Allylation of carbonyl compounds with allylic gallium reagents

Article abstract of DOI:10.1246/cl.2002.2

Allylic gallium reagents, prepared from gallium trichloride and the corresponding allylic Grignard reagents, allylated carbonyl compounds in good yields in an aqueous medium as well as in organic solvent.

Full text of DOI:10.1246/cl.2002.2

2
Chemistry Letters 2002
Allylation of Carbonyl Compounds with Allylic Gallium Reagents
Takashi Tsuji, Shin-ichi Usugi, Hideki Yorimitsu, Hiroshi Shinokubo, Seijiro Matsubara, and Koichiro OshimaÃ
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501
(Received June 25, 2001; CL-010599)
Allylic gallium reagents, prepared from gallium trichloride
Table 1. Allylation of benzaldehyde (1a), decanal (1b), and
acetophenone (1c) with allylic gallium reagents.
and the corresponding allylic Grignard reagents, allylated
carbonyl compounds in good yields in an aqueous medium as
well as in organic solvent.
Allylation of carbonyl compounds is a fundamental reaction
in organic synthesis. Various allylic metals have been developed
and used for stereo- and regio-selective reactions.1 Among them,
allylic indium species are known for their stability in aqueous
media.2 The usefulness of allylic indium compounds is illustrated
in syntheses of natural products, especially a concise synthesis of
a sialic acid starting from allylation of unprotected mannose.3 On
the other hand, allylation with allylic gallium4 in the presence of
water is not known to our knowledge.5;6 Here we wish to report
allylation of carbonyl compounds with allylic gallium reagents in
aqueous media as well as in organic solvent.
We first examined the allylation in THF. The allylgallium
reagent used here was prepared by mixing gallium trichloride and
an equimolar amount of allylmagnesium chloride. Allylmagne-
sium chloride (0.8 M THF solution, 1.9 mL, 1.5 mmol) was
added to gallium trichloride (1.0 M hexane solution, 1.5 mL,
ꢀ
1.5 mmol, diluted with 3 mL of THF) at 0 C. After the mixture
was stirred for 5 min, benzaldehyde (1a, 1.0 mmol) was added to
the allylgallium reagent. The resulting mixture was stirred for
ꢀ
30 min at 0 C. Workup and silica gel column purification
provided 1-phenyl-3-buten-1-ol in 94% yield.
Reactions of allylic gallium reagents including crotyl-,7
methallyl-, and prenylgallium reagents are summarized in
Table 1. Decanal (1b) also reacted efficiently with the allylgal-
lium reagent (Entry 2). However, ketone was less reactive.
Acetophenone (1c) underwent allylation to proꢀvide the corre-
sponding homoallylic alcohol in 35% yield at 0 C, and in 73%
yield even at elevated temperature (Entries 3 and 4).8 ꢀ–
Allylation proceeded predominantly in the reactions with the
crotyl- and prenylgallium reagents (Entries 5, 6, 8, and 9). The
reaction with the gallium reagent, prepared from allenylmagne-
sium bromide9 and gallium trichloride, yielded the corresponding
homopropargylic alcohols (Scheme 1).
Scheme 1.
Table 2. Allylation of aromatic aldehydes with the allylgallium
reagents.
Allylation of various aldehydes was examined, and the
results are shown in Table 2. Selective allylation of the formyl
moieties of nitro-, cyano-, and methoxycarbonylbenzaldehyde
was successfully achieved. Interestingly, aldehydes having a
hydroxy or a carboxyl group were also allylated efficiently
(Entries 5 and 6). Treatment of o-phthalaldehydic acid (3g) with
1.5 molar amounts of the allylgallium reagent furnished a
mixture of hydroxy carboxylic acid 4g and lactone 5 (Scheme
2). The mixture was stirred in 1M HCl to afford 5 in 86% overall
yield. Treatment of cinnamaldehyde with allylgallium dichloride
afforded the 1,2-adduct selectively in 97% yield.
hand, benzoin methyl ether (6b) was less reactive. Heating a
reaction mixture at reflux inTHF was required to give a mixture of
diastereomers. These contrastive results suggest the formation of
gallium alkoxide 8 and the efficient activation of the carbonyl
group.
Allylation of benzoin (6a) proceeded smoothly to yield
erythro-7a as a single diastereomer (Scheme 3). On the other
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
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Scheme 2.
Scheme 5.
Scheme 3.
We turned our attention to the reaction in aqueous media. The
allylgalliums were prepared as described above. The reagents
were treated with water (1 mL) prior to addition of aldehyde. The
results are summarized in Table 3 and Scheme 4. Although we
anticipated some changes in stereo- and/or regioselectivity, the
allylation in aqueous media proceeded efficiently with similar
selectivity. In similar fashion to the reaction in anhydrous organic
solvent, allylation of cinnamaldehyde provided the 1,2-adduct in
the presence of water (99% yield).
Scheme 6.
prenylgallium reagent afforded dl-diol 13 exclusively. The
control of facial selectivity by the chelation would operate in
this system as in the case of Scheme 3.
This work was supported by Grants-in-Aid for Scientific
Research (Nos. 12305058 and 10208208) from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
H. Y. is grateful to JSPS for financial support.
Table 3. Allylation of aldehyde with allylic gallium reagents in
aqueous media
Dedicated to Prof. Teruaki Mukaiyama on the occasion of his
75th birthday.
References and Notes
N. Asao and Y. Yamamoto, Chem. Rev., 93, 2207 (1993).
1
2a) C.-J. Li and T.-H. Chan, Tetrahedron Lett., 32, 7017 (1991).
b) S. Araki, S. Jin, Y. Idou, and Y. Butsugan, Bull. Chem. Soc.
Jpn., 65, 1736 (1992).
3
a) T.-H. Chan and C.-J. Li, J. Chem. Soc., Chem. Commun.,
1992, 747. b) C.-J. Li, Chem. Rev., 93, 2023 (1993).
Allylation with allylgallium reagents in organic solvent has
been reported: a) Y. Han and Y.-Z. Huang, Tetrahedron Lett.,
35, 9433 (1994). b) Y. Han, Z. Chi, and Y.-Z. Huang, Synth.
Commun., 29, 1287 (1999). c) S. Araki, H. Ito, and Y. Butsugan,
Appl. Organomet. Chem., 2, 4757 (1988).
4
5
6
Radical allylation with allylic galliums has been reported: S.
Usugi, H. Yorimitsu, and K. Oshima, Tetrahedron Lett., 42,
4535 (2001).
Other examples of allylation with allylic metals in aqueous
media: a) M. Wada and N. Miyoshi, J. Syn. Org. Chem. Jpn., 57,
689 (1999). b) T. Akiyama, J. Iwai, and M. Sugano,
Tetrahedron, 55, 7499 (1999). c) A. Yanagisawa, M. Moro-
dome, H. Nakashima, and H. Yamamoto, Synlett, 1997, 1309. d)
S. Kobayashi, S. Nagayama, and T. Busujima, Chem. Lett.,
1997, 959. e) L.-H. Li, Y. Meng, X.-H. Yi, J. Ma, and T.-H.
Chan, J. Org. Chem., 63, 7498 (1999) and references therein.
Formation of the crotylgallium reagent, not 1-methyl-2-
propenyl form, was confirmed. See Ref. 5.
Scheme 4.
Commercially available aqueous aldehydes could be used for
the allylation with the allylic galliums (Scheme 5). For instance,
an aqueous solution of pyruvaldehyde (9a) was added to
methallylgallium dichloride in THF/hexane. Selective allylation
took place to yield ꢁ-hydroxy ketone 10a in excellent yield.
However, reactions of aqueous solutions of glyoxylic acid (9b)
and formaldehyde (9c) were unsatisfactory. Treatment of glyoxal
(11) solution with three equimolar amounts of the allylgallium
species provided diol 12 in 62% yield as a mixture of
diastereomers (Scheme 6). In contrast, reaction of 11 with the
7
8
9
Allylation of ketone with allylic indium and bismuth reagents
proceeded smoothly. See Refs. 3b and 6a.
H. Shinokubo, H. Miki, T. Yokoo, K. Oshima, and K. Utimoto,
Tetrahedron, 51, 11681 (1995).