Triethylborane-induced radical reactions with gallium- and indium hydrides

Article abstract of DOI:10.1016/S0040-4020(03)01016-0

A gallium hydride reagent, HGaCl₂, was found to act as a radical mediator. Treatment of alkyl halides with the gallium hydride reagent, generated from gallium trichloride and sodium bis(2-methoxyethoxy)aluminum hydride, provided the corresponding reduced products in excellent yields. Radical cyclization of halo acetals was also successful with not only the stoichiometric gallium reagent but also a catalytic amount of gallium trichloride combined with stoichiometric aluminum hydride as a hydride source. An indium hydride reagent, HInCl₂, prepared from indium trichloride and diisobutylaluminum hydride also worked as a radical mediator. HInCl₂ could reduce aryl iodides and bromides in the presence of Et₃B as a radical initiator.

Full text of DOI:10.1016/S0040-4020(03)01016-0

Tetrahedron 59 (2003) 6627–6635
Triethylborane-induced radical reactions with gallium-
and indium hydrides
*
Kazuaki Takami, Satoshi Mikami, Hideki Yorimitsu, Hiroshi Shinokubo and Koichiro Oshima
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Received 4 April 2003; accepted 23 June 2003
Abstract—A gallium hydride reagent, HGaCl2, was found to act as a radical mediator. Treatment of alkyl halides with the gallium hydride
reagent, generated from gallium trichloride and sodium bis(2-methoxyethoxy)aluminum hydride, provided the corresponding reduced
products in excellent yields. Radical cyclization of halo acetals was also successful with not only the stoichiometric gallium reagent but also a
catalytic amount of gallium trichloride combined with stoichiometric aluminum hydride as a hydride source. An indium hydride reagent,
HInCl2, prepared from indium trichloride and diisobutylaluminum hydride also worked as a radical mediator. HInCl2 could reduce aryl
iodides and bromides in the presence of Et3B as a radical initiator.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Organotin hydrides have played an important role in
synthetic radical chemistry because of their excellent
reactivity as a radical mediator.1 However, organotin
compounds are toxic2 and difficult to remove completely
from the desired reaction products. Many efforts have been
devoted to invent alternatives to organotin reagents.3,4
Silanes5 and germanes,6 group 14 metal hydrides, have been
proposed to be alternatives to tributyltin hydride. The
phosphorus–hydrogen bond in phosphites, phosphines, and
hypophosphorous acid is weak, allowing these reagents to
act as hydrogen donor agents and radical chain carriers.7
Recently, we have reported the Cp2Zr(H)Cl-mediated
radical reaction involving homolytic cleavage of the
zirconium–hydrogen bond.8 Here we wish to introduce
group 13 metal hydrides, a gallium hydride9 and an indium
hydride10 reagent, as efficient radical mediators. These
reagents show high reactivity and have great ability as an
alternative to tin hydride reagents; they display, on the
contrary, more ionic reactivity than tin hydride reagents.
2.1. Reduction of alkyl halides with gallium hydride
reagent
Gallium trichloride (2.0 mmol) was treated with sodium
bis(2-methoxyethoxy)aluminum hydride (Red-Alw,
1.0 mmol) in THF at 08C for 30 min to prepare dichloro-
gallane.11,12 To the mixture, 1-iodododecane (1.0 mmol)
and triethylborane (0.20 mmol) as an initiator13 were
sequentially added and the whole mixture was stirred for
Table 1. Radical reduction of alkyl halides
Entry
R–X
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
10
1-Iodododecane
4
5
5
5
5
5
6
5
9
9
92
88a
81a,b
81b
78a
91a
84
1-Bromododecane
1-Bromododecane
2-Bromododecane
1-Bromododecane
10-Bromo-1-decanol
c-C12H23-OC(¼S)SMe
3-Bromopropyl benzoate
4-Iodobutyrophenone
1-Bromododecanec
88a
80
0d,e
Unless otherwise noted, R–X (1.0 mmol), GaCl3 (2.0 mmol), Red-Alw
(1.0 mmol), Et3B (0.20 mmol) and THF (5 mL) were used.
a
An equimolar amount (1.0 mmol) of Et3B was employed.
Diisobutylaluminum hydride (2.0 mmol) was used instead of Red-Alw.
Along with an equimolar amount of decanal.
b
c
Keywords: indium hydrides; radical mediator; gallium hydride.
*
d
Corresponding author. Tel.: þ81-75753-5523; fax: þ81-75753-4863;
GaCl3 (1.0 mmol), Red-Alw (0.50 mmol), Et3B (1.0 mmol) were used.
Instead, 1-decanol was obtained in 93% yield.
e
e-mail: oshima@fm1.kuic.kyoto-u.ac.jp
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)01016-0

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K. Takami et al. / Tetrahedron 59 (2003) 6627–6635
Table 2. Radical cyclization of halo acetals with gallium hydride
Entry
1
X
R1
R2
R3
R4
R5
2
Yield (%)a
1
2
3
4
5
6
7
8
9
10
1a
1b
1c
1d
1e
1f
1g
1h
1i
I
Br
I
Br
I
Br
I
Br
I
Br
(CH2)3
(CH2)3
(CH2)3
(CH2)3
(CH2)3
(CH2)3
H
H
H
H
n-Pen
n-Pen
H
H
n-Pen
n-Pen
Me
Me
n-Pr
n-Pr
H
Me
Me
H
H
H
H
H
H
H
2a
2a
2c
2c
2e
2e
2g
2g
2i
87 (70/30)
82 (71/29)b
85 (84/16)
80 (84/16)b
85 (57/43)
80 (56/44)b
97 (72/28)
79 (72/28)b
99 (50/50)
94 (52/48)b
H
n-Bu
n-Bu
n-Bu
n-Bu
H
H
H
H
n-Pr
n-Pr
H
1j
H
H
2i
a
Isolated yields. Diastereomer ratios are shown in parentheses.
An equimolar amount (1.0 mmol) of Et3B was used.
b
4 h. Dodecane was obtained in 92% yield after aqueous
workup and purification. The results of the reduction of
various halides were summarized in Table 1.
mixing GaCl3 and Red-Alw in 1/1 ratio. For example, the
reaction of 1g provided 2g in 74% yield. Furthermore,
treatment of 1f with H2GaCl (1.5 mmol) afforded a complex
mixture. Red-Alw itself worked far less efficiently compared
with HGaCl2. Treatment of 1c and 1e with Red-Alw in the
presence of triethylborane provided 2c and 2e in 23% and
,1% yields, respectively. The starting materials 1c (57%)
and 1e (74%) were recovered.
Alkyl bromides were also reduced to the corresponding
hydrocarbons in excellent yields, although a larger amount
of triethylborane (1.0 equiv.) was necessary. Without Red-
Alw and gallium trichloride, treatment of 1-bromododecane
with triethylborane in THF resulted in quantitative recovery
of the starting material. A combination of gallium
trichloride and 1.0 equiv. of diisobutylaluminum hydride
was also effective to form the gallium hydride reagent
(entries 3 and 4). Unfortunately, alkyl chlorides and aryl
iodides remained almost unchanged. Radical deoxygenation
via a dithiocarbonate was successful (entry 7). Interestingly,
reduction of a ketone moiety did not take place at all under
the reaction conditions (entry 9). When the mixture of an
alkyl bromide and an aldehyde was exposed to the reaction
conditions, ionic reduction of the aldehyde proceeded
exclusively and the alkyl bromide was recovered quanti-
tatively (entry 10). The reaction of a benzylic bromide,
4-bromobenzyl bromide, resulted in recovery of the starting
material (89%).14
Gallium trichloride is not inexpensive. Therefore, it is of
importance to reduce the amount of GaCl3 employed for the
reaction. Thus, the catalytic reaction was examined. The
cyclization of 1a was performed with a slow addition (2 h)
of Red-Alw (1.5 mmol) to a solution of 1a (1.0 mmol),
GaCl3 (0.20 mmol) and Et3B (0.20 mmol) in THF. The
mixture was stirred for an additional 1 h to yield 2a in 79%
yield (Table 3, entry 1). The slow addition was essential for
the success of the catalytic reaction. Treatment of GaCl3
with excess Red-Alw at one time resulted in poor conversion
(2a, 10%; 1a, 65% recovered). In this case, the reaction
would afford gallane (GaH3), which would be unstable
Table 3. Radical cyclization of halo acetals with a catalytic amount of
gallium trichloride
2.2. Radical cyclization with gallium hydride reagent
We turned our attention to the radical cyclization of halo
acetals.15 Substrates shown in Table 2 underwent 5-exo
reductive cyclization smoothly by the action of the gallium
hydride reagent in the presence of triethylborane.
Entry
Halo acetal
Time (h)a
Product
Yield (%)b
The reaction of 1a did not proceed in the absence of
triethylborane. An addition of 2,2,6,6-tetramethylpiperi-
dine-N-oxyl (TEMPO) completely inhibited the reaction.
The reaction of halo acetals 1a, 1c and 1e with tributyltin
hydride under the similar reaction conditions provided the
corresponding products 2a, 2c and 2e in moderate yields
with the same diastereoselectivities (2a: 60% (69/31), 2c:
63% (86/14), 2e: 46% (52/48)) as the reaction with HGaCl2.
These results strongly support a radical mechanism for the
present reaction. The reaction proceeded less efficiently
with chlorogallane (H2GaCl), which was prepared by
1
1a
1a
1c
1e
1b
2þ1
2þ1
2þ8
2þ4
2þ4
2a
2a
2c
2e
2a
79 (70/30)
36 (68/32)d
64 (88/12)
95 (59/41)
6 (69/31)f
2c
3
4
5e
Red-Alw was added slowly over 2 h and the resulting mixture was stirred
additionally for the indicated time.
Isolated yields. Diastereomer ratios are shown in parentheses.
The reaction was performed with 0.10 mmol of GaCl3.
The starting material 1a was recovered in 40%.
a
b
c
d
e
f
The reaction was carried out with 1.0 mmol of Et3B.
The starting material 1b was recovered in 74%.

K. Takami et al. / Tetrahedron 59 (2003) 6627–6635
Table 5. Radical cyclization of haloaryl ethers
6629
Entry
5
X
R
6
Yield (%)a
1
2
3
5b
5c
5d
I
Br
Cl
Me
Me
H
6b
6b
6a
92
71b
0c
a
Isolated yields.
Starting material was recovered in 17% yield.
Starting material was completely recovered.
b
c
cyclization product 6a in 87% yield (Table 4, entry 1).17 The
reaction proceeded more smoothly at room temperature
(entry 2). For completion of the reaction, 1.1 equiv. of
HInCl2 was sufficient (entries 2 and 3). Although spon-
taneous cleavage of indium–hydrogen bond has been
reported, the reaction without triethylborane resulted in a
lower yield (entry 4).
Scheme 1.
under these reaction conditions.11c The fewer amount of
GaCl3 was used, the lower yield was obtained (entry 2). This
procedure could not be applied to cyclization of a bromo
acetal (entry 5).
We tried to apply this reaction conditions to cyclization of
other haloaryl ethers. These results were shown in Table 5.
Interestingly, bromoaryl ether 5c afforded the cyclized
product 6c in moderate yield (entry 2). Unfortunately, the
reaction of chloroaryl ether 5d provided none of the
cyclized product and the starting material was recovered
(entry 3).
We assume the catalytic mechanism as shown in Scheme 1,
in analogy with the reaction with tributyltin hydride. An
ethyl radical, generated from Et3B by the action of a trace
amount of oxygen, abstracts hydrogen homolytically from
HGaCl2 to give gallium radical †GaCl2.16 Halogen
abstraction by †GaCl2 from a substrate, 1a for example,
affords GaCl2I and radical 3. Ring closure followed by
hydride donation from HGaCl2 to the radical 4 provides
the product 2a and regenerates †GaCl2. GaCl2I, formed
in the propagation step, is transformed into HGaCl2 with
aluminum hydride, and the gallium hydride works again as
a hydride source for the carbon-centered radical.
We next attempted to carry out the cyclization reaction of
halo acetals18 by using dichloroindane and triethylborane.
Cyclization of various halo acetals is achieved without any
further optimization. These results were listed in Table 6.
Reactions of iodo acetals 1c and 1i provided cyclized
products 2c and 2i, respectively, in good yields (entries 1
and 2). Moreover, bromo acetals 1b, 1g and 1k could be
employed in this reaction (entries 3–5). The cyclization
reaction with chloro acetal 1l, however, did not proceed
under the same reaction conditions and the starting material
1l was recovered (entry 6).
2.3. Radical cyclization with indium hydride reagent
A hexane solution of diisobutylaluminum hydride (DIBAL-
H) was added to a THF solution of indium trichloride
(1.15 mmol) at 08C and stirred for 30 min to prepare
dichloroindane (HInCl2).10c,d,g To a solution of HInCl2 were
added 5a and triethylborane (1.0 M hexane solution,
0.10 mL, 0.10 mmol) as a radical initiator. Stirring for
30 min followed by acidic workup provided reductive 5-exo
The use of alkynyl acetal 7 as a substrate yielded the ring
closing product 8 as a mixture of E/Z isomers (Scheme 2).
In terms of costs and atom economy, it is naturally desirable
to reduce the amount of InCl3 employed. Unfortunately,
monochloroindane (H2InCl) and indane (H3In)19 could not
endure the reaction conditions and were decomposed
immediately. Our next trial was to conduct the reaction
with a catalytic amount of InCl3. A hexane solution of
DIBAL-H (1.1 mmol) was dropped at a slow speed (1 h) to a
mixture of InCl3 (0.20 mmol), 1i (1.0 mmol) and Et3B
(0.20 mmol) in THF at room temperature. After additional
stirring for 1 h, 2i was obtained in 72% yield (Table 7, entry
1). Slow dropping of DIBAL-H was required to achieve a
sufficient yield. This catalytic process could also be applied
to cyclization of aryl halides such as 5b (entry 2). More than
0.1 equiv. of InCl3 was necessary for complete consumption
of the starting material.
Table 4. Radical cyclization of 5a with HInCl2
Entry
HInCl2 (equiv.)
Et3B (equiv.)
Temperature
Yield (%)a
1
2
3
4
5
1.1
1.1
1.2
1.2
1.2
0.10
0.10
0.10
None
0.20
08C
rt
rt
08C
08C
87
93 (98)
(97)
(83)
(98)
The substrate 5a (1.0 mmol) and THF (10 mL) were used.
NMR yields, calculated from integrations of proper protons and an
internal standard (Bn2O), are in parentheses.
a
We suppose that the reaction proceeds in a catalytic

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K. Takami et al. / Tetrahedron 59 (2003) 6627–6635
Table 6. Radical cyclization of halo acetals
Entry
1
X
R1
R2
H
R3
R4
R5
2
Yield (%)a
1
2
3
4
5
6
1c
1i
1b
1g
1k
1l
I
I
Br
Br
Br
Cl
(CH2)3
(CH2)3
H
n-Pen
H
H
Ph
H
n-Pr
H
Me
n-Pr
H
H
H
Me
H
H
2c
2i
2a
2g
2k
2l
70 (84/16)
92 (86/14)
66 (70/30)
84 (83/17)
65 (55/45)
0
n-Bu
n-Bu
n-Bu
n-Bu
H
H
H
n-Pr
H
a
Isolated yields. Diastereomer ratios are shown in parentheses.
Scheme 2.
mechanism outlined in Scheme 3. An ethyl radical,
generated from Et3B and a trace amount of O2, reacts with
HInCl2 to provide an indium radical (†InCl2). The indium
radical abstracts iodine to give InCl2I and radical 9, which
then cyclizes to radical 10. Hydride abstraction from HInCl2
by radical 10 provides 2c and regenerates the indium
radical. HInCl2 is regenerated through transmetalation of
InCl2I and DIBAL-H, and then acts again as the hydride
source.
3. Conclusion
We have disclosed that dichlorogallium hydride and
dichloroindium hydride can be used as radical mediators
in a radical cyclization reaction. These reagents can be
prepared in ease and work effectively under mild conditions.
The success of these reactions shows novel reactivities of
gallium and indium hydride reagents.
2.4. Chemoselective reduction with indium hydride
reagent
We tried to investigate the chemoselectivity of the indium
hydride reagent (Table 8). When alkyl bromides, which
have ester or ketone linkages, were treated with HInCl2,
reduction of alkyl bromide moieties proceeded exclusively
(entries 1 and 2). On the other hand, ionic reduction of an
aldehyde underwent prior to radical reduction of an alkyl
bromide (entry 3).
Table 7. Radical cyclization with a catalytic amount of indium trichloride
Entry Substrate InCl3 (mmol) Time (h)a Product Yield (%)b
1
2
3
4
5
1i
0.20
0.20
0.15
0.10
0.05
1þ1
1þ1
1þ1
1þ1
1þ3
2i
72 (57/43)c
67
5b
5b
5b
5b
6b
6b
6b
6b
74
64d
17e
a
DIBAL-H was added slowly over 1 h and the resulting mixture was
stirred additionally for the indicated time.
After purification by column chromatography.
Diastereomer ratio is shown in parentheses.
The starting material 5b was recovered in 8%.
The starting material 5b was recovered in 57%.
b
c
d
e
Scheme 3.

K. Takami et al. / Tetrahedron 59 (2003) 6627–6635
6631
Table 8. Chemoselectivity of indium hydride
Entry
1
Substrate
HInCl2 (mmol)
1.3
Product
Yield (%)a
99b
2
3
1.0
78
n-C12H25Brþn-C9H19CHO
1.0
n-C12H25Brþn-C10H21OH
quant., 88
An alkyl bromide (1.0 mmol) and Et3B (0.10 mmol) were used, unless otherwise noted.
a
After purification by column chromatography.
NMR yield, calculated from intergration of proper protons and an inernal standard (Bn2O).
b
4. Instrumentation and materials
THF) and triethylborane (1.0 M hexane solution, 0.10 mL,
0.10 mmol) were sequentially added. After being stirred for
4 h at 08C, the reaction was quenched with 1.0 M
hydrochloric acid (20 mL), and the mixture was extracted
with hexane (20 mL£3). Combined organic layers were
dried over anhydrous sodium sulfate and concentrated in
vacuo. Silica gel column purification afforded 156 mg of
dodecane in 92% yield. Reduction of bromides was
performed with 1.0 mmol of triethylborane.
1NMR (300 MHz) and 13C NMR (75.3 MHz) spectra were
taken on a Varian GEMINI 300 spectrometer in CDCl3 as a
solvent, and chemical shifts were given in d value with
tetramethylsilane as an internal standard. IR spectra were
determined on a JASCO IR-810 spectrometer. TLC
analyses were performed on commercial glass plates
bearing a 0.25-mm layer of Merck Silica gel 60F254. Silica
gel (Wakogel 200 mesh) was used for column chroma-
tography. The elemental analyses were carried out at the
Elemental Analysis Center of Kyoto University.
5.2. Typical procedure for cyclization of halo acetals
with gallium hydride
Unless otherwise noted, materials obtained from commer-
cial suppliers were used without further purification.
Tetrahydrofuran (THF) was freshly distilled from sodium
benzophenone ketyl before use. Gallium trichloride and
triethylborane were purchased from Aldrich Chemicals and
were diluted to prepare a 1.0 M hexane solution to handle
easily. Anhydrous indium trichloride was obtained from
Aldrich and was used after removal of water (vide infra).
Red-Alw (70 wt% in toluene) was purchased from Nacalai
Tesque Inc., and was diluted with toluene to prepare a 2.0 M
solution. Diisobutylaluminum hydride was obtained from
Aldrich and was used as a 1.0 M hexane solution. These
solutions were stored under argon. Halo acetals were
prepared according to the literature (Ref. 15).
Halo acetal 1a (296 mg, 1.0 mmol) in 2 mL of THF was
added to a solution of the gallium hydride (1.5 mmol)
prepared as above, and triethylborane (1.0 M hexane
solution, 0.20 mL, 0.20 mmol) was added. After being
stirred for 5 h at 08C, the mixture was poured into 1.0 M
HCl (20 mL) and was stirred for 15 min. Extraction with
hexane/ethyl acetate (10/1¼v/v%, 20 mL£3) followed by
silica gel column purification afforded 2a (146 mg) in 86%
1
yield. Diastereomer ratio was determined by the H NMR
experiment of the product, judging from the integrations of
the proper protons.
5.3. Radical cyclization with a catalytic amount of GaCl3
A mixture of gallium trichloride (1.0 M hexane solution,
0.20 mL, 0.20 mmol), 1a (296 mg, 1.0 mmol), and triethyl-
borane (1.0 M hexane solution, 0.20 mL, 0.20 mmol) in
THF (5 mL) was placed in a reaction flask. Red-Alw
(0.75 mL, 1.5 mmol) was added to the reaction mixture
over 2 h with a syringe pump at 08C. After the slow addition
was completed, the whole mixture was stirred for 1 h.
Quenching the reaction with hydrochloric acid followed
by extraction with hexane/ethyl acetate (10/1¼v/v%,
20 mL£3), concentration, and silica gel column purifi-
cation yielded 134 mg of 2a (0.79 mmol, 79%) as a
colorless oil.
5. Experimental
The reaction was performed in a reaction flask equipped
with a toy balloon that was filled with argon unless
otherwise noted. Oxygen, which is necessary to produce
an ethyl radical from triethylborane, penetrates the balloon
easily. Any further addition of oxygen is not necessary.
5.1. Procedure for reduction of alkyl halides with
gallium hydride reagent
5.4. Typical procedure for triethylborane-induced
radical cyclization with indium hydride
Gallium trichloride in hexane (1.0 M solution prepared in
advance, 2.0 mL, 2.0 mmol) was placed in a reaction flask
under argon and was diluted with 3 mL of THF. Sodium
bis(2-methoxyethoxy)aluminum hydride (Red-Alw, 2.0 M
toluene solution, 0.50 mL, 1.0 mmol) was then added to the
solution at 08C and the resulting mixture was stirred for
30 min. 1-Iodododecane (296 mg, 1.0 mmol in 2 mL of
Anhydrous indium trichloride (226 mg, 1.2 mmol) was
placed in a reaction flask and was heated in vacuo for 2 min.
THF (20 mL) was added at room temperature. Cooling the
resulting clear solution to 2788C gave a white suspension.

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K. Takami et al. / Tetrahedron 59 (2003) 6627–6635
To the suspension, diisobutylaluminum hydride (1.0 M
hexane solution, 1.1 mL, 1.1 mmol) was added dropwise,
and the mixture was stirred for 30 min at the same
temperature. After an addition of 5a (260 mg, 1.0 mmol in
1.0 mL of THF) and triethylborane (1.0 M THF solution,
0.10 mL, 0.10 mmol), the whole mixture was stirred for
30 min. The reaction was quenched with 1.0 M hydrochloric
acid (10 mL). The crude mixture was extracted with hexane/
ethyl acetate (10/1¼v/v%, 10 mL£3) and the organic layers
were dried with anhydrous sodium sulfate. Silica gel
column purification afforded 6a (125 mg, 0.93 mmol,
93%). The diastereomeric ratio of the product was
6.6 Hz, 1H); 13C NMR (CDCl3) d 13.71, 22.13, 25.47,
29.46, 32.64, 34.28, 63.26, 68.73, 101.01, 125.29, 135.00.
Found: C, 42.76; H, 6.27%. Calcd for C11H19IO2: C, 42.60;
H, 6.17%.
5.7.3. 2-Bromoethanal butyl (E)-2-hexenyl acetal (1g). IR
(neat) 2959, 2874, 1722, 1458, 1379, 1350, 1117, 1043,
970 cm21; 1H NMR (CDCl3) d 0.90 (t, J¼7.5 Hz, 3H), 0.93
(t, J¼7.5 Hz, 3H), 1.66–1.47 (m, 2H), 1.53–1.63 (m, 2H),
1.59 (quint., J¼7.5 Hz, 2H), 2.03 (dt, J¼6.9, 7.5 Hz, 2H),
3.38 (d, J¼5.4 Hz, 2H), 3.50 (dt, J¼9.0, 6.6 Hz, 1H), 3.62
(dt, J¼9.0, 6.6 Hz, 1H), 4.04 (dd, J¼6.0, 11.7 Hz, 1H), 4.11
(dd, J¼6.0, 11.7 Hz, 1H), 4.70 (t, J¼5.4 Hz, 1H), 5.55 (dt,
J¼15.3, 6.0 Hz, 1H), 5.73 (dt, J¼15.3, 6.6 Hz, 1H); 13C
NMR (CDCl3) d 13.72, 13.87, 19.31, 22.19, 31.77 (2C),
34.34, 66.39, 67.52, 100.62, 125.50, 135.00. Found: C,
51.60; H, 8.04%. Calcd for C12H23BrO2: C, 51.62; H,
8.30%.
1
determined with H NMR experiment.
5.5. Procedure for radical cyclization with a catalytic
amount of indium trichloride
Indium trichloride (44 mg, 0.20 mmol) was dried as above
and was dissolved with THF (20 mL) at 258C. Then, 1i
(354 mg, 1.0 mmol in 1.0 mL of THF) and triethylborane
(1.0 M hexane solution, 0.20 mL, 0.20 mmol) were sequen-
tially added. To the mixture, a hexane solution of DIBAL-H
(0.10 M, 11 mL, 1.1 mmol) was added over 1 h with a
syringe pump and the resulting mixture was stirred for
additional 1 h. Quenching with 1.0 M hydrochloric acid
(10 mL) and extraction with hexane/ethyl acetate (10/1¼
v/v%, 10 mL£3) followed by silica gel column chroma-
tography afforded 165 mg of 2i (57/43 isomeric mixture) in
72% yield.
5.7.4. 2-Iodoethanal butyl 1-vinylhexyl acetal (1i, 50/50
mixture of diastereomers). IR (neat) 2932, 1458, 1416,
1107, 1022, 926 cm21; 1H NMR (CDCl3) d 0.83–1.02 (m,
6H), 1.21–1.72 (m, 12H), 3.16–3.31 (m, 2H), 3.36–3.66
(m, 2H), 3.86 (q, J¼6.9 Hz, 0.50H), 3.99 (q, J¼6.9 Hz,
0.50H), 4.61 (dt, J¼8.7, 5.1 Hz, 1H), 5.12–5.28 (m, 2H),
5.61–5.84 (m, 1H); 13C NMR (CDCl3) d 6.18 (0.50C),
6.44 (0.50C), 13.94 (0.50C), 14.10 (0.50C), 19.31 (0.50C),
19.41 (0.50C), 22.61, 24.85 (0.50C), 24.95 (0.50C), 31.59
(0.50C), 31.72, 31.87 (0.50C), 35.28 (0.50C), 35.44
(0.50C), 65.03 (0.50C), 66.59 (0.50C), 78.51 (0.50C),
79.20 (0.50C), 99.00 (0.50C), 100.74 (0.50C), 116.26
(0.50C), 117.55 (0.50C), 138.41 (0.50C), 139.17 (0.50C).
Found: C, 47.39; H, 7.82%. Calcd for C14H27IO2: C, 47.46;
H, 7.68%.
5.6. Procedure for reduction of alkyl bromides with
indium hydride
HInCl2 (1.0 mmol) was prepared in THF (5 mL) as
described above. At ambient temperature, 4-bromobutyro-
phenone (225 mg, 1.0 mmol) and triethylborane (1.0 M
hexane solution, 0.10 mL, 0.10 mmol) were added. After
being stirred for 1 h, the reaction mixture was quenched
with 1.0 M HCl. Extraction with hexane/ethyl acetate (10/1)
followed by silica gel column purification afforded
butyrophenone (116 mg, 0.78 mmol).
5.7.5. 2-Bromoethanal butyl 1-phenyl-2-propenyl acetal
(1k, 50/50 mixture of diastereomers). IR (neat) 2959,
1
2874, 1603, 1454, 1421, 1115, 1026, 930, 700 cm21; H
NMR (CDCl3) d 0.88 (t, J¼7.5 Hz, 1.50H), 0.93 (t, J¼
7.5 Hz, 1.50H), 1.24–1.47 (m, 2H), 1.47–1.64 (m, 2H),
3.31–3.47 (m, 2H), 3.48–3.58 (m, 2H), 4.64 (t, J¼5.4 Hz,
0.50H), 4.88 (t, J¼5.4 Hz, 0.50H), 5.07–5.39 (m, 3H),
5.86–6.08 (m, 1H), 7.28–7.43 (m, 5H); 13C NMR (CDCl3)
d 13.91, 13.95, 19.30, 19.36, 31.73, 31.81, 31.97, 32.11,
65.76, 65.93, 79.22, 79.45, 99.22, 99.45, 115.80, 117.30,
126.59, 127.14, 127.60, 127.86, 128.28, 128.41, 137.79,
138.54, 139.76, 140.55. Found: C, 57.30; H, 6.71%. Calcd
for C15H21BrO2: C, 57.52; H, 6.76%.
5.7. Characterization data
5.7.1. 3-Bromo-2-(3-methyl-2-propenyloxy)tetrahydro-
pyran (1b). IR (neat) 2930, 2855, 1676, 1441, 1204,
1
1130, 1072, 1022, 870 cm21; H NMR (CDCl3) d 1.49–
1.60 (m, 1H), 1.69 (s, 3H), 1.76 (s, 3H), 1.88–2.00 (m, 2H),
2.35–2.46 (m, 1H), 3.55–3.62 (m, 1H), 3.90–4.02 (m, 2H),
4.06 (dd, J¼7.2, 11.7 Hz, 1H), 4.23 (dd, J¼6.6, 11.7 Hz,
1H), 4.64 (d, J¼4.5 Hz, 1H), 5.36 (t, J¼7.2 Hz, 1H); 13C
NMR (CDCl3) d 18.10, 23.40, 25.92, 30.19, 49.64, 62.48,
64.36, 99.90, 119.97, 138.02. Found: C, 48.23; H, 6.64%.
Calcd for C10H17BrO2: C, 48.21; H, 6.88%.
5.7.6. 7-Isopropyl-2,9-dioxabicyclo[4.3.0]nonane (2a, 70/
30 mixture of diastereomers). Faster moving band, Rf¼
0.53 (hexane/ethyl acetate¼3/1). IR (neat) 2936, 1467,
1402, 1253, 1142, 1114, 1087, 1031, 1000, 950, 898 cm21
;
1H NMR (CDCl3) d 0.78 (d, J¼6.6 Hz, 3H), 0.91 (d,
J¼6.6 Hz, 3H), 1.27–1.43 (m, 1H), 1.50–1.74 (m, 4H),
1.85–1.95 (m, 2H), 3.64–3.79 (m, 3H), 3.92 (dd, J¼7.8,
7.8 Hz, 1H), 5.27 (d, J¼3.0 Hz, 1H); 13C NMR (CDCl3) d
18.74, 20.88, 21.65, 23.21, 26.22, 35.67, 48.90, 60.70,
68.99, 102.11. Found: C, 70.40; H, 10.86%. Calcd for
C10H18O2: C, 70.55; H, 10.66%.
5.7.2. 2-[(E)-2-Hexenyloxy]-3-iodotetrahydropyran (1c).
IR (neat) 2927, 2872, 1464, 1437, 1202, 1123, 1069, 1022,
866, 696 cm21; 1H NMR (CDCl3) d 0.91 (t, J¼7.2 Hz, 3H),
1.42 (quint., J¼7.5 Hz, 2H), 1.51–1.66 (m, 1H), 1.72–1.84
(m, 1H), 1.96–2.09 (m, 3H), 2.33–2.44 (m, 1H), 3.54–3.62
(m, 1H), 4.00 (dd, J¼6.9, 11.7 Hz, 2H), 4.11 (dt, J¼9.0,
4.5 Hz, 1H), 4.21 (dd, J¼5.7, 11.7 Hz, 1H), 4.68 (d, J¼
5.1 Hz, 1H), 5.56 (dt, J¼15.3, 6.6 Hz, 1H), 5.73 (dt, J¼15.3,
Slower moving band, Rf¼0.47 (hexane/ethyl acetate¼3/1).
IR (neat) 3510, 2876, 1468, 1387, 1369, 1221, 1149, 1115,

K. Takami et al. / Tetrahedron 59 (2003) 6627–6635
6633
1089, 1061, 1029, 949, 894, 746 cm21; 1H NMR (CDCl3) d
0.85 (d, J¼6.6 Hz, 3H), 0.93 (d, J¼6.9 Hz, 3H), 1.29–1.39
(m, 1H), 1.58–1.75 (m, 2H), 1.75–1.92 (m, 3H), 2.08
(dddd, J¼7.2, 8.1, 8.1, 8.7 Hz, 1H), 3.41 (ddd, J¼2.4, 11.4,
11.4 Hz, 1H), 3.66 (dd, J¼8.1, 8.4 Hz, 1H), 3.86 (ddd,
J¼3.3, 3.9, 11.4 Hz, 1H), 4.16 (dd, J¼8.4, 8.7 Hz, 1H), 4.97
(d, J¼3.6 Hz, 1H); 13C NMR (CDCl3) d 19.37, 20.65, 21.36,
23.43, 29.98, 41.27, 44.31, 64.26, 71.03, 102.50. Found: C,
70.32; H, 10.39%. Calcd for C10H18O2: C, 70.55; H,
10.66%.
67.33, 71.76, 104.38. For minor isomer: d 13.90, 14.05,
19.43, 22.82, 30.69, 31.88, 33.74, 37.00, 39.32, 66.86,
72.48, 103.99. Found: C, 71.69; H, 12.30%. Calcd for
C12H24O2: C, 71.95; H, 12.08%.
5.7.10. 2-Butoxy-4-methyl-5-pentyltetrahydrofuran (2i,
50/50 mixture of diastereomers). IR (neat) 2932, 2862,
1460, 1379, 1344, 1097, 995, 930 cm21; 1H NMR (CDCl3)
d 0.90 (t, J¼6.0 Hz, 3H), 0.92 (t, J¼7.2 Hz, 3H), 1.02 (d,
J¼6.0 Hz, 1.50H), 1.04 (d, J¼6.6 Hz, 1.50H), 1.22–1.62
(m, 13H), 1.74 (dtq, J¼6.6, 8.1, 9.2 Hz, 0.50H), 2.05 (dd,
J¼6.6, 11.7 Hz, 0.50H), 2.00–2.18 (m, 0.50H), 2.32 (ddd,
J¼5.7, 9.2, 13.2 Hz, 0.50H), 3.33 (dt, J¼6.5, 9.3 Hz,
0.50H), 3.38 (dt, J¼6.6, 9.6 Hz, 0.50H), 3.46–3.56 (m,
1H), 3.68 (dt, J¼6.9, 9.3 Hz, 0.50H), 3.69 (dt, J¼6.8,
9.6 Hz, 0.50H), 5.00 (d, J¼5.1 Hz, 0.50H), 5.07 (dd, J¼3.0,
5.7 Hz, 0.50H); 13C NMR (CDCl3) d 13.75, 13.93, 13.97,
17.09, 17.17, 19.27, 19.33, 22.53, 25.95, 25.99, 31.77,
31.82, 31.90, 31.95, 33.68, 35.84, 36.81, 38.16, 41.31,
41.88, 66.57, 67.26, 83.91, 86.90, 103.24, 103.40. Found: C,
73.40; H, 12.30%. Calcd for C14H28O2: C, 73.63; H,
12.36%.
5.7.7. 7-Butyl-2,9-dioxabicyclo[4.3.0]nonane (2c, 83/17
mixture of diastereomers). IR (neat) 2928, 2860, 1468,
;
1252, 1146, 1022 cm21 1H NMR (CDCl3) d 0.90 (t,
J¼6.9 Hz, 3H), 1.13–1.47 (m, 7H), 1.53–1.76 (m, 3H),
1.80–2.00 (m, 1H), 2.24–2.39 (m, 1H), 3.42 (ddd, J¼11.4,
11.4, 1.8 Hz, 0.17H), 3.54 (dd, J¼8.4, 8.4 Hz, 0.17H),
3.60–3.69 (m, 1.66H), 3.70–3.80 (m, 0.83H), 3.84–3.93
(m, 0.17H), 3.95 (dd, J¼8.1, 8.1 Hz, 0.83H), 4.28 (dd, J¼
8.4, 8.4 Hz, 0.17H), 5.00 (d, J¼3.3 Hz, 0.17H), 5.29 (d,
J¼3.6 Hz, 0.83H); 13C NMR (CDCl3) for major isomer: d
14.05, 19.24, 22.91, 23.29, 26.71, 30.49, 36.51, 41.01,
60.92, 70.11, 101.94. For minor isomer: d 20.79, 22.47,
22.96, 30.49, 30.77, 32.45, 37.83, 44.15, 64.45, 74.26,
102.07. Found: C, 71.43; H, 10.65%. Calcd for C11H20O2:
C, 71.70; H, 10.94%.
5.7.11. 5-Butoxy-3-methyl-2-phenyltetrahydrofuran
(2k). Faster moving band, Rf¼0.43 (hexane/ethyl acetate¼
10/1). IR (neat) 2959, 2872, 1605, 1454, 1377, 1097, 1015,
754, 700 cm21; 1H NMR (CDCl3) d 0.92 (t, J¼7.5 Hz, 3H),
1.06 (d, J¼6.6 Hz, 3H), 1.31–1.44 (m, 2H), 1.53–1.69 (m,
3H), 1.97–2.09 (m, 1H), 2.51 (ddd, J¼5.7, 9.0, 15.0 Hz,
1H), 3.43 (dt, J¼9.6, 6.6 Hz, 1H), 3.77 (dt, J¼9.6, 6.9 Hz,
1H), 4.49 (d, J¼9.3 Hz, 1H), 5.31 (dd, J¼3.6, 5.7 Hz, 1H),
7.26–7.40 (m, 5H); 13C NMR (CDCl3) d 14.01, 16.27,
19.47, 31.93, 41.61, 42.16, 67.80, 85.92, 103.87, 126.41,
127.61, 128.25, 140.60. Found: C, 76.97; H, 9.32%. Calcd
for C15H22O2: C, 76.88; H, 9.46%.
5.7.8. 7-Methyl-2,9-dioxa-8-pentylbicyclo[4.3.0]nonane
(2e, 56/44 mixture of diastereomers). Faster moving
band, Rf¼0.56 (hexane/ethyl acetate¼5/1). IR (neat) 3440,
2928, 2870, 1648, 1459, 1402, 1380, 1251, 1146, 1114,
1
1073, 994, 965, 918 cm21; H NMR (CDCl3) d 0.86 (t,
J¼6.9 Hz, 3H), 0.93 (d, J¼6.6 Hz, 3H), 1.18–1.70 (m,
12H), 1.86–2.02 (m, 2H), 3.59 (ddt, J¼3.6, 11.1, 1.5 Hz,
1H), 3.68–3.79 (m, 2H), 5.25 (d, J¼3.6 Hz, 1H); 13C NMR
(CDCl3) d 11.48, 13.90, 20.06, 22.49, 23.16, 25.84, 31.94,
35.02, 39.02, 40.70, 61.00, 82.70, 100.90. Found: C, 73.33;
H, 11.58%. Calcd for C13H24O2: C, 73.54; H, 11.39%.
Slower moving band, Rf¼0.36 (hexane/ethyl acetate¼10/1).
IR (neat) 2959, 2872, 1605, 1456, 1379, 1090, 1005, 752,
700 cm21; 1H NMR (CDCl3) d 0.96 (t, J¼7.5 Hz, 3H), 1.03
(d, J¼6.3 Hz, 3H), 1.37–1.51 (m, 2H), 1.64 (quint., J¼
7.5 Hz, 2H), 1.78 (dt, J¼5.2, 12.3 Hz, 1H), 2.18 (dd, J¼6.3,
12.3 Hz, 1H), 2.29–2.42 (m, 1H), 3.44 (dt, J¼9.3, 6.6 Hz,
1H), 3.87 (dt, J¼9.6, 6.6 Hz, 1H), 4.41 (d, J¼9.3 Hz, 1H),
5.16 (d, J¼5.2 Hz, 1H), 7.26–7.46 (m, 5H); 13C NMR
(CDCl3) d 14.08, 15.66, 19.59, 31.97, 40.90, 42.24,
67.33, 89.46, 103.59, 126.75, 127.41, 128.14, 142.01.
Found: C, 77.00; H, 9.30%. Calcd for C15H22O2: C,
76.88; H, 9.46%.
Slower moving band, Rf¼0.47 (hexane/ethyl acetate¼5/1).
IR (neat) 3500, 2926, 1458, 1377, 1340, 1221, 1156, 1128,
1
1097, 1043, 980, 943, 900, 864, 810, 750 cm21; H NMR
(CDCl3) d 0.86 (t, J¼6.6 Hz, 3H), 0.97 (d, J¼6.3 Hz, 3H),
1.21–1.40 (m, 6H), 1.46–1.73 (m, 5H), 1.74–1.83 (m, 2H),
1.92 (ddq, J¼8.1, 11.9, 6.3 Hz, 1H), 3.36 (ddd, J¼2.1, 11.7,
11.7 Hz, 1H), 3.54 (dt, J¼8.9, 6.0 Hz, 1H), 3.85 (ddd,
J¼2.1, 2.1, 11.7 Hz, 1H), 4.92 (d, J¼3.6 Hz, 1H); 13C NMR
(CDCl3) d 13.91, 15.11, 20.59, 21.72, 22.52, 26.13,
31.83, 36.09, 37.58, 46.21, 64.45, 87.84, 101.52. Found:
C, 73.68; H, 11.35%. Calcd for C13H24O2: C, 73.54; H,
11.39%.
5.7.12. 2-(2-Propenoxy)iodobenzene (5a). IR (neat) 3069,
2939, 1649, 1582, 1472, 1439, 1275, 1248, 1018, 930,
748 cm21; 1H NMR (CDCl3) d 4.61 (d, J¼4.5 Hz, 2H), 5.32
(dd, J¼1.5, 10.8 Hz, 1H), 5.53 (dd, J¼1.5, 17.4 Hz, 1H),
6.01–6.13 (m, 1H), 6.72 (t, J¼7.5 Hz, 1H), 6.81 (d, J¼
7.5 Hz, 1H), 7.28 (t, J¼7.5 Hz, 1H), 7.78 (d, J¼7.5 Hz, 1H);
13C NMR (CDCl3) d 69.50, 86.55, 112.29, 117.42, 122.47,
129.19, 132.34, 139.26, 156.77. Found: C, 41.85; H, 3.39%.
Calcd for C9H9IO: C, 41.56; H, 3.49%.
5.7.9. 2-Butoxy-4-butyltetrahydrofuran (2g, 83/17 mix-
ture of diastereomers). IR (neat) 2930, 2862, 1466, 1346,
1
1097, 1032 cm21; H NMR (CDCl3) d 0.89 (t, J¼7.2 Hz,
1.02H), 0.92 (t, J¼7.2 Hz, 4.98H), 1.19–1.62 (m, 11H),
1.99–2.09 (m, 0.17H), 2.10–2.30 (m, 1.66H), 2.31–2.45
(m, 0.17H), 3.31–3.40 (m, 0.17H), 3.36 (dt, J¼6.6, 9.3 Hz,
0.83H), 3.45 (dd, J¼8.1, 8.1 Hz, 1H), 3.52–3.62 (m,
0.17H), 3.67 (dt, J¼6.6, 9.3 Hz, 0.83H), 3.93 (dd, J¼8.1,
8.1 Hz, 0.83H), 4.04 (dd, J¼8.1, 8.1 Hz, 0.17H), 5.06–5.13
(m, 1H); 13C NMR (CDCl3) for major isomer: d 13.90,
14.05, 19.43, 22.82, 30.91, 31.88, 32.79, 38.62, 39.11,
5.7.13. 2-(3-Methyl-2-butenoxy)iodobenzene (5b). IR
(neat) 2972, 2914, 1676, 1582, 1470, 1275, 1240, 1016,
1
748 cm21; H NMR (CDCl3) d 1.75 (s, 3H), 1.80 (s, 3H),
4.59 (d, J¼6.6 Hz, 2H), 5.48–5.54 (m, 1H), 6.70 (t, J¼

6634
K. Takami et al. / Tetrahedron 59 (2003) 6627–6635
8.1 Hz, 1H), 6.82 (d, J¼8.1 Hz, 1H), 7.28 (t, J¼8.1 Hz, 1H),
7.77 (d, J¼8.1 Hz, 1H); 13C NMR (CDCl3) d 18.42, 25.80,
66.14, 86.81, 112.48, 119.36, 122.23, 129.13, 137.61,
139.22, 157.16. Found: C, 46.11; H, 4.52%. Calcd for
C11H13IO: C, 45.85; H, 4.55%.
71.43; H, 10.65%. Calcd for C15H20O2: C, 71.70; H,
10.94%.
Acknowledgements
5.7.14. 2-Bromophenyl 3-methyl-2-propenyl ether (5c).
IR (neat) 2914, 1585, 1477, 1277, 1242, 1051, 1030, 995,
This work was supported by Grants-in-Aid for Scientific
Research (Nos. 12305058 and 10208208) and Grant-in-Aid
for Scientific Research on Priority Areas (No. 14078215)
from the Ministry of Education, Science Sports, and
Culture, Japan. H. Y. acknowledges the JSPS Research
Fellowship for Young Scientists.
1
746 cm21; H NMR (CDCl3) d 1.75 (s, 3H), 1.79 (s, 3H),
4.60 (d, J¼6.3 Hz, 2H), 5.48–5.56 (m, 1H), 6.82 (dt, J¼1.5,
7.5 Hz, 1H), 6.90 (dd, J¼1.5, 7.8 Hz, 1H), 7.24 (dt, J¼1.5,
7.5 Hz, 1H), 7.53 (dd, J¼1.5, 7.8 Hz, 1H); 13C NMR
(CDCl3) d 18.56, 26.01, 66.18, 112.24, 113.58, 119.24,
121.53, 128.06, 133.09, 137.78, 154.89. Found: C, 54.90; H,
5.41%. Calcd for C11H13BrO: C, 54.79; H, 5.43%.
References
5.7.15. 3-Methyl-2,3-dihydrobenzofuran (6a). IR (neat)
2964, 2872, 1597, 1481, 1462, 1227, 966, 835, 750 cm21
;
1. (a) Neumann, W. P. Synthesis 1987, 665–683. (b) Curran,
D. P.; Porter, N. A.; Giese, B. Stereochemistry of Radical
Reactions; VCH: Weinheim, 1996. (c) Giese, B.; Kopping, B.;
1H NMR (CDCl3) d 1.31 (d, J¼7.5 Hz, 3H), 3.45–3.58 (m,
1H), 4.04 (t, J¼7.5 Hz, 1H), 4.65 (t, J¼8.7 Hz, 1H), 6.78 (d,
J¼7.5 Hz, 1H), 6.85 (t, J¼7.5 Hz, 1H), 7.10 (t, J¼7.5 Hz,
1H), 7.13 (d, J¼7.5 Hz, 1H); 13C NMR (CDCl3) d 19.33,
36.46, 78.35, 109.31, 120.27, 123.63, 127.81, 132.07,
159.49. Found: C, 80.57; H, 7.57%. Calcd for C9H10O: C,
80.56; H, 7.51%.
¨
Gobel, T.; Dickhaut, J.; Thoma, G.; Kulicke, K. J.; Trach, F.
Org. React. 1996, 48, 301–856.
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(b) Clive, D. L. J.; Yang, W. J. Org. Chem. 1995, 60,
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1989, 54, 3140–3157. (d) Curran, D. P.; Hadida, S. J. Am.
5.7.16. 3-(1-Methylethyl)-2,3-dihydrobenzofuran (6b).
IR (neat) 2961, 1595, 1483, 1232, 959, 750 cm21 1H
;
NMR (CDCl3) d 0.86 (d, J¼6.6 Hz, 3H), 0.94 (d, J¼6.6 Hz,
3H), 1.89–2.00 (m, 1H), 3.30 (quint., J¼4.8 Hz, 1H), 4.36
(dd, J¼4.8, 9.3 Hz, 1H), 4.49 (t, J¼9.3 Hz, 1H), 6.77 (d,
J¼4.5 Hz, 1H), 6.83 (t, J¼4.5 Hz, 1H), 7.11 (t, J¼4.5 Hz,
1H), 7.17 (d, J¼4.5 Hz, 1H); 13C NMR (CDCl3) d 18.46,
19.83, 31.71, 48.12, 73.74, 109.19, 119.90, 124.90, 127.96,
129.24, 160.19. Found: C, 81.62; H, 8.64%. Calcd for
C11H14O: C, 81.44; H, 8.70%.
¨
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Walton, J. C. Angew. Chem., Int. Ed. Engl. 1998, 37,
3072–3082.
5.7.17. 2-Bromoethanal butyl 3-phenyl-2-propynyl
acetal (7). IR (neat) 2959, 2872, 2245, 1724, 1491, 1117,
5. (a) Chatgilialoglu, C. Acc. Chem. Res. 1992, 25, 188–194.
(b) Chatgilialoglu, C.; Guerrini, A.; Seconi, G. Synlett 1990,
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1 1991, 103–112. (e) Barton, D. H. R.; Jang, D. O.;
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4681–4684. (g) Lesage, M.; Simoes, J. A. M.; Griller, D.
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1043, 758, 691 cm21
;
1H NMR (CDCl3) d 0.93 (t, J¼
7.5 Hz, 3H), 1.35–1.48 (m, 2H), 1.62 (quint., J¼7.5 Hz,
2H), 3.46 (d, J¼5.4 Hz, 2H), 3.56–3.67 (m, 1H), 3.67–3.77
(m, 1H), 4.52 (s, 2H), 4.94 (t, J¼5.4 Hz, 1H), 7.29–7.36 (m,
3H), 7.42–7.49 (m, 2H); 13C NMR (CDCl3) d 13.88, 19.29,
31.64, 31.73, 54.73, 67.13, 84.38, 86.48, 100.37, 122.22,
128.15, 128.44, 131.56. Found: C, 58.17; H, 6.05%. Calcd
for C15H19BrO2: C, 57.89; H, 6.15%.
5.7.18. 2-Butoxy-3-(phenylmethyliden)tetrahydrofuran
(8, E/Z547/53). IR (neat) 2932, 2870, 1599, 1491, 1448,
1
1344, 1184, 1097, 1034, 928, 754, 692 cm21; H NMR
(CDCl3) d 0.91 (t, J¼7.5 Hz, 3H), 1.31–1.42 (m, 2H),
1.49–1.61 (m, 2H), 2.71 (d, J¼16.5 Hz, 0.53H), 2.83 (d,
J¼17.1 Hz, 0.47H), 2.93 (d, J¼16.2 Hz, 1H), 3.43 (ddt,
J¼2.4, 13.5, 6.6 Hz, 1H), 3.71 (ddt, J¼1.8, 9.6, 6.9 Hz, 1H),
4.57 (q, J¼13.2 Hz, 1H), 4.69 (s, 1H), 5.21 (d, J¼5.1 Hz,
0.53H), 5.33 (d, J¼4.2 Hz, 0.47H), 6.39 (d, J¼16.2 Hz,
1H), 7.13 (d, J¼7.2 Hz, 1H), 7.16–7.24 (m, 1H), 7.24–7.36
(m, 3H); 13C NMR (CDCl3) for major isomer: d
13.95, 19.44, 31.77, 37.94, 67.11, 70.81, 104.24, 119.99,
126.31, 127.85, 128.20, 137.28, 138.50. For minor isomer:
d 13.95, 19.44, 31.77, 41.14, 67.03, 67.87, 102.09,
121.41, 126.40, 127.70, 128.32, 137.30, 139.00. Found: C,
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MacInnes, A. N. Encyclopedia of Inorganic Chemistry; King,
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present text, would exist as a certain dimeric or polymeric
form: Duke, B. J.; Hamilton, T. P.; Schaefer, III., H. F. Inorg.
Chem. 1991, 30, 4225–4229, and references cited therein.
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9. The reaction of dichlorogallane with ethyl halides has been
reported, although the reaction was concluded to proceed via
´
s-bond metathesis: (a) Csakvari, B.; Jenei, S.; Knausz, D.;
´
Meszticzky, A. Acta Chim. Acad. Sci. Hung. 1969, 59,
´
´
225–227. (b) Meszticzky, A.; Knausz, D.; Csakvari, B.;
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14. Probably, the propagation steps can not proceed because the
benzylic radical intermediate is too stable to abstract hydrogen
from HGaCl2.
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combination of sodium borohydride and indium trichloride,
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18. Only one example of a cyclization of halo acetal with indium
hydride species has been reported. In that case, only 50% of
cyclized product was obtained. See Ref. 10g.
11. Examples of gallium hydride reagents, especially LiGaH4
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carbonyl groups and halides: (a) Schmidba, H.; Findeiss, W.;
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3.0 equiv. of DIBAL-H, respectively.