Full Paper
[
21]
stituted with a monocarboxylate ester. Thus, 1,1-dicarboxy-
late ester substituents were not always necessary for stabiliza-
tion of the radical generated after ring cleavage. Not only aro-
matic aldehydes but also aliphatic aldehydes underwent effec-
tive coupling to give the corresponding homoallylic alcohols
and 1d, which have rarely been used in conventional transi-
tion-metal and Lewis acid catalyzed reactions, were also suita-
ble for this protocol.
3
k–n (entries 1–4).
Experimental Section
Besides carboxylate ester groups, substituents with less elec-
Generation of allyltin by hydrostannation of vinylcyclopro-
panes
tron-withdrawing features such as acetoxymethylene groups
were tolerated on the ring of VCP 1d (Table 4), although the
reactions required a higher temperature of 408C. In addition to
A 10 mL round-bottom flask was dried by using a heat gun under
a nitrogen atmosphere. After filling with nitrogen, Bu SnI (0.243 g,
2
2
0
.5 mmol) was added to a solution of Bu SnH (0.117 g, 0.5 mmol)
2 2
in THF (1.0 mL) to generate Bu SnIH by the redistribution reaction.
Vinylcyclopropane 1a (0.212 g, 1.0 mmol) was added and the re-
[
a]
2
Table 4. Coupling of VCP 1d with aldehydes.
sulting mixture was stirred at 258C for 48 h when IR absorption of
À1
SnÀH at 1855 cm disappeared. CHCl (5 mL) was added to com-
3
pletely decompose the remaining tin hydride, and volatiles were
removed under reduced pressure. The residue was subjected to
column chromatography (hexane/EtOAc, gradient 9:1 to 5:5; the
desired product was obtained at hexane/EtOAc, 6:4). Allyltin prod-
[
b]
Entry
R
Product
Yield of 3 [%]
d.r.
1
2
3
4
5
6
p-MeOC
6
H
4
3o
3p
3q
3r
3s
3t
41
>99
83
79
62
55:45
64:36
65:35
56:44
58:42
86:14
1
uct 2a (0.573 g, quant.) was characterized by H NMR spectroscop-
PhCH
PhCH
nPr
2
CH
2
ic analysis. Further purification was performed by recycling GPC,
2
eluting with CHCl to give the product (0.458 g, 80%).
3
iBu
iPr
44
Tin-catalyzed coupling of vinylcyclopropanes with alde-
hydes
[a] Reaction conditions: 1 (1 mmol), 2 (1 mmol), solvent (1 mL), Bu
2
SnIH
(
0.1 mmol), V-70L (0.1 mmol), hydrosilane (1 mmol). [b] Determined by
H NMR spectroscopic analysis.
1
A 10 mL round-bottom flask was dried by using a heat gun under
a
nitrogen atmosphere. After filling with nitrogen, Bu SnH
2 2
(0.012 g, 0.05 mmol) was added to a solution of Bu SnI (0.024 g,
2 2
0
.05 mmol) in MeCN (1 mL) at RT. To the mixture was added suc-
the reaction that used an aromatic aldehyde to give 3o
entry 1), primary aliphatic aldehydes underwent effective cou-
cessively V-70L (0.1 mmol), Ph SiH (1 mmol), vinylcyclopropane 1a
2
2
(
(0.212 g, 1 mmol), PhCHO (0.106 g, 1 mmol), and MeOH (0.032 g,
pling to give the corresponding homoallylic alcohols 3p–s (en-
tries 2–5). A secondary aliphatic aldehyde gave the correspond-
ing homoallylic alcohol 3t, albeit in diminished yield (entry 6).
Notably, the use of VCPs 1c and 1d is rare in conventional
1
mmol), and the resulting mixture was stirred at 258C for 24 h.
After quenching with H O (2 mL), the reaction mixture was extract-
ed with Et O (3ꢁ10 mL). The combined organic layer was dried
over MgSO and concentrated. The diastereoselectivity of 3a was
determined by H NMR spectroscopic analysis (0.320 g, quant, anti/
2
2
4
[
2–11]
1
transition-metal and Lewis acid-catalyzed reactions.
When
syn ratio 85:15). The residue was subjected to column chromatog-
raphy (hexane/EtOAc, gradient 9:1 to 5:5; the desired product was
obtained at hexane/EtOAc, 6:4). Silane residues were removed by
this treatment. Further purification was performed by GPC eluting
with CHCl3.
substituted for VCPs 1a–d, a simple vinylcyclopropane afford-
ed no coupling reaction due to the absence of electronegative
substituents on the ring. It is assumed that functional groups
such as COOEt and OAc in 1a–d are able to coordinate with
the Bu ISn radical. The coordinated tin radical then attacks the
2
C=C double bond in an intramolecular fashion more easily
than a free tin radical. Oxygen functional groups can coordi- Acknowledgements
nate only to acidic Bu ISn species because of halogen substitu-
2
tion on tin. This feature of tin offers a plausible explanation for
This research was supported by a Grant-in-Aid for Scientific Re-
why the reaction performs better with Bu SnIH than with
search from the Ministry of Education, Science, Sports, and Cul-
ture and the Naito Foundation.
2
Bu SnH.
3
Conclusion
Keywords: allylation · hydrides · hydrostannation · small-ring
systems · tin
We have developed a novel type of hydrostannation of vinylcy-
clopropanes by using dibutyliodotin hydride (Bu SnIH). The re-
2
[
sultant allylic tin compounds reacted easily with aldehydes.
The advantage of Bu SnIH over conventional Bu SnH was clear.
2
3
2
In addition, these results establish a tin-catalyzed coupling re-
action of VCPs with aldehydes to give homoallylic alcohols.
The characteristic feature is that the coupling reactions pro-
ceeded without the use of transition-metal catalysts. VCPs 1c
&
&
Chem. Eur. J. 2015, 21, 1 – 7
4
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