Regioselective synthesis of polysubstituted benzenes from Baylis-Hillman adducts via [4+2] annulation protocol

Article abstract of DOI:10.1016/j.tet.2006.01.028

A new and regioselective [4+2] benzannulation protocol toward polysubstituted benzenes was developed. A nitroalkane derivative, which was prepared from Baylis-Hillman adduct, served as the four-carbon unit and a Michael acceptor as a two-carbon unit. Viny

Full text of DOI:10.1016/j.tet.2006.01.028

Tetrahedron 62 (2006) 3128–3136
Regioselective synthesis of polysubstituted benzenes from
Baylis–Hillman adducts via [4D2] annulation protocol
*
Mi Jung Lee, Ka Young Lee, Da Yeon Park and Jae Nyoung Kim
Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, Republic of Korea
Received 12 December 2005; accepted 6 January 2006
Available online 2 February 2006
Abstract—A new and regioselective [4C2] benzannulation protocol toward polysubstituted benzenes was developed. A nitroalkane
derivative, which was prepared from Baylis–Hillman adduct, served as the four-carbon unit and a Michael acceptor as a two-carbon unit.
Vinyltriphenylphosphonium salt could also be used as a Michael acceptor efficiently.
q 2006 Elsevier Ltd. All rights reserved.
1. Introduction
between bielectrophiles and binucleophiles,7 and 1,6-
electrocyclization reaction.8 Recently, an efficient approach
was developed for the synthesis of highly substituted
phenols using a [5C1] benzannulation strategy by the
reaction of a-alkenoyl ketene-(S,S)-acetals and nitro-
alkane.9 Ballini and co-workers also reported an interesting
synthetic approach for acetophenones and methyl benzoates
via an anionic domino process from the reaction of primary
1,3-dinitroalkanes with 2-ene-1,4-dione or 2-ene-4-oxo
ester derivatives.10
Polysubstituted aromatic compounds are highly useful
entities, which are widely used in industry as well as in
the laboratory. The synthesis of polysubstituted aromatic
compounds in high yields in a regioselective manner is one
of the challenging problems in organic synthesis.1 Classical
methods for the synthesis of polysubstituted aromatics are
based on aromatic substitution, which introduces a
substituent to the given arene. A variety of synthetic
methodologies based on this route have been developed
including the electrophilic or nucleophilic substitutions,
catalyzed coupling reactions, and metalation–functionali-
zation reactions. However, these methods suffer from a long
multi-step reaction sequence, low yields of products, and
production of regiochemical ambiguities originating from
the activating or deactivating and orienting effects of the
substituents.
2. Results and discussion
The Baylis–Hillman reaction and chemical transformations
of the Baylis–Hillman adducts have been investigated
deeply by us and other groups.11,12 Recently, we have
reported an efficient regioselective construction method of
polysubstituted pyridine ring starting from Baylis–Hillman
adducts via sequential introduction of tosylamide, Michael
reaction, aldol condensation, and elimination of TsH
(Scheme 1).12a As an extension, we envisioned that we
could prepare highly substituted benzene ring in a regio-
controlled manner if we used nitroalkane derivative 2
(Scheme 2) instead of the tosylamide derivative in
Scheme 1. Appropriate Michael acceptor can serve as the
remaining two-carbon unit for the purpose as depicted in
Scheme 2.13
Numerous approaches for the synthesis of aromatic
compounds from acyclic precursors have received growing
interest due to their short synthetic steps and the avoidance
of regioisomeric problems. These general features are
common in the most useful benzannulation reactions such
2
¨
as [3C2C1] Dotz reaction of Fisher carbene complexes,
Danheiser alkyne-cyclobutenone [4C2] cyclization,3 [4C
2] cycloaddition of metalacyclopentadienes and alkynes,4
transition-metal-catalyzed [2C2C2] and [4C2] cyclo-
additions,5 [4C2] Yamamoto benzannulation of o-alkynyl
benzaldehyde and alkyne,6 [3C3] cyclocondensation
The synthesis of starting material 2 (four-carbon unit) was
carried out by the addition–elimination protocol from the
acetate of the Baylis–Hillman adduct of methyl (or ethyl)
vinyl ketone 1 and primary nitroalkane in the presence of
K2CO3.14–16 The benzylidene moiety, which will be
Keywords: Polysubstituted benzenes; Baylis–Hillman adducts; Michael
acceptor; Schweizer reagent.
Corresponding author. Tel.: C82 62 530 3381; fax: C82 62 530 3389;
e-mail: kimjn@chonnam.ac.kr
*
0040–4020/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.01.028

M. J. Lee et al. / Tetrahedron 62 (2006) 3128–3136
3129
O
O
OAc O
TsNH2
K2CO3
CH2=CH-EWG
DBU, THF
Ph
R
Ph
R
Ph
R
EWG
NH
N
Ts
R
Ts
HO
R
R
Cs2CO3
DMF
p-TsOH
benzene
EWG
EWG
EWG
Ph
Ph
Ph
N
N
N
Ts
Ts
Scheme 1.
R1
1. B–H reaction
2. acetylation
R2CH2NO2
K2CO3, DMF
OAc R1
O
R1
EWG
Ph
O
Ph
O
Ph
O
1
R2 NO2
R2
NO2
2
R1
HO
R1
Michael acceptor
DBU, CH3CN
p-TsOH (cat)
benzene, reflux
EWG
Ph
Ph
O
EWG
NO2
R2
R2 NO2
4 (not separated)
3
R1
R1
DBU
THF, reflux
EWG
EWG
Ph
Ph
R1 = Me, Et
R2 = Me, Et, n-butyl
EWG = COMe, COEt, COOMe, CN, SO2Ph
R2 NO2
R2
5
6
Scheme 2.
isomerized at the final stage to benzyl group, is essential for
the construction of benzene ring at the final aromatization
stage (vide infra). The next step was the construction of six-
membered ring intermediate 4 via the consecutive Michael
addition of 2 to the Michael acceptor and aldol-type
cyclization, which occurred with the aid of DBU in
CH3CN in good yield. The intermediate 4 was not separated
due to the complex nature of 4 by the formation of
diasteroisomeric mixtures. Thus, we subjected the crude
mixtures, afterusual workup, in the dehydration conditions(p-
TsOH, benzene, reflux) and obtained the dehydration product
5 in good overall yield. The final step was the elimination of
HNO2 and isomerization of the exo-double bond to the desired
benzene ring. We expected that elimination of HNO2 can
occur with DBU and the isomerization will also occur
simultaneously due to the favorable aromatization effect. As
expected, the final step occurred in good yield with DBU in
THF under refluxing conditions to our delight.
vinyl ketone, phenyl vinyl sulfone, methyl acrylate, and
acrylonitrile were similar (TLC monitoring). But, the
reactivities of the next aldol cyclization reaction were found
to be different depending on the nature of the electron-
withdrawing group of the Michael acceptors presumably due
to the different acidities of the a-protons nearby the EWG
groups of the Michael acceptors. Fortunately, the following
dehydration, elimination, and aromatization reactions from 4
to the final product 6 were all straightforward in these cases
also (entries 4, 6, and 7). The use of acrylonitrile (entry 7) as
the Michael acceptor required a long reaction time for the
cyclizationandgavelowyieldof5g(41%).Actually, wecould
isolate the Michael addition product 3g in 41% after the whole
reaction. Thistype ofMichael additionproduct was alsofound
in the cases of methyl acrylate (entry 6) and phenyl vinyl
sulfone (Scheme 3). Especially, when we used phenyl vinyl
sulfoneastheMichaelacceptorwefoundtheformationofexo-
methylene compound 5h0, which showed the same reactivity
to give 6h.
As shown in Table 1, variation of the substituents of the
Baylis–Hillman adducts or of nitroalkanes did not alter the
reactivity (entries 1–3 and 5). However, the reactivity was
affected by the nature of the Michael acceptor. The reaction
rates of the Michael addition of 2 to methyl vinyl ketone, ethyl
For the next trial, we examined the reaction of 2 and
vinyltriphenylphosphonium bromide, which was known as
Schweizer reagent,17 as the other effective Michael acceptor
(two-carbon unit). Our synthetic rationale is shown in

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M. J. Lee et al. / Tetrahedron 62 (2006) 3128–3136
Table 1. Synthesis of regioselectively substituted benzenes
Entry
Substrate (%)
Conditions
Cyclohexene (%)
Product (%)a
O
O
O
O
(1) DBU (1.0 equiv), MVK
(1.5 equiv), CH3CN, rt, 30 min;
(2) aq workup; (3) p-TsOH
(0.1 equiv), PhH, reflux, 1 h
Ph
Ph
Ph
1
NO2
NO2
6a (86)
Ph
2a (79)
5a (83)
O
O
(1) DBU (1.0 equiv), MVK
(1.5 equiv), CH3CN, rt, 30 min;
(2) aq workup; (3) p-TsOH
(0.1 equiv), PhH, reflux, 1 h
Ph
Ph
2
NO2
NO2
2b (61)
5b (75)
6b (78)
O
O
O
(1) DBU (1.0 equiv), MVK
(1.8 equiv), CH3CN, rt, 5 h;
(2) aq workup; (3) p-TsOH
(0.1 equiv), PhH, reflux, 1 h
Ph
Ph
Ph
3
NO2
NO2
2c (79)
6c (80)
5c (71)
O
O
O
O
(1) DBU (1.0 equiv), EVK
(1.5 equiv), CH3CN, rt, 1 h;
(2) aq workup; (3) p-TsOH
(0.1 equiv), PhH, reflux, 3 h
Ph
Ph
4
5
2a
NO2
6d (85)
5d (78)
O
O
(1) DBU (1.0 equiv), MVK
(1.5 equiv), CH3CN, rt, 12 h;
(2) aq workup; (3) p-TsOH
(0.1 equiv), PhH, reflux, 3 h
Ph
Ph
Ph
NO2
NO2
2d (82)
5e (73)
6e (89)
O
(1) DBU (2.0 equiv), methyl
acrylate (1.8 equiv), CH3CN, rt,
40 h; (2) aq workup; (3) p-TsOH
(0.1 equiv), PhH, reflux, 4 h
OMe
OMe
Ph
Ph
6
7
2a
5f (65)b
NO2
CN
6f (80)
CN
(1) DBU (2.0 equiv), acrylonitrile
(2.0 equiv), CH3CN, rt, 4 days;
(2) aq workup; (3) p-TsOH
Ph
Ph
2a
(0.1 equiv), PhH, reflux, 15 h
5g (41)c
NO2
6g (91)
a DBU (2 equiv), THF, reflux, 5–96 h.
b Michael addition product 3f was isolated in 7%.
c Michael addition product 3g was isolated in 41% yield.
Scheme 4. The reaction of 2 and vinyltriphenylphosphonium
bromide could provide benzylidene cyclohexene intermediate
7 via the successive Michael addition and Wittig reaction in
the presence of appropriate base. The compound 7 could be
converted into the aromatized product 8 under basic
conditions via elimination of nitrous acid followed by
isomerization of double bond.
the corresponding intermediates 7 (see, Section 3). However,
we could confirm the structure of corresponding intermediate
7a, which was obtained in 48% yield when we carried out the
reaction at around 40–50 8C for 3 h.
As shown in Table 2, changes of the structure of starting
materials 2 did not affect the reaction progress (entries 1–3).
When we used 2e and 2f, which were made from ethyl
nitroacetate, the reaction was completed in a short time at
lower temperature (entries 4 and 6). However, when we
used propenyltriphenylphosphonium bromide17c (entry 5)
the yield of product 8e was low.
As expected, the reaction of 2a and vinyltriphenyl-
phosphonium bromide in the presence of DBU (3 equiv) in
CH3CN at refluxing temperature for 18 h gave desired 8a in
86% yield. We were encouraged by the first successful results
and extended the trial to the synthesis of a variety of
polysubstituted benzene derivatives 8b–f as summarized in
Table 2. The synthesis of8 was carried out without isolation of
We examined the reaction of nitroalkane derivative 2g,
which was made from the acetate of the Baylis–Hillman

M. J. Lee et al. / Tetrahedron 62 (2006) 3128–3136
3131
1. phenyl vinyl sulfone
(1.2 equiv)
DBU (2.0 equiv)
CH3CN, rt, 7 days
O
SO2Ph
SO2Ph
Ph
Ph
Ph
2a
SO2Ph
2. aq workup
3. p-TsOH (0.1 equiv)
benzene, reflux, 2 h
NO2
3h (11%)
NO2
5h'
NO2
5h
(42%, 3:1 based on 1H NMR)
DBU (2 equiv)
THF, reflux, 18 h
SO2Ph
Ph
6h (78%)
Scheme 3.
COR1
R3
R3
Br
PPh3
- HBr
2
PPh3
R1
Br
DBU, CH3CN
R2 NO2
R1
COR1
R3
Ph
heating
- HNO2
- Ph3P=O
Ph
PPh3
R3
R3
NO2
R2
NO2
R2
R2
8
7
Scheme 4.
adduct of n-hexanal and nitroethane.15d However, unfortu-
nately, intractable complex mixtures were observed on TLC
under the same reaction conditions of Scheme 2 with methyl
vinyl ketone, as shown in Scheme 5. The reaction of 2a and
2-cyclohexen-1-one also showed a complex nature and we
could not obtain the desired product.
were carried out at Korea Research Institute of Chemical
Technology, Taejon, Korea. All reagents were purchased
from commercial sources and used without further
treatment. The separations were carried out by flash column
chromatography over silica gel (230–400 mesh ASTM).
Organic extracts were dried over anhydrous MgSO4 and the
solvents were evaporated on a rotary evaporator under water
aspirator pressure.
In summary, we disclosed a new route for the synthesis of
polysubstituted benzene derivatives starting from Baylis–
Hillman adducts via a regioselective [4C2] benzannulation
protocol. Nitroalkane derivative, which was prepared from
Baylis–Hillman adduct, served as the four-carbon unit and
Michael acceptor including Schweizer reagent as a two-
carbon unit.
3.2. Synthesis of starting material 2
The starting materials 2a–d and 2g were prepared according
to the previous paper.14–16 Compounds 2e and 2f were
synthesized analogously by using ethyl nitroacetate and the
spectroscopic data are as follows.
3. Experimental
3.2.1. Compound 2e. 73%; clear oil; IR (film) 1751, 1666,
1558, 1373, 1254, 1215 cmK1; 1H NMR (CDCl3, 300 MHz)
d 1.22 (t, JZ7.2 Hz, 3H), 2.47 (s, 3H), 3.35 (dd, JZ14.4,
6.6 Hz, 1H), 3.49 (dd, JZ14.4, 9.3 Hz, 1H), 4.12–4.23 (m,
2H), 5.52 (dd, JZ9.3, 6.6 Hz, 1H), 7.30–7.46 (m, 5H), 7.75
(s, 1H); 13C NMR (CDCl3, 75 MHz) d 13.73, 25.76, 27.37,
62.89, 85.65, 128.72, 128.82, 129.27, 134.15, 135.04,
145.03, 164.01, 199.47; ESIMS m/z 292.1 (MCCH).
Anal. Calcd for C15H17NO5: C, 61.85; H, 5.88; N, 4.81.
Found: C, 61.97; H, 5.75; N, 4.96.
3.1. General procedure
1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were
recorded in CDCl3. The signal positions are reported in ppm
relative to TMS (d scale) used as an internal standard. IR
spectra are reported in cmK1. Mass spectra were obtained
from the Korea Basic Science Institute (Gwangju branch).
Melting points are uncorrected. The elemental analyses

3132
M. J. Lee et al. / Tetrahedron 62 (2006) 3128–3136
Table 2. Synthesis of regioselectively substituted benzenes
Entry
1
Substrate (%)
Conditions
Product (%)
Ph
CH2]CHPPh3Br (1.2 equiv), DBU (3.0 equiv), CH3CN
reflux, 18 h
2a
8a (86)
8b (81)
Ph
CH2]CHPPh3Br (1.2 equiv), DBU (3.0 equiv), CH3CN
reflux, 40 h
2
3
2b
2d
Ph
Ph
CH2]CHPPh3Br (1.2 equiv), DBU (3.0 equiv), CH3CN
reflux, 28 h
8c (74)
O
Ph
CH2]CHPPh3Br (1.2 equiv), DBU (3.0 equiv), CH3CN
40–50 8C, 5 h
4
NO2
COOEt
2e (73)
COOEt
8d (88)
Ph
Ar
CH2]CHCH2PPh3Br (1.2 equiv), DBU (3.0 equiv),
CH3CN reflux, 40 h
5
2a
8e (40)
O
Ar
CH2]CHPPh3Br (1.2 equiv), DBU (3.0 equiv), CH3CN
40–50 8C, 3 h
6a
NO2
COOEt
2f (79)
COOEt
8f (86)
a Ar is 4-chlorophenyl.
O
methyl vinyl ketone
complex mixtures
DBU, CH3CN
NO2
2g
Scheme 5.
3.2.2. Compound 2f. 79%; clear oil; IR (film) 2985, 1751,
stirred at rt for 30 min. TLC observation showed complete
disappearance of starting material 2a and the formation of
diastereomeric mixtures of 4a. After aq workup the crude
diastereomeric mixtures were dissolved in benzene (5 mL),
added p-TsOH (20 mg, 0.1 mmol), and heated to reflux for
1 h. After the usual workup and column chromatographic
purification process (hexanes/ether, 5:1) we obtained
desired 5a as a white solid, 237 mg (83%). The other
compounds 5b–h were synthesized analogously and the
spectroscopic data of prepared compounds are as follows.
1
1670, 1562, 1377, 1250, 1215 cmK1; H NMR (CDCl3,
300 MHz) d 1.24 (t, JZ7.2 Hz, 3H), 2.46 (s, 3H), 3.30 (dd,
JZ14.4, 6.3 Hz, 1H), 3.44 (dd, JZ14.4, 9.3 Hz, 1H), 4.16–
4.26 (m, 2H), 5.53 (dd, JZ9.3, 6.3 Hz, 1H), 7.27 (d, JZ
8.4 Hz, 2H), 7.41 (d, JZ8.4 Hz, 2H), 7.68 (s, 1H); 13C NMR
(CDCl3, 75 MHz) d 13.74, 25.75, 27.42, 62.99, 85.61,
129.10, 130.06, 132.55, 135.33, 135.55, 143.65, 163.90,
199.21. Anal. Calcd for C15H16ClNO5: C, 55.31; H, 4.95; N,
10.88. Found: C, 55.26; H, 4.92; N, 10.67.
3.3. Synthesis of the intermediate 5
3.3.1. Compound 5a.13 83%; white solid, mp 81–83 8C; IR
1
(KBr) 1685, 1539, 1350, 1234 cmK1; H NMR (CDCl3,
Typical procedure for the synthesis of cyclohexene
intermediate 5a: to a stirred solution of 2a (233 mg,
1.0 mmol) and methyl vinyl ketone (105 mg, 1.5 mmol) in
CH3CN (5 mL) was added DBU (153 mg, 1.0 mmol) and
300 MHz) d 1.58 (s, 3H), 2.03 (t, JZ1.8 Hz, 3H), 2.37 (s,
3H), 2.66 (dd, JZ17.7, 1.8 Hz, 1H), 2.82 (dd, JZ15.3,
1.8 Hz, 1H), 3.28 (d, JZ17.7 Hz, 1H), 3.43 (d, JZ15.3 Hz,
1H), 6.92 (s, 1H), 7.25–7.42 (m, 5H); 13C NMR (CDCl3,

M. J. Lee et al. / Tetrahedron 62 (2006) 3128–3136
3133
75 MHz) d 15.78, 25.74, 29.82, 36.34, 36.62, 86.01, 127.36,
128.34, 128.98, 131.18, 133.09, 133.66, 133.83, 136.60,
204.25. Anal. Calcd for C17H19NO3: C, 71.56; H, 6.71; N,
4.91. Found: C, 71.76; H, 6.83; N, 4.87.
3.3.7. Compound 5g. 41%; white solid, mp 83–85 8C; IR
(KBr) 2206, 1543, 1450, 1346, 1265 cmK1 1H NMR
;
(CDCl3, 300 MHz) d 1.59 (s, 3H), 2.29 (t, JZ1.5 Hz, 3H),
2.70 (dd, JZ17.7, 1.8 Hz, 1H), 2.80 (dd, JZ15.6, 1.8 Hz,
1H), 3.31 (d, JZ17.7 Hz, 1H), 3.49 (d, JZ15.6 Hz, 1H),
7.01 (s, 1H), 7.27–7.44 (m, 5H); 13C NMR (CDCl3,
75 MHz) d 18.28, 25.81, 35.91, 36.92, 85.07, 105.45,
118.50, 128.15, 128.52, 129.10, 130.89, 134.25, 135.43,
148.07. Anal. Calcd for C16H16N2O2: C, 71.62; H, 6.01; N,
10.44. Found: C, 71.77; H, 6.25; N, 10.26.
3.3.2. Compound 5b. 75%; clear oil; IR (film) 2974, 1685,
1539, 1442, 1354, 1234 cmK1; 1H NMR (CDCl3, 300 MHz)
d 0.83 (t, JZ7.5 Hz, 3H), 1.81–1.99 (m, 2H), 2.01 (t, JZ
1.8 Hz, 3H), 2.38 (s, 3H), 2.65 (d, JZ17.4 Hz, 1H), 2.78
(dd, JZ15.6, 1.8 Hz, 1H), 3.25 (d, JZ17.4 Hz, 1H), 3.46 (d,
JZ15.6 Hz, 1H), 6.89 (s, 1H), 7.24–7.41 (m, 5H); 13C NMR
(CDCl3, 75 MHz) d 7.76, 15.83, 29.87, 32.17, 34.46, 34.61,
89.68, 127.33, 128.36, 128.95, 130.97, 132.98, 133.69,
133.96, 136.67, 204.60. Anal. Calcd for C18H21NO3: C,
72.22; H, 7.07; N, 4.68. Found: C, 72.16; H, 7.19; N, 4.65.
3.3.8. Compound 5h. 42%; clear oil; IR (film) 2927, 1539,
1
1300, 1146 cmK1; H NMR (CDCl3, 300 MHz) d 1.59 (s,
3H), 2.32 (s, 3H), 2.67 (d, JZ15.3 Hz, 1H), 2.97 (d, JZ
18.9 Hz, 1H), 3.51 (d, JZ15.3 Hz, 1H), 3.66 (d, JZ
1
18.9 Hz, 1H), 7.07 (s, 1H), 7.21–7.96 (m, 10H). In the H
NMR spectrum of 5h small amounts (25%) of 5h0 was
mixed: 1.66 (s, 3H), 2.38–2.50 (m, 1H), 2.81–2.88 (m, 1H),
3.06–3.16 (m, 1H), 3.44–3.70 (m, 1H), 4.16–4.22 (m, 1H),
4.66 (s, 1H), 5.41 (s, 1H), 6.60 (s, 1H), 7.21–7.96 (m, 10H).
We did not take 13C NMR due to the lack of pure 5h.
3.3.3. Compound 5c. 71%; clear oil; IR (film) 2958, 1685,
1539, 1442, 1354, 1234 cmK1; 1H NMR (CDCl3, 300 MHz)
d 0.83 (t, JZ6.9 Hz, 3H), 1.04–1.29 (m, 4H), 1.77–1.90 (m,
2H), 2.02 (t, JZ1.5 Hz, 3H), 2.38 (s, 3H), 2.65 (dd, JZ18.0,
1.8 Hz, 1H), 2.78 (dd, JZ15.6, 1.8 Hz, 1H), 3.25 (d, JZ
18.0 Hz, 1H), 3.46 (d, JZ15.6 Hz, 1H), 6.89 (s, 1H), 7.26–
7.42 (m, 5H); 13C NMR (CDCl3, 75 MHz) d 13.63, 15.84,
22.31, 25.31, 29.87, 34.86, 35.00, 38.88, 89.37, 127.32,
128.36, 128.94, 130.96, 133.04, 133.70, 133.98, 136.70,
204.59. Anal. Calcd for C20H25NO3: C, 73.37; H, 7.70; N,
4.28. Found: C, 73.51; H, 7.69; N, 4.31.
3.4. Synthesis of benzene derivatives 6a–h
Typical procedure for the synthesis of cyclohexene
intermediate 6a: to a stirred solution of 5a (143 mg,
0.5 mmol) in THF (3 mL) was added DBU (152 mg,
1.0 mmol) and heated to reflux for 6 h. After the usual
workup and column chromatographic purification process
(hexanes/ether, 10:1) we obtained desired 6a as a white
solid, 103 mg (86%). The other compounds 6b–h were
synthesized analogously and the spectroscopic data of
prepared compounds are as follows (reaction time was noted
in the parenthesis).
3.3.4. Compound 5d. 78%; clear oil; IR (film) 2931, 1689,
1539, 1450, 1346, 1261 cmK1; 1H NMR (CDCl3, 300 MHz)
d 1.15 (t, JZ7.2 Hz, 3H), 1.58 (s, 3H), 1.97 (t, JZ1.8 Hz,
3H), 2.60–2.70 (m, 3H), 2.82 (dd, JZ15.3, 1.8 Hz, 1H),
3.25 (d, JZ17.7 Hz, 1H), 3.43 (d, JZ15.3 Hz, 1H), 6.87 (s,
1H), 7.25–7.42 (m, 5H); 13C NMR (CDCl3, 75 MHz) d 7.83,
15.84, 25.80, 35.23, 36.39, 36.73, 86.09, 127.34, 128.39,
129.02, 130.55, 132.20, 132.98, 134.21, 136.70, 208.10.
Anal. Calcd for C18H21NO3: C, 72.22; H, 7.07; N, 4.68.
Found: C, 72.18; H, 7.19; N, 4.51.
3.4.1. Compound 6a.13 86% (6 h); white solid, mp 40–
41 8C; IR (KBr) 2924, 1685 cmK1 1H NMR (CDCl3,
;
300 MHz) d 2.26 (s, 3H), 2.32 (s, 3H), 2.54 (s, 3H), 3.99 (s,
2H), 7.05–7.29 (m, 7H); 13C NMR (CDCl3, 75 MHz) d
15.97, 20.86, 30.45, 39.57, 126.01, 126.80, 128.41, 128.55,
132.06, 133.65, 134.84, 139.96, 140.34, 140.53, 204.00;
ESIMS m/z 239.1 (MCCH). Anal. Calcd for C17H18O: C,
85.67; H, 7.61. Found: C, 85.71; H, 7.75.
3.3.5. Compound 5e. 73%; white solid, mp 79–81 8C; IR
(KBr) 2974, 1689, 1539, 1350, 1238 cmK1 1H NMR
;
(CDCl3, 300 MHz) d 1.14 (t, JZ7.5 Hz, 3H), 1.58 (s, 3H),
2.36 (s, 3H), 2.40–2.50 (m, 2H), 2.64 (d, JZ17.4 Hz, 1H),
2.81 (dd, JZ15.3, 1.8 Hz, 1H), 3.27 (d, JZ17.4 Hz, 1H),
3.41 (d, JZ15.3 Hz, 1H), 6.95 (s, 1H), 7.26–7.42 (m, 5H);
13C NMR (CDCl3, 75 MHz) d 14.68, 22.12, 25.60, 29.59,
36.47, 36.58, 85.96, 127.34, 128.34, 128.99, 130.93 (2C),
133.09, 136.66, 139.41, 203.95. Anal. Calcd for
C18H21NO3: C, 72.22; H, 7.07; N, 4.68. Found: C, 72.43;
H, 7.12; N, 4.69.
3.4.2. Compound 6b. 78% (48 h); clear oil; IR (film) 2966,
1685, 1454, 1354, 1281 cmK1; 1H NMR (CDCl3, 300 MHz)
d 1.22 (t, JZ7.5 Hz, 3H), 2.26 (s, 3H), 2.55 (s, 3H), 2.61 (q,
JZ7.5 Hz, 2H), 4.01 (s, 2H), 7.07–7.29 (m, 7H); 13C NMR
(CDCl3, 75 MHz) d 14.52, 15.03, 27.27, 29.48, 38.70,
124.59, 125.01, 127.41, 127.54, 131.35, 131.55, 138.98,
139.36, 139.67, 140.28, 203.09; ESIMS m/z 253.1 (MCC
H). Anal. Calcd for C18H20O: C, 85.67; H, 7.99. Found: C,
85.59; H, 7.81.
3.3.6. Compound 5f. 65%; white solid, mp 74–76 8C; IR
(KBr) 2951, 1716, 1539, 1435, 1242 cmK1 1H NMR
;
(CDCl3, 300 MHz) d 1.55 (s, 3H), 2.26 (t, JZ1.8 Hz, 3H),
2.76 (dd, JZ18.3, 1.8 Hz, 1H), 2.85 (dd, JZ14.7, 1.5 Hz,
1H), 3.36 (d, JZ14.7 Hz, 1H), 3.37 (d, JZ18.3 Hz, 1H),
3.80 (s, 3H), 7.02 (s, 1H), 7.02–7.42 (m, 5H); 13C NMR
(CDCl3, 75 MHz) d 16.00, 25.49, 36.22, 37.23, 51.78,
85.84, 124.20, 127.49, 128.36, 129.03, 132.41, 133.64,
136.56, 140.52, 168.45. Anal. Calcd for C17H19NO4: C,
67.76; H, 6.36; N, 4.65. Found: C, 67.94; H, 6.44; N, 4.58.
3.4.3. Compound 6c. 80% (72 h); clear oil; IR (film) 2927,
1685, 1454, 1354, 1284 cmK1; 1H NMR (CDCl3, 300 MHz)
d 0.92 (t, JZ7.2 Hz, 3H), 1.23–1.43 (m, 2H), 1.52–1.76 (m,
2H), 2.26 (s, 3H), 2.54 (s, 3H), 2.58 (t, JZ7.8 Hz, 2H), 4.01
(s, 2H), 7.06–7.28 (m, 7H); 13C NMR (CDCl3, 75 MHz) d
13.88, 16.02, 22.29, 30.47, 33.54, 35.04, 39.69, 125.99,
126.17, 128.40, 128.52, 132.34, 133.11, 139.94, 140.00,
140.25, 140.56, 204.08; ESIMS m/z 281.2 (MCCH).

3134
M. J. Lee et al. / Tetrahedron 62 (2006) 3128–3136
Anal. Calcd for C20H24O: C, 85.67; H, 8.63. Found: C,
85.91; H, 8.61.
for C17H21NO5: C, 63.94; H, 6.63; N, 4.39. Found: C, 64.02;
H, 6.61; N, 4.45.
3.4.4. Compound 6d. 85% (5 h); clear oil; IR (film) 2931,
1693, 1454, 1342, 1161 cmK1; 1H NMR (CDCl3, 300 MHz)
d 1.17 (t, JZ7.5 Hz, 3H), 2.20 (s, 3H), 2.30 (s, 3H), 2.83 (q,
JZ7.5 Hz, 2H), 3.98 (s, 2H), 7.02 (s, 1H), 7.07–7.29 (m,
6H); 13C NMR (CDCl3, 75 MHz) d 8.29, 15.86, 20.86,
35.99, 39.54, 125.78, 125.99, 128.39, 128.57, 131.34,
133.05, 134.85, 139.97, 140.16, 141.14, 207.62; ESIMS
m/z 253.2 (MCCH). Anal. Calcd for C18H20O: C, 85.67; H,
7.99. Found: C, 85.73; H, 7.89.
3.5.2. Compound 3g. 41%; white solid, mp 93–95 8C; IR
(KBr) 2249, 1670, 1543 cmK1
;
1H NMR (CDCl3,
300 MHz) d 1.36 (s, 3H), 1.85–1.95 (m, 1H), 2.15–2.35
(m, 3H), 2.49 (s, 3H), 3.25 (d, JZ13.8 Hz, 1H), 3.34 (d, JZ
13.8 Hz, 1H), 7.14–7.48 (m, 5H), 7.80 (s, 1H); 13C NMR
(CDCl3, 75 MHz) d 12.50, 22.10, 25.70, 33.51, 34.23,
89.53, 118.31, 128.32, 129.02, 129.13, 134.69, 136.68,
144.56, 199.36; ESIMS m/z 287.1 (MCCH). Anal. Calcd
for C16H18N2O3: C, 67.12; H, 6.34; N, 9.78. Found: C,
67.35; H, 6.19; N, 9.73.
3.4.5. Compound 6e. 89% (12 h); clear oil; IR (film) 2966,
1689 cmK1; H NMR (CDCl3, 300 MHz) d 1.09 (t, JZ
1
3.5.3. Compound 3h. 11%; clear oil; IR (film) 2927, 1670,
1
1539, 1308, 1149 cmK1; H NMR (CDCl3, 300 MHz) d
7.5 Hz, 3H), 2.30 (s, 3H), 2.55 (s, 3H), 2.74 (q, JZ7.5 Hz,
2H), 4.03 (s, 2H), 7.02 (s, 1H), 7.08–7.29 (m, 6H); 13C NMR
(CDCl3, 75 MHz) d 15.64, 20.86, 22.30, 30.61, 38.45,
126.00, 127.07, 128.38, 128.61, 134.06, 134.91, 138.28,
139.69, 140.06, 140.61, 203.79; ESIMS m/z 253.1 (MCC
H). Anal. Calcd for C18H20O: C, 85.67; H, 7.99. Found: C,
85.47; H, 8.08.
1.28 (s, 3H), 1.90–2.01 (m, 1H), 2.22–2.38 (m, 1H), 2.44 (s,
3H), 2.85–3.01 (m, 2H), 3.22 (d, JZ14.1 Hz, 1H), 3.31 (d,
JZ14.1 Hz, 1H), 7.25–7.71 (m, 8H), 7.75 (s, 1H), 7.80–7.84
(m, 2H); 13C NMR (CDCl3, 75 MHz) d 22.27, 25.65, 31.62,
33.80, 51.30, 89.28, 128.02, 128.41, 128.97, 129.04, 129.37,
133.98, 134.70, 136.71, 138.44, 144.26, 199.31; ESIMS m/z
402.1 (MCCH). Anal. Calcd for C21H23NO5S: C, 62.82; H,
5.77; N, 3.49. Found: C, 62.98; H, 5.65; N, 3.47.
3.4.6. Compound 6f. 80% (96 h); clear oil; IR (film) 2924,
1724, 1454, 1308, 1207 cmK1; 1H NMR (CDCl3, 300 MHz)
d 2.30 (s, 3H), 2.36 (s, 3H), 3.87 (s, 3H), 4.01 (s, 2H), 7.06–
7.09 (m, 3H), 7.15–7.29 (m, 3H), 7.48 (d, JZ1.2 Hz, 1H);
13C NMR (CDCl3, 75 MHz) d 16.15, 20.75, 39.70, 51.88,
126.00, 128.41, 128.52, 128.74, 131.50, 134.45 (2C),
134.87, 140.00, 140.05, 169.21; ESIMS m/z 255.1 (MCC
H). Anal. Calcd for C17H18O2: C, 80.28; H, 7.13. Found: C,
80.19; H, 7.27.
3.6. Synthesis of 7a and 8a–f
Typical procedure for the synthesis of intermediate 7a and
benzene derivative 8a: to a stirred solution of 2a (233 mg,
1.0 mmol) and vinyltriphenylphosphonium bromide
(443 mg, 1.2 mmol) in CH3CN (5 mL) was added DUB
(456 mg, 3 mmol) and heated to reflux for 18 h. After usual
workup and column chromatographic purification process
(hexanes/ether, 40:1) we obtained the desired benzene
derivative 8a (169 mg, 86%). We could obtain the
corresponding intermediate 7a in 48% yield when we
carried out the reaction at around 40–50 8C for 3 h. We
3.4.7. Compound 6g. 91% (9 h); clear oil; IR (film) 2924,
1
2225, 1454 cmK1; H NMR (CDCl3, 300 MHz) d 2.30 (s,
3H), 2.39 (s, 3H), 3.98 (s, 2H), 7.04–7.08 (m, 2H), 7.14 (s,
1H), 7.16–7.32 (m, 4H); 13C NMR (CDCl3, 75 MHz) d
17.32, 20.61, 39.40, 113.51, 118.74, 126.36, 128.52, 128.59,
131.15, 135.36, 136.18, 137.45, 139.05, 140.12; ESIMS m/z
222.1 (MCCH). Anal. Calcd for C16H15N: C, 86.84; H,
6.83; N, 6.33. Found: C, 86.87; H, 6.95; N, 6.18.
synthesized
other
benzene
derivatives
8b–f
analogously without isolation of the corresponding inter-
mediates. The spectroscopic data of prepared compounds
are as follows.
3.4.8. Compound 6h. 78% (18 h); white solid, mp 113–
114 8C; IR (KBr) 2924, 1450, 1304, 1149 cmK1; H NMR
1
3.6.1. Compound 7a. 48%; clear oil; IR (film) 1539, 1450,
1
1346 cmK1; H NMR (CDCl3, 300 MHz) d 1.54 (s, 3H),
(CDCl3, 300 MHz) d 2.26 (s, 3H), 2.38 (s, 3H), 3.94 (s, 2H),
6.98–7.86 (m, 11H), 8.00 (s, 1H); 13C NMR (CDCl3,
75 MHz) d 15.39, 20.92, 39.35, 126.24, 127.34, 128.39,
128.47, 128.52, 128.94, 132.80, 133.43, 135.86, 136.40,
139.18, 139.25, 141.52, 141.79; ESIMS m/z 337.1 (MCC
H). Anal. Calcd for C21H20O2S: C, 74.97; H, 5.99. Found:
C, 75.07; H, 5.93.
1.93 (s, 3H), 2.49 (d, JZ18.0 Hz, 1H), 2.89 (d, JZ15.3 Hz,
1H), 3.07 (d, JZ18.0 Hz, 1H), 3.33 (d, JZ15.3 Hz, 1H),
5.63–5.67 (m, 1H), 6.62 (s, 1H), 7.21–7.39 (m, 5H); 13C
NMR (CDCl3, 75 MHz) d 19.60, 25.43, 36.16, 36.56, 86.91,
123.30, 126.81, 126.97, 128.25, 129.05, 133.27, 133.37,
137.03. Anal. Calcd for C15H17NO2: C, 74.05; H, 7.04; N,
5.76. Found: C, 74.03; H, 7.21; N, 5.71.
3.5. Analytical data of Michael addition products 3f–h
3.6.2. Compound 8a.18a 86%; clear oil; IR (film) 2920,
3.5.1. Compound 3f. 7%; clear oil; IR (film) 1739, 1674,
1
1496, 1450 cmK1; H NMR (CDCl3, 300 MHz) d 2.28 (s,
3H), 2.78 (s, 3H), 3.94 (s, 2H), 6.92–7.28 (m, 8H); ESIMS
1
1539 cmK1; H NMR (CDCl3, 300 MHz) d 1.30 (s, 3H),
1.83–1.95 (m, 1H), 2.02–2.34 (m, 3H), 2.48 (s, 3H), 3.24 (d,
JZ14.1 Hz, 1H), 3.36 (d, JZ14.1 Hz, 1H), 3.63 (s, 3H),
7.26–7.45 (m, 5H), 7.74 (s, 1H); 13C NMR (CDCl3,
75 MHz) d 21.82, 25.77, 28.72, 33.95, 34.00, 51.80,
90.07, 128.44, 128.83, 128.85, 134.95, 137.43, 143.67,
172.51, 199.54; ESIMS m/z 320.1 (MCCH). Anal. Calcd
m/z 197.1 (MCCH).
3.6.3. Compound 8b.18b 81%; clear oil; IR (film) 2962,
1
2927, 1496, 1454 cmK1; H NMR (CDCl3, 300 MHz) d
1.20 (t, JZ7.5 Hz, 3H), 2.18 (s, 3H), 2.57 (q, JZ7.5 Hz,

M. J. Lee et al. / Tetrahedron 62 (2006) 3128–3136
3135
R. F. J. Am. Chem. Soc. 1990, 112, 3093. (b) Danheiser, R. L.;
Gee, S. K. J. Org. Chem. 1984, 49, 1672.
2H), 3.95 (s, 2H), 6.94–7.27 (m, 8H); ESIMS m/z 211.1
(MCCH).
4. (a) Xi, Z.; Sato, K.; Gao, Y.; Lu, J.; Takahashi, T. J. Am. Chem.
Soc. 2003, 125, 9568. (b) Takahashi, T.; Ishikawa, M.; Huo, S.
J. Am. Chem. Soc. 2002, 124, 388.
3.6.4. Compound 8c. 74%; clear oil; IR (film) 2962, 2924,
1496, 1454 cmK1 1H NMR (CDCl3, 300 MHz) d 1.11
;
5. (a) Saito, S.; Yamamoto, Y. Chem. Rev. 2000, 100, 2901. (b)
Bonaga, L. V. R.; Zhang, H.-C.; Moretto, A. F.; Ye, H.;
Gauthier, D. A.; Li, J.; Leo, G. C.; Maryanoff, B. E. J. Am.
Chem. Soc. 2005, 127, 3473.
(t, JZ7.5 Hz, 3H), 2.27 (s, 3H), 2.56 (q, JZ7.5 Hz, 2H),
3.98 (s, 2H), 6.92 (s, 1H), 6.98–7.28 (m, 7H); 13C NMR
(CDCl3, 75 MHz) d 14.98, 20.94, 25.33, 38.72, 125.81,
127.32, 128.31, 128.39, 128.67, 131.09, 135.22, 137.91,
139.38, 141.05; ESIMS m/z 211.1 (MCCH). Anal. Calcd
for C16H18: C, 91.37; H, 8.63. Found: C, 91.29; H, 8.71.
6. (a) Asao, N.; Nogami, T.; Lee, S.; Yamamoto, Y. J. Am. Chem.
Soc. 2003, 125, 10921. (b) Asao, N.; Takahashi, K.; Lee, S.;
Kasahara, T.; Yamamoto, Y. J. Am. Chem. Soc. 2002, 124,
12650. (c) Asao, N.; Aikawa, H.; Yamamoto, Y. J. Am. Chem.
Soc. 2004, 126, 7458.
3.6.5. Compound 8d. 86%; clear oil; IR (film) 1720,
1265 cmK1
; d 1.36
1H NMR (CDCl3, 300 MHz)
7. (a) Langer, P.; Bose, G. Angew. Chem., Int. Ed. 2003, 42,
4033. (b) Katritzky, A. R.; Li, J.; Xie, L. Tetrahedron 1999, 55,
8263.
(t, JZ7.2 Hz, 3H), 2.52 (s, 3H), 4.02 (s, 2H), 4.34 (q, JZ
7.2 Hz, 2H), 7.06–7.28 (m, 6H), 7.81–7.85 (m, 2H); 13C
NMR (CDCl3, 75 MHz) d 14.28, 19.83, 39.39, 60.69,
126.04, 127.73, 128.31, 128.40, 128.48, 130.37,
131.13, 138.95, 139.67, 142.28, 166.72; ESIMS m/z 255.1
(MCCH). Anal. Calcd for C17H18O2: C, 80.28; H, 7.13.
Found: C, 80.34; H, 7.29.
8. (a) Serra, S.; Fuganti, C.; Moro, A. J. Org. Chem. 2001, 66,
7883. (b) Turnbull, P.; Moore, H. W. J. Org. Chem. 1995, 60,
644.
9. (a) Bi, X.; Dong, D.; Liu, Q.; Pan, W.; Zhao, L.; Li, B. J. Am.
Chem. Soc. 2005, 127, 4578. (b) Barun, O.; Nandi, S.; Panda,
K.; Ila, H.; Junjappa, H. J. Org. Chem. 2002, 67, 5398.
10. Ballini, R.; Barboni, L.; Fiorini, D.; Giarlo, G.; Palmieri, A.
Chem. Commun. 2005, 2633.
3.6.6. Compound 8e.18c 40%; clear oil; IR (film) 2920,
1496, 1454 cmK1 1H NMR (CDCl3, 300 MHz) d 2.16
;
(s, 3H), 2.19 (s, 3H), 2.21 (s, 3H), 3.91 (s, 2H), 6.88 (s, 1H),
6.93 (s, 1H), 7.09–7.27 (m, 5H); ESIMS m/z 211.1
(MCCH).
11. (a) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev.
2003, 103, 811. (b) Ciganek, E. In Paquette, L. A., Ed.;
Organic Reactions; Wiley: New York, 1997; Vol. 51,
pp 201–350. (c) Basavaiah, D.; Rao, P. D.; Hyma, R. S.
Tetrahedron 1996, 52, 8001. (d) Kim, J. N.; Lee, K. Y. Curr.
Org. Chem. 2002, 6, 627.
3.6.7. Compound 8f. 86%; clear oil; IR (film) 1716,
1
1269 cmK1; H NMR (CDCl3, 300 MHz) d 1.38 (t, JZ
7.2 Hz, 3H), 2.24 (s, 3H), 3.98 (s, 2H), 4.35 (q, JZ7.2 Hz,
2H), 7.02 (d, JZ8.1 Hz, 2H), 7.22 (d, JZ8.1 Hz, 2HC1H),
7.82 (s, 1H), 7.84 (d, JZ8.1 Hz, 1H); 13C NMR (CDCl3,
75 MHz) d 14.31, 19.81, 38.77, 60.78, 127.95, 128.45,
128.54, 129.82, 130.51, 131.05, 131.88, 138.19, 138.44,
142.18, 166.64; ESIMS m/z 255.1 (MCCH). Anal. Calcd
for C17H17ClO2: C, 70.71; H, 5.93. Found: C, 70.58; H,
5.89.
12. For our recent publications on the chemical transformations of
Baylis–Hillman adducts: (a) Park, D. Y.; Lee, M. J.; Kim,
T. H.; Kim, J. N. Tetrahedron Lett. 2005, 46, 8799. (b)
Gowrisankar, S.; Lee, K. Y.; Kim, J. N. Tetrahedron Lett.
2005, 46, 4859. (c) Kim, J. M.; Lee, K. Y.; Lee, S.; Kim, J. N.
Tetrahedron Lett. 2004, 45, 2805. (d) Lee, M. J.; Lee, K. Y.;
Lee, J. Y.; Kim, J. N. Org. Lett. 2004, 6, 3313. (e)
Gowrisankar, S.; Lee, K. Y.; Lee, C. G.; Kim, J. N.
Tetrahedron Lett. 2004, 45, 6141. (f) Lee, K. Y.;
Gowrisankar, S.; Kim, J. N. Tetrahedron Lett. 2005, 46,
5387. (g) Lee, C. G.; Lee, K. Y.; Lee, S.; Kim, J. N.
Tetrahedron 2005, 61, 1493 and further references cited
therein.
Acknowledgements
This work was supported by the grant (R-05-2003-000-
10042-0) from the Basic Research Program of Korea
Research Foundation.
13. The first part of this paper was published as a preliminary
form without experimental details: Lee, M. J.; Lee, K. Y.;
Gowrisankar, S.; Kim, J. N. Tetrahedron Lett. 2006, 47,
1355.
14. For the synthesis of starting materials 2a–d, see Lee, M. J.;
Lee, K. Y.; Park, D. Y.; Kim, J. N. Bull. Korean Chem. Soc.
2005, 26, 1281.
References and notes
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