Gold and platinum catalyzed cascade reaction of propargyl acetates bearing terminal alkynes or methyl ketones

Article abstract of DOI:10.1016/j.tet.2010.12.010

A gold (III)-catalyzed cascade reaction of propargyl acetates bearing an extra terminal alkyne (1) afforded γ-keto esters 3 and lactones 4. These products should be generated through allenyl ketone intermediate B via a 1,2-acyloxy cyclization/fragmentatio

Full text of DOI:10.1016/j.tet.2010.12.010

Tetrahedron 67 (2011) 1511e1517
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Tetrahedron
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Gold and platinum catalyzed cascade reaction of propargyl acetates bearing
terminal alkynes or methyl ketones
*
Taichi Kusakabe, Keisuke Kato
Faculty of Pharmaceutical Sciences, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 October 2010
Received in revised form 3 December 2010
Accepted 4 December 2010
Available online 16 December 2010
A gold (III)-catalyzed cascade reaction of propargyl acetates bearing an extra terminal alkyne (1) afforded
g
-keto esters 3 and lactones 4. These products should be generated through allenyl ketone intermediate
B via a 1,2-acyloxy cyclization/fragmentation/cycloisomerization/hydrolysis sequence. On the other
hand, the cascade reaction of -acetoxy ketones bearing terminal alkynes 5 afforded lactone 6 via allenyl
a
ketone intermediate A. This reaction involves
a
[3,3]-sigmatropic acyloxy rearrangement/cyclo-
isomerization/hydrolysis sequence.
Keywords:
Ó 2010 Published by Elsevier Ltd.
Propargyl acetate
Gold(III)
Platinium(IV)
Cycloisomerization
Acyloxy migration
1,2-acyloxy migration / cycloisomerization
tBu
Au cat. or
1. Introduction
O
tBu
tBu
O
Me
AcO
Ph
3
OAc
Ph
[M]
O
Ph
2(5H)-Furanones and 2(3H)-furanones are well known as basic
components of natural products, some of which display a wide
range of characteristic physiological properties.1 Gold and plati-
num catalyzed transformations of propargyl esters have been
widely used for the construction of a variety of carbo- and het-
erocycles.2 An appropriately situated O-ester group undergoes an
internal 1,2- or [3,3]-sigmatropic acyloxy rearrangement upon
electrophilic activation of the alkyne moiety to give rearranged
products or reactive intermediates. More specifically, the re-
actions of propargyl esters possessing a 1,4-diyne structure pro-
vide cyclopentanones,3a furans,3b pyrroles,3c and pyrazoles.3d
Gevorgyan’s group extensively studied the formation of furan
O
O
Cu cat. or
Ag cat.
Me
Me
Me
Scheme 1. V. Gevorgyan et al. Reaction of a-acetoxy ketones bearing internal alkynes.
rings from a-acetoxy ketones bearing internal alkynes. The oxy-
gen atom of the acetate was introduced in the C3 position of the
furan ring via a 1,2-acyloxy migration/cycloisomerization se-
quence (Scheme 1).4
Scheme 2. This work (1).
In a preliminary communication, we reported that cascade
reactions of propargyl acetates bearing an extra terminal alkyne 1
afforded
experiments were performed using compounds 2e6 as the sub-
strates. During the course of this study, we found a [3,3]-sig-
matropic acyloxy rearrangement/cycloisomerzation/hydrolysis
g
-keto esters 3 and lactones 4 (Scheme 2).3e In the
process of investigating the mechanism of the reaction, control
sequence for
a-acetoxy ketones bearing terminal alkynes 5 cat-
alyzed by PtCl4. In contrast with the reaction of internal alkynes
(Scheme 1), in the case of terminal alkynes, the oxygen atom of
the acetate is introduced in the C2 position of the furan ring
(Scheme 3).
* Corresponding author. Tel.: þ81 047 472 1805; fax: þ81 047 472 1825; e-mail
address: kkk@toho-u.ac.jp (K. Kato).
0040-4020/$ e see front matter Ó 2010 Published by Elsevier Ltd.
doi:10.1016/j.tet.2010.12.010

1512
T. Kusakabe, K. Kato / Tetrahedron 67 (2011) 1511e1517
substrates 1 were converted to corresponding compounds 2 and 5
(Table 2). The reaction of 1 with AuCl3 (3 mol %) in methanol at 0 ꢀC
afforded 2 in 56e98% yield. Treatment of 2 with 10% HCl(aq) in
CH3CN/H2O at room temperature gave the corresponding ketone 5
in 79e99% yield.
Table 2
Scheme 3. This work (2). Reaction of a-acetoxy ketones bearing terminal alkynes.
Preparation of 2 and 5
2. Results and discussion
The reaction of 1a with HAuCl4$3H2O (5 mol %) in methanol at
60 ꢀC afforded
-keto ester 3a and lactone 4a in 51% and 39% yields,
g
respectively (Table 1, entry 1).
Entry
R
Yield of 2 (%)
Yield of 5 (%)
1
2
3
4
5
6
7
8
Ph(CH2)2
PhCH2
1-NaphthyleCH2
4-MethylphenyleCH2
Octyl
Pentyl
CyclohexyleCH2
Cyclohexyl
86:2a
88:2c
68:2d
56:2e
93:2f
71:2g
63:2h
98:2i
99:5a
92:5c
81:5d
79:5e
85:5f
84:5g
99:5h
97:5i
Table 1
Cascade reaction of 1,1-diethynyl acetate 1
Entry
R
Yield of 3 (%)
Yield of 4 (%)
To investigate the mechanism of the present reaction (Table 1),
some control experiments were performed. As expected, the re-
action of 2a gave similar results to that of 1a (Scheme 5). On the
other hand, the reaction of 5a afforded diketone 8a as a major
product (53%) together with 3a (31%) and 4a (13%) (Scheme 6).
Compound 8a is likely produced by neighboring group participa-
tion in the hydration of the terminal alkyne.5 These results in-
dicated that 2a is the first intermediate of the reaction.
1
Ph(CH2)2
Ph(CH2)2
Ph(CH2)2
PhCH2
51:3a
52:3b
Complex mixture
53:3c
46:3d
50:3e
46:3f
46:3g
36:3h
39:4a
26:4a
2a
3b
4
27:4c
18:4d
20:4e
47:4f
40:4g
38:4h
51:4i
5
6
7
8
9
10
1-NaphthyleCH2
4-MethylphenyleCH2
Octyl
Pentyl
CyclohexyleCH2
Cyclohexyl
31:3i
a
i
Carried out in BuOH; iButyl ester 3b was obtained together with 4a.
b
Carried out in toluene.
Although commercially available AuCl, HAuCl4$3H2O, PtCl4,
PtCl2, AuCl3, and cationic Ph3PAuCl/AgSbF6 exhibited nearly the
Scheme 5. Reaction of orthoester 2a.
same catalytic activity (3a: 40e54%, 4a: 19e30%), the use of
i
HAuCl4$3H2O provided a better total yield. When BuOH was used
i
as the solvent, butyl ester 3b and lactone 4a were obtained in
similar yields (entry 2). A complex mixture was obtained, however,
when toluene was used as the solvent (entry 3). With the optimized
conditions in hand (entry 1), the scope of the reaction was explored.
For substrates 1aee containing an arylmethylene chain, the re-
action proceeded well (entries 1, 2, 4e6). Alkyl-substituted sub-
strates 1fei provided 3fei (31e46%) and 4fei (38e51%) in good
combined yields (entries 7e10). In the case of internal alkynes 1i
and 1j, methyl ether 7i and 7j were obtained in 91 and 80% yields,
respectively (Scheme 4).
Scheme 6. Reaction of ketone 5a.
Next, the products 3a and 4a were independently treated under
the reaction conditions depicted in Table 1. Interconversion be-
tween 3a and 4a was not observed. These results indicated that the
products 3a and 4a were produced by independent pathways. In
general, 2-methoxyfurans are unstable in the presence of acid and
afford hydrolyzed 2-furanones or g
-keto esters.6 For example, 2-
methoxy-5-pentylfuran7a was treated with HAuCl4$3H2O (5 mol %)
in methanol at room temperature for 0.5 h to give methyl 4-oxo-
nonanoate7b (83%) by acid hydrolysis. Based on these control ex-
periments, a plausible mechanism for the present reaction is
shown in Scheme 7. 5-exo-dig Cyclization of 1,1-diethynyl acetate 1
via nucleophilic attack of the first alkyne by a carbonyl oxygen in
accordance with Markovnikov’s rule, followed by protonolysis,
generates the intermediate 2. Elimination of AcOMe should induce
a nucleophilic attack of the second alkyne by methanol with anti-
Scheme 4. Reaction of internal alkynes 1j and 1k.
Thin-layer chromatography suggested that the orthoester 2 is
the first intermediate in the transformation 1/3 and 4. In general,
orthoesters are easily converted to the corresponding ketones un-
der acidic conditions. We expected that the orthoester 2 and ketone
5 are the possible intermediates in this cascade reaction, and thus

T. Kusakabe, K. Kato / Tetrahedron 67 (2011) 1511e1517
1513
MeO
O
H
O
decreased yields (Table 3, entries 7 and 8). A plausible mechanism
of the reaction is proposed as shown in Scheme 8. [3,3]-Sigmatropic
acyloxy rearrangement of 5 provides allenyl ketone intermediate A,
which undergoes cycloisomerization to produce the furan in-
termediate D. Hydrolysis of the furan intermediate D gives the
product 6, which is an olefinic isomer of 4. In this step, the acetoxy
group acts as a preferential leaving group. In contrast with the re-
action of internal alkynes (Scheme 1), in the case of terminal al-
kynes, the oxygen atom of the acetate is introduced at the C2
position of the furan ring.
MCln
O
OMe
R
OMe
O
•
O
R
R
R
O
O
Me
Me
C
Me
MeO
2
Me
B
1
O
R
6
Me
not isolated
H
OAc
O
OAc
OMe
+
OMe
O
O
O
O
CO2Me
Me
H+
H2O
H2O
or
O
O
O
C
•
- H+
R
R
R
R
R
H
O
R
O
Me
O
3
R
Me
Me
Me
5
+
Me
D
Me
A
OMe
+
OMe
or
O
H
O
O
O
OAc
+
OAc
O
- H+
R
O
2
R
Me
4
H+
Me
H2O
Me
O
O
D
- H+
R
Scheme 7. Proposed mechanism for the reaction of propargyl acetate with terminal
R
R
aklynes.
Me
Me
Me
6
Scheme 8. .Proposed mechanism for the reaction of propargyl acetate with methyl
ketones.
Markovnikov regioselectivity to give allenyl ketone intermediate B,
followed by cyclization to produce the 2-methoxyfuran in-
termediate C. Hydrolysis of the 2-methoxyfuran intermediate C
gives the products 3 and 4. In this situation, we could not explain
why lactone 6 was not isolated. It was purely by chance that lactone
6 was obtained from the reaction of ketone 5 (Table 3). Treatment of
3. Conclusion
We have reported two kinds of cascade reactions of propargyl
acetates catalyzed by gold or platinium. The reaction of propargyl
acetates bearing an extra terminal alkyne (1) afforded g-keto esters
3 and lactones 4 through allenyl ketone intermediate B via
a 1,2-acyloxy cyclization/fragmentation/cycloisomerization/hydro-
6a under the present reaction conditions gave g-keto ester 3a in
47% yield along with an unidentified mixture of compounds.8 Thus
lactone 6 could be converted to 3 if it is produced in the reaction
mixture.
lysis sequence. On the other hand, the reaction of a-acetoxy ke-
tones bearing terminal alkynes (5) afforded lactones 6 through
allenyl ketone intermediate A via a [3,3]-sigmatropic acyloxy
rearragement/cycloisomerization/hydrolysis sequence.
Table 3
Cascade reaction of ketone 5 with terminal alkynes
OAc
R
O
O
PtCl4
(6.5 mol %)
Me
2
4. Experimental section
4.1. General
•
O
R
O
O
O
R
Toluene
5
Me
Me
6
Me
A
All melting points were measured on a Yanaco MP-3S micro
melting point apparatus and are uncorrected. 1H and 13C NMR
spectra were recorded on JEOL AL 400 and JEOL Lambda 500
spectrometers in CDCl3 with Me4Si as an internal reference. 13C
NMR spectra were recorded at 100 MHz. High-resolution mass
spectra (HR-MS) and fast atom bombardment mass spectra (FAB-
MS) were obtained with JEOL GC Mate II, JMS-SX102, and JEOL JMS
600H spectrometers. IR spectra were recorded with a JASCO FT/IR-
300 spectrometer. All reagents were purchased from commercial
sources and used without purification. All evaporations were per-
formed under reduced pressure. For column chromatography,
silica-gel (Kieselgel 60) was employed.
Entry
R
Condition
rt, 5.5h
Yield of 6 (%)
1
2
3
4
5
6
7
8
Ph(CH2)2
PhCH2
1-NaphthyleCH2
p-TolyleCH2
Octyl
Pentyl
CyclohexyleCH2
Cyclohexyl
68:6a
76:6c
60:6d
71:6e
63:6f
55:6g
51:6h
46:6i
rt ꢁ60 ꢀC, 75 min
rt ꢁ60 ꢀC, 75 min
rt ꢁ60 ꢀC, 75 min
rt ꢁ60 ꢀC, 75 min
rt ꢁ60 ꢀC, 2 h
rt ꢁ60 ꢀC, 45 min
rt ꢁ60 ꢀC, 75 min
Although 5a was not an intermediate for the reaction, we were
interested in the reaction of terminal alkyne 5a depicted in Scheme
6, because the reaction sequence was different from that of internal
alkynes reported by Gevorgyan’s group4 (Scheme 1). Thus, we in-
vestigated the gold and platinum catalyzed reaction of 5a in detail.
The reaction of 5a with PtCl4 (6.5 mol %) in toluene afforded the
lactone 6a in 68% yield (Table 3, entry 1). Although AuCl,
HAuCl4$3H2O, and PtCl2 exhibited nearly the same catalytic activity
(6a: 53e66%), the use of PtCl4 gave better yields. The use of CH2Cl2
and CH3CN reduced yields. Substrates bearing an arylmethylene
chain or long alkyl chain gave moderate yields (Table 3, entries
1e6), whereas the presence of a cyclohexyl side chain resulted in
4.2. Preparation of substrates 1
Substrates 1 were prepared as we already described. 1a,3e 1c,3e
1d,3a 1e,3a 1f,3e 1g,3e and 1h3a were known compounds.
4.2.1.
needles; mp 75e76 ꢀC (heptane); 1H NMR (400 MHz, CDCl3)
1.19e1.32 (5H, m), 1.76 (1H, br d, J¼11.6 Hz), 1.83e1.94 (3H, m),
2.04e2.12 (2H, m), 2.09 (3H, s), 2.63 (2H, s); 13C NMR (100 MHz,
CDCl3) 21.3, 25.8, 26.1, 26.9, 47.7, 70.4, 74.1, 79.4, 168.3; IR (KBr)
a,a-Diethynylcyclohexanemethanol-1-acetate (1i). Colorless
d
d

1514
T. Kusakabe, K. Kato / Tetrahedron 67 (2011) 1511e1517
3267, 2932, 2855, 2120, 1738, 1376, 1244, 989, 689 cmꢁ1; HRMS-EI
q, J¼6.8 Hz), 5.67 (1H, d, J¼6.8 Hz), 7.06 (2H, d, J¼8.0 Hz), 7.15 (2H, d,
m/z: [Mþ] calcd for C13H16O2 204.1150; found 204.1146.
J¼8.0 Hz); 13C NMR (100 MHz, CDCl3)
d 18.3, 21.1, 34.2, 79.9, 116.6,
128.8, 129.7, 132.5, 137.1, 172.7, 173.1; IR (ATR) 1744, 1638, 1514, 1167,
1062, 948 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C13H14O2 202.0994;
found 202.0998.
4.2.2.
yellow needles; mp 82e83 ꢀC; 1H NMR (CDCl3)
2.55e2.60 (2H, m), 3.07e3.11 (2H, m), 7.21e7.24 (1H, m), 7.27e7.33
(10H, m), 7.49e7.52 (4H, m); 13C NMR (CDCl3)
21.5, 30.9, 44.5, 68.1,
a
,a
-Bis(2-phenylethynyl)benzenepropanol-1-acetate (1j). Pale
d
2.12 (3H, s),
d
4.3.5.
b
-Acetyl-cyclohexanebutanoic acid methyl ester(3h). Colorless
0.86e0.92 (2H, m), 1.18e1.22 (5H,
85.3, 85.9, 122.0, 126.1, 128.2, 128.5, 128.6, 128.8, 132.1, 141.0, 168.3;
IR (ATR) 2925, 2244, 1744, 1489, 1227 cmꢁ1; HRMS-EI m/z: [Mþ]
calcd for C27H22O2 378.1620; found 378.1611.
oil; 1H NMR (400 MHz, CDCl3)
d
m), 1.46e1.49 (1H, m), 1.60e1.72 (5H, m), 2.23 (3H, s), 2.35 (1H, dd,
J¼16.8, 4.0 Hz), 2.71 (1H, dd, J¼16.8, 10.0 Hz), 3.06e3.08 (1H, m),
3.65 (3H, s); 13C NMR (100 MHz, CDCl3)
d 26.1, 26.2, 26.4, 29.4, 32.9,
4.2.3.
(1k). Colorless solid; mp 92e93 ꢀC; 1H NMR (CDCl3)
2.06 (3H, s), 2.33e2.37 (2H, m), 2.89e2.93 (2H, m), 7.18e7.32 (5H,
m); 13C NMR (CDCl3)
0.2, 21.7, 31.1, 44.9, 67.8, 90.7, 101.5, 126.3,
a
,
a
-Bis(2-trimethylsilylethynyl)benzenepropanol-1-acetate
33.7, 35.3, 35.4, 39.0, 45.3, 51.7, 173.0, 211.3; IR (ATR) 2923, 2851,
1737, 1713, 1437, 1354, 1159 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for
C13H22O3 226.1569; found 226.1570.
d
0.20 (18H, s),
d
128.7, 128.8, 141.4, 168.1; IR (ATR) 2968, 2171, 1746, 1366, 1227, 1130,
1023 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C21H30O2Si2 370.1784;
found 370.1788.
4.3.6. 4-Cyclohexylmethyl-5-methyl-2(5H)-furanone (4h). Colorless
oil; 1H NMR (400 MHz, CDCl3 )
d 0.88e1.04 (2H, m), 1.15e1.29 (3H,
m), 1.42 (3H, d, J¼6.8 Hz), 1.54e1.56 (1H, m), 1.71e1.75 (5H, m),
2.14e2.30 (2H, m), 4.92 (1H, q, J¼6.8 Hz), 5.76 (1H, d, J¼1.2 Hz); 13C
4.3. General procedure for the reaction of 1 (Table 1)
NMR (100 MHz, CDCl3) d 18.3, 26.0, 26.1, 26.2, 33.0, 33.6, 35.8, 36.4,
80.5, 115.9, 173.1, 173.1; IR (ATR) 2924, 2851, 1745, 1636, 1448, 1320,
1170, 947,cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C12H18O2 194.1307;
found 194.1309.
A 20 mL round-bottom flask, containing a magnetic stirring bar,
catalyst (0.015 mmol), 1 (0.3 mmol), and MeOH (5 mL) was fitted
with a Dimroth condenser capped with a rubber septum. After being
stirred for 12e24 h at 60 ꢀC, the mixture was diluted with EtOAc
(20 mL) and washed with 3% NaHCO3 aq (20 mL). The organic layers
were separated and the aqueous layer extracted with EtOAc (30 mL).
The combined organic layers were then dried over MgSO4 and
concentrated in vacuo. The crude product was purified by column
chromatography on silica-gel. The fraction eluted with hexane/ethyl
acetate (100/1 to 50/1) and (10/1) afforded 3 and 4, respectively. 3a,
3b, 3c, 3f, 3g, 4a, 4c, 4f, and 4g were known compounds.3e
4.3.7.
b
-Acetyl-cyclohexanepropanoicacidmethylester(3i). Colorless
oil; 1H NMR (400 MHz, CDCl3)
d
0.89e0.98 (1H, m), 1.05e1.32 (5H,
m), 1.55e1.67 (3H, m), 1.72e1.82 (2H, m), 2.24 (3H, s), 2.37 (1H, dd,
J¼16.8, 3.2 Hz), 2.76 (1H, dd, J¼16.8, 11.4 Hz), 2.89e2.94 (1H, m),
3.64 (3H, s); 13C NMR (100 MHz, CDCl3)
d 26.2, 26.4, 26.5, 29.4, 30.9,
31.4, 32.4, 39.5, 51.7, 53.5, 173.5, 211.2; IR (KBr) 2929, 2854, 1738,
1712, 1449, 1438, 1359, 1162 cmꢁ1; HRMS-FAB m/z:[MþþH] calcd
for C12H21O3 213.1491; found 213.1519.
4.3.1.
b
-Acetyl-1-naphthalenebutanoic acid methyl ester (3d). Pale
4.3.8. 4-Cyclohexyl-5-methyl-2(5H)-furanone (4i). Colorless oil; 1H
yellow oil; 1H NMR (CDCl3)
d
2.04 (3H, s), 2.39 (1H, dd, J¼17.2,
NMR (CDCl3)
J¼6.8 Hz), 1.65e1.93 (3H, m), 2.11e2.26 (2H, m), 5.02 (1H, qd, J¼6.8,
1.2 Hz), 5.73 (1H, s); 13C NMR (CDCl3)
18.4, 25.6, 25.8, 26.1, 30.7,
d 0.92e1.04 (1H, m), 1.16e1.40 (5H, m), 1.44 (3H, d,
4.4 Hz), 2.85 (1H, dd, J¼17.2, 9.6 Hz), 3.07 (1H, dd, J¼13.6, 8.0 Hz),
3.36 (1H, dd, J¼13.6, 7.4 Hz), 3.47e3.50 (1H, m), 3.59 (3H, s), 7.26
(1H, d, J¼6.0 Hz), 7.38 (1H, dd, J¼8.0, 7.0 Hz), 7.49e7.59 (2H, m), 7.75
(1H, d, J¼8.4 Hz), 7.87 (1H, dd, J¼8.0, 0.8 Hz), 8.04 (1H, d, J¼8.4 Hz);
d
32.3, 37.0, 79.4, 113.6, 173.3, 179.0; IR (KBr) 2928, 2855, 1757, 1631,
1449, 1175 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C11H16O2 180.1150;
found 180.1151.
13C NMR (CDCl3)
d 30.7, 35.0, 35.6, 48.4, 51.7, 123.3, 125.4, 125.8,
126.4, 127.5, 127.7, 129.0, 131.6, 134.0, 134.2, 172.6, 211.0; IR (ATR)
1739, 1712, 1436, 1355, 1162 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for
C17H18O3 270.1256; found 270.1258.
4.3.9. Methyl ether (7j). Yellow solid; mp 53e56 ꢀC; 1H NMR (CDCl3)
d
2.40e2.44 (2H, m), 3.04e3.08 (2H, m), 3.66 (3H, s), 7.17e7.28 (1H,
m), 7.26e7.34 (10H, m), 7.49e7.51 (4H, m); 13C NMR (CDCl3)
d
31.0,
4.3.2. 4-(1-Naphthylmethyl)-5-methyl-2(5H)-furanone (4d). Yellow
44.7, 53.3, 71.0, 85.3, 86.8,122.2,125.9,128.3,128.4,128.5,128.7,131.9,
oil; 1H NMR (400 MHz, CDCl3)
d
1.55 (3H, d, J¼6.8 Hz), 3.97 (1H, dd,
141.6; IR (ATR) 2943, 2214, 1598, 1489, 1454, 1289, 1102, 1061 cmꢁ1
;
J¼18.0, 1.6 Hz), 4.18 (1H, d, J¼18.0 Hz), 4.98 (1H, q, J¼6.8 Hz),
5.49e5.50 (1H, m), 7.35 (1H, d, J¼6.8 Hz), 7.44 (1H, dd, J¼6.8,
8.4 Hz), 7.49e7.53 (2H, m), 7.76e7.79 (1H, m), 7.83 (1H, d, J¼8.4 Hz),
HRMS-EI m/z: [Mþ] calcd for C26H22O 350.1671; found 350.1664.
4.3.10. Methyl ether (7k). Yellow solid; mp 48e51 ꢀC; 1H NMR
(CDCl3) 0.2 (18H, s), 2.16e2.21 (2H, m), 2.87e2.91 (2H, m), 3.49
(3H, s), 7.16e7.30 (5H, m); 13C NMR (CDCl3)
0.2, 31.0, 44.8, 53.2,
7.88e7.91 (1H, m); 13C NMR (100 MHz, CDCl3)
d
18.5, 32.3, 80.1,
d
117.2, 123.3, 125.5, 126.1, 126.7, 127.5, 128.5, 129.1, 131.5, 131.7, 134.0,
172.5, 172.6; IR (ATR) 1739, 1639, 1169 cmꢁ1; HRMS-EI m/z: [Mþ]
calcd for C16H14O2 238.0994; found 238.0994.
d
70.8, 90.1, 102.7, 126.0, 128.6, 128.7, 141.9; IR (ATR) 2963, 2163, 1738,
1456, 1251, 1099, 1058 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for
C20H30OSi2 342.1835; found 342.1824.
4.3.3.
b
-Acetyl-4-methylphenylbutanoic acid methyl ester (3e). Pale
2.12 (3H, s), 2.32 (3H, s), 2.35 (1H, dd,
yellow oil; 1H NMR (CDCl3)
d
J¼17.0, 4.4 Hz), 2.56 (1H, dd, J¼13.6, 8.4 Hz), 2.74 (1H, dd, J¼17.0,
4.4. General procedure for the preparation of 2 (Table 2)
10.0 Hz), 2.89 (1H, dd, J¼13.6, 6.8 Hz), 3.22e3.26 (1H, m), 7.04 (2H,
d, J¼8.0 Hz), 7.10 (2H, d, J¼8.0 Hz); 13C NMR (CDCl3)
d
21.0, 30.3,
A mixture of AuCl3 (4.2 mg, 0.014 mmol) and 1 (0.47 mmol) in
MeOH (5 mL) was stirred for 0.5e1 h at 0 ꢀC. The reaction was
quenched with powdered NaHCO3 (50 mg), and the mixture was
then diluted with EtOAc (20 mL) and washed with 5% NaHCO3 aq
(40 mL). The organic layers were separated and the aqueous layer
extracted with EtOAc (30 mL). The combined organic layers were
then dried over MgSO4 and concentrated in vacuo. The crude
product was purified by column chromatography on silica-gel. The
35.0, 37.3, 49.8, 51.7, 128.8, 129.4, 135.1, 136.3, 172.8, 210.8; IR (ATR)
1734, 1713, 1515, 1437, 1356, 1162 cmꢁ1; HRMS-EI m/z: [Mþ] calcd
for C14H18O3 234.1256; found 234.1259.
4.3.4. 5-Methyl-4-[(4-methylphenyl)methyl]-2(5H)-furanone
(4e). Yellow oil; 1H NMR (400 MHz, CDCl3)
2.34 (3H, s), 3.51 (1H, d, J¼16.6 Hz), 3.71 (1H, d, J¼16.6 Hz), 4.91 (1H,
d
1.45 (3H, d, J¼6.8 Hz),

T. Kusakabe, K. Kato / Tetrahedron 67 (2011) 1511e1517
1515
fraction eluted with hexane/ethyl acetate (50/1 to 10/1) afforded
orthoester 2.
diastereomers, ratio¼1.5:1; 1H NMR (CDCl3) (major diastereomer)
d 0.96e1.34 (6H, m), 1.66e1.84 (7H, m), 1.62 (3H, s), 2.61 (1H, s),
3.36 (3H, s), 4.10 (1H, d, J¼2.9 Hz), 4.42 (1H, d, J¼2.9 Hz); 13C NMR
4.4.1. 4-Ethynyl-2-methoxy-2-methyl-5-methylene-4-(2-phenyl-
ethyl)-1,3-dioxolane (2a)3e. Colorless oil, inseparable mixture of
diastereomers, ratio¼2.3:1; 1H NMR (CDCl3) (major diastereomer)
(CDCl3) (major diastereomer) d 24.4, 26.2, 26.3, 26.3, 34.1, 34.4, 34.6,
49.7, 50.0, 73.7, 79.3, 80.3, 83.1, 123.1, 161.1; IR (ATR) 3290, 2922,
2851, 2116, 1685, 1448, 1385, 1152, 1052 cmꢁ1; HRMS-EI m/z: [Mþ]
calcd for C15H22O3 250.1569; found 250.1567.
d
1.66 (3H, s), 2.05e2.25 (2H, m), 2.66 (1H, s), 2.79e2.96 (2H, m),
3.40 (3H, s), 4.18 (1H, d, J¼2.8 Hz), 4.50 (1H, d, J¼2.8 Hz), 7.18e7.32
(5H, m); 13C NMR (CDCl3) (major diastereomer)
d
24.0, 30.3, 44.4,
4.4.8. 4-Cyclohexyl-4-ethynyl-2-methoxy-2-methyl-5-methylene-
1,3-dioxolane (2i). Colorless oil, inseparable mixture of di-
astereomers, ratio¼4:1; 1H NMR (CDCl3) (major diastereomer)
50.1, 73.9, 78.8, 80.8, 82.4, 123.1, 126.1, 128.4, 128.5, 141.0, 159.8; IR
(KBr) 3287, 2117, 1687, 1052 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for
C16H18O3 258.1256; found 258.1258.
d
1.13e1.30 (5H, m), 1.64 (3H, s), 1.54e2.10 (6H, m), 2.59 (1H, s), 3.38
(3H, s), 4.13 (1H, d, J¼2.8 Hz), 4.51 (1H, d, J¼2.8 Hz); 13C NMR
4.4.2. 4-Ethynyl-2-methoxy-2-methyl-5-methylene-4-(phenyl-
methyl)-1,3-dioxolane (2c). Colorless oil, inseparable mixture of
diastereomers, ratio¼3:1; 1H NMR (CDCl3) (major diastereomer)
(CDCl3) (major diastereomer) d 23.2, 26.1, 26.1, 26.2, 26.5, 27.3, 47.7,
50.3, 74.1, 81.7, 82.3, 82.6, 122.7, 159.0; IR (KBr) 3283, 2935, 2855,
2111, 1686, 1453, 1387, 1285, 1153, 1043 cmꢁ1; HRMS-EI m/z: [Mþ]
calcd for C14H20O3 236.1413; found 236.1407.
d
1.31 (3H, s), 2.64 (1H, s), 3.15 (1H, d, J¼14.0 Hz), 3.19 (1H, d,
J¼14.0 Hz), 3.34 (3H, s), 4.17 (1H, d, J¼3.0 Hz), 4.52 (1H, d, J¼3.0 Hz),
7.27e7.30 (5H, m); 13C NMR (CDCl3) (major diastereomer)
d
23.9,
4.5. General procedure for the preparation of 5 (Table 2)
48.0, 50.0, 74.6, 79.3, 81.4, 82.8, 123.4, 127.3, 127.9, 131.2, 134.4,
159.3; IR (ATR) 3286, 2110, 1685, 1387, 1151, 1101, 1046 cmꢁ1
;
To a solution of 2 (0.46 mmol) in CH3CN (4 mL)/H2O (1.5 mL) was
added 10% HCl (0.5 mL), and the mixture stirred for 0.4e1 h at room
temperature. The reaction was quenched with powdered NaHCO3
(50 mg), and the mixture was then diluted with EtOAc (20 mL) and
5% NaHCO3 aq (20 mL). The organic layers were separated and the
aqueous layer extracted with EtOAc (30 mL). The combined organic
layers were dried over MgSO4 and concentrated in vacuo. The crude
product was purified by column chromatography on silica-gel. The
HRMS-EI m/z: [Mþ] calcd for C15H16O3 244.1100; found 244.1109.
4.4.3. 4-Ethynyl-2-methoxy-2-methyl-5-methylene-4-(1-naph-
thylmethyl)-1,3-dioxolane (2d). Colorless oil, inseparable mixture of
diastereomers, ratio¼8:1; 1H NMR (CDCl3) (major diastereomer)
d
0.94 (3H, s), 2.64 (1H, s), 3.32 (3H, s), 3.48 (1H, d, J¼14.4 Hz), 3.94
(1H, d, J¼14.4 Hz), 4.29 (1H, d, J¼3.0 Hz), 4.57 (1H, d, J¼3.0 Hz),
7.41e7.51 (4H, m), 7.76e7.80 (2H, m), 8.18 (1H, d, J¼8.1 Hz); 13C
fraction eluted with hexane/ethyl acetate (30/1 to 10/1) afforded a-
acetoxy ketone 5.
NMR (CDCl3) (major diastereomer) d 23.3, 44.0, 50.0, 74.7, 79.8, 81.7,
83.2,123.5,125.0,125.2,125.4,125.5,128.1,128.4,129.5,130.8,133.4,
133.7, 159.5; IR (ATR) 3287, 2105, 1685, 1386, 1151, 1099, 1048 cmꢁ1
;
4. 5.1. 3-Acetyloxy-3-(2-phenylethyl)-4-pentyn-2-one
(5a). Colorless oil; 1H NMR (CDCl3)
2.11 (3H, s), 2.16e2.19 (2H, m),
2.41 (3H, s), 2.78 (1H, s), 2.86 (2H, t, J¼8.6 Hz), 7.19e7.31 (5H, m);
13C NMR (CDCl3)
20.6, 25.1, 30.1, 39.1, 77.0, 79.3, 79.7, 126.3, 128.4,
HRMS-EI m/z: [Mþ] calcd for C19H18O3 294.1256; found 294.1261.
d
4.4.4. 4-Ethynyl-2-methoxy-2-methyl-5-methylene-4-[(4-methyl-
phenyl)methyl]-1,3-dioxolane (2e). Colorless oil, inseparable mix-
ture of diastereomers, ratio¼4:1; 1H NMR (CDCl3) (major
d
128.6, 140.5, 169.3, 201.0; IR (ATR) 3274, 2129, 1730, 1369, 1236,
699 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C15H16O3 244.1099; found
244.1101.
diastereomer)
d 1.34 (3H, s), 2.32 (3H, s), 2.64 (1H, s), 3.10 (1H, d,
J¼13.6 Hz), 3.15 (1H, d, J¼13.6 Hz), 3.34 (3H, s), 4.16 (1H, d,
J¼2.8 Hz), 4.52 (1H, d, J¼2.8 Hz), 7.10 (2H, d, J¼8.0 Hz), 7.20 (2H, d,
J¼8.0 Hz); 13C NMR (CDCl3) (major diastereomer)
d 21.1, 24.0, 47.7,
4.5.2. 3-Acetyloxy-3-phenylmethyl-4-pentyn-2-one (5c). Colorless
oil; 1H NMR (CDCl3)
d 2.11 (3H, s), 2.19 (3H, s), 2.73 (1H, s), 3.15 (1H,
50.0, 74.6, 79.4, 81.3, 82.8, 123.4, 128.6, 131.1, 131.3, 136.9, 159.4; IR
(ATR) 3286, 2110, 1685, 1387, 1152, 1047 cmꢁ1; HRMS-EI m/z: [Mþ]
calcd for C16H18O3 258.1256; found 258.1254.
d, J¼13.2 Hz), 3.23 (1H, d, J¼13.2 Hz), 7.30e7.31 (5H, m); 13C NMR
(CDCl3)
d 20.6, 27.2, 43.5, 77.8, 79.2, 79.8, 127.6, 128.2, 130.8, 133.2,
169.2, 201.8; IR (ATR) 3277, 3032, 2118, 1731, 1369, 1224, 699 cmꢁ1
;
HRMS-EI m/z: [Mþ] calcd for C14H14O3 230.0943; found 230.0946.
4.4.5. 4-Ethynyl-2-methoxy-2-methyl-5-methylene-4-(1-octyl)-
1,3-dioxolane (2f). Colorless oil, inseparable mixture of diastereomers,
ratio¼2:1; 1H NMR (CDCl3) (major diastereomer)
d 0.88 (3H, t,
4.5.3. 3-Acetyloxy-3-(1-naphthylmethyl)-4-pentyn-2-one
(5d). Colorless oil; 1H NMR (CDCl3)
d 2.03 (3H, s), 2.23 (3H, s), 2.64
J¼6.4 Hz),1.23e1.36 (10H, m),1.54e1.61 (2H, m), 1.63 (3H, s), 1.78e1.90
(2H, m), 2.60 (1H, s), 3.37 (3H, s), 4.12 (1H, d, J¼2.8 Hz), 4.45 (1H, d,
(1H, s), 3.61 (1H, d, J¼14.0 Hz), 3.76 (1H, d, J¼14.0 Hz), 7.43e7.50
J¼2.8 Hz); 13CNMR(CDCl3)(majordiastereomer)
d14.1, 22.7, 23.8, 24.0,
24.1, 29.2, 29.4, 31.9, 42.5, 50.1, 73.5, 79.3, 80.4, 82.9, 123.0, 160.2; IR
(4H, m), 7.80e7.84 (2H, m), 8.17 (1H, d, J¼8.0 Hz); 13C NMR (CDCl3)
d
20.7, 27.0, 39.3, 78.2, 79.6, 79.9, 124.8, 125.0, 125.6, 125.7, 128.5,
(ATR) 3310, 2925, 2855, 2136, 1686, 1465, 1386, 1154, 1053 cmꢁ1
;
128.6, 129.6, 129.7, 132.9, 133.8, 169.2, 201.8; IR (ATR) 3274, 2121,
1721, 1354, 1227 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C18H16O3
280.1100; found 280.1103.
HRMS-EI m/z: [Mþ] calcd for C16H26O3 266.1882; found 266.1883.
4.4.6. 4-Ethynyl-2-methoxy-2-methyl-5-methylene-4-(1-pentyl)-
1,3-dioxolane (2g). Colorless oil, inseparable mixture of di-
astereomers, ratio¼1.4:1; 1H NMR (CDCl3) (major diastereomer)
4.5.4. 3-Acetyloxy-3-[(4-methylphenyl)methyl]-4-pentyn-2-one
(5e). Pale yellow oil; 1H NMR (CDCl3)
d 2.10 (3H, s), 2.19 (3H, s), 2.34
d
0.90e0.92 (3H, m), 1.32e1.36 (4H, m), 1.54e1.61 (2H, m), 1.63 (3H,
(3H, s), 2.72 (1H, s), 3.11 (1H, d, J¼13.3 Hz), 3.18 (1H, d, J¼13.3 Hz),
7.11 (2H, d, J¼8.1 Hz), 7.17 (2H, d, J¼8.1 Hz); 13C NMR (CDCl3)
d
20.7,
s),1.78e1.90 (2H, m), 2.60 (1H, s), 3.37 (3H, s), 4.12 (1H, d, J¼2.8 Hz),
4.45 (1H, d, J¼2.8 Hz); 13C NMR (CDCl3) (major diastereomer)
d 14.0,
21.1, 27.3, 43.2, 77.7, 79.3, 80.0, 128.9, 130.0, 130.6, 137.3, 169.3,
201.9; IR (ATR) 3278, 2926, 2111, 1729, 1516, 1368, 1224 cmꢁ1
;
23.5, 24.0, 24.1, 31.5, 42.5, 50.1, 73.5, 79.3, 80.4, 82.9, 123.1, 160.2; IR
(ATR) 3294, 2951, 2872, 2124, 1210, 1154, 1052, 979 cmꢁ1; HRMS-EI
m/z: [Mþ] calcd for C13H20O3 224.1413; found 224.1410.
HRMS-EI m/z: [Mþ] calcd for C15H16O3 244.1100; found 244.1098.
4.5.5. 3-Acetyloxy-3-ethynyl-undecan-2-one (5f). Colorless oil; 1H
NMR (CDCl3)
0.88 (3H, t, J¼6.8 Hz), 1.27e1.30 (10H, m), 1.48e1.54
(2H, m), 1.82e1.87 (2H, m), 2.11 (3H, s), 2.39 (3H, s), 2.69 (1H, s); 13C
4.4.7. 4-Cyclohexylmethyl-4-ethynyl-2-methoxy-2-methyl-5-methy-
lene-1,3-dioxolane (2h). Colorless oil, inseparable mixture of
d

1516
T. Kusakabe, K. Kato / Tetrahedron 67 (2011) 1511e1517
NMR (CDCl3)
d
14.1, 20.7, 22.6, 23.6, 26.1, 29.2, 29.3, 29.4, 31.8, 37.6,
J¼7.6 Hz), 2.71 (2H, t, J¼7.6 Hz), 3.03e3.04 (2H, m), 7.13 (2H, d,
J¼6.8 Hz), 7.19e7.22 (1H, m), 7.06e7.31 (2H, m); 13C NMR (CDCl3)
76.4, 79.6, 80.1, 169.4, 201.5; IR (ATR) 3274, 2925, 2855, 2117, 1732,
1369, 1233 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C15H24O3 252.1726;
found 252.1730.
d
10.9, 27.4, 34.7, 36.0, 111.1, 126.3, 128.3, 128.6, 140.8, 147.1, 176.1; IR
(KBr) 2923, 1790, 1496, 1454, 1234 cmꢁ1; HRMS-EI m/z: [Mþ] calcd
for C13H14O2 202.0994; found 202.0995.
4.5.6. 3-Acetyloxy-3-ethynyl-octan-2-one (5g). Colorless oil; 1H
NMR (CDCl3)
(2H, m), 1.82e1.86 (2H, m), 2.11 (3H, s), 2.39 (3H, s), 2.71 (1H, s); 13C
NMR (CDCl3) 13.9, 20.7, 22.4, 23.2, 26.1, 31.5, 37.6, 76.4, 79.6, 80.1,
169.4, 201.5; IR (ATR) 3273, 2956, 2932, 2871, 2117, 1732, 1369,
1237 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C12H18O3 210.1256; found
210.1262.
d
0.90 (3H, t, J¼7.2 Hz), 1.31e1.34 (4H, m), 1.49e1.55
4.7.2. 5-Methyl-4-phenylmethyl-2(3H)-furanone (6c). Colorless oil;
1H NMR (CDCl3)
d
2.05 (3H, t, J¼2.4 Hz), 2.99e3.00 (2H, m), 3.44
(2H, br s), 7.12 (2H, d, J¼6.8 Hz), 7.21e7.26 (1H, m), 7.29e7.33 (2H,
m); 13C NMR (CDCl3)
11.2, 32.0, 35.8, 111.4, 126.7, 128.2, 128.8,
d
d
138.3, 147.1, 175.8; IR (KBr) 2912, 1795, 1704, 1495, 1455, 1388,
1243 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C12H12O2 188.0837; found
188.0836.
4.5.7. 3-Acetyloxy-3-[(cyclohexyl)methyl]-4-pentyn-2-one
(5h). Colorless oil; 1H NMR (CDCl3)
d
0.97e1.05 (2H, m), 1.13e1.19
(1H, m), 1.24e1.30 (2H, m), 1.61e1.76 (7H, m), 1.87e1.90 (1H, m),
2.10 (3H, s), 2.38 (3H, s), 2.72 (1H, s); 13C NMR (CDCl3)
20.8, 25.7
4. 7. 3. 4-(1-Naphtylmethyl)-5-methyl-2(3H)-furanone
(6d). Colorless oil; 1H NMR (CDCl3)
d 2.09 (3H, br s), 2.95e2.97 (2H,
d
m), 3.89 (2H, br s), 7.27 (1H, d, J¼7.7 Hz), 7.41 (1H, dd, J¼8.2, 7.1 Hz),
(2C), 26.1, 26.1, 26.2, 34.0, 34.4, 44.0, 76.7, 79.7, 80.2, 169.2, 201.2; IR
(ATR) 3269, 2923, 2851, 2121,1731,1448,1368,1226 cmꢁ1; HRMS-EI
m/z: [Mþ] calcd for C14H20O3 236.1413; found 236.1409.
7.49e7.55 (2H, m), 7.77 (1H, d, J¼8.2 Hz), 7.87e7.94 (2H, m); 13C
NMR (CDCl3) d 11.4, 29.3, 36.2, 111.0, 123.1, 125.6, 125.9, 126.2, 126.3,
127.7, 129.0, 131.7, 133.9, 134.1, 147.0, 175.8; IR (ATR) 2929, 1790,
1597, 1510, 1386, 1218, 1134 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for
C16H14O2 238.0994; found 238.0995.
4.5.8. 3-Acetyloxy-3-cyclohexyl-4-pentyn-2-one (5i). Colorless oil;
1H NMR (CDCl3)
d
1.12e1.35 (5H, m), 1.57e1.92 (6H, m), 2.08 (3H, s),
2.41 (3H, s), 2.68 (1H, s); 13C NMR (CDCl3)
d
20.6, 25.8, 25.8, 25.9,
4.7.4. 5-Methyl-4-[(4-methylphenyl)methyl]-2(3H)-furanone
26.7, 26.9, 28.1, 45.1, 76.8, 79.4, 82.3, 169.6, 202.7; IR (KBr) 3293,
2929, 2860, 2116, 1740, 1373, 1354, 1241 cmꢁ1; HRMS-EI m/z: [Mþ]
calcd for C13H18O3 222.1256; found 222.1257.
(6e). Pale yellow oil; 1H NMR (CDCl3)
d 2.04 (3H, br s), 2.33 (3H, s),
2.98e3.00 (2H, m), 3.39 (2H, s), 7.01 (2H, d, J¼8.0 Hz), 7.11 (2H, d,
J¼8.0 Hz); 13C NMR (CDCl3)
d 11.2, 21.0, 31.6, 35.8, 111.6, 128.1, 129.4,
135.2, 136.3, 146.9, 175.9; IR (ATR) 2923, 1793, 1514, 1386, 1240,
1126 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C13H14O2 202.0994; found
202.0992.
4.6. Control experiment (Scheme 6)
4. 6.1. 3-Hydroxy-3-(2-phenylethyl)-pentan-2, 4-dione
(8a). Colorless oil; 1H NMR (CDCl3)
d
2.22 (6H, s), 2.26e2.29 (2H,
4.7.5. 5-Methyl-4-(1-octyl)-2(3H)-furanone (6f). Colorless oil; 1H
m), 2.53e2.57 (2H, m), 4.79 (1H, s), 7.15e7.29 (5H, m); 13C NMR
NMR (CDCl3)
d
0.89 (3H, t, J¼6.8 Hz), 1.27e1.40 (12H, m), 1.93 (3H, t,
(CDCl3)
d
25.2, 29.6, 38.2, 90.8, 126.3, 128.5, 128.5, 140.8, 207.2; IR
J¼2.4 Hz), 2.09 (2H, t, J¼7.4 Hz), 3.07e3.09 (2H, m); 13C NMR
(ATR) 3446, 1702, 1355, 1125, 700 cmꢁ1; HRMS-EI m/z: [Mþ] calcd
(CDCl3) d 11.1, 14.1, 22.6, 25.4, 28.3, 29.2, 29.2, 29.3, 31.8, 35.9, 112.3,
for C13H16O3 220.1100; found 220.1109.
146.2, 176.4; IR (ATR) 2925, 2855, 1740, 1707, 1461, 1377, 1163 cmꢁ1
;
HRMS-EI m/z: [Mþ] calcd for C13H22O2 210.1620; found 210.1620.
4.6.2. 4-Oxononanoate. To a solution of 2-methoxy-5-pentylfuran
(50.5 mg, 0.3 mmol) in MeOH (5 mL) was added HAuCl4$3H2O
(5.9 mg, 0.015 mmol) and the mixture stirred at room temperature
for 0.5 h. The reaction mixture was then quenched with powdered
NaHCO3 (100 mg), diluted with CH2Cl2 (30 mL) and washed with
satd NaHCO3(aq) (20 mL). The layers were separated and the
aqueous layer extracted with CH2Cl2 (30 mL). The combined
organic layers were dried over MgSO4 and concentrated in vacuo.
The crude product was purified by column chromatography on
silica-gel with hexane/ethyl acetate (10/1) as eluent to afford 4-
oxononanoate7b as a colorless oil (46.5 mg, 83%).
4.7.6. 5-Methyl-4-(1-pentyl)-2(3H)-furanone (6g). Colorless oil; 1H
NMR (CDCl3)
d
0.90 (3H, t, J¼7.2 Hz), 1.24e1.41 (6H, m), 1.93 (3H, t,
J¼2.8 Hz), 2.10 (2H, t, J¼7.6 Hz), 3.07e3.09 (2H, m); 13C NMR (CDCl3)
d
11.1, 14.0, 22.4, 25.4, 28.0, 31.3, 35.9, 112.3, 146.2, 176.4; IR (ATR)
2955, 2931, 2867, 1740, 1717, 1387, 1251, 1157 cmꢁ1; HRMS-EI m/z:
[Mþ] calcd for C10H16O2 168.1150; found 168.1145.
4.7.7. 4-[(Cyclohexyl)methyl]-5-methyl-2(3H)-furanone
(6h). Colorless oil; 1H NMR (CDCl3)
d 0.84e0.93 (2H, m), 1.09e1.38
(4H, m), 1.60e1.74 (5H, m), 1.92 (3H, t, J¼2.4 Hz), 1.97 (2H, d,
J¼7.2 Hz), 3.07e3.08 (2H, m); 13C NMR (CDCl3)
d 11.2, 26.1(2C), 26.4,
4.7. General procedure for the reaction of 5 (Table 3)
33.2(2C), 33.4, 36.5, 36.9, 111.1, 147.0, 176.4; IR (KBr) 2926, 2852,
1798, 1449, 1386, 1241, 1165 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for
C12H18O2 194.1307; found 194.1304.
A 20 mL round-bottomed flask containing a magnetic stirring
bar, PtCl4 (2.6 mg, 0.007 mmol), 5 (0.11 mmol), and toluene (5 mL)
was fitted with a Dimroth condenser capped with a rubber septum.
The mixture was stirred for a period of time at an appropriate
temperature. The reaction was quenched with powdered NaHCO3
(50 mg), and the mixture was then diluted with EtOAc (20 mL) and
washed with 5% NaHCO3 aq (40 mL). The organic layers were
separated, and the aqueous layer was then extracted with EtOAc
(30 mL). The combined organic layers were dried over MgSO4 and
then concentrated in vacuo. The crude product was purified by
column chromatography on silica-gel. The fraction eluted with
hexane/ethyl acetate (50/1 to 30/1) afforded lactone 6.
4.7.8. 4-Cyclohexyl-5-methyl-2(3H)-furanone (6i). Pale yellow oil;
1H NMR (CDCl3)
d 1.10e1.22 (3H, m), 1.26e1.36 (2H, m), 1.61e1.79
(5H, m), 1.94 (3H, t, J¼2.4 Hz), 2.22e2.29 (1H, m), 3.07 (2H, dd,
J¼2.0, 2.4 Hz); 13C NMR (CDCl3)
d 11.2, 25.8, 26.2(2C), 32.2(2C), 33.5,
35.2, 117.3, 144.9, 176.5; IR (KBr) 2925, 2850, 1794, 1711, 1451, 1389,
1250, 1220, 1166 cmꢁ1; HRMS-EI m/z: [Mþ] calcd for C11H16O2
180.1150; found 180.1153.
Acknowledgements
4.7.1. 5-Methyl-4-(2-phenylethyl)-2(3H)-furanone (6a). Pale yellow
This work was supported by a Grant-in-Aid for Scientific Re-
search (C) (No. 21590026).
oil; 1H NMR (CDCl3)
d
1.77 (3H, dd, J¼2.4, 0.4 Hz), 2.43 (2H, t,

T. Kusakabe, K. Kato / Tetrahedron 67 (2011) 1511e1517
1517
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