Phosphine-mediated [3+2] cycloaddition reactions of ethyl 5,5-diarylpenta-2,3,4-trienoates with arylmethylidenemalononitriles and N-tosylimines

Article abstract of DOI:10.1021/jo802489t

Ethyl 5,5-diarylpenta-2,3,4-trienoates were synthesized and utilized in the phosphine-mediated [3+2] cycloaddition reactions with arylmethyhdenemalononitriles and N-tosylimines in the presence of tributylphosphine. These reactions provide an easy access t

Full text of DOI:10.1021/jo802489t

Phosphine-Mediated [3+2] Cycloaddition Reactions of Ethyl
5,5-Diarylpenta-2,3,4-trienoates with Arylmethylidenemalononitriles
and N-Tosylimines
Xiao-Yang Guan and Min Shi*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China
mshi@mail.sioc.ac.cn
ReceiVed NoVember 6, 2008
Ethyl 5,5-diarylpenta-2,3,4-trienoates were synthesized and utilized in the phosphine-mediated [3+2]
cycloaddition reactions with arylmethylidenemalononitriles and N-tosylimines in the presence of
tributylphosphine. These reactions provide an easy access to a variety of novel polysubstituted
cyclopentenes or pyrrolidines in good to excellent yields under mild conditions.
Introduction
cycloaddition reactions between 2,3-butadienoates and N-
tosylimines or arylmethylidenemalononitriles catalyzed by
tertiary phosphines were reported.5,6 During our ongoing
investigation on the phosphine or nitrogen-containing Lewis
base-catalyzed reactions of allenic ketones and esters with a
variety of electrophiles, we envisaged that ethyl 5,5-diarylpenta-
2,3,4-trienoates, a family of unsymmetrical cumulene deriva-
tives, would undergo cycloaddition reactions with arylmeth-
ylidenemalononitriles or N-tosylimines if using tertiary phosphines
or amines as the catalysts.7 It is anticipated that introducing a
double bond with two phenyl groups at the terminal of 2,3-
butadienoates could affect the facial selectivity which should
be important in asymmetric catalysis. The corresponding mul-
tifunctionalized [3+2] cycloaddition products could be more
useful in organic synthesis. Herein, we would like to report the
synthesis of ethyl 5,5-diarylpenta-2,3,4-trienoates and their
[3+2] cycloaddition reactions with arylmethylidenemalononi-
triles and N-tosylimines in the presence of tertiary phosphine
under mild conditions.
Cumulene derivatives have attracted much attention in organic
chemistry because of their high unique reactivities serving as
nucleophiles, electrophiles, and occasionally as dienophiles in
many reactions.1 Among these derivatives, allenes have resulted
in excellent regio- and stereoselectivities for many nucleophilic
and electrophilic reactions if the electronic and steric nature of
suitable catalysts were fine-tuned.2 Although many fundamental
reactions of butatrienes, such as oxidation, hydrogenation,
halogenation, metalation, metal complexation, and sulfurization
have been extensively investigated in the past years, much work
on this unique cumulative system is still needed.3 These
reactions usually are focused on the symmetrical cumulene
derivatives attached with alkyl or aryl groups on both sides of
butatrienes. Thus far, there have been few reports regarding the
reactivity of unsymmetrical cumulene derivatives.4
Recently, the phosphine-containing Lewis base-catalyzed
cycloaddition and nucleophilic substitution reactions have been
reported including several reviews after Lu’s pioneering [3+2]
* Corresponding author. Fax: 86-21-64166128.
(1) Furuta, T.; Asakawa, T.; Iinuma, M.; Fujii, S.; Tanakaa, K.; Kan, T. Chem.
Commun. 2006, 3648–3650.
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Chem. Lett. 2006, 35, 512–513. (b) Toda, F.; Yamamoto, M.; Tanaka, K.; Mak,
T. C. W. Tetrahedron Lett. 1985, 26, 631–634. (c) Vo-Quang, L.; Battioni, P.;
Vo-Quang, Y. Tetrahedron 1980, 36, 1331–1336. (d) Saalfrank, R. W.; Welch,
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10.1021/jo802489t CCC: $40.75
Published on Web 01/27/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 1977–1981 1977

Guan and Shi
SCHEME 1. The Synthesis of 1a and 1b
Results and Discussion
Ratts and Partos8 in the preparation of Ph2CdCdCdPPh3 via
bromoalkenylphosphonium salt Va. Recently, Browne et al.
have successfully prepared the corresponding cumulene diester
from the reaction of Va with mesoxalic ester in 53% yield in
the presence of triethylamine (eq 1).9
Since there has been no report on the preparation of ethyl
5,5-diarylpenta-2,3,4-trienoates, we attempted to synthesize these
compounds according to the previously reported procedure by
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Agapiou, K.; Jang, H.-Y.; Krische, M. J. J. Am. Chem. Soc. 2002, 124, 2402–
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Therefore, the corresponding tertiary alcohols IIa and IIb
were first prepared in moderate yields from the reaction of
ketones Ia and Ib with ethylmagnesium bromide in diethyl
ether at room temperature (20 °C). Then, the two alcohols
were used to synthesize compounds IIIa and IIIb upon
treating with bromine in acetic acid at 80 °C within 5 min
(Scheme 1). Further treatment of compounds IIIa and IIIb
with bromine in chloroform by photoirradiation afforded
compounds IVa and IVb in 88% and 62% yield, respectively,
which can be further transformed into the corresponding
phosphonium salts Va and Vb in 77% and 89% yield,
respectively, by treatment with PPh3 in toluene at 80 °C for
3 h. The reactions of Va and Vb with ethyl glyoxylate in
the presence of Et3N produced ethyl 5,5-diarylpenta-2,3,4-
trienoates 1a and 1b as solid products in moderate yields in
acetonitrile at 0 °C for 10 min (Scheme 1).
Initial examinations with ethyl 5,5-diphenylpenta-2,3,4-
trienoate 1a and benzylidenemalononitrile 2a as the substrates
in the presence of 50 mol % of PBu3 in toluene at different
temperatures were aimed at determining the optimal condi-
tions and the results of these experiments are summarized
in Table 1. When 1a, 2a, and 50 mol % of PBu3 were stirred
in toluene at 80 °C for 9 h, the polysubstituted cyclopentene
derivative 3a was obtained in 84% yield (Table 1, entry 1).
Lowering the reaction temperature to 40 and 20 °C (room
temperature) afforded 3a in lower yields (Table 1, entries 2
and 3). A survey of the other reaction parameters was next
performed and the results are also summarized in Table 1.
The examination of a variety of phosphine-containing Lewis
bases revealed that PPh2Me and PPhMe2 (50 mol %) are more
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3686–3694. (j) Zhao, G.; Shi, M. Org. Lett. 2005, 7, 4527–4530. (k) Shi, Y.;
Shi, M. Synlett 2005, 17, 2623–2626. (l) Shi, Y.; Shi, M. Org. Biomol. Chem.
2005, 3, 1620–1621. (m) Shi, M.; Xu, Y.; Shi, Y. Chem. Eur. J. 2005, 11, 1794–
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Shi, Y.; Zhao, G. AdV. Synth. Catal. 2006, 348, 967–972. (p) Guo, Y.; Shi, Y.;
Li, H.; Shi, M. Tetrahedron 2006, 62, 5875–5882. (q) Shi, Y.; Shi, M.
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1978 J. Org. Chem. Vol. 74, No. 5, 2009

Phosphine-Mediated [3+2] Cycloaddition Reactions
TABLE 1. Survey of the Reaction Parameters for the
Phosphine-Mediated [3+2] Cycloaddition of 1a and 2a
TABLE 2. Scope of the PBu3-Mediated [3+2] cycloaddition of 1
and 2
entrya
Ar
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
p-ClC6H4
p-ClC6H4
R
yield (%)b
temp
(°C)
time
(h)
yield
(%)b
entrya
Lewis base
solvent
toluene
1
2
3
4
5
6
7
8
p-MeC6 H4
p-ClC6H4
p-MeOC6H4
p-NO2C6H4
m-MeC6H4
m-FC6H4
o-BrC6H4
o-ClC6H4
3-pyridyl
2-furyl
3b, 91
3c, 99
3d, 98
3e, 73
3f, 82
3g, 96
3h, 99
3i, 99
3j, 93
3k, 95
3l, 86
3m, 92
3n, 29
3o, 52
3o, 43
1
2
3
4
5
6
7
8
PBu3 (5 0 mol %)
PBu3 (5 0 mol %)
PBu3 (5 0 mol %)
PPh3 (5 0 mol %)
PPh2Me (5 0 mol %)
PPhMe2 (5 0 mol %)
PtBu3 (50 mol %)
PMe3 (5 0 mol %)
PBu3 (5 0 mol %)
PBu3 (5 0 mol %)
PBu3 (5 0 mol %)
PBu3 (5 0 mol %)
PBu3 (5 0 mol %)
PBu3 (2 0 mol %)
PBu3 (1 0 mol %)
80
40
rt
9
84
57
56
60
84
79
trace
65
61
93
95
70
93
67
49
toluene
toluene
toluene
toluene
toluene
toluene
toluene
DMF
1,4-dioxane
THF
CH3CN
DCE
26
26
24
11
11
22
11
1
1
1
1
1
80
80
80
80
80
80
80
60
80
80
60
60
9
9
10
11
12
13
14c
15d
10
11
12
13
14
15
(E)-C6H5CHdCH
1-naphthyl
Et
C6H5
C6H5
THF
THF
10
10
a All reactions were carried out with 1 (0.1 mmol) and 2 (0 0.1
mmol) in the presence of PBu3 (50 mol %) in THF (1.0 mL) under
argon atmosphere. b Isolated yields. c This reaction was carried out at 6
0 °C for 4 h. d This reaction was carried out at room temperature for 2
4 h.
a All reactions were carried out with 1a (0.1 mmol) and 2a (0.1
mmol) in the presence of Lewis base in solvent (1 0.0 mL) under argon
atmosphere. b Isolated yields.
effective catalysts than PPh3 and PMe3 under identical
conditions, providing 3a in 84% and 79% yield after 11 h,
respectively, and PtBu3 did not catalyze the reaction presum-
ably due to the steric hindrance (Table 1, entries 4-8). With
use of PBu3 as the optimized catalyst, the examination of
solvent effects revealed that tetrahydrofuran (THF), 1,4-
dioxane, and 1,2-dichloroethane (DCE) are suitable solvents
to give 3a in higher yields and the reaction could complete
within 1 h in these solvents (Table 1, entries 9-13). Both of
the employed amounts of the Lewis base and the reaction
temperature in THF are crucial to the reaction outcomes. For
example, using 20 mol % of PBu3 as the catalyst afforded
3a in 67% yield at 60 °C and carrying out the reaction at 60
°C with 10 mol % of PBu3 as the catalyst provided 3a in
49% yield under otherwise identical conditions (Table 1,
entries 14 and 15). Accordingly, we also attempted to use
somenitrogen-containingLewisbases,suchas1,4-diazabicyclo-
[2.2.2]octane(DABCO),N,N-4-dimethylaminopyridine(DMAP),
and imidazole, as the catalysts to promote the reaction under
similar conditions. However, it was found that using DMAP
as the catalyst afforded 3a in only 36% yield, and using
DABCO or imidazole as the catalyst, no reaction occurred.
Under these optimized reaction conditions, we next utilized
50 mol % of PBu3 as the catalyst and THF as the solvent to
examine the scope and limitations of this reaction using 1a
and 1b as the substrates with a variety of arylmethyliden-
emalononitriles 2 bearing different substituents on the
benzene rings and the results of these experiments are
summarized in Table 2. As shown in Table 2, whether
electron-withdrawing or electron-donating substituent was
introduced at teh ortho, meta, or para position of the benzene
ring of 2 or the heterocycle-containing benzylidenemalono-
nitriles were employed, the reactions proceeded smoothly to
afford 3 in good to excellent yields (Table 2, entries 1-12).
As for alkylmethylidenemalononitriles, the corresponding
product 3n was formed in 29% yield (Table 2, entry 13).
Using butatriene 1b bearing a electron-withdrawing group,
such as Cl atom on the benzene ring, provided the corre-
sponding product 3o in 52% yield at 60 °C and 43% yield at
20 °C (room temperature), respectively (Table 2, entries 14
and 15). Moreover, the crystal structure of 3i has been
unambiguously determined by X-ray diffraction and its CIF
data have been presented in the Supporting Information.10
Furthermore, ethyl 5,5-diarylpenta-2,3,4-trienoates could also
react with N-tosylimines 4 smoothly to give the corresponding
polysubstituted pyrrolidines in moderate to good yields in the
presence of a variety of phosphine-containing Lewis bases.
When this reaction was carried out at 80 °C in toluene with
PBu3 (50 mol %) as the catalyst, the corresponding [3+2]
cycloaddition product 5a was obtained in 72% yield after 20 h.
The examination of the other reaction parameters revealed that
PBu3 is the best catalyst and the reaction should be carried out
at 80 °C (Table 3, entries 1-5). To improve the yield of 5a,
we added some additives such as H2O (20 mol %) together with
Et3N (5 mol %)5y as well as 4-nitrophenol (50 mol %) into
the reaction system, but this provided no improvement on the
reaction outcomes (Table 3, entries 6 and 7). Changing the
employed solvent to THF, 1,4-dioxane, and DCE and raising
the reaction temperature to 140 °C in DMF or p-xylene did not
improve the yield of 5a (Table 3, entries 8-12). Using DACBO
or DMAP as the catalyst, no reaction occurred under the
standard conditions. The best reaction conditions were found
to be to carry out the reaction in toluene at 80 °C with PBu3
(50 mol %) as the catalyst.
Under these optimized reaction conditions, we next similarly
examined the scope and limitations of this reaction using a
(10) The crystal data of 3i have been deposited in CCDC with no. 713030.
Empirical formula: C29H21ClN2O2. Formula weight: 464.93. Crystal size: 0.503
× 0.450 × 0.378. Crystal color, habit: colorless, prismatic. Crystal system:
triclinic. Lattice type: primitive. Lattice parameters: a ) 10.2036(10) Å, b )
11.2203(11) Å, c ) 11.5131(12) Å, R ) 84.328(2)°, ꢀ ) 66.732(2)°, γ )
3
79.838(2)°, V ) 1191.3(2) Å . Space group: P1. Z ) 2. Dcalcd ) 1.296 g/cm3.
j
F000 ) 484. R1 ) 0.0593, wR2 ) 0.1626. Diffractometer: Rigaku AFC7R.
J. Org. Chem. Vol. 74, No. 5, 2009 1979

Guan and Shi
TABLE 3. Survey of the Reaction Parameters for the Phosphine-Mediated [3+2] Cycloaddition of 1a and 4a
entrya
Lewis base
solvent
toluene
temp (°C)
time (h)
yield (%)b
1
2
3
4
PBu3 (50 mol %)
PBu3 (50 mol %)
PPh3 (50 mol %)
80
40
80
80
80
80
80
60
80
20
26
24
20
20
24
24
20
20
20
20
20
72
46
35
36
67
52
28
69
65
65
33
50
toluene
toluene
toluene
toluene
toluene
toluene
THF
1,4-dioxane
DCE
DMF
PPh Me (50 mol %)
2
5
PPhMe2 (50 mol %)
PBu3 (50 mol %)
PBu3 (50 mol %)
PBu3 (50 mol %)
PBu3 (50 mol %)
PBu3 (50 mol %)
PBu3 (50 mol %)
PBu3 (50 mol %)
6c
7d
8
9
10
11
12
80
140
140
p-xylene
a All reactions were carried out with 1a (0.1 mmol) and 4a (0.1 mmol) in the presence of Lewis base in solvent (1.0 mL) under argon atmosphere.
b Isolated yields. c Et3N (5 mol %) and H2O (20 mol %) were added. d 4-Nitrophenol (50 mol %) was added.
TABLE 4. Scope of the PBu3-Mediated [3+2] Cycloaddition of 1
and 4
FIGURE 1. The structure of 5n.
SCHEME 2. A Plausible Reaction Mechanism of These Two
Reactions
entrya
Ar1
C6H5
Ar
yield (%)b
2
1
2
3
4
5
6
7
8
p-MeOC6H4
p-ClC6H4
p-NO2C6H4
o-MeOC6H4
o-BrC6H4
5b, 74
5c, 59
5d, 48
5e, 67
5f, 73
5g, 59
5h, 77
5i, 71
5j, 75
5k, 68
5l, 66
5m, 57
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
p-ClC6H4
m-FC6H4
o,m-Cl2C6H3
m-MeC6H4
(E)-C6H5CHdCH
1-naphthyl
2-furyl
9
10
11
12
C6H5
a All reactions were carried out with 1 (0 0.1 mmol) and 4 (0 0.1
mmol) in the presence of PBu3 (50 mol %) in toluene (1.0 mL) under
argon atmosphere. b Isolated yields.
variety of 4 bearing different substituents on the benzene ring
and the results of these experiments are summarized in Table
4. As can be seen in Table 4, both aromatic and heterocyclic
N-tosylimines are suitable substrates in this reaction, providing
the corresponding [3+2] cycloaddition products 5 in moderate
to good yields (Table 4, entries 1-11). Using butatriene 1b as
the substrate provided the corresponding product 5m in 57%
yield (Table 4, entry 12). The product structure of 5f was further
determined by X-ray diffraction and its CIF data are presented
in the Supporting Information.11 This reaction is sluggish as
compared with the reaction of 1 with 2, presumably due to the
lower reactivity of N-tosylimines 4. Moreover, since ethyl 5,5-
diarylpenta-2,3,4-trienoates are not stable at 80 °C during a long
reaction time, this could be the reason to explain why the yields
of 5 in the reactions between 1 and 4 are lower.
We also utilized aliphatic N-tosylimines such as N-(cyclo-
hexylmethylene)-4-methylbenzenesulfonamide and N-butylidene-
4-methylbenzenesulfonamide in this reaction, but it was found
that the product 5n was formed in 36% and 31% yield,
respectively, rather than the [3+2] cycloaddition product. This
may be due to that the aliphatic N-tosylimine might decompose
to give TsNH2 and aldehyde under the reaction conditions. The
direct nucleophilic addition of TsNH2 to 1a resulted in the
formation of 5n (Figure 1).
A plausible reaction mechanism is shown in Scheme 2 on
the basis of the previously reported phosphine-catalyzed [3+2]
cycloaddition reactions between 2,3-butadienoates and N-
tosylimines or arylmethylidenemalononitriles.6 The first step is
the nucleophilic attack of PBu3 to ethyl 5,5-diarylpenta-2,3,4-
trienoate 1 to generate zwitterionic intermediate A. Nucleophilic
attack of intermediate A to arylmethylidenemalononitrile 2
(or N-tosylimine 4) followed by an intramolecular conjugate
(11) The crystal data of 5f have been deposited in CCDC with no. 708170.
Empirical formula: C33H28BrNO4S. Formula weight: 614.53. Crystal size: 0.470
× 0.303 × 0.167. Crystal color, habit: colorless, prismatic. Crystal system:
triclinic. Lattice type: primitive. Lattice parameters: a ) 10.0258(14) Å, b )
10.2798(15) Å, c ) 16.313(2) Å, R ) 88.121(3)°, ꢀ ) 76.794(3)°, γ )
3
65.924(3)°, V ) 1874.8(3) Å . Space group: P1. Z ) 2. Dcalcd ) 1.369 g/cm3.
j
F000 ) 632. R1 ) 0.0627, wR2 ) 0.1457. Diffractometer: Rigaku AFC7R.
1980 J. Org. Chem. Vol. 74, No. 5, 2009

Phosphine-Mediated [3+2] Cycloaddition Reactions
Hz), 7.33-7.40 (m, 8H), 7.56 (d, 2H, J ) 8.7 Hz); 13C NMR
(CDCl3, 75 MHz, TMS) δ 13.9, 21.6, 60.7, 70.6, 127.4, 127.5,
127.7, 127.8, 128.3, 128.4, 128.7, 129.4, 130.4, 130.6, 134.4, 136.0,
138.2, 138.4, 139.3, 140.8, 141.3, 144.0, 162.6; IR (CH2Cl2) ν 3045,
2976, 2906, 1701, 1595, 1442, 1363, 1245, 1167, 1089, 988, 817,
769, 698, 660 cm-1; MS (ESI) m/z (%) 558 (M + Na+, 100), 574
(M + K+, 40), 536 (M + H+, 25). Anal. Calcd for C33H29NO4S:
C, 73.99; H, 5.46; N, 2.61. Found: C, 73.99; H, 5.45; N, 2.45.
Compound 5n: yellow oil, 16 mg (36% yield); 1H NMR (CDCl3,
300 MHz, TMS) δ 0.99 (t, 3H, J ) 7.2 Hz), 2.34 (s, 3H), 3.88 (q,
2H, J ) 7.2 Hz), 6.32 (s, 1H), 7.20-7.24 (m, 4H), 7.30-7.37 (m,
7H), 7.41-7.45 (m, 3H), 7.70 (d, 2H, J ) 8.4 Hz); 13C NMR
(CDCl3, 75 MHz, TMS) δ 13.9, 21.5, 61.5, 122.6, 123.0, 127.6,
128.2, 128.3, 128.4, 128.6, 128.8, 129.4, 130.6, 135.5, 136.1, 138.6,
141.3, 143.9, 151.9, 164.5; IR (CH2Cl2) ν 3252, 3058, 2981, 2927,
1709, 1616, 1494, 1446, 1410, 1370, 1338, 1265, 1240, 1166, 1091,
814, 771, 702, 670 cm-1; MS (ESI) m/z (%) 470 (M + Na+, 100),
448 (M + H+, 25); HRMS (ESI) calcd for C26H25NO4SNa (M +
Na+) requires 470.1414, found 470.13965.
addition produced the ylide-type intermediate B. The catalytic
cycle completes to produce 3 or 5 via intermediate C after a
proton transfer and the subsequent elimination of PBu3.
Experimental Section
Compound 1a: yellow solid, mp 83-85 °C; 1H NMR (CDCl3,
300 MHz, TMS) δ 1.36 (t, 3H, J ) 7.2 Hz), 4.25 (q, 2H, J ) 7.2
Hz), 5.81 (s, 1H), 7.40-7.44 (m, 6H), 7.55-7.58 (m, 2H),
7.67-7.70 (m, 2H); 13C NMR (CDCl3, 75 MHz, TMS) δ 14.2,
60.8, 96.8, 128.5, 129.6, 129.7, 130.0, 134.8, 136.9, 137.2, 154.5,
165.5, 168.8; IR (CH2Cl2) ν 3056, 2980, 2925, 2359, 2341, 2053,
1733, 1699, 1489, 1446, 1365, 1329, 1243, 1185, 1150, 757, 692
cm-1; MS (EI) m/z (%) 276 [M+] (73.2), 202 (100.0), 204 (78.0),
203 (73.5), 276 (73.2), 231 (25.7), 201 (25.1), 200 (21.5), 101
(17.8); HRMS (EI) calcd for C19H16O2 (M+) requires 276.1150,
found 276.1153.
Compound 1b: yellow solid, mp 87-89 °C; 1H NMR (CDCl3,
300 MHz, TMS) δ 1.36 (t, 3H, J ) 6.9 Hz), 4.25 (q, 2H, J ) 6.9
Hz), 5.85 (s, 1H), 7.37-7.41 (m, 4H), 7.45-7.48 (m, 2H),
7.56-7.59 (m, 2H); 13C NMR (CDCl3, 75 MHz, TMS) δ 14.3,
61.0, 98.1, 128.90, 128.94, 130.8, 131.0, 131.7, 135.0, 135.9, 136.1,
155.0, 165.1, 168.2; IR (CH2Cl2) ν 3053, 2980, 2359, 2341, 2053,
1702, 1585, 1488, 1405, 1366, 1322, 1300, 1244, 1189, 1152, 1092,
1012, 833, 749 cm-1; MS (EI) m/z (%) 344 [M+] (8.0), 57 (100.0),
91 (63.4), 56 (49.5), 131 (43.6), 92 (39.7), 77 (29.8), 128 (29.3),
55 (27.4); HRMS (EI) calcd for C19H14Cl2O2 (M+) requires
344.0371, found 344.0369.
Conclusion
Ethyl 5,5-diarylpenta-2,3,4-trienoates were successfully
synthesized and utilized as a three-carbon source in the [3+2]
cycloaddition reactions with arylmethylidenemalononitriles
or N-tosylimines in the presence of PBu3 (50 mol %) in THF
and toluene, respectively. These reactions show a broad
substrate scope for a variety of arylmethylidenemalononitriles
or N-tosylimines. In the reactions of ethyl 5,5-diarylpenta-
2,3,4-trienoates with arylmethylidenemalononitriles, the cor-
responding [3+2] cycloaddition products could be obtained
in 43-99% yields within 1 h at 60 °C, and in the reactions
of ethyl 5,5-diarylpenta-2,3,4-trienoates with N-tosylimines,
the cycloadducts were obtained in 57-74% yields after 24 h
at 80 °C. Efforts are in progress to elucidate further
mechanistic details of these reactions and to understand their
scope and limitations. Moreover, the asymmetric [3+2]
cycloaddition reactions of ethyl 5,5-diarylpenta-2,3,4-
trienoates with arylmethylidenemalononitriles or N-to-
sylimines are in progress in our laboratory.
Compound 3a: white solid, 42 mg (95% yield), mp 138-140
°C; 1H NMR (CDCl3, 300 MHz, TMS) δ 1.13 (t, 3H, J ) 6.9 Hz),
4.08-4.14 (m, 2H), 4.91 (s, 1H), 7.23-7.28 (m, 4H), 7.36-7.44
(m, 12H); 13C NMR (CDCl3, 75 MHz, TMS) δ 13.9, 44.7, 61.2,
61.6, 111.3, 116.4, 128.0, 128.6, 128.8, 129.1, 129.37, 129.41,
129.5, 129.7, 129.9, 132.6, 134.7, 137.7, 138.1, 139.8, 140.1, 149.6,
162.9; IR (CH2Cl2) ν 3061, 3031, 2982, 2932, 2229, 1720, 1593,
1571, 1493, 1455, 1370, 1240, 1181, 1031, 771, 697, 615 cm-1
;
MS (EI) m/z (%) 430 [M+] (7.9), 384 (100.0), 385 (33.8), 356
(22.5), 319 (20.0), 355 (16.9), 227 (11.3), 328 (10.9), 357 (10.7).
Anal. Calcd for C29H22N2O2: C, 80.91; H, 5.15; N, 6.51. Found: C,
80.93; H, 5.05; N, 6.32.
Compound 3l: yellow oil, 39 mg (86% yield); 1H NMR (CDCl3,
400 MHz, TMS) δ 1.02 (t, 3H, J ) 7.2 Hz), 1.31 (t, 3H, J ) 7.2
Hz), 1.99-2.10 (m, 2H), 3.78 (ddd, 1H, J1 ) 6.4 Hz, J2 ) 4.4 Hz,
J3 ) 0.8 Hz), 4.21-4.31 (m, 2H), 7.13 (d, 1H, J ) 0.8 Hz),
7.14-7.16 (m, 2H), 7.37-7.43 (m, 5H), 7.45-7.48 (m, 3H); 13C
NMR (CDCl3, 100 MHz, TMS) δ 10.1, 14.2, 24.5, 42.5, 56.3, 61.3,
111.9, 116.3, 128.5, 128.9, 129.3, 129.4, 129.6, 130.0, 133.1, 137.9,
138.4, 139.2, 140.1, 148.1, 163.4; IR (CH2Cl2) ν 3058, 2972, 2928,
2249, 1712, 1601, 1445, 1460, 1371, 1242, 1181, 1093, 769, 701
cm-1; MS (EI) m/z (%) 382 [M+] (36.5), 84 (100.0), 308 (90.3),
86 (66.0), 382 (36.5), 307 (31.5), 293 (31.4), 309 (23.6), 149 (20.9);
HRMS (EI) calcd for C25H22N2O2 (M+) requires 382.1681, found
382.1679.
Acknowledgment. We thank the Shanghai Municipal
CommitteeofScienceandTechnology(06XD14005,08dj1400100-
2), National Basic Research Program of China (973)-
2009CB825300, and the National Natural Science Foundation
of China (20872162, 20672127, and 20732008).
Supporting Information Available: 1H NMR and 13C
spectroscopic and analytic data for 1a, 1b, 3, and 5, and X-ray
crystal structure of 3i and 5f. This material is available free of
charge via the Internet at http://pubs.acs.org.
Compound 5a: yellow solid, 39 mg (72% yield), mp 219-221
°C; 1H NMR (CDCl3, 300 MHz, TMS) δ 1.05 (t, 3H, J ) 6.6 Hz),
2.43 (s, 3H), 4.00 (q, 2H, J ) 6.6 Hz), 6.06 (d, 1H, J ) 0.9 Hz),
7.02 (d, 1H, J ) 0.9 Hz), 7.11-7.18 (m, 5H), 7.23 (d, 4H, J ) 8.4
JO802489T
J. Org. Chem. Vol. 74, No. 5, 2009 1981