In-mediated synthesis of 2-(2-hydroxyethyl)homoallenylsilanes

Article abstract of DOI:10.1016/S0040-4039(00)01290-9

Indium-mediated homoallenylation of aldehydes with 4-bromo-3-[(trimethylsilyl)methyl]-1,2-butadiene in DMF afforded 2-(2-hydroxyethyl)homoallenylsilanes at room temperature in good yields. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)01290-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 7521–7524
In-mediated synthesis of
2-(2-hydroxyethyl)homoallenylsilanes
Phil Ho Lee,a,* Keukchan Bang,a Kooyeon Lee,a Chang-Hee Leea and Sukbok Changb
aDepartment of Chemistry, Kangwon National University, Chuncheon 200-701, South Korea
bDepartment of Chemistry, Ewha Womans University, Seoul 120-750, South Korea
Received 30 June 2000; accepted 24 July 2000
Abstract
Indium-mediated homoallenylation of aldehydes with 4-bromo-3-[(trimethylsilyl)methyl]-1,2-butadiene
in DMF afforded 2-(2-hydroxyethyl)homoallenylsilanes at room temperature in good yields. © 2000
Elsevier Science Ltd. All rights reserved.
Keywords: indium; homoallenylation; 2-(2-hydroxyethyl)homoallenylsilanes.
Allyl metal-mediated carbonꢀcarbon bond formation is one of the fundamental processes in
organic synthesis.1 Although allyl metal-mediated allylation of a variety of aldehydes and
ketones has received much attention, less attention has been paid to homoallenylation of the
carbonyl compounds. As part of our continuing effort to synthesize 2-methyl-3-trimethylsilyl-
methyl dihydrofuran derivatives from homoallenyl alcohols, we needed a versatile method to
prepare 2-(2-hydroxyethyl)homoallenylsilanes. Generally, 2-(2-hydroxyethyl)allylsilanes can be
prepared by lithiation followed by silylation of 3-methylhomoallylic alcohols,2 by ring opening
reactions of epoxides with organometallic reagents derived from 2-haloallylsilanes3 and by
indium-mediated allylsilylation of carbonyl compounds.4 To the best of our knowledge none of
these methods has been applied to the synthesis of 2-(2-hydroxyethyl)homoallenylsilanes. The
addition of organometallic reagents derived from the halomethylhomoallenylsilanes on alde-
hydes or ketones could be used to produce 2-(2-hydroxyethyl)homoallenylsilane. However, we
could not effectively prepare the corresponding Grignard reagents from the halomethylhomo-
allenylsilanes. In addition Grignard reagents must be employed in excess in reactions with
electrophiles having any acidic hydrogens to obtain the desired products in good yields.
Therefore, we turned our attention to other organometallic reagents to synthesize 2-(2-hydroxy-
ethyl)homoallenylsilanes. Of all the metals, indium has been employed frequently in numerous
* Corresponding author. Tel: +82-33-250-8493; fax: +82-33-253-7582; e-mail: phlee@kangwon.ac.kr
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01290-9

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organic conversions especially in recent years because it has some prominent advantages such as
easy handling, high reactivity and selectivity, and low toxicity.5 Indeed, it has been shown to be
effective in the allylation of carbonyl compounds6 and aldimines,7 in ring expansion reaction,8
in Prins type cyclization,9 and in intramolecular carbocyclizations.10 We tried to take advantage
of indium-promoted allylations and here we report our initial results on the indium-mediated
homoallenylation of aldehydes (Scheme 1).
Scheme 1.
To find optimum conditions for indium-mediated homoallenylation, benzaldehyde was ini-
tially reacted with 4-bromo-3-[(trimethylsilyl)methyl]-1,2-butadiene (1)11 in the presence of
indium in various solvents. Of the solvents tested such as H2O, THF, CH2Cl2 and DMF, the
best results were obtained in DMF. The indium-mediated reaction of benzaldehyde with
homoallenyl bromide 1 in DMF afforded the homoallenylated product 5 in 92% yield (entry
4).12 The same reaction in other solvents, however, gave lower yields as well as a longer reaction
time.
As can be seen in Table 1, various aliphatic aldehydes (entries 1ꢀ3) gave the desired
compounds 2, 3 and 4 in good yields.13 For the aromatic aldehydes, the presence of various
substituents, such as methyl (entry 5), bromo (entry 6), chloro (entry 7), nitro (entry 8),
monomethoxy (entry 9), or dimethoxy (entry 10) on the aromatic ring showed little effects on
either the reaction rate or yields of the reaction. It is especially noteworthy that a substrate
having an acidic hydrogen such as 4-formylbenzoic acid was also reacted to produce the
corresponding homoallenyl alcohol 12 in 88% yield (entry 11). The present method reaches a
limit with ketones. Acetophenone did not react with 4-bromo-3-[(trimethylsilyl)methyl]-1,2-buta-
diene under the identical conditions while an indium reagent derived from 3-iodo-2-(trimethyl-
silylmethyl)propene reacted with acetophenone.
In summary, indium-mediated homoallenylation of aldehydes with 4-bromo-
3[(trimethylsilyl)methyl]-1,2-butadiene in DMF afforded 2-(2-hydroxyethyl)homoallenylsilanes
in good to excellent yields under mild conditions. Because synthetic methods for the preparation
of 2-(2-hydroxyethyl)allylsilanes were reported mainly in previous works, the present method
complements the existing synthetic methods. Further studies on the synthesis of 2-methyl-3-
trimethylsilylmethyl dihydrofurans using 2-(2-hydroxyethyl)homoallenylsilanes are now in
progress.
Acknowledgements
This work was supported by a Korea Research Foundation Grant (KRF-99-005-D00048).
The gas chromatograms were provided by GC facility, supported by Research Center for
Advanced Mineral Aggregate Composite Products.

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Table 1
Indium-mediated homoallenylation of aldehydes

7524
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11. 4-Bromo-3-[(trimethylsilyl)methyl]-1,2-butadiene was prepared from 2-butyn-1,4-diol as in the following scheme.
12. To a solution of indium [indium powder (99.99%) purchased from Aldrich Chem. Co.; 58 mg, 0.5 mmol) in DMF
(0.6 mL) was added 4-bromo-3-[(trimethylsilyl)methyl]-1,2-butadiene (110 mg, 0.5 mmol) in DMF (0.6 mL). After
the reaction mixture was stirred for 30 min at room temperature, benzaldehyde (37 mg, 0.35 mmol) was added.
After 40 min at room temperature, the reaction mixture was quenched with saturated aqueous NaHCO3 solution.
The aqueous layer was extracted with ether (3×25 mL), and the combined organic layers were washed with water
(20 mL), brine (20 mL), dried with MgSO4, filtered and concentrated in vacuo. The residue was purified by silica
gel chromatography (hexane:EtOAc=20:1) leading to 1-phenyl-3-trimethylsilylmethyl-3,4-pentadien-l-ol (80 mg,
92%).
1
13. All new compounds have satisfactory analytical data including H, 13C NMR, MS and IR spectroscopy.
.