Homodimeric coupling-cyclization reaction of 2,3-allenamides

Article abstract of DOI:10.1016/j.tet.2009.03.083

The PdCl₂/NaI/K₂CO₃-catalyzed highly stereoselective homodimeric coupling-cyclization reaction of 2,3-allenamides afforded Z-bis(furanimine) derivatives. The addition of K₂CO₃ is crucial for this reac

Full text of DOI:10.1016/j.tet.2009.03.083

Tetrahedron 65 (2009) 4547–4550
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Homodimeric coupling–cyclization reaction of 2,3-allenamides
*
Guofei Chen, Yong Li, Chunling Fu, Shengming Ma
Laboratory of Molecular Recognition and Synthesis, Department of Chemistry, Zhejiang University, 310027 Hangzhou, Zhejiang, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The PdCl2/NaI/K2CO3-catalyzed highly stereoselective homodimeric coupling–cyclization reaction of
2,3-allenamides afforded Z-bis(furanimine) derivatives. The addition of K2CO3 is crucial for this reaction
and a possible mechanism is proposed.
Received 6 February 2009
Received in revised form 23 March 2009
Accepted 27 March 2009
Available online 1 April 2009
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
The chemistry of allenes has been becoming one of the hottest
research areas in organic chemistry.1,2 Especially, the transition
metal-catalyzed cyclization of functionalized allenes provides
many efficient routes for the synthesis of cyclic products.1,2
Recently, the transition metal-catalyzed cyclizative dimerization
reaction of two functionalized allenes has started to provide new
pathways for the preparation of cyclic compounds with unique
structural features. For example, Hashmi et al. first reported the
PdCl2(MeCN)2 or AuCl3 catalyzed homodimerization reaction of
1,2-allenyl ketones.3,4 In our research group, the homodimeri-
zation reactions of 2,3-allenoic acids5 and 2,3-allenols6 have
been studied to provide bisbutenolides and 1,3-alkadien-2-yl-
2,5-dihydrofunans, respectively. As it is known that the cycliza-
tions of 2,3-allenamides have two types of reactions: N-attack
Initially, we used N-benzyl 4-methyl-penta-2,3-dienamide 1a
to try the dimerization reaction. The corresponding results under
different conditions are summarized in Table 1. At first, different
catalytic systems were tested for this homodimerization coupling–
cyclization reaction. Although PdCl2 failed to catalyze this reaction
(entry 1, Table 1), fortunately, when we used the PdCl2/NaI catalytic
system, which has been used for the dimeric cyclization of 2,3-alle-
nols,6 bis(furanimine) 2a was formed in 29% yield with 32% recovery
of the starting material 1a within 16 h (entry 2, Table 1). After ana-
lyzing the NMR spectra ofcrude and pure product after the reaction, it
Table 1
Homodimeric coupling–cyclization reaction of N-benzyl 4-methyl-penta-2,3-dien-
amide (1a)a
forming the
g-lactams and O-attack furnishing furanimines
n
N
B
(Scheme 1),7 it is interesting to see, which reaction type would
occur in the dimerization of 2,3-allenamides. Herein, we wish to
report the homodimeric coupling–cyclization reaction of 2,3-
allenamides.
O
Cat.
Solvent
80 °C
CONHBn
N
B
O
Z-2a
1a
n
R5
R1
R2
R3
Entry
Cat.b
Solvent
T (h)
Yield of Z-2ac
Recovery of 1ac
N-attack
1
2
3
4
5
6
7
8
9
10
PdCl2
PdCl2/NaI
PdCl2/NaI/K2CO3
PdCl2/K2CO3
PdI2/K2CO3
PdCl2/NaI/K2CO3
PdCl2/NaI/K2CO3
PdCl2/NaI/K2CO3
PdCl2/NaI/K2CO3
PdCl2/NaI/K2CO3
DMF
DMF
DMF
DMF
DMF
DMA
DMSO
MeCN
THF
12
16
8
12
12
14
22
22
23
23
0
29
77
26
59
67
46
53
15
9
58
32
0
0
0
0
5
4
30
49
R1
R2
R3
O
N
R4
CONHR4
R5
R1
R2
R3
O-attack
R4
N
O
Scheme 1.
DCE
a
The reaction was carried out using 0.2 mmol of 1a and 5 mol % of Pd at 80 ꢀC.
NaI (50 mol %) or K2CO3 (1.0 equiv) was used, if any.
b
c
* Corresponding author.
E-mail address: masm@mail.sioc.ac.cn (S. Ma).
Yields were determined by 1H NMR analysis with mesitylene as the internal
standard.
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.083

4548
G. Chen et al. / Tetrahedron 65 (2009) 4547–4550
Table 2
1 mol% PdCl2
50 mol% NaI
Bn
Homodimeric coupling–cyclization reaction of 2,3-allenamidesa
O
N
K2CO3 (1.0 equiv)
R4
N
R1
R2
5 mol% PdCl2
CONHBn
DMF, 80 °C, 22.5 h
60%
O
R1
R2
R3
50 mol% NaI
K2CO3 (1.0 equiv)
R3
N
Bn
O
Z-2a
NHR4
R3
R1
R2
DMF or DMA
80 °C
1a
O
N
O
Z-2
R4
1 mol% PdCl2
50 mol% NaI
Bn
N
1
O
K2CO3 (1.0 equiv)
Entry
R1
R2
R3
R4
Solvent
T (h)
Yieldb (%)
CONHBn
DMA, 80 °C, 21.5 h
60%
1
2
3
4
5
6
7
8
Me
Me
Me
Me
Me
Et
H
H
H
H
H
H
H
H
H
H
H
Me
Bn (1a)
n-Bu (1b)
t-Bu (1c)
i-Pr (1d)
Bn (1e)
n-Bu (1f)
Bn (1g)
n-Bu (1h)
Bn (1i)
DMF
DMF
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMF
DMA
DMA
8
68 (2a)
66 (2b)
65 (2c)
73 (2d)
58 (2e)
66 (2f)
72 (2g)
64 (2h)
66 (2i)
74 (2j)
69 (2k)c
88 (2l)
N
Bn
Me
Me
Me
Et
11
14
10
21
15
10
28
14
14
14
14
O
Z-2l
1l
Scheme 2.
Et
Et
n-Pr
n-Pr
n-Bu
–(CH2)5–
Me
Me
n-Pr
n-Pr
n-Bu
9
Ph
Et
H
PdCl2/NaI/K2CO3
10
11
12
Bn (1j)
Bn (1k)
Bn (1l)
no reaction
27%-32% recovery
Et
Me
DMF or DMA
80 °C
CONHBn
1m
a
The reaction was carried out using 0.2 mmol of 1, 5 mol % of PdCl2, 50 mol % of
NaI and 1.0 equiv of K2CO3 in DMF or DMA at 80 ꢀC.
Me
Et
PdCl2/NaI/K2CO3
DMF, 80 °C
b
Isolated yield.
A 1:1 mixture of two diastereomers.
c
H
CONHBn
1n
no expected products
no starting material
remained
was confirmed that only bis(furanimine) was formed. To enhance the
nucleophilicity of amide functionality, 1.0 equiv of K2CO3 was added
to afford 2a in 77% yield with complete conversion of the starting
material 1awithin 8 h (entry 3, Table 1). Although the combination of
PdCl2 or PdI2 with K2CO3 smoothly consumed the starting allene, the
yield was much lower (entries 4 and 5, Table 1). The solventeffect was
also tested. From Table 1, it is noted that the reaction in DMA yielded
the product 2a in 67% yield (entry 6, Table 1). Other solvents such as
DMSO, MeCN, THF, DCE led to inferior results with some of the
starting material 1a remaining (entries 7–10, Table 1).
n-
C5H11
H
H
PdCl2/NaI/K2CO3
DMF, 80 °C
CONHBn
1o
Scheme 3.
However, when N-benzyl 4-phenyl-2,3-hexadienamide 1m was
applied, no reaction occurred. In addition, 2,4-disubstituted 2,3-
allenamide 1n or 4-substituted 2,3-allenamide 1o failed to afford
the corresponding products under the standard reaction conditions
although the starting materials were completely consumed
(Scheme 3).
A rationale for this reaction is depicted in Scheme 4. The in-
teraction of allenamides with Pd(II) would form a coordination
complex, which may undergo an oxypalladation to form imi-
nyllactonyl palladium(II) intermediate M1. Then the Pd(II) in-
termediate M1 may promote the second oxypalladation with
another molecule of the allenamide to form bis(iminyllactonyl)
palladium intermediate M2. The addition of K2CO3 increased the
nucleophilicity of the amide functionality. Subsequent reductive
elimination generates the bis(furanimine)s and Pd(0). Finally, the in
With the optimized reaction conditions in hand, the scope of the
reaction was explored with some typical results summarized in
Table 2. In some cases, the solvent was changed to DMA for higher
yield or consuming the starting material more efficiently. The sub-
stituents at 4-position, i.e., R1 and R2, can be an alkyl group such as
methyl, ethyl, propyl, butyl; the a
-substituent R3 can be H and alkyl
group; the substituent R4 can be benzyl, butyl, tert-butyl, iso-propyl
group. When R1 is different with R2 such as methyl and ethyl group,
a 1:1 diastereoisomeric mixture was formed as expected (entry 11,
Table 2). The structure of the product 2e was further confirmed by
the X-ray diffraction studies (Fig. 1).8 When the amount of catalyst
PdCl2 was reduced to 1 mol %, the reaction of allenamides 1a and 1l
also completed to afford Z-2a and Z-2l in 60% yields (Scheme 2).
Figure 1.

G. Chen et al. / Tetrahedron 65 (2009) 4547–4550
4549
z): 332 (Mþ, 31.44), 289 (100); IR (KBr, cmꢂ1): 2958, 2932, 2871,
1670, 1460, 1369, 1276, 1194, 1130. Anal. Calcd for C20H32N2O2: C,
72.25; H, 9.70; N, 8.43. Found: C, 72.23; H, 9.75; N, 8.52.
R4
N
R2
R1
PdII R3
R1
R2
R4
N
O
R1
R2
O
R3
Pd(0)
R3
R3
4.3. 2,20-Bis(tert-butylimino)-5,5,50,50-tetramethyl-2,5,20,50-
tetrahydro[4,40]bifuranyl (Z-2c)
R1
R2
N
N
O
O
M2
R1
R4
oxidation
PdCl2 + NaI
R4
R3
CONHR4
The reaction of 33.1 mg (0.20 mmol) of 1c, 1.7 mg (0.010 mmol)
of PdCl2, 14.7 mg (0.10 mmol) of NaI and 27.6 mg (0.20 mmol) of
K2CO3 in DMA (2 mL) afforded 21.3 mg (65%) of Z-2c. White solid,
mp: 228.9–230.3 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
K2CO3
R2
R3
PdI2
R1
R2
R3
PdII
R1
R2
anti-oxypalladation
CDCl3):
CDCl3):
d
6.08 (s, 2H), 1.53 (s, 12H), 1.29 (s, 18H); 13C NMR (75 MHz,
158.8, 149.9, 124.4, 90.5, 53.7, 29.6, 26.5; MS (m/z): 332
K2CO3
NH
R4
N
O
M1
d
O
R4
(Mþ, 2.73), 317 (100); IR (KBr, cmꢂ1): 2975, 2930, 2869, 1677, 1454,
1371, 1361, 1270, 1228, 1190, 1115. Anal. Calcd for C20H32N2O2: C,
72.25; H, 9.70; N, 8.43. Found: C, 72.37; H, 9.65; N, 8.45.
Scheme 4.
4.4. 2,20-Bis(isopropylimino)-5,5,50,50-tetramethyl-2,5,20,50-
situ generated Pd(0) was oxidized to Pd(II) to finish the catalytic
cycle via the oxidation with the in situ generated I2 from NaI and O2
in air.5b The Z-selectivity referring to the C]N bond may be
explained by the steric interaction of R3 and R4 in the E-products.7
tetrahydro[4,40]bifuranyl (Z-2d)
The reaction of 31.8 mg (0.21 mmol) of 1d, 1.7 mg (0.010 mmol)
of PdCl2, 14.8 mg (0.10 mmol) of NaI and 28.0 mg (0.20 mmol) of
K2CO3 in DMA (2 mL) afforded 23.2 mg (73%) of Z-2d. White solid,
mp: 161.9–162.9 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
3. Conclusions
We have developed a PdCl2/NaI/K2CO3-catalyzed highly ster-
eoselective homodimeric coupling-cyclization reaction of 2,3-alle-
namides, which provides an efficient route to Z-bis(furanimine)
derivatives. The addition of K2CO3 is crucial for this reaction. Fur-
ther studies in this area are being carried out in our laboratory.
CDCl3):
d
6.10 (s, 2H), 3.87 (heptet, J¼6.3 Hz, 2H), 1.53 (s, 12H), 1.12
(d, J¼6.3 Hz, 12H); 13C NMR (75 MHz, CDCl3):
d 159.8, 150.7, 123.2,
90.0, 47.3, 26.6, 23.7; MS (m/z): 304 (Mþ, 13.06), 289 (100); IR (KBr,
cmꢂ1): 2966, 2934, 2870, 1672, 1458, 1386, 1369, 1344, 1282, 1270,
1195, 1120. Anal. Calcd for C18H28N2O2: C, 71.02; H, 9.27; N, 9.20.
Found: C, 71.10; H, 9.26; N, 9.13.
4. Experimental
4.5. 2,20-Bis(benzylimino)-5,5,50,50-tetraethyl-2,5,20,50-
4.1. Preparation of 2,20-bis(benzylimino)-5,5,50,50-
tetramethyl-2,5,20,50-tetrahydro[4,40]bifuranyl
(Z-2a). General procedure
tetrahydro[4,40]bifuranyl (Z-2e)
The reaction of 45.6 mg (0.20 mmol) of 1e, 2.0 mg (0.011 mmol)
of PdCl2, 14.4 mg (0.10 mmol) of NaI and 27.6 mg (0.20 mmol) of
K2CO3 in DMA (2 mL) afforded 26.4 mg (58%) of Z-2e. White solid,
mp: 176.6–177.2 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
K2CO3 (27.6 mg, 0.20 mmol), PdCl2 (1.9 mg, 0.011 mmol), NaI
(15.0 mg, 0.10 mmol), 1a (40.0 mg, 0.20 mmol) and 2 mL of DMF
were added sequentially to a reaction tube. The resulting solution
was heated at 80 ꢀC with stirring. After 8 h as monitored by TLC, the
reaction was quenched with 10 mL of H2O, extracted with ether
(25 mLꢁ3), washed with brine and dried over anhydrous Na2SO4.
After filtration and evaporation, chromatography on neutral Al2O3
(eluent: petroleum ether/ethyl acetate¼4:1) of the crude product
afforded Z-2a (27.2 mg, 68%) as a white solid. Mp: 164.2–165.3 ꢀC
CDCl3):
d 7.43–7.29 (m, 8H), 7.27–7.20 (m, 2H), 6.35 (s, 2H), 4.58 (s,
4H), 2.10–1.95 (m, 4H),1.95–1.78 (m, 4H), 0.76 (t, J¼7.4 Hz,12H); 13C
NMR (75 MHz, CDCl3):
d 162.6, 147.4, 140.5, 128.4, 127.9, 126.5,
125.2, 96.2, 51.7, 31.2, 7.4; MS (m/z): 456 (Mþ, 26.91), 91 (100); IR
(KBr, cmꢂ1): 3076, 2971, 2935, 2857, 1670, 1494, 1450, 1343, 1284,
1224, 1137, 1045, 1021. Anal. Calcd for C30H36N2O2: C, 78.91; H, 7.95;
N, 6.13. Found: C, 78.96; H, 7.97; N, 6.11.
(Et2O). 1H NMR (300 MHz, CDCl3):
(m, 2H), 6.23 (s, 2H), 4.56 (s, 4H), 1.61 (s, 12H); 13C NMR (75 MHz,
d 7.41–7.29 (m, 8H), 7.28–7.20
4.6. 2,20-Bis(n-butylimino)-5,5,50,50-tetraethyl-2,5,20,50-
tetrahydro[4,40]bifuranyl (Z-2f)
CDCl3):
d 161.4, 151.2, 140.6, 128.4, 127.9, 126.6, 123.0, 90.4, 51.6,
26.7; MS (m/z): 400 (Mþ, 74.35), 91 (100); IR (KBr, cmꢂ1): 3072,
2983, 2939, 2855, 1670, 1449, 1289, 1132, 1044, 1023. Anal. Calcd for
C26H28N2O2: C, 77.97; H, 7.05; N, 6.99. Found: C, 77.92; H, 7.08; N,
6.91.
The reaction of 38.9 mg (0.20 mmol) of 1f, 1.8 mg (0.010 mmol)
of PdCl2, 15.0 mg (0.10 mmol) of NaI and 26.8 mg (0.19 mmol) of
K2CO3 in DMA (2 mL) afforded 25.4 mg (66%) of Z-2f. White solid,
mp: 99.4–100.1 ꢀC (n-hexane). 1H NMR (300 MHz, CDCl3):
d 6.25 (s,
The reaction of 40.3 mg (0.20 mmol) of 1a, 0.4 mg (0.002 mmol)
of PdCl2, 15.7 mg (0.10 mmol) of NaI and 28.1 mg (0.20 mmol) of
K2CO3 in DMF (2 mL) afforded 23.9 mg (60%) of Z-2a (Scheme 2).
2H), 3.34 (t, J¼7.1 Hz, 4H), 2.04–1.73 (m, 8H), 1.63–1.50 (m, 4H),
1.46–1.30 (m, 4H), 0.92 (t, J¼7.2 Hz, 6H), 0.72 (t, J¼7.4 Hz, 12H); 13C
NMR (75 MHz, CDCl3):
d 162.2, 147.0, 125.0, 95.7, 47.2, 33.1, 31.2,
4.2. 2,20-Bis(n-butylimino)-5,5,50,50-tetramethyl-2,5,20,50-
tetrahydro[4,40]bifuranyl (Z-2b)
20.6, 13.9, 7.3; MS (m/z): 388 (Mþ, 100); IR (KBr, cmꢂ1): 3071, 2971,
2953, 2936, 2871,1665,1453,1378,1333,1270,1216,1137,1111,1061,
1035. Anal. Calcd for C24H40N2O2: C, 74.18; H, 10.38; N, 7.21. Found:
C, 74.12; H, 10.40; N, 7.18.
The reaction of 34.0 mg (0.20 mmol) of 1b, 1.9 mg (0.011 mmol)
of PdCl2, 15.7 mg (0.10 mmol) of NaI and 27.6 mg (0.20 mmol) of
K2CO3 in DMF (2 mL) afforded 22.4 mg (66%) of Z-2b. White solid,
mp: 109.0–110.0 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
4.7. 2,20-Bis(benzylimino)-5,5,50,50-tetra(n-propyl)-2,5,20,50-
tetrahydro[4,40]bifuranyl (Z-2g)
CDCl3):
d
6.12 (s, 2H), 3.31 (t, J¼6.9 Hz, 4H), 1.62–1.50 (m, 4H), 1.54
(s, 12H), 1.44–1.30 (m, 4H), 0.91 (t, J¼7.2 Hz, 6H); 13C NMR (75 MHz,
The reaction of 50.4 mg (0.20 mmol) of 1g, 1.9 mg (0.011 mmol)
of PdCl2, 14.5 mg (0.10 mmol) of NaI and 27.9 mg (0.20 mmol) of
CDCl3):
d
160.9, 150.8, 122.8, 90.0, 47.1, 33.1, 26.6, 20.6, 13.9; MS (m/

4550
G. Chen et al. / Tetrahedron 65 (2009) 4547–4550
K2CO3 in DMA (2 mL) afforded 36.3 mg (72%) of Z-2g. White solid,
mp: 146.5–147.7 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
mp: 162.6–164.0 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
CDCl3): 7.44–7.28 (m, 16H), 7.28–7.18 (m, 4H), [6.28 (s), 6.27 (s),
d
CDCl3):
d
7.44–7.29 (m, 8H), 7.27–7.20 (m, 2H), 6.31 (s, 2H), 4.55 (s,
4H], 4.57 (s, 8H), 2.10–1.78 (m, 8H), [1.59 (s), 1.58 (s), 12H], 0.81–
0.68 (m, 12H); MS (m/z): 428 (Mþ, 34.51), 91 (100); IR (KBr, cmꢂ1):
3076, 2977, 2934, 2876, 2858, 1669, 1602, 1494, 1451, 1441, 1376,
1343, 1313, 1284, 1228, 1134, 1043, 1034, 1016. Anal. Calcd for
C28H32N2O2: C, 78.47; H, 7.53; N, 6.54. Found: C, 78.49; H, 7.46; N,
6.53.
4H), 2.01–1.86 (m, 4H), 1.84–1.66 (m, 4H), 1.35–1.14 (m, 4H), 1.13–
0.94 (m, 4H), 0.87 (t, J¼7.1 Hz, 12H); 13C NMR (75 MHz, CDCl3):
d
162.6, 148.4, 140.5, 128.4, 127.9, 126.6, 124.5, 95.8, 51.7, 40.6, 16.3,
13.9; MS (m/z): 512 (Mþ, 5.88), 91 (100); IR (KBr, cmꢂ1): 2960, 2942,
2908, 2873, 1674, 1603, 1582, 1493, 1445, 1347, 1284, 1230, 1212,
1138, 1046, 1014. Anal. Calcd for C34H44N2O2: C, 79.65; H, 8.65; N,
5.46. Found: C, 79.68; H, 8.68; N, 5.42.
4.12. 2,20-Bis(benzylimino)-3,5,5,30,50,50-hexamethyl-2,5,20,50-
tetrahydro[4,40]bifuranyl (Z-2l)
4.8. 2,20-Bis(n-butylimino)-5,5,50,50-tetra(n-propyl)-2,5,20,50-
tetrahydro[4,40]bifuranyl (Z-2h)
The reaction of 43.3 mg (0.20 mmol) of 1l, 1.8 mg (0.010 mmol)
of PdCl2, 15.1 mg (0.10 mmol) of NaI and 28.4 mg (0.21 mmol) of
K2CO3 in DMA (2 mL) afforded 38.1 mg (88%) of Z-2l. Colourless
The reaction of 43.6 mg (0.20 mmol) of 1h, 1.9 mg (0.011 mmol)
of PdCl2, 15.6 mg (0.10 mmol) of NaI and 27.3 mg (0.20 mmol) of
K2CO3 in DMA (2 mL) afforded 27.8 mg (64%) of Z-2h. White solid,
mp: 102.5–103.2 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
liquid. 1H NMR (300 MHz, CDCl3):
d
7.42 (d, J¼7.5 Hz, 4H), 7.39–7.29
(m, 4H), 7.29–7.20 (m, 2H), 4.61 (s, 4H),1.79 (s, 6H),1.50 (s, 12H); 13C
NMR (75 MHz, CDCl3):
d 162.2, 148.9, 140.9, 131.6, 128.2, 127.7,
126.3, 89.5, 50.9, 27.5, 10.9; MS (m/z): 428 (Mþ, 41.82), 91 (100); IR
(KBr, cmꢂ1): 3027, 2979, 2929, 2869, 1762, 1682, 1495, 1453, 1379,
1353, 1328, 1291, 1255, 1191, 1087, 1029. Anal. Calcd for C28H32N2O2:
C, 78.47; H, 7.53; N, 6.54. Found: C, 78.48; H, 7.52; N, 6.55.
CDCl3):
d
6.21 (s, 2H), 3.32 (t, J¼7.1 Hz, 4H), 1.94–1.80 (m, 4H), 1.78–
1.65 (m, 4H),1.63–1.50 (m, 4H),1.45–1.31 (m, 4H),1.30–1.11 (m, 4H),
1.09–0.90 (m, 4H), 0.92 (t, J¼7.2 Hz, 6H), 0.84 (t, J¼7.1 Hz, 12H); 13C
NMR (75 MHz, CDCl3):
d 162.1, 148.0, 124.4, 95.3, 47.2, 40.6, 33.1,
20.6, 16.3, 13.95, 13.91; MS (m/z): 444 (Mþ, 95.50), 401 (100); IR
(KBr, cmꢂ1): 3065, 2956, 2932, 2872, 1666, 1465, 1338, 1272, 1255,
1213, 1142, 1046. Anal. Calcd for C28H48N2O2: C, 75.62; H, 10.88; N,
6.30. Found: C, 75.66; H, 10.80; N, 6.25.
Acknowledgements
Financial support from National Natural Science Foundation of
China (No. 20732005 and No. J0830413) and the Major State Basic
Research Development Program (2006CB806105) is greatly ap-
preciated. S.M. is a Qiushi Adjunct Professor at Zhejiang University.
This work was conducted at Zhejiang University. We thank Mr.
Guobi Chai in our group for reproducing the results presented in
entries 11 and 12 of Table 2.
4.9. 2,20-Bis(benzylimino)-5,5,50,50-tetra(n-butyl)-2,5,20,50-
tetrahydro[4,40]bifuranyl (Z-2i)
The reaction of 56.3 mg (0.20 mmol) of 1i, 1.8 mg (0.010 mmol)
of PdCl2, 14.5 mg (0.10 mmol) of NaI and 27.4 mg (0.20 mmol) of
K2CO3 in DMA (2 mL) afforded 37.0 mg (66%) of Z-2i. White solid,
mp: 179.7–180.6 ꢀC (n-hexane/CH2Cl2). 1H NMR (300 MHz, CDCl3):
Supplementary data
d
7.42–7.29 (m, 8H), 7.27–7.19 (m, 2H), 6.31 (s, 2H), 4.56 (s, 4H),
2.02–1.88 (m, 4H), 1.87–1.72 (m, 4H), 1.35–1.09 (m, 12H), 1.06–0.89
Supplementary data in association with this article can be found
in the online version, at doi:10.1016/j.tet.2009.03.083.
(m, 4H), 0.83 (t, J¼7.1 Hz, 12H); 13C NMR (75 MHz, CDCl3):
d 162.7,
148.3, 140.5, 128.4, 128.0, 126.6, 124.7, 95.7, 51.8, 38.4, 25.2, 22.6,
14.0; MS (m/z): 568 (Mþ, 8.94), 91 (100); IR (KBr, cmꢂ1): 3065, 3022,
2951, 2927, 2867, 1664, 1495, 1464, 1451, 1441, 1378, 1345, 1284,
1234, 1205, 1143, 1086, 1045, 1018. Anal. Calcd for C38H52N2O2: C,
80.24; H, 9.21; N, 4.92. Found: C, 80.24; H, 9.28; N, 4.99.
References and notes
1. For books, see: (a) The Chemistry of the Allenes; Landor, S. R., Ed.; Academic:
London, 1982; Vol. 1; (b) Modern Allene Chemistry; Krause, N., Hashmi, A. S. K.,
Eds.; Wiley-VCH: Weinheim, 2004; Vols. 1–2; (c) Allenes in Organic Synthesis;
Schuster, H. F., Coppola, G. M., Eds.; Wiley: New York, NY, 1984; (d) The Chemistry
of Ketenes, Allenes, and Related Compounds; Patai, S., Ed.; Wiley: New York, NY,
1980.
2. For some of the most recent reviews, see: (a) Zimmer, R.; Dinesh, C. U.; Nan-
danan, E.; Khan, F. A. Chem. Rev. 2000, 100, 3067; (b) Hoffmann-Ro¨der, A.;
Krause, N. Angew. Chem., Int. Ed. 2004, 43, 1196; (c) Ma, S. Acc. Chem. Res. 2003,
36, 701; (d) Ma, S. Chem. Rev. 2005, 105, 2829; (e) Ma, S. Aldrichimica Acta 2007,
40, 91.
3. (a) Hashmi, A. S. K. Angew. Chem., Int. Ed. Engl. 1995, 34, 1581; (b) Hashmi, A. S. K.;
Ruppert, T. L.; Kno¨fel, T.; Bats, J. W. J. Org. Chem. 1997, 62, 7295; (c) Hashmi, A. S.
K.; Schwarz, L.; Choi, J. H.; Frost, T. M. Angew. Chem., Int. Ed. 2000, 39, 2285; (d)
Hashmi, A. S. K.; Schwarz, L.; Bolte, M. Eur. J. Org. Chem. 2004, 1923.
4. For a recent report, see: Alcaide, B.; Almendros, P.; Martı´nez del Campo, T. Eur. J.
Org. Chem. 2007, 2844.
4.10. 2,20-Bis(benzylimino)[4,40]bi[1-oxa-spiro[4.5]dec-3-
enyl] (Z-2j)
The reaction of 48.4 mg (0.20 mmol) of 1j, 1.7 mg (0.010 mmol)
of PdCl2, 15.2 mg (0.10 mmol) of NaI and 26.8 mg (0.20 mmol) of
K2CO3 in DMF (2 mL) afforded 35.7 mg (74%) of Z-2j. White solid,
mp: 187.7–188.2 ꢀC (n-hexane/ethyl acetate). 1H NMR (300 MHz,
CDCl3):
d 7.42–7.29 (m, 8H), 7.28–7.20 (m, 2H), 6.34 (s, 2H), 4.58 (s,
4H), 2.00–1.60 (m, 18H), 1.33–1.12 (m, 2H); 13C NMR (75 MHz,
CDCl3): d 161.8, 151.4, 140.7, 128.3, 127.9, 126.5, 123.1, 92.4, 51.7, 34.8,
24.6, 22.1; MS (m/z): 480 (Mþ, 37.74), 91 (100); IR (KBr, cmꢂ1): 3023,
2939, 2861, 1680, 1497, 1450, 1355, 1305, 1287, 1270, 1212, 1135,
1043. Anal. Calcd for C32H36N2O2: C, 79.96; H, 7.55; N, 5.83. Found:
C, 79.82; H, 7.53; N, 5.83.
5. (a) Ma, S.; Yu, Z. Org. Lett. 2003, 5, 1507; (b) Ma, S.; Yu, Z.; Gu, Z. Chem.dEur. J.
2005, 11, 2351.
6. For an selective homodimerization rection of 2,3-allenols, see: Deng, Y.; Yu, Y.;
Ma, S. J. Org. Chem. 2008, 73, 585; Hashmi, A. S. K.; Blanco, M. C.; Fischer, D.; Bats,
J. W. Eur. J. Org. Chem. 2006, 1387.
7. (a) Ma, S.; Xie, H. Org. Lett. 2000, 2, 3801; (b) Ma, S.; Xie, H. J. Org. Chem. 2002, 67,
6575; (c) Ma, S.; Xie, H. Tetrahedron 2005, 61, 251; (d) Ma, S.; Gu, Z.; Yu, Z. J. Org.
Chem. 2005, 70, 6291.
4.11. 2,20-Bis(benzylimino)-5,50-diethyl-5,50-dimethyl-
2,5,20,50-tetrahydro[4,40]bifuranyl (Z-2k)
8. Crystal data for compound 2e: C15H18ON, Mw¼228.30, orthorhombic, space
group Pbca, Mo K
a
, final R indices [I>2
s
(I)], R1¼0.0364, wR2¼0.0951, a¼7.8526
(3) Å, b¼12.3101 (5) Å, c¼26.5628 (10) Å,
a
¼90ꢀ,
b
¼90ꢀ,
g
¼90ꢀ, V¼2567.73
The reaction of 43.9 mg (0.20 mmol) of 1k, 1.8 mg (0.010 mmol)
of PdCl2, 14.9 mg (0.10 mmol) of NaI and 27.3 mg (0.20 mmol) of
K2CO3 in DMA (2 mL) afforded 30.3 mg (69%) of Z-2k. White solid,
(17) Å3, T¼296 (2) K, Z¼8, number of reflections collected/unique: 27,674/2265
(Rint¼0.0260), number of observations: 1961 [I>2
s(I)], parameters 155. CCDC
702814 contains the supplementary crystallographic data.