Rhodium-catalyzed decarboxylative and dehydrogenative coupling of maleic acids with alkynes and alkenes

Article abstract of DOI:10.1021/jo401992d

The dehydrogenative coupling of maleic acids with alkynes proceeds smoothly accompanied by decarboxylation under rhodium catalysis to produce variously substituted α-pyrone derivatives. The catalyst system is also applicable to the coupling with 1,3-diyne

Full text of DOI:10.1021/jo401992d

Article
pubs.acs.org/joc
Rhodium-Catalyzed Decarboxylative and Dehydrogenative Coupling
of Maleic Acids with Alkynes and Alkenes
Masaki Itoh,† Masaki Shimizu,† Koji Hirano,† Tetsuya Satoh,*,†,‡ and Masahiro Miura*,†
†Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
‡JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
S
* Supporting Information
ABSTRACT: The dehydrogenative coupling of maleic acids
with alkynes proceeds smoothly accompanied by decarbox-
ylation under rhodium catalysis to produce variously
substituted α-pyrone derivatives. The catalyst system is also
applicable to the coupling with 1,3-diynes and alkenes.
Scheme 1. Dehydrogenative Coupling of Acrylic and Maleic
Acids with Alkynes and Alkenes
INTRODUCTION
■
α-Pyrones with various substitution patterns are found in a
wide range of natural products and in a number of
pharmacologically active compounds.1 Therefore, development
of methods for the selective syntheses of the family of α-
pyrones has attracted much attention. As one of the step-
economical synthetic routes to them, we developed the
rhodium-catalyzed dehydrogenative coupling of substituted
acrylic acids with internal alkynes.2 Thus, 2-substituted acrylic
acids such as methacrylic acid underwent the coupling
smoothly to produce 3,5,6-trisubstituted α-pyrones. However,
the reaction of acrylic acid itself did not proceed efficiently even
with an increased rhodium loading, giving the corresponding
5,6-disubstituted α-pyrone in a moderate yield. Such 5,6-
disubstituted3 as well as 6-monosubstituted α-pyrones4 are of
particular importance because of their androgen-like and
antifungal activities, respectively. In the context of our studies
on the rhodium-catalyzed dehydrogenative coupling of
carboxylic acids,5,6 we found that the 3-unsubstituted α-pyrones
can be synthesized in good yields by using maleic acid in place
of acrylic acid (Scheme 1). Since maleic acids are comparably
cheap, readily available build blocks,7 we investigated their
decarboxylative coupling8 further. Consequently, it was found
that the couplings of acrylate esters and relevant alkenes
selectively give acyclic products, dienoic acids, rather than cyclic
butenolides, which are obtained in the reaction of 2-substituted
acrylic acids.2 The results obtained with respect to these
reactions are described herein.
5,6-diphenyl-2H-pyran-2-one (3a) in a moderate yield (entry 1
in Table 1). In contrast, maleic acid (1b) reacted with 2a
efficiently accompanied by decarboxylation to afford 3a almost
quantitatively (entry 2). At 100 °C, both the reaction rate and
the product yield decreased considerably (entry 3). In the
presence of Cu(OAc)2·H2O (1 mmol) as an oxidant in place of
Ag2CO3, the yield of 3a was low (entry 4).
Next, we examined the reactions of 1b with various alkynes
2. Under the conditions employed for entry 2 in Table 1, 1b
coupled with para-substituted diphenylacetylene 2b−d to form
the corresponding pyrones 3b−d in 84−96% yields (entries 1−
3 in Table 2). The reactions with di(2-thienyl)acetylene (2e),
4-octyne (2f), and 8-hexadecyne (2g) also proceeded smoothly
to give 5,6-dithienyl- (3e) and 5,6-dialkyl-α-pyrones 3f,g in
RESULTS AND DISCUSSION
■
Under similar conditions to those for the reaction of
methacrylic acid with alkynes in our previous work using 1
mol % of [Cp*RhCl2]2 and 1 equiv of Ag2CO3 in DMF at 120
°C,2 the reaction of acrylic acid (1a) (0.5 mmol) with
diphenylacetylene (2a) (0.5 mmol) was sluggish to produce
Received: September 9, 2013
Published: October 15, 2013
© 2013 American Chemical Society
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a
Table 1. Reaction of Acrylic- or Maleic Acid 1 with
Diphenylacetylene (2a)
Table 2. Reaction of Acid 1 with Alkynes 2
a
entry
1
temp (°C)
time (h)
yield of 3a (%)
b
1
2
3
1a
1b
1b
1b
120
120
100
160
4
39 (44)
b
2
97 (98)
b
10
6
(70)
c
b
4
(29)
a
Reaction conditions: 1 (0.5 mmol), 2a (0.5 mmol), [Cp*RhCl2]2
b
(0.005 mmol), Ag2CO3 (0.5 mmol), DMF (2.5 mL) under N2. GC
yield. Cu(OAc)2·H2O (1 mmol) was used in place of Ag2CO3.
c
good yields (entries 4−6). Unsymmetrical alkylphenylacety-
lenes 2h and 2i coupled with 1b to form 5-alkyl-6-phenyl-α-
pyrones 3h and 3i predominantly, along with minor amounts of
separable regioisomers 3h′ and 3i′ (entries 7 and 8). The
reaction of ethyl phenylpropiolate (2j) required a higher
temperature (140 °C), which resulted in a lower regioselectivity
(entry 9). In contrast, the reaction with 2-methyl-4-phenylbut-
3-yn-2-ol (2k) gave 3k exclusively, with no other isomer being
detected by GC and GC-MS (entry 10). In the reaction of 2-
methylmaleic acid (1c) with 2a, regioselective decarboxylation
took place efficiently to afford 3l in 90% yield (entry 11). 2-
Phenylmaleic acid (1d) also reacted with a series of
diarylacetylenes 2a,c-f to selectively produce 3,5,6-triaryl-α-
pyrones 3m−q in 78−98% yields (entries 12−16). The
electron-withdrawing groups in 2 tend to retard the reaction.
A possible mechanism for the coupling of maleic acids 1 with
2 is illustrated in Scheme 2, in which neutral ligands are
omitted. Coordination of the carboxyl oxygen atoms of 1 to a
Cp*Rh(III)X2 species gives a rhodium(III) dicarboxylate A.
Subsequent decarboxylation to form a five-membered rhoda-
cycle B, alkyne insertion to give C, and reductive elimination
take place to produce 3. The resulting Cp*Rh(I) species may
be oxidized in the presence of Ag2CO3 to regenerate
Cp*Rh(III)X2. In the cases using 2-substituted maleic acids,
the decarboxylation takes place at the C3-position to selectively
form B rather than B′. The reason for the facile formation of B
is not clear at the present stage. In addition, it is possible that
the decarboxylation is induced by the silver salt rather than Rh.9
However, it was confirmed that the decarboxylation of 1d (R1 =
Ph) did not proceed at all by treatment with Ag2CO3 in the
absence of [Cp*RhCl2]2. Thus, under conditions using 1 equiv
of Ag2CO3 in DMF at 120 °C, 1d was quantitatively recovered.
In contrast to reactive internal alkynes 2, terminal alkynes
could not be employed for the reaction.10 Actually, treatment of
1b with phenylacetylene did not give desired 6-phenyl-α-
pyrone at all. However, the monosubstituted α-pyrone could be
prepared via (1) the coupling of 1b with 2k and (2) the
palladium-catalyzed deprotection (Scheme 3).11 Thus, treat-
ment of 3k (0.2 mmol), formed in entry 10 in Table 2, by using
a
Reaction conditions: 1 (0.5 mmol), 2 (0.5 mmol), [Cp*RhCl2]2
(0.005 mmol), Ag2CO3 (0.5 mmol) in DMF (2.5 mL) at 120 °C
b
c
under N2 for 2 h. An isomer 3h′ (1%) was also formed. An isomer
d
e
3i′ (7%) was also formed. At 140 °C for 4 h. Isomer 3j′ (10%) was
f
g
h
i
also formed. For 8 h. For 4 h. For 24 h. For 72 h.
Pd(OAc)2 (10 mol %), P(1-naphthyl)3 (20 mol %),
bromobenzene (20 mol %), and Cs2CO3 (20 mol %) in
refluxing o-xylene for 16 h gave 6-phenyl-α-pyrone (4) in 80%
yield.
It was found that not only monoynes 2 but also 1,3-diynes 5
react with 1b to furnish 6H,6′H-[2,2′-bipyran]-6,6′-dione
frameworks. Under the standard conditions, 1b coupled with
octa-3,5-diyne (5a) in a 2:1 manner to form 6a in 54% yield
(Scheme 4). At 140 °C, the reaction was completed within 2 h
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a
Scheme 2. Possible Mechanism for the Reaction of 1a with 2
Table 3. Reaction of Maleic Acids 1 with Alkenes 2
Scheme 3. Deprotection of 3k
and the yield of 6a was enhanced to 86% yield. Similarly, the
reaction with deca-4,6-diyne (5b) gave 6b in 84% yield.
Scheme 4. Reaction of 1b with 1,3-Diynes 5
a
Reaction conditions: (1) 1 (0.5 mmol), 7 (1 mmol), [Cp*RhCl2]2
(0.01 mmol), Ag2CO3 (0.5 mmol) in DMF (2.5 mL) under N2 at 140
°C under N2 for 1 h; (2) with the addition of R3I (2.5 mmol) and
b
K2CO3 (1.5 mmol) at rt for 3 h. With [Cp*RhCl2]2 (0.005 mmol)
c
d
e
for 6 h. Cy = cyclohexyl. With 7 (2.5 mmol) for 2 h. Nap =
naphthyl.
Finally, we examined the decarboxylative coupling of maleic
acids 1 with alkenes 7. First, 1b (0.5 mmol) was treated with
butyl acrylate (7a) (1 mmol) in the presence of [Cp*RhCl2]2
(1 mol %) and Ag2CO3 (1 equiv) in DMF at 140 °C. After 1 h,
GC and GC-MS analyses of the resulting mixture did not show
any coupling/cyclization product including a butenolide, which
was formed in the reaction of 2-substituted acrylic acids with 7a
(Scheme 1).2 Instead, after esterification using MeI (5 equiv)
and K2CO3 (3 equiv) at rt for 3 h for quantification, 1-n-butyl
6-methyl hexa-2,4-dienedioate (8a) was obtained as a mixture
of two geometric isomers in 57% yield (entry 1 in Table 3). At
the present stage, however, the reason the acyclic product was
selectively formed involving partial 2E−2Z isomerization is
obscure. Increasing the Rh-catalyst loading (2 mol %)
somewhat improved the yield of 8a (entry 2). The ratio of
geometric isomers was determined to be (2E,4E):(2Z,4E) =
1.1:1. Similarly, a di-n-butyl ester 8b was obtained by using n-
BuI in the esterification step after the coupling (entry 3). The
coupling of 1b with ethyl acrylate (7b) and subsequent
esterification with EtI gave diethyl ester 8c in 71% yield (entry
4). Cyclohexyl (7c) and t-butyl acrylate (7d) also underwent
the reaction to produce the corresponding hexadienedioates 8d
and 8e in 80% and 77% yields, respectively (entries 5 and 6).
Not only acrylates but also N-t-butylacrylamide (7e), styrene
(7f), and 2-vinylnaphthalene (7g) coupled with 1b (entries 7−
9). The reaction of 1c with 7a gave the corresponding (2Z,4E)-
hexa-2,4-dienedioate 8i almost exclusively (entry 10). The
methyl group in 1c seems to suppress 2E−2Z isomerization
because of steric reasons.
CONCLUSIONS
■
We have demonstrated that the decarboxylative and dehydro-
genative coupling of maleic acids with alkynes and alkenes can
be performed efficiently under rhodium catalysis. The
procedure provides simple synthetic routes to α-pyrones and
dienoic acid derivatives.
EXPERIMENTAL SECTION
■
General. H and 13C NMR spectra were recorded at 400 and 100
1
MHz for CDCl3 solutions. HRMS data were obtained by EI using a
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double focusing mass spectrometer, unless noted. GC analysis was
carried out using a silicon OV-17 column (i.d. 2.6 mm × 1.5 m). GC-
MS analysis was carried out using a CBP-1 capillary column (i.d. 0.25
mm × 25 m). The structures of all products listed below were
unambiguously determined by 1H and 13C NMR with the aid of NOE,
COSY, HMQC, and HMBC experiments.
Diarylacetylenes 2b-e were prepared according to published
procedures.12 All starting materials and reagents were commercially
available.
General Procedure for the Reaction of Maleic Acids with
Alkynes. To a 20 mL two-necked flask with a reflux condenser, a
balloon, and a rubber cup were added maleic acid 1 (0.5 mmol),
alkyne 2 (0.5 mmol), [(Cp*RhCl2)2] (0.005 mmol, 3 mg), Ag2CO3
(0.5 mmol, 138 mg), 1-methylnaphthalene (ca. 40 mg) as internal
standard, and DMF (2.5 mL). Then, the resulting mixture was stirred
under nitrogen at 120 °C for 2 h. After cooling, the reaction mixture
was extracted with ethyl acetate (100 mL). The organic layer was
washed by water (100 mL, three times), and dried over Na2SO4. After
evaporation of the solvent under vacuum, product 3 was isolated by
column chromatography on silica gel using hexane−ethyl acetate
(10:1, v/v) as eluant.
hexane−ethyl acetate; 1H NMR (400 MHz, CDCl3) δ 6.24 (d, J = 9.2
Hz, 1H), 6.98 (dd, J = 3.9, 5.0 Hz, 1H), 7.08 (dd, J = 1.3, 3.5 Hz, 1H),
7.14 (dd, J = 3.6, 5.1 Hz, 1H), 7.34 (d, J = 9.5 Hz, 1H), 7.37 (dd, J =
1.1, 5.1 Hz, 1H), 7.41 (dd, J = 1.3, 3.9 Hz, 1H), 7.50 (dd, J = 1.3, 5.3
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 108.9, 112.3, 127.3, 128.0,
128.1, 129.1, 130.5, 130.7, 133.8, 135.9, 147.9, 154.6, 160.6; MS m/z
260 (M+). Anal. Calcd for C13H8O2S2: C, 59.98; H, 3.10. Found: C,
59.93; H, 3.10.
5,6-Di(n-propyl)-2(2H)-pyran-2-one (3f).13 Oil, 77 mg (85%);
hexane−ethyl acetate 90:10 (v/v, eluent); 1H NMR (400 MHz,
CDCl3) δ 0.93−0.99 (m, 6H), 1.46−1.56 (m, 2H), 1.65−1.75 (m,
2H), 2.28 (t, J = 7.7 Hz, 2H), 2.48 (t, J = 7.5 Hz, 2H), 6.14 (d, J = 9.5
Hz, 1H), 7.17 (d, J = 9.5 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
13.6, 13.7, 21.0, 23.3, 31.1, 32.5, 113.3, 115.0, 147.0, 161.8, 162.9;
HRMS m/z Calcd for C11H16O2 (M+) 180.1150, found 180.1157.
5,6-Di(n-heptyl)-2(2H)-pyran-2-one (3g). Oil, 130 mg (89%);
hexane−ethyl acetate 90:10 (v/v, eluent); 1H NMR (400 MHz,
CDCl3) δ 0.87−0.91 (m, 6H), 1.28−1.32 (m, 16H), 1.44−1.48 (m,
2H), 1.60−1.67 (m, 2H), 2.28 (t, J = 7.7 Hz, 2H), 2.48 (t, J = 7.7 Hz,
2H), 6.14 (d, J = 9.2 Hz, 1H), 7.16 (d, J = 9.2 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 14.0 (overlapped), 22.6 (overlapped), 27.6, 29.0,
29.06, 29.09, 29.2, 29.3, 30.2, 30.8, 31.67, 31.72, 113.3, 115.1, 147.0,
161.9, 163.0; MS m/z 292 (M+). Anal. Calcd for C19H32O2: C, 78.03;
H, 11.03. Found: C, 77.82; H, 10.74.
General Procedure for the Reaction of Maleic Acids with
Alkenes. To a 20 mL two-necked flask with a reflux condenser, a
balloon, and a rubber cup were added maleic acid 1 (0.5 mmol),
alkene 7 (1−2.5 mmol), [(Cp*RhCl2)2] (0.01 mmol, 6 mg), Ag2CO3
(0.5 mmol, 138 mg), 1-methylnaphthalene (ca. 40 mg) as internal
standard, and DMF (2.5 mL). Then, the resulting mixture was stirred
under nitrogen at 140 °C for 1−2 h. After cooling, alkyliodide (2.5
mmol) and K2CO3 (1.5 mmol, 207 mg) were added and the resulting
mixture was stirred under air at room temperature for 3 h. GC and
GC-MS analyses of the mixtures confirmed formation of 8. Then, the
reaction mixture was extracted with ethyl acetate (100 mL). The
organic layer was washed by water (100 mL, three times) and dried
over Na2SO4. After evaporation of the solvent under vacuum, product
8 was isolated by column chromatography on silica gel using hexane−
ethyl acetate (10:1, v/v) as eluant.
5-Methyl-6-phenyl-2(2H)-pyran-2-one (3h).14 Mp 102−108 °C
(white solid), 68 mg (73%); hexane−ethyl acetate 85:15 (v/v, eluent);
1H NMR (400 MHz, CDCl3) δ 2.17 (s, 3H), 6.28 (d, J = 9.5 Hz, 1H),
7.30 (d, J = 9.5 Hz, 1H), 7.44−7.48 (m, 3H), 7.57−7.59 (m, 2H); 13
C
NMR (100 MHz, CDCl3) δ 16.7, 111.2, 114.4, 128.3, 128.7, 129.8,
132.5, 148.4, 157.6, 162.2; HRMS m/z Calcd for C12H10O2 (M+)
186.0681, found 186.0685.
6-Methyl-5-phenyl-2(2H)-pyran-2-one (3h′).15 Oil, 1.3 mg (1%);
hexane−ethyl acetate 85:15 (v/v, eluent); 1H NMR (400 MHz,
CDCl3) δ 2.27 (s, 3H), 6.25 (d, J = 9.2 Hz, 1H), 7.24−7.26 (m, 2H),
7.34 (d, J = 9.5 Hz, 1H), 7.35−7.45 (m, 3H); 13C NMR (100 MHz,
CDCl3) δ 18.5, 113.2, 117.9, 127.9, 128.8 (overlapped), 135.8, 146.7,
159.5, 162.2; HRMS m/z Calcd for C12H10O2 (M+) 186.0681, found
186.0685.
5,6-Diphenyl-2(2H)-pyran-2-one (3a).2 Mp 85−88 °C (yellow
1
solid), 120 mg (97%); hexane−ethyl acetate 90:10 (v/v, eluent); H
5-(n-Butyl)-6-phenyl-2(2H)-pyran-2-one (3i).3a Oil, 86 mg (75%);
hexane−ethyl acetate 90:10 (v/v, eluent); 1H NMR (400 MHz,
CDCl3) δ 0.88 (t, J = 7.4 Hz, 3H), 1.27−1.36 (m, 2H), 1.48−1.56 (m,
2H), 2.43 (t, J = 7.9 Hz, 2H), 6.31 (d, J = 9.6 Hz, 1H), 7.35 (d, J = 9.5
Hz, 1H), 7.44−7.46 (m, 3H), 7.51−7.54 (m, 2H); 13C NMR (100
MHz, CDCl3) δ 13.7, 22.2, 29.1, 32.2, 114.7, 116.2, 128.4, 128.7,
129.8, 132.5, 147.0, 158.0, 162.2; HRMS m/z Calcd for C15H16O2
(M+) 228.1150, found 228.1153.
6-(n-Butyl)-5-phenyl-2(2H)-pyran-2-one (3i′). Oil, 8.4 mg (7%);
hexane−ethyl acetate 90:10 (v/v, eluent); 1H NMR (400 MHz,
CDCl3) δ 0.84 (t, J = 7.4 Hz, 3H), 1.24−1.33 (m, 2H), 1.63−1.70 (m,
2H), 2.51 (t, J = 7.7 Hz, 2H), 6.23 (d, J = 9.2 Hz, 1H), 7.22−7.25 (m,
2H), 7.30 (d, J = 9.6 Hz, 1H), 7.35−7.45 (m, 3H); 13C NMR (100
MHz, CDCl3) δ 13.6, 22.3, 29.7, 31.2, 113.0, 117.9, 127.9, 128.8,
128.9, 136.0, 146.9, 162.5, 163.2; HRMS m/z Calcd for C15H16O2
(M+) 228.1150, found 228.1152.
NMR (400 MHz, CDCl3) δ 6.37 (d, J = 9.6 Hz, 1H), 7.15−7.38 (m,
10H), 7.46 (d, J = 9.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 114.0,
117.8, 127.9, 128.1, 128.9, 129.1, 129.2, 129.9, 132.0, 136.2, 147.8,
158.0, 161.7; HRMS m/z Calcd for C17H12O2 (M+) 248.0837, found
248.0840.
5,6-Bis(4-methylphenyl)-2(2H)-pyran-2-one (3b). Mp 113−115
°C (pale yellow solid), 120 mg (87%); hexane−ethyl acetate 90:10 (v/
v, eluent); 1H NMR (400 MHz, CDCl3) δ 2.31 (s, 3H), 2.35 (s, 3H),
6.32 (d, J = 9.2 Hz, 1H), 7.03−7.07 (m, 4H), 7.13 (d, J = 8.4 Hz, 2H),
7.27 (d, J = 8.1 Hz, 2H), 7.42 (d, J = 9.5 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ 21.2, 21.4, 113.6, 117.4, 128.9, 129.0, 129.1, 129.3,
129.7, 133.4, 137.7, 140.2, 148.1, 158.1, 162.0; MS m/z 276 (M+).
Anal. Calcd for C19H16O2: C, 82.58; H, 5.84. Found: C, 82.36; H, 5.91.
5,6-Bis(4-methoxyphenyl)-2(2H)-pyran-2-one (3c). Mp 135−136
°C (yellow solid), 148 mg (96%); hexane−ethyl acetate 85:15 (v/v,
1
eluent); H NMR (400 MHz, CDCl3) δ 3.79 (s, 3H), 3.82 (s, 3H),
6.29 (d, J = 9.2 Hz, 1H), 6.75 (d, J = 8.8 Hz, 2H), 6.86 (d, J = 8.8 Hz,
2H), 7.10 (d, J = 8.4 Hz, 2H), 7.33 (d, J = 9.2 Hz, 2H), 7.41 (d, J = 9.5
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 55.3 (overlapped), 113.0,
113.6, 114.5, 116.5, 124.6, 128.7, 130.3, 130.7, 148.3, 157.8, 159.2,
160.7, 162.1; MS m/z 308 (M+). Anal. Calcd for C19H16O4: C, 74.01;
H, 5.23. Found: C, 73.87; H, 5.16.
5,6-Bis(4-chlorophenyl)-2(2H)-pyran-2-one (3d). Mp 133−136 °C
(yellow solid), 133 mg (84%); hexane−ethyl acetate 85:15 (v/v,
eluent); 1H NMR (400 MHz, CDCl3) δ 6.39 (d, J = 9.5 Hz, 1H), 7.11
(d, J = 8.8 Hz, 2H), 7.24−7.33 (m, 6H), 7.41 (d, J = 9.5 Hz, 1H); 13C
NMR (100 MHz, CDCl3) δ 114.6, 116.9, 128.7, 129.4, 130.2, 130.4,
130.5, 134.3, 134.4, 136.4, 147.2, 157.0, 161.2; MS m/z 316, 318, 320
(M+). Anal. Calcd for C17H10Cl2O2: C, 64.38; H, 3.18; Cl, 22.36.
Found: C, 64.36; H, 3.25; Cl, 22.10.
Ethyl 2-Oxo-6-phenyl-2H-pyran-5-calboxylate (3j). Oil, 49 mg
(40%); hexane−ethyl acetate 90:10 (v/v, eluent); 1H NMR (400
MHz, CDCl3) δ 1.09 (t, J = 7.1 Hz, 3H), 4.15 (q, J = 7.1 Hz, 2H), 6.33
(d, J = 9.9 Hz, 1H), 7.43−7.56 (m, 5H), 7.85 (d, J = 9.5 Hz, 1H); 13C
NMR (100 MHz, CDCl3) δ 13.7, 61.5, 109.9, 113.3, 128.0, 129.0,
131.1, 132.3, 144.2, 160.3, 164.6, 167.2; MS m/z 244 (M+). Anal.
Calcd for C14H12O4: C, 68.85; H, 4.95. Found: C, 68.57; H, 4.97.
Ethyl 2-Oxo-5-phenyl-2H-pyran-6-calboxylate (3j′). Oil, 12 mg
(10%); hexane−ethyl acetate 90:10 (v/v, eluent); 1H NMR (400
MHz, CDCl3) δ 1.14 (t, J = 7.1 Hz, 3H), 4.18 (q, J = 7.2 Hz, 2H), 6.55
(d, J = 9.5 Hz, 1H), 7.25−7.27 (m, 2H), 7.38 (d, J = 9.5 Hz, 1H),
7.41−7.44 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 13.7, 62.2, 119.2,
123.9, 128.3, 128.5, 128.6, 134.7, 146.50, 146.54, 159.3, 159.9; HRMS
m/z Calcd for C14H12O4 (M+) 244.0736, found 244.0742.
5,6-Di(2-thienyl)-2(2H)-pyran-2-one (3e). Mp 152−155 °C
(brown solid), 108 mg (83%); purified by recrystallization with
5-(2-Hydroxypropan-2-yl)-6-phenyl-2(2H)-pyran-2-one (3k). Mp
83−84 °C (white solid), 67 mg (58%); hexane−ethyl acetate 50:50
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(v/v, eluent); H NMR (400 MHz, CDCl3) δ 1.33 (s, 6H), 2.25 (s,
3,3′-Dipropyl-6H,6′H-[2,2′-bipyran]-6,6′-dione (6b). Mp 59−60
°C (yellow solid), 115 mg (84%); hexane−ethyl acetate 50:50 (v/v,
eluent); 1H NMR (400 MHz, CDCl3) δ 0.94 (t, J = 7.3 Hz, 6H), 1.59
(tq, J = 7.3, 7.3 Hz, 4H), 2.34 (t, J = 7.3 Hz, 4H), 6.41 (d, J = 9.6 Hz,
2H), 7.35 (d, J = 9.6 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 13.5,
22.5, 31.1, 117.7, 120.6, 146.0, 148.4, 160.3; HRMS m/z Calcd for
C16H18O4 (M+) 274.1205, found 274.1206.
1-(n-Butyl) 6-Methyl hexa-2,4-dienedioate [(2E,4E):(2Z,4E) =
1.1:1] (8a). 72 mg (68%); hexane−ethyl acetate 90:10 (v/v, eluent);
1H NMR (400 MHz, CDCl3) δ 0.96−1.01 (m, 3H), 1.41−1.50 (m,
1H), 6.29 (d, J = 10.0 Hz, 1H), 7.37−7.46 (m, 5H), 7.80 (d, J = 10.0
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 31.5, 70.6, 114.4, 124.2,
128.1, 129.1, 129.8, 134.2, 145.2, 157.8, 161.9; HRMS m/z Calcd for
C14H14O3 (M+) 230.0943, found 230.0942.
3-Methyl-5,6-diphenyl-2(2H)-pyran-2-one (3l).2 Mp 127−128 °C
(yellow solid), 118 mg (90%); hexane−ethyl acetate 90:10 (v/v,
1
eluent); H NMR (400 MHz, CDCl3) δ 2.19 (d, J = 1.1 Hz, 3H),
7.16−7.35 (m, 11H); 13C NMR (100 MHz, CDCl3) δ 16.4, 117.9,
123.7, 127.7, 128.0, 128.8, 129.0, 129.2, 129.5, 132.2, 136.5, 143.9,
155.3, 163.0; HRMS m/z Calcd for C18H14O2 (M+) 262.0994, found
262.0990.
2H), 1.68−1.74 (m, 2H), 3.82 (s, 3H), 4.21−4.24 (m, 2H), 6.01 (d, J
= 10.5 Hz, 1H, 2Z,4E), 6.15 (d, J = 15.6 Hz, 1H, 2Z,4E), 6.23−6.26
(m, 2H, 2E,4E), 6.69 (t, J = 11.5 Hz, 1H, 2Z,4E), 7.32−7.37 (m, 2H,
2E,4E), 8.41 (dd, J = 11.9, 15.6 Hz, 1H, 2Z,4E); 13C NMR (100 MHz,
CDCl3) δ 13.6, 13.7, 19.07, 19.12, 30.57, 30.59, 51.6, 51.9, 64.6, 64.7,
124.1, 127.8, 128.6, 129.2, 138.3, 140.6, 140.7, 141.0, 165.7, 165.9,
166.1, 166.3; HRMS m/z Calcd for C11H16O4 (M+) 212.1049, found
212.1050.
3,5,6-Triphenyl-2(2H)-pyran-2-one (3m).2 Mp 141−143 °C
(yellow solid), 154 mg (95%); hexane−ethyl acetate 90:10 (v/v,
eluent); 1H NMR (400 MHz, CDCl3) δ 7.20−7.42 (m, 13H), 7.59 (s,
1H), 7.75 (d, J = 7.0 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 118.5,
125.4, 127.9, 128.06, 128.13, 128.4, 128.5, 128.9, 129.07, 129.14,
129.8, 131.8, 134.3, 136.3, 144.2, 156.6, 161.1; HRMS m/z Calcd for
C23H16O2 (M+) 324.1150, found 324.1149.
Di(n-Butyl) Hexa-2,4-dienedioate [(2E,4E):(2Z,4E) = 1.1:1] (8b).16
1
5,6-Bis(4-methoxyphenyl)-3-phenyl-2(2H)-pyran-2-one (3n). Mp
157−158 °C (yellow solid), 184 mg (96%); hexane−ethyl acetate
75:25 (v/v, eluent); 1H NMR (400 MHz, CDCl3) δ 3.77 (s, 3H), 3.80
(s, 3H), 6.75 (d, J = 9.2 Hz, 2H) 6.88 (d, J = 8.7 Hz, 2H), 7.16 (d, J =
8.7 Hz, 2H), 7.34−7.42 (m, 5H), 7.56 (s, 1H), 7.74 (d, J = 6.9 Hz,
2H); 13C NMR (100 MHz, CDCl3) δ 55.2 (overlapped), 113.5, 114.4,
117.1, 124.29, 124.33, 128.1, 128.29, 128.34, 128.8, 130.3, 130.6,
134.5, 144.9, 156.4, 159.1, 160.6, 161.4; HRMS m/z Calcd for
C25H20O4 (M+) 384.1362, found 384.1360.
90 mg (71%); hexane−ethyl acetate 90:10 (v/v, eluent); H NMR
(400 MHz, CDCl3) δ 0.93−0.98 (m, 6H), 1.37−1.46 (m, 4H), 1.63−
1.71 (m, 4H), 4.17−4.20 (m, 4H), 5.96 (d, J = 11.5 Hz, 1H, 2Z,4E),
6.11 (d, J = 15.6 Hz, 1H, 2Z,4E), 6.21 (dd, J = 3.2, 11.5 Hz, 2H,
2E,4E), 6.64 (t, J = 11.5 Hz, 1H, 2Z,4E), 7.31 (dd, J = 3.2, 11.5 Hz,
2H, 2E,4E), 8.39 (dd, J = 11.5, 15.6 Hz, 1H, 2Z,4E); 13C NMR (100
MHz, CDCl3) δ 13.6 (2E,4E, 2Z,4E), 19.05 (2E,4E), 19.09 (2Z,4E),
30.51 (2Z,4E), 30.54 (2E,4E), 30.6 (2Z,4E), 64.5 (2Z,4E), 64.6
(2Z,4E), 64.7 (2E,4E), 124.6 (2Z,4E), 128.3 (2E,4E), 129.0 (2Z,4E),
138.4 (2Z,4E), 140.3 (2Z,4E), 140.7 (2E,4E), 165.4 (2Z,4E), 166.0
(2E,4E), 166.1 (2Z,4E); HRMS m/z Calcd for C14H22O4 (M+)
254.1518, found 254.1517.
5,6-Bis(4-chlorophenyl)-3-phenyl-2(2H)-pyran-2-one (3o). Mp
150−151 °C (yellow solid), 186 mg (95%); hexane−ethyl acetate
90:10 (v/v, eluent); H NMR (400 MHz, CDCl3) δ 7.17 (d, J = 8.2
1
Hz, 2H), 7.24 (d, J = 8.7 Hz, 2H), 7.32 (d, J = 8.7 Hz, 2H), 7.33 (d, J
= 8.2 Hz, 2H), 7.36−7.44 (m, 3H), 7.53 (s, 1H), 7.72 (d, J = 6.9 Hz,
2H); 13C NMR (100 MHz, CDCl3) δ 117.6, 126.0, 128.1, 128.5,
128.6, 128.8, 129.4, 129.9, 130.3, 130.4, 134.0, 134.2, 134.4, 136.2,
143.5, 155.5, 160.7; HRMS m/z Calcd for C23H14Cl2O2 (M+)
392.0371, found 392.0369.
5,6-Bis[4-(tert-butyl)phenyl]-3-phenyl-2(2H)-pyran-2-one (3p).
Mp 185−186 °C (yellow solid), 214 mg (98%); hexane−ethyl acetate
90:10 (v/v, eluent); 1H NMR (400 MHz, CDCl3) δ 1.28 (s, 9H), 1.34
(s, 9H), 7.19 (d, J = 8.2 Hz, 2H), 7.25 (d, J = 8.7 Hz, 2H), 7.34−7.41
(m, 7H), 7.58 (s, 1H), 7.74 (d, J = 6.9 Hz, 2H); 13C NMR (100 MHz,
CDCl3) δ 31.0, 31.2, 34.6, 34.7, 118.0, 124.8, 125.0, 125.9, 128.1,
128.36, 128.38, 128.7, 128.8, 129.0, 133.5, 134.5, 144.9, 150.9, 153.2,
156.6, 161.3; HRMS m/z Calcd for C31H32O2 (M+) 436.2402, found
436.2404.
3-Phenyl-5,6-bis[4-(trifluoromethyl)phenyl]-2(2H)-pyran-2-one
(3q). Mp 65−66 °C (yellow solid), 179 mg (78%); hexane−ethyl
acetate 85:15 (v/v, eluent); 1H NMR (400 MHz, CDCl3) δ 7.38−7.47
(m, 5H), 7.51 (d, J = 8.7 Hz, 2H), 7.55 (d, J = 8.7 Hz, 2H), 7.58 (s,
1H), 7.64 (d, J = 8.2 Hz, 2H), 7.75 (dd, J = 1.4, 8.2 Hz, 2H); 13C
NMR (100 MHz, CDCl3) δ 118.3, 123.5 (q, J = 272.2 Hz), 123.8 (q, J
= 272.2 Hz), 125.4 (q, J = 3.8 Hz), 126.2 (q, J = 3.8 Hz), 127.0, 128.2,
128.6, 129.1, 129.5, 129.6, 130.5 (q, J = 32.6 Hz), 131.9 (q, J = 32.6
Hz), 133.8, 134.8, 139.5, 143.0, 155.3, 160.4; HRMS m/z Calcd for
C25H14F6O2 (M+) 460.0898, found 460.0901.
Diethyl Hexa-2,4-dienedioate [(2E,4E):(2Z,4E) = 1.4:1] (8c).17 70
1
mg (71%); hexane−ethyl acetate 90:10 (v/v, eluent); H NMR (400
MHz, CDCl3) δ 1.30−1.35 (m, 6H), 4.22−4.27 (m, 4H), 5.96 (d, J =
11.5 Hz, 1H, 2Z,4E), 6.10 (d, J = 15.6 Hz, 1H, 2Z,4E), 6.20 (dd, J =
3.2, 11.5 Hz, 2H, 2E,4E), 6.64 (t, J = 11.5 Hz, 1H, 2Z,4E), 7.32 (dd, J
= 3.2, 11.5 Hz, 2H, 2E,4E), 8.40 (dd, J = 11.5, 15.6 Hz, 1H, 2Z,4E);
13C NMR (100 MHz, CDCl3) δ 14.1 (2E,4E), 14.2 (2Z,4E), 60.6
(2Z,4E), 60.7 (2Z,4E), 60.8 (2E,4E), 124.6 (2Z,4E), 128.3 (2E,4E),
129.0 (2Z,4E), 138.4 (2Z,4E), 140.4 (2Z,4E), 140.7 (2E,4E), 165.3
(2Z,4E), 165.9 (2E,4E), 166.0 (2Z,4E); HRMS m/z Calcd for
C10H14O4 (M+) 198.0892, found 198.0891.
1-Cyclohexyl 6-Methyl Hexa-2,4-dienedioate [(2E,4E):(2Z,4E) =
1.5:1] (8d). 95 mg (80%); hexane−ethyl acetate 90:10 (v/v, eluent);
1H NMR (400 MHz, CDCl3) δ 1.26−1.55 (m, 6H), 1.75−1.89 (m,
4H), 3.78 (s, 3H, 2Z,4E), 3.79 (s, 3H, 2E,4E), 4.83−4.88 (m, 1H),
5.96 (d, J = 11.5 Hz, 1H, 2Z,4E), 6.11 (d, J = 15.6 Hz, 1H, 2Z,4E),
6.16−6.24 (m, 2H, 2E,4E), 6.65 (t, J = 11.5 Hz, 1H, 2Z,4E), 7.26−7.36
(m, 2H, 2E,4E), 8.36 (dd, J = 11.5, 15.6 Hz, 1H, 2Z,4E); 13C NMR
(100 MHz, CDCl3) δ 23.6 (2Z,4E), 23.7 (2E,4E), 25.25 (2E,4E),
25.29 (2Z,4E), 31.50 (2Z,4E), 31.52 (2E,4E), 51.6 (2Z,4E), 51.9
(2E,4E), 73.0 (2Z,4E), 73.2 (2E,4E), 123.9 (2Z,4E), 127.6 (2E,4E),
129.2 (2E,4E), 129.8 (2Z,4E), 138.0 (2Z,4E), 140.3 (2E,4E), 140.8
(2Z,4E), 141.1 (2E,4E), 165.3 (2E,4E), 165.4 (2Z,4E), 165.7 (2Z,4E),
166.3 (2E,4E); HRMS m/z Calcd for C13H18O4 (M+) 238.1205, found
238.1203.
6-Phenyl-2(2H)-pyran-2-one (4).15 Mp 66−67 °C (yellow solid),
27 mg (80%); hexane−ethyl acetate 75:25 (v/v, eluent); H NMR
(400 MHz, CDCl3) δ 6.29 (dd, J = 0.9, 9.2 Hz, 1H), 6.67 (dd, J = 0.9,
6.9 Hz, 1H), 7.41−7.47 (m, 4H), 7.80−7.85 (m, 2H); 13C NMR (100
MHz, CDCl3) δ 101.0, 114.0, 125.6, 128.9, 130.9, 131.3, 143.7, 161.1,
162.0; HRMS m/z Calcd for C11H8O2 (M+) 172.0524, found
172.0523.
3,3′-Diethyl-6H,6′H-[2,2′-bipyran]-6,6′-dione (6a). Mp 111−113
°C (yellow solid), 100 mg (81%); hexane−ethyl acetate 50:50 (v/v,
eluent); 1H NMR (400 MHz, CDCl3) δ 1.19 (t, J = 7.8 Hz, 6H), 2.39
(q, J = 7.8 Hz, 4H), 6.43 (d, J = 9.6 Hz, 2H), 7.37 (d, J = 9.6 Hz, 2H);
13C NMR (100 MHz, CDCl3) δ 13.9, 22.6, 117.9, 122.0, 145.7, 148.0,
160.3; HRMS m/z Calcd for C14H14O4 (M+) 246.0892, found
246.0893.
1-(tert-Butyl) 6-Methyl Hexa-2,4-dienedioate [(2E,4E):(2Z,4E) =
1.8:1] (8e).18 82 mg (77%); hexane−ethyl acetate 90:10 (v/v, eluent);
1H NMR (400 MHz, CDCl3) δ 1.50 (s, 9H, 2E,4E), 1.51 (s, 9H,
1
2Z,4E), 3.77 (s, 3H, 2Z,4E), 3.78 (s, 3H, 2E,4E), 5.94 (d, J = 11.5 Hz,
1H, 2Z,4E), 6.04 (d, J = 15.6 Hz, 1H, 2Z,4E), 6.11−6.20 (m, 2H,
2E,4E), 6.63 (t, J = 11.5 Hz, 1H, 2Z,4E), 7.18−7.35 (m, 2H, 2E,4E),
8.28 (dd, J = 11.5, 15.6 Hz, 1H, 2Z,4E); 13C NMR (100 MHz, CDCl3)
δ 28.0 (2E,4E), 28.1 (2Z,4E), 51.6 (2Z,4E), 51.9 (2E,4E), 80.9
(2Z,4E), 81.1 (2E,4E), 123.6 (2Z,4E), 127.3 (2E,4E), 130.6 (2E,4E),
131.2 (2Z,4E), 137.5 (2Z,4E), 139.7 (2E,4E), 140.9 (2Z,4E), 141.3
(2E,4E), 165.1 (2E,4E), 165.3 (2Z,4E), 165.8 (2Z,4E), 166.4 (2E,4E);
HRMS m/z Calcd for C11H16O4 (M+) 212.1049, found 212.1051.
Methyl 6-(tert-Butylamino)-6-oxohexa-2,4-dienoate [(2E,4E):
(2Z,4E) = 1.3:1] (8f). 54 mg (51%); hexane−ethyl acetate 50:50 (v/
11431
dx.doi.org/10.1021/jo401992d | J. Org. Chem. 2013, 78, 11427−11432

The Journal of Organic Chemistry
Article
v, eluent); 1H NMR (400 MHz, CDCl3) δ 1.400 (s, 9H, 2Z,4E), 1.402
(s, 9H, 2E,4E), 3.76 (s, 3H, 2Z,4E), 3.77 (s, 3H, 2E,4E), 5.85 (s, 1H,
2Z,4E), 5.88 (d, J = 11.5 Hz, 1H, 2Z,4E), 5.95 (s, 1H, 2E,4E), 6.09−
9.22 (m, 2H, 2E,4E), 6.20 (d, J = 15.3 Hz, 1H, 2Z,4E), 6.60 (t, J = 11.5
Hz, 1H, 2Z,4E), 7.18−7.32 (m, 2H, 2E,4E), 8.15 (dd, J = 11.5, 15.3
Hz, 1H, 2Z,4E); 13C NMR (100 MHz, CDCl3) δ 28.61, 28.64, 51.5,
51.6, 51.7, 122.7, 126.2, 132.7, 133.72, 133.74, 136.3, 140.9, 141.6,
164.0, 164.5, 165.9, 166.7; HRMS m/z Calcd for C11H18NO3 (M+H+)
212.1287, found 212.1282.
Org. Chem. 2007, 72, 5362. See also a review: (c) Satoh, T.; Miura, M.
Chem.Eur. J. 2010, 16, 11212.
(6) Selected recent examples for the Rh- and Ru-catalyzed
dehydrogenative coupling of carboxylic acids, esters, and amides:
(a) Padala, K.; Pimparkar, S.; Madasamy, P.; Jeganmohan, M. Chem.
Commun. 2012, 48, 7140. (b) Graczyk, K.; Ma, W.; Ackermann, L.
Org. Lett. 2012, 14, 4110. (c) Chinnagolla, R. K.; Jeganmohan, M.
Chem. Commun. 2012, 48, 2030. (d) Besset, T.; Kuhl, N.; Patureau, F.
W.; Glorius, F. Chem.Eur. J. 2011, 17, 7167. (e) Ackermann, L.;
Lygin, A. V.; Hofmann, N. Angew. Chem., Int. Ed. 2011, 50, 6379.
(f) Ackermann, L.; Lygin, A. V.; Hofmann, N. Org. Lett. 2011, 13,
3278. (g) Park, S. H.; Kim, J. Y.; Chang, S. Org. Lett. 2011, 13, 2372.
(h) Stuart, D. R.; Alsabeh, P.; Kuhn, M.; Fagnou, K. J. Am. Chem. Soc.
2010, 132, 18326. (i) Song, G.; Chen, D.; Pan, C.-L.; Crabtree, R. H.;
Li, X. J. Org. Chem. 2010, 75, 7487. (j) Hyster, T. K.; Rovis, T. J. Am.
Chem. Soc. 2010, 132, 10565. (k) Patureau, F. W.; Glorius, F. J. Am.
Chem. Soc. 2010, 132, 9982. (l) Su, Y.; Zhao, M.; Han, K.; Song, G.; Li,
X. Org. Lett. 2010, 12, 5462. (m) Wang, F.; Song, G.; Li, X. Org. Lett.
2010, 12, 5430. (n) Guimond, N.; Gouliaras, C.; Fagnou, K. J. Am.
Chem. Soc. 2010, 132, 6908.
Methyl (2E,4E)-5-Phenylpenta-2,4-dienoate [(2E,4E):(2Z,4E) =
5:1] (8g).18 35 mg (37%); hexane−ethyl acetate 90:10 (v/v, eluent);
1H NMR (400 MHz, CDCl3) δ 3.77 (s, 3H), 6.00 (d, J = 15.4 Hz,
1H), 6.88−6.90 (m, 2H), 7.31−7.49 (m, 6H); 13C NMR (100 MHz,
CDCl3) δ 51.6, 120.8, 126.2, 127.2, 128.8, 129.1, 135.9, 140.5, 144.8,
167.5; HRMS m/z Calcd for C12H12O2 (M+) 188.0837, found
188.0838.
Methyl (2E,4E)-5-(Naphthalen-2-yl)penta-2,4-dienoate [(2E,4E):
(2Z,4E) = 6:1] (8h).19 44 mg (37%); hexane−ethyl acetate 90:10 (v/v,
eluent); 1H NMR (400 MHz, CDCl3) δ 3.78 (s, 3H), 6.03 (d, J = 15.3
Hz, 1H), 6.94−7.07 (m, 2H), 7.44−7.83 (m, 8H); 13C NMR (100
MHz, CDCl3) δ 51.6, 120.8, 123.3, 126.5, 126.6, 126.7, 127.7, 128.2,
128.3, 128.5, 133.4, 133.5, 133.6, 140.7, 144.9, 167.5; HRMS m/z
Calcd for C16H14O2 (M+) 238.0994, found 238.0993.
(7) For Ni-catalyzed decarbonylative coupling of disubstituted maleic
anhydrides with alkynes, see: Kajita, Y.; Kurahashi, T.; Matsubara, S. J.
Am. Chem. Soc. 2008, 130, 17226.
6-(n-Butyl) 1-Methyl (2Z,4E)-2-Methylhexa-2,4-dienedioate
(8) For selected reviews concerning transition-metal-catalyzed
decarboxylative coupling, see: (a) Cornella, J.; Larrosa, I. Synthesis
2012, 653. (b) Rodriguez, N.; Goossen, L. J. Chem. Soc. Rev. 2011, 40,
5030. (c) Weaver, V.; Recio, A., III; Grenning, A. J.; Tunge, J. A. Chem.
Rev. 2011, 111, 1846. (d) Satoh, T.; Miura, M. Synthesis 2010, 3395.
(e) Goossen, L. J.; Rodriguez, N.; Goossen, K. Angew. Chem., Int. Ed.
2008, 47, 3100. (f) Baudoin, O. Angew. Chem., Int. Ed. 2007, 46, 1373.
(9) (a) Goossen, L. J.; Linder, C.; Rodríguez, N.; Lange, P. P.;
Fromm, A. Chem. Commun. 2009, 7173. (b) Cornella, J.; Sanchez, C.;
Banawa, D.; Larrosa, I. Chem. Commun. 2009, 7176.
(10) Kuninobu, Takai, and co-workers reported a-pyrone synthesis
using terminal alkynes under Re- and Mn-catalyses: Kuninobu, Y.;
Kawata, A.; Nishi, M.; Takata, H.; Takai, K. Chem. Commun. 2008,
6360.
(11) (a) Terao, Y.; Nomoto, M.; Satoh, T.; Miura, M.; Nomura, M. J.
Org. Chem. 2004, 69, 6942. For reviews concerning coupling via C-C
bond cleavage, see: (b) Murakami, M.; Matsuda, T. Chem. Commun.
2011, 47, 1100. (c) Yorimitsu, H.; Oshima, K. Bull. Chem. Soc. Jpn.
2009, 82, 778.
[(2Z,4E):(2E,4E) = 19:1] (8i). 60 mg (53%); hexane−ethyl acetate
1
90:10 (v/v, eluent); H NMR (400 MHz, CDCl3) δ 0.95 (t, J = 7.3
Hz, 3H), 1.39−1.44 (m, 2H), 1.63−1.70 (m, 2H), 2.06 (s, 3H), 3.82
(s, 3H), 4.17 (t, J = 6.9 Hz, 2H), 5.98 (d, J = 15.6 Hz, 1H), 6.48 (d, J =
11.9 Hz, 1H), 8.10 (dd, J = 11.9, 15.6 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ 13.7, 19.1, 21.2, 30.6, 51.9, 64.4, 125.9, 134.5, 135.7, 139.9,
166.6, 167.2; HRMS m/z Calcd for C12H18O4 (M+) 226.1205, found
226.1207.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Copies of H and 13C NMR spectra of products. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: satoh@chem.eng.osaka-u.ac.jp.
*E-mail: miura@chem.eng.osaka-u.ac.jp.
Notes
(12) Novak, Z.; Nemes, P.; Kotschy, A. Org. Lett. 2004, 6, 4917.
(13) Kotora, M.; Ishikawa, M.; Tsai, F.-Y.; Takahashi, T. Tetrahedron
1999, 55, 4969.
(14) Dubuffet, T.; Cimetiere, B.; lavielle, G. Synth. Commun. 1997,
27, 1123.
The authors declare no competing financial interest.
(15) Rickborn, B. Org. React. 1998, 53, 223.
(16) Bestmann, H. J.; Schobert, R. Angew. Chem., Int. Ed. 1985, 24,
790.
(17) Hu, C.; Geng, Z.; Ma, J.; Huang, Y.; Chen, R. Chem. Asian J.
2012, 7, 2032.
ACKNOWLEDGMENTS
■
This work was supported by Grants-in-Aid from MEXT, JSPS,
and JST, Japan.
(18) Ferrie, L.; Amans, D.; Reymond, S.; Bellosta, V.; Capdevielle, P.;
Cossy, J. J. Organomet. Chem. 2006, 691, 5456.
(19) Kresze, G.; Firl, J.; Braun, H. Tetrahedron 1969, 25, 4481.
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