Rhodium-catalyzed synthesis of γ-butyrolactams and pyrrolidines via cycloisomerization of N-tethered 1,6-enynes

Article abstract of DOI:10.1016/j.tet.2010.03.097

A rhodium-catalyzed cycloisomerization reaction of N-tethered 1,6-enynes with an intramolecular halogen shift has been developed, providing a useful process for the synthesis of stereo defined γ-butyrolactam and pyrrolidine derivatives in good to excellent yields. Effects of both electronic feature and steric structure of the substrates on the outcome of the reaction were investigated.

Full text of DOI:10.1016/j.tet.2010.03.097

Tetrahedron 66 (2010) 4212e4217
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Rhodium-catalyzed synthesis of
g
-butyrolactams and pyrrolidines via
cycloisomerization of N-tethered 1,6-enynes
,b,
Jianping Wang a, Xiaomin Xie a, Fangfang Ma a, Zhiyong Peng a, Lei Zhang a, Zhaoguo Zhang a
*
a School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
b State Key Laboratory of Organometallics, Shanghai Institute of Organic Chemsitry, 345 Lingling Road, Shanghai 200032, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A rhodium-catalyzed cycloisomerization reaction of N-tethered 1,6-enynes with an intramolecular halogen
shift has been developed, providing a useful process for the synthesis of stereo defined -butyrolactam and
pyrrolidine derivatives in good to excellent yields. Effects of both electronic feature and steric structure of
the substrates on the outcome of the reaction were investigated.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 4 December 2009
Received in revised form 22 March 2010
Accepted 26 March 2010
g
Available online 14 April 2010
1. Introduction
a few N-tethered enyne substrates, we became interested in the
cyclization of broader N-tethered 1,6-enynes using the same rho-
g
-Butyrolactam and pyrrolidine structures are important build-
dium catalytic system. Herein we wish to report the construction of
-chloroalkylidene- -butyrolactams and pyrrolidines from cationic
rhodium-catalyzed intramolecular cyclization of N-tethered 1,
ing blocks in the syntheses of many natural products and pharma-
ceuticals.1 Because of their important biological activities, such as
cytotoxicity, antitumor, and anti-inflammation activities, the
development of new methodologies to access these five-membered
heterocyclic rings in regio- and stereo-controlled fashion appears to
be highly desirable.2 Recently, the use of transition metal catalysts in
the carbonecarbon bond formation and the cyclization of enynes
have been reported, which offer the unique means to construct
various carbo-andheterocycles withhighefficiency. Many transition
metals, such as Pd,3 Ru,4 and Pt,5 have been applied to catalyze these
kinds of reactions. Zhangetal. firstlyreported thecycloisomerization
of 1,6-enyne catalyzed by Rh(I), which offers a potential methodol-
a
g
6-enynes with a chloromethyl group at the alkene moiety.
ogy to the synthesis of g
-butyrolactam and pyrrolidine structures.6a
Scheme 1. Cyclization of O-tethered enynes catalyzed by rhodium catalyst.
The substrates with a functional group (OH, OAc, OBz, alkyl) at the
allylic position can be cycloisomerized via a metallacyclopentane
intermediate in excellent yields, regio- and enantioselectivity.6bee,7
Our group have developed a rhodium-catalyzed cycloisomerization
of 1,6-enynes with a halogen atom at the allylic position to form
2. Results and discussion
Initial attempts at cycloisomerization with cationic rhodium
catalysis focused on the reaction of (Z)-N-benzyl-N-(4-chlorobut-2-
enyl)-but-2-ynamide (1a) as a model substrate. Employing of [Rh
(COD)Cl]2 as a precatalyst and common bisphosphine and mono-
phosphine ligands, moderate to good yields of cyclization products
(Table 1, entries 1e6) were obtained. The exocyclic CeC double
bond in 2a was believed to be in the E-configuration as compared
the chemical shifts of the methyl protons adjacent to the exocyclic
CeC double bond with its analogues.8 When the reaction was car-
ried out in 1,2-dichloroethane (DCE) with dppb as ligand, the
highest yield could be achieved (Table 1, entry 4). The reaction was
also evaluated with respect to solvents. Poor yields were observed
when the reaction was performed in other noncoordinating sol-
vents such as toluene and dichloromethane (Table 1, entries 7
stereo defined
a
-halomethylene-
g
-butyrolactones, accompanying
with a formal halogen shift (Scheme 1).8 This sort of reactions pro-
ceeds through a
p
-allyl or enyl (sþp
)9 rhodium intermediate rather
than a metallacyclopentane intermediate.6 In particular, deriving
from the vinyl-chlorine structure activated by the carbonyl group,
many further reactions could be easily achieved from the cyclization
products (e.g., Suzuki coupling reaction, Stille coupling reaction).
With the given success of the cycloisomerization of O-tethered and
* Corresponding author. Tel.: þ86 21 54748925; fax: þ86 21 54741297; E-mail
address: zhaoguo@sjtu.edu.cn (Z. Zhang).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.03.097

J. Wang et al. / Tetrahedron 66 (2010) 4212e4217
4213
and 8). Because coordinating solvents have been reported competing
the coordination with substrate to catalyst, resulting sluggish
reaction,6,8 we did not perform the reaction in polar solvents.
high yields (Table 2, entries 1e6). Change of the substituents on the
nitrogen atom and variation of groups at the alkyne moiety have
little influence on the reactivity, which proves that this kind of re-
action has a wide substrates tolerance. In addition, despite the NMR
spectra revealed that the substrates of 1a, 1b, and 1c were trans/cis-
mixtures (the trans-isomers of these enyne amides have been
reported unfavorable for the cycloisomerization,6e Scheme 2), good
to excellent yields were obtained under the reaction conditions.
These results revealed that this cationic Rh-catalytic system was
greatly efficient to the cycloisomerization of enyne amides with
a chloromethyl group at the alkene moiety as we expected.
Table 1
a
Optimization for cycloisomerization of amide enyne catalyzed by [Rh(COD)Cl]2
Entry
Solvent
Ligand
Time (h)
Yieldc (%)
b
1
2
3
4
5
6
7
8
DCE
DCE
DCE
DCE
DCE
DCE
PPh3
24
24
24
24
48
48
48
48
64
77
78
82
46
37
Trace
29
dppe
dppp
dppb
dppf
rac-binap
dppb
dppb
Toluene
DCMd
Scheme 2. Rh-catalyzed cyclization reaction of trans/cis-isomers of amide.
a
All of the reactions were carried out with 1a (0.2 mmol), [Rh(COD)Cl]2 (9.9 mg,
0.02 mmol), bisphosphine (0.044 mmol), and AgSbF6 (13.7 mg, 0.04 mmol) in DCE
(3 mL) at 80 ꢀC.
b
When we changed the substrates to electron-rich enynes
(1gek), to our surprise, the reaction results were highly dependent
on the structures of substrates, which were quite different from the
electron-poor substrates (Table 2, entries 7e11). Moderate yields
could be achieved when the amines with an electron-withdrawing
group (tosyl group) on the nitrogen atom were used as substrates,
while no cyclization product was obtained when those substrates
with electron-donating substituents (benzyl and 4-methoxy-
phenyl) were used (Table 1, entries 7 vs 10, 9 vs 11). We failed in
making stable substrates with other electron-withdrawing groups,
such as 4-nitrophenyl or 4-trifluoromethylphenyl. Luckily, when
we started from N-(3-phenylprop-2-yn-1-yl)-4-(trifluoromethyl)
aniline and (Z)-1,4-dichloro-2-butene to make the enyne substrate,
we did isolated the desired product, but it cyclized in the absence of
any catalyst at 10e15 ꢀC in 2 days to give 1-(4-(trifluoromethyl)
phenyl)-2,5-dihydro-1H-pyrrole; under the catalytic conditions,
the substrates reacted much faster albeit to give the same product
as when no catalyst was used (Scheme 3).
PPh3 (0.084 mmol) was used.
Isolated yields.
The reaction was performed at 50 ꢀC.
c
d
With the experimental conditions optimized, the scope of the
reaction was explored. At the onset, we assessed the reactivity of the
electron-poor substrates (1aef) by the reaction of (Z)-N-R2-N-(4-
chlorobut-2-enyl)-3-R1-propiolamides (R1, R2¼substituted groups,
Table 2) in the presence of the cationic rhodium catalyst. The re-
actions were carried out in 1,2-dichloroethane (DCE) at 80 ꢀC and
weremonitored byTLC. Mostof thereactions proceeded smoothly to
afford the g-butyrolactams with an intramolecular chloride shift in
Table 2
Cycloisomerization of N-tethered 1,6-enynes catalyzed by [Rh(COD)Cl]2/dppb/
AgSbF6
a
Cl
Cl
NaH, DMF
HN
Cl
CF3
+
rt, 2 days
N
CF3
R1
R2
Y
2
Time (h)
Yieldc (%)
N
Entry
1
CF3
1
2
3
4
5
6
7
8
1ab
1bb
1cb
1d
1e
1f
1g
1h
1i
Me
Ph
n-Bu
Me
Ph
n-Bu
Me
Ph
n-Bu
Me
n-Bu
Bn
Bn
Bn
Ts
Ts
Ts
Ts
Ts
O
O
O
O
O
O
H2
H2
H2
H2
H2
2a
2b
2c
2d
2e
2f
2g
2h
2i
18
24
10
10
24
10
24
24
24
24
24
82
94
76
87
80
82
82
50
Scheme 3. Synthesis and reaction of 4-trifluoromethylphenyl substituted enyne
substrate.
Lu et al. have reported that the nitrogen atom of the N-allylic
alkynamides might coordinate with palladium to stabilize the
carbonepalladium bond in the palladium(II)-catalyzed asym-
9
10
11
Ts
Bn
77
metric synthesis of (Z)-a-alkylidene-g
-butyrolactams.11 Based on
1j
1k
d
Chaosd
Chaosd
4-OMeePh
d
the supposition and the mechanism of this cycloisomerization as
we mentioned in our previous work, we reasoned that the
nitrogen atom may also play the role of a ligand in the catalytic
cycle. In the way of the conceivable mechanism (Scheme 4), the
a
All of the reactions were carried out with 1 (0.2 mmol), [Rh(COD)Cl]2 (9.9 mg,
0.02 mmol), dppb (18.8 mg, 0.044 mmol), and AgSbF6 (13.7 mg, 0.04 mmol) in DCE
(3 mL) at 80 ꢀC.
b
trans/cis-Mixtures.
p
-allyl intermediate (b) formed by the reaction of enyne-
coordinated Rh species (a) with an allylic chloride is in equi-
librium with the complex (c) via h3 h1 isomerization. In this
process, the electronic effect of the substrates might influence
c
All exocyclic double bonds of 2 were in the E-form as compared the chemical
shifts of the protons in the group adjacent to the exocyclic CeC double bond with
e
their analogues, see Ref. 8 and 10.
d
The products were complicated and the target molecule was not detected.

4214
J. Wang et al. / Tetrahedron 66 (2010) 4212e4217
Table 3
the coordinating ability of the nitrogen atom. Therefore, there
might be a competition between the alkyne moiety and the
nitrogen atom in the coordination with the rhodium species. For
the electron-poor substrates, the weak coordinating ability of
the nitrogen atom made it easier for the alkyne moiety to co-
ordinate with the rhodium and undergo addition of the rhodium
chloride bond to the alkyne. Therefore, high yields could be
achieved with amide substrates. For the electron-rich substrates,
the nitrogen atom of the amines, to some extent, had stronger
coordinating ability; in this case, the reaction result became
sensitive to the substituents on the nitrogen atom. The electron-
donating substituents further increased the coordinating ability
of the amino group, which might block the alkyne to coordinate
with the rhodium species. Therefore, no cyclization product was
isolated with these substrates. In our initial work, we have
found that the cationic Rh species was poor catalyst for the
cyclization of (E)-isomers of O-tethered enyne substrates
(Scheme 5).8 However, when we subjected (E)-isomers of amide
substrates to the optimized reaction condition, good yields could
be obtained. The results are shown in Table 3. The different
results between O-tethered and N-tethered enynes could also be
speculated based on the explanation above (Scheme 6). For the
amide substrate, the nitrogen atom serves as a ligand for the
cationic Rh species, which makes it easier for species (e) to
transform to species (f). Therefore, it imparts significantly higher
reactivity in comparison to O-tethered enynes.
Cycloisomerization of (E)-isomers of amide enynes catalyzed by [Rh(COD)Cl]2/dppb/
a
AgSbF6
Entry
1
R1
R2
2
Yield (%)b
1
2
3
4
5
1lc
Me
Ph
n-Bu
Ph
n-Bu
Bn
Bn
Bn
Ts
2a
2b
2c
2e
2f
80
87
86
88
80
1mc
1nc
1o
1p
Ts
a
All of the reactions were carried out with 1 (0.2 mmol), [Rh(COD)Cl]2 (9.9 mg,
0.02 mmol), dppb (18.8 mg, 0.044 mmol), and AgSbF6 (13.7 mg, 0.04 mmol) in DCE
(3 mL) at 80 ꢀC.
b
Isolated yields.
trans-/cis- Mixtures.
c
Scheme 6. A plausible mechanism for cyclization of (E)-isomer of amide enyne
substrates.
3. Conclusions
In conclusion, we have developed a cationic rhodium species
catalyzed cyclization of N-tethered 1,6-enynes with a chloromethyl
group at the alkene moiety. The amide substrates showed high
reactivity and wide substrates tolerance, however, the cyclization of
amine substrates was highly dependent on the substituents on the
nitrogen atom: the amines with electron-withdrawing group on
the nitrogen atom gave content results, while those with electron-
donating group gave no cyclization product. The (E)-isomers of the
amide enynes could also cyclize in content yields with the cationic
Rh species in contrast to the O-tethered substrates. The reaction
represents a useful process for the synthesis of
a-chloroalkylidene-
g-butyrolactams and pyrrolidines. Further studies on the asym-
metric reaction are in progress.
4. Experimental section
Scheme 4. A proposed mechanism involving a
p-allyl rhodium species.
4.1. General procedure for the electron-poor enyne
substrates; representative preparation of (Z)-N-benzyl-
N-(4-chlorobut-2-enyl)but-2-ynamide (1a)
To a solution of but-2-ynoic acid (2.9 g, 35.0 mmol) and phenyl-
methanamine (3.2 g, 29.2 mmol) in CH2Cl2 (30 mL) was added
dropwise a solution of DCC (7.2 g, 35.0 mmol) and DMAP (850 mg,
7.0 mmol) in CH2Cl2 (30 mL) at 0 ꢀC. After being stirred at room
temperature for 4 h, the reaction mixture was filtered to remove any
precipitate and the filtrate was concentrated and purified bycolumn
chromatography (300e400 mesh silica gel, petroleum ether/ethyl
acetate) to give N-benzylbut-2-ynamide; yield: 4.9 g (97%).
To a solution of NaH (0.9 g, 50 wt %, 18.7 mmol) in DMF (20 mL)
was added dropwise a solution of N-benzylbut-2-ynamide (2.5 g,
14.4 mmol) in DMF (15 mL) at 0 ꢀC. After being stirred at room
Scheme 5. Cyclization of (E)-isomer of O-tethered enyne.

J. Wang et al. / Tetrahedron 66 (2010) 4212e4217
4215
temperature for 30 min, (Z)-1,4-dichlorobut-2-ene (2.7 g,
21.6 mmol) was added in one portion. After further stirred at 60 ꢀC
for 20 h, the mixture was cooled to 0 ꢀC and water (20 mL) was
added carefully. The mixture was extracted with diethyl ether
(3ꢁ25 mL) and the combined organic phase was washed with brine
(20 mL), dried over Na2SO4, concentrated under reduced pressure
and purified by the flash chromatography to afford the title com-
pound; yield: 1.02 g (27%). 1H NMR (400 MHz, CDCl3) two isomers:
17.6 mmol) in DMF (10 mL) at 0 ꢀC. After being stirred at room
temperature for 30 min, a solution of 1-bromobut-2-yne (2.1 g,
16.0 mmol) in DMF (5 mL) was added dropwise, and then the re-
action mixture was stirred for an additional 4 h at 60 ꢀC. After the
mixture was cooled to room temperature, water (20 mL) was added
and the solution was extracted with diethyl ether (3ꢁ20 mL). The
organic phase was combined, dried over Na2SO4, concentrated
under reduced pressure, and purified by chromatography to give
tert-butyl but-2-ynyl(tosyl)carbamate; yield: 3.9 g (75%).
To a solution of tert-butyl but-2-ynyl(tosyl)carbamate (3.9 g,
12.1 mmol) in CH2Cl2 (20 mL) was added dropwise TFA (4.1 g,
36.0 mmol). After stirring for 4 h at room temperature, saturated
NaHCO3 solution (40 mL) was added carefully and the mixture was
extracted with CH2Cl2 (3ꢁ20 mL). The combined extracts were
dried over Na2SO4, concentrated under reduced pressure, and pu-
rified by the flash chromatography to afford N-(but-2-ynyl)-4-
methylbenzenesulfonamide; yield: 2.4 g (90%).
d
2.01 (s, 1.8H), 2.03 (s, 1.2H), 3.95e3.99 (m, 3.2H), 4.17 (dd, J¼1.6,
6.8 Hz, 0.8H), 4.59 (s, 0.8H), 4.76 (s, 1.2H), 5.48e5.60 (m, 1H),
5.76e5.86 (m, 1H), 7.24e7.40 (m, 5H); 13C NMR (100 MHz, CDCl3)
two isomers:
d 4.04, 4.07, 38.31, 38.56, 39.60, 44.35, 46.80, 51.92,
73.12, 89.65, 90.07, 127.56, 127.69, 127.99, 128.06, 128.22, 128.69,
128.84, 128.98, 129.14, 129.38, 136.04, 136.18, 154.67, 154.69.
4.1.1. (Z)-N-Benzyl-N-(4-chlorobut-2-enyl)-3-phenylpropiolamide
(1b). 1H NMR (400 MHz, CDCl3) two isomers:
d 3.96e4.07 (m,
3.2H), 4.27 (dd, J¼1.6, 7.2 Hz, 0.8H), 4.66 (s, 0.8H), 4.85 (s, 1.2H),
To a solution of NaH (0.26 g, 50 wt %, 5.4 mmol) in DMF (20 mL)
5.53e5.90 (m, 2H), 7.29e7.56 (m, 10H); 13C NMR (100 MHz, CDCl3)
was added dropwise
a solution of N-(but-2-ynyl)-4-methyl-
two isomers:
d
38.28, 38.57, 39.88, 44.48, 46.93, 52.14, 81.28, 81.39,
benzenesulfonamide (1.0 g, 4.5 mmol) in DMF (10 mL) at 0 ꢀC.
After being stirred at room temperature for 30 min, (Z)-1,4-
dichlorobut-2-ene (0.85 g, 6.8 mmol) was added in one portion,
and then the reaction mixture was stirred for an additional 4 h at
60 ꢀC. After the mixture was cooled to room temperature, water
(20 mL) was added and the solution was extracted with diethyl
ether (3ꢁ20 mL). The organic phase was combined, dried over
Na2SO4, concentrated under reduced pressure, and purified by
chromatography to give the title compound; yield: 732.3 mg
90.67, 91.08, 120.17, 120.19, 127.65, 127.77, 127.98, 128.10, 128.31,
128.49, 128.53, 128.76, 128.92, 129.09, 129.28, 129.53, 130.15, 130.19,
132.37, 132.42, 135.93, 136.10, 154.56, 154.60.
4.1.2. (Z)-N-Benzyl-N-(4-chlorobut-2-enyl)hept-2-ynamide (1c). 1H
NMR (400 MHz, CDCl3) two isomers:
d
0.87 (t, J¼7.2 Hz, 1.8H), 0.92
(t, J¼7.2 Hz, 1.2H), 1.35e1.46 (m, 2H), 1.51e1.59 (m, 2H), 2.33e2.40
(m, 2H), 3.94e3.99 (m, 3H), 4.17 (dd, J¼1.6, 7.2 Hz, 1H), 4.59 (s,
0.8H), 4.75 (s, 1.2H), 5.49e5.61 (m, 1H), 5.76e5.87 (m, 1H),
(52%). 1H NMR (400 MHz, CDCl3):
d
1.55 (t, J¼2.4 Hz, 3H), 2.43 (s,
7.25e7.39 (m, 5H); 13C NMR (100 MHz, CDCl3) two isomers:
d
13.37,
3H), 3.88 (dd, J¼1.2, 7.6 Hz, 2H), 4.01 (q, J¼2.0 Hz, 2H), 4.11 (dd,
J¼0.8, 7.6 Hz, 2H), 5.54e5.60 (m, 1H), 5.82e5.89 (m, 1H), 7.31 (d,
J¼8.0 Hz, 2H), 7.73 (d, J¼8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3)
13.42, 18.56, 18.61, 21.86, 21.96, 29.65, 29.71, 38.30, 38.57, 39.66,
44.35, 46.72, 51.96, 73.75, 73.85, 93.73, 94.16, 127.53, 127.65, 127.94,
128.14, 128.24, 128.66, 128.79, 128.98, 129.21, 129.31, 136.11, 136.26,
154.72. HRMS calcd for C18H22ClNO: 303.1390. Found: 303.1430.
d
3.20, 21.49, 36.55, 38.42, 42.38, 71.30, 81.96, 127.86, 127.88,
129.33, 130.64, 135.60, 143.49. HRMS calcd for C15H18ClNO2S:
311.0747. Found: 311.0758.
4.1.3. (Z)-N-(4-Chlorobut-2-enyl)-N-tosylbut-2-ynamide
NMR (400 MHz, CDCl3):
(1d). 1H
d
2.01 (s, 3H), 2.44 (s, 3H), 4.26 (dd, J¼1.2,
4.2.1. (Z)-N-(4-Chlorobut-2-enyl)-4-methyl-N-(3-phenylprop-2-
7.8 Hz, 2H), 4.69 (dd, J¼1.2, 7.0 Hz, 2H), 5.65e5.72 (m, 1H),
5.84e5.90(m, 1H), 7.32 (dd, J¼0.9, 8.4 Hz, 2H), 7.85 (d, J¼8.4 Hz,
ynyl)benzenesulfonamide (1h). 1H NMR (400 MHz, CDCl3):
d 2.36
(s, 3H), 3.98 (dd, J¼0.8, 7.6 Hz, 2H), 4.13 (dd, J¼0.8, 7.6 Hz, 2H),
4.30 (s, 2H), 5.62e5.68 (m, 1H), 5.89e5.95 (m, 1H), 7.08 (d,
J¼6.8 Hz, 2H), 7.23e7.30 (m, 5H), 7.78 (d, J¼8.4 Hz, 2H); 13C NMR
2H); 13C NMR (100 MHz, CDCl3)
d 4.29, 21.65, 38.62, 43.49, 73.27,
93.58, 128.43, 128.57, 129.41, 129.44, 135.77, 145.19, 152.16.
(100 MHz, CDCl3)
d 21.34, 36.79, 38.33, 42.54, 81.19, 85.83, 121.79,
4.1.4. (Z)-N-(4-Chlorobut-2-enyl)-3-phenyl-N-tosylpropiolamide
127.56, 127.73, 128.09, 128.48, 129.56, 131.01, 131.41, 135.40, 143.69.
(1e). 1H NMR (400 MHz, CDCl3):
d
2.43 (s, 3H), 4.28 (d, J¼7.9 Hz,
2H), 4.75 (d, J¼7.0 Hz, 2H), 5.72e5.77 (m, 1H), 5.86e5.91 (m, 1H),
4.2.2. (Z)-N-(4-Chlorobut-2-enyl)-N-(hept-2-ynyl)-4-methyl-
7.30e7.56 (m, 7H), 7.88e7.91 (m, 2H); 13C NMR (100 MHz, CDCl3)
benzenesulfonamide (1i). 1H NMR (400 MHz, CDCl3):
d 0.82e0.86
d
21.67, 38.65, 43.49, 81.37, 93.84, 119.22, 128.24, 128.52, 128.72,
(m, 3H), 1.19e1.24 (m, 4H), 1.89e1.94 (m, 2H), 2.43 (s, 3H), 3.89 (dd,
J¼1.2, 7.2 Hz, 2H), 4.05 (t, J¼2.0 Hz, 2H), 4.11 (dd, J¼1.2, 7.6 Hz, 2H),
5.55e5.62 (m,1H), 5.83e5.90 (m,1H), 7.30 (d, J¼8.4 Hz, 2H), 7.73 (d,
129.59,129.73,131.12,132.76,135.77,145.32,152.28. HRMS calcd for
C20H18ClNO3SþH: 388.0774. Found: [MþþH]: 388.0786.
J¼8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d 13.40, 17.96, 21.39,
4.1.5. (Z)-N-(4-Chlorobut-2-enyl)-N-tosylhept-2-ynamide (1f). 1H
NMR (400 MHz, CDCl3):
21.73, 30.20, 36.41, 38.31, 42.21, 71.85, 86.51, 127.71, 127.78, 129.31,
130.62, 135.59, 143.36.
d
0.90 (t, J¼7.5 Hz, 3H), 1.36e1.42 (m, 2H),
1.49e1.55 (m, 2H), 2.35 (t, J¼7.1 Hz, 2H), 2.44 (s, 3H), 4.26 (dd, J¼0.7,
7.8 Hz, 2H), 4.69 (dd, J¼1.1, 7.0 Hz, 2H), 5.65e5.72 (m, 1H),
5.84e5.90 (m, 1H), 7.32 (d, J¼7.6 Hz, 2H), 7.85 (d, J¼8.8 Hz, 2H). 13C
4.2.3. (Z)-N-Benzyl-N-(but-2-ynyl)-4-chlorobut-2-en-1-amine
(1j). 1H NMR (400 MHz, CDCl3):
d
1.81 (t, J¼2.0 Hz, 3H), 3.91e4.02
NMR (100 MHz, CDCl3)
d
13.40, 18.76, 21.63, 21.94, 29.26, 38.63,
(m, 2H), 4.13e4.17 (m, 2H), 4.58 (s, 2H), 4.76 (d, J¼6.0 Hz, 2H),
43.55, 73.90, 97.74, 128.41, 128.56, 129.43, 135.81, 145.14, 152.25.
HRMS calcd for C18H22ClNO3SþH: 368.1087. Found: [MþþH]:
368.1090.
5.76e5.87 (m, 2H), 7.25e7.35 (m, 5H); 13C NMR (100 MHz, CDCl3)
d
3.47, 36.07, 38.74, 48.96, 60.62, 73.81, 127.44, 127.55, 128.14,
128.51, 129.47, 136.97, 155.63.
4.2. General procedure for the electron-rich enyne substrates;
representative preparation of (Z)-N-(but-2-ynyl)-N-(4-
chlorobut-2-enyl)-4-methylbenzenesulfonamide (1g)
4.2.4. (Z)-N-(4-Chlorobut-2-enyl)-N-(hept-2-ynyl)-4-methoxyani-
line (1k). 1H NMR (400 MHz, CDCl3):
d
0.88 (t, J¼7.2 Hz, 3H),
1.33e1.39 (m, 2H), 1.41e1.48 (m, 2H), 2.16 (tt, J¼2.0, 7.2 Hz, 2H),
3.77 (s, 3H), 3.87e3.90 (m, 4H), 4.06e4.07 (m, 2H), 5.84e5.86 (m,
To a solution of NaH (0.92 g, 50 wt %, 19.2 mmol) in DMF (20 mL)
2H), 6.836e6.838 (m, 4H); 13C NMR (100 MHz, CDCl3)
d
13.56,
was added dropwise a solution of tert-butyl tosylcarbamate (4.8 g,
18.36, 21.86, 30.83, 41.25, 44.56, 53.01, 55.61, 75.49, 84.81, 114.40,

4216
J. Wang et al. / Tetrahedron 66 (2010) 4212e4217
117.14, 128.09, 131.59, 143.11, 152.89. HRMS calcd for C18H24ClNO:
305.1546. Found: 305.1537.
4.3.1. (E)-1-Benzyl-3-(1-chloroethylidene)-4-vinylpyrrolidin-2-one
(2a). In accordance with the general procedure above, a solution of
substrate 1a (52.4 mg, 0.2 mmol, 100 mol %), [Rh(COD)Cl]2 (9.9 mg,
0.02 mmol, 10 mol %), and dppb (18.8 mg, 0.044 mmol, 22 mol %) in
DCE (2 mL) was stirred for 2 min, and then AgSbF6 (13.7 mg,
0.04 mmol, 20 mol %) in DCE (1 mL) was added to the system. The
reaction was performed at 80 ꢀC and monitored by TLC. Purification
by flash column chromatography (silica gel, ethyl acetate/
hexane¼1:20) provides the title compound; yield: 43.0 mg (82%).
4.2.5. (E)-N-Benzyl-N-(4-chlorobut-2-enyl)but-2-ynamide (1l). 1H
NMR (400 MHz, CDCl3) two isomers:
d 2.01 (s, 1.6H), 2.02 (s, 1.4H),
3.91 (d, J¼4.0 Hz, 1H), 4.00e4.01 (m, 1H), 4.04 (d, J¼5.6 Hz, 1H),
4.08 (d, J¼4.4 Hz, 1H), 4.59 (s, 1H), 4.76 (s, 1H), 5.65e5.67 (m, 1H),
5.70e5.74 (m, 1H), 7.22e7.39 (m, 5H); 13C NMR (100 MHz, CDCl3)
two isomers:
d 3.96, 43.76, 43.96, 44.25, 46.64, 48.88, 51.74, 73.02,
73.13, 89.49, 89.61, 127.50, 127.82, 128.19, 128.42, 128.54, 128.70,
129.14,129.37,129.57,136.03,136.22,154.55,154.70. HRMS calcd for
C15H16ClNO: 261.0920. Found: 261.0923.
1H NMR (400 MHz, CDCl3):
d
2.71 (d, J¼1.2 Hz, 3H), 2.98 (dd, J¼1.6,
10.1 Hz, 1H), 3.45 (dd, J¼7.6, 9.6 Hz, 1H), 3.65e3.66 (m, 1H), 4.42 (d,
J¼14.5 Hz, 1H), 4.58 (d, J¼15.1 Hz, 1H), 5.06e5.10 (m, 2H),
5.66e5.75 (m, 1H), 7.22e7.35 (m, 5H); 13C NMR (100 MHz, CDCl3)
4.2.6. (E)-N-Benzyl-N-(4-chlorobut-2-enyl)-3-phenylpropiolamide
d 22.24, 41.10, 46.93, 48.97, 115.66, 127.63, 128.08, 128.68, 129.55,
135.90, 136.01, 142.17, 165.73.
(1m). 1H NMR (400 MHz, CDCl3) two isomers:
d
3.99e4.06 (m, 3H),
4.18 (d, J¼4.4 Hz, 1H), 4.66 (s, 1H), 4.85 (s, 1H), 5.71e5.73 (m, 1H),
5.77e5.81 (m, 1H), 7.27e7.43 (m, 8H), 7.50e7.56 (m, 2H); 13C NMR
4.3.2. (E)-1-Benzyl-3-(chloro(phenyl)methylene)-4-vinylpyrrolidin-
(100 MHz, CDCl3) two isomers:
d
43.72, 43.95, 44.53, 46.90, 49.03,
2-one (2b). 1H NMR (400 MHz, CDCl3)
d
3.04 (dd, J¼1.7, 10.4 Hz,
51.92, 81.22, 81.39, 90.51, 90.60,120.10,120.15,127.57,127.60,127.91,
128.26, 128.29, 128.41, 128.44, 128.60, 128.78, 128.90, 129.58,
129.78, 130.08, 132.26, 132.33, 135.91, 136.11, 154.45, 154.62. HRMS
calcd for C20H18ClNO: 323.1077. Found: 323.1077.
1H), 3.54 (dd, J¼7.4, 9.6 Hz, 1H), 3.81e3.85 (m, 1H), 4.34 (d,
J¼14.4 Hz, 1H), 4.58 (d, J¼15.2 Hz, 1H), 5.15e5.22 (m, 2H),
5.76e5.85 (m, 1H), 7.20e7.50 (m, 10H); 13C NMR (100 MHz, CDCl3)
d
41.92, 47.03, 48.87, 116.12, 127.59, 127.68, 128.23, 128.68, 129.18,
129.37, 131.08, 135.53, 135.96, 136.49, 141.07, 164.09.
4.2.7. (E)-N-Benzyl-N-(4-chlorobut-2-enyl)hept-2-ynamide (1n). 1H
NMR (400 MHz, CDCl3) two isomers:
d
0.87 (t, J¼7.2 Hz, 1.6H), 0.92
4.3.3. (E)-1-Benzyl-3-(1-chloropentylidene)-4-vinylpyrrolidin-2-one
(t, J¼7.2 Hz, 1.4H), 1.35e1.46 (m, 2H), 1.49e1.59 (m, 2H), 2.34e2.39
(m, 2H), 3.92 (d, J¼3.6 Hz, 1H), 4.01e4.02 (m, 1H), 4.05 (d, J¼5.2 Hz,
1H), 4.09 (d, J¼4.0 Hz, 1H), 4.59 (s, 1H), 7.46 (s, 1H), 5.66e5.68 (m,
1H), 5.71e5.75 (m, 1H), 7.23e7.39 (m, 5H); 13C NMR (100 MHz,
(2c). 1H NMR (400 MHz, CDCl3)
d
0.95 (t, J¼7.0 Hz, 3H), 1.35e1.45
(m, 2H), 1.58e1.69 (m, 2H), 2.97 (dd, J¼1.6, 9.5 Hz, 1H), 3.07e3.14
(m, 1H), 3.25e3.32 (m, 1H), 3.44 (dd, J¼7.4, 10.0 Hz, 1H), 3.63e3.67
(m, 1H), 4.43 (d, J¼15.1 Hz, 1H), 4.57 (d, J¼15.6 Hz, 1H), 5.06e5.10
(m, 2H), 5.67 (m, 1H), 7.21e7.36 (m, 5H); 13C NMR (100 MHz, CDCl3)
CDCl3) two isomers:
d 13.32, 13.36, 18.49, 18.50, 21.80, 21.86, 29.57,
29.61, 43.75, 43.98, 44.32, 46.68, 48.88, 51.74, 73.68, 73.82, 93.60,
93.69, 127.46, 127.76, 128.21, 128.49, 128.52, 128.66, 129.07, 129.34,
129.46, 136.08, 136.27, 154.63, 154.78. HRMS calcd for
C18H22ClNOꢂCl: 268.1701. Found: [MþꢂCl]: 268.1725.
d 0.99, 13.90, 21.97, 30.24, 33.96, 41.14, 46.96, 49.03, 115.56, 127.64,
128.11, 128.70, 129.46, 136.04, 136.10, 147.46, 165.57. HRMS calcd for
C18H22ClNO: 303.1390. Found: 303.1397.
4.3.4. (E)-3-(1-Chloroethylidene)-1-tosyl-4-vinylpyrrolidin-2-one
4.2.8. (E)-N-(4-Chlorobut-2-enyl)-3-phenyl-N-tosylpropiolamide
(2d). 1H NMR (400 MHz, CDCl3):
d
2.44 (s, 3H), 2.57 (d, J¼1.2 Hz,
(1o). 1H NMR (400 MHz, CDCl3):
d
2.43 (s, 3H), 4.08 (d, J¼6.4 Hz,
3H), 3.69e3.74 (m, 1H), 3.78 (dd, J¼1.6, 10.2 Hz, 1H), 3.90 (dd, J¼7.6,
10.0 Hz, 1H), 5.09e5.16 (m, 2H), 5.68e5.77 (m, 1H), 7.35 (d,
J¼8.8 Hz, 2H), 7.93 (d, J¼8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3)
2H), 4.69 (d, J¼5.6 Hz, 2H), 5.89e6.03 (m, 2H), 7.31 (d, J¼7.6 Hz, 2H),
7.38e7.42(m, 2H), 7.47e7.50 (m, 1H), 7.53e7.55 (m, 2H), 7.91 (d,
J¼8.8 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d
21.57, 43.77, 47.73,
d 21.70, 22.87, 40.88, 48.92, 116.77, 127.91, 128.18, 129.69, 134.54,
81.28, 93.29, 119.10, 128.60, 128.64, 129.43, 130.40, 131.03, 132.61,
135.53, 145.23, 152.29. HRMS calcd for C20H18ClNO3S: 387.0696.
Found: 387.0671.
134.92, 145.29, 148.26, 163.73.
4.3.5. (E)-3-(Chloro(phenyl)methylene)-1-tosyl-4-vinylpyrrolidin-2-
one (2e). 1H NMR (400 MHz, CDCl3):
d
2.41 (s, 3H), 3.84 (dd, J¼1.5,
4.2.9. (E)-N-(4-Chlorobut-2-enyl)-N-tosylhept-2-ynamide (1p). 1H
9.8 Hz, 1H), 3.87e3.91 (m, 1H), 3.99 (dd, J¼7.5, 9.8 Hz, 1H),
NMR (400 MHz, CDCl3):
d
0.91 (t, J¼7.2 Hz, 3H), 1.35e1.44 (m,
5.19e5.24 (m, 2H), 5.78e5.87 (m, 1H), 7.26e7.39 (m, 7H), 7.86 (d,
2H), 1.50e1.57 (m, 2H), 2.35 (t, J¼6.8 Hz, 2H), 2.44 (s, 3H), 4.07
(d, J¼6.4 Hz, 2H), 4.63 (d, J¼5.6 Hz, 2H), 5.83e5.98 (m, 2H), 7.31
(d, J¼8.8 Hz, 2H), 7.87 (d, J¼8.8 Hz, 2H); 13C NMR (100 MHz,
J¼8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3):
d 21.58, 41.76, 48.82,
116.99, 127.76, 128.04, 128.82, 128.98, 129.58, 130.10, 134.23, 134.81,
135.30, 145.10, 146.60, 161.81. HRMS calcd for C20H18ClNO3S:
387.0696. Found: 387.0692.
CDCl3)
d 13.35, 18.64, 21.57, 21.87, 29.20, 43.77, 47.75, 73.89,
97.20, 128.72, 128.85, 129.32, 130.20, 135.65, 145.06, 152.29.
HRMS calcd for C18H22ClNO3S: 367.1009. Found: 367.1013.
4.3.6. (E)-3-(1-Chloropentylidene)-1-tosyl-4-vinylpyrrolidin-2-one
(2f). 1H NMR (400 MHz, CDCl3):
d
0.87 (t, J¼7.3 Hz, 3H), 1.24e1.34
(m, 2H), 1.49e1.57 (m, 2H), 2.45 (s, 3H), 2.85e2.92 (m, 1H),
3.06e3.14 (m, 1H), 3.69e3.72 (m, 1H), 3.78 (dd, J¼1.5, 9.5 Hz, 1H),
3.88 (dd, J¼7.5, 9.9 Hz, 1H), 5.08e5.16 (m, 2H), 5.69e5.78 (m, 1H),
7.34 (d, J¼8.0 Hz, 2H), 7.92 (d, J¼8.4 Hz, 2H); 13C NMR (100 MHz,
4.3. General procedure for the cycloisomerization of N-
tethered enynes with the cationic Rh-catalytic system
Under nitrogen atmosphere, a 25 mL Schlenk tube was charged
with enyne substrate (0.2 mmol, 100 mol %), [Rh(COD)Cl]2 (9.9 mg,
0.02 mmol, 10 mol %), ligands (0.044 mmol, 22 mol %), and DCE
(2 mL). After being stirred for 2 min, silver salt (0.04 mmol, 20 mol
%) in DCE (1 mL) was added to the system. The reaction was carried
out at the indicated temperature and monitored by TLC. After the
reaction was completed, the reaction mixture was evaporated and
directly subjected to column chromatography using petroleum
ether/ethyl acetate as eluent to give the cyclization product.
CDCl3) d 13.81, 21.70, 21.90, 30.09, 34.54, 40.90, 48.98, 116.67,
127.73, 128.14, 129.68, 134.63, 134.97, 145.21, 153.58, 163.46. HRMS
calcd for C18H22ClNO3S: 367.1009. Found: 367.1007.
4.3.7. (E)-3-(1-Chloroethylidene)-1-tosyl-4-vinylpyrrolidine (2g). 1H
NMR (400 MHz, CDCl3):
d
1.98 (d, J¼1.2 Hz, 3H), 2.44 (s, 3H), 3.14
(dd, J¼6.4, 9.6 Hz, 1H), 3.40 (dd, J¼1.6, 9.2 Hz, 1H), 3.45e3.48 (m,
1H), 3.60e3.63 (m, 1H), 3.94e3.98 (m, 1H), 5.04e5.11 (m, 1H),
5.64e5.72 (m, 1H), 7.34 (d, J¼8.0 Hz, 2H), 7.70 (d, J¼8.4 Hz, 2H); 13C

J. Wang et al. / Tetrahedron 66 (2010) 4212e4217
4217
Roessner, C. A.; Scott, A. I. J. Am. Chem. Soc. 1996, 118, 1657e1662; (d) Neya, S.;
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N.; Ozturk, O. J. Org. Chem. 2002, 67, 7457e7464.
NMR (100 MHz, CDCl3)
d 21.55, 23.31, 46.24, 50.19, 53.14, 115.90,
124.32, 127.86, 129.74, 132.05, 132.74, 135.04, 143.94. HRMS calcd
for C15H18ClNO2SꢂCl: 276.1058. Found: [MþꢂCl] 276.1064.
3. (a) Trost, B. M. Acc. Chem. Res. 1990, 23, 34e42 and references therein; (b)
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4.3.8. (E)-3-(Chloro(phenyl)methylene)-1-tosyl-4-vinylpyrrolidine
(2h). 1H NMR (400 MHz, CDCl3):
d 2.43 (s, 3H), 3.33e3.40 (m, 2H),
3.65e3.68 (m, 1H), 3.71 (d, J¼14.4 Hz, 1H), 4.06 (dd, J¼1.6, 14.4 Hz,
1H), 5.11e5.21 (m, 2H), 5.70e5.79 (m, 1H), 7.27e7.39 (m, 7H), 7.63
(d, J¼8.8 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d 21.48, 47.03, 50.97,
52.50, 116.36, 126.91, 127.68, 127.81, 128.42, 128.93, 129.69, 132.44,
134.72, 135.27, 137.39, 143.85.
4.3.9. (E)-3-(1-Chloropentylidene)-1-tosyl-4-vinylpyrrolidine
(2i). 1H NMR (400 MHz, CDCl3):
d
0.89 (t, J¼6.8 Hz, 3H), 1.24e1.27
(m, 2H), 1.47e1.51 (m, 2H), 2.19 (dt, J¼3.2, 7.2 Hz, 2H), 2.45 (s, 3H),
3.13 (dd, J¼7.2, 10.0 Hz, 1H), 3.40 (dd, J¼1.6, 9.2 Hz, 1H), 3.47e3.51
(m, 1H), 3.65 (d, J¼13.6 Hz, 1H), 3.98 (dd, J¼1.2, 13.6 Hz, 1H),
5.04e5.11 (m, 2H), 5.65e5.73 (m, 1H), 7.35 (d, J¼8.4 Hz, 2H), 7.70 (d,
J¼8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3)
d 13.87, 21.52, 21.79, 29.11,
36.23, 46.15, 49.94, 52.96, 115.80, 127.83, 129.51, 129.69, 132.02,
132.53, 135.09, 143.88.
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Acknowledgements
We thank the National Natural Science Foundation of China, the
Science and Technology Commission, and the Education Commis-
sion of Shanghai Municipality for financial support.
References and notes
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