Catalytic intramolecular decarbonylative coupling of 3-aminocyclobutenones and alkenes: A unique approach to [3.1.0] bicycles

Article abstract of DOI:10.1016/j.tet.2015.02.087

Here we describe a rhodium-catalyzed intramolecular decarbonylative coupling between 3-aminocyclobutenones and alkenes for synthesis of substituted [3.1.0] bicycles. This transformation represents a formal cyclopropanation reaction, in which the cyclobute

Full text of DOI:10.1016/j.tet.2015.02.087

Tetrahedron 71 (2015) 4478e4483
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Catalytic intramolecular decarbonylative coupling
of 3-aminocyclobutenones and alkenes: a unique approach
to [3.1.0] bicycles
Xuan Zhou, Imran Zafar, Guangbin Dong *
Department of Chemistry, University of Texas at Austin, Austin, TX 78712, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Here we describe a rhodium-catalyzed intramolecular decarbonylative coupling between 3-
Received 28 January 2015
Received in revised form 23 February 2015
Accepted 25 February 2015
Available online 5 March 2015
aminocyclobutenones and alkenes for synthesis of substituted [3.1.0] bicycles. This transformation rep-
resents a formal cyclopropanation reaction, in which the cyclobutenones serve as a one-carbon-unit
synthon.
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
CeC cleavage
Cyclobutenone
Rhodium catalysis
Decarbonylation
Cyclopropanation
1. Introduction
synthesis of poly-substituted cyclobutenone substrates is non-
trivial. We were particularly inspired by an efficient method re-
4
,5
Cyclobutenones are a unique class of compounds, and often
serve as important synthetic intermediates due to their high re-
activity driven by strain release. Conventionally, cyclobutenones
ported by Danheiser and co-workers for preparing multi-
5
substituted 3-aminocyclobutenones from readily available of
1
6
7
ynamides and ketenes. Here, as an exploratory study, we describe
our development of a Rh-catalyzed decarbonylative coupling of 3-
aminocyclobutenones with alkenes leading to [3.1.0] bicycles
are often employed as a vinyl-ketene equivalent through a retro-4
p
cyclization.2 During the past two decades, novel transformations
of cyclobutenones have been realized through transition metal-
catalyzed carbonecarbon (CeC) bond cleavage followed by CeC
bond formation.2 These reactions often lead to complex scaffolds
that are challenging to prepare using traditional approaches. For
example, using Ni, Co, Ru and Rh as catalysts, intermolecular or
intramolecular cyclization of cyclobutenones with alkenes, alkynes
and other strained rings can provide five to eight-membered ring
systems efficiently.2
a
Our group has been interested in applying catalytic CeC bond
activation methods in complex molecule synthesis. Recently, we
have demonstrated fused-ring and spirocycle synthesis through
3
Rh-catalyzed CeC activation of benzocyclobutenones (Scheme 1a).
An intriguing question is whether non-benzo-type cyclobutenones
will behave similarly in the catalytic intramolecular coupling re-
actions, which, to our knowledge, has not been explored previously.
One potential challenge for this study is that regioselective
1
*
Corresponding author. Tel./fax: þ1 512 232 8220; e-mail address: gbdong@cm.
Scheme 1. Rh -catalyzed intramolecular cyclization between cyclobutenones and
alkenes.
utexas.edu (G. Dong).
http://dx.doi.org/10.1016/j.tet.2015.02.087
0
040-4020/Ó 2015 Elsevier Ltd. All rights reserved.

X. Zhou et al. / Tetrahedron 71 (2015) 4478e4483
4479
(
Scheme 1b). Compared to the corresponding benzocyclobute-
Table 1
Selected reaction optimization conditions
nones, a distinct reactivity with 3-aminocyclobutenones was dis-
covered during this study.
2
. Results and discussions
As illustrated in Scheme 2, the tethered alkene-cyclobutenone
substrates can be efficiently synthesized in three steps from read-
5
,8
ily available enyne substrates.
Our initial study of the intra-
9
molecular cyclization reaction employed cyclobutenone 4a as the
ꢀ
model substrate. When directly heating 4a in 1,4-dioxane at 130 C,
0
vinyl cyclobutanones 6a and 6a were slowly formed (their struc-
10
tures were unambiguously confirmed by X-ray crystallography)
(
[
entry 1, Table 1). The reaction likely proceeds through a retro-
2þ2] of the cyclobutenone to give a vinyl ketene and then a [2þ2]
Yield [%]a
Entry
Rh catalyst
Ligand
None
Solvent
11
cycloaddition with the alkene (vide infra, Scheme 3). It is in-
teresting to note that compounds 6a and 6a represent a pair of
0
0
1
2
3
4
5
6
7
8
9
None
[Rh(cod)Cl]
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Toluene
6a15%, 6a 15%
0
2
P(C
None
P(C
6
F
5
)
3
3
6a15%, 6a 15%
c
conformational isomers and can be separated using regular silica-
gel chromatography. The C3eN bond cannot freely rotate likely
caused by the significant steric hindrance between the tetra-
[Rh(CO) Cl]2
5
68%
2
[Rh(CO)
[Rh(CO)
[Rh(CO)
[Rh(CO)
[Rh(CO)
[Rh(CO)
[Rh(CO)
[Rh(CO)
[Rh(CO)
2
Cl]
2
Cl]
2
Cl]
2
Cl]
2
Cl]
2
Cl]
2
Cl]
2
Cl]
2
Cl]
2
2
2
2
2
2
2
2
2
6
F
5
)
5 84%
5 60%
5 35%
5 50%
5 43%
5 78%
5 80%
5 65%
5 81%
b
dppp
b
dppm
substituted olefin and the bulky cyclobutanone. [Rh(cod)Cl]
not influence the reaction, because almost the same results were
obtained when using [Rh(cod)Cl] in combination with bidentate
phosphine ligands (dppp, dppf and dppb) as well as monodentate
P(C ligand (entry 2). However, when the more electron-
deficient [Rh(CO) Cl] was employed as the catalyst, an in-
2
did
dppbb
PPh
3
P(C
P(C
P(C
P(C
6
F
5
)
5
)
5
)
5
)
3
3
3
3
2
1
1
1
0
1
2
6
6
6
F
F
F
m-Xylene
THF
PhCl
6 5 3
F )
2
2
a
b
c
Determined by 1H NMR spectroscopy using mesitylene as the internal standard.
teresting bicycle[3.1.0]-hexane compound 5 was observed as the
dominating product in 68% yield (entry 3). The yield can be further
6
mol % of the ligand was used.
is a mixture of inseparable isomers: 5a and 5a (1:1).
0
5
6 5 3
improved to 84% by adding P(C F ) as an additional ligand, in
0
which cyclobutanones 6a and 6a (the major byproducts) only
formed in 10% yield (entry 4); in contrast, using more electron-rich
ligands gave diminished yields (entries 5e8). The solvent effect was
also investigated (entries 9e12) and 1,4-dioxane remained to be
optimal.
Scheme 2. General approach for synthesizing the 3-aminocyclobutenone substrates.
Scheme 3. Proposed catalytic cycle.
With the optimized conditions in hand, we next examined the
12
scope of this decarbonylative cyclization reaction (Table 2). First,
change of the substituents on the nitrogen of the amino-
cyclobutenones did not significantly affect the reactivity (entries
cyclobutanone product in 84% yield (entry 10).13 In contrast, use of
a 1,2-disubstituted olefin and elongation of the linkage led to
a complex unidentifiable mixture (entries 11 and 12).
1
e3). While the methyl formate substrates (4a and 4b) all gave
a pair of conformational isomers, the less hindered oxazolidone
substrates afforded a single isomer (entries 3e10). Besides the
nitrogen-based linker (entries 3e4), oxygen and carbon-based
linkers are also effective (entries 5e7). Different substituents on
the cyclobutenone C2 position were also examined. When replac-
ing the gem-dimethyls to a cyclopentane group, the desired vinyl
It is well known that decarbonylation of cyclobutanones to cy-
clopropanes can be catalyzed by transition metals, such as Rh(I)
14
complexes. Thus, it is natural to concern whether the [3.1.0] bi-
0
cycle (e.g., 5a/5a ) comes from the direct decarbonylation of
0
a cyclobutanone intermediate (e.g., 6a/6a ). Hence, the following
0
experiment was conducted. When treating a mixture of 6a and 6a
cyclopropane 5h was isolated in 42% yield and a ring-opening diene
0
under the standard reaction conditions, no decarbonylation prod-
(
5h ) was found as the major byproduct (entry 8). The exact reason
0
0
0
uct 5a/5a was observed (Eq. 2), suggesting that the [3.1.0] bicycle
of forming diene 5h remains unclear. It is likely that 5h did not
come from the decomposition of 5h as treatment of 5h under the
should come from a different reaction pathway.
0
reaction conditions did not yield any 5h . It was surprising to note
that the diethyl analogue (4i) gave the ring-opening diene 5i as the
sole product (entry 9), which suggests the steric hindrance at the
C2 position of the cyclobutenone plays an important role in the
selectivity of the reaction.
An interesting observation is that the substrate tethered with
a 1,1-disubstituted olefin gave a complete selectivity for the [2þ2]

4
480
X. Zhou et al. / Tetrahedron 71 (2015) 4478e4483
a
Table 2
Each reaction was ran on a 0.1 mmol scale in a sealed 4 mL vial, using 5 mol %
Substrate scopea
[Rh(CO)
Cl]
Yields of isolated products.
ꢀ
2 6 5 3
and 12 mol % P(C F ) , in 1,4-dioxane (1.5 mL), at 130 C, for 18 h.
2
b
Entry
1
Substrate
Product
Yield [%]b
c
The number in parentheses represents the yield based on recovered starting
material (brsm).
d
The ratio was determined by 1H NMR.
e
80
The structure of 5c was confirmed by a series of 2D NMRs, DEPT, and HRMS.
0
d
f
0
5a:5a ¼1:1
5h and 5i were isolated as a single olefin-geometric isomer; the exact olefin
geometry for each was not determined.
2
75
b:5b ¼1:1
The proposed catalytic cycle is depicted in Scheme 3.15 First,
0
d
5
a retro-4p cyclization of cyclobutenones should give a reactive
vinyl ketene intermediate (7), which can undergo either a [2þ2]
cycloaddition with the tethered alkene to give cyclobutanone 6
(background reaction) or a cyclometalation reaction mediated by
3
4
72
45
Rh to give a five-membered metallacycle 8 (catalytic reaction).
Subsequent CO de-insertion from complex 8 followed by reductive
elimination should provide cyclopropane 5.
3. Conclusion
In summary,
a Rh-catalyzed intramolecular coupling of
3-aminocyclobutenones with alkenes has been studied. In this
transformation, the cyclobutenone serves as a one-carbon synthon
leading to an unprecedented cyclopropanation reaction. This re-
action offers a unique approach for synthesizing heavily substituted
vinyl cyclopropanes and [3.1.0]-bicycle skeletons. Stimulated by
this work, efforts on investigating the coupling of less substituted
cyclobutenones with alkenes, alkynes and allenes are ongoing in
this laboratory.
5
6
65
72 (86)c
4
4
. Experimental
.1. General
7
8
76 (90)
THF, 1,4-dioxane and toluene were purchased from Fischer
Scientific, distilled freshly over sodium and freeze-pump-
thawed. Other commercially available chemicals were pur-
chased and used without additional purification unless noted
otherwise. All reactions were carried out under nitrogen with
stirring bar in a rubber septum sealed flask. Reaction tempera-
tures were reported as the temperatures of the bath surrounding
the flasks or vials. Sensitive reagents and solvents were trans-
ferred under nitrogen into a nitrogen-filled glove-box with
standard techniques. Analytical thin-layer chromatography (TLC)
was carried out using 0.2 mm commercial silica gel plates (silica
gel 60, F254, EMD chemical). Vials (15ꢁ45 mm 1 dram (4 mL)/
9
45
84
2
7.75ꢁ95 mm 10 dram (40 mL) with PTFE lined cap attached)
were purchased from Qorpak and flame-dried or put in an oven
overnight and cooled in a dessicator. High-resolution mass
spectra (HRMS) were obtained on a Karatos MS9 and are re-
ported as m/z (relative intensity). Accurate masses are reported
10
þ
þ
ꢂ
þ
for the molecular ion [MþNa] , [MþH] , [MꢂH] or [M] . In-
frared spectra were recorded on a Nicolet 380 FTIR using neat
thin film technique. Nuclear magnetic resonance spectra ( H
1
1
3
NMR and
C NMR) were recorded with a Varian Gemini
1
13
(
400 MHz, H at 400 MHz, C at 100 MHz). Unless otherwise
noted, all spectra were acquired in CDCl . Chemical shifts are
reported in parts per million (ppm, ), downfield from tetrame-
thylsilane (TMS,
¼0.00 ppm) and are referenced to residual
solvent (CDCl
1
1
1
2
0
0
3
d
d
1
13
3
,
d
¼7.26 ppm ( H) and 77.00 ppm ( C)). Cou-
1
plingconstants were reported in Hertz (Hz). Data for H NMR
spectra were reported as follows: s¼singlet, d¼doublet, t¼triplet,
q¼quartet, quin¼quintet, dd¼doublet of doublets, td¼triplet of
doublets, ddd¼doublet of doublet of doublets, m¼multiplet,
coupling constant (Hz), and integration.

X. Zhou et al. / Tetrahedron 71 (2015) 4478e4483
4481
4
.2. General procedure for synthesis of cyclobutenone com-
(400 MHz, CDCl
3
)
d
5.70e5.59 (m, 1H), 5.21e5.17 (m, 1H), 5.12e5.09
pounds through [2D2] cyclization
(m, 1H), 4.57e4.53 (m, 2H), 4.28e4.24 (m, 2H), 3.69 (s, 6H), 2.73 (d,
13
J¼7.2 Hz, 2H), 2.66 (s, 2H), 1.31 (s, 6H). C NMR (100 MHz, CDCl
3
)
Acyl chloride (3.0 mmol) and Et
3
N (0.70 ml, 5.0 mmol) were
d
195.4, 170.9, 167.3, 152.3, 132.2, 119.8, 118.0, 63.0, 61.5, 57.5, 52.6,
added drop wise to a solution of ynamide (1.0 mmol) in anhydrous
44.1, 37.8, 26.5, 20.7. IR:
1207,1126, 1042, 913 cm . HRMS calcd for C18
388.1372, found: 388.1370.
n
2957, 1784, 1734, 1611, 1437, 1371, 1328,
ꢀ
ꢂ1
þ
þ
DCM (10 mL) at 0 C under N
2
. The resulting mixture was stirred for
H
23NNaO
7
[MþNa] :
ꢀ
4
8 h at 40 C, and then quenched with saturated aqueous NaHCO
3
solution. The layers were separated, and the aqueous layers were
extracted with EtOAc (3ꢁ20 mL). The organic layers were combined
4.2.7. Compound 4g. Compound 4g was obtained in 72% yield as
1
and washed with brine (20 mL), which were then dried over MgSO
4
a colorless oil. R
CDCl 5.73e5.63 (m, 1H), 5.23e5.19 (m, 1H), 5.13e5.10 (m, 1H),
4.57e4.53 (m, 2H), 4.30e4.26 (m, 2H), 4.21e4.09 (m, 4H), 2.75 (d,
f
¼0.50, DCM/Acetone¼10:1, H NMR (400 MHz,
and concentrated. Compounds 4ae4l were purified via silica gel
flash chromatography. (For details, see Supplementary data).
3
) d
1
3
J¼7.6 Hz, 2H), 2.65 (s, 2H), 1.31 (s, 6H), 1.32 (t, J¼7.2 Hz, 6H).
C
4
.2.1. Compound 4a. Compound 4a was obtained in 85% yield as
NMR (100 MHz, CDCl 195.5, 170.5, 167.3, 152.3, 132.3, 119.8,
3
) d
1
a white solid. R
CDCl 7.54e7.52 (m, 2H), 7.40e7.39 (m, 2H), 7.32e7.30 (m, 1H),
.30e7.21 (m, 4H), 5.66e5.56 (m, 1H), 5.28 (s, 2H), 5.26e5.21 (m,
f
¼0.60, hexans/EtOAc¼2:1, H NMR (400 MHz,
118.2, 62.9, 61.6, 61.5, 57.4, 44.1, 37.6, 26.3, 20.8, 13.9. IR:
n
2982,
ꢂ1
3
)
d
1785, 1730, 1612, 1395, 1203, 1042, 913 cm . HRMS calcd for
þ
þ
7
1
2
C
20
H
27NNaO
7
[MþNa] : 416.1685, found: 416.1681.
H), 5.06e5.03 (m, 1H), 3.86 (s, 3H), 3.71 (d, J¼6.0 Hz, 2H), 3.49 (s,
13
H), 2.39 (s, 3H), 1.33 (s, 6H). C NMR (100 MHz, CDCl
3
)
d
195.8,
4.2.8. Compound 4h. Compound 4h was obtained in 7% yield (70%
1
173.0, 152.3, 143.6, 136.1, 135.1, 132.9, 129.6, 128.8, 127.5, 127.3,
brsm yield) as a colorless oil. R
(400 MHz, CDCl
f
¼0.60, hexans/EtOAc¼1:1, H NMR
1
25.2, 118.5, 115.9, 63.1, 54.4, 51.0, 39.7, 21.4, 20.6. IR:
n
1752, 1595,
3
)
d
7.61 (d, J¼8.0 Hz, 2H), 7.30 (d, J¼8.0 Hz, 2H),
ꢂ1
1437, 1395, 1346, 1305, 1262, 1185, 1160, 1090, 1044, 743 cm
.
5.64e5.56 (m,1H), 5.26e5.21 (m,1H), 5.12e5.09 (m,1H), 4.63e4.58
þ
þ
HRMS calcd for C26
5
H
30
N
2
NaO
5
S
[MþNa] : 505.1773, found:
(m, 2H), 4.47e4.43 (m, 2H), 3.76 (s, 2H), 3.76 (d, J¼6.8 Hz, 2H), 2.41
ꢀ
13
05.1765. Mp ( C): 100e102.
(s, 3H), 1.99e193 (m, 2H), 1.78e1.70 (m, 2H), 1.69e1.63 (m, 4H).
C
3
NMR (100 MHz, CDCl ) d 195.1, 165.7, 152.0, 143.9, 135.4, 132.3,
4
.2.2. Compound 4b. Compound 4b was obtained in 55% yield (90%
129.9, 127.1, 119.5, 117.6, 70.2, 63.2, 51.0, 44.9, 38.7, 31.4, 26.5, 21.5.
1
ꢂ1
brsm yield) as a white solid. R
f
¼0.30, hexans/EtOAc¼5:1, H NMR
7.63 (d, J¼8.0 Hz, 2H), 7.28 (d, J¼8.0 Hz, 2H),
.69e5.59 (m, 1H), 5.21e5.15 (m, 1H), 5.07e5.04 (m, 1H), 3.87 (s,
H), 3.81 (s, 2H), 3.73 (dt, J¼1.2, 6.0 Hz, 2H), 3.55 (s, 3H), 2.39 (s,
H), 1.22 (s, 6H). 13C NMR (100 MHz, CDCl
195.7, 173.4, 152.2,
43.6, 135.3, 133.0, 129.7, 127.3, 118.5, 115.6, 62.8, 54.2, 50.9, 39.8,
IR:
for C22
n
2924, 1781, 1751, 1607, 1401, 1275, 1260, 913 cm . HRMS calcd
þ
þ
(
400 MHz, CDCl
3
)
d
H N
27 2
O
5
S
[MþH] : 431.1641, found: 431.1636.
5
3
3
4.2.9. Compound 4i. Compound 4i was obtained in 35% yield (81%
1
3
)
d
brsm yield) as a colorless oil. R
(400 MHz, CDCl
f
¼0.60, hexans/EtOAc¼1:1, H NMR
1
3
)
d
7.66 (d, J¼6.4 Hz, 2H), 7.32 (d, J¼8.0 Hz, 2H),
3
6.3, 21.4, 20.5. IR:
n
2959, 2927, 1494, 1428, 1263, 1090, 1043, 955,
5.52e5.44 (m, 1H), 5.25e5.20 (m, 1H), 5.12e5.10 (m, 1H), 4.63e4.59
(m, 2H), 4.47e4.43 (m, 2H), 3.85 (s, 2H), 3.81 (d, J¼6.4 Hz, 2H), 2.43
ꢂ1
þ
þ
916 cm . HRMS calcd for C20
H
26
N
2
NaO
5
S
[MþNa] : 429.1460,
ꢀ
13
found: 429.1456. Mp ( C): 83e85.
(s, 3H), 1.85e175 (m, 4H), 0.83 (d, J¼7.6 Hz, 6H). C NMR (100 MHz,
3
CDCl ) d 194.3, 166.1, 152.2, 143.9, 135.5, 131.1, 129.8, 127.3, 120.2,
4
.2.3. Compound 4c. Compound 4c was obtained in 60% yield (86%
119.5, 72.2, 63.3, 50.2, 45.1, 37.7, 25.5, 21.5, 10.1. IR:
n
2965, 1784,
1
ꢂ1
brsm yield) as a colorless oil. R
f
¼0.55, hexans/EtOAc¼1:1, H NMR
7.62e7.60 (m, 2H), 7.31e7.26 (m, 2H), 5.65e5.56
m, 1H), 5.25e5.23 (m, 1H), 5.15e5.12 (m, 1H), 4.62e4.60 (m, 2H),
1752, 1607, 1401, 1340, 1186, 1157, 1120, 913 cm . HRMS calcd for
þ
þ
(
(
400 MHz, CDCl
3
)
d
C
22
H
29
N
2
O
5
S
[MþH] : 433.1797, found: 433.1780.
13
4
.47e4.45 (m, 2H), 3.77e3.74 (m, 4H), 2.42 (s, 3H), 1.32 (s, 6H).
195.1, 168.7, 151.9, 144.0, 135.2, 132.3,
29.9, 127.1, 119.5, 115.8, 63.2, 62.3, 51.0, 45.0, 38.7, 21.5, 20.3. IR:
C
4.2.10. Compound 4j. Compound 4j was obtained in 60% yield (89%
1
NMR (100 MHz, CDCl
1
3
)
d
brsm yield) as a colorless oil. R
(400 MHz, CDCl
f
¼0.50, hexans/EtOAc¼1:1, H NMR
n
3
)
d
7.59 (d, J¼8.0 Hz, 2H), 7.29 (d, J¼8.0 Hz, 2H),
ꢂ1
1784, 1754, 1344, 1223, 1192, 1159, 1121, 1091, 913, 743 cm . HRMS
5.27 (d, J¼0.8 Hz,1H), 4.98 (s, 1H), 4.62e4.58 (m, 2H), 4.45e4.41 (m,
þ
þ
calcd for C20
H
25
N
2
O
5
S
[MþH] : 405.1484, found: 405.1482.
2H), 3.73 (s, 2H), 3.66 (s, 2H), 2.39 (s, 3H), 1.68 (s, 3H), 1.22 (s, 6H).
13
3
C NMR (100 MHz, CDCl ) d 195.1, 168.1, 151.9, 143.9, 140.3, 135.2,
4
.2.4. Compound 4d. Compound 4d was obtained in 86% yield as
129.8, 127.1, 116.0, 114.3, 63.2, 62.2, 55.0, 44.8, 39.5, 21.4, 19.9. IR:
n
1
ꢂ1
a colorless oil. R
CDCl 5.76e5.69 (m, 1H), 5.16e5.11 (m, 2H), 4.58e4.54 (m, 2H),
.41e4.38 (m, 2H), 3.90 (d, J¼5.6 Hz, 2H), 3.83 (s, 2H), 1.40 (s, 9H),
.35 (s, 6H). 13C NMR (100 MHz, CDCl
195.9, 166.7, 155.2, 152.1,
33.4, 118.4, 116.6, 80.0, 63.1, 61.9, 49.6, 44.3, 37.1, 28.3, 20.6. IR:
f
¼0.40, DCM/Acetone¼10:1, H NMR (400 MHz,
2926,1784, 1753, 1610, 1272, 1224,1191, 1119,1046, 913 cm . HRMS
þ
þ
3
)
d
calcd for C21H
26
N
2
NaO
5
S
[MþNa] : 441.1460, found: 441.1456.
4
1
1
2
3
)
d
4.2.11. Compound 4k. Compound 4k was obtained in 52% yield
1
n
(82% brsm yield) as a colorless oil. R
NMR (400 MHz, CDCl
7.61 (d, J¼8.4 Hz, 2H), 7.29 (d, J¼8.0 Hz,
2H), 5.63e5.56 (m, 1H), 5.27e5.20 (m, 1H), 4.62e4.58 (m, 2H),
.45e4.41 (m, 2H), 3.73 (s, 2H), 3.69 (d, J¼6.4 Hz, 2H), 2.40 (s, 3H),
f
¼0.50, hexans/EtOAc¼1:1, H
ꢂ1
978, 2928, 1754, 1687, 1611, 1458, 1366, 1166, 1145, 1102 cm
.
3
) d
þ
þ
HRMS calcd for C18
H
26
N
2
NaO
5
[MþNa] : 373.1739, found: 373.1736.
4
1
3
4.2.5. Compound 4e. Compound 4e was obtained in 79% yield as
1.57 (dd, J¼0.8, 6.4 Hz, 3H),1.30 (s, 6H). C NMR (100 MHz, CDCl
3
)
1
a colorless oil. R
CDCl
4
2
f
¼0.25, hexans/EtOAc¼1:1, H NMR (400 MHz,
d
195.1, 168.6, 152.0, 143.8, 135.4, 131.2, 129.7, 127.2, 124.5, 116.1,
3
)
d
5.89e5.80 (m, 1H), 5.28e5.23 (m, 1H), 5.20e5.17 (m, 1H),
63.3, 62.1, 50.4, 45.0, 38.3, 21.4, 20.4, 17.7. IR:
n
2963, 1785, 1754,
ꢂ1
.59e4.55 (m, 2H), 4.31e4.27 (m, 2H), 3.96e3.93 (m, 2H), 3.92 (s,
1468, 1341, 1221, 1191, 1158, 1130, 1048 cm . HRMS calcd for
13
þ
þ
H), 1.39 (s, 3H), 1.38 (s, 3H). C NMR (100 MHz, CDCl
3
)
d
194.9,
C H
21 26
N
2
NaO
5
S
[MþNa] : 441.1460, found: 441.1453.
168.9, 151.8, 133.9, 118.7, 117.9, 71.4, 63.0, 62.4, 58.3, 44.5, 20.7. IR: n
ꢂ1
2
C
926, 1782, 1755, 1410, 1218, 1190, 1121, 1072 cm . HRMS calcd for
4.2.12. Compound 4l. Compound 4l was obtained in 75% yield as
þ
þ
1
13
H
18NO
4
[MþH] : 252.1236, found: 252.1227.
a colorless oil. R
f
¼0.40, hexans/EtOAc¼1:1, H NMR (400 MHz,
CDCl 7.62e7.59 (m, 2H), 7.31e7.29 (m, 2H), 5.70e5.60 (m, 1H),
3
) d
4
.2.6. Compound 4f. Compound 4f was obtained in 61% yield (76%
5.04e4.97 (m, 2H), 4.63e4.59 (m, 2H), 4.47e4.43 (m, 2H), 3.74 (s,
2H), 3.11e3.07 (m, 2H), 2.41 (s, 3H), 2.28e2.23 (m, 2H), 1.35 (s, 6H).
1
brsm yield) as a colorless oil. R
f
¼0.40, DCM/Acetone¼10:1, H NMR

4
482
X. Zhou et al. / Tetrahedron 71 (2015) 4478e4483
13C NMR (100 MHz, CDCl
d
195.3, 169.4, 151.9, 144.0, 134.7, 134.5,
3
)
3
(400 MHz, CDCl ) d 4.41e4.37 (m, 2H), 3.77e3.74 (m, 2H),
129.9, 127.2, 117.1, 115.4, 63.3, 62.5, 48.1, 45.0, 39.4, 33.4, 21.4, 20.4.
3.65e3.55 (m, 2H), 3.49e3.46 (m, 1H), 3.27e3.24 (m, 1H), 1.86 (d,
IR:
n
2962, 2926, 1785, 1754, 1609, 1404, 1314, 1290, 1220, 1133,
J¼4.0 Hz, 3H), 1.69 (s, 3H), 1.69e1.67 (m, 1H), 1.42 (s, 9H), 0.99 (dd,
ꢂ1
þ
þ
13
1090 cm . HRMS calcd for C21
26
H N
2
NaO
5
S
[MþNa] : 441.1460,
J¼4.4, 8.0 Hz, 1H), 0.66e0.64 (m, 1H). C NMR (100 MHz, CDCl
3
)
found: 441.1458.
d
156.6,154.8,136.8,126.3, 79.6, 61.9, 52.1, 48.2, 47.9, 46.1, 45.9, 28.4,
2
4.0, 20.2, 16.5. IR:
n
2360, 2342, 1750, 1690, 1406, 1259, 1171,
ꢂ1
þ
þ
4
.3. General procedure for synthesis of Bicyclo[3.1.0]hexane
913 cm . HRMS calcd for C17
found: 345.1786.
H
26
N
2
NaO
4
[MþNa] : 345.1790,
and its analogues
Cyclobutenone substrates (0.1 mmol), [Rh(CO)
2
Cl]
2
(1.95 mg,
4.3.5. Compounds 5e. Compound 5e was obtained in 65% yield as
1
0
.05 mmol), P(C
6
F
5
)
3
(6.4 mg, 0.12 mmol), and anhydrous 1,4-Di-
a colorless oil. R
CDCl 4.42e4.34 (m, 2H), 3.87e3.84 (m, 3H), 3.80e3.77 (m, 1H),
3.64e3.58 (m, 2H), 1.87 (s, 3H), 1.82e1.76 (m, 1H), 1.70 (s, 3H), 0.89
f
¼0.20, hexans/EtOAc¼1:1, H NMR (400 MHz,
oxane (1.5 mL) were added into a 4.0 mL vial in glove box, which
3
) d
ꢀ
were then stirred at 130 C under N
2
for 18 h. The reaction was
solution (10 mL). The
13
quenched with saturated aqueous NaHCO
3
(dd, J¼4.4, 8.0 Hz, 1H), 0.82 (t, J¼4.0 Hz, 1H). C NMR (100 MHz,
layers were then separated, and the aqueous layers were extracted
CDCl
14.0. IR:
calcd for C12
3
)
d
156.6, 126.4, 125.2, 72.4, 69.6, 61.9, 46.1, 29.7, 25.1, 20.2,
ꢂ1
with EtOAc (3ꢁ10 mL). The organic layers were combined, washed
n
2919, 1746, 1410, 1297, 1275, 1105, 1039, 913 cm . HRMS
þ
þ
with brine (20 mL), dried over MgSO
4
and concentrated. The
H
17NNaO
3
[MþNa] : 246.1106, found: 246.1101.
decarbonylative coupling products were purified via silica gel flash
chromatography.
4.3.6. Compounds 5f. Compound 5f was obtained in 72% yield as
1
a colorless oil from 4f. R
(400 MHz, CDCl
f
¼0.30, hexans/EtOAc¼1:1, H NMR
0
0
4.3.1. Compounds 5a and 5a . Compounds 5a and 5a were ob-
3
)
d
4.40 (t, J¼8.0 Hz, 2H), 3.74e3.68 (m, 2H), 3.72 (s,
0
tained from 4a in 80% yield as a colorless oil, 5a and 5a in a 1:1 ratio
3H), 3.69 (s, 3H), 2.83 (d, J¼13.6 Hz, 1H). 2.64e2.58 (m, 2H), 2.41
0
1
(
the ratio of 5a and 5a was determined by crude H NMR). R
f
¼0.55,
7.63e7.60 (m, 4H),
.33e7.30 (m, 4H), 7.27e7.20 (m, 4H), 7.12e7.07 (m, 6H), 4.70 (d,
J¼14.4 Hz, 1H), 4.43 (d, J¼14.4 Hz, 1H), 4.21 (d, J¼14.4 Hz, 1H), 4.16
d, J¼14.4 Hz, 1H), 3.70e3.62 (m, 2H), 3.62 (s, 3H), 3.40e3.34 (m,
H), 3.32 (s, 3H), 3.03e2.99 (m, 2H), 2.85e2.79 (m, 2H), 2.42 (s, 6H),
.69 (s, 3H), 1.62 (s, 3H), 1.43 (s, 3H), 1.38 (s, 3H), 1.29e1.23 (m, 1H),
(dd, J¼1.6, 13.6 Hz, 1H), 1.84 (s, 3H), 1.66 (s, 3H), 1.60e1.55 (m, 1H),
1
13
hexans/EtOAc¼2:1, H NMR (400 MHz, CDCl
3
)
d
0.77e0.73 (m, 1H), 0.44e0.42 (m, 1H). C NMR (100 MHz, CDCl
3
)
7
d
173.0,172.1, 156.5, 128.2, 61.9, 59.4, 53.0, 52.9, 45.9, 41.3, 36.1, 29.8,
ꢂ1
20.2, 20.0. IR:
calcd for C17
n
2953, 1734, 1436, 1256, 1203, 1098, 913 cm . HRMS
þ
þ
(
2
1
H
23NNaO
6
[MþNa] : 360.1423, found: 360.1420.
4.3.7. Compounds 5g. Compound 5g was obtained in 76% yield as
1
1
.12e1.08 (m, 1H), 0.73 (t, J¼4.4 Hz, 1H), 0.65 (dd, J¼4.4, 8.0 Hz, 1H),
a colorless oil from 4g. R
(400 MHz, CDCl
f
¼0.45, hexans/EtOAc¼1:1, H NMR
1
3
0
.48 (t, J¼4.4 Hz, 1H), 0.35 (dd, J¼4.8, 8.0 Hz, 1H). C NMR
156.7, 156.6, 143.4, 143.3, 137.6, 137.5, 136.3,
34.8, 134.0, 133.5, 130.4, 130.1, 129.6, 129.5, 129.0, 128.5, 128.3,
28.2, 127.9, 127.7, 127.5, 127.3, 53.7, 53.5, 52.8, 52.4, 49.7, 49.6, 29.9,
3
)
d
4.37 (t, J¼7.6 Hz, 2H), 4.21e4.10 (m, 4H),
(
100 MHz, CDCl
3
)
d
3.79e3.82 (m, 1H), 3.72e3.65 (m, 1H), 2.82 (d, J¼14.0 Hz, 1H),
2.64e2.56 (m, 2H), 2.38 (dd, J¼1.2, 13.6 Hz, 1H), 1.84 (s, 3H), 1.66 (s,
3H), 1.63e1.55 (m, 1H), 1.26 (t, J¼7.2 Hz, 3H), 1.20 (t, J¼7.2 Hz, 3H),
1
1
2
2
C
13
9.8, 24.7, 23.0, 21.5, 21.5, 20.4, 20.2, 20.1, 20.1, 16.7, 14.9. IR:
n
2360,
3
0.75e0.72 (m, 1H), 0.47e0.45 (m, 1H). C NMR (100 MHz, CDCl )
ꢂ1
342, 1700, 1347, 1294, 1165, 1131, 1093, 913 cm . HRMS calcd for
d
172.6, 171.7, 156.5, 128.3, 61.9, 61.8, 61.6, 59.6, 45.8, 41.2, 36.0, 29.7,
þ
þ
H
25 30
N
2
NaO
4
S
[MþNa] : 477.1824, found: 477.1816.
20.2, 20.0, 13.9. IR:
n
2983, 1729, 1444, 1410, 1251, 1197, 1096, 1069,
ꢂ1
þ
þ
913 cm . HRMS calcd for C19
H
27NNaO
6
[MþNa] : 388.1736, found:
0
0
0
4.3.2. Compounds 5b and 5b . Compound 5b and 5b were obtained
388.1732.
in 75% yield as a colorless oil from 4b, 5b and 5b in a 1:1 ratio
1
1
0
determined by crude H NMR. R
400 MHz, CDCl
f
¼0.50, hexans/EtOAc¼2:1, H NMR
4.3.8. Compounds 5h and 5h . Compound 5h was obtained in 42%
1
(
3
)
d
7.66e7.63 (m, 4H), 7.32e7.29 (m, 4H),
yield as a colorless oil from 4h. R
(400 MHz, CDCl
f
¼0.30, hexans/EtOAc¼1:1, H NMR
3
3
.65e3.62 (m, 2H), 3.59 (s, 3H), 3.53e3.50 (m, 2H), 3.25 (s, 3H),
.21e3.16 (m, 1H), 3.06e3.02 (m, 3H), 2.83 (s, 3H), 2.77 (s, 3H), 2.42
3
)
d
7.68 (d, J¼6.8 Hz, 2H), 7.34 (d, J¼8.4 Hz, 2H),
4.33 (t, J¼8.0 Hz, 2H), 3.66e3.61 (m, 2H), 3.56e3.52 (m, 2H), 3.21
(dd, J¼3.6, 9.6 Hz, 1H), 3.06 (d, J¼9.2 Hz, 1H), 2.43 (s, 3H), 2.23e2.15
(
1
s, 3H), 2.41 (s, 3H), 1.69 (s, 3H), 1.68 (s, 3H), 1.54 (s, 3H), 1.53 (s, 3H),
.51e1.46 (m, 1H), 1.43e1.39 (m, 1H), 0.92e0.90 (m, 1H), 0.82e0.79
(m, 3H), 2.04e1.99 (m, 1H), 1.65e1.59 (m, 5H), 0.87 (dd, J¼4.4,
1
3
13
(
m, 1H), 0.74e0.68 (m, 2H). C NMR (100 MHz, CDCl
3
)
d
156.2,
8.0 Hz,1H), 0.80 (t, J¼4.8 Hz,1H). C NMR (100 MHz, CDCl
3
) d 155.9,
143.5,134.9,134.2,133.1,132.9,131.8,131.4,129.6,129.5,127.6,127.4,
148.2, 143.5, 133.3, 129.6, 127.4, 122.3, 62.0, 52.5, 49.7, 45.4, 30.9,
5
3.9, 53.4, 52.6, 52.2, 50.0, 49.7, 36.5, 36.4, 30.1, 30.0, 23.5, 23.1, 21.5,
30.5, 29.2, 26.4, 25.7, 23.9, 21.5, 14.6. IR:
n
2954, 2869, 1747, 1410,
ꢂ1
þ
21.4, 19.9, 19.8, 19.7, 15.9, 15.6. IR:
n
1773, 1418, 1346, 1275, 1260,
1343, 1164, 1095, 1036 cm . HRMS calcd for C21
26
H N
2
NaO
4
S
ꢂ1
þ
þ
þ
1161, 1113, 913 cm . HRMS calcd for C19
27
H N
2
O
4
S
[MþH] :
[MþNa] : 425.1511, found: 425.1508.
0
379.1692, found: 379.1693.
Compound 5h was obtained in 30% yield as colorless oil:
1
R
f
¼0.45, hexans/EtOAc¼1:1, H NMR (400 MHz, CDCl
3
) d 7.70 (d,
4.3.3. Compounds 5c. Compound 5c was obtained in 72% yield as
J¼6.4 Hz, 2H), 7.33 (d, J¼8.0 Hz, 2H), 5.76e5.75 (m, 1H), 4.42 (t,
J¼8.0 Hz, 2H), 3.96 (d, J¼15.2 Hz, 1H), 3.83 (d, J¼15.2 Hz, 2H),
3.66e3.57 (m, 2H), 3.32 (dd, J¼6.4, 9.2 Hz, 1H), 3.14e3.11 (m, 1H),
3.04 (dd, J¼3.2, 9.2 Hz, 1H), 2.44e2.39 (m, 7H), 1.95e1.89 (m, 2H),
1
a white solid from 4c. R
400 MHz, CDCl
7.67 (d, J¼8.4 Hz, 2H), 7.33 (d, J¼8.0 Hz, 2H),
.33 (d, J¼8.4 Hz,1H), 4.31 (d, J¼7.6 Hz,1H), 3.63e3.46 (m, 4H), 3.23
dd, J¼3.6, 9.6 Hz, 1H), 3.04 (d, J¼9.2 Hz, 1H), 2.42 (s, 3H), 1.68e1.58
f
¼0.50, hexans/EtOAc¼1:1, H NMR
(
4
3
) d
13
(
(
1.08 (d, J¼6.8 Hz, 3H). C NMR (100 MHz, CDCl
3
) d 155.5, 143.8,
13
m, 7H), 0.86e0.80 (m, 2H). C NMR (100 MHz, CDCl
3
)
d
156.5,
140.8, 137.0, 132.6, 131.9, 129.7, 127.8, 124.9, 62.1, 55.2, 50.5, 44.8,
1
2
43.6, 137.5, 133.2, 129.6, 127.4, 125.6, 61.9, 53.2, 49.7, 45.9, 28.5,
35.3, 33.7, 32.3, 23.5, 21.5, 19.6. IR:
1161, 1092, 913 cm . HRMS calcd for C21
425.1511, found: 425.1505.
n
2923, 2342, 1750, 1409, 1343,
ꢂ1
þ
þ
4.3, 21.5, 20.2, 20.0, 14.9. IR:
n
2918, 2361, 1748, 1410, 1344, 1165,
H
26
N
2
NaO
4
S
[MþNa] :
ꢂ1
þ
þ
1
3
107, 1033, 913 cm . HRMS calcd for C19
H N
24 2
NaO
4
S
[MþNa] :
ꢀ
99.1354, found: 399.1349. Mp ( C): 103e105.
4
.3.9. Compounds 5i. Compound 5i was obtained in 45% yield as
1
4
.3.4. Compounds 5d. Compound 5d was obtained in 45% yield as
a colorless oil from 4i. R
(400 MHz, CDCl
f
¼0.45, hexans/EtOAc¼1:1, H NMR
1
a colorless oil from 4d. R
f
¼0.30, hexans/EtOAc¼1:1, H NMR
3
) d
7.71 (d, J¼7.6 Hz, 2H), 7.33 (d, J¼7.6 Hz, 2H), 5.54

X. Zhou et al. / Tetrahedron 71 (2015) 4478e4483
4483
(
(
3
2
t, J¼6.8 Hz, 1H), 4.39e4.30 (m, 2H), 3.92 (d, J¼14.4 Hz, 1H), 3.77
dd, J¼1.6, 14.4 Hz, 1H), 3.54e3.49 (m, 2H), 3.44e3.40 (m, 1H),
P. H.; Xu, T.; Dong, G. Angew. Chem., Int. Ed. 2014, 53, 1674e1678; (d) Xu, T.;
Savage, N. A.; Dong, G. Angew. Chem., Int. Ed. 2014, 53, 1891e1895; (e) Xu, T.;
Dong, G. Angew. Chem., Int. Ed. 2014, 53, 10733e10736.
. (a) Danheiser, R. L.; Sard, H. Tetrahedron Lett. 1983, 24, 23e26; (b) Danheiser, R. L.;
Savariar, S.; Cha, D. D. Organic Syntheses; Wiley: New York, NY, 1993, Collect. Vol.
VIII, pp 82e86; (c) Wasserman, H. H.; Piper, J. U.; Dehmlow, E. V. J. Org. Chem.1973,
.09e3.03 (m, 1H), 2.79 (dd, J¼5.6, 9.6 Hz, 1H), 2.43 (s, 3H),
.23e2.16 (m, 1H), 1.88e1.79 (m, 1H), 1.69 (d, J¼6.8 Hz, 3H), 0.95 (d,
4
13
J¼6.8 Hz, 3H), 0.92 (t, J¼7.6 Hz, 3H). C NMR (100 MHz, CDCl
3
)
38,1451e1455; (d) Danheiser, R. L.; Gee, S. K. J. Org. Chem.1984, 49,1672e1674; (e)
d
155.0, 143.7, 137.6, 135.6, 132.2, 129.7, 129.5, 128.1, 127.8, 62.0, 55.2,
Danheiser, R. L.; Nishida, A.; Savariar, S.; Trova, M. P. Tetrahedron Lett. 1988, 29,
5
0.6, 44.5, 35.4, 21.5, 21.4, 18.4, 13.4, 12.5. IR:
n
2968, 2924, 1750,
4917e4920; (f) Kowalski, C. J.; Lal, G. S. J. Am. Chem. Soc. 1988, 110, 3693e3695.
ꢂ1
þ
5. Kohnen, A. L.; Mak, X. Y.; Lam, T. Y.; Dunetz, J. R.; Danheiser, R. L. Tetrahedron
006, 62, 3815e3822.
1407, 1343, 1161, 1092, 913 cm . HRMS calcd for C21
29
H N
2
O
4
S
2
þ
[MþH] : 405.1848, found: 405.1839.
6
. For recent reviews on the chemistry of ynamides, see: (a) DeKorver, K. A.; Li, H.;
Lohse, A. G.; Hayashi, R.; Lu, Z.; Zhang, Y.; Hsung, R. P. Chem. Rev. 2010, 110,
5
064e5106; (b) Evano, G.; Coste, A.; Jouvin, K. Angew. Chem., Int. Ed. 2010, 49,
2840e2859.
. (a) Science of Synthesis (HoubeneWeyl); Danheiser, R. L., Ed.; Thieme: Stuttgart,
4
.3.10. Compounds 6j. Compound 6j was obtained in 84% yield as
1
a colorless oil from 4j. R
CDCl
f
¼0.2, hexans/EtOAc¼1:1, H NMR (400 MHz,
7
3
)
d
7.70 (d, J¼8.0 Hz, 2H), 7.36 (d, J¼8.0 Hz, 2H), 4.44e4.39 (m,
Germany, 2006; Vol. 23; (b) Tidwell, T. T. Ketenes, 2nd ed.; Wiley Interscience:
Hoboken, NJ, 2006; (c) Tidwell, T. T. Eur. J. Org. Chem. 2006, 563e576; (d) Fu, N.;
Tidwell, T. T. Tetrahedron 2008, 64, 10465e10496; (e) Arrieta, A.; Lecea, B.;
Cossio, F. P. Top. Heterocycl. Chem. 2010, 22, 313e347.
1
3
2
H), 4.35e4.28 (m, 1H), 3.87e3.80 (m, 2H), 3.68 (d, J¼9.6 Hz, 1H),
.52e3.46 (m, 1H), 3.19 (d, J¼18.4 Hz, 1H), 3.05 (d, J¼6.4 Hz, 1H),
.98e2.92 (m, 2H), 2.44 (s, 3H), 1.67 (s, 3H), 1.48 (s, 3H), 1.25 (s, 3H).
8. Cyclobutenone was synthesized from known compound in three steps, detail
please see support information and references below: (a) Lam, T. Y.; Wang, Y. P.;
Danheiser, R. L. J. Org. Chem. 2013, 78, 9396e9414; (b) Song, H.; Liu, Y.; Wang, Q.
Org. Lett. 2013, 15, 3274e3277.
1
3
3
C NMR (100 MHz, CDCl ) d 208.3, 157.4, 144.2, 139.1, 131.4, 129.7,
1
IR:
27.9,123.1, 76.1, 62.5, 59.7, 57.6, 57.2, 46.5, 44.1, 21.5, 21.2, 20.2,19.4.
ꢂ1
n
1780, 1742, 1419, 1347, 1252, 1167, 1091, 1037, 913 cm . HRMS
9. The corresponding di-hydrogen and mono-methyl substituted cyclobutenones
þ
þ
calcd for C21
H
26
N
2
NaO
5
S
[MþNa] : 441.1460, found: 441.1456.
are much more challenging to prepare compared to the gem-dialkyl substituted
ones. For details, see Refs. 1,4 and 5.
0
1
0. X-ray structures of 6a and 6a (For details, see SI). CCDC 1045429 and 1045428
Acknowledgements
contain the supplementary crystallographic data for compounds 6a and 6a
0
respectively. These data can be obtained free of charge from the Cambridge
Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
We thank UT Austin and CPRIT (R1118) for a startup fund, Na-
tional Institute of General Medical Sciences (R01GM109054-01)
and the Welch Foundation (F 1781) for research grants. GD is
a Searle Scholar. We are also grateful to Johnson Matthey for
a generous donation of Rh salts.
Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2015.02.087.
References and notes
1
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2
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3
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15. Another possible mechanism was suggested by one reviewer, which can be
found in the Supplementary data.