Efficient synthesis of (E)-3-alkylidene-2(3H)-furanones from 3-(1-hydroxyalkyl)-2-silyloxyfurans

Article abstract of DOI:10.1055/s-2006-944202

Several unsubstituted (E)-3-alkylmethylidene- and (E)-3-(arylmethylidene)- 2(3H)-furanones have been synthesized in highly stereoselective fashion by mesylation-elimination of 3-(1-hydoxyalkyl)-2-silyloxyfurans. The latter were prepared from 2-tri-isopropylsilyloxy-3-bromofuran by halogen-lithium exchange and reaction of the in situ generated 3-lithiated silyloxyfuran with aldehydes. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-944202

LETTER
1511
Efficient Synthesis of (E)-3-Alkylidene-2(3H)-furanones from 3-(1-Hydroxy-
alkyl)-2-silyloxyfurans
Synthesis
o
of
(
E
)-3-Alk
h
ylidene-2(
3
H
n
)-furanones Boukouvalas,* Olivier Marion
Département de Chimie, Université Laval, Quebec City, Quebec G1K 7P4, Canada
Fax +1(418)6567916; E-mail: john.boukouvalas@chm.ulaval.ca
Received 16 February 2006
more, 3-ylidene-2(3H)-furanones are valuable intermedi-
Abstract: Several unsubstituted (E)-3-alkylmethylidene- and (E)-
3-(arylmethylidene)-2(3H)-furanones have been synthesized in
highly stereoselective fashion by mesylation–elimination of 3-(1-
hydoxyalkyl)-2-silyloxyfurans. The latter were prepared from 2-tri-
isopropylsilyloxy-3-bromofuran by halogen–lithium exchange and
reaction of the in situ generated 3-lithiated silyloxyfuran with alde-
hydes.
ates in the synthesis of other compounds,6,7 including
coumarins,6 naphthalenes8 and 3-ylidene-3H-pyrrolin-2-
ones.9
Traditionally, 3-ylidene-2(3H)-furanones have been pre-
pared by cyclodehydration of g-keto acids and ensuing
aldol condensation with aromatic aldehydes. Although
this process has been widely used,6 it is restricted to the
preparation of 5-substituted derivatives,10 and even then
its utility can be hampered by poor E/Z stereoselectivity
and overall efficiency,6 as noted during the synthesis of
BE-23372M.1c In recent years, several alternative routes
have been reported,11–16 most of them involving transi-
tion-metal-catalyzed cyclization or cyclocarbonylation of
appropriately functionalized acetylenic or allenic sub-
strates.13–16 All of these methods, however, also involve
de novo construction of the lactone ring and are only
applicable to furanones bearing a C5 substituent11–15 and/
or a disubstituted methylidene appendage.12,16
Key words: 2-silyloxyfurans, bromination, lithiation, lactones,
stereoselectivity
The 3-ylidene-2(3H)-furanone unit characterizes a small
but pharmacologically important group of natural prod-
ucts and semi-synthetic derivatives, comprising the highly
selective EGF receptor kinase inhibitor BE-23372M (1),1
the andrographolide-derived potent anti-HIV agents
DASM (cf. 2),2 and the medicinal plant constituents
peronemin D1 (3)3 and guttoside (4, Figure 1).4
We report here a fundamentally different approach that
overcomes these limitations and enables expedient access
to a range of hitherto unknown, unsubstituted (E)-3-alkyl-
idene-2(3H)-furanones 5 from readily available starting
materials (Scheme 1).
HO
O
HO
O
HO
O
HO
O
H
HO
R
OMs
OCO(CH2)2CO2H
Li
1
2
R
+ RCHO
O
O
O
TIPS
OTIPS
O
O
O
O
O
5
6
7
O
H
Scheme 1
OH
The strategy we followed relies on an unprecedented
elimination of silyloxyfurylcarbinol mesylates 6, envi-
sioned to arise by addition of 3-lithio-2-silyloxyfuran 7 to
aldehydes (Scheme 1). 3-Bromo-2-triisopropylsilyloxy-
furan (10) was viewed as a stable precursor of 7 and also
as a key building block, obtainable in two steps from com-
mercially available furanone 8 (Scheme 2). Thus, bromi-
nation of 8 and subsequent dehydrohalogenation of the
crude dibromide adduct17 provided the known 3-bromo-
2(5H)-furanone (9) in 91% yield.18 Exposure of 9 to
TIPSOTf/Et3N in dichloromethane19,20 afforded bromosi-
lyloxyfuran 10 in 89% yield after flash chromatography.21
GluO
O
H
O
4
3
Figure 1
Conceivably, these substances may produce their biologi-
cal effects by acting as alkylating agents in Michael-type
reactions with thiol-containing bionucleophiles.5 Further-
SYNLETT 2006, No. 10, pp 1511–1514
Advanced online publication: 12.06.2006
2
1
.0
6
.2
0
0
6
DOI: 10.1055/s-2006-944202; Art ID: S01506ST
© Georg Thieme Verlag Stuttgart · New York

1512
J. Boukouvalas, O. Marion
LETTER
Br
noteworthy since the latter can be regarded as a simplified
analogue of diterpene lactones 2–4 (Figure 1). Likewise,
furylcarbinols bearing an a-aryl, biaryl or heteroaryl sub-
stituent (cf. 11e–j) were transformed to the corresponding
3-arylmethylidenefuranones in consistently excellent
yields (entries 5–10). Significantly, elimination proceeds
with high E-stereoselectivity, regardless of the nature of
the R group.23 This can best be explained by considering
conformers 6A and 6B which may undergo elimination by
a concerted mechanism or via formation of the corre-
sponding carbocations 12A and 12B (Figure 2). Conform-
ers 6A and 12A are favored over 6B and 12B on steric
grounds since the latter are substantially destabilized by
allylic 1,3-strain25 between the triisopropylsilyloxy
(TIPSO) and R substituents.
Br
OTIPS
Br2, CCl4, ∆
TIPSOTf
O
O
then Et3N
CH2Cl2, 0 °C
(91%)
Et3N, CH2Cl2
0 °C to r.t.
(89%)
O
O
O
8
9
10
Scheme 2
The requisite 3-(1-hydroxyalkyl)-2-silyloxyfurans 11
were prepared from 10 by halogen–metal exchange with
n-butyllithium, followed by in situ reaction of the result-
ing 2-lithio-3-triisopropylsilyloxyfuran with aldehydes
(Table 1).20,22 With the exception of p-nitrobenzaldehyde
(entry 7), all of the aliphatic and aromatic aldehydes tried
gave excellent carbinol yields although the quality of
aldehyde proved to be critical for optimal results.22
Treatment of alcohol 11a with MsCl/Et3N in dichloro-
methane (–78 °C to r.t.) accomplished mesylation and
ensuing elimination to furnish 3-hexylidenefuranone 5a
(E:Z = 17:1) which was obtained essentially free from its
Z-isomer after purification on silica gel (42% yield, >97%
E).23 The yield of 5a was only slightly improved when
TBAF was used in conjunction with MsCl/Et3N (52%;
entry 1).24 Nonetheless, higher yields of 3-alkylidenefura-
nones were obtained from furylcarbinols with branched
alkyl substituents (entries 2–4).
R
H
H
H
R
R
+
O
O
H
H
OMs
O
O
O
6A
12A
O
Si(i-Pr)3
Si(i-Pr)3
E-5
H
H
H
OMs
H
R
+
O
O
H
R
R
O
O
6B
12B
O
The smooth conversion of isovaleraldehyde-derived
carbinol 11b to furanone 5b (96%, entry 2) is especially
Si(i-Pr)3
Si(i-Pr)3
O
Z-5
Figure 2
Table 1 Preparation of 3-(E)-Alkylidene-2(3H)-furanones
R
OH
n-BuLi, THF
–78 °C, 0.5 h
MsCl, Et3N, CH2Cl2
–78 °C, 1 h
It is worthy of note that the propensity of silyloxyfuryl-
carbinol mesylates 6 to undergo in situ elimination to 5
(Scheme 1), sharply contrasts the behavior of their un-
masked furanone counterparts which have been isolated
on several occasions and shown to undergo nucleophilic
displacement with high efficiency.26 Indeed, mesylation
of alcohol 13a, obtained by hydrolysis of silyloxyfuran
11a, proceeded smoothly to furnish mesylate 14a in high
yield (Scheme 3). Moreover, exposure of 14a to DBU did
not provide 3-hexylidenefuranone 5a but led to 3-(E)-hex-
enylfuranone 15a instead as the main reaction product.27
Br
OTIPS
R
OTIPS
O
then RCHO
–78 °C, 2 h
then TBAF
–78 °C to r.t., 1–2 h
O
O
O
10
11a–j
5a–j
Entry
R
Yield (%)
Yield (%)
E:Zb
of 11a
of 5a
1
2
Me(CH2)4
Me2CHCH2
i-Pr
92 (11a)
93 (11b)
99 (11c)
96 (11d)
98 (11e)
82 (11f)
58 (11g)
91 (11h)
80 (11i)
98 (11j)
52 (5a)c
96 (5b)
73 (5c)
61 (5d)
93 (5e)
97 (5f)
90 (5g)
97 (5h)
96 (5i)
91 (5j)
17:1
17:1
3
23:1
4
t-Bu
>30:1
>30:1
>30:1
>30:1
>30:1
>30:1
>30:1
OH
OH
n-Bu
n-Bu
5
Ph
aq 10% HCl/THF
OTIPS
O
or TBAF/THF
95–100%
6
p-MeO-Ph
p-NO2-Ph
m-Cl-Ph
p-Ph-Ph
2-Furyl
O
O
11a
13a
7
MsCl, Et3N
CH2Cl2
8
94%
–78 °C to r.t.
9
OMs
10
n-Bu
n-Bu
DBU, CH2Cl2, r.t.
ca. 80%
a All yields refer to chromatographically purified products.
b Ratios were determined by 1H NMR.
O
O
O
O
c The yield of 5a was 42% when the experiment was performed
15a
14a
without using TBAF.
Scheme 3
Synlett 2006, No. 10, 1511–1514 © Thieme Stuttgart · New York

LETTER
Synthesis of (E)-3-Alkylidene-2(3H)-furanones
1513
(18) (a) Bromofuranone 9 has been previously prepared in three
steps from 2,5-dimethoxy-2,5-dihydrofuran: Bella, M.;
Piancatelli, G.; Squarcia, A. Tetrahedron 2001, 57, 4429;
and references therein. (b) See also: Vaz, B.; Alvarez, R.;
Brückner, R.; de Lera, A. R. Org. Lett. 2005, 7, 545.
(19) Boukouvalas, J.; Lachance, N. Synlett 1998, 31.
(20) For the preparation and addition of metallated silyloxyfurans
to carbonyl compounds, see: (a) Boukouvalas, J.; Cheng,
Y.-X.; Robichaud, J. J. Org. Chem. 1998, 63, 228.
(b) Kanoh, N.; Ishihara, J.; Yamamoto, Y.; Murai, A.
Synthesis 2000, 1878. (c) Xin, Z.; Zheng, G. Z.; Stewart, A.
O. Synlett 2000, 1324. (d) Sibi, M. P.; He, L. Org. Lett.
2004, 6, 1749. (e) Paintner, F. F.; Allmendinger, L.;
Bauschke, G. Synlett 2005, 2735.
In conclusion, the first synthesis of unsubstituted (E)-3-
alkylidene-2(3H)-furanones has been achieved by a high-
ly regio- and stereocontrolled pathway from 3-bromo-2-
triisopropylsilyloxyfuran. The simplicity and inherent
flexibility of this new methodology set the stage for the
synthesis of several natural and unnatural products of
biomedical importance.
Acknowledgment
We are indebted to the Natural Sciences and Engineering Research
Council of Canada (NSERC), Merck Frosst Canada and Eisai Rese-
arch Institute (MA, USA) for financial support.
(21) Data for 10: colorless liquid. 1H NMR (400 MHz, CDCl3):
d = 1.10 (18 H, d, J = 7.2 Hz), 1.29 (3 H, m), 6.27 (1 H, d,
J = 2.4 Hz), 6.80 (1 H, d, J = 2.4 Hz). 13C NMR (100 MHz,
CDCl3): d = 12.3, 17.4, 73.3, 114.1, 131.7, 153.4. HRMS:
m/z calcd: 318.0651 [M+]; found: 318.0656.
References and Notes
(1) (a) Okabe, T.; Yoshida, E.; Chieda, S.; Endo, K.; Kamiya,
S.; Osada, K.; Tanaka, S.; Okura, A.; Suda, H. J. Antibiotics
1994, 47, 289. (b) Tanaka, S.; Okabe, T.; Nakajima, S.;
Yoshida, E.; Suda, H. J. Antibiotics 1994, 47, 294.
(c) Tanaka, S.; Okabe, T.; Nakajima, S.; Yoshida, E.;
Morishima, H. J. Antibiotics 1994, 47, 297.
(2) (a) Chang, R. S.; Ding, L.; Gai-Qing, C.; Qi-Choa, P.; Ze-
Lin, Z.; Smith, K. M. Proc. Soc. Exp. Biol. Med. 1991, 197,
59. (b) Basak, A.; Cooper, S.; Roberge, A. G.; Banik, U. K.;
Chrétien, M.; Seidah, N. G. Biochem. J. 1999, 338, 107.
(c) Basak, A.; Zhong, M.; Munzer, J. S.; Chrétien, M.;
Seidah, N. G. Biochem. J. 2001, 353, 537.
(22) Typical Procedure.
To a solution of bromofuran 10 (0.720 g, 2.26 mmol) in
anhyd THF (30 mL) stirred at –78 °C under nitrogen was
added n-BuLi (2.5 M in hexane, 1.08 mL, 2.49 mmol). After
30 min at –78 °C, a solution of freshly distilled n-hexanal
(0.450 g, 4.53 mmol) in THF (10 mL) was added dropwise
and the mixture was stirred at –78 °C for 2 h. Then, H2O was
added (150 mL) and the solution was extracted twice with
EtOAc. The combined extracts were washed with H2O, aq
sat. NaCl, dried (Na2SO4) and concentrated in vacuo.
Purification by flash chromatography (95:5:1, hexane–
Et2O–Et3N) afforded furylcarbinol 11a (0.708 g, 92%). All
furylcarbinols 11a–j were obtained as oils and characterized
by 1H NMR, 13C NMR, and HRMS; data for representative
compounds are provided below.
(3) (a) Kitagawa, I.; Simanjuntak, P.; Hori, K.; Nagami, N.;
Mahmud, T.; Shibuya, H.; Kobayashi, M. Chem. Pharm.
Bull. 1994, 42, 1050. (b) The alkylidene geometry of
peronemin D1 has not been assigned.
Data for 11a: 1H NMR (300 MHz, CDCl3): d = 0.87–1.80
(32 H, m), 2.17 (1 H, m), 4.60 (1 H, m), 6.27 (1 H, d, J = 1.9
Hz), 6.76 (1 H, d, J = 1.9 Hz). 13C NMR (75 MHz, CDCl3):
d = 12.0, 14.0, 17.7, 22.7, 25.6, 31.7, 37.4, 65.9, 99.7, 109.7,
131.3, 152.3. HRMS: m/z calcd: 297.1886 [M – C3H7]+;
found: 297.1891.
(4) Yadav, R. D.; Kataky, J. C. S.; Mathur, R. K. Indian J.
Chem., Sect B: Org. Chem. Incl. Med. Chem. 1999, 38, 248.
(5) Janeki, T.; Blaszczyk, E.; Studzian, K.; Janecka, A.;
Krajewska, U.; Rózalski, M. J. Med. Chem. 2005, 48, 3516;
and references therein.
(6) Rao, Y. S. Chem. Rev. 1976, 76, 625.
Data for 11e: 1H NMR (400 MHz, CDCl3): d = 1.07 (18 H,
m), 1.27 (3 H, m), 2.05 (1 H, d, J = 3.0 Hz), 5.75 (1 H, d,
J = 3.0 Hz), 6.12 (1 H, d, J = 2.4 Hz), 6.71 (1 H, d, J = 2.4
Hz), 7.30 (5 H, m). 13C NMR (100 MHz, CDCl3): d = 12.5,
17.8, 67.9, 99.9, 110.5, 126.2, 127.3, 128.5, 131.6, 143.8,
153.5. HRMS: m/z calcd: 346.1964 [M+]; found: 346.1961.
Data for 11f: 1H NMR (400 MHz, CDCl3): d = 1.08 (18 H,
m), 1.27 (3 H, m), 2.17 (1 H, d, J = 3.6 Hz), 3.73 (3 H, s),
5.71 (1 H, s), 6.16 (1 H, d, J = 2.2 Hz), 6.71 (1 H, d, J = 2.2
(7) Shanmugasundaram, M.; Raghunathan, R.; Malar, E. J. P.
Heteroat. Chem. 1998, 9, 517.
(8) Rischmann, M.; Mues, R.; Geiger, H.; Laas, H. J.; Eicher, T.
Phytochemistry 1989, 28, 867.
(9) Egorova, A. Y. Russ. Chem. Bull., Int. Ed. 2002, 51, 183.
(10) Khan, R. H.; Rastogi, R. C. J. Chem. Res., Synop. 1991, 260.
(11) (a) Shurov, S. N.; Zhikina, I. A.; Podvintsev, I. B. Russ. J.
Org. Chem. 2002, 38, 862. (b) See also: Shurov, S. N.;
Zhikina, I. A. Russ. J. Gen. Chem. 2000, 70, 1779.
(12) Nair, V.; Bindu, S.; Sreekumar, V.; Rath, N. P. Org. Lett.
2003, 5, 665.
(13) (a) Huang, Y.; Alper, H. J. Org. Chem. 1991, 56, 4534.
(b) See also: El Ali, B.; Alper, H. Synlett 2000, 161.
(14) Rossi, R.; Bellina, F.; Bechini, C.; Mannina, L.; Vergamini,
P. Tetrahedron 1998, 54, 135.
(15) Lim, S.-G.; Kwon, B.-I.; Choi, M.-G.; Jun, C.-H. Synlett
2005, 1113.
(16) (a) Sigman, M. S.; Kerr, C. E.; Eaton, B. E. J. Am. Chem.
Soc. 1993, 115, 7545. (b) Trifonov, L. S.; Orahovats, A. S.;
Linden, A.; Heimgartner, H. Helv. Chim. Acta 1992, 75,
1872.
Hz), 6.85 (2 H, d, J = 8.4 Hz), 7.31 (2 H, d, J = 8.4 Hz). 13
C
NMR (100 MHz, CDCl3): d = 12.5, 17.8, 55.4, 67.6, 100.1,
110.6, 113.8, 127.5, 131.6, 136.2, 153.3, 158.9. HRMS: m/z
+
calcd: 333.1522 [M – C3H7 ]; found: 333.1518.
Data for 11g: 1H NMR (400 MHz, CDCl3): d = 1.08 (18 H,
m), 1.26 (3 H, m), 2.42 (1 H, br s), 5.81 (1 H, s), 6.04 (1 H,
d, J = 2.2 Hz), 6.71 (1 H, d, J = 2.2 Hz), 7.54 (2 H, d, J = 9.1
Hz), 8.14 (2 H, d, J = 9.1 Hz). 13C NMR (100 MHz, CDCl3):
d = 12.5, 17.8, 67.0, 98.9, 110.0, 123.7, 126.9, 132.1, 147.2,
151.3, 153.8. HRMS: m/z calcd: 392.1893 [MH+]; found:
392.1890.
(23) The E-stereochemistry of compounds 5a–j was determined
by NOESY experiments. The Z-isomers of 5a–c are clearly
distinguished by 1H NMR from their E-isomers by the
upfield shift of the three olefin protons (Dd ca. 0.1–0.3 ppm).
(24) Typical Procedure.
(17) (a) Ochoa de Echagüen, C.; Ortuño, R. M. Tetrahedron
1994, 50, 12457. (b) Grossmann, G.; Poncioni, M.;
Bornand, M.; Jolivet, B.; Neuburger, M.; Séquin, U.
Tetrahedron 2003, 59, 3237. (c) Posner, G. H.; Afarinkia,
K.; Dai, H. Org. Synth. 1995, 73, 231.
To a solution of furylcarbinol 11e (0.190 g, 0.55 mmol) in
anhyd CH2Cl2 (5 mL) stirred at –78 °C under nitrogen was
Synlett 2006, No. 10, 1511–1514 © Thieme Stuttgart · New York

1514
J. Boukouvalas, O. Marion
LETTER
added Et3N (0.056 g, 0.55 mmol) and MsCl (0.063 g, 0.55
mmol). The mixture was stirred at –78 °C for 1 h and TBAF
(1.0 M in THF, 0.55 mL, 0.55 mmol) was added. The
mixture was slowly warmed to r.t. with stirring over 1 h.
Purification by column chromatography (4:1, hexane–Et2O)
provided furanone 5e (0.088 g, 93%).
127.6, 132.4, 137.8, 146.5, 161.9, 170.1. HRMS: m/z calcd:
202.0630 [M+]; found: 202.0624.
Data for 5g: yellow solid, mp 212–213 °C. 1H NMR (400
MHz, CDCl3): d = 6.55 (1 H, dd, J = 3.7, 1.0 Hz), 7.25 (1 H,
dd, J = 3.7, 1.6 Hz), 7.44 (1 H, m), 7.68 (2 H, dd, J = 6.9, 1.6
Hz), 8.28 (2 H, dd, J = 6.9, 1.6 Hz). 13C NMR (100 MHz,
CDCl3): d = 106.0, 124.5, 126.7, 130.7 (2×), 134.1, 140.8,
149.8, 168.5. Anal. Calcd for C12H7NO4: C, 60.83; H, 3.25;
N, 6.45. Found: C, 60.56; H, 3.05; N, 6.38.
Data for 5a: colorless oil. 1H NMR (400 MHz, CDCl3): d =
0.86 (3 H, t, J = 7.1 Hz), 1.28 (4 H, m), 1.48 (2 H, m), 2.31
(2 H, m), 6.12 (1 H, dd, J = 4.0, 1.0 Hz), 6.74 (1 H, m), 6.94
(1 H, m). 13C NMR (100 MHz, CDCl3): d = 14.1, 22.6, 28.3,
30.7, 31.6, 105.4, 126.2, 144.1, 145.4, 168.3. HRMS: m/z
calcd: 166.0994 [M+]; found: 166.0991.
Data for 5h: yellow solid, mp 92–93 °C. 1H NMR (400
MHz, CDCl3): d = 6.55 (1 H, dd, J = 3.5, 0.8 Hz), 7.17 (1 H,
dd, J = 3.5, 1.8), 7.40 (4 H, m), 7.51 (1 H, m). 13C NMR (100
MHz, CDCl3): d = 106.2, 124.6, 128.5, 129.8, 130.6 (2×),
135.3, 135.9, 136.5, 148.3, 169.1. HRMS: m/z calcd:
206.0135 [M+]; found: 206.0129.
Data for 5b: colorless oil. 1H NMR (400 MHz, CDCl3): d =
0.95 (6 H, d, J = 6.8 Hz), 1.85 (1 H, m), 2.24 (2 H, t, J = 6.4
Hz), 6.15 (1 H, dd, J = 3.6, 0.8 Hz), 6.78 (1 H, m). 13C NMR
(100 MHz, CDCl3): d = 22.7, 38.6, 39.7, 105.5, 126.9, 143.0,
145.6, 168.3. HRMS: m/z calcd: 152.0837 [M+]; found:
152.0842.
Data for 5i: yellow solid, mp 222–223 °C. 1H NMR (400
MHz, CDCl3): d = 6.63 (1 H, dd, J = 3.4, 0.8 Hz), 7.15 (1 H,
dd, J = 3.4, 1.8 Hz), 7.44 (4 H, m), 7.64 (6 H, m). 13C NMR
(100 MHz, CDCl3): d = 106.5, 123.1, 127.3, 127.9, 128.4,
129.2, 131.0, 133.8, 137.4, 140.0, 143.5, 147.4, 169.7. Anal.
Calcd for C17H12O2: C, 82.24; H, 4.87. Found: C, 81.97; H,
4.66.
Data for 5c: colorless oil. 1H NMR (400 MHz, CDCl3): d =
1.11 (6 H, d, J = 6.4 Hz), 2.70 (1 H, m), 6.15 (1 H, dd,
J = 3.6, 0.8 Hz), 6.61 (1 H, dq, J = 10.0, 0.8 Hz), 6.97 (1 H,
m). 13C NMR (100 MHz, CDCl3): d = 22.2, 30.5, 105.4,
124.1, 145.4, 150.0, 168.8. HRMS: m/z calcd: 138.0681
[M+]; found: 138.0676.
Data for 5j: yellow solid, mp 191–192 °C (dec.). 1H NMR
(400 MHz, CDCl3): d = 6.55 (1 H, dd, J = 3.4, 1.6 Hz), 6.80
(2 H, m), 7.07 (1 H, dd, J = 3.4, 1.6 Hz), 7.12 (1 H, m), 7.63
(1 H, d, J = 1.6 Hz). 13C NMR (100 MHz, CDCl3): d = 108.1,
113.4, 119.3, 120.3, 122.1, 146.0, 146.8, 151.9, 169.9.
HRMS: m/z calcd: 162.0317 [M+]; found: 162.0322.
(25) Hoffmann, R. W. Chem. Rev. 1989, 89, 1841.
(26) (a) Wollenberg, R. H. Tetrahedron Lett. 1980, 21, 3139.
(b) Tanaka, K.; Terauchi, M.; Kaji, A. Bull. Chem. Soc. Jpn.
1982, 55, 3935. (c) Chen, S.-Y.; Joullié, M. M. Tetrahedron
Lett. 1983, 24, 5027.
(27) For alternative routes to 3-alkenylfuranones, see: (a) Yu,
W.-Y.; Alper, H. J. Org. Chem. 1997, 62, 5684. (b) Dixon,
D. J.; Ley, S. V.; Reynolds, D. J. Angew. Chem. Int. Ed.
2000, 39, 3622. (c) Johansson, M.; Köpcke, B.; Anke, H.;
Sterner, O. Tetrahedron 2002, 58, 2523. (d) Oh, C. H.;
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45, 7039.
Data for 5d: colorless oil. 1H NMR (400 MHz, CDCl3): d =
1.22 (9 H, s), 6.34 (1 H, dd, 3.8, 0.8 Hz), 6.77 (1 H, dd,
J = 1.9, 0.8 Hz), 6.99 (1 H, dd, J = 3.8, 1.9 Hz). 13C NMR
(100 MHz, CDCl3): d = 29.9, 35.6, 105.8, 122.4, 145.4,
153.7, 169.9. HRMS: m/z calcd: 152.0837 [M+]; found:
152.0833.
Data for 5e: yellow solid, mp 190–192 °C. 1H NMR (400
MHz, CDCl3): d = 6.58 (1 H, dd, J = 3.6, 1.0 Hz), 7.12 (1 H,
dd, J = 3.6, 2.0 Hz), 7.43 (4 H, m), 7.53 (2 H, m). 13C NMR
(100 MHz, CDCl3): d = 106.4, 123.3, 129.3, 130.4, 130.8,
134.8, 137.9, 147.5, 169.6. HRMS: m/z calcd: 172.0524
[M+]; found: 172.0519.
Data for 5f: yellow solid, mp 129–130 °C. 1H NMR (400
MHz, CDCl3): d = 3.83 (3 H, s), 6.55 (1 H, dd, J = 3.4, 0.8
Hz), 6.92 (2 H, dd, J = 7.0, 1.8 Hz), 7.08 (1 H, dd, J = 3.4,
2.0 Hz), 7.37 (1 H, m), 7.51 (2 H, dd, J = 7.0, 2.0 Hz).
13C NMR (100 MHz, CDCl3): d = 55.7, 106.4, 114.9, 120.7,
Synlett 2006, No. 10, 1511–1514 © Thieme Stuttgart · New York