NbCl3-Catalyzed intermolecular [2+2+2] Cycloaddition of alkynes and α,ω-dienes: Highly chemo- and regioselective formation of 5-ω-alkenyl-1,4-substituted-1,3-cyclohexadiene derivatives

Article abstract of DOI:10.1021/jo101229u

Intermolecular [2+2+2] cycloaddition of tert-butylacetylene with α,ω-dienes was successfully achieved by NbCl₃(DME) catalyst to afford 5-ω-alkenyl-1,4-disubstituted-1,3-cyclohexadienes in excellent yields with high chemo- and regioselectivity.

Full text of DOI:10.1021/jo101229u

pubs.acs.org/joc
access of these compounds include tandem diene-alkyne
NbCl3-Catalyzed Intermolecular [2þ2þ2]
Cycloaddition of Alkynes and r,ω-Dienes:
Highly Chemo- and Regioselective Formation of
5-ω-Alkenyl-1,4-substituted-1,3-cyclohexadiene
Derivatives
metathesis4 and 1,6-electrocyclic reaction of 1,3,5-hexatrienes.5
In contrast, transition metal-catalyzed [2þ2þ2] intermolecular
cycloaddition by the reaction of two molecules of mono alkynes
and one molecule of alkenes is one of the most simple and
atom-economical methods for preparing 1,3-cyclohexadiene
derivatives. However, this methodology mainly leads to the
cyclotrimerization of alkynes6,7 in preference to the desired
cross-cyclotrimerization between alkynes and alkenes. There-
fore, only a limited amount of work has been reported so far.8,9
As a pioneering work for this synthetic protocol, Rothwell and
co-workers reported the intermolecular cycloaddition of al-
kynes and alkenes leading to 1,3-cyclohexadienes by titana-
cyclopentadiene catalyst.8 However, this method generally
affords 1,3-cyclohexadienes in unsatisfactory yields and selec-
tivities. In addition, this reaction pathway typically includes an
isomerization step through 1,5-hydrogen shift of unstable low-
valent titanium species such as the titananorbornene inter-
mediate.8 Alternatively, NbCl3(DME) is a thermally stable
low-valent early transition metal complex that shows high
reactivity in several stoichiometric and catalytic reactions with
alkynes.10-13 As a preliminary attempt, we reported NbCl3-
(DME)-catalyzed intermolecular cycloaddition of alkynes and
alkenes to substituted 1,3-cyclohexadienes.14 However, this
approach is still problematic with regard to access of the desired
1,3-cyclohexadienes in high yield and selectivity, which gener-
ally gives a cyclotrimerization byproduct of alkyne in substan-
tial yields.14 Therefore, the development of a novel and efficient
methodology for chemo- and regioselective formation of 1,3-
cyclohexadienes by [2þ2þ2] cycloaddition of alkenes and
Yasushi Obora,* Yasushi Satoh, and Yasutaka Ishii*
Department of Chemistry and Materials Engineering,
Faculty of Chemistry, Materials and Bioengineering and
ORDIST, Kansai University, Suita, Osaka 564-8680, Japan
obora@kansai-u.ac.jp
Received June 23, 2010
Intermolecular [2þ2þ2] cycloaddition of tert-butylacetylene
with R,ω-dienes was successfully achieved by NbCl3(DME)
catalyst to afford 5-ω-alkenyl-1,4-disubstituted-1,3-cyclo-
hexadienes in excellent yields with high chemo- and
regioselectivity.
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these compounds have been utilized as monomers for good
transparency and heat resistance polymers.2 Therefore, vari-
ous methods for the preparation of substituted 1,3-cyclo-
hexadienes have been investigated.3 Recent methods to the
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6046 J. Org. Chem. 2010, 75, 6046–6049
Published on Web 08/03/2010
DOI: 10.1021/jo101229u
r
2010 American Chemical Society

Obora et al.
JOCNote
TABLE 1. NbCl3-Catalyzed Reaction of tert-Butylacetylene (1a) with
1,9-Decadiene (2a)a
1a and 2a was carried out with 1:2 molar ratio (entry 1). As
the amount of 2a was reduced, the yield of 3a was lowered
(entries 2 and 3). However, it is noteworthy that the reaction
was exclusively subjected to react only the single alkene side
of R,ω-dienes with the alkyne and 3a was the sole cross-
cycloaddition product.
The reaction was greatly affected by the solvent employed and
halogenated solvents such as 1,2-dichloroethane and 1,4-dichloro-
butane realized high selectivity of 3a (entries 1 and 4). On the
other hand, the use of other solvents such as THF, toluene, and
DME resulted in a decrease in the yields of 3a (entries 5-7).
As for the catalyst precursor of this reaction, a low-valent
Nb(III) complex, NbCl3(DME), is highly efficient. When the
Ta(III) analogue, TaCl3(DME), was used as a catalyst, even
though 1a was evidently converted during the reaction
course, no desired 1,3-cyclohexadiene adduct was produced
at all (entry 8). Other Nb(IV), Nb(V), and V(III) complexes
such as NbCl5, Cp2NbCl2, and VCl3(THF)3 were totally
ineffective catalysts for the formation of cycloaddition pro-
ducts (entries 9-11).
Under the optimized condition as shown in Table 1, entry 1,
reactions of various 1-alkynes (1a-d) with R,ω-dienes (2b-e)
were examined (Table 2). The yields of the 1,3-cyclohexadiene
adducts (3) were somewhat influenced by the alkyl chain
lengthof the R,ω-dienes (2) and the reactionof 1a with various
R,ω-dienes (2) gave the corresponding 5-ω-alkenyl-1,4-
di-tert-butyl-1,3-cyclohexadienes (2b-e) in good to excellent
yields (56-97%) with high to excellent chemo- and regios-
electivity (86f99%) (entries 1-5). In this reaction, the yield
and selectivity of the reaction were greatly affected by the
bulkiness and electronic nature of alkyne substituents. The
best yield and selectivity for the formation of 3a was achieved
when the reaction was carried out with tert-butylacetylene
(1a). Onthe other hand, the reactionof trimethylsilylacetylene
(1b) with 2a led to the mixture of the corresponding inter-
molecular cycloaddition products (3f) and the alkyne cyclo-
trimerizationproduct (4b) (entry 6). Alkynes havinglessbulky
substituents such as 1-hexyne (1c) and phenylacetylene (1d)
resulted in alkyne tricyclomerization products (4c-d) as
major adducts (entries 7 and 8).
yieldb/%
entry
catalyst
solvent
3a
4a
1
2c
3d
4
5
6
7
8
9
10
11
NbCl3(DME)
NbCl3(DME)
NbCl3(DME)
NbCl3(DME)
NbCl3(DME)
NbCl3(DME)
NbCl3(DME)
TaCl3(DME)
NbCl5
Cl(CH2)2Cl
Cl(CH2)2Cl
Cl(CH2)2Cl
Cl(CH2)4Cl
THF
DME
toluene
Cl(CH2)2Cl
Cl(CH2)2Cl
Cl(CH2)2Cl
Cl(CH2)2Cl
97 [81] (92)
65 (90)
27 (94)
83 (91)
9 (46)
nde
trace
7
9
trace
26
ne
nde
nde
nde
nde,f
nde
nde
nde
nde,f
Cp2NbCl2
VCl3(THF)3
nde
nde
a1a (2 mmol) was allowed to react with 2a (4 mmol) in the presence of
catalyst (0.2 mmol, 10 mol % based on 1a) in solvent (1 mL) at 40 °C for
2 h. bYields were determined by GC based on 1a used. The number in
square bracket shows isolated yield. The numbers in parentheses show
the selectivity (%) of 1,4,5-substituted adduct. The regiochemistry of
other isomers was not determined. c1a (2 mmol) and 2a (2 mmol) were
d
e
used. 1a (2 mmol) and 2a (1 mmol) were used. Not detected by GC.
fThe substrates 1a and 2a were converted thoroughly and an intractable
mixture of unidentified oligomerization products was obtained.
alkynes remains an unsoluble problem and a challenging target.
In this paper, we would like to report the excellent chemo- and
regioselective [2þ2þ2] intermolecular cycloaddition reaction
of 1-alkynes with R,ω-unconjugated dienes under the influence
of NbCl3(DME),5a affording 1,4,5-trisubstituted-1,3-cyclohex-
adiene derivatives in high to excellent yields (eq 1). The present
reaction provides a novel protocol for the selective formation of
ω-alkenyl-substituted-1,3-cyclohexadiene derivatives, which
also enables the conversion to ω-acetyl-substituted 1,3-cyclo-
hexadiene derivatives.
The reaction can be extended to the formation of ω-acetoxy-
substituted 1,3-cyclohexadiene (eq 2). For instance, the reac-
tion of 1a (2 mmol) with methyl vinylacetate (5) (2 mmol)
under optimized conditions afforded 6 in 68% yield as a single
regioisomer (1,4,5-adduct) along with the formation of 4a in
8% yield (eq 2).
tert-Butylacetylene (1a) and 1,9-decadiene (2a) were chosen
as model substrates and the reaction was carried out under
various conditions (Table 1). For instance, a mixture of 1a
(2 mmol) and 2a (4 mmol) in dichloroethane (1 mL) was
allowed to react under the influence of a catalytic amount of
NbCl3(DME) (0.2 mmol, 10 mol %) at 40 °C for 4 h, giv-
ing 1,4-di-tert-butyl-5-(7-heptenyl)-1,3-cyclohexadiene (3a) in
excellent yield (entry 1). In contrast to the previous paper,14
the reaction proceeded highly chemo- and regioselectively
to afford 1,4,5-trisubstituted-1,3-cyclohexadiene (3a) almost
exclusively. In this reaction, only a negligible amount of tri-
tert-butylbenzenes (5a) was detected by GC (entry 1). The
regiostructure of the 1,4,5-substituted cycloaddition pro-
duct (3a) was characterized by 1H and 13C NMR, which reso-
nances were assigned by means of 2D HMQC and HMBC
spectroscopies.
For further exploitation of the synthetic application of
the 5-ω-alkenyl-1,4-substituted-1,3-cyclohexadienes, the
Pd(II)-catalyzed Wacker oxidation reaction of 3c was carried
The yield of 3a was influenced by the ratio of the substrate
1a to 2a and the best yield was obtained when the reaction of
J. Org. Chem. Vol. 75, No. 17, 2010 6047

Obora et al.
JOCNote
TABLE 2. NbCl3-Catalyzed Reaction of Terminal Alkynes (1) with R,ω-Dienes (2)a
yield/%b
entry
alkyne (1) R
R,ω-diene (2)
3
4
1
2
3
4
5
6
7
8
t-Bu (1a)
t-Bu (1a)
t-Bu (1a)
t-Bu (1a)
t-Bu (1a)
Me3Si (1b)
n-C4H9 (1c)
Ph (1d)
1,9-decadiene (n = 6) (2a)
1,5-hexadiene (n = 2) (2b)
1,7-octadiene (n = 4) (2c)
1,11-dodecadiene (n = 8) (2d)
1,13-tetradecadiene (n = 10) (2e)
2a
2a
2a
97 [81] (92) (3a)
78 [63] (86) (3b)
84 [64] (91) (3c)
73 [64] (95) (3d)
56 [36] (>99) (3e)
[65] (>99) (3f)
nd
trace
6 (4a)
trace
trace
nd
18 (4b)
64 (4c)
48 (4d)
trace
a1 (2 mmol) was allowed to react with 2 (4 mmol) in the presence of NbCl3(DME) (0.2 mmol, 10 mol % based on 1) in 1,2-dichloroethane (1 mL) at
40 °C for 2 h. bYields were determined by GC based on 1 used. The numbers in square brackets show isolated yields. The numbers in parentheses show the
selectivity (%) of 1,4,5-substituted adducts. The regiochemistry of the other isomers was not determined.
SCHEME 1. A Plausible Reaction Pathway
out. The reaction of 3c in the presence of PdCl2 combined with
CuCl under O2 (1 atm)15 led to the formation of 7, as ω-acetyl-
functionalized 1,3-cyclohexadienes in 56% isolated yield
(eq 3). Since the substrates having oxo-functionality like
ketones and aldehydes are not generally tolerated under the
conditions in the low-valent early transition metal catalyst
system,10-12 this two-step synthesis provides an efficient
protocol for the 1,3-cyclohexadienes having oxo-functionality
in the molecule.
With regard to the reaction mechanism, the reaction would
proceed in a similar manner to the previously reported pathway
via the formation of a niobacyclopentadiene A by the reaction of
two alkyne molecules, followed by the reaction with R,ω-dienes
to form niobanorbornene species B as a key intermediate
(Scheme 1).14 In the present reaction, however, it was found that
the ω-alkenyl moiety on the R,ω-dienes markedly affects the
reactivity of the cycloaddition reaction as well as chemo- and
regioselectivity. Although all attempts at isolation and spectral
observation of the relevant niobium intermediates were unsuc-
cessful, the ω-alkenyl group would coordinate to the niobium
metal center as a directing group, which hampered the formation
of undesired alkyne cyclotrimerization products (path A,
Scheme 1). The directing group effect of the ω-alkenyl moiety
presumably enhanced the reactivity of the alkenes, as well as
improved selectivity of the resulting 1,3-cyclohexadiene products.
However, the effect the chain length of the R,ω-dienes exerted on
the regiochemistry of the reaction is not clearly explained at this
moment. The detailed elucidation on the reaction mechanism
based on the experimental evidence is currently in progress.
In conclusion, we have developed a new protocol to the
highly chemo- and regioselective reaction for [2þ2þ2] cyclo-
addition of alkynes and alkenes leading to 5-ω-alkenyl-1,4-
substituted-1,3-cyclohexadienes in high to excellent yields.
Here, the ω-alkenyl group can be easily converted to the
ω-acetyl group.
Further study on the scope and further synthetic applica-
tion of this reaction will be performed in future work.
Experimental Section
A Typical Reaction Procedure for the Preparation of 3a (entry 1,
Table 1). A mixture of tert-butylacetylene (1a) (164 mg, 2 mmol),
1,9-decadiene (2a) (552 mg, 4 mmol), NbCl3(DME) (58 mg,
0.2 mmol), and 1,2-dichloroethane (1 mL) was stirred for 2 h at
40 °C under Ar. The yields of the products were estimated from
the peak areas based on the internal standard technique using GC
and 3a was obtained in 97% yield. The product 3a was isolated by
silica gel column chromatography (n-hexane as eluent) in 81%
yield (489 mg) as a colorless liquid.
3a: 1H NMR (400 MHz, CDCl3) δ 0.85-1.02 (m, 2H), 1.05
(s, 9H), 1.09 (s, 9H), 1.28-1.55 (m, 10H), 2.04 (m, 1H), 2.32,
(15) Tsuji, J.; Nagashima, H.; Nemoto, H. Org. Synth. 1990, 7, 137.
6048 J. Org. Chem. Vol. 75, No. 17, 2010

Obora et al.
JOCNote
(d, 2H), 4.92 (dt, J = 10.1, 1.7 Hz, 1H), 4.98 (dt, J = 15.4, 1.7 Hz,
1H), 5.69 (s, 2H) 5.74 (tt, J = 12.4, 5.2 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 27.5 (CH2), 28.1 (CH2), 28.2 (CH2), 28.5
(CH3), 28.7 (CH2), 28.9 (CH2), 29.2 (CH2), 29.6 (CH3), 33.2
(CH), 33.8 (CH2), 35.0 (C), 35.6 (C), 114.1 (CH2), 115.4 (CH),
(d, 3J = 14.9 Hz, 2H), 4.92 (dt, J = 10.2, 1.7 Hz, 1H), 4.98 (dt,
J = 15.4, 1.7 Hz, 1H), 5.63 (s, 2H), 5.79 (m, 1H); 13C NMR (100
MHz, CDCl3) δ 27.0 (CH2), 28.0 (CH2), 28.2 (CH2), 28.5 (CH3),
29.1 (CH2), 29.6 (CH3), 33.2 (CH), 33.8 (CH2), 35.0 (C), 35.6
(C), 114.2 (CH2), 115.4 (CH), 115.5 (CH), 139.1 (CH), 143.5 (C),
150.1 (C); IR (neat, cm-1) 2964, 2871, 1736, 1465, 1363, 1062,
885; GC-MS (EI) m/z (rel intensity) 274 (8) [M]þ, 175 (6), 83 (1),
79 (1), 57 (100); HRMS(EI) m/z calcd for C20H34 [M]þ 274.2661,
found 274.2653.
115.5 (CH), 139.2 (CH), 143.6 (C), 150.2 (C); IR (neat, cm-1
)
3069, 1830, 1768, 1648, 1597, 1361, 1103, 921; GC-MS (EI) m/z
(rel intensity) 302 (9) [Mþ], 190 (1), 175 (6), 119 (4), 79 (1), 57
(100); HRMS (EI) m/z calcd for C22H38 [M]þ 302.2974, found
302.2979.
The Reaction of 1a with 5 (eq 2). A mixture of tert-butylace-
tylene (1a) (164 mg, 2 mmol), methyl vinylacetate (5) (200 mg,
2 mmol), NbCl3(DME) (58 mg, 0.2 mmol), and 1,2-dichloro-
ethane (1 mL) was stirred for 2 h at 40 °C under Ar. The yields of
the products were estimated from the peak areas based on the
internal standard technique using GC (68% (6) and 8% (4a)).
The product 6 was isolated as pure form by silica gel column
chromatography (n-hexane/ethyl acetate = 8/2 as eluent) in
55% yield (156 mg).
3d: colorless liquid; 1H NMR (400 MHz, CDCl3) δ 1.05
(s, 9H), 1.09 (s, 9H), 1.18-1.36 (m, 14H), 1.52 (m, 2H), 2.06
(m, 1H), 2.32 (d, J = 15.1, 2H), 4.93 (dt, J = 10.1, 1.4 Hz, 1H),
4.99 (dt, J = 15.6, 1.4 Hz, 1H), 5.69 (s, 2H), 5.81 (m, 1H); 13
C
NMR (100 MHz, CDCl3) δ 27.5 (CH2), 28.1 (CH2), 28.2 (CH2),
28.4 (CH3), 28.9 (CH2), 29.1 (CH2), 29.4 (CH2), 29.5 (CH3), 29.6
(CH2), 29.7 (CH2), 33.2 (CH3), 33.8 (CH2), 35.0 (C), 35.6 (C),
114.1 (CH2), 115.3 (CH), 115.5 (CH), 139.2 (CH), 143.6 (C),
150.3 (C); IR (neat, cm-1) 3056, 1818, 1769, 1642, 1363, 1062,
885; GC-MS (EI) m/z (rel intensity) 330 (8) [M]þ, 190 (1), 135
(1), 79 (1), 57 (100); HRMS(EI) m/z calcd for C24H42 [M]þ
330.3289, found 330.3294.
6: colorless liquid; 1H NMR (400 MHz, CDCl3) δ 0.96 (s, 9H),
1.03 (s, 9H), 2.04 (m, 2H), 2.25-2.50 (m, 2H), 2.73 (m, 1H), 3.53
(s, 3H) 5.65(s, 2H); 13C NMR (100 MHz, CDCl3) δ 28.3 (CH),
29.2 (CH2), 29.3 (CH3), 29.5 (CH3), 33.3 (CH2), 34.9 (C), 35.6
(C), 51.3 (CH3), 115.6 (CH), 117.0 (C), 143.8 (C), 147.3 (C),
173.6 (C); IR (neat, cm-1) 2961, 2823, 1738, 1644, 1465, 1362,
1090 885; GC-MS (EI) m/z (rel intensity) 264 (2) [M]þ, 190 (16),
175 (100), 79 (1), 57 (55); HRMS (EI) m/z calcd for C17H28O2
[M]þ 264.2089, found 264.2089.
Preparation of 7 from 3c (eq 3). A mixture of 3c (822 mg,
3 mmol), PdCl2 (53 mg, 0.3 mmol), CuCl (297 mg, 3 mmol), and
H2O/DMF (0.3/2.7 mL) was stirred for 24 h at room tempera-
ture under O2 (1 atm). The product 7 was isolated (by silica gel
column chromatography with n-hexane/ethyl acetate=8:2 as
eluent) in 56% yield as pure form (483 mg).
3e: colorless liquid; 1H NMR (400 MHz, CDCl3) δ 0.98
(s, 9H), 1.19-1.49 (m, 18H), 1.18-1.36 (d, J=15.2, 2H), 1.32
(s, 9H), 1.94-2.03 (m, 3H), 4.85 (dt, J = 10.3, 1.4 Hz, 1H),
4.92 (dt, J = 15.6, 1.4 Hz, 1H), 5.61 (s, 1H), 5.62 (s, 1H), 5.73 (m,
1H); 13C NMR (100 MHz, CDCl3) δ 27.6 (CH2), 28.1 (CH2),
28.2 (CH2), 28.5 (CH3), 28.9 (CH2), 29.2 (CH2), 29.5 (CH2),
29.60 (CH3), 29.63 (CH2), 29.7 (CH2), 29.8 (CH2), 33.2
(CH), 33.8 (CH2), 35.0 (C), 35.6 (C), 114.0 (CH2), 115.3 (CH),
115.5 (CH), 139.2 (CH), 143.4 (C), 150.2 (C); GC-MS (EI) m/z (rel
intensity) 358 (8) [M]þ, 190 (1), 175 (6), 91 (3), 57 (100); HRMS
(EI) m/z calcd for C26H46 [M]þ 358.3602, found 358.3617.
1
3f: colorless liquid; H NMR (400 MHz, CDCl3) δ 0.00 (s,
9H), 0.03 (s, 9H), 1.11-1.32 (m, 10H), 1.95-2.25 (m, 2H),
1.95-2.27 (d, J = 15.3 Hz, 2H), 2.07 (s, 1H), 4.89 (dt, J =
15.3 Hz, 1H), 5.73 (m, 2H), 6.11 (s, 2H); 13C NMR (100 MHz,
CDCl3) δ -2.7 (CH3), -1.5 (CH3), 27.3 (CH2), 27.6 (CH2), 28.7
(CH2), 28.9 (CH2), 29.0 (CH2), 29.4 (CH2), 32.8 (CH), 33.6
(CH2), 113.9 (CH2), 130.8 (CH), 131.5 (CH), 138.2 (CH), 139.0
(C), 145.4 (C); IR (neat, cm-1) 3075, 1640, 1602, 1440, 1247,
1169, 1071, 992; GC-MS (EI) m/z (rel intensity) 334 (3) [M]þ,
260 (1), 223 (2), 187 (1), 135 (47), 73 (100), 41 (3); HRMS (EI) m/
z calcd for C20H38Si2 [M]þ 334.2512, found 334.2524
7: colorless liquid, 1H NMR (400 MHz, CDCl3) δ 0.97 (s, 9H),
1.01 (s, 9H), 1.22-1.47 (m, 6H), 1.98 (m, 1H), 2.04 (s, 3H), 2.22
(m, 2H), 2.33 (t, J = 7.6 Hz, 2H), 5.62 (s, 2H); 13C NMR
(100 MHz, CDCl3) δ 23.9 (CH2), 27.0 (CH2), 27.9 (CH2), 28.1
(CH2), 28.4 (CH3), 29.5 (CH3), 29.8 (CH3), 33.0 (CH), 34.9 (C),
35.6 (C), 43.7 (CH2), 115.5 (CH), 115.6 (CH), 143.5 (C), 149.9
(C), 209.3 (C); IR (neat, cm-1) 3052, 1718, 1462, 1359, 1264, 834;
GC-MS (EI) m/z (rel intensity) 290 (9) [M]þ, 191 (1), 177 (9), 99
(2), 79 (2), 57 (100); HRMS (EI) m/z calcd for C20H34O [M]þ
290.2610 found 290.2613
3b: colorless liquid; 1H NMR (400 MHz; CDCl3) δ 0.98
(s, 9H), 1.01 (s, 9H), 1.24-1.47 (m, 2H), 1.85-2.10 (m, 2H),
1.98-2.10 (m, 1H), 2.23 (d, J = 15.1 Hz, 2H), 4.85 (dt, J = 10.1,
1.8 Hz, 1H), 4.91 (dt, J = 15.1, 1.8 Hz, 1H), 5.63 (s, 2H), 5.71 (tt,
J = 11.7, 4.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 27.3
(CH2), 28.0 (CH2), 28.5 (CH3), 29.6 (CH3), 31.7 (CH2), 32.4
(CH), 35.0 (C), 35.6 (C), 114.4 (CH2), 115.7 (CH), 115.8 (CH),
138.8 (CH), 143.4 (C), 149.8 (C); IR (neat, cm-1) 2963, 2869,
1641, 1479, 1392, 1367, 1264, 1021, 910; GC-MS (EI) m/z (rel
intensity) 246 (12) [M]þ, 189 (3), 133 (4), 119 (8), 57 (100); HRMS
(EI) m/z calcd for C18H30 [M]þ 246.2348, found 246.2352.
3c: colorless liquid; 1H NMR (400 MHz; CDCl3) δ 1.05
(s, 9H), 1.09 (s, 9H), 1.15-1.59 (m, 8H), 2.07 (m, 1H), 2.32
Acknowledgment. This work was supported by a Grant-in-
Aid for Scientific Research from MEXT, Japan, Japan Science
and Technology Agency (JST), Kansai University Research
Grants (Grant-in Aid for Encouragement of Scientists, 2009),
and “Strategic Project to Support the Formation of Research
Bases at Private Universities” (Matching Fund Subsidy from
MEXT).
1
Supporting Information Available: Copies of H, 13C, and
2D (HMQC and HMBC) NMR spectra of the products. This
material is available free of charge via the Internet at http://
pubs.acs.org.
J. Org. Chem. Vol. 75, No. 17, 2010 6049