 0.63 (t, J = 7.1 Hz, 3H).
29.01, 27.69, 25.88, 14.76, 14.35. HRMS (ESI) calcd for 1H NMR (400 MHz, CDCl3): δ (ppm) 2nd dias. (trans isomer)
C13H22NS2 [M + H]+: 256.1194; found, 256.1197.
(40%) 7.77-7.19 (m, 19H), 4.89 (t, J = 10.8 Hz, 1H), 4.22 (t, J =
Synthesis of acridine derived (SNS) ruthenium pincer complex 11.2 Hz, 1H), 3.67-2.10 (m, 7H), 1.5-0.8 (m, 5H), 0.69 (t, J = 6.9
1: To a solution of 4,5-bis(ethylthiomethyl)acridine (0.235 g, Hz, 3H). 13C{1H} NMR (100 MHz, CDCl3): δ (ppm) 1st+2nd dias.
0.721 mmol) in dry CH2Cl2 (10 mL) was added a solution of 140.75, 139.95, 136.94, 136.56, 136.29, 135.96, 135.90, 134.77,
RuCl2(PPh3)3 (0.553g, 0.576 mmol) in dry CH2Cl2 (10 mL) and 134.67, 132.19, 131.06, 130.33, 130.16, 129.07, 128.75, 128.70,
stirred 12 h at room temperature under argon. The solvent was 127.51, 127.46, 127.43, 127.37, 54.97, 54.66, 51.89, 51.51,
evaporated and the brown solid was washed with diethyl ether 35.57, 32.01, 31.04, 30.73, 30.03, 29.54, 26.00, 12.95, 12.88,
several times and dried under vacuum, resulting in the pure 12.67. 31P{1H} δ (ppm) 45.23 and 43.41. Anal. Calc. for
complex as a brown solid (Yield 0.372 g, 85%). The single crystal C31H36Cl2NPRuS2 C, 53.99; H, 5.26; N, 2.03 found C, 53.53; H,
was grown by slow diffusion of diethyl ether in the CHCl3/CH3CN 5.38; N, 2.22; HRMS (ESI) calcd for C31H36Cl2NPRuS2 [M - Cl]+:
solution of the complex.
654.0759; found, 654.0759.
1H NMR (600 MHz, CDCl3): δ (ppm) 9.02 (s, 1H), 8.10 (d, J = 8.04 Representative procedure for the catalytic aza-Wittig type
Hz, 2H), 7.77 (t, J = 9 Hz, 6H), 7.72 (d, J = 6.24 Hz , 2H), 7.50 (t, J reaction of alcohol and azide.
= 7.32 Hz , 3H), 7.35-7.29 (m, 8H), 5.69 (d, J = 13.02 Hz, 2H), 4.29 In a two necked round bottom flask, equipped with a
(d, J = 13.08 Hz, 2H), 1.53-1.47 (m, 2H), 0.92 (t, J = 7.2 Hz, 6H), condenser, complex (0.01 mmol), KOH (0.05 mmol) and dry
0.60-0.54 (m, 2H); 13C{1H} NMR (150 MHz, CDCl3): δ (ppm) toluene (3 ml) were added under argon atmosphere. To this
149.74, 143.22, 134.90 (d, J = 8.37 Hz), 134.62 (d, J = 46.48 Hz), suspension alcohol (1 mmol), azide (1 mmol) and PPh3 (1 mmol)
134.32, 130.85, 130.73, 129.35, 128.63, 127.25 (d, J = 9.36 Hz), in dry toluene (2 ml) were subsequently added under argon
124.34, 35.54, 22.49, 12.46; 31P{1H} δ (ppm) 54.84; Anal. Calc. atmosphere. The solution was refluxed to 135 °C (bath
for C37H36Cl2NPRuS2 C, 58.34; H, 4.76; N, 1.84 found C, 58.35; H, temperature) with stirring under argon atmosphere for the
4.71; N, 1.84; HRMS (ESI) calcd for C37H36Cl2NPRuS2 [M - Cl]+: specified time. Then the reaction mixture was allowed to cool
726.0759; found, 726.0757.
to the room temperature and was filtered through celite. After
Synthesis of ruthenium pincer complex 2: Ligand, 2-(ethylthio)- that, the solvent was removed and 1,4-dioxane or acetonitrile
N-(pyridin-2-ylmethyl)aniline (0.030g, 0.13 mmol) was taken in was added as internal standard to the reaction mixture and take
1 mL dry THF and was added dropwise to the solution of 1H NMR in CDCl3 to get the NMR yield. Purification was done by
[RuCl2(PPh3)3] (0.107g, 0.11 mmol) in 4 mL degassed dry THF column chromatography over silica gel using 0.5:10 mixture of
under argon. Then, it was refluxed for 6 hours. After cooling it ethyl acetate-hexane containing 2 % triethylamine as eluent to
down to the room temperature, 20 ml diethyl ether was added. afforded pure imine product. Characterization data of the
The resulting precipitate was thoroughly washed with diethyl products are given below.
ether and dried under vacuum to get brown solid (Yield 0.046g, Representative procedure for the catalytic Wittig type
83%). The single crystal was grown by slow diffusion of diethyl reaction of alcohol and phosphonium salt.
ether in the CHCl3 solution of the complex.
In a two-necked round bottom flask, equipped with a
1H NMR (600 MHz, CDCl3): δ (ppm) 8.68 (d, J = 5.6 Hz, 1H), 7.70 condenser, complex (0.01 mmol), alcohol (1 mmol),
(q, J = 8.4, 7.1 Hz, 6H), 7.61 – 7.56 (m, 2H), 7.47 (t, J = 7.7 Hz, phosphonium salt (1.2 mmol), tBuOK (1.3 mmol) and dry
1H), 7.43 – 7.30 (m, 12H), 6.91 (t, J = 6.6 Hz, 1H), 5.46 (t, J = 12.6 dioxane (5 ml) were added under argon atmosphere. The
°
Hz, 1H), 5.17-5.13 (m, 1H), 2.71-2.66 (m, 1H), 2.41-2.36 (m, 1H), solution was then refluxed to 135 C (bath temperature) with
0.92 (t, J = 7.5 Hz, 3H). 13C{1H} NMR (150 MHz, CDCl3): δ (ppm) stirring under argon for the specified time. Then the reaction
163.13, 157.24, 146.37, 140.09, 135.67 (d, J= 10.5 Hz), 135.45, mixture was allowed to cool to the room temperature and was
134.92 (d, J = 9.8 Hz), 133.77, 129.82, 129.24, 127.67 (d, J = 9.1 filtered through celite and the solvent was removed. The crude
Hz), 127.58, 124.33, 123.47, 121.58, 57.01, 35.04, 13.49. 31P{1H} product was analyzed by 1H NMR to determine the E/Z.
δ (ppm) 50.15; Anal. Calc. for C32H31Cl2N2PRuS C, 56.64; H, 4.60; Purification was done by column chromatography over silica gel
N, 4.13 found C, 56.69; H, 4.60; N, 4.12; HRMS (ESI) calcd for using hexane or 0.5:10 mixture of ethyl acetate-hexane as
C32H31Cl2N2PRuS2 [M - Cl]+: 643.0678; found, 643.0650.
Synthesis of ruthenium pincer complex 3: Ligand, 2-(ethylthio)- Synthesis
N-(2-(ethylthio)benzyl)ethan-1-amine (0.058 g, 0.22 mmol) was benzo[e]pyrrolo[1,2-a][1,4]diazepin-5-one (13). In
eluent to afforded pure alkene product.
of (S)-1,2,3,10,11,11a-hexahydro-5H-
two-
a
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necked round bottom flask, the complex (0.005 mmol), (S)-(2-
azidophenyl)(2-(hydroxymethyl)pyrrolidin-1-yl)methanone (0.5 Pale yellow oil. H NMR (600 MHz, CDCl3): δ (ppm) 8.38 (s, 1H),
mmol) (8), PPh3 (0.5 mmol), KOH (5 mol%) and dry toluene (5 7.76 (d, J = 8.4 Hz, 2H), 7.62 (d, J = 8.4 Hz, 2H), 7.51 (d, J = 8.6
ml) were placed under Argon atmosphere. The mixture was Hz, 2H), 7.09 (d, J = 8.6 Hz, 2H); 13C{1H} NMR (150 MHz, CDCl3):
stirred at 135 ˚C for 18 h under argon atmosphere. After that, δ (ppm) 159.47, 150.68, 134.93, 132.40, 132.25, 130.34, 126.36,
the reaction mixture was cooled to room temperature and 122.70, 119.78.
ARTICLE
4-Bromo-N-[(4-bromophenyl)methylene]benzenamine (6i).28
View Article Online
1
DOI: 10.1039/C8DT04725A
filtered through celite. Then the solvent was removed under
4-Methoxy-N-[(4-methoxyphenyl)methylene]benzenamine
1
reduced pressure and the crude reaction mixture was purified (6j).26 Pale yellow oil. H NMR (600 MHz, CDCl3): δ (ppm) 8.41
by column chromatography (silica gel; 75% ethyl acetate and (s, 1H), 7.83 (d, J = 8.7 Hz, 2H), 7.21 (d, J = 8.8 Hz, 2H), 6.98 (d, J
hexane).
= 8.7 Hz, 2H), 6.93 (d, J = 8.8 Hz, 2H), 3.87 (s, 3H), 3.83 (s, 3H);
13C{1H} NMR (150 MHz, CDCl3): δ (ppm) 162.08, 158.07, 158.03,
(S)-1,2,3,11a-tetrahydro-5H-benzo[e]pyrrolo[1,2-
a][1,4]diazepin-5-one (14). In a two-necked round bottom 145.34, 130.36, 129.55, 122.19, 114.44, 114.25, 55.60, 55.53.
flask, the complex (0.005 mmol), (S)-(2-azidophenyl)(2-
N-(2-Naphthalenylmethylene)benzenemethanamine (6k).29
1
(hydroxymethyl)pyrrolidin-1-yl)methanone (0.5 mmol) (8), PPh3 White solid. H NMR (400 MHz, CDCl3): δ (ppm) 8.53 (s, 1H),
(0.5 mmol), KOH (5 mol %), diphenylacetylene (0.75 mmol) and 8.07- 8.04 (m, 2H), 7.90-7.83 (m, 3H), 7.52-7.50 (m, 2H), 7.39-
dry toluene (5 ml) were placed under argon atmosphere. The 7.24 (m, 5H), 4.88 (s, 2H) ; 13C{1H} NMR (100 MHz, CDCl3): δ
mixture was stirred at 135 ˚C for 18 h under argon atmosphere. (ppm) 162.18, 139.44, 134.89, 133.98, 133.22, 130.25, 128.75,
After the reaction finished, the reaction mixture was cooled to 128.66, 128.61, 128.17, 128.01, 127.30, 127.16, 126.59, 124.08,
room temperature and filtered through celite. Then the solvent 65.27
was removed under reduced pressure and the crude reaction
mixture was purified by column chromatography (silica gel; 75% 1H NMR (400 MHz, CDCl3): δ (ppm) 8.62 (s, 1H), 8.20 -8.16 (m,
ethyl acetate and hexane). 2H), 7.95- 7.87 (m, 3H), 7.56 -7.53 (m, 2H), 7.44 -7.40 (m, 2H),
N-(2-Naphthalenylmethylene)benzenamine (6l).26 White solid.
N-benzylidene-1-phenylmethanamine (6a).25 Pale yellow oil. 7.28-7.25 (m, 3H) ; 13C{1H} NMR (100 MHz, CDCl3): δ (ppm)
1H NMR (600 MHz, CDCl3): δ (ppm) 8.43 (s, 1H), 7.83-7.81 (m, 160.52, 152.26, 135.18, 134.10, 133.25, 131.40, 129.34, 128.93,
2H), 7.46-7.45 (m, 3H), 7.38-7.37 (m, 4H), 7.31-7.27 (m, 1H), 128.83, 128.09, 127.70, 126.77, 126.15, 124.07, 121.08.
4.83 (s, 2H). 13C{1H} NMR (150 MHz, CDCl3): δ (ppm) 162.14,
139.40, 136.27, 130.90, 128.73, 128.62, 128.41, 128.11, 127.12, NMR (400 MHz, CDCl3): δ (ppm) 7.97 (d, J = 8.1 Hz, 2H), 7.47-
65.19. 7.44 (m, 3H), 7.35 (t, J = 8.1 Hz, 2H), 7.08 (t, J = 7.5 Hz, 1H), 6.80
N-(1-Phenylethylidene)benzenamine (6n).30 White solid. 1H
N-benzylideneaniline (6b).26 Pale yellow oil. 1H NMR (600 MHz, (d, J = 8.3 Hz, 2H), 2.27 (s, 3H); 13C{1H} NMR (150 MHz, CDCl3): δ
CDCl3): δ (ppm) 8.49 (s, 1H), 7.95-7.94 (m, 2H), 7.52- 7.51 (m, (ppm) 165.64, 151.83, 139.63, 130.61, 129.09, 128.51, 127.31,
3H), 7.43 (t, J = 7.8 Hz, 2H), 7.29-7.24 (m, 3H); 13C{1H} NMR (150 123.36, 119.52, 17.54.
MHz, CDCl3): δ (ppm) 160.57, 152.21, 136.33, 131.52, 129.28,
128.94, 128.91, 126.07, 121.00.
N-Benzylidene-α-methylbenzylamine (6o).31 Pale yellow oil. 1H
NMR (400 MHz, CDCl3): δ (ppm) 8.36 (s, 1H), 7.78-7.76 (m, 2H),
N-(4-chlorobenzylidene)aniline (6c).26 Pale yellow oil. 1H NMR 7.43-7.42 (m, 2H), 7.39-7.38 (m, 3H), 7.33 (t, J = 5.1 Hz, 2H), 7.23
(600 MHz, CDCl3): δ (ppm) 8.34 (s, 1H), 7.77 (d, J = 8.4 Hz, 2H), (t, J = 4.8 Hz, 1H), 4.53 (q, J = 6.6 Hz, 1H), 1.59 (d, J = 6.7 Hz, 3H).
7.37 (d, J = 8.4 Hz, 2H), 7.34-7.31 (m, 2H ), 7.18-7.13 (m, 3H); 13C{1H} NMR (150 MHz, CDCl3): 159.62, 145.25, 136.45, 130.69,
13C{1H} NMR (150 MHz, CDCl3): δ (ppm) 158.98, 151.80, 137.51, 128.64, 128.53, 128.37, 126.94, 126.74, 69.87, 24.96.
134.83, 130.09, 129.34, 129.22, 126.34, 120.98.
N-[(2-Aminophenyl)methylene]benzenamine (6p):32 Pale
N-(4-Fluorobenzylidene)aniline (6d).27 Pale yellow oil. 1H NMR yellow oil. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.46 (s, 1H), 7.34-
(600 MHz, CDCl3): δ (ppm) 8.33 (s, 1H), 7.83-7.81 (m, 2H), 7.31 7.25 (m, 3H), 7.16- 7.11 (m, 4H), 6.66 (t, J = 7.88 Hz, 2H); 6.46
(t, J = 7.5 Hz, 2H), 7.17-7.14 (m, 1H), 7.12 (dd, J = 7.3 Hz, 1.1 Hz, (brs, 2H). 13C{1H} NMR (150 MHz, CDCl3): δ (ppm) 163.29,
2H), 7.08 (t, J = 8.5 Hz, 2H); 13C{1H} NMR (150 MHz, CDCl3): δ 152.07, 148.95, 134.53, 131.96, 129.30, 125.67, 121.10, 117.81,
(ppm) 164.82( d, J = 250 Hz), 158.95, 151.97, 132.70 (d, J = 3.03 116.40, 115.94. HRMS (ESI) calcd for C14H13N2 [M + H]+:
Hz), 130.91 (d, J = 8.74 Hz), 129.31, 126.15, 120.96, 116.06 (d, J 197.1079; found, 197.1073.
= 21.85 Hz).
N-[(2-Nitrophenyl)methylene]benzenamine (6q).33 White
N-(4-methoxybenzylidene)aniline (6e).25 Pale yellow oil. 1H solid. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.95 (s, 1H), 8.32 (d, J
NMR (600 MHz, CDCl3): δ (ppm) 8.42 (s, 1H), 7.90 (d, J = 8.7 Hz, = 7.8 Hz, 1H), 8.08 (d, J = 8.2 Hz, 1H) 7.75 (t, J = 8.2 Hz, 1H), 7.64-
2H), 7.43 (t, J = 8.3 Hz, 2H), 7.26-7.25 (m, 3H), 7.02 (d, J = 8.8 Hz) 7.60 (m, 1H), 7.43 (t, J = 7.92 Hz, 2H), 7.30- 7.26 (m, 3H). 13C{1H}
2H), 3.89 (s, 3H); 13C{1H} NMR (150 MHz, CDCl3): δ (ppm) 162.29, NMR (100 MHz, CDCl3): δ (ppm) 156.02, 151.22, 149.47, 133.75,
159.75, 152.40, 130.57, 129.31, 129.17, 125.63, 120.95, 114.24, 131.34, 130.28, 129.91, 129.44, 127.08, 124.70, 121.34.
55.45.
3-Hydroxybenzalaniline (6r).34 White solid. 1H NMR (600 MHz,
N-(4-bromobenzylidene)aniline (6h).26 Pale yellow oil. 1H NMR CDCl3): δ (ppm) 8.37 (s, 1H), 7.46 (s, 1H), 7.41 (t, J = 7.7 Hz, 2H),
(600 MHz, CDCl3) δ 8.42 (s, 1H), 7.85 (d, J = 8.4 Hz, 2H), 7.45 (d, 7.37 (d, J = 7.4 Hz, 1H), 7.31 (t, J = 7.6 Hz, 1H), 7.27 (d, J = 6.6 Hz,
J = 8.5 Hz, 2H), 7.42- 7.38 (m, 2H), 7.22-7.20 (m, 2H). 13C{1H} 1H), 7.23 (d, J = 7.4 Hz, 2H), 6.98 (d, J = 8.0 Hz, 1H). 13C{1H} NMR
NMR (150 MHz, CDCl3): δ (ppm) 158.99, 151.81, 137.52, 134.83, (150 MHz, CDCl3): δ (ppm) 161.49, 156.62, 151.38, 137.14,
130.10, 129.34, 129.22, 126.34, 120.99.
130.22, 129.39, 126.44, 122.31, 121.13, 119.50, 114.51. HRMS
(ESI) calcd for C13H11NO [M + H]+: 198.0919; found, 198.0911.
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N-(2-Thienylmethylene)benzenemethanamine (6s).26 Pale (E)-1-Methyl-3-(4-methylstyryl)benzene (9f). WVhieitweArstioclleidO.nlinHe
yellow oil. 1H NMR (600 MHz, CDCl3): δ (ppm) 8.50 (s, 1H), 7.45- NMR (400 MHz, CDCl3): δ (ppm) 7.42 (d,DJO=I: 710.9.1603H9/zC,82DHT)0,4772.352A
7.37 (m, 6H), 7.35-7.32 (m, 1H), 7.12 (t, J = 6.6 Hz, 1H), 4.85 (s, (d, J = 9.8 Hz, 2H), 7.25 (t, J = 8.0 Hz, 1H), 7.17 (d, J = 7.8 Hz, 2H),
2H); 13C{1H} NMR (150 MHz, CDCl3): 155.17, 142.44, 139.07, 7.12-7.02 (m, 3H), 2.38 (s, 3H), 2.37 (s, 3H). 13C{1H} NMR (100
130.67, 129.04, 128.49, 128.02, 127.37, 127.01, 64.42.
MHz, CDCl3): δ (ppm) 138.32, 137.63, 137.56, 134.83, 129.53,
N-(2-Pyridinylmethylene)benzenemethanamine (6t).35 Yellow 128.69, 128.59, 128.38, 127.99, 127.25, 126.55, 123.74, 21.57,
oil. 1H NMR (400 MHz, CDCl3): δ (ppm) 8.66 (d, J = 6 Hz, 1H), 21.37.
8.56 (s, 1H), 8.08 (d, J = 8.0 Hz, 1H), 7.75-7.62 (m, 2H), 7.42-7.33 E-2-Styryl-furan (9g).38 White solid. 1H NMR (400 MHz, CDCl3):
(m, 2H), 7.18 (m, 1H), 5.01 (s, 1H); 13C{1H} NMR (100 MHz, δ (ppm) 7.45-7.19 (m, 6H), 7.00 (d, J = 16.2 Hz, 1H), 6.85 (d, J =
CDCl3): δ (ppm) 164.08, 158.85, 154.51, 149.63, 149.50, 136.83, 16.3 Hz, 1H), 6.39-6.38 (m, 1H), 6.31 (d, J = 3.2 Hz, 1H). 13C{1H}
136.70, 125.07, 122.51, 122,28, 121.64, 66.70.
NMR (100 MHz, CDCl3): δ (ppm) 153.46, 142.28, 137.20, 128.83,
N-(2-Pyridinylmethylene)benzenamine (6u).36 Light Yellow oil. 127.72, 127.32, 126.48, 116.71, 111.78, 108.68.
1H NMR (600 MHz, CDCl3): δ (ppm) 8.64 (d, J = 6.5 Hz, 1H), 8.53 E-1,2-bis(2-pyridyl)ethylene (9h).43 Yellow solid. H NMR (400
(s, 1H), 8.13 (d, J = 11.8 Hz, 1H), 7.74 (t, J = 11.5 Hz, 1H), 7.36- MHz, CDCl3): δ (ppm) 8.55 (d, J = 5.6 Hz, 2H), 7.62-7.57 (m, 4H),
7.28 (m, 3H), 7.23-7.19 (m, 3H) ; 13C{1H} NMR (150 MHz, CDCl3): 7.38-7.35 (m, 2H), 7.12-7.09 (m, 2H), 13C{1H} NMR (100 MHz,
δ (ppm) 160.77, 154.70, 151.10, 149.84, 136.80, 129.36, 126.85, CDCl3): δ (ppm) 155.14, 149.87, 136.77, 131.89, 123.40, 122.77.
1
125.27, 122.02, 121.23.
(E/Z)-1,2-Diphenylprop-1-ene (9i).44 White solid. 7.52 (d, J =
N-Hexyllidenehexane-1-amine (6v).25 Light yellow oil. 1H NMR 7.88 Hz, 2H), 7.40-7.36 (m, 6H), 7.31-7.25 (m, 2H), 6.84 (s, 1H,
(400 MHz, CDCl3): δ (ppm) 7.59 (s, 1H), 3.31 (t, J = 6.9 Hz, 3H), E-isomer), 6.48 (s, 1H, Z-isomer), 2.29 (s, 3H, E-isomer), 2.21 (s,
2.20-2.18 (m, 2H), 1.56-1.51 (m, 2H), 1.50-1.46 (m, 2H), 1.30- 3H, Z-isomer). 13C{1H} NMR (100 MHz, CDCl3): δ (ppm) (E)
1.25 (m, 10H), 0.88-0.84 (m, 6H). 13C{1H} NMR (150 MHz, CDCl3): 144.15, 138.53, 137.59, 129.30, 128.6, 128.47, 127.98, 127.87,
δ (ppm) 165.02, 61.53, 35.90, 31.72, 31.58, 30.82, 27.00, 25.93, 126.61, 126.16, 17.62. (Z) 142.28, 138.9, 137.78, 129.08,
22.73, 22.57, 14.16, 14.08.
128.60, 127.98, 127.04, 126.72, 126.67, 126.22, 27.25.
N-octyl-1-phenylmethanimine (6w).37 Light yellow oil. 1H NMR Z-1-Penten-1-ylbenzene (9j).45 Colourless liquid. 1H NMR (400
(400 MHz, CDCl3): δ (ppm) 8.27 (s, 1H), 7.73-7.71 (m, 2H), 7.41- MHz, CDCl3): δ (ppm) 7.27-7.19 (m, 4H), 7.14-7.08 (m, 1H), 6.35-
7.39 (m, 3H), 3.60 (t, J = 8.0 Hz, 2H), 1.71-1.68 (m, 2H), 1.33-1.27 6.28 (m, 1H), 6.18-5.55 (m, 1H), 2.24-2.20 (m, 2H), 1.43-1.39 (m,
(m, 10H), 0.88 (t, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3): 2H), 0.87-0.84 (m, 3H). 13C{1H} NMR (100 MHz, CDCl3): δ (ppm)
δ (ppm) 160.85, 130.56, 128.70, 128.15, 61.97, 31.99, 31.06, 138, 133.17, 129.01, 128.91, 128.23, 126.55, 30.83, 23.30,
29.56, 29.41, 27.50, 22.80, 14.24.
13.98.
E-stilbene (9a).38 White solid. H NMR (400 MHz, CDCl3): δ E-1-Penten-1-ylbenzene (9j).5 1H NMR (400 MHz, CDCl3): δ (ppm)
(ppm) 7.58-7.56 (m, 4H), 7.44-7.40 (m, 4H), 7.34-7.31 (m, 2H), 7.27-7.19 (m, 4H), 7.14-7.08 (m, 1H), 6.35-6.28 (m, 1H), 2.11 (q,
7.17 (s, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ (ppm) 137.49, J = 7.2 Hz, 1H), 1.43-1.39 (m, 2H), 0.87-0.84 (m, 3H).13C{1H} NMR
1
128.86, 128.82, 127.75, 126.66.
(100 MHz, CDCl3): δ (ppm) 138.12, 133.17, 131.10, 130.06,
E-1-Methoxy-4-styryl-benzene (9b).38 White solid. 1H NMR (400 128.60, 126.89, 126.06, 35.27, 22.70, 13.86.
MHz, CDCl3): δ (ppm) 7.41 (d, J = 5.1 Hz, 2H), 7.38 (d, J = 5.3 Hz, E-non-1-en-1-ylbenzene (9k).5 Colourless liquid. H NMR (400
2H), 7.27 (t, J = 7.6 Hz, 2H), 7.17-7.15 (m, 1H), 6.99 (d, J = 16.3 MHz, CDCl3): δ (ppm) 7.42-7.33 (m, 4H), 7.27-7.23 (m, 1H), 6.45
Hz, 1H), 6.90 (d, J = 16.3 Hz, 1H), 6.83 (d, J = 8.7 Hz, 2H), 3.75 (s, (d, J = 15.8 Hz, 1H), 6.33-6.28 (m, 1H), 2.27 (td, J = 7.9, 1.1 Hz,
1
3H).
159.39,137.75.130.24, 128.78, 128.31, 127.84, 127.35, 126.71, MHz, CDCl3): δ (ppm) 138.14, 131.42, 129.83, 128.60, 126.87,
126.37, 114.24, 55.47. 126.05, 33.20, 32.00, 29.85, 29.55, 29.35, 22.82, 14.24.
13C{1H} NMR (100 MHz, CDCl3):
δ
(ppm) 1H), 1.41-1.33 (m, 10H), 0.96 (t, J = 7.0 Hz, 3H). 13C{1H} NMR (100
E-1-Bromo-4-styryl-benzene (9c).39 White solid. H NMR (400 E-2-styrylaniline (9l). White solid. H NMR (400 MHz, CDCl3):
MHz, CDCl3): δ (ppm) 7.44-7.40 (m, 4H), 7.31-7.2 (m, 4H), 7.22- δ (ppm) 7.54 (d, J = 7.5 Hz, 2H), 7.43 (d, J = 7.7 Hz, 1H), 7.39 (t, J
7.18 (m, 1H), 7.02 (d, J = 16.2 Hz, 1H), 6.95 (d, J = 16.3 Hz, 1H). = 8.0 Hz, 2H), 7.31-7.27 (m, 1H), 7.20 (d, J = 16.1 Hz, 1H), 7.14 (t,
13C{1H} NMR (100 MHz, CDCl3): δ (ppm) 137.11, 136.45, 131.93, J = 7.8 Hz, 1H), 7.02 (d, J = 16.1 Hz, 1H). 13C{1H} NMR (100 MHz,
1
46
1
129.59, 128.89, 128.12, 128.05, 127.56, 126.71, 121.46.
CDCl3): δ (ppm) 144.14, 137.77, 130.53, 128.85, 127.72, 127.43,
40
1
E-1-(4-bromostyryl)-3-methylbenzene (9d).
White solid. H 126.59, 124.47, 124.17, 119.33, 116.41.
NMR (400 MHz, CDCl3): δ (ppm) 7.39 (d, J= 7.5 Hz, 2H), 7.30-7.17 (S)-1,2,3,11a-tetrahydro-5H-pyrrolo[1,2-a][1,4]benzodiazepin-
1
(m, 5H), 7.03-7.01 (m, 1H), 6.99 (d, J = 16.0 Hz, 1H), 6.93 (d, J = 5-one (14).47 White solid. H NMR (600 MHz, CDCl3): δ (ppm)
16.3 Hz, 1H). 13C{1H} NMR (100 MHz, CDCl3): δ (ppm) 138.45, 8.04 (d, J = 7.7 Hz, 1H), 7.78 (d, J = 4.5 Hz, 1H), 7.53 (t, J = 7.7 Hz,
137.06, 136.56, 131.92, 129.72, 128.89, 128.78, 128.09, 127.41, 1H), 7.33 (t, J = 8.6 Hz, 2H), 3.89-3.83 (m, 1H), 3.76-3.72 (m, 1H),
127.36, 123.92, 121.37, 21.56.
3.60-3.53 (m, 1H), 2.35-2.30 (m, 2H), 2.10-2.04 (m, 2H). 13C{1H}
E-1-Methyl-3-styryl-benzene (9e).41 White solid. H NMR (400 NMR (150 MHz, CDCl3): δ (ppm) 165.07, 164.56, 145.82, 131.54,
MHz, CDCl3): δ (ppm) 7.48 (d, J = 7.3 Hz, 2H), 7.34-7.28 (m, 4H), 130.40, 127.77, 126.93, 126.70, 53.65, 46.97, 29.70, 24.32.
7.24-7.20 (m, 2H), 7.06-7.04 (m, 3H), 2.35 (s, 3H). 13C{1H} NMR []d24.6 +354 (c 0.02, CHCl3); HRMS (ESI) calcd for C12H12N2O [M
(100 MHz, CDCl3): δ (ppm) 138.36, 137.61, 137.44, 128.98, + H]+: 201.1028; found, 201.1033.
1
128.81, 128.72, 128.66, 128.60, 127.68, 127.36, 126.63, 123.86, (S)-1,2,3,10,11,11a-hexahydro-5H-benzo[e]pyrrolo[1,2-
21.57.
a][1,4]diazepin-5-one (13).48 Yellow oil. 1H NMR (600 MHz,
8 | J. Name., 2012, 00, 1-3
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J. Coetzee, D. J. Cole-Hamilton, J. r. Klankermayer, W. Leitner,
CDCl3): δ (ppm) 7.94 (d, J = 8.0 Hz, 1H), 7.13 (t, J = 7.2 Hz, 1H),
6.72 (t, J = 7.6 Hz, 1H), 6.51 (d, J = 8.1 Hz, 1H), 3.85-3.81 (m, 1H),
3.78-3.74 (m, 1H), 3.64-3.60 (m, 1H), 3.49 (m, 1H), 3.29-3.26 (m,
1H), 2.21- 2.15 (m, 1H), 1.88-1.86 (m, 1H), 1.82-1.77 (m, 1H),
1.67-1.62 (m, 1H); 13C{1H} NMR (100 MHz, CDCl3): δ (ppm)
166.85, 145.37, 133.00, 131.93, 119.20, 118.05, 118.00, 57.00,
View Article Online
J. Am. Chem. Soc., 2014, 136, 13217-13225.
DOI: 10.1039/C8DT04725A
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We thank SERB, DST (ECR/2016/000108) and DST-INSPIRE (IFA-
14/CH-143) for the financial support. We are also thankful to
the CIF and the Department of Chemistry, IIT-Guwahati, for the
instrumental facilities, infrastructural support and startup
grant. We would also like to thank Gauhati University for the
measurement of Single Crystal XRD. N.B. and K.D are thankful
to the institute and B.S. is thankful to CSIR for their fellowship.
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Dalton Transactions
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DOI: 10.1039/C8DT04725A
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Acceptorless dehydrogenative construction of C=N and C=C bond catalysed by air stable
ruthenium complexes.
PPh3 Br
R3
R2 N3
Cat (1mol%)
R2
Cat (1mol%)
R1
R1
N
R1
OH
R3
tBuOK (1.3 eq)
KOH (5 mol%)
PPh3, Toluene, 135 o
C
Dioxane, 135 o
C
N
H
R1, R2, R3- alkyl, aryl, heteroaryl
N
O
Pyrrolo[1,4]benzodiazepine