A catalyst-economic one-pot protocol for the synthesis and conversion of functionalized vinylstannanes

Article abstract of DOI:10.1002/ejoc.201201593

A wide range of functionalized compounds can easily be obtained by a Pd-catalyzed one-pot hydrostannylation/elimination/distannylation/radical allylation sequence. The Pd catalyst used can be involved in up to five different reaction steps. A wide range of functionalized compounds can easily be obtained by a Pd-catalyzed one-pot hydrostannylation/elimination/ distannylation/radical allylation sequence. In this highly catalyst-economic protocol, the Pd catalyst can be involved in up to 5 different reactions. Copyright

Full text of DOI:10.1002/ejoc.201201593

Job/Unit: O21593
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Date: 05-02-13 18:43:17
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FULL PAPER
DOI: 10.1002/ejoc.201201593
A Catalyst-Economic One-Pot Protocol for the Synthesis and Conversion of
Functionalized Vinylstannanes
Manuel R. Klos[a] and Uli Kazmaier*[a]
Dedicated to Professor G. Huttner on the occasion of his 75th birthday
Keywords: Allylation / Distannylations / Hydrostannylations / Tin / Palladium / Radicals
A wide range of functionalized compounds can easily be ob- catalyst used can be involved in up to five different reaction
tained by a Pd-catalyzed one-pot hydrostannylation/elimi-
nation/distannylation/radical allylation sequence. The Pd
steps.
strates can easily be obtained by regioselective hydro-
stannylations of the corresponding propargyl esters cata-
lyzed by Mo(CO)3(CNtBu)3 (MoBl3).[14] This protocol al-
lows the regioselective metallation of a wide range of
propargyl alcohol derivatives, including phenyl ethers
(Scheme 1).[15] If these stannylated allyl phenyl ethers are
treated with hexabutyldistannane in the presence of a Pd
catalyst, distannylated alkenes 1 are obtained by an elimi-
nation/addition mechanism.[16]
Introduction
Organotin compounds are reasonably stable organome-
tallic reagents (the C–Sn bond-dissociation energy is ap-
proximately 50 kJ/mol) that have found widespread applica-
tion in organic synthesis.[1] Vinyl- and arylstannanes are
popular substrates for Pd-catalyzed cross-coupling reac-
tions (Stille couplings),[2] and allylstannanes can be used in
allylation reactions. These can be carried out under Lewis
acid catalysis,[3] under thermal[4] or radical conditions.[5]
Therefore, distannylated alkenes such as 1,[6] containing
both a vinyl- and an allylstannane unit, should be ideal sub-
strates for combinatorial synthesis, combining either carb-
onyl additions[7] or radical allylations[8] with subsequent
Stille couplings (Figure 1).
Figure 1. Distannylated alkene 1.
Our group is also involved in the synthesis of function-
alized vinylstannanes, investigating their synthetic poten-
tial.[9] Besides stannylated allyl sulfones[10] and phos-
phates,[11] allyl acetates and carbonates have been found to
be especially valuable synthetic building blocks.[12] The allyl
acetate or carbonate moiety allows allylic substitutions, and
subsequently, Stille couplings can be carried out on the vin-
ylstannane subunit.[13] The required stannylated allylic sub-
Scheme 1. Syntheses of distannane 1.
Although stannylated allyl phenyl ethers are stable in the
absence of Pd0, in its presence, elimination of Bu3SnOPh
is observed, resulting in an alkene–Pd complex (which can
eliminate allene), which undergoes Pd-catalyzed distannane
addition. Bearing in mind that hexabutyldistannane is
formed by a Pd-catalyzed decomposition of Bu3SnH, and
that Pd0 also catalyzes the hydrostannylation of alkynes, 1
can also be obtained directly from phenyl propargyl ether.
Although the yield is lower than in the Mo-catalyzed pro-
cess (because of the lower regioselectivity in the hydrostan-
nylation step),[17] this protocol is the more convenient one.
The only disadvantage results from the difficulties in the
separation of 1 from the (Bu3Sn)2 formed.
[a] Institute for Organic Chemistry, Saarland University
P. O. Box 151150, 66041 Saarbrücken, Germany
Fax: +49-681-302-2409
E-mail: u.kazmaier@mx.uni-saarland.de
Homepage:
er.html
http://www.uni-saarland.de/lehrstuhl/kazmai-
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201593
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M. R. Klos, U. Kazmaier
FULL PAPER
On the other hand, (Bu3Sn)2 is an excellent initiator for Table 2. Allylation of several halogenated compounds with di-
stannane 1.
radical reactions, since the Sn–Sn bond can easily be
cleaved thermally or under irradiation.[18] Therefore, we
were interested to see whether the preparation of 1 could
be combined with a subsequent radical substitution.
Results and Discussion
As a model experiment, we investigated the reaction of
bromomalonate with crude 1, containing around 50%
(Bu3Sn)2. Bromomalonate generates a well-stabilized elec-
trophilic radical that should react nicely with the electron-
rich distannane. In initial experiments, we investigated sev-
eral sets of reaction conditions to find the best conditions
for the allylation (Table 1). With a slight excess of the di-
stannane, high yields could be obtained under all condi-
[19]
tions. The very mild protocol using BEt3/O2
as well as
the photochemical reaction provided the expected product
in around 80% yield (Table 1, Entries 1 and 2). Under ther-
mal conditions, more than 90% yield could be obtained
(Table 1, Entry 3), even after 5 min.[20] In this case, the
(Bu3Sn)2 acts as a radical initiator, and so the addition of
AIBN had no further positive effect (Table 1, Entry 4).
protocol. The hydrostannylation/elimination/distannylation
sequence proceeds under completely neutral conditions, as
does the radical allylation. Therefore, a one-pot process
should be possible. Bearing in mind that the Pd-catalyzed
hydrostannylation proceeds with lower regioselectivity than
the Mo version, 2 equiv. of alkyne (relative to the halide)
were used. If Bu3SnH was used as the single tin source, at
least 3 equiv. (relative to the alkyne) were necessary. Be-
cause the “wrong isomer” of the hydrostannylation cannot
undergo elimination to form the allene, the unconsumed
(Bu3Sn)2 can act as radical initiator. The results obtained
in this one-pot process are summarized in Table 3 and are
comparable to those obtained in the single-step process
Table 1. Allylation of diethyl bromomalonate with distannane 1.
Entry
Reaction conditions
Yield [%]
1
2
3
4
BEt3 (0.5 equiv.)/O2, THF, 0 °C, 5 min
PhH, hν, 15 min
PhH, 80 °C, 5 min
PhH, AIBN (20 mol-%), 80 °C, 5 min
76[a]
83[a]
93[b]
88[b]
[a] 1.5 equiv. 1. [b] 1.2 equiv. 1.
To prove the generality of this protocol and to evaluate (Table 3, Entries 1–5). Interestingly, the o-brominated phen-
the range of radical precursors that could be used, we sub- acyl bromide gave a significantly lower yield than did the
jected a series of other halogenated compounds to these non-ring-brominated ketone (Table 3, Entries 4 and 6).
reaction conditions. In general, the reactions were stopped Probably this is the result of competing aryl radical reac-
after the halogenated compound was consumed (as deter- tions caused by an unselective Br abstraction by the tin rad-
mined by TLC). The results are summarized in Table 2, and ical. Another reason might be that the product formed (i.e.
the conditions that gave the best results are shown in each 2g) undergoes further reactions.[21] In addition, we observed
case. Besides bromomalonate, α-brominated esters, lac- that under the one-pot conditions, less electrophilic radicals
tones, and ketones (Table 2, Entries 1–3) also gave good re- react more slowly and give lower product yields, but in prin-
sults. In principle, other halides can also be used, but the ciple they can be used as well (Table 3, Entries 9 and 10).
yields obtained with chlorides are significantly worse than
those with bromides or iodides (Table 2, Entries 4 and 5).
Not only the functionalities arising from the halogenated
compound are suitable candidates for further modifications,
Stabilization of the in situ formed radical by an electron- but also those from the vinyltin unit. For example, the one-
withdrawing carbonyl group has a positive effect on the re- pot reaction can be combined with a tin/iodine exchange
action, while simple alkyl bromides or α-brominated acetals resulting in an umpolung of the allyl chain and the forma-
gave lower yields (Table 2, Entry 6). With such a substrate, tion of an electrophilic vinyl iodide (3) (Scheme 2). Because
the best result was obtained by the BEt3-method; under ir- the allylation reaction proceeds quickly and under mild
radiation conditions only 20% yield was obtained.
conditions, the Pd catalyst is unaffected during the radical
Encouraged by the good results obtained with the elec- reaction and retains its reactivity. Therefore, it should be
trophilic radicals, next we tried to combine the generation possible to add a final Stille coupling to the one-pot se-
of the distannanes with the radical substitution to a one-pot quence.
2
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Functionalized Vinylstannanes
Table 3. Syntheses of vinylstannanes by a one-pot hydrostan-
nylation/elimination/distannylation/radical allylation sequence.
A yield of 42% is not overwhelming at first sight, but
one should keep in mind how many steps are involved, and
how many functions were taken on by the Pd catalyst,
which was used only in small amounts (1 mol-%). The
whole scenario described for the last example is summa-
rized in Scheme 3. The first step is a Pd-catalyzed hydro-
stannylation of phenyl propargyl ether giving rise to the in-
ternally stannylated allyl ether with moderate regioselecti-
vity (ca. 65%).[16] Under the influence of the Pd catalyst,
this stannylated ether undergoes elimination of PhOSnBu3
to give the allene.[12c] After the elimination, the allene, at
least for some time, remains coordinated to Pd, otherwise
it would evaporate under the reaction conditions (60 °C).
In parallel, the Pd complex catalyzes the decomposition of
Bu3SnH to (Bu3Sn)2, which is added to the allene, also un-
der the influence of Pd0. In addition, the (Bu3Sn)2 also initi-
ates the addition of the phenacyl bromide to the distannane,
which is followed by the Pd-catalyzed Stille coupling.
When the allylation reaction mixture with o-bromophen-
acyl bromide was subsequently heated to 90 °C overnight,
cyclized ketone 4 was formed. The yield obtained was al-
most the same as for stannylated ketone 2g (Table 3, En-
try 6), indicating that the intramolecular Stille reaction
must proceed in almost quantitative yield. Interestingly, no
isomerization of the exocyclic double bond was observed,
even though the product of such an isomerization would be
a naphthol derivative.
Scheme 3. Proposed mechanism of the one-pot reaction leading to
4.
Conclusions
We were able to develop a straightforward one-pot pro-
cess for the conversion of phenyl propargyl ether into a
Scheme 2. Expanded one-pot reactions.
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M. R. Klos, U. Kazmaier
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119Sn NMR: δ = –42.9 ppm. HRMS (CI): calcd. for C18H33O4Sn
wide range of functionalized vinylstannanes, which can be
modified even further. This process is characterized by a
high catalyst economy, because the Pd catalyst used can
catalyze up to five different processes. The Bu3SnH used is
also involved in several steps of the sequence. Applications
of this new protocol to the synthesis of more complex struc-
[M – C4H9]+ 433.1401; found 433.1432.
3-[2-(Tributylstannyl)allyl]dihydrofuran-2(3H)-one (2b): According
to GP1 by starting from α-bromo-γ-butyrolactone (84.2 mg,
0.50 mmol) and 1 (675 mg, 55%, 0.60 mmol, containing 45% hexa-
butyldistannane) in toluene, after workup and purification (silica,
tures such as natural products are currently under investiga- hexanes/ethyl acetate, 97:3 + 2% NEt3) of the brown, liquid crude
material, compound 2b (160 mg, 0.39 mmol, 78%) was obtained as
a colorless oil. 1H NMR: δ = 0.90 (t, J = 7.3 Hz, 9 H), 0.92 (m,
JC,Sn = 50.3 Hz, 6 H), 1.32 (m, 6 H), 1.54 (m, 6 H), 1.90 (m, 1 H),
2.25 (dd, J = 14.6, 11.2 Hz, 1 H), 2.31 (m, 1 H), 2.61 (m, 1 H),
2.94 (dddd, J = 14.6, 3.4, 1.6, 1.6, JC,Sn = 37.6 Hz, 1 H), 4.21 (m,
1 H), 4.33 (m, 1 H), 5.23 (m, JC,Sn = 60.5 Hz, 1 H), 5.72 (m, JC,Sn
tion.
Experimental Section
General Remarks: All air- and moisture-sensitive reactions were
carried out in dried glassware under argon. All radical reactions
were carried out in degassed solvents (argon). In photochemical
reactions, a 300 W lamp with a Pyrex filter served as light source.
The products were purified by flash chromatography on silica gel
columns (0.063–0.2 mm). Mixtures of hexanes and ethyl acetate
were generally used as eluents. 1H, 13C, and 119Sn NMR spectra
were recorded in CDCl3 (1H: 400 MHz; 13C: 100 MHz; 119Sn:
149 MHz). Chemical shifts are reported in ppm (δ) relative to
Me4Si by using CHCl3 as internal standard. Calibration of 119Sn
experiments was done numerically with respect to a standard refer-
ence value. Mass spectra were recorded with a quadrupole spec-
trometer by using the CI technique.
= 131 Hz, 1 H) ppm. 13C NMR: δ = 9.6, 13.7, 27.3 (JC,Sn
=
56.4 Hz), 28.5, 29.1, 38.8, 41.8, 66.5, 126.9, 151.8, 179.1 ppm. 119Sn
NMR: δ = –43.1 ppm. HRMS (CI): calcd. for C19H37O2Sn [M +
H]+ 417.1813; found 417.1811.
Benzyl 4-(Tributylstannyl)pent-4-enoate (2c): According to GP1,
benzyl bromoacetate (122 mg, 0.51 mmol) and 1 (661 mg, 55%,
0.59 mmol, 55:45 mixture with hexabutyldistannane) reacted in
toluene. After workup and purification (silica, hexanes/ethyl acet-
ate, 99:1 + 2% NEt3) of the brown, liquid crude material, com-
pound 2c (198 mg, 0.41 mmol, 81%) was isolated as a colorless oil.
1H NMR: δ = 0.88 (t, J = 7.3 Hz, 9 H), 0.90 (m, JC,Sn = 50.5 Hz,
6 H), 1.31 (m, 6 H), 1.54 (m, 6 H), 2.46 (m, 2 H), 2.58 (m, JC,Sn
=
General Procedure for the Photochemical Allylation with Distannane
(GP1): A solution of halide (1.0 equiv.) and allyl stannane (1.2 or
1.5 equiv., ca. 50:50 mixture with hexabutyldistannane) in dry, de-
gassed benzene or toluene (0.5 m) was irradiated until no more con-
sumption of the starting material was observed (TLC). During irra-
diation, the internal temperature rose to 60 °C. After cooling to
room temperature, the solvent was evaporated under reduced pres-
sure, and the residue was purified by flash chromatography.
39.1 Hz, 2 H), 5.12 (s, 2 H), 5.15 (dt, J = 2.3, 1.2, JC,Sn = 62.5 Hz,
1 H), 5.69 (m, JC,Sn = 135 Hz, 1 H), 7.29–7.40 (m, 5 H) ppm. 13C
NMR: δ = 9.5 (JC,Sn = 333 Hz), 13.7, 27.4 (JC,Sn = 57.0 Hz), 29.1
(JC,Sn = 20.1 Hz), 34.0, 35.6, 66.2, 125.4, 128.2 (2 C), 128.5, 136.0,
153.0, 173.0 ppm. 119Sn NMR: δ = –43.9 ppm. HRMS (CI): calcd.
for C20H32O2Sn [M – C4H9 + H]+ 424.1424; found 424.1422.
1-Phenyl-4-(tributylstannyl)pent-4-en-1-one (2d): According to GP2,
phenyl propargyl ether (139 mg, 1.03 mmol) was distannylated by
using tetrakis(triphenylphosphane)palladium (11.5 mg, 9.95 μmol)
and tributyltin hydride (939 mg, 3.23 mmol) and treated in the sec-
ond step with 2-bromoacetophenone (102 mg, 0.50 mmol). Workup
and purification (silica, hexanes/ethyl acetate, 99:1 + 2% NEt3) of
the yellow, liquid crude product delivered compound 2d (181 mg,
0.40 mmol, 81%) as a colorless oil. 1H NMR: δ = 0.88 (t, J =
7.3 Hz, 9 H), 0.92 (m, JC,Sn = 50.2 Hz, 6 H), 1.32 (m, 6 H), 1.54
(m, 6 H), 2.67 (m, JC,Sn = 40.0 Hz, 2 H), 3.07 (m, 2 H), 5.18 (dt,
J = 2.4, 1.2, JC,Sn = 62.7 Hz, 1 H), 5.75 (m, JC,Sn = 136 Hz, 1 H),
7.47 (m, 2 H), 7.56 (m, 1 H), 7.97 (m, 2 H) ppm. 13C NMR: δ =
9.6, 13.7, 27.4 (JC,Sn = 54.0 Hz), 29.1 (JC,Sn = 19.8 Hz), 35.0, 38.2,
125.2, 128.0, 128.6, 133.0, 137.0, 153.7, 199.7 ppm. 119Sn NMR: δ
= –43.6 ppm. C23H38OSn (449.26): calcd. C 61.49, H 8.53; found
C 61.64, H 8.31. HRMS (CI): calcd. for C19H29OSn [M – C4H9]+
393.1241; found 393.1238.
General Procedure for the One-Pot Hydrostannylation/Elimination/
Distannylation/Radical Allylation Sequence (GP2): Tributyltin hy-
dride (3.2 equiv.) was slowly added to a solution of phenyl prop-
argyl ether (1.0 equiv.) and tetrakis(triphenylphosphane)palla-
dium(0) (1 mol-%) in dry, degassed toluene (0.75 m) at 0 °C. The
color of the yellow solution changed to brown, and an efferves-
cence of hydrogen gas was observed. After the tin hydride addition,
the reaction mixture was stirred at 60 °C for 16 h. After completion
of the distannylation (TLC), the corresponding halide was added,
and the mixture was irradiated and stirred at 60 °C until no more
consumption of the radical precursor was observed (TLC). After
cooling to room temperature, the solvent was evaporated under
reduced pressure, and the residue was purified by flash chromatog-
raphy.
Diethyl 2-[2-(Tributylstannyl)allyl]malonate (2a):[12c] Diethyl 2-
bromomalonate (131 mg, 90%, 0.49 mmol) and 1[16] (956 mg, 55%,
0.78 mmol, containing 45% hexabutyldistannane) were dissolved in
dry, degassed benzene (1 mL), and the reaction mixture was stirred
at 80 °C for 5 min. After completion of the allylation, the solvent
was evaporated under reduced pressure at room temperature, and
the brown, liquid residue was purified by flash chromatography
(silica, hexanes/ethyl acetate, 98:2 + 2% NEt3). Compound 2a
(225 mg, 0.46 mmol, 93%) was isolated as a colorless oil. 1H NMR:
δ = 0.89 (t, J = 7.3 Hz, 9 H), 0.93 (m, JC,Sn = 50.6 Hz, 6 H), 1.26
N,N-Diethyl-4-(tributylstannyl)pent-4-enamide (2e): According to
GP1 1,2-iodo-N,N-diethylacetamide (115 mg, 0.46 mmol) and 1
(639 mg, 58%, 0.60 mmol, 58:42 mixture with hexabutyldistann-
ane) reacted in toluene. After workup and purification (silica, hex-
ane/ethyl acetate, 95:5 + 2% NEt3) of the brown, semisolid crude
material, compound 2e (144 mg, 0.32 mmol, 71%) was isolated as
1
a pale yellow oil. H NMR: δ = 0.88 (t, J = 7.3 Hz, 9 H), 0.91 (m,
JC,Sn = 50.2 Hz, 6 H), 1.11 (t, J = 7.1 Hz, 3 H), 1.17 (t, J = 7.1 Hz,
(t, J = 7.1 Hz, 6 H), 1.31 (m, 6 H), 1.54 (m, 6 H), 2.82 (dt, J = 7.6, 3 H), 1.31 (m, 6 H), 1.53 (m, 6 H), 2.37 (m, 2 H), 2.57 (m, JC,Sn
=
1.2, JC,Sn = 39.1 Hz, 2 H), 3.48 (t, J = 7.6 Hz, 1 H), 4.18 (q, J = 40.7 Hz, 2 H), 3.30 (q, J = 7.2 Hz, 2 H), 3.38 (q, J = 7.1 Hz, 2 H),
7.1 Hz, 4 H), 5.18 (dt, J = 2.1, 1.1, JC,Sn = 61.2 Hz, 1 H), 5.71 (m, 5.15 (dt, J = 2.3, 1.1, JC,Sn = 63.2 Hz, 1 H), 5.72 (dt, J = 2.5, 1.6,
JC,Sn = 132 Hz, 1 H) ppm. 13C NMR: δ = 9.6 (JC,Sn = 334 Hz),
13.7, 14.1, 27.4, 29.0, 39.3, 51.6, 61.3, 127.0, 150.6, 169.1 ppm.
JC,Sn = 137 Hz, 1 H) ppm. 13C NMR: δ = 9.5, 13.1, 13.7, 14.4,
27.4, 29.1 (3J6,Sn = 19.8 Hz), 33.0, 36.2, 40.1, 41.9, 124.9, 154.2,
4
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Functionalized Vinylstannanes
171.6 ppm. 119Sn NMR: δ = –44.0 ppm. HRMS (CI): calcd. for
(m, 6 H), 0.86 (t, J = 7.3 Hz, 9 H), 1.27 (m, 6 H), 1.42 (m, 6 H),
2.59 (m, JC,Sn = 35.6 Hz, 2 H), 3.14 (m, 2 H), 5.16 (dt, J = 1.8,
1.2, JC,Sn = 59.5 Hz, 1 H), 5.64 (dt, J = 1.8, 1.6, JC,Sn = 128 Hz, 1
H), 7.58 (m, 2 H), 7.67 (t, J = 7.4 Hz, 1 H), 7.92 (m, 2 H) ppm.
13C NMR: δ = 9.5 (JC,Sn = 328 Hz), 13.6, 27.3 (JC,Sn = 56.5 Hz),
29.0 (JC,Sn = 20.0 Hz), 33.1, 55.7, 126.6, 128.1, 129.3, 133.7, 139.0,
150.2 ppm. 119Sn NMR: δ = –41.3 ppm. C22H38O2SSn (485.32):
calcd. C 54.45, H 7.89; found C 54.48, H 7.51. HRMS (CI): calcd.
for C22H39O2SSn [M + H]+ 487.1690; found 487.1689.
C17H34NOSn [M – C4H9]+ 388.1663; found 388.1668.
Tributyl-(5,5-dimethoxypent-1-en-2-yl)stannane (2f): Triethylborane
(0.25 mL, 1 m in THF, 0.25 mmol) was added to a solution 2-
bromo-1,1-dimethoxyethane (88.4 mg, 0.51 mmol) and 1 (643 mg,
58%, 0.60 mmol, 58:42 mixture with hexabutyldistannane) in dry,
degassed THF (0.5 m), at 0 °C. Air (5 mL) was discharged into the
solution by cannula. The reaction mixture was stirred at 0 °C for
5 min and warmed to room temperature to complete the reaction
(TLC). The solvent was evaporated under reduced pressure at room
temperature, and the residue was purified by flash chromatography
(silica, hexanes/ethyl acetate, 98:2 + 2% NEt3), giving rise to 2f
Ethyl 4-[3-(Tributylstannyl)but-3-enyl]benzoate (2k): According to
GP2, phenyl propargyl ether (134 mg, 1.00 mmol) was treated with
tetrakis(triphenylphosphane)palladium (11.6 mg, 10.0 μmol) and
tributyltin hydride (940 mg, 3.23 mmol) and treated in the second
step with ethyl 4-(bromomethyl)benzoate (128 mg, 0.51 mmol).
Workup and purification (silica, petroleum ether/ethyl acetate, 99:1
+ 2% NEt3) of the yellow, liquid crude material delivered benzoate
1
(66 mg, 0.16 mmol, 31%) as colorless oil. H NMR: δ = 0.89 (t, J
= 7.3 Hz, 9 H), 0.91 (m, JC,Sn = 50.0 Hz, 6 H), 1.32 (m, 6 H), 1.49
(m, 6 H), 1.69 (m, 2 H), 2.29 (m, JC,Sn = 43.9 Hz, 2 H), 3.32 (s, 6
H), 4.36 (t, J = 5.7 Hz, 1 H), 5.13 (dt, J = 2.4, 1.0, JC,Sn = 63.1 Hz,
1 H), 5.70 (m, JC,Sn = 138 Hz, 1 H) ppm. 13C NMR: δ = 9.6 (JC,Sn
= 331 Hz), 13.7, 27.4 (JC,Sn = 56.9 Hz), 29.1 (JC,Sn = 19.7 Hz), 32.2,
35.9, 52.7, 104.1, 125.1, 154.4 ppm. 119Sn NMR: δ = –45.0 ppm.
C19H40O2Sn (419.24): calcd. C 54.43, H 9.62; found C 54.39, H
9.60. LRMS (CI): calcd. for C15H31Sn [M – C4H9O2]+ 331.1; found
331.1.
1
2k (92 mg, 0.19 mmol, 37%) as a colorless oil. H NMR: δ = 0.90
(t, J = 7.3 Hz, 9 H), 0.91 (m, 6 H), 1.33 (m, 6 H), 1.39 (t, J =
7.1 Hz, 3 H), 1.55 (m, 6 H), 2.54 (m, JC,Sn = 42.0 Hz, 2 H), 2.75
(m, 2 H), 4.37 (q, J = 7.1 Hz, 2 H), 5.17 (dt, J = 2.1, 0.9, JC,Sn
=
63.0 Hz, 1 H), 5.71 (dt, J = 2.6, 1.5, JC,Sn = 137 Hz, 1 H), 7.24 (d,
J = 8.4 Hz, 2 H), 7.96 (d, J = 8.4 Hz) ppm. 13C NMR: δ = 9.6,
13.7, 14.4, 27.4, 29.1 (JC,Sn = 19.7 Hz), 36.1, 42.6, 60.8, 125.5,
126.6, 128.4, 129.6, 147.6, 154.2, 166.7 ppm. 119Sn NMR: δ =
–44.8 ppm. C25H42O2Sn (493.32): calcd. C 60.87, H 8.58; found C
61.20, H 8.45. HRMS (CI): calcd. for C21H33O2Sn [M – C4H9]+
437.1503; found 437.1493.
1-(2-Bromophenyl)-4-(tributylstannyl)pent-4-en-1-one (2g): Accord-
ing to GP2, phenyl propargyl ether (132 mg, 0.99 mmol) was di-
metallated by using tetrakis(triphenylphosphane)palladium(0)
(11.4 mg, 9.86 μmol) and tributyltin hydride (921 mg, 3.16 mmol)
and treated in the second step with 2,2Ј-dibromoacetophenone
(161 mg, 85%, 0.49 mmol). Workup and purification (silica, hex-
anes/ethyl acetate, 99:1 + 2% NEt3) of the yellow-brown, liquid
crude product delivered stannane 2g (111 mg, 0.21 mmol, 43%) as
Ethyl 6-(Tributylstannyl)hept-6-enoate (2l): According to GP2,
phenyl propargyl ether (140 mg, 1.05 mmol) was dimetallated by
using tetrakis(triphenylphosphane)palladium (11.5 mg, 9.95 μmol)
and tributyltin hydride (942 mg, 3.24 mmol) and treated in the sec-
ond step with ethyl 4-bromobutyrate (101 mg, 0.51 mmol). Workup
and purification (silica, petroleum ether/ethyl acetate, 99:1 + 2%
NEt3) of the yellow, liquid crude product provided compound 2l
(68.0 mg, 0.15 mmol, 29%) as a colorless oil. 1H NMR: δ = 0.89
(t, J = 7.3 Hz, 9 H), 0.89 (m, JC,Sn = 49.7 Hz, 6 H), 1.26 (t, J =
7.2 Hz, 3 H), 1.30 (m, 6 H), 1.36–1.60 (m, 8 H, 4-H), 1.62 (m, 2
H), 2.25 (m, 2 H), 2.30 (m, 2 H), 4.13 (q, J = 7.2 Hz, 2 H), 5.11
(dt, J = 2.5, 0.9, JC,Sn = 63.7 Hz, 1 H), 5.67 (dt, J = 2.8, 1.5, JC,Sn
= 140 Hz, 1 H) ppm. 13C NMR: δ = 9.6, 13.7, 14.3, 24.6, 29.0,
27.4, 29.1, 34.2, 40.8, 60.2, 125.0, 155.0, 173.7 ppm. 119Sn NMR: δ
= –45.7 ppm. C21H42O2Sn (445.28): calcd. C 56.65, H 9.51; found
C 56.48, H 9.82. HRMS (CI): calcd. for C17H33O2Sn [M – C4H9]+
389.1503; found 389.1511.
1
a pale yellow oil. H NMR: δ = 0.88 (t, J = 7.3 Hz, 9 H), 0.90 (m,
6 H), 1.30 (m, 6 H), 1.54 (m, 6 H), 2.64 (m, JC,Sn = 38.5 Hz, 2 H),
3.02 (m, 2 H), 5.17 (dt, J = 2.3, 1.2, JC,Sn = 62.5 Hz, 1 H), 5.72
(m, J = 135 Hz, 1 H), 7.29 (m, 1 H), 7.34–7.38 (m, 2 H), 7.60 (m,
1 H) ppm. 13C NMR: δ = 9.5, 13.7, 27.4 (JC,Sn = 57.1 Hz), 29.1
(JC,Sn = 24.9 Hz), 34.9, 42.4, 118.6, 125.4, 127.4, 128.5, 131.4,
133.6, 142.0, 153.2, 203.9 ppm. 119Sn NMR: δ = –43.8 ppm.
HRMS (CI): calcd. for C19H28BrOSn [M – C4H9]+ 471.0346; found
471.0339.
4-(Tributylstannyl)pent-4-enenitrile (2h): According to GP2, phenyl
propargyl ether (141 mg, 1.05 mmol) was treated with tetrakis(tri-
phenylphosphane)palladium(0) (11.6 mg, 10.0 μmol) and tributyl-
tin hydride (936 mg, 3.22 mmol) and in the second step with
bromoacetonitrile (61.0 mg, 0.49 mmol). Workup and purification
(silica, petroleum ether/ethyl acetate, 98:2 + 2% NEt3) of the yel-
low, liquid crude material provided compound 2h (163 mg,
0.44 mmol, 89%) as a colorless oil. 1H NMR: δ = 0.90 (t, J =
7.3 Hz, 9 H), 0.93 (m, 6 H), 1.32 (m, 6 H), 1.49 (m, 6 H), 2.42 (m,
Diethyl 2-(2-Iodoallyl)malonate (3): According to GP2, phenyl
propargyl ether (140 mg, 1.05 mmol) was treated with tetrakis(tri-
phenylphosphane)palladium(0) (12.1 mg, 10.5 μmol) and tributyl-
tin hydride (937 mg, 3.22 mmol) and in the second step with diethyl
2-bromomalonate (133 mg, 90%, 0.50 mmol). As a third step,
iodine (773 mg, 3.05 mmol) was added at 0 °C, and the reaction
mixture was warmed to ambient temperature within 3.5 h.[14b] Af-
ter iododestannylation was complete, the excess iodine was reduced
by using concd. Na2S2O3 solution. The aqueous phase was ex-
tracted twice with Et2O, and the combined organic extracts were
dried with Na2SO4. The solvent was removed in vacuo, and the
yellow residue was purified by flash chromatography (silica, hex-
2 H), 2.57 (m, JC,Sn = 35.6 Hz, 2 H), 5.29 (dt, J = 1.7, 1.2, JC,Sn
=
C
60.0 Hz, 1 H), 5.77 (dt, J = 1.7, 1.6, JC,Sn = 128 Hz, 1 H) ppm. 13
NMR: δ = 9.6 (JC,Sn = 336 Hz), 13.6, 16.9, 27.3 (JC,Sn = 56.5 Hz),
29.0 (JC,Sn = 20.4 Hz), 35.8, 119.4, 127.0, 150.7 ppm. 119Sn NMR:
δ = –42.3 ppm. HRMS (CI): calcd. for C13H22NSn [M – C4H9
–
2H]+ 312.0774; found 312.0801.
Tributyl[4-(phenylsulfonyl)but-1-en-2-yl]stannane (2i): According to
GP2, phenyl propargyl ether (128 mg, 0.95 mmol) was distannyl-
ated by using tetrakis(triphenylphosphane)palladium (12.5 mg,
10.8 μmol) and tributyltin hydride (940 mg, 3.23 mmol) and treated
in the second step with bromomethyl phenyl sulfone (121 mg,
0.50 mmol). Workup and purification (silica, hexanes/ethyl acetate,
97:3 + 2% NEt3) of the yellow crude liquid yielded sulfone 2i
(138 mg, 0.28 mmol, 56%) as a colorless oil. 1H NMR: δ = 0.85
anes/ethyl acetate, 100:0 to 95:5). Vinyl iodide
3 (130 mg,
0.40 mmol, 80%) was obtained as a yellowish brown oil. 1H NMR:
δ = 1.27 (t, J = 7.1 Hz, 6 H), 2.98 (d, J = 7.5 Hz, 2 H), 3.73 (t, J
= 7.5 Hz, 1 H), 4.21 (q, J = 7.3 Hz, 4 H), 5.77 (d, J = 1.6 Hz, 1
H), 6.13 (d, J = 1.5 Hz, 1 H) ppm. 13C NMR: δ = 14.1, 44.2, 51.6,
61.7, 105.7, 128.7, 168.0 ppm. HRMS (CI): calcd. for C10H16IO4
[M + H]+ 327.0093; found 327.0068.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Job/Unit: O21593
/KAP1
Date: 05-02-13 18:43:17
Pages: 7
M. R. Klos, U. Kazmaier
FULL PAPER
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10.4 μmol) and tributyltin hydride (938 mg, 3.22 mmol), and was
treated in the second step with 2,2Ј-dibromoacetophenone (153 mg,
90%, 0.50 mmol). Subsequently, the reaction mixture was heated
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1
yield 4 (34.0 mg, 0.21 mmol, 42%) as a pale yellow oil. H NMR:
δ = 2.77 (m, 2 H), 2.86 (m, 2 H), 5.27 (br. d, J = 0.7 Hz, 1 H), 5.59
(br. s, 1 H), 7.40 (dd, J = 7.5, 7.5 Hz, 1 H), 7.54 (ddd, J = 7.6, 7.6,
1.4 Hz, 1 H), 7.65 (d, J = 7.9 Hz, 1 H), 8.04 (dd, J = 7.9, 1.3 Hz,
1 H) ppm. 13C NMR: δ = 32.4, 39.3, 111.6, 124.7, 127.1, 128.4,
131.2, 133.7, 140.9, 141.7, 197.8 ppm. HRMS (CI): calcd. for
C11H10O [M]+ 158.0732; found 158.0725.
[9] a) S. Braune, M. Pohlman, U. Kazmaier, J. Org. Chem. 2004,
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Supporting Information (see footnote on the first page of this arti-
cle): Copies of NMR spectra of all new compounds.
Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft is
gratefully acknowledged.
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[20] In principle, such stannylated allyl malonates can also be ob-
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alkylations, albeit in significant lower yields (see ref.[12c]). An
alternative approach is based on the Pd-catalyzed hydrostann-
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[21] To test this possibility, we irradiated 2g in the presence of Pd0
and (Bu3Sn)2. After up to 6 h, mainly starting material was
recovered (55%), but no definite by-product was formed.
Received: November 26, 2012
Published Online: ᭿
6
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O21593
/KAP1
Date: 05-02-13 18:43:17
Pages: 7
Functionalized Vinylstannanes
One-Pot Reaction
A wide range of functionalized compounds
can easily be obtained by a Pd-catalyzed
one-pot hydrostannylation/elimination/dis-
tannylation/radical allylation sequence. In
this highly catalyst-economic protocol, the
Pd catalyst can be involved in up to 5 dif-
ferent reactions.
M. R. Klos, U. Kazmaier* ................. 1–7
A Catalyst-Economic One-Pot Protocol for
the Synthesis and Conversion of Func-
tionalized Vinylstannanes
Keywords: Allylation / Distannylations /
Hydrostannylations / Tin / Palladium /
Radicals
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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