Synthetic utility of tribenzyltin hydride and its derivatives as easily accessible, removable, and decomposable organotin reagents

Article abstract of DOI:10.1016/j.jorganchem.2012.11.007

Radical reactions using tribenzyltin hydride (Bn₃SnH) easily prepared from tin and benzyl chloride were studied. The Et₃B- initiated reduction and cyclization of haloalkanes and haloalkenes with Bn ₃SnH proceeded efficiently. Homolytic hydrostannylation of alkynes with Bn₃SnH followed by treatment with electrophiles gave functionalized alkenes in good to high yields. The organotin byproducts formed could be easily removable by filtration and silica-gel column chromatography without any pretreatment. It was also found that tribenzyltin chloride (Bn ₃SnCl) easily decomposed to benzyl alcohol in a basic solution of H₂O₂.

Full text of DOI:10.1016/j.jorganchem.2012.11.007

Journal of Organometallic Chemistry 724 (2013) 129e134
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthetic utility of tribenzyltin hydride and its derivatives as easily accessible,
removable, and decomposable organotin reagents
*
Takeshi Yamakawa, Hidenori Kinoshita, Katsukiyo Miura
Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-ohkubo, Sakura-ku, Saitama 338-8570, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Radical reactions using tribenzyltin hydride (Bn3SnH) easily prepared from tin and benzyl chloride were
studied. The Et3B-initiated reduction and cyclization of haloalkanes and haloalkenes with Bn3SnH
proceeded efficiently. Homolytic hydrostannylation of alkynes with Bn3SnH followed by treatment with
electrophiles gave functionalized alkenes in good to high yields. The organotin byproducts formed could
be easily removable by filtration and silica-gel column chromatography without any pretreatment. It was
also found that tribenzyltin chloride (Bn3SnCl) easily decomposed to benzyl alcohol in a basic solution of
H2O2.
Received 10 August 2012
Received in revised form
18 October 2012
Accepted 6 November 2012
Keywords:
Organotin hydride
Radical reaction
Ó 2012 Elsevier B.V. All rights reserved.
Removable organotin reagent
Decomposable organotin reagent
1. Introduction
2. Results and discussion
Triorganotin hydrides (R3SnH) are highly valuable as radical
mediators and stannylating agents [1e4]. Particularly, tributyltin
hydride (Bu3SnH) is commercially available and has frequently
been used to these ends. Radical reactions mediated by R3SnH
provide chemo- and stereoselective methods not only for reduction
of organic halides and pseudohalides but also for inter- and intra-
molecular CeC bond formation [5]. Hydrostannylation of alkynes
and alkenes with R3SnH is convenient to prepare alkenyl- and
alkylstannanes [1e4,6], which are synthetically useful for further
transformations utilizing the CeSn bonds formed [2,4,7]. Unfortu-
nately, synthetic use of Bu3SnH and their derivatives has two
serious problems. Since the organotin byproducts Bu3SnX
(X ¼ halogen, OH, OSnBu3) have high lipophilicity, their removal by
silica-gel column chromatography is difficult without pretreatment
of the reaction mixture [1,8]. In addition, Bu3SnX are stable, hardly
decomposable, and toxic [9]. Thus far a variety of R3SnH have been
developed to facilitate product isolation [1e3]. However, the
preparation of these reagents is costly and laborious. We herein
report synthetic utility of tribenzyltin hydride (Bn3SnH) as an
easily accessible, removable, and decomposable substitute for
Bu3SnH.
2.1. Synthesis of Bn3SnH
Bn3SnH can be prepared from tin andbenzyl chloride by two steps
(Scheme 1). The first step is the aqueous reaction of tin with benzyl
chloride [10]. The Bn3SnCl obtained was rapidly and efficiently con-
verted into Bn3SnH by treatment with LiAlH4 [11,12]. Bn3SnH, a white
solid, is storable in a sealed bottle purged with an inert gas at ꢀ20 ꢁC
(in a refrigerator). Under the atmosphere Bn3SnH can be handled at
room temperature in several minutes although it gradually decom-
poses. On exposure to air for 1 day at room temperature, Bn3SnH
suffered ca. 70% conversion into unidentified products.
2.2. Reactivities of Bn3SnH and alkenyltribenzylstannanes
To test the utility of Bn3SnH, radical reduction of organic halides
was first conducted. In the presence of Et3B as radical initiator,
Bn3SnH reacted smoothly with various simple and functionalized
haloalkanes 1 at room temperature to give the corresponding
dehalogenated products 2 in high yields (Table 1) [13]. Like Bu3SnH,
* Corresponding author. Tel.: þ81 48 838 3514; fax: þ81 48 838 3516.
E-mail address: kmiura@apc.saitama-u.ac.jp (K. Miura).
Scheme 1. Synthesis of Bn3SnH.
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.11.007

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T. Yamakawa et al. / Journal of Organometallic Chemistry 724 (2013) 129e134
Table 1
Table 2
Reduction of haloalkanes 1 with Bn3SnH.a
Hydrostannylation of terminal alkynes with Bn3SnH.a
Entry
R1
Time (h)
Product
Yield (%)b
E:Zc
67:33
81:19
64:36
73:27
78:22
98:2
Entry
ReX
Product
Yield (%)b
1
2
3
n-C10H21
n-C10H21
HO(CH2)4
HO(CH2)4
c-C6H11
Ph
3
12
3
24
24
3
7a
7a
7b
7b
7c
7d
7e
92
quant
82
82
85
1
2
3
4
5
6
7
8
n-C12
n-C12
PhCO2(CH2)4-I (1b-I)
PhCO2(CH2)4-Br (1b-Br)
CH3C(O)(CH2)11eBr (1c)
CH3CH(OH)(CH2)11eBr (1d)
PhCH(OH)(CH2)5eBr (1e)
CH3CH(OTBS)(CH2)11eBr (1f)
H
25eI (1a-I)
2a
2a
2b
2b
2c
2d
2e
2f
96c
90c
96
97
90
92
91
95
H25eBr (1a-Br)
4d,e
5e
6
99
80
7
Me3Si
24
>99:1
a
Unless otherwise noted, all reactions were carried out with 6 (0.50 mmol),
Bn3SnH (0.60 mmol) and Et3B (1 M in hexane, 0.05 mL, 0.05 mmol) in toluene
(2 mL).
a
Unless otherwise noted, all reactions were carried out with 1 (0.50 mmol),
Bn3SnH (0.60 mmol) and Et3B (1 M in hexane, 0.05 mL, 0.05 mmol) in hexane (2 mL).
b
b
Isolated yield of 7.
Isolated yield of 2.
Determined by GC analysis.
c
Determined by 1H NMR analysis.
c
d
With Bn3SnH (0.70 mmol).
With Et3B (0.10 mmol).
e
Bn3SnH is reactive enough for radical reduction of haloalkanes. It is
worthy of note that the tin byproducts Bn3SnX (X ¼ Br, I) precipi-
tated in hexane and most of those could be removed by filtration.
The crude product contaminated with a small amount of Bn3SnX
could be easily purified by silica-gel column chromatography
without pretreatment. The methylene signals of the Bn3Sn moiety
completely disappeared in 1H NMR spectra of the isolated products.
Additionally Bn3SnX do not have such an unpleasant smell as
caused by Bu3SnX. Thus Bn3SnH turned out more convenient than
Bu3SnH from the viewpoint of product purification.
Bn3SnH is useful also for radical cyclization. The Et3B-initiated
reactions of iodoalkenes 3a and 3b afforded the cyclized products
4a and 4b, respectively, in high yields (Scheme 2). The pure prod-
ucts were easily obtained by direct column chromatography of the
concentrated reaction mixtures on silica-gel.
attributable to fast hydrogen abstraction of the dodecyl radical
intermediate from Bn3SnH. Under the same conditions, the use of
Bu3SnH instead of Bn3SnH improved the molar ratio of 5 to 2a
although the conversion of 1a-I was not good. This fact implies that
Bn3SnH has higher hydrogen-donating ability than Bu3SnH (vide
infra).
In the presence of Et3B, hydrostannylation of terminal alkynes
6 with Bn3SnH proceeded efficiently with moderate to high
E-selectivity (Table 2) [14,15]. Under the same conditions, the
reaction of 1-dodecyne (6a) with Bu3SnH gave the corresponding
adduct in 5% yield (E:Z ¼ 2:3, 92% recovery of 6a). Thus Bn3SnH is
more reactive than Bu3SnH toward homolytic hydrostannylation.
The E-selectivity of alkenylstannanes 7 increased with the reaction
time (entries 1e4). A most plausible explanation for this observa-
tion is that (Z)-7 are isomerized to the thermodynamically favored
E-isomers by addition and elimination (reversible addition) of
a tribenzylstannyl radical (Bn3Snꢂ) [16].
As shown in Table 2, the homolytic hydrostannylation of alkynes
with Bn3SnH provides a convenient route to alkenylstannanes bearing
a tribenzylstannyl group. We therefore examined synthetic utility of
these compounds by reaction with heteroatom and carbon electro-
philes. Iodine was first employed as the electrophile. The Et3B-initiated
hydrostannylation followed by treatment with iodine in a one-pot
manner gave iodoalkenes 8 in high yields without any problem of
Bn3SnH was next used for radical addition of 1-iodododecane
(1a-I) to t-butyl acrylate (Scheme 3). In contrast to the successful
radical cyclization, the Bn3SnH-mediated intermolecular reaction
resulted in a low yield of the desired adduct 5. Since considerable
formation of 2a was observed, the discouraging result is
Table 3
Hydrostannylation of terminal alkynes followed by iodonolysis.a
R1
Time (h)
Product
Yield (%)b
E:Zc
Scheme 2. Cyclization of haloalkenes 3 with Bn3SnH.
Entry
1
n-C10H21
HO(CH2)4
c-C6H11
Ph
12
24
24
3
8a
8b
8c
8d
88
89
81
94
80:20
72:28
82:18
98:2
2d,e
3e
4
a
Unless otherwise noted, all reactions were carried out with 6 (0.50 mmol),
Bn3SnH (0.60 mmol), Et3B (1 M in hexane, 0.05 mL, 0.05 mmol), and iodine
(0.60 mmol) in toluene (2 mL).
b
Isolated yield of 8.
c
Determined by 1H NMR analysis.
d
With Bn3SnH (0.70 mmol).
With Et3B (0.10 mmol).
e
Scheme 3. Intermolecular addition of 1-iodododecane with Bn3SnH.

T. Yamakawa et al. / Journal of Organometallic Chemistry 724 (2013) 129e134
131
Scheme 4. Cyclization of enyne 9 followed by iodonolysis.
purification (Table 3). These results clearly indicate that iodine reacts
site-selectively at the alkenyleSn bond rather than at the benzyleSn
bonds, and that alkenylstannanes 7 serve as efficient alkenyl donors.
When enyne 9 was subjected to the same reaction conditions, cyclized
iodoalkene 11 was formed as a single stereoisomer in 94% yield via
radical cyclization of 9 to alkenylstannane 10 (Scheme 4) [17].
Alkenylstannanes 7 are valuable also for Pd-catalyzed cross-
coupling reactions (Scheme 5) [7]. Under catalysis by Pd2(dba)3-
PPh3, (E)-7d reacted smoothly with benzoyl chloride. The crude
product containing Bn3SnCl could be directly purified by silica-gel
column chromatography to give chalcone (12) in high yield. The
cross-coupling between (E)-7d and p-iodotoluene proceeded in the
presence of CsF. In these reactions, benzyl group transfer to the
electrophiles was not observed.
Scheme 6. Radical clock experiment using bromoalkene 14.
87 mg/kg) [21], tribenzyltin compounds Bn3SnX also have similar
levels of acute toxicity, irrespective of the heteroatom substituent
X. Since the LD50 (rat) value of Bn3SnCl is reported to be 175 mg/kg
[21], it is predicted that Bn3SnX would be slightly more toxic than
Bu3SnX. However, as described above, tribenzyltin byproducts
Bn3SnX are easily removable. In addition, they are easily decom-
posable by treatment with a basic solution of H2O2. For example,
the reaction of Bn3SnCl with excess amounts of H2O2 and KHCO3 in
THF at 80 ꢁC gave BnOH in 79% yield (Scheme 7) [22]. This yield
corresponds to the cleavage of 2.4 carbonetin bonds per one
molecule of Bn3SnCl. No methylene signals of the Bn3Sn moiety
were observed in 1H NMR spectra of the crude product. The
decomposition reaction proceeded even at room temperature.
2.3. Radical clock experiment
To evaluate the hydrogen-donating ability of Bn3SnH, the rate
constant for hydrogen abstraction by a primary alkyl radical (kH
(Bn3SnH)) was determined by a radical clock experiment using
bromoalkene 14 (Scheme 6) [18,19]. The reaction of 14 in the
presence of a large excess of Bn3SnH (pseudo-first-order condi-
tions) gave acyclic product 15 and cyclic product 16 with the ratio of
1.73:1. This product ratio was used for the determination of kH
(Bn3SnH) with the known rate constant for cyclization of the acyclic
radical intermediate (kC) and the average concentration of Bn3SnH.
The rate constant kH (Bn3SnH) was estimated to be 1.9 ꢃ 107, which
is between the values of kH (Bu3SnH) (6.4 ꢃ 106) and kH (Ph3SnH)
(2.2 ꢃ 107) [20]. This result proves that Bn3SnH has higher
hydrogen-donating ability than Bu3SnH. The reactivity of Bn3SnH
well agrees with the fact that the Bn3SnH-mediated addition of 1a-I
to t-butyl acrylate is subject to competitive reduction of 1a-I to 2a
(Scheme 3). In addition, the fast hydrostannylation of alkynes with
Bn3SnH (Table 2) is probably because its high hydrogen-donating
ability accelerates hydrogen abstraction of alkenyl radical inter-
mediates formed by reversible addition of Bn3Snꢂ to alkynes.
3. Conclusions
In conclusion we have demonstrated that Bn3SnH is valuable as
an easily accessible, removable organotin reagent for radical
reduction of haloalkanes and radical cyclization of iodoalkenes. The
tin byproducts formed can be removed by filtration and silica-gel
column chromatography without any pretreatment. Bn3SnH is
more reactive toward homolytic hydrostannylation of alkynes than
Bu3SnH. The alkenylstannanes thus prepared serve as alkenyl
donors in iodonolysis and Pd-catalyzed cross-coupling reactions.
The removal of tin byproducts can be easily conducted also in these
reactions. Additionally we have disclosed the hydrogen-donating
ability of Bn3SnH and the decomposability of Bn3SnCl. This study
has proved that introduction of a tribenzylstannyl group can
improve the synthetic utility of organotin reagents.
4. Experimental
4.1. General experimental methods
2.4. Decomposability of Bn3SnCl
Unless otherwise noted, all reactions and distillation of solvents
were carried out under an argon atmosphere. Commercially avail-
able dry THF stored in a stainless container under an argon atmo-
sphere was used as received. Hexane, dichloromethane, toluene,
and benzene were dried by distillation from CaH2. 1-Iodododecane
(1a-I),1-bromododecane (1a-Br), terminal alkynes (6), Bu3SnH, and
t-butyl acrylate were purchased from chemical companies and
Judging from the similarity of tributyltin compounds Bu3SnX in
LD50 (rat) values (X ¼ Cl, 129 mg/kg; X ¼ Br,138 mg/kg; X ¼ OSnBu3,
Scheme 7. Decomposition of Bn3SnCl.
Scheme 5. Pd-catalyzed cross-coupling reactions of alkenylstannane (E)-7d.

132
T. Yamakawa et al. / Journal of Organometallic Chemistry 724 (2013) 129e134
simply distilled. Other commercially available organic and inor-
ganic reagents were used as received. Organic halides 1b-I [23], 1b-
Br [24], 1c [25], 1d [26], 1e [26], 1f [26], 3a [26], 3b [26], and 14
[19b], and enyne 9 [27] were prepared by the reported methods.
The substrates prepared were purified by silica-gel column chro-
matography or distillation before their use. Analytical thin layer
chromatography was performed using 0.25 mm silica-gel plates.
Column chromatography was performed on silica-gel (spherical,
isolated products were identified by 1H and 13C NMR analysis.
The NMR data obtained well agree with the reported data [30].
4.5. Intermolecular radical addition of 1-iodododecane 1a-I
A solution of Bn3SnH (236 mg, 0.600 mmol) in toluene (1.5 mL)
was slowly added to a stirred solution of 1a-I (148 mg, 0.500 mmol),
t-butyl acrylate (192 mg, 1.50 mmol), and Et3B (1.0 M in hexane,
0.050 mL, 0.050 mmol) in toluene (0.5 mL) over 30 min at room
temperature. After 1.5 h CCl4 (0.10 mL, 1.0 mmol) was added to the
reaction mixture. After 10 min undecane (72.4 mg) was added to
the resultant mixture as an internal standard. The yield of dodecane
and the recovery of 1a-I were determined by GC analysis using
a calibration curve (50% yield of dodecane; less than 5% recovery of
1a-I). After evaporation of the reaction mixture, purification of the
crude product by silica-gel column chromatography gave t-butyl
pentadecanoate (5, 54 mg, 0.18 mmol) in 36% yield. The isolated
product was identified by 1H and 13C NMR analysis. The NMR data
obtained well agree with the reported data [19c]. The reaction
using Bu3SnH was performed by a similar method. The GC analysis
of the reaction mixture showed that the yield of dodecane was 17%,
and that the recovery of 1a-I was 36%. The yield of 5 was deter-
mined to be 47% by 1H NMR analysis of the crude mixture.
neutral, 63e210
100, or 125.8 MHz), and 119Sn NMR (186.5 MHz) were recorded in
CDCl3 or C6D6. The chemical shifts ( ) are reported with reference at
m
m). 1H (300, 400, or 500 MHz), 13C NMR (75.0,
d
0.00 ppm (Me4Si), 7.15 ppm (C6HD5), or 7.26 ppm (CHCl3) for the
proton, at 77.0 ppm (centered on the signal of CDCl3) or 128.0 ppm
(centered on the signal of C6D6) for the carbon, and at 0.00 ppm
(Me4Sn) for the tin. Analytical GLPC was performed by a GC
instrument equipped with
a
DB-1 capillary column
(30 m ꢃ 0.25 mm) using nitrogen as carrier gas. High resolution
mass was recorded on a MS instrument by EI method.
4.2. Synthesis of tribenzyltin hydride [12]
A solution of Bn3SnCl (8.55 g, 20.0 mmol) [10] in THF (80 mL)
was added to a suspension of LiAlH4 (835 mg, 22.0 mmol) in Et2O
(20 mL) at 0 ꢁC. After the addition of Bn3SnCl, the mixture was
stirred for 30 min. The reaction mixture was quenched with 20 wt%
aqueous potassium sodium tartrate (100 mL) and extracted with
Et2O (3 ꢃ 40 mL). The combined organic layer was dried over
Na2SO4 and evaporated. Purification of the crude product by flash
column chromatography on silica-gel (hexane) gave the title
compound (6.86 g, 17.4 mmol) in 87% yield. Rapid work-up and
purification are required to prevent Bn3SnH from decomposition.
4.6. General procedure for homolytic hydrostannylation of alkynes
An alkyne 6 (0.500 mmol) and Et3B (1.0 M in hexane, 0.050 mL,
0.050 mmol) were added to a stirred solution of Bn3SnH (236 mg,
0.600 mmol) in toluene (2.0 mL) at room temperature. After a given
reaction time, the reaction was quenched with CCl4 (0.10 mL,
1.00 mmol) for 10 min. The resultant mixture was evaporated and
purified by flash column chromatography on silica-gel. Since the
stannylated products 7 are subject to protiodestannylation on
silica-gel, the elution should be rapidly performed under an
increased pressure.
Mp 51e52 ꢁC (hexane). 1H NMR (C6D6)
d
2.17 (d, J ¼ 1.5 Hz, 2J
(
117,119Sne1H) ¼ 62 Hz, 6H), 5.71 (sept, J ¼ 1.5 Hz, 1J (117/119Sne
1H) ¼ 1694/1772 Hz, 1H), 6.75e6.80 (m, 6H), 6.91e6.95 (m, 3H),
7.06e7.10 (m, 6H); 13C NMR (C6D6)
d
17.8 (1J (117/119Sne13C) ¼ 275/
288 Hz), 124.2 (5J (117,119Sne13C) ¼ 16 Hz), 127.7 (3J (117,119Sne
13C) ¼ 26 Hz), 128.9 (4J (117,119Sne13C) ¼ 14 Hz), 142.0 (2J
(
(
117,119Sne13C) ¼ 40 Hz); 119Sn NMR (C6D6)
119Sne1H) ¼ 1773 Hz, 2J (119Sne1H) ¼ 62 Hz).
d
ꢀ85.4 (d-sept, 1J
4.6.1. 1-(Tribenzylstannyl)dodec-1-ene (7a, E:Z ¼ 67:33)
Colorless oil. IR (neat) 2924, 2852, 1207, 754, 696 cmꢀ1. 1H NMR
(CDCl3)
d
0.87e0.91 (m, 3H) including 0.88 (t, J ¼ 7.0 Hz, Z) and 0.89
4.3. General procedure for radical reduction of haloalkanes
(t, J ¼ 6.5 Hz, E), 1.20e1.35 (m, 16H), 1.75e1.79 (m, 0.66H), 2.02e
2.05 (m, 1.34H), 2.28 (s, 2J (117/119Sne1H) ¼ 61.0/62.0 Hz, 4.02H, E),
2.31 (s, 2J (117,119Sne1H) ¼ 61.0 Hz, 1.98H, Z), 5.52 (d, J ¼ 12.0 Hz,
0.33H, Z), 5.59 (dt, J ¼ 18.8,1.0 Hz, 0.67H, E), 5.71 (dt, J ¼ 18.8, 6.0 Hz,
0.67H, E), 6.47 (dt, J ¼ 12.0, 7.0 Hz, 0.33H, Z), 6.83e6.86 (m, 6H),
A haloalkane 1 (0.500 mmol) and Et3B (1.0 M in hexane,
0.050 mL, 0.050 mmol) were added to a stirred mixture of Bn3SnH
(236 mg, 0.600 mmol) and hexane (2.0 mL) at room temperature.
After 30 min CCl4 (0.050 mL, 0.50 mmol) was added to the reaction
mixture to convert the remaining Bn3SnH into Bn3SnCl. After 5 min
the resultant mixture was filtered and evaporated. The crude
product was purified by silica-gel column chromatography. In the
reduction of 1a-I and 1a-Br, the yields of dodecane were deter-
mined by GC analysis of the crude product. The product was
identified by comparison with the authentic sample in GCeMS
analysis. Other isolated products were identified by 1H and 13C
NMR analysis. The NMR data obtained well agree with the reported
data (2b [28], 2d [26], 2e [29], and 2f [26]) or the data of
commercial samples (2c).
6.98e7.01 (m, 3H), 7.13e7.18 (m, 6H); 13C NMR (CDCl3)
d 14.1, 19.0
(1J (117/119Sne13C) ¼ 273/285 Hz, E), 19.8 (Z), 22.67, 22.69, 28.6, 28.9,
29.0, 29.1, 29.33, 29.36, 29.46, 29.51, 29.53, 29.61, 29.63, 29.65,
31.89, 31.92, 33.8, 37.7, 123.45 (E), 123.54 (Z), 124.6 (E), 125.5 (Z),
127.39 (Z), 127.44 (E), 128.36 (E), 128.42 (Z), 141.7, 151.0 (Z), 152.1 (E).
HRMS (EIþ) calcd for C33H44Sn [Mþ]: 560.2465. Found: 560.2455.
4.6.2. 6-(Tribenzylstannyl)hex-5-ene-1-ol (7b, E:Z ¼ 64:36)
Colorless oil. IR (neat) 3300 (br s), 2933, 1207, 754, 696 cmꢀ1. 1H
NMR (CDCl3)
d
1.18 (t, J ¼ 5.2 Hz, 1H), 1.25e1.50 (m, 4H), 1.72e1.78
(m, 0.72H, Z), 2.04e2.10 (m, 1.28H, E), 2.29 (s, 2J (117,119Sne
1H) ¼ 61.2 Hz, 3.84H, E), 2.32 (s, 2J (117,119Sne1H) ¼ 60.8 Hz,
2.16H, Z), 3.56e3.65 (m, 2H), 5.42e5.77 (m, 1.64H) including 5.56
(d, J ¼ 12.4 Hz, Z) and 5.61 (d, J ¼ 19.0 Hz, E) and 5.68 (dt, J ¼ 19.0,
5.6 Hz, E), 6.46 (dt, J ¼ 12.4, 6.8 Hz, 0.36H, Z), 6.85 (d, J ¼ 7.6 Hz, 6H),
4.4. Radical cyclization of iodoalkenes 3a and 3b
A solution of Bn3SnH (236 mg, 0.600 mmol) in CH2Cl2 (1.5 mL)
was slowly added to a stirred mixture of 3a or 3b (0.500 mmol),
Et3B (1.0 M in hexane, 0.050 mL, 0.050 mmol), and CH2Cl2 (0.5 mL)
over 15 min at room temperature. After completion of the radical
cyclization, the reaction mixture was evaporated. The crude
product was purified by silica-gel column chromatography. The
6.98e7.02 (m, 3H), 7.14e7.18 (m, 6H); 13C NMR (CDCl3) 19.0 (1J (117/
d
119Sne13C) ¼ 273/285 Hz, E), 19.7 (Z), 24.6 (E), 25.6 (Z), 31.9 (E), 32.3
(Z), 37.2, 62.6 (Z), 62.7 (E), 123.4 (E), 123.5 (Z), 125.2 (E), 125.9 (Z),
127.3 (Z), 127.4 (E), 128.3 (E), 128.4 (Z), 141.6, 150.4 (Z), 151.3 (E).
HRMS (EIþ) calcd for C27H32OSn [Mþ]: 492.1475. Found: 492.1479.

T. Yamakawa et al. / Journal of Organometallic Chemistry 724 (2013) 129e134
133
4.6.3. 1-Cyclohexyl-2-(tribenzylstannyl)ethene (7c, E:Z ¼ 78:22)
1H), 6.82 (d, J ¼ 7.0 Hz, 6H), 6.97e7.02 (m, 3H), 7.11e7.17 (m, 6H);
Colorless oil. IR (neat) 2922, 2848, 1207, 754, 696 cmꢀ1. 1H NMR
13C NMR (CDCl3)
d
13.90, 13.92, 16.7, 19.3 (1J (117/119Sne13C) ¼ 273/
(CDCl3)
d
0.95e1.27 (m, 5H), 1.45e1.50 (m, 0.44H), 1.60e1.72 (m,
285 Hz, three carbons), 21.0, 29.7, 34.1, 43.7 (3J 117,119Sne
(
4.78H), 1.85e1.93 (m, 0.78H, E), 2.28 (s, 2J (117/119Sne1H) ¼ 61.0/
62.0 Hz, 4.68H, E), 2.31 (s, 2J (117,119Sne1H) ¼ 61.5 Hz, 1.32H, Z),
5.46 (d, J ¼ 12.0 Hz, 0.22H, Z), 5.55 (dd, J ¼ 19.0, 1.0 Hz, 0.78H, E),
5.64 (dd, J ¼ 19.0, 6.0 Hz, 0.78H, E), 6.31 (dd, J ¼ 12.0, 9.5 Hz, 0.22H,
Z), 6.85 (d, J ¼ 7.0 Hz, 6H), 6.98e7.02 (m, 3H), 7.13e7.17 (m, 6H); 13C
13C) ¼ 32.7 Hz), 50.8 (3J (117,119Sne13C) ¼ 55.3 Hz), 58.3, 61.25,
61.31, 116.7 (1J (117/119Sne13C) ¼ 402/421 Hz), 123.4 (5J (117,119Sne
13C) ¼ 16.3 Hz, three carbons), 127.3 (3J (117,119Sne13C) ¼ 23.9 Hz,
six carbons), 128.3 (4J (117,119Sne13C) ¼ 13.8 Hz, six carbons), 141.5
(2J (117,119Sne13C) ¼ 37.7 Hz, three carbons), 162.3, 171.26, 171.31.
HRMS (EIþ) calcd for C36H44O4Sn [Mþ]: 660.2262. Found: 660.2271.
NMR (CDCl3)
d
19.0 (1J (117/119Sne13C) ¼ 272/284 Hz, E), 19.9 (Z), 25.7
(Z), 25.8 (Z), 25.9 (E), 26.2 (E), 32.2 (E), 33.0 (Z), 45.0 (E), 47.4 (Z),
121.5 (E), 123.41 (E), 123.47 (Z), 123.54 (Z), 127.35 (Z), 127.42 (E),
128.3 (4J (117,119Sne13C) ¼ 12.6 Hz, E), 128.4 (Z), 141.7 (2J (117,119Sne
13C) ¼ 37.7 Hz), 156.3 (Z), 157.4 (E). HRMS (EIþ) calcd for C29H34Sn
[Mþ]: 502.1682. Found: 502.1695.
4.7.2. Diethyl 3-((E)-iodomethylene)-4-isopropylcyclopentane-1,1-
dicarboxylate (11)
Colorless oil. IR (neat) 2960, 1732, 1464, 1367, 1252, 1190 cmꢀ1
.
1H NMR (CDCl3)
d
0.83 (d, J ¼ 7.0 Hz, 3H), 0.94 (d, J ¼ 7.0 Hz, 3H),
1.23e1.29 (m, 6H), 1.87e2.07 (m, 2H), 2.54e2.63 (m, 2H), 2.75 (dt,
J ¼ 17.5, 2.5 Hz, 1H), 3.10 (dt, J ¼ 17.5, 1.5 Hz, 1H), 4.17e4.24 (m, 4H),
4.6.4. 1-Phenyl-2-(tribenzylstannyl)ethene (7d, E:Z ¼ 98:2)
Yellow oil. IR (neat) 3024, 1597, 1493, 1452, 1205, 756, 729,
5.88e5.91 (m, 1H); 13C NMR (CDCl3)
d13.9 (two carbons), 16.9, 21.0,
696 cmꢀ1. 1H NMR (CDCl3) for the E-isomer
d
2.39 (s, 2J (117/119Sne
29.3, 35.5, 45.7, 50.3, 57.5, 61.5, 61.6, 70.6, 153.9, 171.1, 171.2. HRMS
1H) ¼ 61.0/62.0 Hz, 6H), 6.49 (s, 2J (117/119Sne1H) ¼ 72.5/76.0 Hz,
2H), 6.89 (d, J ¼ 7.0 Hz, 6H), 7.00e7.05 (m, 3H), 7.15e7.20 (m, 6H),
7.22e7.27 (m, 3H), 7.29e7.32 (m, 2H), resolved signals of the Z-
(EIþ) calcd for C15H23IO4 [Mþ]: 394.0641. Found: 394.0619.
4.8. Pd-catalyzed reaction of alkenylstannane (E)-7d with benzoyl
chloride
isomer:
d
2.18 (s, 0.12H), 5.90 (d, J ¼ 12.8 Hz, 0.02H), 7.63 (d,
J ¼ 12.8 Hz, 0.02H); 13C NMR (CDCl3) for the E-isomer
d
19.2 (1J (117/
119Sne13C) ¼ 278/291 Hz, three carbons), 123.6 (5J (117,119Sne
13C) ¼ 16.3 Hz, three carbons), 126.0 (two carbons), 126.6, 127.5
(3J (117,119Sne13C) ¼ 25.0 Hz, six carbons),127.9,128.4 (two carbons),
128.5 (six carbons), 138.1, 141.3 (2J (117,119Sne13C) ¼ 38.8 Hz, three
carbons), 147.7 (2J (117,119Sne13C) ¼ 11.3 Hz). HRMS (EIþ) calcd for
C29H28Sn [Mþ]: 496.1213. Found: 496.1221.
Benzoyl chloride (70.3 mg, 0.500 mmol) and (E)-7d (258 mg,
0.521 mmol) were added to a stirred solution of Pd2(dba)3 (7.0 mg,
0.0076 mmol) and Ph3P (8.0 mg, 0.030 mmol) in THF (1.0 mL) at
room temperature. After being stirred for 24 h, the reaction mixture
was filtrated through a celiteÒ pad and evaporated. Purification of
the crude product by silica-gel column chromatography (hexanee
AcOEt 10:1) gave chalcone (12, 94.5 mg, 0.454 mmol) in 91%
yield. The NMR data well agree with the reported data [35].
4.6.5. (E)-1-Tribenzylstannyl-2-(trimethylsilyl)ethene (7e,
E:Z ¼ >99:1)
Colorless oil. IR (neat) 3022, 2952, 1491, 1246, 1205, 754,
696 cmꢀ1 1H NMR (CDCl3) 0.01 (s, 9H), 2.30 (s, 2J (117,119Sne
. d
4.9. Pd-catalyzed reaction of alkenylstannane (E)-7d with
p-iodotoluene
1H) ¼ 60.0 Hz, 6H), 6.39 (d, J ¼ 22.5 Hz, J (117/119Sne1H) ¼ 112/
118 Hz, 1H), 6.61 (d, J ¼ 22.5 Hz, J (117/119Sne1H) ¼ 120/126 Hz,
1H), 6.84 (d, J ¼ 7.5 Hz, 6H), 6.98e7.02 (m, 3H), 7.13e7.18 (m,
Alkenylstannane (E)-7d (258 mg, 0.521 mmol) was added to
a stirred mixture of p-iodotoluene (109 mg, 0.500 mmol), Pd2(dba)3
(7.0 mg, 0.0076 mmol), Ph3P (8.0 mg, 0.030 mmol), CsF (152 mg,
1.00 mmol), and THF (1.0 mL) at room temperature. After being
stirred for 24 h, the reaction mixture was filtrated through a celiteÒ
pad and evaporated. Purification of the crude product by silica-gel
column chromatography (hexane) gave 1-methyl-4-((E)-2-
phenylethenyl)benzene (13, 70.5 mg, 0.363 mmol) in 73% yield.
The NMR data well agree with the reported data [36].
6H); 13C NMR (CDCl3) -1.7 (three carbons), 18.9 (1J (117/119Sne
d
13C)
¼
263/275 Hz, three carbons), 123.5 (5J 117,119Sne
(
13C) ¼ 15.0 Hz, three carbons), 127.5 (3J (117,119Sne13C) ¼ 23.8 Hz,
six carbons), 128.4 (4J (117,119Sne13C) ¼ 12.5 Hz, six carbons), 141.6
(2J (117,119Sne13C) ¼ 38.8 Hz, three carbons), 146.3, 157.6 (1J
(
117,119Sne13C) ¼ 25.0 Hz). HRMS (EIþ) calcd for C26H32SiSn [Mþ]:
492.1295. Found: 492.1323.
4.7. General procedure for hydrostannylation of alkynes followed by
iodonolysis
4.10. Radical clock experiment
An alkyne 6 (0.500 mmol) and Et3B (1.0 M in hexane, 0.050 mL,
0.050 mmol) were added to a stirred solution of Bn3SnH (236 mg,
0.600 mmol) in toluene (2.0 mL) at room temperature. After a given
reaction time, the reaction was quenched with I2 (152 mg,
0.600 mmol) for 20 min. The resultant mixture was evaporated and
purified by flash column chromatography on silica-gel. The isolated
products 8 were identified by 1H and 13C NMR analysis. The NMR
data well agree with the reported data (8a [31], 8b [32], 8c [33], and
8d [34]).
7-Bromo-1,1-diphenylhept-1-ene (14, 75.7 mg, 0.230 mmol)
was added to a stirred solution of AIBN (11.8 mg, 0.072 mmol) and
Bn3SnH (0.74 mL, 967 mg, 2.46 mmol) in benzene (10 mL at 20 ꢁC,
10.77 mL at 80 ꢁC). The mixture was heated to 80 ꢁC and stirred for
10 h. Then CCl4 (0.24 mL, 2.5 mmol) was added to the resultant
mixture for conversion of the unreacted Bn3SnH. After being stirred
for 10 min, the reaction mixture was cooled to room temperature
and evaporated. The molar ratio of 1,1-diphenyl-1-heptene (15) to
(diphenylmethyl)cyclohexane (16) ([15]/[16]) was determined by
1H NMR analysis of the crude product. The average ratio obtained
by three runs ([15]/[16]: 1.64 (first run), 1.84 (second run), 1.71
(third run)) was 1.73. The rate constant kH (Bn3SnH) was calculated
by the reported method (kH ¼ 1.9 ꢃ 107) [19]. In the second run, the
yields of 15 and 16 were estimated to be 46% and 25%, respectively,
by 1H NMR analysis using dibenzyl ether as the internal standard.
The NMR data of isolated products well agree with the reported
data [19,37].
4.7.1. Diethyl 3-((E)-tribenzylstannylmethylene)-4-
isopropylcyclopentane-1,1-dicarboxylate (10)
Colorless oil. IR (neat) 2958, 1732, 1599, 1491, 1248, 1101, 756,
698 cmꢀ1
.
1H NMR (CDCl3)
d
0.73 (d, J ¼ 6.5 Hz, 3H), 0.88 (d,
J ¼ 6.5 Hz, 3H), 1.23 (t, J ¼ 7.0 Hz, 3H), 1.27 (t, J ¼ 7.0 Hz, 3H), 1.78e
1.90 (m, 2H), 2.26e2.50 (m, 9H) including 2.33 (s), 2.71 (dd, J ¼ 16.0,
1.5 Hz, 1H), 4.11e4.26 (m, 4H), 5.34 (s, 1J (117,119Sne1H) ¼ 79.4 Hz,

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KHCO3 (601 mg, 6.00 mmol), THF (10 mL), and water (3 mL). The
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Acknowledgments
This work was partly supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science
and Technology, Japan.
Appendix A. Supplementary material
Supplementary material related to this article can be found at
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