An expedient aralkylation of Baylis-Hillman adduct via the Pd-catalyzed decarboxylative protonation strategy

Article abstract of DOI:10.1016/j.tetlet.2009.01.151

An expedient protocol of aralkylation of Baylis-Hillman adducts has been developed. This method used Pd-catalyzed decarboxylative protonation strategy to the allyl ester precursor that was made from the Baylis-Hillman adduct and allyl phenylacetate.

Full text of DOI:10.1016/j.tetlet.2009.01.151

Tetrahedron Letters 50 (2009) 1734–1737
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An expedient aralkylation of Baylis–Hillman adduct via the Pd-catalyzed
decarboxylative protonation strategy
*
Jeong Mi Kim, Se Hee Kim, Hyun Seung Lee, 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:
An expedient protocol of aralkylation of Baylis–Hillman adducts has been developed. This method used
Pd-catalyzed decarboxylative protonation strategy to the allyl ester precursor that was made from the
Baylis–Hillman adduct and allyl phenylacetate.
Received 26 December 2008
Revised 22 January 2009
Accepted 27 January 2009
Available online 5 February 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Baylis–Hillman adducts
Palladium
Decarboxylative protonation
Introduction of aryl group at the primary position of the
Baylis–Hillman adduct has been carried out in a variety of
ways.1–3 Friedel–Crafts reaction of Baylis–Hillman alcohol, ace-
tate, and aza-Baylis–Hillman adduct with arenes has been used
most frequently.2 Recently, Pd-catalyzed cross-coupling protocol
was reported.3 However, an efficient method for the introduc-
tion of arylmethyl group at the Baylis–Hillman adducts has
used electron-deficient aryl and heterocyclic moieties as the
electron-accommodating group in their Pd-assisted decarboxyla-
tive allylation.9 Thus, we selected para-nitro derivative 3a as the
model substrate and examined the whole process: introduction
of allyl p-nitrophenylacetate (2a) at the primary position of the
bromide of Baylis–Hillman adduct 1a to make 3a, and the fol-
lowing Pd-catalyzed decarboxylative protonation to desired com-
pound 4a (Table 1). The plausible mechanism for the Pd-
catalyzed decarboxylative protonation is depicted in Scheme 1
(vide supra).
Introduction of 2a was carried out using K2CO3/CH3CN at room
temperature in good yield (88%).10 With compound 3a we exam-
ined the conditions of decarboxylative protonation as shown in Ta-
ble 1. The formation of compounds 5a and 6a was also observed
during the reaction besides that of 4a.10 As shown, variable ratios
of compounds 4a–6a were observed, and were dependent on the
ratio/amounts of Et3N/HCOOH and reaction temperature. Best re-
sult was observed with 1.1 equiv of Et3N and 1.1 equiv of HCOOH
conditions in refluxing CH3CN (entry 1). The reaction at room tem-
perature produced carboxylic acid 6a as the major compound (en-
try 4), and excess amounts of Et3N/HCOOH increased the amounts
of amino compound 5a (entries 2 and 3). The use of ammonium
formate showed similar results (entry 5).
not been reported although the product
a-substituted acrylate
ester has been used extensively in organic synthesis.4 Very re-
cently, Roy and co-workers reported on the preparation of these
compounds via Cp2TiCl-mediated radical-induced addition
protocol.4
After Tsuji’s brilliant contributions, Pd-mediated decarboxyla-
tive protonation and allylation have been used widely in organic
synthesis.5–8 Recently, we also reported on Pd-catalyzed decarb-
oxylative protonation protocol for the synthesis of 1,5-dicarbonyl
compounds from Baylis–Hillman adducts.7 During the project we
imagined that we could introduce arylmethyl moiety at the pri-
mary position of the Baylis–Hillman adduct and could prepare
homologous series of the Friedel–Crafts products by using the
Pd-catalyzed decarboxylative protonation strategy as in Scheme
1.
As is often the case, the corresponding
p-allylpalladium car-
boxylate intermediate cannot lose carbon dioxide without an
electron-accommodating group.5–8 Many functional groups have
been reported as the electron-accommodating moieties including
ester, nitrile, and acetyl groups.5–8 Recently, Waetzig and Tunge
Encouraged by the successful results, we prepared various start-
ing materials 3a–g by the reaction of allyl arylacetates 2a–d and
the bromide of Baylis–Hillman adducts 1a–c in good yields (52–
91%). In some cases when the use of K2CO3 is less effective, we used
Cs2CO3 or TBAF (n-tetrabutylammonium fluoride, THF solution) as
in entries 5–7. The next Pd-catalyzed decarboxylative protonation
reactions were carried out under the optimized conditions (entry 1
* 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.2009.01.151

J. M. Kim et al. / Tetrahedron Letters 50 (2009) 1734–1737
1735
Pd-catalyzed
decarboxylative
protonation
Ar
EWG
COOallyl
EWG
Ar
OH
EWG
Br
Ph
Ph
COOallyl
2a-d
HBr
Ph
EWG
Ph
Ar
4a-g
1a-c
B-H adduct
3a-g
O
HCOOH/Et3N
- propene
- CO2
- Pd(0)
H
EWG
EWG
EWG
Ph
Pd(0)
Ph
- CO2
Ph
O
O
3a-g
4a-g
Pd
Ar
Pd
Ar
Pd
O
Ar
Scheme 1.
Table 1
Optimization of reaction conditions with 3a
COOMe
Ph
COOMe
COOMe
COOMe
COOH
COOMe
COOallyl
Ph
Ph
Ph
Ph
Br
1a
K2CO3/CH3CN
rt, 5 h
conditions
NO2
+
+
NO2
NH2
NO2
COOallyl
2a
NO2
3a (88%)
4a
5a
6a
Entry
Conditions
Products (%)
1
2
3
4
5
Pd(OAc)2 (5 mol %), PPh3 (10 mol %), Et3N (1.1 equiv), HCOOH (1.1 equiv), CH3CN, reflux, 2 h
Pd(OAc)2 (5 mol %), PPh3 (10 mol %), Et3N (2.4 equiv), HCOOH (2.4 equiv), CH3CN, reflux, 3 h
Pd(OAc)2 (5 mol %), PPh3 (10 mol %), Et3N (3.0 equiv), HCOOH (6.0 equiv), CH3CN, reflux, 24 h
Pd(OAc)2 (5 mol %), PPh3 (10 mol %), Et3N (2.0 equiv), HCOOH (2.0 equiv), CH3CN, rt, 5 h
Pd(OAc)2 (5 mol %), PPh3 (10 mol %), HCOONH4 (1.1 equiv), CH3CN, reflux, 4 h
4a (90), no 5a
4a (68), 5a (18)
4a (13), 5a (51)
4a (12), 6a (82)
4a (79), 5a (5)
Table 2
Aralkylation of Baylis–Hillman adducts at the primary position
K2CO3
(Cs2CO3 or TBAF)
Pd(OAc)2 / PPh3
Et3N / HCOOH
EWG
COOallyl
EWG
R
EWG
Br
R
Ph
Ph
Ph
+
Ar
COOallyl
CH3CN, reflux
Ar
3
R
Ar
1
2
4
For compounds 3 and 4
1a: EWG = COOMe
1b: EWG = COMe
1c: EWG = CN
2a: Ar = 4-NO2C6H4, R = H
2b: Ar = 4-NO2C6H4, R = Me
2c: Ar = 2-NO2C6H4, R = H
2d: Ar = 4-MeSO2C6H4, R = H
a: EWG = COOMe, Ar = 4-NO2C6H4, R = H
b: EWG = COOMe, Ar = 4-NO2C6H4, R = Me
c: EWG = COOMe, Ar = 2-NO2C6H4, R = H
d: EWG = COMe, Ar = 4-NO2C6H4, R = H
e: EWG = COMe, Ar = 2-NO2C6H4, R = H
f: EWG = CN, Ar = 4-NO2C6H4, R = H
g: EWG = COOMe, Ar = 4-MeSO2C6H4, R = H
Entry
Conditions
Compound 3 (%)
Conditionsa (h)
Compound 4 (%)
1
2
3
4
5
6
7
K2CO3 (1.5 equiv), CH3CN, rt, 5 h
3a (88)
3b (62)
3c (91)
3d (60)
3e (74)
3f (52)b,c
3g (74)
2
2
12
3
4a (90)
4b (88)
4c (96)
4d (94)
4e (96)
4f (88)c
4g (80)
K2CO3 (1.5 equiv), CH3CN, 50 °C, 24 h
K2CO3 (1.5 equiv), CH3CN, rt, 12 h
K2CO3 (1.5 equiv), CH3CN, rt, 7 h
Cs2CO3 (2.0 equiv), CH3CN, rt, 4 h
TBAF (2.0 equiv), THF, rt, 30 min
Cs2CO3 (2.0 equiv), CH3CN, rt, 12 h
4
2
3d
a
Conditions: Pd(OAc)2 (5 mol %), PPh3 (10 mol %), Et3N (1.1 equiv), HCOOH (1.1 equiv), CH3CN, reflux.
Appreciable amounts of 1:2 adduct of 2 and 1 were formed (40%) as a side product.
The stereochemistry is Z.
b
c
d
DMF was used as solvent (80 °C).
in Table 1). Good to excellent yields of products 4a–g were ob-
tained, and the results are summarized in Table 2.
The reaction of methanesulfonyl derivative 3g did not produce
4g under the same conditions in CH3CN (24 h, reflux). Instead of
4g, we isolated acid compound 6g in 56% (Scheme 2). However,
we could prepare 4g in good yield (80%) by exchanging the solvent
CH3CN to DMF (entry 7 in Table 2 and Scheme 2). Due to the rela-
tively weak electron-accommodating ability of methanesulfonyl
group than the nitro group of compounds 3a–f, the reaction was
sluggish in CH3CN. However, decarboxylation was effective in

1736
J. M. Kim et al. / Tetrahedron Letters 50 (2009) 1734–1737
COOMe
COOH
COOMe
Ph
COOMe
SO2Me
Ph
Ph
COOallyl
same conditions
same conditions
DMF, 80 oC, 3 h
(entry 7 in Table 2)
CH3CN, reflux, 24 h
6g (56%)
4g (80%)
SO2Me
SO2Me
COOMe
COOallyl
3g
COOMe
COOH
Ph
Ph
same conditions
same conditions
6h (75%)
DMF, 80 oC, 24 h
then reflux, 24 h
CH3CN, reflux, 24 h
6h (78%)
3h
Cl
Cl
Scheme 2.
more polar solvent DMF, fortunately. The reaction of p-chloro
derivative 3h produced the corresponding carboxylic acid com-
pound 6h (78%). In this case, decarboxylation was impossible due
during the preparation of compound 3k from the reaction of 1a
and 2e, inseparable mixture of primary 3k and secondary 3l was
obtained (88%, 1:1 mixture) as shown in Scheme 5. Thus, we used
the mixture without separation in the next decarboxylative pro-
tonation reaction and obtained compounds 4k (38%) and 4l (39%).
As the last manipulation, we examined Pd-catalyzed decarboxy-
lative allylation with compound 3a as shown in Scheme 6 under
the conditions of Pd(OAc)2/PPh3 in dry toluene,5,8,9 and obtained
product 8 (75%) as the major compound together with small
amounts of 4a (19%). The compound 8 could also be prepared from
the Pd-catalyzed decarboxylative protonation reaction of com-
pound 9 that was synthesized by the allylation of 3a with allyl
bromide.
to lack of p-electron-accommodating substituent even in DMF sol-
vent under very harsh conditions (reflux, 24 h) as shown in Scheme
2. As expected, the reaction of ethyl ester 3i did not produce any
trace amounts of product 4a under the same conditions (Scheme
3). We isolated amino compound 7 in 42% after 20 h.
As a next entry, we examined the feasibility for the introduction
of arylmethyl moiety at the secondary position of the Baylis–Hill-
man adduct as shown in Scheme 4. Required starting material 3j
was synthesized using DABCO salt concept11 from the acetate 1d
in 88% yield as a diastereomeric mixture (2:1). The next Pd-medi-
ated decarboxylative protonation was carried out under the same
conditions and we obtained 4j in excellent yield (97%). However,
In summary, we disclosed an efficient aralkylation protocol at
either primary or secondary position of the Baylis–Hillman adducts
COOMe
COOMe
Ph
Ph
COOEt
COOEt
same conditions
no 4a
3i (45%)
+
+
CH3CN, reflux, 20 h
NH2
NO2
7 (42%)
3i
Scheme 3.
O2N
O2N
Pd(OAc)2 / PPh3
Et3N / HCOOH
OAc
1. aq THF, DABCO, 10 min
COOMe
COOallyl
COOMe
Ph
CH3CN, reflux, 2 h
2. 2a, Cs2CO3 (2.0 equiv)
rt, 10 h
COOMe
Ph
Ph
1d
4j (97%)
3j (88%, 2:1 mixture)
Scheme 4.
COOMe
COOallyl
N
Ph
COOMe
N
Ph
N
TBAF (2.0 equiv)
THF, rt, 30 min
same conditions
CH3CN, reflux, 3 h
N
+
1a
+
3k
COOMe
Ph
N
COOallyl
2e
COOallyl
4l (39%)
4k (38%)
COOMe
Ph
3l
88% (1:1 mixture)
Scheme 5.

J. M. Kim et al. / Tetrahedron Letters 50 (2009) 1734–1737
1737
COOMe
COOallyl
COOMe
Ph
Ph
Pd(OAc)2 / PPh3
dry toluene
Pd(OAc)2 / PPh3
Et3N / HCOOH
allyl bromide
Cs2CO3
3a
3a
reflux, 3 h
CH3CN, reflux, 5 h
CH3CN, reflux, 24 h
8 (75%) + 4a (19%)
8 (71%)
9 (65%)
8
NO2
NO2
Scheme 6.
Mashima, K. Org. Lett. 2007, 9, 3371–3374; (f) Kitamura, M.; Tanaka, S.;
Yoshimura, M. J. Org. Chem. 2002, 67, 4975–4977; (g) Burger, E. C.; Tunge, J. A.
Chem. Commun. 2005, 2835–2837; (h) Constant, S.; Tortoioli, S.; Muller, J.;
Lacour, J. Angew. Chem., Int. Ed. 2007, 46, 2082–2085; (i) Burger, E. C.; Tunge, J.
A. Org. Lett. 2004, 6, 2603–2605; (j) Corey, E. J.; William, S. J. Org. Chem. 1973,
38, 3223–3224; (k) Tunge, J. A.; Burger, E. C. Eur. J. Org. Chem. 2005, 1715–1726.
and further references cited therein.
via the novel Pd-mediated decarboxylative protonation protocol as
the key step.
Acknowledgments
This work was supported by the Korea Research Foundation
Grant funded by the Korean Government (MOEHRD, KRF-2008-
313-C00487). Spectroscopic data were obtained from the Korea Ba-
sic Science Institute, Gwangju branch.
9. For the Pd-mediated decarboxylative allylation and related reactions involving
nitro arene or pyridine moiety, 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.
10. Typical procedure for the synthesis of 3a and 4a: A mixture of 1a (306 mg,
1.2 mmol), 2a (221 mg, 1.0 mmol), and K2CO3 (207 mg, 1.5 mmol) in CH3CN
(3 mL) was stirred at room temperature for 5 h. After the usual aqueous
workup and column chromatographic purification process (hexanes/CH2Cl2/
EtOAc, 10:1:1), compound 3a was isolated as a white solid, 348 mg (88%). A
stirred mixture of 3a (198 mg, 0.5 mmol), Pd(OAc)2 (6 mg, 5 mol %), PPh3
(13 mg, 10 mol %), HCOOH (25 mg, 0.55 mmol), and Et3N (56 mg, 0.55 mmol)
in CH3CN (3 mL) was heated to reflux for 2 h. After the usual aqueous workup
and column chromatographic purification process (hexanes/EtOAc, 9:1),
References and notes
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) Ciganek, E.. In
Organic Reactions; Paquette, L. A., Ed.; John Wiley & Sons: New York, 1997; Vol.
51, pp 201–350; (c) Basavaiah, D.; Rao, P. D.; Hyma, R. S. Tetrahedron 1996, 52,
8001–8062; (d) Kim, J. N.; Lee, K. Y. Curr. Org. Chem. 2002, 6, 627–645; (e) Lee,
K. Y.; Gowrisankar, S.; Kim, J. N. Bull. Korean Chem. Soc. 2005, 26, 1481–1490; (f)
Singh, V.; Batra, S. Tetrahedron 2008, 64, 4511–4574. and further references
cited therein.
compound 4a was isolated as
a white solid, 140 mg (90%). Selected
spectroscopic data of prepared compounds, 3a, 4a, 4j, and 8 are as follows.
Compound 3a: 88%; white solid, mp 56–58 °C; IR (film) 2951, 1736, 1712,
1522, 1348, 1259 cmÀ1 1H NMR (CDCl3, 300 MHz) d 3.20–3.34 (m, 2H), 3.80
;
2. For the synthesis of aryl-substituted rearranged Baylis–Hillman adducts via
Friedel–Crafts reaction, see: (a) Basavaiah, D.; Krishnamacharyulu, M.; Hyma,
R. S.; Pandiaraju, S. Tetrahedron Lett. 1997, 38, 2141–2144; (b) Basavaiah, D.;
Pandiaraju, S.; Padmaja, K. Synlett 1996, 393–395; (c) Basavaiah, D.; Reddy, R.
M. Tetrahedron Lett. 2001, 42, 3025–3027; (d) Lee, H. J.; Seong, M. R.; Kim, J. N.
Tetrahedron Lett. 1998, 39, 6223–6226; (e) Lee, H. J.; Kim, T. H.; Kim, J. N. Bull.
Korean Chem. Soc. 2001, 22, 1063–1064; (f) Das, B.; Majhi, A.; Banerjee, J.;
Chowdhury, N.; Venkateswarlu, K. Chem. Lett. 2005, 34, 1492–1493; (g)
Shanmugam, P.; Rajasingh, P. Chem. Lett. 2005, 34, 1494–1495.
3. For the synthesis of arylated Baylis–Hillman adducts using metal catalyst, see:
(a) Kabalka, G. W.; Venkataiah, B.; Dong, G. Org. Lett. 2003, 5, 3803–3805; (b)
Kabalka, G. W.; Dong, G.; Venkataiah, B.; Chen, C. J. Org. Chem. 2005, 70, 9207–
9210; (c) Navarre, L.; Darses, S.; Genet, J.-P. Chem. Commun. 2004, 1108–1109;
(d) Navarre, L.; Darses, S.; Genet, J.-P. Adv. Synth. Catal. 2006, 348, 317–322; (e)
Kantam, M. L.; Kumar, K. B. S.; Sreedhar, B. J. Org. Chem. 2008, 73, 320–322; (f)
Ranu, B. C.; Chattopadhyay, K.; Jana, R. Tetrahedron Lett. 2007, 48, 3847–3850.
4. Mandal, S. K.; Paira, M.; Roy, S. C. J. Org. Chem. 2008, 73, 3823–3827. and further
(s, 3H), 4.07 (dd, J = 9.3 and 6.6 Hz, 1H), 4.45–4.49 (m, 2H), 5.14–5.21 (m, 2H),
5.72–5.85 (m, 1H), 7.07–7.10 (m, 2H), 7.20 (d, J = 9.0 Hz, 2H), 7.29–7.33 (m,
3H), 7.67 (s, 1H), 7.98 (d, J = 9.0 Hz, 2H); 13C NMR (CDCl3, 75 MHz) d 30.5,
49.9, 52.2, 65.8, 118.5, 123.4, 128.5, 128.6, 128.7, 128.8, 129.2, 131.5, 134.9,
142.3, 145.1, 147.1, 168.0, 171.8; ESIMS m/z 396 (M++1).
Compound 4a: 90%; white solid, mp 77–79 °C; IR (film) 2955, 1706, 1509,
1349, 1248 cmÀ1 1H NMR (CDCl3, 300 MHz) d 2.83–2.97 (m, 4H), 3.84 (s, 3H),
;
7.22–7.40 (m, 7H), 7.74 (s, 1H), 8.09 (d, J = 8.7 Hz, 2H); 13C NMR (CDCl3,
75 MHz) d 28.8, 35.0, 52.1, 123.6, 128.5, 128.6, 128.8, 129.2, 131.5, 135.4,
140.6, 146.5, 149.2, 168.4; ESIMS m/z 312 (M++1). Anal. Calcd for C18H17NO4:
C, 69.44; H, 5.50; N, 4.50. Found: C, 69.58; H, 5.37; N, 4.42.
Compound 4f: 88%; pale yellow solid, mp 142–144 °C; IR (film) 2928, 2208,
1511, 1346 cmÀ1 1H NMR (CDCl3, 300 MHz) d 2.72–2.78 (m, 2H), 3.07–3.12
;
(m, 2H), 6.84 (s, 1H), 7.34–7.42 (m, 5H), 7.63–7.68 (m, 2H), 8.17 (d, J = 8.7 Hz,
2H); 13C NMR (CDCl3, 75 MHz) d 34.3, 37.5, 109.3, 118.3, 123.9, 128.6, 128.9,
129.4, 130.3, 133.2, 144.8, 146.8, 147.4; ESIMS m/z 279 (M++1). Anal. Calcd
for C17H14N2O2: C, 73.37; H, 5.07; N, 10.07. Found: C, 73.59; H, 5.34; N, 9.86.
references cited therein for the synthetic usefulness of
esters.
a-substituted acrylate
Compound 4j: 97%; pale yellow oil; IR (film) 2951, 1720, 1519, 1346 cmÀ1 1H
;
NMR (CDCl3, 300 MHz) d 3.14 (dd, J = 13.5 and 9.3 Hz, 1H), 3.33 (dd, J = 13.5
and 6.3 Hz, 1H), 3.66 (s, 3H), 4.20 (dd, J = 9.3 and 6.3 Hz, 1H), 5.71 (s, 1H),
6.34 (s, 1H), 7.10–7.25 (m, 7H), 8.02 (d, J = 8.7 Hz, 2H); 13C NMR (CDCl3,
75 MHz) d 40.4, 47.7, 51.9, 123.2, 124.9, 126.8, 128.0, 128.3, 129.7, 140.5,
142.6, 146.3, 147.6, 166.8.
5. For Tsuji’s contribution on Pd-assisted decarboxylative protonation and
allylation, see: (a) Tsuji, J.; Nisar, M.; Shimizu, I. J. Org. Chem. 1985, 50, 3416–
3417; (b) Mandai, T.; Imaji, M.; Takada, H.; Kawata, M.; Nokami, J.; Tsuji, J. J.
Org. Chem. 1989, 54, 5395–5397; (c) Tsuji, J. Pure Appl. Chem. 1986, 58, 869–
878.
6. For the other contributions on Pd-assisted decarboxylative protonation, see: (a)
Marinescu, S. C.; Nishimata, T.; Mohr, J. T.; Stoltz, B. M. Org. Lett. 2008, 10,
1039–1042; (b) Ragoussis, V.; Giannikopoulos, A. Tetrahedron Lett. 2006, 47,
683–687.
Compound 8: 75%; pale yellow oil; IR (film) 2949, 1712, 1519, 1346,
1255 cmÀ1 1H NMR (CDCl3, 300 MHz) d 2.26–2.47 (m, 2H), 2.85–3.09 (m,
;
3H), 3.76 (s, 3H), 4.90–4.97 (m, 2H), 5.49–5.61 (m, 1H), 7.01–7.07 (m, 4H),
7.28–7.33 (m, 3H), 7.61 (s, 1H), 7.95 (d, J = 9.0 Hz, 2H); 13C NMR (CDCl3,
75 MHz) d 33.2, 40.0, 44.9, 52.0, 117.0, 123.2, 128.3, 128.4, 128.6, 128.7,
130.8, 135.4, 135.5, 141.0, 146.4, 151.6, 168.4; ESIMS m/z 352 (M++1). Anal.
Calcd for C21H21NO4: C, 71.78; H, 6.02; N, 3.99. Found: C, 71.45; H, 6.23; N,
3.67..
7. For our recent contribution: Gowrisankar, S.; Kim, K. H.; Kim, S. H.; Kim, J. N.
Tetrahedron Lett. 2008, 49, 6241–6244.
8. For some examples on the formation of p-allylmetal complex and its synthetic
applications, see: (a) Blacker, A. J.; Clark, M. L.; Loft, M. S.; Williams, J. M. J.
Chem. Commun. 1999, 913–914; (b) Blacker, A. J.; Clark, M. L.; Loft, M. S.;
Mahon, M. F.; Humphries, M. E.; Williams, J. M. J. Chem. Eur. J. 2000, 6, 353–360;
(c) Kadota, J.; Komori, S.; Fukumoto, Y.; Murai, S. J. Org. Chem. 1999, 64, 7523–
7527; (d) Kadota, J.; Katsuragi, H.; Fukumoto, Y.; Murai, S. Organometallics
2000, 19, 979–983; (e) Utsunomiya, M.; Miyamoto, Y.; Ipposhi, J.; Ohshima, T.;
11. For the regioselective introduction of nucleophiles at the secondary positions
of Baylis–Hillman adducts by using the DABCO salt concept, see: (a) Kim, J. N.;
Kim, J. M.; Lee, K. Y.; Gowrisankar, S. Bull. Korean Chem. Soc. 2004, 25, 1733–
1736; (b) Lee, K. Y.; Gowrisankar, S.; Kim, J. N. Bull. Korean Chem. Soc. 2005, 26,
1481–1490. and further references cited therein.