HBF4·OEt2: An efficient fluorinated acid catalyst for the one-pot synthesis of secondary and tertiary N-homoallylic carbamates

Article abstract of DOI:10.1016/j.jfluchem.2014.06.028

An efficient method for the one-pot synthesis of secondary and tertiary N-homoallylic carbamates using catalytic amount of HBF₄·OEt₂is described. The reaction proceeded smoothly to afford the corresponding N-homoallylic carbamates in good to high yields. Operationally simple and easily scalable features make this method more practical over existing methods. Use of HBF₄·OEt₂as an acid catalyst also proves the catalytic activity of fluorinated acid catalyst in this important organic transformation.

Full text of DOI:10.1016/j.jfluchem.2014.06.028

Journal of Fluorine Chemistry 166 (2014) 1–7
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
HBF4ÁOEt2: An efficient fluorinated acid catalyst for the one-pot
synthesis of secondary and tertiary N-homoallylic carbamates
*
Gakul Baishya , Nabajyoti Hazarika, Barnali Sarmah
Natural Products Chemistry Division, CSIR-North East Institute of Science & Technology, Jorhat 785006, Assam, India
A R T I C L E I N F O
A B S T R A C T
Article history:
An efficient method for the one-pot synthesis of secondary and tertiary N-homoallylic carbamates using
catalytic amount of HBF4ÁOEt2 is described. The reaction proceeded smoothly to afford the corresponding
N-homoallylic carbamates in good to high yields. Operationally simple and easily scalable features make
this method more practical over existing methods. Use of HBF4ÁOEt2 as an acid catalyst also proves the
catalytic activity of fluorinated acid catalyst in this important organic transformation.
ß 2014 Elsevier B.V. All rights reserved.
Received 11 April 2014
Received in revised form 26 June 2014
Accepted 30 June 2014
Available online 8 July 2014
Key-words:
Fluorinated acid catalyst HBF4ÁOEt2
Three-component reaction
Secondary and tertiary N-homoallylic
carbamates
1. Introduction
Cu(OTf)2 [1f] have also been employed as catalysts to promote this
important consecutive C-N and C-C bond forming reaction to
The three-component reaction of aldehyde or ketone, carba-
mate and semi metallic allyl-reagent of Si [1] or Sn [2] for the
synthesis of N-homoallylic carbamate or N-protected homoallylic
amines has become an important C–C bond forming reaction. In
recent years, this synthetic transformation has been utilized as a
direct method for the introduction of an amino group into carbon
frameworks, because this eliminates the prior isolation of
aldimines or its precursors amidosulfones and their subsequent
allylation [3,4]. The resultant N-homoallylic carbamates and their
derivatives are found to be useful intermediates in natural
produce secondary N-homoallylic carbamates. Phosphomolybdic
acid [1e] is also known to catalyze this one-pot three-component
reaction. Although a number of methods have already been
reported in the literature for the synthesis of N-homoallylic
carbamates, most of them possess at least one of the following
drawbacks: (i) excess use of acid catalysts [1c,9], (ii) use of
expensive metal triflates [1c,1f], (iii) prior silylation of the
carbamates [1a] and (iv) long reaction time [1f]. Although I2 has
been used as a cheap, readily available and efficient catalyst for this
transformation; it has not been explored with any ketone
counterpart [1d]. Recently, Ghorai et al. [10] described an efficient
method for the one-pot synthesis of secondary and tertiary N-
homoallylic carbamates in high yields from aldehydes or ketones,
carbamates and allyltrimethylsilane under mild reaction condition
(Scheme 1). But authors used very expensive Re2O7 as a transition
metal catalyst. Hence, a novel method employing readily available,
inexpensive and easy-to-handle transition metal-free catalyst
which can efficiently promote this important transformation is still
of interest for synthetic chemists (Scheme 1).
products synthesis [5] and in
b-lactam chemistry [6], and also
in drug discovery [7]. Although allylsilanes are less reactive than
allyltins, their stability and low toxicity make themselves more
desirable reagents from the point of green chemistry. Panek et al.
[8] first reported the one-pot synthesis of homoallylic amines by
using a stoichiometric amount of Lewis acid BF3.OEt2 as a
promoter. Subsequently, Veenstra et al. [9] established an
improved method by using carbamates instead of amines to
afford the N-protected homoallylic amines or N-homoallylic
carbamates. However, the main drawback of this method is the
use of stoichiometric amount of the promoter. Other Lewis acids
such as triphenyl methyl perchlorate [1a], Bi(OTf)3 [1c], I2 [1d],
Recently, the fluorinated acid HBF4ÁOEt2 has been used as a
catalyst as well as fluorinating agent in different organic
transformations [11,12]. B.V.S. Reddy et al. reported that an
equivalent amount of HBF4ÁOEt2 smoothly promoted the Ritter
reaction of olefins with nitriles under mild reaction conditions
[13]. The same group also explored HBF4ÁOEt2 as a catalyst cum
fluorinating agent for the synthesis of various fluorinated
*
Corresponding author. Tel.: +91 376 2371283; fax: +91 376 2370011.
E-mail addresses: b.gakul@gmail.com, gbaishya@rrljorhat.res.in (G. Baishya).
http://dx.doi.org/10.1016/j.jfluchem.2014.06.028
0022-1139/ß 2014 Elsevier B.V. All rights reserved.

2
G. Baishya et al. / Journal of Fluorine Chemistry 166 (2014) 1–7
O
O
HN
OR''
HN
R'
OR''
s
d
i
c
R
a
y
l
R
R'
o
P
/
s
R
d
i
e
c
a
R = alkyl,aryl
R' = H,
f
R
R = alkyl,aryl
.
e
2
1
s
i
0
R' = H, alkyl,
O
7
w
e
O
R" = methyl, benzyl
L
R" = ethyl, benzyl
,
H2N
OR''
O
+
R
R'
SiMe3
CH3CN
30 mol% HBF4.OEt2
Present work
O
HN
OR''
R = alkyl,aryl
R' = H, R" = benzyl
R
R'
Scheme 1. Synthesis of N-homoallylic carbamates via one-pot three-component reaction of aldehydes or ketones, carbamates and allyltrimethylsilane.
Table 1
Optimization of the reaction conditions with p-anisaldehyde (1c), amines (2) and allyltrimethyl silane (3) using HBF4ÁOEt2.a
NHP
CHO
HBF4.OEt2
solvent, rt
P
SiMe3
+
+
H2N
.
MeO
OMe
1c
3
2a-c
4ca, P = Cbz
4cc, P = Ts
P = Cbz, Boc, Ts,
Entry
1
HBF4ÁOEt2 (mol%)
Allyl-TMS 3 (equiv.)
Amine 2
Solvent
CH3CN
Product
Yieldb (%)
53
20
1.2
Cbz-NH2
NHCbz
2a
MeO
2
3
4
5
30
30
20
20
1.2
1.5
1.5
1.5
2a
CH3CN
CH3CN
CH2Cl2
CH3CN
4ca
4ca
4ca
–
70
2a
86
2a
43
Boc-NH2
2b
N.R.
6
7
8
30
30
20
1.5
1.5
1.5
2b
CH3CN
CH2Cl2
CH3CN
–
–
N.R.
N.R.
40
2b
Ts-NH2
2c
NHTs
MeO
9
30
30
1.5
1.5
2c
2c
CH3CN
CH2Cl2
4cc
4cc
47
20
10
a
Reaction performed with 1c (1 mmol), 2 (1.2 mmol) and various mmol of 3.
b
Isolated yield. n.r.: no reaction.

G. Baishya et al. / Journal of Fluorine Chemistry 166 (2014) 1–7
3
tetrahydropyran [14] and piperidine [15] derivatives. To the best
our knowledge, there have been no reports as yet of the use of
86% yield of the product 4ca was obtained when 1.5 mmol of
allyltrimethylsilane was used (Table 1, entry 3). In further
investigation of reaction conditions, we found that acetonitrile
was the solvent of choice and benzyl carbamate, the appropriate
amine counterpart. Thus, the optimal reaction conditions involved
the use of 30 mol% HBF4ÁOEt2 catalyst, aldehyde 1c (1.0 mmol),
HBF4ÁOEt2 as
a fluorinated acid catalyst to promote this
synthetically important reaction for the one-pot synthesis of
secondary and tertiary N-homoallylic carbamates.
2. Results and discussion
benzylcarbamate 2a (1.2 mmol) and allyltrimethylsilane 3
(1.5 mmol) in acetonitrile at room temperature.
In order to exemplify our ongoing work on development of
novel synthetic methods [16] we herein report an alternative and
versatile method for the synthesis of secondary and tertiary
N-homoallylic carbamates in good to high yields from aldehydes or
ketones using HBF4ÁOEt2 as an acid catalyst (Scheme 1, present
work). Initially, we attempted the reaction of p-anisaldehyde 1c
(1 mmol) with benzyl carbamate 2a (1.2 mmol) and allyltri-
methylsilane 3 (1.2 mmol) in the presence of 20 mol% of HBF4ÁOEt2
in acetonitrile at room temperature for 3 h, which afforded only
53% yield of the corresponding N-homoallylic carbamate 4ca
(Table 1, entry 1). The reaction was repeated under similar
conditions using 30 mol% of HBF4ÁOEt2 to obtain 70% yield of the
product 4ca (Table 1, entry 2). In a search for an even better yield,
we also varied the amount of allyltrimethylsilane and significantly,
After the optimal reaction conditions were known, we tried to
explore our protocol with various aromatic, heteroaromatic and
aliphatic aldehydes, and also with different cyclic and acyclic
ketones to generate a variety of N-homoallylic carbamates. The
results of this one-pot three-component synthesis of N-homo-
allylic benzyl carbamates are summarized in Table 2.
It was observed that yields of N-homoallylic carbamates were
considerably variable according to the nature of the substituent
present in the arene ring. Aldehydes with electron donating
substituents at para-position of arene ring gave very good yields of
the products 4ca–4ga (Table 2, entries 3–7). Aldehydes with
electron withdrawing substituents at para-, ortho- and meta-
position of arene ring also underwent this important three-
component reaction, but their corresponding products 4ha–ka
Table 2
Synthesis of secondary N-homoallylic benzyl carbamates using HBF4ÁOEt2 as a catalyst.a
O
HN
OBn
O
30 mol% HBF4.OEt2
.
SiMe3
+
+
RCHO
R
H2N
OBn
CH3CN, rt
4aa-na
3
1a-n
2a
Entry
R
Productc
Time (h)
Yield (%)b
1
2
C6H5
4aa
4ba
3
83
80
2.5
3
4
4-MeOC6H4
4ca
4da
2.0
2.5
86
84
O
O
5
6
7
4-BnOC6H4
4-MeC6H4
4ea
4fa
4ga
2.0
2.5
3.0
90
82
88
8
9
4-ClC6H4
2,4-Cl2C6H3
3-ClC6H4
4-BrC6H4
4ha
4ia
4ja
4ka
4la
3.5
4.0
3.0
3.0
3.0
78
66
74
80
67
10
11
12
S
13
14
4ma
4na
5.0
3.0
76
78
Me
Me
a
Reaction performed with 1 (1 mmol), 2a (1.2 mmol) and 3 (1.5 mmol) in acetonitrile at rt.
Isolated yields.
Structures of products confirmed by their IR, 1H NMR, 13C NMR and mass spectra.
b
c

4
G. Baishya et al. / Journal of Fluorine Chemistry 166 (2014) 1–7
Table 3
Synthesis of tertiary N-homoallylic benzyl carbamates using HBF4ÁOEt2 as a catalyst.a
O
O
O
HN
OBn
40 mol% HBF4.OEt2
SiMe3
+
.
R'
R''
+
CH3CN, rt
H2N
OBn
R'
R"
6aa-ga
5a-g
2a
3
Entry
Ketone
Product
Time (h)
Yield (%)b
1
2
3
4
5
Cyclopentanone
Cyclohexanone
Cycloheptanone
Cyclooctanone
6aa
6ba
6ca
6da
6ea
7
8
50
56
6
52
12
12
n.r.
n.r.
O
6
7
6fa
12
12
n.r
O
3-Pentanone
6ga
n.r.
n.r.: no reaction.
a
Reaction performed with 5a–g (1.0 mmol) and 2a (1.5 mmol) and 3 (2.0 mmol).
b
Isolated yield.
were obtained in lower yields (Table 2, entries 8–11). Sterically
hindered aldehyde such as 2-naphthaldehyde also underwent this
three-component reaction to afford its corresponding N-homo-
allylic carbamate 4ba in high yield (Table 2, entry 2). We also
explored our protocol with hetero aromatic aldehyde. When 2-
thiophene carbaldehyde was reacted with benzyl carbamate and
allyltrimethylsilane under the same reaction conditions, the
corresponding N-Cbz protected homoallylic amine 4la was
obtained in good yield (Table 2, entry l2). This also proved the
scope and general applicability of our protocol.
reaction to afford their corresponding N-Cbz protected homoallylic
amines 4ma–na in good yields (Table 2, entries 13 & 14).
The efficacy of our protocol has also been examined with
various cyclic and acyclic ketones. Thus, the reaction of cyclohex-
anone 5b (1.0 mmol) with benzyl carbamate 2a (1.5 mmol) and
allyltrimethylsilane
3 (2.0 mmol) has been performed using
30 mol% HBF4ÁOEt2 under the same reaction conditions which
led to a 25% yield of the corresponding tertiary N-homoallylic
carbamate 6ba. However, when the same reaction was repeated
using 40 mol% HBF4ÁOEt2, a significant enhancement of the yield
was observed leading to a 56% yield of 6ba (Table 3, entry 2).
Similarly, cyclopentanone and cycloheptanone also underwent
this one-pot three-component reaction to give their corresponding
products 6aa and 6ca in moderate yields (Table 3, entries 1 & 3).
To explore the utility of this protocol further, we also performed
the reaction with various aliphatic aldehydes under the optimal
reaction conditions. For example, cyclohexanecarbaldehyde
and isobutyraldehyde also underwent smooth three-component
Table 4
Comparison of HBF4ÁOEt2 vs various Lewis acids catalysts for the synthesis of 4ca.a
O
CHO
HN
OBn
O
Lewis acid
CH3CN, rt
SiMe3
+
.
+
H2N
OBn
OMe
1c
MeO
4ca
2a
3
Entry
Catalyst
Quantity (mol%)
Time (h)
Yield (%)b
Ref.
1
2
3
4
5
6
7
HBF4ÁOEt2
BF3.OEt2
Bi(OTf)3
Sc(OTf)3
In(OTf)3
Cu(OTf)2
I2
30
30
10
10
10
5
2
86
40
76
70
77
79
80
–
4
[9]
[1c]
–
3
4
6
–
8
[1f]
[1d]
10
0.5
a
Reaction performed with 1c (1 mmol), 2a (1.2 mmol) and 3 (1.5 mmol) in acetonitrile at rt.
b
Isolated yields.

G. Baishya et al. / Journal of Fluorine Chemistry 166 (2014) 1–7
5
O
CHO
O
HN
OBn
HBF4.OEt2 (0.483 g, 3 mmol))
SiMe3
+
+
H2N
OBn
CH3CN (10 mL), rt
OMe
1c
MeO
4ca
2a
3
1.82 g
Yield 80%
1.71 g
1.36 g
1.81 g
15 mmol
10 mmol
12 mmol
Scheme 2. Scaling-up experiment.
O
O
O
+
CO2Bn
NHCO2Bn
HBF4.OEt2
HBF4.OEt2
H NCO Bn
N
H2N
Ph
R
H
R
NHCO2Bn
A
-
2
2
R
B
_
_
BF4
H
Si
+
N
BF4
..
CO2Bn
_
BF4
H
R
BnO2C
BnO2C
R
Si
HBF4.OEt2
NH
N
+
+
SiMe3
H2O
R
C
D
E
BnO2C
R
Si
NHCO2Bn
-HBF4
N
R
F
Scheme 3. A plausible reaction mechanism in the case of aldehydes.
But other two cyclic ketones, cycloocatanone and
a
-tetralone did
3. Conclusion
not yield a trace amount of their corresponding tertiary homo-
allylic amines 6da and 6ea (Table 3, entries 4 & 5). In a similar
fashion, we also performed the reaction with acyclic ketones viz.
propeophenone and 3-pentanone, but they remained unchanged
after 12 h of the reaction time in each case (Table 3, entries 6 & 7).
The results are summarized in Table 3.
Finally, the efficacy of our protocol has also been compared with
other reported methods that use various Lewis acids catalysts for
the synthesis of N-homoallylic carbamate 4ca. The results are
summarized in Table 4. It was concluded from the result of Table 4
that our protocol to use inexpensive HBF4ÁOEt2 as an acid catalyst
for the one-pot synthesis of N-homoallylic carbamate is superior to
all other existing methods with respect to the reaction rate as well
as the yield of the product.
The application of this methodology has also been examined in
the large scale preparation of N-homoallylic carbamate. Thus, the
reaction of 1c with 2a and 3 in the presence of 30 mol% HBF4ÁOEt2
was carried out in 10 mmol scale (Scheme 2). The reaction afforded
80% yield of the product 4ca which is very much comparable to the
yield obtained in small scale reaction (Table 2, entry 3).
In conclusion, the fluorinated catalyst HBF4ÁOEt2 has been
found to be an efficient acid catalyst for the one-pot synthesis of
secondary and tertiary N-homoallylic carbamates. A variety of
aromatic aldehydes with both electron donating and electron
withdrawing substituents, and also aliphatic aldehydes undergo
HBF4ÁOEt2 catalyzed one-pot three-component reaction with
benzyl carbamate and allyltrimethylsilane to generate a library
of secondary N-homoallylic carbamates under mild conditions. The
catalyst is also equally effective with medium size cyclic ketones to
afford their corresponding tertiary N-homoallylic carbamates. The
advantages of this method over other existing methods are
reduced reaction time, higher yields, mild reaction conditions,
easily scalable and use of readily available catalyst. We feel that the
use of HBF4ÁOEt2 as an efficient fluorinated acid catalyst will also
find some other catalytic activities in the field of synthetic organic
chemistry.
4. Experimental
To demonstrate the involvement of the fluorinated acid
catalyst HBF4ÁOEt2 in the reaction, a plausible reaction mecha-
nism [17] has been proposed in Scheme 3. We assume that in
presence of HBF4ÁOEt2, the reaction between the aldehyde and
the amine Cbz-NH2 initially forms the isolable bisurethane A
[9,18,19] which actually generates the intermediate acylimine B
in situ. First, the intermediate acyliminie B will be protonated by
HBF4ÁOEt2 to generate the iminium salt C which will undergo the
Melting points were measured with a Buchi B-540 melting
point apparatus and are uncorrected. IR spectra were recorded on a
SHIMADZU FTIR-8400. NMR spectra were recorded on Bruker DPX
300 MHz and AV500 Advance-III 500 MHz spectrometer using
tetramethylsilane (TMS) as an internal standard. Mass spectra
were recorded on ESQUIRE 3000 Mass spectrometer. All the
commercially available regents were used without further
purification. All experiments were monitored by thin layer
chromatography using aluminium pre-coated silica gel TLC plates
(Merck). After elution, plate was visualized under UV illumination
at 254 nm for UV active materials. Further visualization was
achieved by staining anisaldehyde charring solution. Column
chromatography was performed on silica gel (100–200 mesh,
Rankem) eluting appropriate ethyl acetate–hexane mixture.
nucleophilic addition by allyltrimethylsilane to give the
b-silyl
carbocation intermediate D. Then, the nitrogen atom attacks the
silicon atom of the intermediate D to give the N-homoallyl-N-
silylated ammonium salt E. The subsequent proton release from E
forms the N-homoallyl-N-silyl amine F which on hydrolysis gives
the product.

6
G. Baishya et al. / Journal of Fluorine Chemistry 166 (2014) 1–7
4.1. General procedure for synthesis of secondary or tertiary N-
homoallylic carbamates
70.0, 66.7, 54.0, 41.0. MS (ESI): m/z = 410 [M+Na]+. Anal. Calcd for
C19H19NO4: C 77.49, H 6.50, N 3.61. Found: C 77.54, H 6.56, N 3.57.
To a solution of an aldehyde 1 or ketone 5 (1 mmol),
benzylcarbamate 2 (1.2 mmol or 1.5 mmol) in dry acetonitrile
(1 mL) was added 30 mol% or 40 mol% HBF4ÁOEt2 [20] and the
mixture was stirred at room temperature for 10 min followed by
4.1.6. Compound 4fa [3c]
White solid, m.p. 67–69 8C. IR (CHCl3): 3328, 3028, 2925, 1702,
1515, 1455, 1251, 1025, 915, 815, 774 cmÀ1 1H NMR (300 MHz,
.
CDCl3):
(s, 1H), 5.11–5.01 (m, 4H), 4.77 (br d, 1H), 2.52 (s, 2H), 2.32 (s, 3H).
13C NMR (75 MHz, CDCl3):
= 155.7, 139.0, 136.9, 136.5, 133.9,
d = 7.33 (s, 5H), 7.17–7.14 (s, 4H), 5.74–5.60 (m, 1H), 5.12
subsequent addition of allyltrimethylsilane
3 (1.5 mmol or
2.0 mmol) and dry acetonitrile (1 mL). After completion of the
reaction (TLC, specified time) saturated aq. NaHCO3 (10 mL)
solution was added to the reaction mixture and extracted with
ethyl acetate (3Â 10 mL). The organic layer was washed with
brine (1Â 10 mL) and dried over anhydrous sodium sulfate. The
organic layer was concentrated under rotary evaporator and
column chromatographed on silica gel (100–200 mesh) using 2:8
ethyl acetate-hexane as the eluent to get pure the N-homoallylic
carbamates. Compounds 4aa, 4ba, 4ca, 4fa, 4ha, 4ja, 4ka, 4ma,
4na, 6ba and 6ca are known in the literature and they have been
confirmed by comparison of their IR, 1H NMR and 13C NMR data
with those reported data (Refs. [1d,3c,10]). Full characteristic
data of all new compounds 4da, 4ea, 4ga, 4ia, 4la and 6aa are as
follows.
d
129.2, 128.8, 128.5, 128.1, 126.2, 118.3, 66.7, 54.3, 41.0, 21.1. MS
(ESI): m/z = 296 [M+1]+.
4.1.7. Compound 4ga
White solid, m.p. 41 8C. IR (CHCl3): 3419, 3344, 2960, 1694,
1642, 1455, 1337, 1251, 1041, 915, 829 cmÀ1 1H NMR (300 MHz,
.
CDCl3):
d = 7.31 (s, 5H), 7.17 (s, 4H), 5.74–5.60 (m, 1H), 5.17 (br s,
1H), 5.12–5.00 (m, 4H), 4.77 (br d, 1H), 2.87 (septet, 1H, J = 6.9 Hz),
2.51 (s, 2H), 1.24 (d, 6H, J = 6.9 Hz). 13C NMR (75 MHz, CDCl3):
d
= 155.9, 147.8, 139.5, 136.6, 134.2, 128.5, 128.2, 126.6, 126.4,
118.1, 66.7, 54.4, 41.1, 33.8, 24.1. MS (ESI): m/z = 346 [M+Na]+.
Anal. Calcd for C21H25NO2: C 77.98, H 7.79, N 4.33. Found: C 77.94,
H 7.85, N 4.37.
4.1.1. Compound 4aa [1d]
White solid, m.p. 63–65 8C. IR (CHCl3): 3328, 3064, 2925, 1712,
1513, 1456, 1250, 1024, 916, 814 cmÀ1. 1H NMR (300 MHz, CDCl3):
4.1.8. Compound 4ha [3c]
White solid, m.p. 65–66 8C. IR (CHCl3): 3342, 3032, 1697, 1511,
1451, 1251, 1035, 915, 820, 776 cmÀ1. 1H NMR (300 MHz, CDCl3):
d
= 7.58–7.05 (m, 10H), 5.73–5.59 (m, 1H), 5.16–5.01 (m, 5H), 4.81
d
= 7.53–7.10 (m, 9H), 5.70–5.57 (m, 1H), 5.11–5.01 (m, 4H), 4.75
(br d, 1H, J = 6.5 Hz), 2.55–2.50 (m, 2H). 13C NMR (75 MHz, CDCl3):
(br s, 1H), 2.52 (s, 2H). 13C NMR (75 MHz, CDCl3):
d
= 155.6, 136.2,
d
= 155.8, 142.1, 136.5, 134.0, 128.6, 128.5, 128.1, 127.3, 126.3,
133.2, 133.0, 128.7, 128.5, 128.2, 127.6, 118.9, 66.9, 53.9, 40.9. MS
(ESI): m/z = 338 [M+Na]+.
118.3, 66.8, 54.7, 41.0. MS (ESI): m/z = 282 [M+1]+.
4.1.2. Compound 4ba [1d]
4.1.9. Compound 4ia
White solid, m.p. 67–68 8C. IR (CHCl3): 3323, 3060, 2936, 1696,
White solid, m.p. 103 8C. IR (CHCl3): 3321, 2927, 1696, 1561,
1532, 1507, 1330, 1254, 1218, 1026, 916, 818, 772 cmÀ1 1H NMR
.
1532, 1471, 1265, 1102, 1039, 819 cmÀ1 1H NMR (300 MHz,
.
(300 MHz, CDCl3):
6.95 (m, 6H), 5.72–5.59 (m, 1H), 5.37 (br s, 1H), 5.11–4.86 (m, 5H),
2.57 (s, 2H). 13C NMR (75 MHz, CDCl3):
= 156.0, 139.6, 136.6,
d = 7.78–7.68 (m, 4H), 7.46–7.40 (m, 2H), 7.36–
CDCl3):
(br s, 1H), 5.15–5.00 (m, 5H), 2.56–2.46 (m, 2H). 13C NMR (75 MHz,
CDCl3): = 155.4, 136.1, 133.4, 133.2, 129.7, 128.5, 128.2, 127.2,
118.2, 67.0, 51.6, 39.0. MS (ESI): m/z = 351 [M+1]+. Anal. Calcd for
18H17Cl2NO2: C 61.73, H 4.89, N 4.00. Found: C 61.77, H 4.93, N
d = 7.47–7.33 (m, 5H), 7.19 (s, 3H), 5.71–5.60 (m, 1H), 5.27
d
d
134.0, 133.4, 132.9, 128.6, 128.5, 128.3, 128.1, 127.8, 126.3, 125.9,
125.1, 124.7, 118.5, 66.9, 54.9, 41.0.MS (ESI): m/z = 354 [M+Na]+.
C
4.04.
4.1.3. Compound 4ca [1d]
White solid, m.p. 68–69 8C. IR (CHCl3): 3323, 2956, 1701, 1612,
1513, 1246, 1178, 1036, 917, 830, 772 cmÀ1 1H NMR (300 MHz,
.
4.1.10. Compound 4ja [1d]
White solid, m.p. 65–66 8C. IR (CHCl3): 3423, 2949, 1655, 1450,
CDCl3):
d = 7.29 (s, 5H), 7.17 (d, 2H, J = 8.0 Hz), 6.83 (d, 2H,
1412, 1113, 1023 cmÀ1. 1H NMR (300 MHz, CDCl3):
d = 7.34 (s, 5H),
J = 8.5 Hz), 5.71–5.58 (m, 1H), 5.33 (br d, 1H, J = 7.6 Hz), 5.09–4.99
(m, 4H), 4.74 (br s, 1H), 3.73 (s, 3H), 2.48 (s, 2H). 13C NMR (75 MHz,
7.26–7.21 (m, 3H), 7.13 (d, 1H, J = 6.6 Hz), 5.71–5.60 (m, 1H), 5.15–
5.03 (m, 5H), 4.78 (br s, 1H), 2.51 (s, 2H). 13C NMR (75 MHz, CDCl3):
= 155.6, 136.2, 134.4, 133.2, 129.8, 128.5, 128.1, 128.0, 127.4,
126.3, 124.5, 118.9, 66.9, 53.7, 40.9. MS (ESI): m/z = 338 [M+Na]+.
CDCl3): d = 158.8, 155.6, 136.4, 133.9, 128.57, 128.51, 128.1, 127.4,
113.9, 66.7, 55.2, 54.0, 41.0. MS (ESI): m/z = 334 [M+Na]+.
d
4.1.4. Compound 4da [3c]
4.1.11. Compound 4ka [1d]
White semi solid. IR (CHCl3): 3328, 3068, 2923, 1702, 1504,
1489, 1444, 1327, 1242, 1039, 927 cmÀ1 1H NMR (300 MHz,
.
White solid, m.p. 86–87 8C. IR (CHCl3): 3323, 3066, 1695, 1531,
1454, 1339, 1250, 1010, 918, 821, 774 cmÀ1 1H NMR (300 MHz,
.
CDCl3):
5.22 (br s, 1H), 5.10–5.00 (m, 4H), 4.68 (br d, 1H), 2.43 (s, 2H). 13
NMR (75 MHz, CDCl3): C 155.7, 147.8, 146.7, 136.5, 136.2, 133.9,
dH 7.31 (s, 5H), 6.72 (s, 3H), 5.90 (s, 2H), 5.69–5.58 (m, 1H),
CDCl3):
d = 7.46 (d, 2H, J = 7.3 Hz) 7.40–7.15 (m, 5H), 7.12 (d, 2H,
C
J = 7.3 Hz), 5.68–5.55 (m, 1H), 5.26 (d, 1H, J = 7.3 Hz), 5.15–5.03 (m,
4H), 4.74 (br s, 1H), 2.46 (s, 2H). 13C NMR (75 MHz, CDCl3):
d
128.5, 128.1, 119.6, 118.3, 108.2, 106.8, 101.0, 66.8, 54.5, 41.1. MS
(ESI): m/z = 348 [M+Na]+. Anal. Calcd for C19H19NO4: C 70.14, H
5.89, N 4.31. Found: C 70.20, H 5.85, N 4.36.
d
= 155.7, 141.2, 136.3, 133.4, 131.6, 128.5, 128.2, 128.0, 127.6,
121.1, 118.8, 66.9, 54.0, 40.8. MS (ESI): m/z = 382 [M+Na]+.
4.1.5. Compound 4ea
4.1.12. Compound 4la
White solid, m.p. 75–76 8C. IR (CHCl3): 3326, 3028, 2924, 1701,
Gummy liquid. IR (CHCl3): 3318, 3371, 3069, 2928, 1699, 1642,
.
1524, 1455, 1328, 1251, 1037, 919, 851, 697 cmÀ1 1H NMR
1610, 1509, 1454, 1237, 1177, 1025, 914, 829, 772 cmÀ1
.
1H NMR
(300 MHz, CDCl3):
6.91 (d, 2H, J = 8.6 Hz), 5.73–5.59 (m, 1H), 5.11–5.01 (m, 7H), 4.73
(br d, 1H), 2.51 (s, 2H). 13C NMR (75 MHz, CDCl3):
= 158.0, 155.6,
137.0, 136.4, 133.9, 128.6, 128.5, 128.1, 128.0, 127.5, 118.3, 114.9,
d
= 7.59–7.24 (s, 10H), 7.16 (d, 2H, J = 8.2 Hz),
(300 MHz, CDCl3):
J = 3.4 Hz), 5.79–5.65 (m, 1H), 5.22 (br s, 1H), 5.13–4.97 (m, 5H),
2.62 (s, 2H). 13C NMR (75 MHz, CDCl3):
= 155.6, 145.9, 136.4,
133.5, 128.5, 128.1, 126.8, 24.2, 123.9, 118.7, 66.9, 50.5, 41.2. MS
d = 7.30 (s, 5H), 7.17–7.13 (m, 1H), 6.90 (d, 2H,
d
d

G. Baishya et al. / Journal of Fluorine Chemistry 166 (2014) 1–7
7
(ESI): m/z = 310 [M+Na]+. Anal. Calcd for C16H17NO2S: C 66.87, H
5.96, N 4.87. Found: C 66.82, H 5.90, N 4.91.
d
= 7.33 (s, 10H), 5.48 (br s, 2H), 5.09 (s, 4H), 4.90–4.70 (m, 1H),
2.3–2.05 (m, 1H), 0.96 (d, 6H, J = 6.6 Hz). 13C NMR (75 MHz, CDCl3):
= 155.5, 136.2, 128.5, 128.1, 128.0, 66.8, 65.6, 33.3, 18.6. Anal.
d
4.1.13. Compound 4ma [3c]
White solid, m.p. 60–61 8C. IR (CHCl3): 3329, 2925, 2851, 1698,
1642, 1525, 1448, 1256, 1214, 1020, 772 cmÀ1. 1H NMR (300 MHz,
Calcd for C20H24N2O4: C 67.40, H 6.79, N 7.86. Found: C 67.35, H
6.75, N 7.80.
CDCl3): d = 7.35 (s, 5H), 5.80–5.65 (m, 1H), 5.12–5.02 (m, 4H), 4.69
Acknowledgements
(br d, 1H), 3.60–3.53 (m, 1H), 2.35–2.11 (m, 2H), 1.96 (m, 1H),
1.80–1.55 (m, 4H), 1.45–0.92 (m, 6H). 13C NMR (75 MHz, CDCl3):
We gratefully thank Department of Science & Technology, New
Delhi for a research grant SR/FT/CS-126/2010 and also for the
fellowship of BS. We thank Dr D Ramaiah, Director, CSIR-NEIST,
Jorhat for his enthusiastic encouragement.
d
= 156.3, 136.7, 134.7, 128.5, 128.0, 117.5, 66.5, 55.2, 41.2, 36.7,
29.7, 28.3, 26.3, 26.2, 26.1.MS (ESI): m/z = 310 [M+Na]+.
4.1.14. Compound 4na [1d]
Colourless oil. IR (CHCl3): 3334, 2924, 1698, 1641, 1523, 1441,
1254, 1213, 1023, 774 cmÀ1. 1H NMR (300 MHz, CDCl3):
d = 7.34 (s,
References
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1H), 0.93 (d, 3H, J = 6.9 Hz), 0.89 (d, 3H, J = 6.9 Hz). 13C NMR
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White solid, m.p. 85–87 8C. IR (CHCl3): 3277, 3075, 2925, 2853,
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813, 758, 666 cmÀ1 1H NMR (300 MHz, CDCl3):
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2H, J = 8.5 Hz), 5.57–5.43 (m, 1H), 5.01 (d, 3H, J = 12.3 Hz), 4.29 (q,
1H, J = 6.7 Hz), 3.74 (s, 3H), 2.51–2.40 (m, 2H), 2.37 (s, 2H). 13C NMR
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(75 MHz, CDCl3): d = 158.8, 143.0, 137.5, 133.3, 132.4, 129.2, 127.7,
127.1, 119.0, 113.7, 56.7, 55.2, 41.8, 21.4. MS (ESI): m/z = 332
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[M+1]+.
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4.1.16. Compound 6aa
Colourless liquid. IR (CHCl3): 3348, 3070, 2958, 2873, 1709, 1523,
1489, 1454, 1412, 1240, 1096, 993, 916, 777, 679 cmÀ1 1H NMR
.
(300 MHz, CDCl3):
4H), 4.70 (br s, 1H), 2.49 (d, 2H), 2.47–2.31 (m, 2H), 1.97–1.62 (m,
6H). 13C NMR (125 MHz, CDCl3):
= 155.4, 136.7, 134.4, 128.3,
127.9, 117.9, 65.9, 63.2, 41.7, 37.4,23.5. MS (ESI):m/z = 282[M+Na]+.
Anal. Calcd for C16H21NO2: C 74.10, H 8.16, N 5.40. Found: C 74.04, H
8.20, N 5.45.
d = 7.34 (m, 5H), 5.84–5.70(m, 1H), 5.06–5.01 (m,
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7911–7918.
d
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4.1.17. Compound 6ba [10]
(b) G.A. Molander, J. Raushel, N.M. Ellis, J. Org. Chem. 75 (2010) 4304–4306;
(c) T. Akiyama, J. Itoh, K. Fuchibe, Synlett 8 (2002) 1269–1272.
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4677;
Colourless gummy liquid. IR (CHCl3): 3350, 2969, 2873, 1713,
1510, 1454, 1247, 1096, 993, 916, 778 cmÀ1 1H NMR (300 MHz,
.
CDCl3):
d = 7.35 (s, 5H), 5.83–5.68 (m, 1H), 5.07–5.02 (m, 4H), 4.54
(b) M.E. Dudely, M.M. Morshed, C.L. Brenan, M.S. Islam, M.S. Ahmad, M.-R. Attu, B.
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4827–4829.
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7H). 13C NMR (75 MHz, CDCl3):
d = 154.5, 136.8, 133.5, 128.5, 128.1,
118.0, 66.0, 54.7, 42.5, 34.7, 25.6, 21.6. MS (ESI): m/z = 296 [M+Na]+.
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4.1.18. Compound 6ca [10]
´
[15] J.S. Yadav, B.V. Subba Reddy, K. Ramesh, G.G.K.S. Narayana Kumar, R. Gree,
Colourless liquid. IR (CHCl3): 3354, 2930, 2861, 1715, 1508,
Tetrahedron Lett. 51 (2010) 1578–1581.
1462, 1100, 9943, 917, 777 cmÀ1 1H NMR (300 MHz, CDCl3):
.
d
[16] G. Baishya, B. Sarmah, N. Hazarika, Synlett 24 (2013) 1137–1141.
[17] The mechanism has been proposed as suggested by the reviewer.
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acetonitrile in the presence of 30 mol% HBF4ÁOEt2 immediately produced the
bisurethane as a solid product. The reaction was quenched with 20 mL of 10%
Na2CO3, then filtered out the sold residue which was again re-crystallized from
isopropanol to give the pure aminal or bisurethane as a white solid.
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5534.
= 7.40–7.27 (m, 5H), 5.81–5.65 (m, 1H), 5.05–4.99 (m, 4H), 4.58
(br s, 1H), 2.50 (d, 2H, J = 7.2 Hz), 1.91–1.82 (m, 2H), 1.70–1.30 (m,
10H). 13C NMR (75 MHz, CDCl3):
= 154.5, 136.8, 134.1, 128.5,
d
128.0, 118.1, 66.0, 58.4, 43.0, 38.4, 29.4, 22.2. MS (ESI): m/z = 310
[M+Na]+.
[20] The active species might be same in the combination of BF3.OEt2 and AcOH which
was employed as promoter in the three-component synthesis of homoallylic
amines by the reaction of aldehyde, amine and triethylallylgermane T. Akiyama, J.
Iwai, Y. Onuma, H. Kagoshima, Chem. Commun. (1999) 2191–2192.
4.1.19. Compound A (R = 2-propyl)
White solid, m.p. 180 8C. IR (CHCl3): 3306, 2956, 1700, 1560,
1517, 1302, 1243 1020, 695 cmÀ1 1H NMR (300 MHz, CDCl3):
.