An expedient synthesis of 2,4,5-trisubstituted 1,4-pentadienes from Baylis-Hillman adducts via the Pd-catalyzed decarboxylation-elimination protocol

Article abstract of DOI:10.1016/j.tetlet.2009.06.142

We disclosed an efficient synthetic method of 2,4,5-trisubstituted 1,4-pentadienes from Baylis-Hillman adducts via the Pd-catalyzed decarboxylation-elimination protocol as the key step.

Full text of DOI:10.1016/j.tetlet.2009.06.142

Tetrahedron Letters 50 (2009) 5322–5325
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Tetrahedron Letters
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An expedient synthesis of 2,4,5-trisubstituted 1,4-pentadienes from
Baylis–Hillman adducts via the Pd-catalyzed decarboxylation–elimination
protocol
*
Ko Hoon Kim, Eun Sun Kim, Jae Nyoung Kim
Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
We disclosed an efficient synthetic method of 2,4,5-trisubstituted 1,4-pentadienes from Baylis–Hillman
adducts via the Pd-catalyzed decarboxylation–elimination protocol as the key step.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 8 June 2009
Revised 29 June 2009
Accepted 30 June 2009
Available online 16 July 2009
Dedicated to the memory of the late
Professor Eung Kul Ryu whose vision and
passion in Organic and Medicinal Chemistry
was an inspiration for all
Keywords:
Baylis–Hillman adducts
1,4-Pentadienes
Palladium
Decarboxylation–elimination.
Recently Baylis–Hillman adducts have been used for the synthe-
sis of many heterocyclic compounds and acyclic compounds.1–3
Among them functionalized 1,4-pentadiene is one of the meaningful
target structures due to the synthetic usefulness of this compound in
organic synthesis.2–4 Basavaiah and co-workers reported an elegant
method for these compounds involving the combination of two po-
larintermediates.2 As shownin Scheme1, nucleophilicpart is a zwit-
terion which is generated in situ from DABCO and acrylonitrile, and
the electrophilic component is a DABCO salt of Baylis–Hillman bro-
mide. The nucleophile attacked the electrophile in a SN20 manner to
produce 2,3,4-trisubstituted 1,4-pentadiene.2
During our recent studies on Pd-catalyzed decarboxylative pro-
tonation and allylations,5 we reasoned out that 2,4,5-trisubstituted
1,4-pentadiene 5a could be synthesized by using Pd-catalyzed
decarboxylation–elimination strategy from modified Baylis–Hill-
man adduct such as 4a, as shown in Scheme 2. Palladium-catalyzed
decarboxylation–elimination was originally studied by Tsuji and
has been used extensively in organic synthesis.6 In order to check
the feasibility of our rationale we prepared starting material 4a
by the reaction of Baylis–Hillman bromide 1a and allyl acetoace-
tate (2a) to prepare 3a and subsequent methylation with iodo-
methane to 4a.7
With this compound 4a we examined the reaction conditions as
shown in Table 1 under the influence of Pd(OAc)2 and PPh3.5,6 As
shown in Table 1, the ratio of Pd(OAc)2/PPh3 was very impor-
tant.5d,6 High loading of PPh3 [PPh3/Pd(OAc)2 = 2.0] increased the
amounts of decarboxylative allylation product (7a, 63%) as in entry
1,7 while low loading of PPh3 [PPh3/Pd(OAc)2 = 1.0–0.5] produced
decarboxylation–elimination product 5a (78–83%) as the major
product as in entries 2 and 3.5d,6,7 The use of 5 mol % Pd(OAc)2
showed a similar but slightly lower yield of 5a (entry 4). As
reported by Tsuji,6 the use of non-polar solvent such as toluene
lowered the yield of 5a (65%), instead the yield of allylation prod-
uct 7a was increased to 20% (entry 5). The use of DMF did not show
better results (entry 6). The use of Pd(PPh3)4 produced 7a as the
major product (60%) presumably due to high ratio of PPh3/
Pd(OAc)2, and compound 5a was not formed at all (entry 7). In
all entries, decarboxylative protonation product 6a was produced
in variable amounts as a side product (4–25%).
The plausible mechanism is depicted in Scheme 3 with 4a as an
example involving the sequential oxidative addition of O-allyl
bond to Pd(0) to produce
boxylation to form a C-bound
and b-elimination to liberate 5a and Pd(0). There can be present
p
-allylpalladium intermediate (I), decar-
p
-allylpalladium intermediate (II),
* Corresponding author. Tel.: +82 62 530 3381; fax: +82 62 530 3389.
E-mail address: kimjn@chonnam.ac.kr (J.N. Kim).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.06.142

K. H. Kim et al. / Tetrahedron Letters 50 (2009) 5322–5325
5323
N
N
CN
CN
CN
COOMe
OH
COOMe
Br
Ph
COOMe
Ph
COOMe
Ref. 10
DABCO
Ref. 2
Ph
Ph
2,3,4-trisubstituted
1,4-pentadiene
N
N
Br
Scheme 1.
EWG1
EWG2
EWG1
EWG2
COOallyl
4a-h
MeI, Cs2CO3
CH3CN, rt
K2CO3
CH3CN, rt
EWG1
EWG2
Pd(OAc)2 (5 mol%)
PPh3 (5 mol%)
Ph
EWG1
Br
Ph
Ph
EWG2
COOallyl
Ph
+
CH3CN, reflux, 1 h
COOallyl
3a-h
5a-h
2,4,5-trisubstituted
1,4-pentadiene
1a: EWG1 = COOMe 2a: EWG2 = COMe
1b: EWG1 = COOEt
1c: EWG1 = COMe
1d: EWG1 = CN
2b: EWG2 = CN
2c: EWG2 = COOEt
Scheme 2.
Table 1
Optimized conditions for the synthesis of 5a from 4a
COOMe
COMe
COOMe
COMe
COOMe
COMe
COOMe
Ph
+
Ph
Ph
Ph
Conditions
+
COMe
COOallyl
6a
5a
7a
4a
Entry
Conditions
Products (%)
1
Pd(OAc)2 (10 mol %), PPh3 (20 mol %), CH3CN, reflux, 1 h
Pd(OAc)2 (10 mol %), PPh3 (10 mol %), CH3CN, reflux, 1 h
Pd(OAc)2 (10 mol %), PPh3 (5 mol %), CH3CN, reflux, 1 h
Pd(OAc)2 (5 mol %), PPh3 (5 mol %), CH3CN, reflux, 1 h
Pd(OAc)2 (10 mol %), PPh3 (10 mol %), toluene, 80–90 °C, 1 h
Pd(OAc)2 (10 mol %), PPh3 (10 mol %), DMF, 80–90 °C, 1 h
Pd(PPh3)4 (10 mol %), CH3CN, reflux, 1 h
5a (0), 6a (23), 7a (63)
5a (83), 6a (8), 7a (0)
5a (78), 6a (5), 7a (0)
5a (79), 6a (4), 7a (0)
5a (65), 6a (5), 7a (20)
5a (79), 6a (5), 7a (0)
5a (0), 6a (25), 7a (60
2a
3
4a
5
6
7
a
Selected conditions for the entries in Table 2.
COOMe
COOMe
Ph
- Pd(0)
- propene
COOMe
COMe
Ph
Ph
Hb
Ha
Hb
Pd(0)
- CO2
COMe
COMe
5a
4a
+
β-Ha elimination
(low loading of PPh3)
decarboxylation
Ha
Pd
(II)
Ha
O
O Pd
8a (not formed)
(via β-Hb elimination)
(I)
7a
Scheme 3.
a competition between b-H elimination to alkene 5a and reductive
elimination of Pd(0) to allylated compound 7a in the intermediate
(II) stage. The competition could be controlled by changing the
ratio of Pd(OAc)2/PPh3 as shown in Table 1 (entries 1–3). Low load-
ing of PPh3 increased the amounts of b-H elimination product 5a.
The regioselectivity between Ha and Hb during the b-H elimination
of intermediate (II) was controlled completely and we obtained 5a
which was formed via the b-Ha elimination. We did not observe the
formation of other alkene product 8a at all in the reaction
mixture.6a,b,8 The selective b-Ha elimination may be attributed to
the small steric hindrance during the elimination process of Ha.
Encouraged by the successful results, we prepared starting
materials 3b–h by the reaction of Baylis–Hillman bromides 1a–d
and allyl esters 2a–c (K2CO3, CH3CN, rt) as summarized in Table
2.5a When the Baylis–Hillman bromide and allyl ester have nitrile
functionality (entries 2, 7, and 8), the yield of compound 3 (3b,
3g, and 3h) was low because of the formation of dialkylation side
product. Subsequent methylation of 3b–h was carried out with
iodomethane (Cs2CO3, CH3CN, rt–60 °C) to make 4b–h (74–92%).
The next decarboxylation–elimination reactions of 4b–h were car-
ried out under the optimized conditions (entries 2 and 4 in Table
1), and the results are summarized in Table 2.

5324
K. H. Kim et al. / Tetrahedron Letters 50 (2009) 5322–5325
Table 2
Synthesis of 2,4,5-trisubstituted 1,4-pentadienes 5
EWG1
EWG2
COOallyl
4a-h
EWG1
EWG2
EWG1
EWG2
EWG1
EWG2
Ph
Ph
EWG1
Br
Ph
Ph
EWG2
Ph
+
COOallyl
COOallyl
3a-h
6a-h
1a-d
2a-c
5a-h
Conditionsc
Entry
1 + 2 (EWG1/EWG2)
3 (%)a
Conditionsb
4 (%)
5 (%), 6 (%)
1
2
3
4
5
6
7
8
1a + 2a (COOMe/COMe)
1a + 2b (COOMe/CN)
1a + 2c (COOMe/COOEt)
1b + 2a (COOEt/COMe)
1c + 2a (COMe/COMe)
1c + 2b (COMe/CN)
1d + 2a (CN/COMe)
1d + 2b (CN/CN)
3a (79)
rt, 6 h
4a (86)
4b (88)
4c (91)
4d (91)
4e (74)
4f (92)
4g (85)i
4h (75)i
A, 1 h
B, 1 h
5a (83), 6a (8)
5b (68), 6b (13)
5c + 6c (55, 3:2)f
5d (72), 6d (–)
5e (72), 6e (10)
5f (54), 6f (17)
5g (73),i 6g (–)
5h (62),i 6h (15)i
3b (68)d
3c (97
rt, 12 h
60 °C, 12 h
rt, 6 h
rt, 48 h
rt, 12 h
rt, 12 h
rt, 12 h
DMF, 2 he
A, 1 h
A, 1 h
A, 1 h
A, 1 h
B, 1 h
3d (81)
3e (75)
3f (65)
3g (55)g,i
3h (26)h,i
a
Conditions: 1 (1.5 mmol), 2 (1.2 equiv), K2CO3 (2.0 equiv), CH3CN, rt, 12 h.
Conditions: MeI (5.0 equiv), Cs2CO3 (2.0 equiv), CH3CN.
b
c
d
e
f
Conditions A (entry 2 in Table 1), conditions B (entry 4 in Table 1).
Bis adduct (1a:2b = 2:1) was isolated in 18% even with 2.5 equiv of 2b.
Run at 140–150 °C.
Mixed together and the ratio of 5c/6c was calculated from 1H NMR.
Bis adduct (1d:2a = 2:1) was isolated in 16% even with 10 equiv of 2a.
Bis adduct (1d:2b = 2:1) was isolated in 69% even with 10 equiv of 2b.
The geometry of benzylidene part is Z when EWG1 is nitrile.
g
h
i
NO2
Cs2CO3 (2.0 equiv)
CH3CN, 60 oC, 12 h
COOMe
Pd(OAc)2 (10 mol%)
PPh3 (10 mol%)
COOMe
Ph
Ph
NO2
NO2
1a
+
CH3CN, reflux, 2 h
COOallyl
COOallyl
5i (56%)
4i (60%)
2d
Scheme 4.
As in Table 2, all entries produced the corresponding 1,4-pent-
As another entry, we examined the reaction of 4i having p-nitro-
phenyl group.5b,9 Synthesis of 4i was performed by the reaction of
1a and allyl arylacetate 2d according to our recent Letter.5b The
reaction of 4i produced decarboxylation–elimination product 5i
in moderate yield (56%) as shown in Scheme 4. In order to synthe-
size more complex 1,4-diene, we prepared compound 4j by benzy-
lation of 3a. Under the same conditions (entry 4 in Table 1) three
types of compounds (3:3:1) were isolated as a mixture in 80%,
which states that stereo- and regiochemistry could not be
controlled in this case (Scheme 5).6a,b,8 The reaction of cyclohexa-
none derivative 4k, prepared from 1a and allyl 2-oxocyclohexane-
adienes 5b–h in moderate to good yields (33–73%) and decarb-
oxylative protonation products were generated together in low
yields (10–22%) as side products. The yields of products were
good when EWG2 is acetyl (5d, 5e, and 5g) while low to moderate
when EWG2 is ester or nitrile (5b, 5c, 5f, and 5h). It is interesting
to note that ester derivative 4c did not produce 5c in CH3CN or in
toluene even at refluxing temperature for a long time. When we
used DMF as a solvent at high temperature (140–150 °C) we
could obtain 5c fortunately, although in low yield as a mixture
with 6c (entry 3 in Table 2).
COOMe
COMe
COOMe
COMe
COOMe
Ph
benzyl bromide
(1.5 equiv)
Ph
Ph
Pd(OAc)2 (5 mol%)
PPh3 (5 mol%)
COMe
+
3a
K2CO3 (2.0 equiv)
CH3CN, rt, 48 h
CH3CN, reflux, 1 h
COOallyl
Ph
Ph
Ph
4j (87%)
80% (three isomers, 3:3:1)
Scheme 5.
COOMe
COOMe
O
Cs2CO3 (2.0 equiv)
DMF, rt, 5h
Pd(OAc)2 (10 mol%)
PPh3 (10 mol%)
Ph
Ph
COOallyl
COOallyl
O
1a
+
CH3CN, reflux, 1 h
O
2e
4k (90%)
5k (78%)
Scheme 6.

K. H. Kim et al. / Tetrahedron Letters 50 (2009) 5322–5325
5325
After the usual aqueous workup and column chromatographic purification
process (hexanes/ether, 10:1) compound 3a was isolated as colorless oil,
375 mg (79%).5a A mixture of 3a (316 mg, 1.0 mmol), MeI (705 mg, 5.0 mmol),
and Cs2CO3 (650 mg, 2.0 mmol) in CH3CN (2 mL) was stirred at room
temperature for 6 h. After the usual aqueous workup and column
chromatographic purification process (hexanes/ether, 10:1) compound 4a
carboxylate (2e), showed decarboxylation–elimination product 5k
in good yield (78%) regioselectively, as shown in Scheme 6.
In summary, we disclosed an efficient method for the synthesis
of various 2,4,5-trisubstituted 1,4-pentadienes by using the Pd-cat-
alyzed decarboxylation–elimination protocol as the key step under
the conditions of low loading of PPh3.
was isolated as colorless oil, 284 mg (86%).
A mixture of compound 4a
(165 mg, 0.5 mmol), Pd(OAc)2 (11 mg, 10 mol %), and PPh3 (13 mg, 10 mol %) in
CH3CN (1 mL) was heated to reflux for 1 h under nitrogen atmosphere. After
filtering through a Celite pad, removal of solvent, and the residue was purified
by column chromatographic purification process (hexanes/CH2Cl2, 1:9) to
afford compound 5a (101 mg, 83%) and 6a (9 mg, 8%). Selected spectroscopic
data of compounds 4a, 5a, 5b, 5g, 5i, 6a, and 7a are as follows.
Acknowledgements
This study was financially supported by Special Research Program
of Chonnam National University, 2009. Spectroscopic data were ob-
tained from the Korea Basic Science Institute, Gwangju branch.
Compound 4a: 86%; colorless oil; IR (film) 2950, 1741, 1714 cmꢀ1 1H NMR
;
(CDCl3, 300 MHz) d 1.11 (s, 3H), 2.07 (s, 3H), 3.31 (d, J = 14.4 Hz, 1H), 3.37 (d,
J = 14.4 Hz, 1H), 3.76 (s, 3H), 4.34–4.42 (m, 1H), 4.52–4.59 (m, 1H), 5.20–5.31
(m, 2H), 5.77–5.90 (m, 1H), 7.26–7.41 (m, 5H), 7.82 (s, 1H); 13C NMR (CDCl3,
75 MHz) d 18.14, 25.95, 29.71, 51.95, 59.26, 65.96, 118.89, 128.37, 128.59,
128.78, 128.97, 131.35, 135.36, 142.60, 168.48, 172.23, 204.12; ESIMS m/z 331
(M++1).
References and notes
Compound 5a: 83%; colorless oil; IR (film) 2951, 1714, 1676 cmꢀ1 1H NMR
;
1. For the general review on Baylis–Hillman reaction, see: (a) Basavaiah, D.; Rao,
A. J.; Satyanarayana, T. Chem. Rev. 2003, 103, 811–891; (b) Singh, V.; Batra, S.
Tetrahedron 2008, 64, 4511–4574; (c) Ciganek, E.. In Organic Reactions;
Paquette, L. A., Ed.; John Wiley & Sons: New York, 1997; Vol. 51, pp 201–350;
(d) Basavaiah, D.; Rao, P. D.; Hyma, R. S. Tetrahedron 1996, 52, 8001–8062; (e)
Drewes, S. E.; Roos, G. H. P. Tetrahedron 1988, 44, 4653–4670; (f) Kim, J. N.; Lee, K.
Y. Curr. Org. Chem. 2002, 6, 627–645; (g) Lee, K. Y.; Gowrisankar, S.; Kim, J. N. Bull.
Korean Chem. Soc. 2005, 26, 1481–1490; (h) Langer, P. Angew. Chem., Int. Ed. 2000,
39, 3049–3052; (i) Krishna, P. R.; Sachwani, R.; Reddy, P. S. Synlett 2008, 2897–
2912; (j) Declerck, V.; Martinez, J.; Lamaty, F. Chem. Rev. 2009, 109, 1–48.
2. For the synthesis of 1,4-dienes from Baylis–Hillman adducts, see: (a) Basavaiah,
D.; Sharada, D. S.; Kumaragurubaran, N.; Reddy, R. M. J. Org. Chem. 2002, 67,
7135–7137; (b) Basavaiah, D.; Kumaragurubaran, N.; Sharada, D. S. Tetrahedron
Lett. 2001, 42, 85–87; (c) Basavaiah, D.; Kumaragurubaran, N.; Sharada, D. S.;
Reddy, R. M. Tetrahedron 2001, 57, 8167–8172.
3. (a) Lee, M. J.; Lee, K. Y.; Kim, J. N. Bull. Korean Chem. Soc. 2005, 26, 477–480; (b)
Lee, M. J.; Kim, S. C.; Kim, J. N. Bull. Korean Chem. Soc. 2006, 27, 140–142; (c)
Gowrisankar, S.; Lee, C. G.; Kim, J. N. Tetrahedron Lett. 2004, 45, 6949–6953.
4. For the synthesis and synthetic usefulness of 1,4-diene compounds, see: (a)
Durand, S.; Parrain, J.-L.; Santelli, M. J. Chem. Soc., Perkin Trans. 1 2000, 253–
273; (b) Nicolaou, K. C.; Ramphal, J. Y.; Petasis, N. A.; Serhan, C. N. Angew.
Chem., Int. Ed. Engl. 1991, 30, 1100–1116; (c) Grigg, R.; Dorrity, M. J.; Heaney, F.;
Malone, J. F.; Rajviroongit, S.; Sridharan, V.; Surendrakumar, S. Tetrahedron
1991, 47, 8297–8322; (d) Grigg, R.; Malone, J. F.; Dorrity, M. J.; Heaney, F.;
Rajviroongit, S.; Sridharan, V.; Surendrakumar, S. Tetrahedron Lett. 1988, 29,
4323–4324; (e) Denmark, S. E.; Guagnano, V.; Dixon, J. A.; Stolle, A. J. Org. Chem.
1997, 62, 4610–4628; (f) Klaps, E.; Schmid, W. J. Org. Chem. 1999, 64, 7537–
7546; (g) Hara, R.; Nishihara, Y.; Landre, P. D.; Takahashi, T. Tetrahedron Lett.
1997, 38, 447–450; (h) Prasad, A. S. B.; Knochel, P. Tetrahedron 1997, 53, 16711–
16720; (i) Matsuhashi, H.; Hatanaka, Y.; Kuroboshi, M.; Hiyama, T. Tetrahedron
Lett. 1995, 36, 1539–1540; (j) Agrios, K. A.; Srebnik, M. J. Org. Chem. 1994, 59,
5468–5472; (k) Matsushita, H.; Negishi, E.-i. J. Am. Chem. Soc. 1981, 103, 2882–
2884; (l) Shimp, H. L.; Hare, A.; McLaughlin, M.; Micalizio, G. C. Tetrahedron
2008, 64, 6831–6837; (m) Lee, S. I.; Hwang, G.-S.; Shin, S. C.; Lee, T. G.; Jo, R. H.;
Ryu, D. H. Org. Lett. 2007, 9, 5087–5089.
(CDCl3, 300 MHz) d 2.42 (s, 3H), 3.53 (t, J = 1.5 Hz, 2H), 3.79 (s, 3H), 5.70 (t,
J = 1.8 Hz, 1H), 6.11 (t, J = 1.8 Hz, 1H), 7.25–7.38 (m, 5H), 7.92 (s, 1H); 13C NMR
(CDCl3, 75 MHz) d 25.92, 28.52, 52.11, 124.79, 128.56, 128.91, 129.03, 129.21,
134.93, 141.79, 146.32, 168.30, 199.01; ESIMS m/z 245 (M++1). Anal. Calcd for
C15H16O3: C, 73.75; H, 6.60. Found: C, 73.89; H, 6.75.
Compound 5b: 68%; colorless oil; IR (film) 2952, 2223, 1714 cmꢀ1 1H NMR
;
(CDCl3, 300 MHz) d 3.49 (t, J = 1.5 Hz, 2H), 3.83 (s, 3H), 5,75 (t, J = 1.8 Hz, 1H),
5.97 (t, J = 1.5 Hz, 1H), 7.30–7.45 (m, 5H) 7.98 (s, 1H); 13C NMR (CDCl3, 75 MHz)
d 32.15, 52.34, 118.50, 120.66, 126.36, 128.80, 128.91, 129.36, 131.03, 134.38,
143.61, 167.39; ESIMS m/z 228 (M++1). Anal. Calcd for C14H13NO2: C, 73.99; H,
5.77; N, 6.16. Found: C, 74.11; H, 5.97; N, 6.03.
Compound 5g: 73%; colorless oil; IR (film) 2209, 1678 cmꢀ1 1H NMR (CDCl3,
;
300 MHz) d 2.39 (s, 3H), 3.36 (s, 2H), 6.08 (t, J = 1.2 Hz, 1H), 6.25 (s, 1H), 7.07 (s,
1H), 7.35–7.44 (m, 3H), 7.70–7.75 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 25.68,
36.86, 108.08, 118.39, 128.24, 128.68, 128.77, 130.19, 133.47, 144.06, 145.77,
198.24; ESIMS m/z 212 (M++1). Anal. Calcd for C14H13NO: C, 79.59; H, 6.20; N,
6.63. Found: C, 79.84; H, 6.13; N, 6.47.
Compound 5i: 56%; colorless oil; IR (film) 1713, 1516, 1345 cmꢀ1 1H NMR
;
(CDCl3, 300 MHz) d 3.69 (t, J = 1.2 Hz, 2H), 3.82 (s, 3H), 5.24 (t, J = 1.8 Hz, 1H),
5.56 (t, J = 1.5 Hz, 1H), 7.34–7.39 (m, 5H), 7.60 (dt, J = 9.0 and 2.7 Hz, 2H), 7.95
(s, 1H), 8.19 (dt, J = 9.0 and 2.4 Hz, 2H); 13C NMR (CDCl3, 75 MHz) d 32.96,
52.25, 115.93, 123.65, 126.79, 128.67, 128.97, 129.06, 129.15, 135.01, 141.83,
144.13, 147.19, 147.78, 168.24; ESIMS m/z 324 (M++1). Anal. Calcd for
C19H17NO4: C, 70.58; H, 5.30; N, 4.33. Found: C, 70.46; H, 5.54; N, 4.30.
Compound 6a: 8%; colorless oil; IR (film) 2951, 1710 cmꢀ1 1H NMR (CDCl3,
;
300 MHz) d 0.99 (d, J = 6.9 Hz, 3H), 2.10 (s, 3H), 2.63–2.69 (m, 1H), 2.76–2.91
(m, 2H), 3.82 (s, 3H), 7.27–7.42 (m, 5H), 7.78 (s, 1H); 13C NMR (CDCl3, 75 MHz)
d 15.66, 28.10, 29.66, 46.10, 52.05, 128.46, 128.55, 129.03, 130.82, 135.39,
141.14, 168.52, 211.63; ESIMS m/z 247 (M++1).
Compound 7a: 63%; colorless oil; IR (film) 2977, 1712, 1707 cmꢀ1 1H NMR
;
(CDCl3, 300 MHz) d 0.92 (s, 3H), 1.88–1.96 (m, 1H), 2.02 (s, 3H), 2.33–2.40 (m,
1H), 2.93 (s, 2H), 3.76 (s, 3H), 4.90–4.96 (m, 2H), 5.39–5.52 (m, 1H), 7.26–7.41
(m, 5H), 7.76 (s, 1H); 13C NMR (CDCl3, 75 MHz) d 20.09, 25.76, 33.86, 42.75,
51.82, 51.86, 118.14, 128.14, 128.50, 128.79, 130.21, 133.58, 135.74, 141.63,
168.90, 211.75; ESIMS m/z 287 (M++1).
5. For our recent Pd-catalyzed decarboxylative protonation and allylation of
modified Baylis–Hillman adducts, see: (a) Gowrisankar, S.; Kim, K. H.; Kim, S.
H.; Kim, J. N. Tetrahedron Lett. 2008, 49, 6241–6244; (b) Kim, J. M.; Kim, S. H.;
Lee, H. S.; Kim, J. N. Tetrahedron Lett. 2009, 50, 1734–1737; (c) Gowrisankar, S.;
Kim, E. S.; Kim, J. N. Bull. Korean Chem. Soc. 2009, 30, 33–34; (d) Kim, S. H.; Lee,
H. S.; Kim, S. H.; Kim, J. N. Tetrahedron Lett. 2009, 50, 3038–3041.
8. Shimizu, I.. In Handbook of Organopalladium Chemistry for Organic Synthesis;
Negishi, E.-i., Ed.; Wiley Interscience, 2002; Vol. 2, pp 1981–1994.
9. For the Pd-catalyzed decarboxylative allylation and related reactions involving
nitro arene or pyridine moiety by Tunge and co-workers, see: (a) Waetzig, S. R.;
Tunge, J. A. J. Am. Chem. Soc. 2007, 129, 14860–14861; (b) Waetzig, S. R.; Tunge,
J. A. J. Am. Chem. Soc. 2007, 129, 4138–4139; (c) Tunge, J. A.; Burger, E. C. Eur. J.
Org. Chem. 2005, 1715–1726. and further references cited therein; (d) Weaver,
J. D.; Tunge, J. A. Org. Lett. 2008, 10, 4657–4660.
10. The cinnamyl bromides were prepared by treatment of the Baylis–Hillman
alcohols with aqueous HBr according to the literature procedure, see: (a)
Buchholz, R.; Hoffmann, H. M. R. Helv. Chim. Acta 1991, 74, 1213–1220; (b)
Ameer, F.; Drewes, S. E.; Emslie, N. D.; Kaye, P. T.; Mann, R. L. J. Chem. Soc.,
Perkin Trans. 1 1983, 2293–2295.
6. For the Pd-catalyzed decarboxylation–elimination, see: (a) Shimizu, I.; Tsuji, J. J.
Am. Chem. Soc. 1982, 104, 5844–5846; (b) Kataoka, H.; Yamada, T.; Goto, K.;
Tsuji, J. Tetrahedron 1987, 43, 4107–4112; (c) Tsuji, J.; Nisar, M.; Minami, I.
Chem. Lett. 1987, 23–24; (d) Tsuji, J.; Nisar, M.; Minami, I. Tetrahedron Lett.
1986, 27, 2483–2486; (e) Tsuji, J.; Minami, I. Acc. Chem. Res. 1987, 20, 140–145.
7. Typical procedure for the synthesis of 3a, 4a, and 5a. Compound 1a was
prepared from Baylis–Hillman adduct by treatment with HBr as reported.10
A
stirred mixture of 1a (383 mg, 1.5 mmol), 2a (256 mg, 1.8 mmol), and K2CO3
(415 mg, 3.0 mmol) in CH3CN (2 mL) was stirred at room temperature for 12 h.