C-H functionalization of tertiary amines by cross dehydrogenative coupling reactions: Solvent-free synthesis of α-aminonitriles and β-nitroamines under aerobic condition

Article abstract of DOI:10.1039/c1ob06466e

A solvent-free synthesis of α-aminonitriles and β-nitroamines by oxidative cross-dehydrogenative coupling under aerobic condition is reported. A catalytic amount of molybdenum(vi) acetylacetonoate was found to catalyze cyanation of tertiary amines to form α-aminonitriles, whereas vanadium pentoxide was found to promote aza-Henry reaction to furnish β-nitroamines. Both of these environmentally benign reactions are performed in the absence of solvents using molecular oxygen as an oxidant.

Full text of DOI:10.1039/c1ob06466e

View Article Online / Journal Homepage / Table of Contents for this issue
Organic &
Biomolecular
Chemistry
Dynamic Article Links
Cite this: Org. Biomol. Chem., 2012, 10, 835
www.rsc.org/obc
PAPER
C–H functionalization of tertiary amines by cross dehydrogenative coupling
reactions: solvent-free synthesis of a-aminonitriles and b-nitroamines under
aerobic condition†
Kaliyamoorthy Alagiri and Kandikere Ramaiah Prabhu*
Received 26th August 2011, Accepted 12th October 2011
DOI: 10.1039/c1ob06466e
A solvent-free synthesis of a-aminonitriles and b-nitroamines by oxidative cross-dehydrogenative
coupling under aerobic condition is reported. A catalytic amount of molybdenum(VI) acetylacetonoate
was found to catalyze cyanation of tertiary amines to form a-aminonitriles, whereas vanadium
pentoxide was found to promote aza-Henry reaction to furnish b-nitroamines. Both of these
environmentally benign reactions are performed in the absence of solvents using molecular oxygen as
an oxidant.
asymmetric synthesis.12,13b Hence, there is a surge in the literature
to develop methods to accomplish a- or b-amino derivatives
Introduction
of tertiary amines.13–14 In continuation of our efforts to design
methodologies under environmentally benign conditions,15 we
undertook an investigation of C–H functionalization of tertiary
amines by oxidative CDC reactions under aerobic conditions. For
this purpose, we employed TMSCN (trimethylsilyl cyanide) and
nitroalkanes as nucleophiles to functionalize tertiary amines to
accomplish bifunctional molecules such as a-aminonitriles and
b-nitroamines as presented in this paper (Scheme1).
The functionalization of C–H bonds by oxidative cross dehydro-
genative coupling (CDC) methods is a fast emerging area with
wide applications.1 Generally, CDC reactions are accomplished
by a variety of conditions using transition metal catalysts.2–5 The
prospect of using unfunctionalized precursors to construct C–
C bonds is one of the greatest advantages of CDC methods over
traditional methods.6 Further, the selectivity and simplicity shown
by these methods started showing promises in their application
in synthesizing complex natural products.1a,7 Hence, user-friendly
protocols by adopting environmentally benign strategies, particu-
larly solvent-free reaction,8 play an important role in developing
economically viable methods. Additionally, synthesis of bifunc-
tional molecules such as a-aminonitriles9 and b-nitroamines10 is
beneficial as these molecules can be easily transformed to a variety
of functional groups.9–10
The occurrence of nitrogen functionalities in biological systems,
which are commercially important molecules, is one of the
major motifs for the development of a variety of methods to
synthesize such molecules.11 In this context, direct incorporation
of nitrogen functionalities in near proximity, for example at either
a- or b-position to an amino functionality, requires a multi-step
operation.9 Functionalization of tertiary amines to synthesize
bifunctional molecules such as a- or b-amino derivatives is an
useful strategy as it provide access to valuable products,9–10 which
can be easily transformed to a variety of intermediates such as
amino acids, a-amino carbonyl compounds, a-amino alcohols
or vicinal diamines which find applications in catalysis and
Scheme 1 Cyanation of tertiary amines.
The application of CDC methods to synthesize a-aminonitriles
was first demonstrated by Murahashi and co-workers by reacting
tertiary amines with ruthenium catalyst along with NaCN, H2O2
and large excess of AcOH at 60 ◦C, 13a–c whereas Han and Ofial13d
reported synthesis of a-aminonitriles by employing Cu or Fe
catalyst along with TBHP (tert-butyl hydroperoxide) as oxidant13d,e
and TMSCN as the cyanide source under inert atmosphere.
Additional examples of synthesizing a-aminonitrile by CDC
methods employed a variety of catalysts such as vanadium,13f
Department of Organic chemistry, Indian Institute of Science, Bangalore, 560
012, Karnataka, India. E-mail: prabhu@orgchem.iisc.ernet.in; Fax: +91-80-
23600529; Tel: +91-80-22932887
† Electronic supplementary information (ESI) available: Experimental
procedures, characterization data, and NMR spectra for all products. See
DOI: 10.1039/c1ob06466e
This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 835–842 | 835
©

View Article Online
Table 1 Optimization of reaction conditions
Yield
Entry
Catalyst (mol%)
2 (equiv)
Oxidant (equiv)
Solvent
T/◦C
t/h
3aa (%)
4a (%)
1
2
3
4
5
6
7
8
5
5
2
2
2
2
2
2
2
3
2
2
2
2
2
2
2.5
1.2
2
H2O2 (2)
H2O2 (2)
TBHP (2)
TBHP (2)
TBHP (2)
TBHP (2)
O2
O2
O2
O2
O2
O2
O2
O2
O2
O2
O2
MeOH
MeOH
none
rt
50
rt
50
rt
50
60
60
75
60
60
80
100
80
80
80
80
28
12
15
15
15
15
12
14
24
24
24
24
22
17
17
24
24
—
—
34
12
50
40
77
79
24
32
12
83
93
96
93
66
trace
99
99
66
88
50
60
23
21
—
—
—
—
—
—
—
—
—
10
10
10
10
10
10
10
10
10
10
10
10
10
10
none
none
MeOH
MeOH
MeOH
MeOH
EtOAc
THF
CHCI3
CH3CN
Toluene
none
9
10
11
12
13
14
15
16
17
none
none
none
a NMR conversion based on tertiary amine; TBHP (5–6 M solution in decane), H2O2 (50% aqueous solution).
iron phthalocyanine,13g etc., as the catalyst. Recently, Hari and
Konig13h reported cyanation of tertiary amines catalyzed by eosin
Y under visible light. Further, most of these methods employ
metal cyanides along with excess of peroxides13b,d,e,g and acid
additives13a–c,f,g and use organic solvents as the reaction media13 or
utilize TMSCN with excess of TBHP (in decane) under anhydrous
conditions13d,e (Scheme 1). Utility of acid additives limit the
use of these methods in the presence of acid sensitive groups.
Additionally, the main focus of most of these methods is func-
tionalization of N,N-dimethylaniline, whereas functionalization
of N-aryltetrahydroisoquinolines are not addressed in greater
detail.13 Therefore, there is great scope to address functionalization
of tertiary amines, particularly N-aryl tetrahydroisoquinolines,
under environmentally benign conditions.
reaction in MeOH resulted in the formation of desired product
3a as the major product along with a minor amount of N-oxide
4 (Table 1, entries 7 and 8). Although, the reaction in solvents
such as EtOAc, THF or CHCl3 resulted in the formation of 3a
as the sole product, the yields were poor (Table 1, entries 9–11).
Interestingly, varying solvent of the reaction to CH3CN or toluene
brought a remarkable change, and furnished 3a as the sole product
in good yields (Table 1, entries 12 and 13). Ultimately, the optimal
reaction condition was reached by heating the reaction mixture
of 1a, MoO2(acac)2 (10 mol%), TMSCN (2 equiv), at 80 ◦C in
molecular oxygen (1 atm) under solvent-free condition to yield
the desired product 3a in excellent yield (96%, Table 1, entry 14).
However, varying the amount of TMSCN and performing the
coupling reaction did not result in improving the yields (Table 1,
entries 15–16). Notably, there was no reaction in the absence of
catalyst (Table 1, entry 17).
To generalize the reaction, a variety of tertiary amines
were reacted with TMSCN (2) using the optimal reaction
conditions, and the results are presented in Table 2. N-
Phenyltetrahydroisoquinoline (1a) underwent a smooth reaction
with 2 and MoO2(acac)2 (10 mol%), in oxygen atmosphere to
furnish the product 3a in excellent yield (96%, Table 2, entry 1).
p-Methoxyphenyl (PMP)-protected tetrahydroisoquinoline (1b)
underwent a smooth reaction with 2 to afford the product 3b
in quantitative yield (Table 2, entry 2). Further, N-phenyl-6,7-
dimethoxy-1,2,3,4-tetrahydroisoquinoline (1c) and heliotropin de-
rived N-phenyltetrahydroisoquinoline (1d) was found to react well
under the optimized condition to produce 3c and 3d in almost
quantitative yields (Table 2, entries 3 and 4). Acyclic tertiary
amines are also good precursor for this reaction, as N, N-dimethyl
aniline (1e) and 4-methyl-N,N-dimethyl aniline (1f) with 2 af-
forded 3e and 3f in good to moderate yields, respectively (Table 2,
Results and discussions
Cyanation of tertiary amines
The optimization studies for C–H functionalization were initiated
by using N-phenyl tetrahydroisoquinoline (1a) as tertiary amine
and TMSCN (2) as cyanide source along with MoO2(acac)2 in
MeOH. As depicted in Table 1, reaction of 1a, and 2 (2 equiv)
with MoO2(acac)2 (5 mol%) using H2O2 (2 equiv, 50% aqueous
solution) as oxidant was performed in MeOH. This reaction did
not furnish the desired product either at room temperature or at
50 ◦C, but produced quantitative yield of corresponding N-oxide
4 as the sole product (Table 1, entries 1 and 2). Varying the oxidant
to TBHP and performing the reaction either at room temperature
or at 50 ◦C, with or without solvent, furnished the mixture of
products 3a and 4, with 4 in major amount (Table 1, entries 3–
6). Using molecular oxygen as the oxidant and performing the
836 | Org. Biomol. Chem., 2012, 10, 835–842
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
Table 2 CDC reaction of tertiary amine and TMSCN catalyzed by
protocol. Hence, we began our studies by employing N-
phenyltetrahydroisoquinoline (1a) and nitromethane (5a) as
model substrates with catalytic amount of MoO2(acac)2 using
environmentally benign oxidants such as H2O2, TBHP or molec-
ular oxygen. Reactions of 1a and 5a (2 equiv) with MoO2(acac)2
(10 mol%) using H2O2, or TBHP as terminal oxidants in solvent
methanol either at room temperature or at 50 ◦C resulted in
the formation of a mixture of b-nitroamine 6a (as the major
product) with the corresponding N-oxide 4 in minor amount
(Table 3, entries 1–3). Our attempts to obtain 6a exclusively by
increasing the amount of nitromethane (5a) to 5 equiv, either
at room temperature or at elevated temperature, also resulted in
the formation of mixture of 6a and 4 (Table 3, entries 4 and 5).
Interestingly, MoO2(acac)2 (10 mol%) catalyzed reaction of 1a
with 5a in methanol in oxygen (1 atm) resulted in the formation
of 6a exclusively, but in lower yield (Table 3, entry 6). Further
exploration revealed that MoO3/TBHP combination in MeOH
is not helpful, as the reaction furnished a mixture of 6a and 4
(Table 3, entries 7 and 8). However, MoO3 catalyzed reaction with
1a in MeOH resulted in the formation of 6a as the only product
in 30% (Table 3, entry 9). Nevertheless, changing the catalyst to
V2O5 brought a striking change in the outcome of the reactions,
which produced the desired product 6a in excellent yields (90–91%,
Table 3, entries 10–12). Hence, reaction of 1a and 5a with V2O5
(5 mol%) in molecular oxygen (1 atm) proceeded well either in
MeOH or in water at 60 ◦C to furnish 6a exclusively in excellent
yields (24 h, 90%, Table 3, entries 10–11). It is noteworthy that the
reaction in water or methanol required only 2 equiv of 5a (entries
10–11). For our delight, the reaction of 1a with 5a in catalytic
amount of V2O5 (5 mol%) in solvent-free condition furnished 6a
in excellent yield (90%, Table 3, entry 12). On the other hand, it was
observed that the reaction of 1a with 5a in the absence of catalyst
also proceeded in oxygen atmosphere to produce 6a in low yield
(20%, Table 3, entry 13). The aza-Henry reaction of 1a catalyzed
by V2O5 (5 mol%) needed only 2 equivalents of 5a in water to
furnish the product 6a in excellent yield (90%, 24 h, entry 11, Table
3), whereas the same reaction in solvent-free condition required
5 equivalents of 5a (90%, 24h, entry 12, Table 3). As solvent-
free reactions are advantageous, we continued further exploration
by employing solvent-free condition. It is important to recognize
that most of the CDC reactions of tertiary amines employ a large
excess of nitroalkanes,14a–b,d–f whereas we used only 5 equivalents
of nitroalkanes.
a
MoO2(acac)2–O2
Entry Amine
1
Product
Yield (%)b,c
96 (80)
2
3
99 (82)
98 (82)
4
98 (86)
5
6
7
82 (70)d
52 (48)d
(50)d
a Reaction conditions: 1a (0.5 mmol), 2 (1 mmol), MoO2(acac)2, (10 mol%),
O2 (1 atm), 80 ◦C, 17 h. b NMR conversion based on tertiary amine.
c Isolated yields. d Reaction at 100 ◦C.
entries 5 and 6). Further, N-phenylpyrrolidine (1g) underwent
coupling with 2 to furnish 3g in moderate yield (50%, Table 2,
entry 7).
With this input, further experiments of tertiary amines with
nitroalkanes (5 equiv) were performed in solvent-free conditions
with a catalytic amount of V2O5 (5 mol%) in molecular oxygen (1
atm) at 60 ◦C for 24 h. A variety of N-aryltetrahydroisoquinolines
were reacted with nitromethane (5a) and nitroethane (5b). N-
Phenyltetrahydroisoquinoline (1a) reacted well with nitromethane
(5a) to furnish b-nitroamine 6a in 90%16 (Table 4, entry 1).
Reaction of p-methoxyphenyl (PMP)-protected tetrahydroiso-
quinoline (1b) proceeded well with 5a to furnish 6b in quan-
titative yield (Table 4, entry 2). Nitromethane 5a reacted well
with N-phenyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (1c)
and heliotropin derived N-phenyltetrahydroisoquinoline (1d) to
furnish the expected products 6c and 6d in good yields (90%
and 89% respectively, Table 4, entries 3–4). Further, it was found
that N-aryl-tetrahydroisoquinoline derivatives 1a–d, reacted well
with nitroethane (5b) to furnish the desired product as mixture of
CDC reaction of tertiary amines with nitroalkanes
After successful oxidative cyanation of tertiary amines, we
turned our attention to CDC reaction of tertiary amines with
nitroalkanes.14 The direct coupling between nitroalkanes with
N-aryltetrahydroisoquinolines was first reported by Li and Li
by using CuBr/TBHP (in decane) system with large excess of
nitroalkanes.14a Further, utility of Ru,14b Pt,14c Ir,14d Fe14e or DDQ14f
(stoichiometric amount) catalysts for coupling of nitroalkanes
with N-aryltetrahydroisoquinolines are documented. Inspired by
the work of Li and Li,14g and continuation of our observation on
the reaction of tertiary amines with TMSCN, we undertook an
investigation on CDC reaction of N-aryltetrahydroisoquinolines
with nitroalkanes to accomplish b-nitroamines.
We started screening the reaction conditions and reagents
with the intention of developing an environmentally benign
This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 835–842 | 837
©

View Article Online
Table 3 Optimization of reaction conditions
Yield (%)
Entry
Catalyst (mol%)
5a (equiv)
Oxidant (equiv)
Solvent
T/◦C
t/h
6aa (%)
4a (%)
1
2
3
4
5
6
7
8
MoO2(acac)2 (10)
MnO2(acac)2 (10)
MnO2(acac)2 (10)
MnO2(acac)2 (10)
MnO2(acac)2 (10)
MnO2(acac)2 (10)
MoO3(10)
MoO3(10)
MoO3(10)
V2O5 (5)
V2O5 (5)
2
2
2
5
5
2
2
2
2
2
2
5
5
H2O2 (2)
TBHP (2)
TBHP (2)
TBHP (2)
TBHP (2)
O2
TBHP (2)
TBHP (2)
O2
O2
O2
O2
O2
MeOH
MeOH
MeOH
None
None
MeOH
None
MeOH
MeOH
MeOH
H2O
None
None
rt
rt
50
rt
50
60
rt
10
10
10
10
10
24
24
24
24
24
24
24
24
53
75
73
69
57
32
40
60
30
91
90
90
20
47
25
27
31
43
—
60
40
—
—
—
—
—
rt
9
60
60
60
60
60
10
11
12
13
V2O5 (5)
None
a NMR conversion based on tertiary amine; TBHP (5–6 M solution in decane); H2O2 (50% aqueous solution).
diastereomers (around 2 : 1 ratios) in good to excellent yields (Table
4, entries 5–8). The reaction of 4-methyl-N,N-dimethylaniline (1f)
with nitromethane (5a) under the standard reaction condition
resulted in the formation of desired product 6i in 30% yield along
with inseparable complex mixture (Table 4, entry 9).
The mechanism of these reactions is not clear at this point of
time. The catalytic CDC reaction of 1a with MoO2(acac)2 or V2O5
using TMSCN or CH3NO2 as nucleophiles were carried out in the
presence of radical scavenger BHT (2,6-bis(1,1-dimethylethyl)-4-
methylphenol)17 to find out that both the reactions proceeded for
completion, thereby eliminating the radical pathway. As N-oxide
is formed in the reactions of 1a with TMSCN or CH3NO2 under
standard reaction conditions, we subjected N-oxide for CDC
reactions under standard reaction conditions with molybdenum
or vanadium catalysts. However, these reactions did not produce
the desired products even after prolonged reaction time. Based on
this information, a tentative mechanism is presented in Scheme
2, which involves coordination of a metal species with tertiary
Scheme 2 Plausible mechanism for CDC reaction of tertiary amine.
amine 1a to give I, which forms iminium ion intermediate II.
Then II reacts with either TMSCN or nitroalkane to furnish the
corresponding products 3a or 6a.
synthesis of natural products and mechanistic study are presently
pursued in our laboratories.
Conclusions
Experimental
In conclusion, we have demonstrated environmentally benign
CDC reactions to accomplish a-aminonitriles and b-nitroamines
in user-friendly methods. The present methods employ molecular
oxygen as the terminal oxidant, and the reactions are performed
under solvent-free conditions. One of the salient features of the
present CDC method is that the reaction is performed in acid-free
and solvent-free conditions. We believe that the simplicity offered
by the present methods to accomplish bifunctional molecule such
as a-aminonitriles or b-nitroamines makes the methodology more
useful and attractive. Application of this methodology for the
Typical experimental procedure for the synthesis of a-aminonitrile
To 10 mol% of MoO2(acac)2 (0.05 mmol) and N-
phenyltetrahydroisoquinoline (0.5 mmol) was added TMSCN
(1.0 mmol). The reaction mixture was stirred at 80 ◦C under oxygen
atmosphere (oxygen balloon) for 17 h. The reaction mixture was
cooled to room temperature, added saturated NaHCO3 solution
and extracted with DCM (3 ¥ 10 mL). The combined organic layer
was dried over Na2SO4 and concentrated under reduced pressure.
The crude product was purified by column chromatography on
838 | Org. Biomol. Chem., 2012, 10, 835–842
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
a
Table 4 CDC reaction of tertiary amine and nitroalkane catalyzed by V2O5–O2
Entry
1
Amine
Nitroalkane
Product
Yield (%)b,c
90 (76)
CH3NO2 5a
2
3
5a
5a
99 (82)d
90 (78)
4
5
6
7
5a
89 (79)e
86 (65)e
99 (70)d,e
85 (71)f
1a
1b
1c
5b
5b
8
9
1d
1f
5b
5a
86 (70)f
(30)
a Reaction conditions: 1a (0.5 mmol), 5a or 5b (2.5 mmol), V2O5 (5 mol%), O2 (1 atm), 60 ◦C, 24 h. b NMR conversion based on tertiary amine. c Isolated
yields. d Reaction has completed in 16 h. e 2 : 1 mixture of diastereomers. f 1.8 : 1 mixture of diastereomers.
silicagel using hexane/ethyl acetate (95 : 5) and furnished a pale
yellow solid (78%, NMR conversion = 96%).
as shown in general experimental procedure. IR (KBr, cm-1): 2824,
2222, 1595, 1496, 1452, 1374, 1273, 1205, 1141, 1027, 936, 888, 745;
1H NMR (400 MHz, CDCl3): d 7.37–7.32 (2H, m), 7.31– 7.26 (3H,
m), 7.23 (1H, d, J = 7.2 Hz), 7.08 (2H, d, J = 7.8 Hz), 7.01 (1H,
t, J = 7.3 Hz), 5.50 (1H, s), 3.76 (1H, dddd, J = 12.4, 5.9, 3.0 and
1.0 Hz), 3.48 (1H, ddd, J = 14.8, 10.7 and 4.0 Hz), 3.19–3.11 (1H,
Characterization data for a-aminonitriles
C◦ompound (3a)13a
.
◦Pale yellow solid; yield: 80%; mp: 99–
101 C (lit.13a 101–102 C); Rf (20% EtOAc/hexane) 0.7; prepared
This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 835–842 | 839
©

View Article Online
m), 2.96 (1H, dt, J1 = 3.5 Hz, J2 = 16.3 Hz); 13C NMR (100 MHz,
CDCl3): d 148.3, 134.6, 129.6, 129.5, 129.3, 128.7, 127.0, 126.8,
121.8, 117.7, 117.6, 53.2, 44.2, 28.5; MS (m/z): 234 (M+); elemental
analysis: calcd for C16H14N2: C, 82.02; H, 6.02; N, 11.96%; found
C, 81.64; H, 6.50; N, 11.88%.
Compound (3g)13d
EtOAc/hexane) 0.3; prepared as shown in general experimental
procedure. IR (Neat, cm-1): 2854, 2230, 1600, 1502, 1360, 1255,
.
Pale yellow liquid; yield 50%; Rf (10%
1
1186, 1157, 749, 691; H NMR (400 MHz, CDCl3): d 7.31–7.28
(2H, m), 6.83 (1H, t, J = 7.3 Hz), 6.69 (2H, d, J = 8.2 Hz), 4.46–4.43
(1H, m), 3.48–3.44 (1H, m), 3.39–3.33 (1H, m), 2.44–2.16 (4H, m);
13C NMR (100 MHz, CDCl3): d 145.1, 129.3, 119.2, 118.0, 112.6,
48.9, 47.3, 31.4, 23.8; MS (m/z): 172 (M+); HRESI-MS (m/z):
Calculated for C11H12N2 (M + H): 173.1079, found (M + H):
173.1077.
Compound (3b)13d
. Pale yellow solid; yield: 82%; mp: 107–
108 ◦C; Rf (20% EtOAc/hexane) 0.5; prepared as shown in general
experimental procedure. IR (KBr, cm-1): 2937, 2222, 1615, 1505,
1260, 1206, 1031, 888, 733; 1H NMR (400 MHz, CDCl3): d 7.30–
7.21 (4H, m), 7.08 (2H, d, J = 8.9 Hz), 6.91 (2H, d, J = 8.9 Hz),
5.36 (1H, s), 3.79 (3H, s), 3.57 (1H, dd, J1 = 6.0 Hz, J2 = 12.0 Hz),
3.43 (1H, td, J1 = 3.9 Hz, J2 = 11.7 Hz), 3.19–3.11 (1H, m),
2.94–2.90 (1H, m); 13C NMR (100 MHz, CDCl3): d 155.6, 142.5,
134.3, 129.7, 129.4, 128.6, 127.0, 126.6, 120.9, 117.6, 114.7, 55.51,
55.5, 44.9, 28.6; MS (m/z): 264 (M+); elemental analysis: calcd for
C17H16N2O: C, 77.25; H, 6.10; N, 10.60%; found: C, 77.39; H, 5.92;
N, 10.87%.
Compound (4). Pale yellow solid; yield 99%; mp: 150–152 ◦C;
Rf (20% EtOAc/hexane) 0.6; prepared as shown in general
experimental procedure. IR (KBr, cm-1): 3424, 2925, 1597, 1489,
1352, 1269, 1115, 1055, 968, 753; 1H NMR (400 MHz, CDCl3): d
7.99–7.97 (2H, m), 7.48–7.46 (2H, m), 7.44– 7.38 (1H, m), 7.29–
7.22 (3H, m), 7.09–7.04 (1H, m), 5.05 (1H, d, J = 15.2 Hz), 4.57
(1H, d, J = 15.2 Hz), 4.17–4.10 (1H, m), 3.81–3.73 (1H, m), 3.68–
3.63 (1H, m), 2.84 (1H, dt, J1 = 4.5 Hz, J2 = 16.8 Hz); 13C NMR (100
MHz, CDCl3): d 154.0, 131.2, 130.0, 129.1, 128.9, 128.5, 127.4,
126.7, 126.3, 120.5, 65.5, 28.4, 26.2; HRESI-MS (m/z): Calculated
for C15H15NO (M + Na): 248.1051, found (M + Na): 248.1044.
Compound (3c). Pale yellow solid; yield 82%; mp: 111–114 ◦C;
Rf (30% EtOAc/hexane) 0.3; prepared as shown in general
experimental procedure. IR (KBr, cm-1): 2933, 2219, 1605, 1506,
1270, 1215, 1025, 856, 761; 1H NMR (400 MHz, CDCl3): d 7.35
(2H, t, J = 8 Hz), 7.09–7.06 (2H, m), 7.03–6.99 (1H, m), 6.75 (1H,
s), 6.68 (1H, s), 5.44 (1H, s), 3.88 (6H, s), 3.79–3.74 (1H, m), 3.44
(1H, td, J1 = 4.0 Hz, J2 = 11.4 Hz), 3.12–3.03 (1H, m), 2.84 (1H,
dt, J1 = 3.2 Hz, J2 = 16.0 Hz); 13C NMR (100 MHz, CDCl3): d
149.3, 148.4, 148.0, 129.5, 126.8, 121.8, 121.1, 117.8, 117.7, 111.5,
109.3, 56.0, 55.9, 53.0, 44.1, 28.0; MS (m/z): 294 (M+); elemental
analysis: calcd for C18H18N2O2: C, 73.45; H, 6.16; N, 9.52%; found
C, 73.18; H, 6.46; N, 9.23%.
Typical experimental procedure for the synthesis of b-nitroamines
To the
5
mol% of V2O5 (0.025 mmol) and N-
phenyltetrahydroisoquinoline (0.5 mmol) was added nitromethane
(2.5 mmol). The reaction mixture was stirred at 60 ◦C under
oxygen atmosphere (oxygen balloon) for 24 h. The reaction
mixture was cooled to room temperature, added saturated
NaHCO3 solution and extracted with DCM (3 ¥ 10 mL). The
combined organic layer was dried over Na2SO4 and concentrated
under reduced pressure. The crude product was purified by
column chromatography on silica gel using hexane/ethyl acetate
(95 : 5) and furnished pale yellow solid (76%, NMR conversion =
90%).
Compound (3d). Pale yellow solid; yield 86%; mp: 154–156 ◦C;
Rf (20% EtOAc/hexane) 0.6; prepared as shown in general
experimental procedure. IR (KBr, cm-1): 2919, 2213, 1598, 1504,
1
1234, 1190, 1037, 948, 838, 755; H NMR (400 MHz, CDCl3):
d 7.35 (2H, t, J = 7.9 Hz), 7.07–7.00 (3H, m), 6.72 (1H, s), 6.66
(1H, s), 5.96 (2H, s), 5.38 (1H, s), 3.75–3.70 (1H, m), 3.43 (1H, td,
J1 = 4.0 Hz, J2 = 11.3 Hz), 3.09–3.01 (1H, m), 2.86–2.82 (1H, m);
13C NMR (100 MHz, CDCl3): d 148.2, 148.1, 146.6, 129.5, 128.3,
122.1, 121.9, 117.7, 117.5, 108.8, 106.6, 101.3, 53.2, 44.1, 28.5;
MS (m/z): 278 (M+); elemental analysis: calcd for C17H14N2O2: C,
73.37; H, 5.07; N, 10.07%; found C, 73.39; H, 5.29; N, 9.70%.
Characterization data for b-nitroamines
Compound (6a)14a
.
Pale yellow solid; yield 76%; mp: 90–92 ◦C
(lit.14a 89–90 ◦C); Rf (20% EtOAc/hexane) 0.5; prepared as shown
in general experimental procedure. IR (KBr, cm-1): 2917, 1598,
1550, 1378, 1217, 1031, 750; 1H NMR (400 MHz, CDCl3): d 7.27–
7.14 (5H, m), 7.10 (1H, d, J = 7.3 Hz), 6.95 (2H, d, J = 8.5 Hz),
6.82 (1H, t, J = 7.3 Hz), 5.52 (1H, t, J = 7.2 Hz), 4.82 (1H, dd, J1 =
7.8 Hz, J2 = 11.8 Hz), 4.51 (1H, dd, J1 = 6.6 Hz, J2 = 11.8 Hz),
3.66–3.54 (2H, m), 3.09–3.01 (1H, m), 2.75 (1H, dt, J1 = 4.9 Hz,
J2 = 16.3 Hz); 13C NMR (100 MHz, CDCl3): d 148.4, 135.2, 132.8,
129.4, 129.1, 128.0, 126.9, 126.6, 119.3, 115.0, 78.7, 58.1, 42.0, 26.3;
MS (m/z): 268 (M+); elemental analysis: calcd for C16H16N2O2: C,
71.62; H, 6.01; N, 10.44%; found C, 71.57; H, 5.93; N, 10.31%.
Compound (3e)13d
. Pale yellow liquid; yield 70%; Rf (20%
EtOAc/hexane) 0.5; prepared as shown in general experimental
procedure. IR (Neat, cm-1): 2927, 2237, 1600, 1499, 1343, 1246,
1
1201, 1118, 1033, 999, 868, 755; H NMR (400 MHz, CDCl3):
d 7.33–7.29 (2H, m), 6.91 (1H, t, J = 7.3 Hz), 6.87 (2H, d, J =
8.3 Hz), 4.16 (2H, s), 3.00 (3H, s); 13C NMR (100 MHz, CDCl3): d
147.7, 129.4, 120.2, 115.4, 114.8, 42.2, 39.2; MS (m/z): 146 (M+).
Compound (3f)13d
EtOAc/hexane) 0.4; prepared as shown in general experimental
procedure. IR (Neat, cm-1): 2923, 2236, 1618, 1518, 1341, 1245,
.
Pale yellow liquid; yield 48%; Rf (10%
Compound (6b)14a
.
◦ Pale yellow solid; yield 82%; mp: 100–
102 ◦C (lit.13j 102–105 C); Rf (20% EtOAc/hexane) 0.5; prepared
as shown in general experimental procedure. IR (KBr, cm-1): 2932,
1548, 1512, 1246, 1183, 1035, 948, 826, 753; 1H NMR (400 MHz,
CDCl3): d 7.25–7.20 (2H, m), 7.17–7.12 (2H, m), 6.91 (2H, d, J =
9.0 Hz), 6.81 (2H, d, J = 9.0 Hz), 5.38 (1H, dd, J1 = 6.0 Hz, J2 =
8.4 Hz), 4.82 (1H, dd, J1 = 8.6 Hz, J2 = 11.9 Hz), 4.55 (1H, dd, J1 =
5.8 Hz, J2 = 11.9 Hz), 3.74 (3H, s), 3.57–3.54 (2H, m), 3.05–2.97
(1H, m), 2.69 (1H, dt, J1 = 4.0 Hz, J2 = 16.5 Hz); 13C NMR (100
1
1194, 1115, 1039, 997, 868, 808; H NMR (400 MHz, CDCl3):
d 7.11 (2H, d, J = 8.2 Hz), 6.78 (2H, d, J = 8.6 Hz), 4.10 (2H,
s), 2.94 (3H, s), 2.28 (3H, s); 13C NMR (100 MHz, CDCl3): d
145.6, 129.9, 129.7, 115.4, 115.3, 42.7, 39.4, 20.3; MS (m/z): 160
(M+); elemental analysis: calcd for C10H12N2: C, 74.97; H, 7.55; N,
17.48%; found C, 74.99; H, 7.41; N, 17.04%.
840 | Org. Biomol. Chem., 2012, 10, 835–842
This journal is
The Royal Society of Chemistry 2012
©

View Article Online
MHz, CDCl3): d 154.0, 143.0, 135.4, 132.9, 129.4, 127.9, 126.9,
126.6, 118.9, 114.7, 78.9, 58.9, 55.6, 43.1, 25.8; MS (m/z): 298
(M+); elemental analysis: calcd for C17H18N2O3: C, 68.44; H, 6.08;
N, 9.39%; found C, 68.42; H, 6.30; N, 9.19%.
elemental analysis: calcd for C18H20N2O3: C, 69.21; H, 6.45; N,
8.97%; found C, 69.00; H, 6.11; N, 8.47%.
Compound (6g). Pale yellow liquid; yield 71%; Rf (30%
EtOAc/hexane) 0.6; prepared as shown in general experimental
procedure. IR (Neat, cm-1): 2927, 1599, 1550, 1518, 1389, 1357,
Compound (6c)14a
. Pale yellow solid; yield 78%; mp: 118–
1
120 ◦C; Rf (30% EtOAc/hexane) 0.5; prepared as shown in general
1259, 1112, 1033, 867, 750; H NMR (400 MHz, CDCl3, 1.8 : 1
experimental procedure. IR (KBr, cm-1): 2932, 1599, 1544, 1264,
1247, 1110, 1031, 988, 852, 752; H NMR (400 MHz, CDCl3):
mixture of diastereoisomers): d 7.28–7.21 (2H, m), 6.98 (2H, t,
J = 8.7 Hz), 6.81 (1H, t, J = 7.2 Hz), 6.64–6.49 (2H, m), 5.17–5.11
(1H, m), 5.07–4.87 (1H, m), 3.86–3.75 (6H, m), 3.64–3.46 (1H, m),
3.00–2.92 (1H, m), 2.82–2.68 (1H, m), 1.69 (1H, d, J = 6.8 Hz), 1.53
(2H, d, J = 6.6 Hz); 13C NMR (100 MHz, CDCl3, 2 : 1 mixture of
diastereoisomers): d 149.2, 148.9, 148.8, 148.6, 147.3, 147.1, 129.3,
129.2, 127.8, 126.8, 125.5, 123.5, 119.4, 118.9, 115.6, 115.0, 111.53,
111.5, 111.1, 110.2, 88.9, 85.3, 62.4, 60.9, 56.0, 55.9, 55.79, 55.76,
43.3, 42.6, 25.9, 25.8, 17.5, 16.1; MS (m/z): 342 (M+); elemental
analysis: calcd for C19H22N2O4: C, 66.65; H, 6.48; N, 8.18%; found
C, 66.68; H, 6.71; N, 8.17%.
1
d 7.28–7.24 (2H, m), 6.96 (2H, d, J = 8.3 Hz), 6.84 (1H, t, J =
7.3 Hz), 6.64 (1H, s), 6.60 (1H, s), 5.45 (1H, t, J = 7.0 Hz), 4.84
(1H, dd, J1 = 8.0 Hz, J2 = 11.8 Hz), 4.55 (1H, dd, J1 = 6.4 Hz, J2 =
11.8 Hz), 3.85 (3H, s), 3.84 (3H, s), 3.70–3.64 (1H, m), 3.60–3.53
(1H, m), 3.03–2.95 (1H, m), 2.67 (1H, dt, J1 = 4.5 Hz, J2 = 16.1 Hz);
13C NMR (100 MHz, CDCl3): d 148.8, 148.6, 147.7, 129.4, 127.4,
124.5, 119.5, 115.5, 111.7, 109.6, 78.7, 57.9, 56.0, 55.9, 42.0, 25.8;
MS (m/z): 328 (M+); elemental analysis: calcd for C18H20N2O4: C,
65.84; H, 6.14; N, 8.53%; found C, 65.71; H, 6.28; N, 8.71%.
Compound (6h). Pale yellow liquid; yield 70%; Rf (20%
EtOAc/hexane) 0.6; prepared as shown in general experimen-
tal procedure. IR (Neat, cm-1): 2903, 1490, 1381, 1241, 1226,
Compound (6d). Pale yellow solid; yield 79%; mp: 121–123 ◦C;
Rf (20% EtOAc/hexane) 0.5; prepared as shown in general
experimental procedure. IR (KBr, cm-1): 2901, 1598, 1548, 1487,
1382, 1233, 1040, 942, 756; 1H NMR (400 MHz, CDCl3): d 7.28–
7.24 (2H, m), 6.94 (2H, d, J = 8.3 Hz), 6.84 (1H, t, J = 7.3 Hz),
6.62 (1H, s), 6.59 (1H, s), 5.91 (2H, s), 5.40 (1H, t, J = 7.2 Hz),
4.81 (1H, dd, J1 = 7.8 Hz, J2 = 11.8 Hz), 4.50 (1H, dd, J1 = 6.6 Hz,
J2 = 11.8 Hz), 3.62–3.51 (2H, m), 2.99–2.91 (1H, m), 2.66 (1H, dt,
J1 = 5.0 Hz, J2 = 16.2 Hz); 13C NMR (100 MHz, CDCl3): d 148.4,
147.4, 146.3, 129.4, 128.8, 125.7, 119.5, 115.2, 108.9, 106.9, 101.1,
78.7, 58.1, 42.1, 26.4; MS (m/z): 312 (M+); elemental analysis:
calcd for C17H16N2O4: C, 65.38; H, 5.16; N, 8.97%; found C, 65.36;
H, 5.29; N, 9.04%.
1
1038, 941, 749; H NMR (400 MHz, CDCl3, 1.8 : 1 mixture of
diastereoisomers): d 7.29–7.21 (2H, m), 6.96 (2H, d, J = 8.1 Hz),
6.84–6.80 (1H, m), 6.61–6.50 (2H, m), 5.93–5.88 (2H, m), 5.13–
4.83 (2H, m), 3.80–3.49 (2H, m), 2.97–2.90 (1H, m), 2.81–2.74
(1H, m), 1.68 (1H, d, J = 6.8 Hz), 1.54 (2H, d, J = 6.5 Hz); 13C
NMR (100 MHz, CDCl3, 2 : 1 mixture of diastereoisomers): d
149.1, 148.9, 147.5, 147.4, 146.1, 145.9, 129.4, 129.3, 129.2, 128.4,
126.7, 124.8, 119.4, 118.9, 115.6, 114.6, 108.9, 108.7, 108.3, 107.6,
101.1, 101.0, 89.0, 85.5, 62.8, 61.1, 43.6, 42.6, 26.7, 26.4, 17.5, 16.5;
MS (m/z): 326 (M+); elemental analysis: calcd for C18H18N2O4: C,
66.25; H, 5.56; N, 8.58%; found C, 66.01; H, 6.10; N, 8.24%.
Compound (6e)14a
. Pale yellow liquid; yield 65%; Rf (20%
Compound (6i)14a
.
Pale yellow liquid; yield 30%; Rf (10%
EtOAc/hexane) 0.6; prepared as shown in general experimental
procedure. IR (Neat, cm-1): 2921, 1598, 1549, 1503, 1388, 1358,
1233, 1117, 948, 750; 1H NMR (400 MHz, CDCl3, 2 : 1 mixture of
diastereoisomers): d 7.29–7.08 (6H, m), 7.01–6.97 (2H, m), 6.83–
6.79 (1H, m), 5.26–5.21 (1H, m), 5.07–4.84 (1H, m), 3.86–3.50
(2H, m), 3.08–3.00 (1H, m), 2.93–2.83 (1H, m), 1.69 (1H, d, J =
6.8 Hz), 1.53 (2H, d, J = 6.6 Hz); 13C NMR (100 MHz, CDCl3, 2 : 1
mixture of diastereoisomers): d 149.1, 148.8, 135.6, 134.7, 133.8,
132.0, 129.4, 129.3, 129.1, 128.7, 128.3, 128.2, 127.2, 126.5, 126.1,
119.3, 118.7, 115.4, 114.4, 88.9, 85.4, 62.7, 61.1, 43.5, 42.6, 26.7,
26.3, 17.4, 16.3; MS (m/z): 282 (M+); elemental analysis: calcd for
C17H18N2O2: C, 72.32; H, 6.43; N, 9.92%; found C, 72.08; H, 6.36;
N, 10.20%.
EtOAc/hexane) 0.35; prepared as shown in general experimental
procedure. IR (Neat, cm-1): 2928, 1654, 1546, 1349, 1122, 1020,
805, 743; 1H NMR (400 MHz, CDCl3): d 7.08 (2H, d, J = 8.3 Hz),
6.66 (2H, d, J = 8.4 Hz), 4.55 (2H, t, J = 6.3 Hz), 3.96 (2H, t, J =
6.3 Hz), 2.94 (3H, s), 2.26 (3H, s); 13C NMR (100 MHz, CDCl3):
d 145.8, 130.0, 127.5, 113.2, 72.6, 51.0, 39.0, 20.2; MS (m/z): 194
(M+); HRESI-MS (m/z): Calculated for C10H14N2O2 (M + H):
195.1134, found (M + H): 195.1133.
Acknowledgements
The authors thank Indian Institute of Science and CSIR, New-
Delhi for financial support of this investigation. Dr A. R. Ramesha
and Prof. Sosale Chandrasekhar for useful discussion. One of
the authors (KA) thanks CSIR, New-Delhi for a senior research
fellowship
Compound (6f)14a
. Pale yellow liquid; yield 70; Rf (20%
EtOAc/hexane) 0.6; prepared as shown in general experimental
procedure. IR (Neat, cm-1): 2925, 1643, 1549, 1512, 1358, 1246,
1100, 949, 755; 1H NMR (400 MHz, CDCl3, 2 : 1 mixture of
diastereoisomers): d 7.24–7.09 (4H, m), 6.92–6.90 (2H, m), 6.83–
6.77 (2H, m), 5.07–4.82 (2H, m), 3.77–3.71 (4H, m), 3.52–3.47
(1H, m), 3.01–2.93 (1H, m), 2.84–2.75 (1H, m), 1.67 (1H, d, J =
6.8 Hz), 1.52 (2H, d, J = 5.9 Hz); 13C NMR (100 MHz, CDCl3,
2 : 1 mixture of diastereoisomers): d 153.8, 153.5, 143.5, 135.8,
135.0, 133.6, 132.0, 129.2, 128.9, 128.3, 128.0, 127.9, 127.2, 126.5,
126.0, 118.85, 118.82, 118.2, 114.7, 114.5, 88.8, 85.7, 63.4, 62.1,
55.6, 55.5, 45.0, 45.0, 26.2, 26.0, 17.1, 16.5; MS (m/z): 312 (M+);
Notes and references
1 CDC reviews: (a) C. S. Yeung and V. M. Dong, Chem. Rev., 2011, 111,
1215; (b) C.-J. Li, Acc. Chem. Res., 2009, 42, 335; (c) C. J. Scheuermann,
Chem.–Asian J., 2010, 5, 436; (d) S.-I. Murahashi and D. Zhang, Chem.
Soc. Rev., 2008, 37, 1490; (e) Z. Li, D. S. Bohle and C.-J. Li, Proc. Natl.
Acad. Sci. U. S. A., 2006, 103, 8928.
2 Indolation by CDC: (a) Z. Li and C.-J. Li, J. Am. Chem. Soc., 2005,
127, 6968; (b) M. Ghobrial, K. Harhammer, M. D. Mihovilovic and
M. Schnurch, Chem. Commun., 2010, 46, 8836; (c) P. Liu, C.-Y. Zhou,
This journal is
The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 835–842 | 841
©

View Article Online
S. Xiang and C. M. Che, Chem. Commun., 2010, 46, 2739; (d) F. Yang,
J. Li, J. Xie and Z.-Z. Huang, Org. Lett., 2010, 12, 5214; (e) M.-Z.
Wang, C.-Y. Zhou, M.-K. Wong and C.-M. Che, Chem.–Eur. J., 2010,
16, 5723.
3 Phosphonation by CDC: (a) O. Basle and C.-J. Li, Chem. Commun.,
2009, 4124; (b) W. Han and A. R. Ofial, Chem. Commun., 2009, 6023;
(c) W. Han, P. Mayer and A. R. Ofial, Adv. Synth. Catal., 2010, 352,
1667.
4 Mannich-like reaction by CDC: (a) A. Sud, D. Sureshkumar and M.
Klussmann, Chem. Commun., 2009, 3169; (b) Y. Shen, M. Li, S. Wang,
T. Zhan, Z. Tan and C.-C. Guo, Chem. Commun., 2009, 953; (c) F.
Yang, J. Li, J. Xie, Huang and Z. –Z, Org. Lett., 2010, 12, 5214.
5 CDC of glycine ester: (a) L. Zhao and C.-J. Li, Angew. Chem., Int. Ed.,
2008, 47, 7075; (b) J. Xie and Z-Z. Huang, Angew. Chem., Int. Ed.,
2010, 49, 10181.
6 (a) R. B. Bedford, C. S. J. Cazin and D. Holder, Coord. Chem. Rev.,
2004, 248, 2283; (b) E.-I. Negishi, Acc. Chem. Res., 1982, 15, 340.
7 (a) F. Kakiuchi and N. Chatani, Adv. Synth. Catal., 2003, 345, 1077,
and references therein; (b) K. R. Campos, Chem. Soc. Rev., 2007, 36,
1069, and references therein.
8 P. J. Walsh, H. Li and C. A. D. Parrodi, Chem. Rev., 2007, 107, 2503.
9 (a) M. North, Angew. Chem., Int. Ed., 2004, 43, 4126, and refereces
therein; (b) D. Enders and J. P. Shilvock, Chem. Soc. Rev., 2000, 29,
359.
10 H. H. Baer and L. Urbas, In The Chemistry of the Nitro and Nitroso
Group, S. Patai, Ed.; Interscience, New York, 1970; Part 2, p 117.
11 C. Geoffrey, Introduction to Alkaloids, Wiley, New York, 1981.
12 (a) L. Bernardi, B. F. Bonini, E. Capito, G. Dessole, M. Comes-
Franchini, M. Fochi and A. Ricci, J. Org. Chem., 2004, 69, 8168, and
references therein; (b) H. Adams, J. C. Anderson, S. Peace and A. M.
K. Pennell, J. Org. Chem., 1998, 63, 9932; (c) R. Ballini and M. Petrini,
Tetrahedron, 2004, 60, 1017, and references therein.
13 Cyanation by CDC: (a) S.-I. Murahashi, N. Komiya, H. Terai and T.
Nakae, J. Am. Chem. Soc., 2003, 125, 15312; (b) S.-I. Murahashi, N.
Komiya and H. Terai, Angew. Chem., Int. Ed., 2005, 44, 6931, and
references therein; (c) S.-I. Murahashi, T. Nakae, H. Terai and N.
Komiya, J. Am. Chem. Soc., 2008, 130, 11005; (d) W. Han and A. R.
Ofial, Chem. Commun., 2009, 5024; (e) Y. Zhang, H. Peng, M. Zhang,
Y. Cheng and C. Zhu, Chem. Commun., 2011, 47, 2354; (f) S. Singhal,
S. L. Jain and B. Sain, Chem. Commun., 2009, 2371; (g) S. Singhal, S.
L. Jain and B. Sain, Adv. Synth. Catal., 2010, 352, 1338; (h) D. P. Hari
and B. Konig, Org. Lett., 2011, 13, 3852; (i) Z. Li and C.-J. Li, Eur. J.
Org. Chem., 2005, 3173; (j) X-Z. Shu, X.-F. Xia, Y.-F. Yang, K.-G. Ji,
X.-Y. Liu and Y.-M. Liang, J. Org. Chem., 2009, 74, 7464.
14 Aza-Henry reaction by CDC: (a) Z. Li and C. J. Li, J. Am. Chem. Soc.,
2005, 127, 3672; (b) A. Yu, Z. Gu, D. Chen, W. He, P. Tan and J. Xiang,
Catal. Commun., 2009, 11, 162; (c) X.-Z. Shu, X. F. Xia, Y.-F. Yang,
K.-G. Ji, X.-Y. Liu and Y.-M. Liang, Org. Biomol. Chem., 2010, 8, 4077;
(d) A. G. Condie, J. C. Gonzalez-Gomez and C. R. J. Stephenson, J.
Am. Chem. Soc., 2010, 132, 1464; (e) T. Zeng, G. Song, A. Moores and
C.-J. Li, Synlett, 2010, 13, 2002; (f) A. S.-K. Tsang and M. H. Todd,
Tetrahedron Lett., 2009, 50, 1199; (g) O. Basle and C-J. Li, Green Chem.,
2007, 9, 1047; (h) O. Basle, N. Borduas, P. Dubois, J. M. Chapuzet, T.-H.
Chan, J. Lessard and C.-J. Li, Chem.–Eur. J., 2010, 16, 8162.
15 (a) M. Lamani and K. R. Prabhu, Angew. Chem., Int. Ed., 2010, 49,
6622; (b) M. Maddani and K. R. Prabhu, J. Org. Chem., 2010, 75,
2327; (c) M. Maddani and K. R. Prabhu, Tetrahedron Lett., 2008, 49,
4526; (d) M. Maddani and K. R. Prabhu, Tetrahedron Lett., 2007, 48,
7151.
16 The products are unstable under column chromatography conditions.
Although the conversions were very good, there was some loss during
purification which resulted in lower yields.14a
.
17 The reaction of vanadium catalyst with 1a and 5a with BHT (2 equiv.)
took longer time and shown 50% of formation of the product.
842 | Org. Biomol. Chem., 2012, 10, 835–842
This journal is
The Royal Society of Chemistry 2012
©