Regio- and stereoselective hydrostannation of allenes using dibutyliodotin hydride (Bu2SnIH) and successive coupling with aromatic halides

Article abstract of DOI:10.1039/b712998j

Regio- and stereoselective hydrostannation of allenes by using di-n-butyliodotin hydride (Bu₂SnIH) was accomplished to give α,β-disubstituted vinyltins, which induced the synthesis of multi-substituted alkenes in a one-pot procedure. The Royal Society of Chemistry.

Full text of DOI:10.1039/b712998j

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Regio- and stereoselective hydrostannation of allenes using
dibutyliodotin hydride (Bu2SnIH) and successive coupling with aromatic
halides{
Naoki Hayashi,a Kazunao Kusano,a Shingo Sekizawa,a Ikuya Shibata,*b Makoto Yasudaa and Akio Baba*a
Received (in Cambridge, UK) 23rd August 2007, Accepted 5th September 2007
First published as an Advance Article on the web 14th September 2007
DOI: 10.1039/b712998j
accepted that no methods are available for the regio- and
stereoselective addition of a tin moiety to the center carbon of
allenes to give 2. Here we wish to report the highly regio- and
stereoselective radical hydrostannation of allenes which was
accomplished by using di-n-butyliodotin hydride (Bu2SnIH)7 to
give a,b-disubstituted vinyltins 2. Furthermore, one-pot synthesis
of multi-substituted alkenes was established by coupling of the
resulting vinyltins without isolation.
Regio- and stereoselective hydrostannation of allenes by using
di-n-butyliodotin hydride (Bu2SnIH) was accomplished to give
a,b-disubstituted vinyltins, which induced the synthesis of multi-
substituted alkenes in a one-pot procedure.
Vinyltin compounds are very useful reagents whose tin moieties
can be transformed to various organic groups through the
Kosugi–Migita–Stille coupling.1 One of the most powerful
synthetic methods for synthesis of vinyltins is hydrostannation of
C–C triple bonds. Regioselective hydrostannation, however, is
generally limited to terminal alkynes, in which the stannation
occurred at the terminal carbon to give b-substituted vinyltins.2
Few methods are available for synthesis of internal tin substituted
adducts (a-substituted vinyltins), even when only monosubstituted
vinyltins are obtained.3 The effective synthesis of multi-substituted
vinyltins remains to be a challenge.
However, hydrostannation of allenes,4 with a regioselectivity
strongly dependent on the conditions employed, has rarely been
reported (Scheme 1). In the hydrostannation of n-octylallene (1a),
Pd-catalysis promotes the stannation of the terminal carbon to
give allyltin 4a9, and Lewis acid B(C6F5)3 selectively produces an
a-substituted terminal vinyltin 3a9.5 Only a radical reaction could
produce an a,b-disubstituted vinyltin 2a9, although a poor
selectivity of 2a9 was obtained.6 As illustrated in Scheme 1, it is
First, hydrostannation of monosubstituted allenes was exam-
ined by using Bu2SnIH generated in situ by the redistribution
between Bu2SnI2 and Bu2SnH2.8 The reaction of n-octylallene (1a)
took place without any promoters to give vinyltin 2a in 65% yield
(Table 1, entry 1). This reaction plausibly proceeds in a radical
manner because a radical scavenger, galvinoxyl, completely
suppressed the reaction (entry 2). In contrast to tributyltin hydride,
a predominant addition of a tin moiety to the allene center carbon
took place in all runs to produce the a,b-disubstituted vinyltins 2
along with a small amount of 3, and no formation of an allylic tin
Table 1 Hydrostannation of monosubstituted allenesa
Product
Entry
Allene (1)
t/h
2: Yield (%) (E : Z)
3: Yield (%)
1
14
14
2a: 65 (58 : 42)
Trace
3a: 14
Trace
2b
3
17
2b: 88 (58 : 42)
3b: 9
4
5
20
44
2c: 70 (93 : 7)
2d: 70 (90 : 10)
3c: 9
3d: 2
Scheme 1 Hydrostannation of allenes by Bu3SnH.
aDepartment of Applied Chemistry, Graduate School of Engineering,
Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan.
E-mail: baba@chem.eng.osaka-u.ac.jp; Fax: +81-6-6879-7387;
Tel: +81-6-6879-7386
6
7
33
21
2e: 59 (1 : .99)
2f: 57 (5 : 95)
3e: 13
bResearch Center for Environmental Preservation, Osaka University, 2-4
Yamadaoka, Suita, Osaka, 565-0871, Japan.
3f: 2
E-mail: shibata@epc.osaka-u.ac.jp; Fax: +81-6-6879-8978;
Tel: +81-6-6879-8974
{ Electronic supplementary information (ESI) available: Experimental
section and spectroscopic data. See DOI: 10.1039/b712998j
a
b
mmol. Galvinoxyl
THF
(0.1 mmol) was added.
1
mL, allene
1
mmol, Bu2SnIH
1
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4 was observed. In the reaction of 1a, using Bu2SnClH instead of
Bu2SnIH resulted in a mixture of 2 (65%), 3 (17%) and 4 (11%).
Although the hydrostannations of n- and sec-alkyl substituted
allenes 1a and 1b furnished E- and Z-isomers of vinyltins 2a and
2b in poor stereoselectivities (entries 1 and 3), the selectivity was
improved by introducing tertiary alkyl substituents to predomi-
nantly give E-alkenes (entries 4 and 5). It was surprising that the
tertiary substituents also depressed the formation of vinyltin 3, in
particular the dimethylphenylmethyl moiety was decreased to only
a 2% yield (entry 5). In contrast, allenes having oxygen substituents
provided vinyltins 2e and 2f with opposite Z-stereochemistry
(entries 6 and 7).
been feasible for use with halogenated organotin nucleophiles
because of the deactivating nature of the halogen. If completed,
however, this one-pot coupling would present a convenient
method for synthesis of multi-substituted alkenes. Kosugi’s group
recently achieved this type of coupling between chlorinated
aryltins and aryl halides.9 Fortunately, our group was able to
apply this catalysis on iodinated vinyltin 2 to produce various
multi-substituted alkenes as shown in Scheme 4. Regio- and
stereoselectivities of all products appeared to depend on the
hydrostannation step. Thus E- and Z-alkenes, 5c and 5f, were
obtained with high regio- and stereoselectivities (eqn (3) and (4)).{
Internal allene 1g gave trisubstituted alkene 5g in moderate yield
(eqn (5)). Tetrasubstituted alkenes, 5h–5j, were also obtained from
the reaction of allenes 1h, 1i, 1j (eqn (6)–(8)). It is worth noting that
alkenes bearing four different substituents, 5h and 5j, were
produced with high stereoselectivities derived from chelation
between the tin moiety and oxygen (eqn (6) and (8)). The
stereochemistry obtained in 5j suggests that the chelation is larger
from the hydroxy moiety than it is that from the methoxy moiety.
In summary, highly regio- and stereoselective hydrostannation
of allenes was accomplished by using dibutyliodotin hydride
(Bu2SnIH). This system could also be applied to a subsequent
coupling reaction to give multi-substituted alkenes in a one-pot
procedure.
Scheme 2 shows the hydrostannation of disubstituted allenes.
Cyclic vinyltin 2g was obtained in 90% yield as a sole product from
internal allene 1g (eqn. (1)). 1,1-Disubstituted allene 1h, having an
oxygen substituent, gave trisubstituted vinyltin 2h with perfect
Z-stereochemistry (eqn. (2)).
?
It has been reported that small amounts of the Bu2ISn radical is
generated through the redistribution between Bu2SnI2 and
Bu2SnH2, and so no radical initiator such as Et3B is required.8
As shown in Scheme 3, the generated tin radical is added to an
allene carbon center to form a stable allyl radical, then a bulky
Bu2SnIH reacts with the less-hindered terminal carbon to produce
?
the desired vinyltin 2, along with regeneration of the Bu2ISn
radical. However, the clear difference between having Bu3SnH and
having Bu2SnIH in the attack position of a tin radical is yet to be
explained. The E-stereoselectivity depends on steric repulsion
between an alkyl substituent and the tin moiety in the formation of
an allyl radical (Scheme 3, top). On the other hand, in the case of
allenes with oxygen substituents, coordination with the acidic
iodotin center helps form the Z-isomers, 2e and 2f (Scheme 3,
bottom). Thus, the iodine-substituted tin moiety plays a very
important role, having characteristics that are both sterically
hindering and electron-withdrawing.
In the next stage, our group attempted to achieve a subsequent
coupling reaction of the products 2 without isolation. The
conventional catalyst for Kosugi–Migita–Stille coupling has not
Scheme 2 Hydrostannation of disubstituted allenes. Reagents: THF
(1 mL), allene (1 mmol), Bu2SnIH (1 mmol).
Scheme 4 Hydrostannation and one-pot coupling reactions. Reagents:
THF (1 mL), allene (1 mmol), Bu2SnIH (1 mmol), PhI (1 mmol), Pd cat.
(0.01 mmol), TBAF (1 M solution in THF, 3.0 mmol). aEt3B (0.1 mmol)
was added at the hydrostannation step; PPh3 (0.04 mmol) was added at
b
the coupling step. Bu2SnIH (1.2 mmol) was used; Et3B (0.1 mmol) was
added at the hydrostannation step; PPh3 (0.04 mmol) was added at the
c
coupling step. PPh3 (0.07 mmol) was added at the coupling step. dPhI
(1.2 mmol) was used.
Scheme 3 Regio- and stereoselective hydrostannation.
4914 | Chem. Commun., 2007, 4913–4915
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2 Recent reviews: (a) A. Baba, I. Shibata and M. Yasuda, in Comprehensive
Organometallic Chemistry III, ed. R. H. Crabtree, D. Michael and
P. Mingos, Elsevier, Oxford, 2006, vol. 9, ch. 8, pp. 341–380; (b)
N. D. Smith, J. Mancuso and M. Lautens, Chem. Rev., 2000, 100, 3257;
(c) A. G. Davis, Organotin Chemistry, VCH, New York, 1997, pp. 37–42;
(d) M. Pereyre, J.-P. Quintard and A. Rahm, Tin in Organic Synthesis,
Butterworth, London, 1987.
This research has been supported by JSPS Research Fellowships
for Young Scientists, and by the Grant-in-Aid for Scientific
Research on Priority Areas (459 and 460) from Ministry of
Education, Culture, Sports, Science and Technology, Japan, and
by the Sumitomo Foundation.
3 We have reported the addition of Bu2SnIH-MgBr2 ate complex,
in which Bu2SnIH by itself gave no products: (a) I. Shibata,
T. Suwa, K. Ryu and A. Baba, J. Am. Chem. Soc., 2001, 123,
4101; Shirakawa has reported the hydrogenation of alkynyltins
and successive rearrangement: (b) E. Shirakawa, R. Morita,
T. Tsuchimoto and Y. Kawakami, J. Am. Chem. Soc., 2004, 126,
13614.
4 Preparation method of allenes: L. Brandsma and H. D. Verkruijsse,
Synthesis of Acetylenes, Allenes and Cumulenes, Elsevier, Amsterdam,
1981.
5 (a) V. Gevorgyan, J.-X. Liu and Y. Yamamoto, J. Org. Chem., 1997, 62,
2963; (b) M. Lautens, D. Ostrovsky and B. Tao, Tetrahedron Lett., 1997,
38, 6343.
6 The reaction employing Ph3SnH was reported to give 51% yield of
a,b-disubstituted vinyltin 2: Y. Ichinose, K. Oshima and K. Utimoto,
Bull. Chem. Soc. Jpn., 1988, 61, 2693.
Notes and references
{ Typical experimental procedure to synthesize multisubstituted alkenes: A
10 mL round-bottom flask was dried by flame under nitrogen atmosphere.
After THF (1.0 mL) was added, Bu2SnH2 (0.117 g, 0.5 mmol) and Bu2SnI2
(0.243 g, 0.5 mmol) were added to generate Bu2SnIH by the redistribution
reaction. To the mixture was added allene 1f (0.070 g, 1.0 mmol) and the
resulting mixture was stirred at rt for 12 h until the IR absorption of Sn–H
at 1855 cm21 disappeared. [In the case of applying initiator, 1 M Et3B
solution (0.1 mL) was added after the addition of allenes.] PhI (0.204 g,
1.0 mmol), Pd2(dba)3–CHCl3 (0.010 g, 1 mol%) and 1 M Bu4NF solution
in THF (3.0 mL) were added and the mixture was stirred at 65 uC for 24 h.
After the reaction, the resulting solution was filtrated using Celite. After
concentration of the filtrate, yield of product 5f was determined by 1H
NMR (81%). Further purification was performed by silica gel column
chromatography eluting with hexane–AcOEt = 95 : 5 followed by
distillation under reduced pressure (0.070 g, 48%).
7 We have studied the reactivity of Bu2SnIH: I. Shibata and A. Baba, Curr.
Org. Chem., 2002, 6, 665.
8 A. G. Davies, W. J. Kinart and D. K. Osei-Kissi, J. Organomet. Chem.,
1994, 474, C11.
9 K. Fugami, S. Ohnuma, M. Kameyama, T. Saotome and M. Kosugi,
Synlett, 1999, 63.
1 (a) R. F. Heck, in Palladium Reagents in Organic Synthesis, Academic,
New York, 1985; (b) J. K. Stille, Angew. Chem., Int. Ed. Engl., 1986, 25,
508.
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Chem. Commun., 2007, 4913–4915 | 4915