Active low-valent niobium catalysts from NbCl5 and hydrosilanes for selective intermolecular cycloadditions

Article abstract of DOI:10.1021/jo201757w

An active niobium catalyst was developed via a simple and nontoxic reduction method from NbCl₅/hydrosilane and utilized for the selective [2 + 2 + 2] cycloaddition reaction of terminal alkynes and alkenes/α,ω-dienes, to give 1,3-cyclohexadiene derivatives in high yields with excellent chemo- and regioselectivity.

Full text of DOI:10.1021/jo201757w

NOTE
pubs.acs.org/joc
Active Low-Valent Niobium Catalysts from NbCl5 and Hydrosilanes for
Selective Intermolecular Cycloadditions
Yasushi Satoh and Yasushi Obora*
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita,
Osaka 564-8680, Japan
S Supporting Information
b
ABSTRACT: An active niobium catalyst was developed via a
simple and nontoxic reduction method from NbCl5/hydrosi-
lane and utilized for the selective [2 + 2 + 2] cycloaddition
reaction of terminal alkynes and alkenes/α,ω-dienes, to give
1,3-cyclohexadiene derivatives in high yields with excellent
chemo- and regioselectivity.
ow-valent early transition-metal-mediated or -catalyzed or-
ganic transformations are intriguing, owing to the inherent
For instance, an active catalyst system, consisting of the salt-
free reduction of NbCl5 (0.2 mmol, 10 mol %) with tris-
(trimethylsilyl)silane ((TMS)3SiH) (0.2 mmol, 10 mol %), in
the presence of tert-butylacetylene (1) (2 mmol), 1-decene (2a)
(2 mmol), and 1,2-dichloroethane (1 mL) at 40 °C for 3 h,
produced 1,4-di-tert-butyl-5-octyl-1,3-cyclohexadiene (3a) ex-
clusively in 90% yield with excellent chemo- and regioselectivity
(Table 1, entry 1). The reaction led exclusively to 3a, in pre-
ference to the formation of any tri-tert-butylbenzenes (4a), which
are produced by the cyclotrimerization of alkynes10 (1) (entry 1).
It is noteworthy that when the reaction was performed in the
absence of the hydrosilane, that is, with NbCl5 solely, no 3a for-
mation was observed (entry 2), indicating that hydrosilane is a
prerequisite for generating active catalyst. Furthermore, the re-
action using the present catalytic system outperformed the con-
ventionally used low-valent Nb complex, NbCl3(DME), in this
transformation (entry 3). When the Ta analogue, TaCl5, was
used combined with (TMS)3SiH under these conditions, 3a was
not obtained at all, but 4a was preferentially obtained in 54% yield
(entry 4). Screening hydrosilanes showed that those bearing bulky
substituents, such as (TMS)3SiH gave the best yields of 3a. How-
ever, besides (TMS)3SiH, a variety of hydrosilanes such as poly-
methylhydrosiloxane (PMHS), Et3SiH, (EtO)3SiH, PhMeSiH2,
PhSiH3, (Me2SiH)2O, and (Me2SiH)2NH were also good redu-
cing agents for NbCl5 (entries 5À11). The best yield for 3a was
obtained when the reaction between 1 and 2a was carried out at a
1:1 ratio. However, even when 1 and 2a were reacted in a
stoichiometric ratio (namely, 1:2a = 2:1), the yield for 3a was still
good (entry 12). The reaction is remarkably effective at low
catalyst loading (2.5 mol %), giving 3a in excellent yield (entry
13). The reaction is affected by the solvent employed; haloge-
nated solvents, such as 1,2-dichloroethane, resulted in 3a in high
yield (entry 1). Benzene could also be employed as solvent in this
reaction (entry 14). However, the use of 1,2-dimethoxyethane
(DME) resulted in a decrease in catalytic activity, since the DME
L
ability of these metals to act as reductants for the activation of
unsaturated compounds.1 To date, reactions with Ti(II),2 Zr-
(II),3 Ta(III),4 and Nb(III)5 have been intensively explored.
Conventionally, these low-valent metals are prepared by reduc-
tion, using harsh reducing agents such as elemental metals (Na,
Li, Zn), alkyllithiums, Grignard reagents, or LiAlH4.2À5 In general,
these low-valent early transition metal species are thermally un-
stable, and their preparation and utilization need to be performed
at low temperature, hampering their practicality for use in
catalytic reactions. Therefore, the development of a method for
the generation of thermally stable and catalytically active low-
valent early transition metals using stable, safe, and nontoxic
reducing agents under mild conditions is highly desirable.
In 1987, Pedersen and co-workers reported the preparation of
NbCl3(DME), a thermally stable low-valent early transition-metal
complex, by the treatment of NbCl5 with Bu3SnH in DME.6 This
complex is currently commercially available and has been utilized
as both a reagent and a catalyst in organic transformations.7 We
recently reported the NbCl3(DME)-catalyzed [2 + 2 + 2]
cycloaddition reaction between alkynes and alkenes, leading to
1,3-cyclohexadiene derivatives.8
In addition, Mashima and co-workers recently reported that a
catalytic system consisting of TaCl5 with 3,6-bis(trimethylsilyl)-
1,4-cyclohexadiene, or its methyl derivative, in the presence of
ethylene led to the ethylene trimerization product.9
In this paper, we wish to report a simple and nontoxic method
for the generation of low-valent niobium species from NbCl5,
using hydrosilanes as reducing agents. This novel NbCl5/hydro-
silane catalyst system surpasses the existing NbCl3(DME) cata-
lyst with regard to both catalytic activity and selectivity in the
intermolecular [2 + 2 + 2] cycloadditions of alkynes and alkenes
to give 1,3-cyclohexadiene derivatives.8
To examine the efficacy of the present Nb catalyst system, the
reaction between tert-butylacetylene (1) and 1-decene (2a) was
selected as a model reaction and carried out under various con-
ditions (Table 1).
Received: August 23, 2011
Published: September 15, 2011
r
2011 American Chemical Society
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|

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NOTE
Table 1. NbCl5/Hydrosilane Catalyzed Reaction of tert-Bu-
tylacetylene (1) and 1-Decene (2a) under Various
Conditionsa
Table 2. NbCl5/(TMS)3SiH Catalyzed Reaction of 1 with
Alkenes 2a
yield (%)
yield (%)b
entry
2 (R1)
n-C4H9 (2b)
3 (selectivityb)
4a
entry
catalyst
NbCl5
hydrosilane
3a (selectivity)c
4a
1
2
3
4
5
6
7
88 (3b)
93 (3c)
89 (3d)
77 (3e)
63d (3f)
49 (3g)
99e (3h)
ndc
ndc
ndc
ndc
10
ndc
ndc
1
(TMS)3SiH
none
90 [88]
ndd
e
n-C6H13 (2c)
2
3f
NbCl5
NbCl3(DME)
TaCl5
ndd
n-C10H21 (2d)
none
61 (91:9)
14
(CH3)2CHCH2CH2 (2e)
PhCH2 (2f)
4
(TMS)3SiH
PMHS
ndd
54
5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
74
8
PhCH2CH2 (2g)
norbornene (2h)
6
Et3SiH
57 (88:12)
7
a Reaction conditions: 1 (2 mmol), 2 (2 mmol), 1,2-dichloroethane
(1 mL), and NbCl5 (0.2 mmol, 10 mol % based on 1 and (TMS)3SiH
(0.2 mmol) at 40 °C for 3 h. b The regioselectivity of 1,4,5-adducts was
7
(EtO)3SiH
PhMeSiH2
PhSiH3
70 (53:47)
18
8
60
trace
4
9
58
>99% unless otherwise noted. Not detected by GC. d A regioisomer
c
10
11
12g
13h
14i
15j
(Me2SiH)2O
(Me2SiH)2NH
(TMS)3SiH
(TMS)3SiH
(TMS)3SiH
(TMS)3SiH
84
trace
trace
ndd
ndd
ndd
ndd
e
mixture of 1,4,5- and 1,3,5-adducts in an 88:12 ratio. exo,exo-Isomer
was obtained exclusively.11
56 (77:23)
73
90
system was used for the reaction, the desired cycloaddition product,
4,7-di-tert-butyl-2,3,3a,7a-tetrahydro-1H-indene (6),12 was ob-
tained in 92% yield, along with a small amount of 4a (5%).
However, NbCl3(DME) showed almost inert catalytic activity
for the formation of 6, and preferentially formed 4a in 37% yield.
53
ndd
a Reaction conditions: 1 (2 mmol), 2a (2 mmol), 1,2-dichloroethane
(1 mL), NbCl5 (0.2 mmol, 10 mol % based on 1), and hydrosilane
(0.2 mmol) at 40 °C for 3 h. b GC yields except the values in the square
brackets. c The regioselectivity of 1,4,5-adducts was >99% unless
otherwise noted. The numbers in the parentheses show the regios-
electivity ratio (%) (1,4,5-adducts:1,3,5-adducts) determined by GC.
d Not detected by GC. e Small amount (<5%) of a mixture of intractable
products including 4a was detected by GC. f Data from ref 8a.
g 1 (2 mmol) and 2a (1 mmol) were used. h Reaction conditions: 1
(4 mmol), 2a (4 mmol), 1,2-dichloroethane (1 mL), NbCl5 (0.1 mmol,
2.5 mol % based on 1), and (TMS)3SiH (0.1 mmol) at 40 °C for 24 h.
i Benzene (1 mL) was used as solvent. 1,2-Dimethoxyethane (1 mL)
j
was used as solvent.
can coordinate to the Nb metal and form stable and catalytically
inert, low-valent niobium species (vide infra) (entry 15) Under
the optimized reaction conditions, as shown in Table 1, entry 1,
the reaction of 1 with various alkenes (2) was examined (Table 2).
Reactions using 1-alkenes (2bÀ2d) gave the corresponding 1,3-
cyclohexadienes (3bÀ3d) in 88À93% yield, with excellent chemo-
and regioselectivity. Similarly, 5-methyl-1-hexene (2e), allylben-
zene (2f), 4-phenyl-1-butene (2g), and norbornene (2h) were
allowed to react with 1, affording the corresponding 1,3-cyclo-
hexadiene derivatives (3eÀh) in good yield (entries 4À7).
Here, to achieve the cross-cycloaddition of alkyne and alkene,
bulky tert-butyl acetylene (1) is indispensable. Thus, the use of
less bulky acetylenes such as 1-hexyne and cyclohexylacetylene
exclusively lead to the alkyne cyclotrimerization products.10
In sharp contrast to the existing NbCl3(DME)-catalyzed re-
action, the present NbCl5/(TMS)3SiH catalyst system success-
fully achieved the cycloaddition reaction between 1 and cyclo-
pentene (5) (eq 1). Thus, when the NbCl5/(TMS)3SiH catalyst
To further explore the synthetic scope and to obtain further
information regarding the reactivity of this new catalyst system,
the reaction of 1 with several α,ω-dienes (7aÀ7c) was examined
(Table 3). The selectivity between the monocycloaddition pro-
duct 8 and the dicycloaddition product 9 was controlled by the
substrate ratio (1:7). Thus, when a reaction between 1 (2 mmol)
and 7 (4 mmol) was carried out, only a single alkene within the
α,ω-diene is subjected to reaction with 1, and the corresponding
5-ω-alkenyl-1,3-cyclohexadiene (8) is obtained, exclusively
(entries 1À3). An almost similar catalytic activity and selectivity
are observed for NbCl5/(TMS)3SiH (entries 1 and 2) and NbCl3-
(DME) (entry 3). However, it is noteworthy that for the reaction
of 1 (2 mmol) and 7 (0.5 mmol) using the NbCl5/(TMS)3SiH
catalyst system both alkene sides of the α,ω-diene react, leading
to dicycloaddition products (9aÀc), exclusively, in high yield
(entries 4À6). No 9 was obtained at all using NbCl3(DME) as
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NOTE
Table 3. Nb-Catalyzed Reaction of 1) with α,ω,-dienes (7)a
of benzene-d6 at 20 °C, alkyne carbon peaks assignable to the
low-valent Nb-alkyne complex [A] appear at 236.7 and 255.6 ppm,
which agrees with the reported values for the (DME)NbCl3-10
complex (237.5 and 256.2 ppm)7a,b (Figure S1 in Supporting
Information). Therefore, the addition of DME to the present
highly catalytic active low-valent niobium species would actually
lower the activity, resulting in a stable low-valent Nb species, as
found for NbCl3(DME).6,7
7
yield (%)
1:7 (mmol) 8 (selectivity)b
9
entry
[cat.]
n
1
NbCl5/(TMS)3SiH
NbCl5/(TMS)3SiH
NbCl3(DME)
4
6
6
4
6
8
4
2:4
77(8a)
ndc
ndc
ndc
2
3d
2:4
90(8b)
81(8b)e
trace
2:4
4
NbCl5/(TMS)3SiH
NbCl5/(TMS)3SiH
NbCl5/(TMS)3SiH
NbCl3(DME)
2:0.5
2:0.5
2:0.5
2:0.5
91(9a)
79(9b)
66(9c)
ndc
5
trace
6
7f
trace
11(8a) g
a Reaction conditions: 1 (2 mmol), 7 (0.5À4 mmol), 1,2-dichloroethane
(1 mL), NbCl5 (0.2 mmol, 10 mol % based on 1), and (Me3Si)3SiH (0.2
mmol) at 40 °C for 3 h. b The regioselectivity of 1,4,5-adducts was >99%
unless otherwise noted. c Not detected by GC. d Data from ref 8b.
e A regioisomer mixture of 1,4,5- and 1,3,5-adducts in a 92:8 ratio.
f In addition to the product 8a, 4a (27%) was formed. g A regioisomer
mixture of 1,4,5- and 1,3,5-adducts in a 95:5 ratio.
Although it is not possible to confirm a detailed reaction
mechanism, NbCl5 could be reduced by (TMS)3SiH to form A
(and (TMS)3SiCl); presumably low-valent Nb species are gen-
erated, on the basis of the experimental data.13 The reaction may
then proceed via oxidative cyclometalation of the two terminal
alkyne molecules (1) to give a niobacyclopentadiene intermedi-
ate. The subsequent reaction with an alkene would exclusively
produce the desired cycloaddition product (Figure S2 in Sup-
porting Information).8,13
catalyst. Instead, 8 formed in low yield (11%), along with the
alkyne trimerization product 4a (27%) (entry 7).
The low-valent niobium species appears critical to obtain
efficient catalytic activity for the present transformation.5,8 Indeed,
no cycloaddition reaction between alkyne with alkene took place
using NbCl5 (Nb(V)) catalyst alone. On the other hand, it is
reported that the low-valent niobium complex NbCl3(DME)
reacts with internal alkynes to form an Nb-alkyne complex, as
confirmed by hydrolysis to give the cis-alkene.6,7a,7b,7d To obtain
structural information regarding the catalytically active low-valent
Nb species generated from NbCl5 and (TMS)3SiH, we initially
carried out a complexation reaction between a mixture of
NbCl5/(TMS)3SiH and 1-phenyl-1-propyne (10), under the
conditions reported for the above-mentioned preparation of the
Nb-alkyne complex from NbCl3(DME).6,7 However, no Nb-alkyne
species was verified by hydrolysis of the reaction mixture, and 10
was evidently converted during the reaction course to give an
intractable mixture of oligomeric products. This implies that the
Nb species generated between NbCl5 and (TMS)3SiH are too
reactive for the analysis of any Nb-alkyne species in a stable form.
Indeed, all attempts to isolate or fully characterize the active Nb
species have been unsuccessful. However, experimental confir-
mation for the formation of the low-valent Nb-alkyne complexes
has been achieved by adding both 1 (1 equiv) and 1,2-dimethox-
yethane (DME) (1 equiv) to a reaction mixture of NbCl5/(TMS)3-
SiH and internal alkyne (eq 2). Thus, 1 (0.7 mmol) and 1,2-
dichloroethane (1 mL) was added to a mixture of NbCl5 (0.7 mmol)
and (TMS)3SiH (0.7 mmol). The reaction mixture was stirred at
40 °C for 3 h. Subsequently, DME (0.7 mmol) and 10 (0.5 mmol)
were added, and the mixture was stirred at 60 °C for 16 h. There-
after, the formation of an Nb-alkyne complex was verified by
hydrolysis or deuteriolysis of the reaction mixture, affording cis-1-
phenyl-1-propene (11) in substantial yield (>99% D incorpo-
rated after deuteriolysis). In the 13C{1H} NMR spectrum for the
reaction mixture of NbCl5/(TMS)3SiH/DME-10, after the addition
In conclusion, we have developed an approach for generating
low-valent Nb(III) species, via a salt-free reduction method from
NbCl5/hydrosilane. These species are active catalysts for the
selective [2 + 2 + 2] cycloaddition reactions of terminal alkynes
and alkenes, to give 1,3-cyclohexadiene derivatives in high yield.
The catalyst system shows remarkable reactivity and selectivity
toward the dicycloadditions of α,ω-dienes, as well as the cyclo-
addition of cyclopentene, with 1, which could not be achieved
using the conventional NbCl3(DME) catalyst system.
’ EXPERIMENTAL SECTION
General. GLC analysis was performed with a flame ionization
1
detector using a 0.22 mm  25 m capillary column (BP-5). H, 13C,
and 29Si NMR were measured at 400, 100, and 78.7 MHz, respectively,
in CDCl3 with Me4Si as the internal standard. The products were
characterized by 1H NMR, 13C NMR, HMQC and HMBC. Compounds
3a,8a 3b,8a 3c,8a 3f,8a 3h,8a 4a,8b 8a,15 8b,15 and 8c15 are known
compounds and have been previously reported.
Typical Reaction Procedure for the Preparation of 3a
(entry 1, Table 1). A mixture of tert-butylacetylene (1a) (164 mg, 2
mmol), 1-decene (2a) (281 mg, 2 mmol), NbCl5 (54 mg, 0.2 mmol),
tris(trimethylsilyl)silane (50 mg, 0.2 mmol), and 1,2-dichloroethane
(1 mL) was stirred for 3 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 90% yield. The product 3a
was isolated by silica gel column chromatography (n-hexane as eluent) in
88% yield (268 mg) a colorless liquid.
Synthesis of 6 from 1a and 5 Using the NbCl5/(TMS)3SiH
Catalyst System (eq 1). A mixture of tert-butylacetylene (1) (164
mg, 2 mmol), cyclopentene (5) (272 mg, 4 mmol), NbCl5 (54 mg, 0.2
mmol), tris(trimethylsilyl)silane (50 mg, 0.2 mmol), and 1,2-dichlor-
oethane (1 mL) was stirred for 3 h at 40 °C under Ar. The product 6 was
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NOTE
isolated by silica gel column chromatography (n-hexane as eluent) in
92% yield (214 mg) as a colorless liquid.
1198, 851; GCÀMS (EI) m/z (relative intensity) 232 (19) [M+], 217
(18), 175 (17), 119 (15), 79 (3), 57 (100), 41 (17). HRMS (EI) m/z
calcd for C17H28 [M]+ 232.2191, found 232.2200
Typical Reaction Procedure for the Preparation of 8a
(Table 3, entry 1). A mixture of tert-butylacetylene (1) (164 mg, 2
mmol), 1,7-octadiene (7a) (441 mg, 4 mmol), NbCl5 (54 mg, 0.2 mmol),
tris(trimethylsilyl)silane (50 mg, 0.2 mmol), and 1,2-dichloroethane
(1 mL) was stirred for 3 h at 40 °C under Ar. The product 8a was isolated
by silica gel column chromatography (n-hexane as eluent) in 77% yield
(211 mg) as a colorless liquid.
Typical Reaction Procedure for the Preparation of 9a
(Table 3, entry 4). A mixture of tert-butylacetylene (1) (164 mg,
2 mmol), 1,7-octadiene (7a) (55 mg, 0.5 mmol), NbCl5 (54 mg, 0.2 mmol),
tris(trimethylsilyl)silane (50 mg, 0.2 mmol), and 1,2-dichloroethane
(1 mL) was stirred for 3 h at 40 °C under Ar. The product 9a was isolated
by silica gel column chromatography (n-hexane as eluent) in 91% yield
(199 mg) as a colorless liquid.
Reaction of NbCl5/(TMS)3SiH with 10 (eq 2). A solution of
NbCl5 (189 mg, 0.7 mmol), (TMS)3SiH (174 mg, 0.7 mmol), and tert-
butylacetylene (1) (57 mg, 0.7 mmol) in 1,2-dichloroethane (1 mL) was
stirred for 3 h at 40 °C under Ar. Subsequently, 1,2-dimethoxyethane
(DME) (63 mg, 0.7 mmol) was added to the reaction mixture and stirred
for 1 h at room temperature under Ar. Then, 1-phenyl-1-propyne (10)
(58 mg, 0.5 mmol) was added to the reaction mixture and stirred for 16 h
at 60 °C under Ar. The yields of the products were estimated from the
peak areas based on the internal standard technique using GC, and 11
was obtained in 58% yield. In the 13C{1H} NMR spectrum for the
reaction mixture of NbCl5/(TMS)3SiH/DME-10 inbenzene-d6 at 20 °C,
alkyne carbon peaks assignable to the low-valent Nb-alkyne complex [A]
appeared at 236.7 and 255.6 ppm, which agrees with the reported values
for the NbCl3(DME)-10 complex (237.5 and 256.2 ppm). The 13C
NMR spectrum is shown in Figure S1 in Supporting Information.
3d: colorless liquid, 1H NMR (400 MHz, CDCl3) δ 0.80 (t, J = 5.7
Hz, 3H), 0.97 (s, 9H), 1.06À1.25 (m, 18H), 1.32 (s, 9H), 2.01À2.27 (m,
2H), 2.23, (d, J = 15 Hz 1H), 5.61 (s, 2H); 13C NMR (100 MHz, CDCl3)
δ 14.1 (CH3), 22.7 (CH2), 27.6 (CH2), 28.2 (CH2), 28.3 (CH2), 28.5
(CH3), 29.4 (CH2), 29.6 (CH3), 29.65 (CH2), 29.68 (CH2), 29.7
(CH2), 29.8 (CH2), 31.9 (CH2), 33.3 (CH), 35.0 (C), 35.6 (C), 115.4
(CH), 115.6 (CH) 143.6 (C), 150.2 (C) ; IR (neat, cmÀ1) 3065, 2924,
1647, 1597, 1465, 1359, 835; GCÀMS (EI) m/z (relative intensity) 332
(6) [M+], 277 (11), 221 (3), 191 (3), 137 (2), 91 (3), 79 (2), 57 (100),
41 (8); HRMS (EI) m/z calcd for C24H44 [M]+ 332.3443, found 332.3450.
3e: colorless liquid, 1H NMR (400 MHz, CDCl3) δ 0.63À0.67 (m,
6H), 0.86 (s, 9H), 0.90 (s, 9H), 1.16À1.36 (m, 4H), 1.83À1.90 (m, 1H),
2.10,2.14 (m, 3H), 5.50 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 23.0
(CH3), 25.9 (CH2), 28.3 (CH2), 28.4 (CH3), 28.5 (CH), 29.6 (CH3),
33.9 (CH), 35.0 (C), 35.6 (C), 37.2 (CH2), 115.3 (CH), 115.6 (CH),
143.7 (C), 150.2 (C); IR (neat, cmÀ1) 3055, 2955, 1645, 1597, 1466,
1367, 1265, 837; GCÀMS (EI) m/z (relative intensity) 262 (14) [M+],
247 (2), 191 (2), 135 (2), 79 (2), 57(100), 43(4). HRMS (EI) m/z calcd
for C19H34 [M]+ 262.2661, found 262.2663.
9a: white solid, mp 65À67 °C. 1H NMR (400 MHz, CDCl3) δ 0.85
(s, 18H), 0.89 (s,18H), 1.10À1.19 (m, 8H), 1.84À2.12 (m, 6H), 5.49 (s,
4H); 13C NMR (100 MHz, CDCl3) δ 28.3 (CH2), 28.5 (CH3), 29.6
(CH3), 31.6 (CH2), 33.0 (CH), 33.51 (CH2), 35.0 (C), 35.6 (C),
115.45 (CH), 115.53 (CH), 143.5 (C), 150.5 (C); IR (KBr, neat, cmÀ1
)
3057, 2964, 1645, 1463, 1360, 1265, 833; GCÀMS (EI) m/z (relative
intensity) 438 (5) [M+], 382 (4), 248 (2), 218 (2), 192 (30), 79 (2), 57
(100), 41(22). HRMS (EI) m/z calcd for C32H54 [M]+ 438.4226, found
438.4222.
9b: white solid, mp 76À78 °C. 1H NMR (400 MHz, CDCl3) δ 0.91
(s, 18H), 0.95 (s, 18H), 1.11À1.20 (m, 8H), 1.30À1.42 (m, 4H),
1.90À2.20 (m, 6H), 5.55 (s, 4H); 13C NMR (100 MHz, CDCl3) δ 27.6
(CH2), 28.1 (CH2), 28.2 (CH2), 28.5 (CH3), 29.6 (CH3), 31.6 (CH2),
33.3 (CH), 35.0 (C), 35.6 (C), 115.4 (CH), 115.6 (CH), 143.5 (C),
150.2 (C); IR (KBr, neat, cmÀ1) 3053, 2964, 1647, 1597, 1463, 1359,
1265, 1198, 837; GCÀMS (EI) m/z (relative intensity) 466 (5) [M+],
353 (1), 207 (1), 175 (4), 131 (1), 91 (2), 57 (100), 41 (6). HRMS (EI)
m/z calcd for C34H58 [M]+ 466.4539, found 466.4529.
9c: white solid, mp 85À88 °C.1H NMR (400 MHz, CDCl3) δ 0.91
(s, 18H), 0.96 (s, 18H), 1.11À1.49 (m, 16H), 1.90À2.20 (m, 6H), 5.55
(s, 4H); 13C NMR (100 MHz, CDCl3) δ 27.6 (CH2), 28.1 (CH2), 28.2
(CH2), 28.5 (CH3), 29.6 (CH3), 29.8 (CH2), 31.6 (CH2), 33.2 (CH),
35.0 (C), 35.6 (C), 115.3 (CH), 115.5 (CH), 143.6 (C), 150.2 (C); IR
(KBr, neat, cmÀ1) 2964, 2853, 2368, 1473, 1359, 1265, 1195, 835;
GCÀMS (EI) m/z (relative intensity) 494 (4) [M]+, 437 (1), 381 (2),
191 (1), 175 (4), 91 (2), 57 (100), 41 (5). HRMS (EI) m/z calcd for
C36H62 [M]+ 494.4852, found 494.4874.
’ ASSOCIATED CONTENT
1
Supporting Information. Figures S1 and S2. H, 13C,
S
b
HMQC, and HMBC NMR spectra for products 3aÀ3h, 6,
8aÀ8b, and 9aÀ9c. This material is available free of charge via
the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: obora@kansai-u.ac.jp.
’ ACKNOWLEDGMENT
This work was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science
and Technology, Japan and the Strategic Project to Support the
Formation of Research Bases at Private Universities (2010À2014),
matching fund subsidy from the Ministry of Education, Culture,
Sports, Science and Technology.
3g: colorless liquid. 1H NMR (400 MHz, CDCl3) δ 0.97 (s, 9H), 1.03
(s, 9H), 1.79À1.86 (m, 2H), 2.08À2.41 (m, 2H), 2.34 (d, J = 15.2 Hz
1H), 2.62 (t, J = 7.1 Hz, 2H), 5.62 (s, 2H), 7.05À7.19 (m, 5H); 13C
NMR (100 MHz, CDCl3) δ 28.1 (CH2), 28.6 (CH3), 29.5 (CH3), 30.4
(CH2), 32.8 (CH), 34.0 (CH2), 35.0 (C), 35.6 (C), 115.8 (2CH), 125.6
(CH), 128.2 (CH), 128.4 (CH), 142.6 (C), 143.4 (C), 149.6 (C); IR
(cmÀ1) 3018, 2964, 2041, 1602, 1463, 1367, 1217, 1029, 929, 725;
GCÀMS (EI) m/z (relative intensity) 296 (13) [M]+, 192 (2), 135 (2),
105 (7), 91 (12), 77(2), 57(100), 41(12). Anal. Calcd for C22H32: C,
89.12; H, 10.88. Found: C, 88.84; H, 10.94.
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