An efficient synthesis of o-terphenyls from Morita-Baylis-Hillman adducts of cinnamaldehydes: A consecutive bromination, Wittig reaction, 6π-electrocyclization, and an aerobic oxidation process

Article abstract of DOI:10.1016/j.tetlet.2013.02.104

An efficient synthetic method of o-terphenyls was developed from Morita-Baylis-Hillman adducts. The synthesis was carried out via a sequential bromination of MBH adducts, Wittig reaction with various aldehydes, 6π-electrocyclization, and a base-mediated aerobic oxidation process.

Full text of DOI:10.1016/j.tetlet.2013.02.104

Tetrahedron Letters 54 (2013) 2476–2479
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An efficient synthesis of o-terphenyls from Morita–Baylis–Hillman adducts
of cinnamaldehydes: a consecutive bromination, Wittig reaction,
6p-electrocyclization, and an aerobic oxidation process
⇑
Cheol Hee Lim, Sung Hwan Kim, Ko Hoon 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:
An efficient synthetic method of o-terphenyls was developed from Morita–Baylis–Hillman adducts. The
Received 10 February 2013
Revised 24 February 2013
Accepted 28 February 2013
Available online 7 March 2013
synthesis was carried out via a sequential bromination of MBH adducts, Wittig reaction with various
aldehydes, 6
p
-electrocyclization, and a base-mediated aerobic oxidation process.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
o-Terphenyls
Morita–Baylis–Hillman adducts
6p
-Electrocyclization
Aerobic oxidation
The synthesis of poly-substituted benzene derivatives including
styrylpenta-2,4-dienoate (4a) in moderate yield (64%).9,10 How-
ortho- and para-terphenyls has received much attention.1–3 Among
ever, the E/Z selectivity (E/Z = 4:1) of the styryl substituent at the
2-position during the Wittig reaction was not high,9a and the
purification of 4a was somewhat difficult.9,10 Thus we examined
the reaction with an E/Z mixture of 4a in CH3CN in the presence
of K2CO3 under an O2 balloon atmosphere. To our delight, o-ter-
the numerous approaches for these compounds, a sequential 6p-
electrocyclization of suitably-substituted 1,3,5-trienes to dihydro-
benzenes and a following oxidation process is one of the important
routes.4,5 The Z-stereochemistry at the 3-position of 1,3,5-trienes is
essential for the 6
p-electrocyclization. Thus, the synthesis of
phenyl 5a was obtained in good yield (91%) via the 6p-electro-
1,3(Z),5-trienes in a stereoselective manner is very important.
The Morita–Baylis–Hillman (MBH) adducts have been used
extensively for the synthesis of poly-substituted benzenes.2,3,6
Very recently, we reported a synthesis of p-terphenyls by a
Diels–Alder reaction of 1,3-diene that was prepared from MBH ad-
duct of benzaldehyde, as shown in Scheme 1.2 As a continuous
interest for the synthesis of terphenyls, we presumed that a Wittig
reaction of the MBH bromide of cinnamaldehyde could provide
1,3,5-triene 4a, and the triene could be used for the synthesis of
o-terphenyl 5a, as shown in Scheme 1. The two styryl moieties of
4a are positioned in the same direction around the 2,3-double
bond, although the systematic nomenclature of the double bond
is E, thus a 6p-electrocyclization of 4a could produce the interme-
diate I by a disrotatory ring-closure.
The MBH bromide 2a was prepared from the MBH adduct of
cinnamaldehyde 1a as reported.7,8 The preparation of a phosphonium
salt of 2a and the following Wittig reaction with benzaldehyde
(3a) in the presence of K2CO3 produced methyl 5-phenyl-2-
cyclization to form a mixture of dihydrobenzene intermediate I
and its diastereomer, and a concomitant base-mediated aerobic
oxidation.2,5 The result stated that the preparation of 4a and
its conversion to 5a could be performed in a one-pot. Thus, we
examined a one-pot synthesis of 5a without isolation of the tri-
ene 4a. As shown in Scheme 2, the preparation of a phospho-
nium salt of 2a was carried out with PPh3 in CH3CN at room
temperature for 2 h. After monitoring the formation of a phos-
phonium salt on TLC, benzaldehyde (1.1 equiv) and K2CO3
(2.0 equiv) were added, and the reaction mixture was stirred
for 12 h at room temperature to form the triene intermediate
4a. The reaction mixture was then heated to reflux for 15 h un-
der O2 balloon atmosphere. The product 5a was obtained in a
one-pot reaction from 2a in moderate yield (55%).11 The yield
of 5a was similar to that of the two-step procedure (58%).
Encouraged by the results various o-terphenyl derivatives were
synthesized analogously, and the results are summarized in
Table 1. The reactions between 2a and various aldehydes such as
p-chlorobenzaldehyde (3b), p-anisaldehyde (3c), p-nitrobenzalde-
hyde (3d), and 4-biphenylcarboxaldehyde (3e) afforded the corre-
sponding o-terphenyls 5b–e in a one-pot reaction in reasonable
⇑
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 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.02.104

C. H. Lim et al. / Tetrahedron Letters 54 (2013) 2476–2479
2477
Previous work
Ph
Ph
Ph
COOMe
Diels-Alder reaction
(DMAD)
OH
COOMe
COOMe
MeOOC
COOMe
COOMe
aerobic
oxidation
MeOOC
Ph
COOMe
Ph
Ph
Ph
p-terphenyl
This work
(E)
2
COOMe
Ph
Ph
Ph
aerobic
OH
Ph
Ph
Ph
3
6π-electrocyclization
oxidation
COOMe
Ph
MeOOC
disrotatory
MeOOC
1a
o-terphenyl 5a
5a (55%)
I
cis
4a
Scheme 1.
O2balloon
Ph
Ph
PBr3 (1.0 equiv)
CH2Cl2, rt, 1 h
(i) PPh3, CH3CN, rt, 2 h
reflux, 15 h
COOMe
Br
Ph
1a
(ii) PhCHO (3a, 1.1 equiv)
K2CO3 (2.0 equiv)
rt, 12 h
MeOOC
4a
2a (61%)
Scheme 2.
Table 1
One-pot synthesis of o-terphenyl derivatives 5 from MBH bromides 2a,b
R1
OH
R2
R3
COOMe
COOMe
iv
R1
ii
iii
R1
COOMe
R1
i
R2
2a-e
R2
R2
Br
R3
1a-e
4a-l
5a-l
COOMe
(i): PBr3 (1.0 equiv), CH2Cl2, rt, 1 h (46-78%). (ii): PPh3 (1.1 equiv), MgSO4, CH3CN, rt, 2 h.
(iii): R3-CHO (3a-h, 1.1 equiv), K2CO3 (2.0 equiv), rt, 12-28 h. (iv): reflux, O2 balloon, 15-22 h.
Cl
OMe
NO2
COOMe
COOMe
COOMe
COOMe
5c (45%)
5d (68%)
5a (55%)
R1=Ph, R2=H
R3=Ph
5b (63%)
R1=Ph, R2=H
R3=p-MeOPh
R1=Ph, R2=H
R3=p-NO2Ph
R1=Ph, R2=H
R3=p-ClPh
Me
Ph
N
O
S
COOMe
COOMe
COOMe
5g (58%)
COOMe
5h (60%)
5e (68%)
R1=Ph, R2=H
R3=p-PhPh
OMe
5f (69%)
R1=Ph, R2=H
R3=4-pyridyl
F
R1=Ph, R2=H
R3=2-furyl
R1=Ph, R2=H
R3=5-Me-2-thienyl
NO2
Me
NO2
Me
COOMe
5l (57%)
COOMe
R1=Me, R2=H
R3=p-NO2Ph
5k (67%)
COOMe
COOMe
R1=Ph, R2=Me
5i (54%)c
5j (59%)
R3=p-NO2Ph
R1=p-MeOPh, R2=H
R1=p-FPh, R2=H
R3=Ph
R3=Ph
a
MBH alcohols 1 and the corresponding MBH bromides 2 were prepared as reported.7,8 For 1a–e and 2a–e: a: R1 = Ph, R2 = H; b: R1 = p-MeOPh, R2 = H; c: R1 = p-FPh, R2 = H; d:
R1 = Ph, R2 = Me; e: R1 = Me, R2 = H. For 3a–h: a: R3 = Ph; b: R3 = p-ClPh; c: R3 = p-MeOPh; d: R3 = p-NO2Ph; e: R3 = p-PhPh; f: R3 = 4-pyridyl; g: R3 = 2-furyl; h: R3 = 5-Me-2-thienyl.
b
The yield of o-terphenyl 5 is one of the three-step, one-pot reactions from MBH bromide 2.
The corresponding MBH acetate was used instead of MBH bromide 2b for the Wittig reaction.
c

2478
C. H. Lim et al. / Tetrahedron Letters 54 (2013) 2476–2479
NO2
Ph
OH
aq HBr
(i) PPh3, CH3CN, rt, 2 h
COMe
Br
COMe
Ph
Ph
CH2Cl2
rt, 1 h
(ii) p-NO2PhCHO (1.1 equiv)
K2CO3 (2.0 equiv), rt, 12 h
(iii) O2 balloon, reflux, 20 h
COMe
1f
2f (71%)
5m (61%)
NO2
Ph
trans
(Z)
same
as above
OH
aq HBr
CN
Ph
Br
Ar
Ph
CH2Cl2
rt, 1 h
Ph
CN
2g (66%)
CN
CN
1g
4g (Ar=p-NO2Ph)
5n (not formed)
Scheme 3.
Ph
(i) PPh3, CH3CN, rt, 2 h
COOMe
2a
+
Ph
(ii) CH3(CH2)4CHO (1.1 equiv)
K2CO3 (2.0 equiv), rt, 18 h
(iii) O2 balloon, reflux, 22 h
6 (19%)
COOMe
5o (47%)
Scheme 4.
yields (45–68%). The yield of 5c was somewhat low as compared to
other entries due to the formation of the hydrolysis product (vide
infra).10 Besides these arylaldehydes, the reactions between 2a and
4-pyridinecarboxaldehyde (3f), 2-furaldehyde (3g) and 5-methyl-
2-thiophenecarboxaldehyde (3h) afforded the corresponding prod-
ucts 5f–h in good yields (58–69%). The use of MBH bromides 2b-e8j
derived from p-methoxycinnamaldehyde, p-fluorocinnamalde-
hyde, a-methylcinnamladehyde, and crotonaldehyde showed sim-
ilar results, and o-terphenyls 5i–l were synthesized in good to
moderate yields (54–67%).
The reaction of MBH bromide 2f bearing an acetyl group
showed the same reactivity to produce 5m in moderate yield
(61%) with p-nitrobenzaldehyde, as shown in Scheme 3. As com-
pared to the stereochemistry of 2a–f, the MBH bromide 2g bearing
a nitrile moiety was formed in the opposite stereochemistry.8j
Thus, the intermediate triene 4g might have a wrong stereochem-
(2012R1A1B3000541). Spectroscopic data were obtained from
the Korea Basic Science Institute, Gwangju branch.
References and notes
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istry around the second double bond, and the 6p-electrocyclization
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cannot occur. Actually, the reaction of 2g did not produce the cor-
responding o-terphenyl 5n in appreciable amount under the same
reaction conditions as expected.
In order to check the scope of the reaction, the reaction of 2a
was examined with n-hexanal although the expected product 5o
is not an o-terphenyl derivative, as shown in Scheme 4. The yield
of 5o was somewhat low (47%) as compared to o-terphenyls 5a–
m derived from arylaldehydes. As noted above, an appreciable
amount of methyl 2-methyl-5-phenylpenta-2,4-dienoate (6), the
reduction product of a phosphonium salt of 2a, were formed dur-
ing the Wittig reaction even in the presence of MgSO4.10c
In summary, various o-terphenyl derivatives were synthesized
in a one-pot reaction from MBH bromides of cinnamaldehydes
4. For some selected examples on 6p-electrocyclizations to form dihydrobenzene
derivatives, see: (a) Hayashi, R.; Walton, M. C.; Hsung, R. P.; Schwab, J. H.; Yu, X.
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Eur. J. Org. Chem. 2007, 3879–3893; (g) Brandange, S.; Leijonmarck, H. Chem.
Commun. 2004, 292–293; (h) Marvell, E. N.; Hilton, C.; Cleary, M. J. Org. Chem.
1983, 48, 4272–4275.
via a sequential Wittig reaction, 6p-electrocyclization, and a
base-mediated aerobic oxidation process.
Acknowledgments
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(a) Moulton, B. E.; Dong, H.; O’Brien, C. T.; Duckett, S. B.; Lin, Z.; Fairlamb, I. J. S.
Org. Biomol. Chem. 2008, 6, 4523–4532; (b) von Essen, R.; Frank, D.;
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This research was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded
by the Ministry of Education, Science and Technology

C. H. Lim et al. / Tetrahedron Letters 54 (2013) 2476–2479
2479
3793–3800; (d) Dell’Erba, C.; Gabellini, A.; Mugnoli, A.; Novi, M.; Petrillo, G.;
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5442.
11. Typical procedure for the synthesis of compound 5a: A mixture of MBH bromide
2a (281 mg, 1.0 mmol),8j PPh3 (288 mg, 1.1 mmol), and MgSO4 (1.0 g) in CH3CN
(3.0 mL) was stirred at room temperature for 2 h to form the phosphonium
salt. Benzaldehyde (117 mg, 1.1 mmol) and K2CO3 (276 mg, 2.0 mmol) were
added into the flask, and the reaction mixture was stirred for 12 h at room
temperature to form triene 4a. The reaction mixture was then heated to reflux
for 15 h under O2 balloon atmosphere. After the usual aqueous extractive
workup and column chromatographic purification process (hexanes/ether,
100:1) compound 5a was obtained as a white solid, 159 mg (55%). Other o-
terphenyls were synthesized similarly, and the spectroscopic data of selected
compounds 5a, 5d, 5g, 5i, 5l, 5m, and 5o are as follows.
a
phosphine-mediated benzannulation reaction between b,c-unsaturated
a-ketoester and MBH carbonate.
6. For the general reviews on MBH reaction, see: (a) Basavaiah, D.; Rao, A. J.;
Satyanarayana, T. Chem. Rev. 2003, 103, 811–891; (b) Basavaiah, D.; Reddy, B. S.;
Badsara, S. S. Chem. Rev. 2010, 110, 5447–5674; (c) Singh, V.; Batra, S.
Tetrahedron 2008, 64, 4511–4574; (d) Declerck, V.; Martinez, J.; Lamaty, F.
Chem. Rev. 2009, 109, 1–48; (e) Ciganek, E. In Organic Reactions; Paquette, L. A.,
Ed.; John Wiley & Sons: New York, 1997; Vol. 51, pp 201–350; (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) Gowrisankar, S.; Lee, H. S.; Kim,
S. H.; Lee, K. Y.; Kim, J. N. Tetrahedron 2009, 65, 8769–8780; (i) Shi, M.; Wang,
F.-J.; Zhao, M.-X.; Wei, Y. The Chemistry of the Morita–Baylis–Hillman Reaction;
RSC Publishing: Cambridge, UK, 2011.
Compound 5a:1h,i 55%; white solid, mp 126–128 °C; IR (KBr) 2982, 1708, 1628,
1265, 1209, 1022 cmÀ1 1H NMR (CDCl3, 300 MHz) d 3.87 (s, 3H), 7.05–7.08
;
(m, 4H), 7.13–7.18 (m, 6H), 7.42 (d, J = 8.1 Hz, 1H), 7.99 (dd, J = 8.1 and 1.8 Hz,
1H), 8.04 (d, J = 1.8 Hz, 1H); ESIMS m/z 289 [M+H]+.
Compound 5d: 68%; yellow solid, mp 124–126 °C; IR (KBr) 3005, 2953, 1725,
1511, 1260 cmÀ1 1H NMR (CDCl3, 300 MHz) d 3.90 (s, 3H), 7.03–7.05 (m, 2H),
;
7. For the preparation of the MBH adducts of cinnamaldehydes, see: Kim, K. H.;
Lee, H. S.; Kim, Y. M.; Kim, J. N. Bull. Korean Chem. Soc. 2011, 32, 1087–1090. and
further references cited therein.
7.18–7.20 (m, 3H), 7.24 (d, J = 8.4 Hz, 2H), 7.48 (d, J = 8.1 Hz, 1H), 8.01
(s, 1H), 8.04–8.08 (m, 3H); 13C NMR (CDCl3, 75 MHz) d 52.36, 123.32, 127.72,
128.40, 129.56, 129.59, 129.71, 130.65, 131.09, 131.46, 138.41, 139.55, 145.18,
146.70, 147.48, 166.50; ESIMS m/z 334 [M+H]+. Anal. Calcd for C20H15NO4:
C, 72.06; H, 4.54; N, 4.20. Found: C, 72.31; H, 4.73; N, 4.11.
8. For the synthesis of MBH bromides in a stereoselective manner from MBH
adducts, see: (a) Gowrisankar, S.; Kim, S. H.; Kim, J. N. Bull. Korean Chem. Soc.
2009, 30, 726–728. and further references cited therein; (b) Basavaiah, D.;
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Banerjee, J.; Ravindranath, N. Tetrahedron 2004, 60, 8357–8361; (d) Fernandes,
L.; Bortoluzzi, A. J.; Sa, M. M. Tetrahedron 2004, 60, 9983–9989; (e) Sa, M. M.;
Ramos, M. D.; Fernandes, L. Tetrahedron 2006, 62, 11652–11656; (f) Deng, J.;
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2008, 73, 2015–2017; (g) Lee, K. Y.; Lee, Y. J.; Kim, J. N. Bull. Korean Chem. Soc.
2007, 28, 143–146; (h) Lee, K. Y.; Park, D. Y.; Kim, J. N. Bull. Korean Chem. Soc.
2006, 27, 1489–1492; (i) Das, B.; Damodar, K.; Bhunia, N.; Shashikanth, B.
Tetrahedron Lett. 2009, 50, 2072–2074; (j) Kim, K. H.; Kim, S. H.; Park, S.; Kim, J.
N. Tetrahedron 2011, 67, 3328–3336.
9. For the Wittig type reaction of MBH adducts and their synthetic application,
see: (a) Zhou, R.; Wang, C.; Song, H.; He, Z. Org. Lett. 2010, 12, 976–979; (b) Lee,
C. G.; Lee, K. Y.; Kim, S. J.; Kim, J. N. Bull. Korean Chem. Soc. 2007, 28, 719–720;
(c) Crist, R. M.; Reddy, P. V.; Borhan, B. Tetrahedron Lett. 2001, 42, 619–621; (d)
Muthiah, C.; Kumar, K. S.; Vittal, J. J.; Swamy, K. C. K. Synlett 2002, 1787–1790;
(e) Palmelund, A.; Myers, E. L.; Tai, L. R.; Tisserand, S.; Butts, C. P.; Aggarwal, V.
K. Chem. Commun. 2007, 4128–4130; For the synthesis of methyl 5-phenyl-2-
styrylpenta-2,4-dienoate (4a), see: (f) Kang, S.-K.; Lee, Y.-T.; Lee, S.-H.
Tetrahedron Lett. 1999, 40, 3573–3576; (g) Janecki, T. Synth. Commun. 1993,
23, 641–650. Although the assignment of stereochemistry and the E/Z ratio of
triene 4a was not clear from its 1H NMR spectrum, the high yield (91%) of o-
terphenyl 5a from 4a stated that the stereochemistry at the 2-position of 4a
must be E, as shown in Scheme 1. In the absence of K2CO3 under N2 balloon
atmosphere (CH3CN, reflux, 40 h), the reaction of 4a produced cis-
Compound 5g: 58%; colorless oil; IR (film) 2979, 1708, 1604, 1513, 1237 cmÀ1
;
1H NMR (CDCl3, 300 MHz) d 3.89 (s, 3H), 5.56 (dd, J = 3.3 and 0.6 Hz, 1H), 6.16
(dd, J = 3.3 and 1.8 Hz, 1H), 7.18–7.22 (m, 2H), 7.26–7.34 (m, 5H), 7.90 (dd,
J = 8.1 and 1.8 Hz, 1H), 8.41 (d, J = 1.8 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d
52.23, 109.65, 111.34, 127.69, 128.09, 128.23, 128.43, 128.67, 129.38, 129.63,
130.97, 141.06, 141.86, 143.56, 151.80, 166.79; ESIMS m/z 279 [M+H]+. Anal.
Calcd for C18H14O3: C, 77.68; H, 5.07. Found: C, 77.49; H, 5.26.
Compound 5i: 54%; pale yellow solid, mp 90–92 °C; IR (KBr) 2952, 2926, 1721,
1309, 1265 cmÀ1 1H NMR (CDCl3, 300 MHz) d 3.70 (s, 3H), 3.86 (s, 3H), 6.69
;
(d, J = 9.0 Hz, 2H), 6.99 (d, J = 9.0 Hz, 2H), 7.07–7.11 (m, 2H), 7.14–7.19 (m, 3H),
7.40 (d, J = 8.1 Hz, 1H), 7.97 (dd, J = 8.1 and 1.8 Hz, 1H), 8.01 (d, J = 1.8 Hz, 1H);
13C NMR (CDCl3, 75 MHz) d 52.13, 55.16, 113.46, 126.76, 128.04, 128.49,
128.75, 129.76, 130.60, 130.83, 131.89, 132.78, 140.54, 140.80, 144.66, 158.77,
166.97; ESIMS m/z 319 [M+H]+. Anal. Calcd for C21H18O3: C, 79.22;
H, 5.70. Found: C, 79.15; H, 5.98.
Compound 5l: 57%; pale yellow solid, mp 106–108 °C; IR (KBr) 2925, 1722,
1519, 1348 cmÀ1 1H NMR (CDCl3, 300 MHz) d 2.25 (s, 3H), 3.85 (s, 3H), 7.32 (d,
;
J = 7.5 Hz, 1H), 7.44 (d, J = 8.4 Hz, 2H), 7.84 (s, 1H), 7.92 (d, J = 7.5 Hz, 1H), 8.24
(d, J = 8.4 Hz, 2H); 13C NMR (CDCl3, 75 MHz) d 20.62, 52.20, 123.56, 128.17,
129.43, 130.10, 130.53, 130.90, 139.72, 140.61, 147.08, 147.62, 166.69; ESIMS
m/z 272 [M+H]+. Anal. Calcd for C15H13NO4: C, 66.41; H, 4.83; N, 5.16. Found: C,
66.72; H, 4.90; N, 5.01.
Compound 5m: 61%; pale yellow solid, mp 136–138 °C; IR (KBr) 2951, 1714,
1593, 1515, 1342 cmÀ1 1H NMR (CDCl3, 300 MHz) d 2.61 (s, 3H), 7.02–7.06
;
(m, 2H), 7.17–7.22 (m, 3H), 7.25 (d, J = 9.0 Hz, 2H), 7.51 (d, J = 8.1 Hz, 1H), 7.95
(d, J = 1.8 Hz, 1H), 7.99 (dd, J = 8.1 and 1.8 Hz, 1H), 8.03 (d, J = 9.0 Hz, 2H); 13C
NMR (CDCl3, 75 MHz) d 26.74, 123.35, 127.78, 128.42, 128.56, 129.55, 130.14,
130.63, 131.24, 136.32, 138.64, 139.44, 145.32, 146.72, 147.50, 197.31; ESIMS
m/z 318 [M+H]+. Anal. Calcd for C20H15NO3: C, 75.70; H, 4.76; N, 4.41. Found: C,
75.96; H, 4.73; N, 4.19.
dihydrobenzene I in good yield (74%) by disrotatory 6
p-electrocyclization
(thermally allowed by the Woodward–Hoffman rules) along with
a
trace
amount of 5a (7%). The 1H NMR data of I were well matched with the reported
data of a similar compound:5d 1H NMR (CDCl3, 300 MHz) d 3.76 (s, 3H), 3.81
(ddd, J = 9.9, 4.5 and 2.1 Hz, 1H), 4.05 (dd, J = 9.9 and 4.2 Hz, 1H), 6.00 (dd,
J = 9.9 and 4.5 Hz, 1H), 6.63–6.73 (m, 5H), 6.94–7.20 (m, 7H); 13C NMR (CDCl3,
75 MHz) d 45.63, 47.24, 51.90, 122.50, 126.66, 126.71, 127.72, 127.82, 127.99,
129.07, 129.09, 130.78, 137.80, 138.28, 139.56, 166.08. The result strongly
confirmed that the major isomer of 4a is an E,E,E-triene, as shown in Scheme 1.
10. In addition, an appreciable amount (5–10%) of the hydrolysis product, methyl
2-methyl-5-phenylpenta-2,4-dienoate (6, see Scheme 4), was formed during
the Wittig reaction. The addition of MgSO4 was helpful for the increase of the
yield of 4a by suppressing the hydrolysis of a phosphonium salt. For the
hydrolysis of phosphonium salt, see: (a) Lee, K. Y.; Na, J. E.; Lee, M. J.; Kim, J. N.
Compound 5o: 47%; colorless oil; IR (film) 2951, 2924, 1721, 1250 cmÀ1 1H
;
NMR (CDCl3, 300 MHz) d 0.73 (t, J = 6.6 Hz, 3H), 1.07–1.18 (m, 4H), 1.39–1.44
(m, 2H), 2.53 (t, J = 7.8 Hz, 2H), 3.87 (s, 3H), 7.16–7.24 (m, 3H), 7.28–7.38
(m, 3H), 7.81 (dd, J = 8.1 and 1.8 Hz, 1H), 7.90 (d, J = 1.8 Hz, 1H); 13C NMR
(CDCl3, 75 MHz) d 13.91, 22.28, 30.87, 31.54, 32.84, 52.08, 126.67, 127.24,
128.11, 128.88, 128.99, 130.14, 130.46, 140.72, 141.02, 146.47, 167.24; ESIMS
m/z 283 [M+H]+. Anal. Calcd for C19H22O2: C, 80.82; H, 7.85. Found: C, 80.67; H,
7.93.