Indium-mediated allylation of gem-diacetates to homoallylic acetates in aqueous media

Article abstract of DOI:10.1016/S0040-4039(00)00242-2

Indium-mediated allylation of gem-diacetates gave excellent yields of the corresponding homoallylic acetates in aqueous media. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00242-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 2695–2697
Indium-mediated allylation of gem-diacetates to homoallylic
†
acetates in aqueous media
∗
J. S. Yadav, B. V. Subba Reddy and G. S. Kiran Kumar Reddy
Organic Division-I, Indian Institute of Chemical Technology, Hyderabad-500 007, India
Received 1 November 1999; revised 26 January 2000; accepted 9 February 2000
Abstract
Indium-mediated allylation of gem-diacetates gave excellent yields of the corresponding homoallylic acetates in
aqueous media. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: gem-diacetates; allyl bromide; indium; homoallylic acetates.
Geminal-diacetates are ambident substrates containing two types of reactive carbon centres, the
carbon atom of a protected aldehyde function and the carbonyl group in the ester moieties. In general,
carbon nucleophiles will predominantly attack the former centre and displace one of the acyloxy groups
1
affording substitution products in good yields. Although, gem-diacetates are readily available from the
corresponding aldehydes, these compounds have received little attention as substrates for nucleophilic
2
3
substitution reactions. Many methods, including palladium*(0) catalyzed substitution reactions are
4
associated with limitations regarding selectivity and compatibility. The recent report on Sc(OTf)3
catalyzed addition of allyltrimethylsilane to aldehydes in the presence of acetic anhydride gave a mixture
of products containing the homoallylic alcohol, diacetate and di-allylated product along with the desired
homoallylic acetates. Thus, an efficient and selective procedure for the substitution reactions of diacetates
is needed.
5
In recent years, there has been increasing interest in indium-mediated transformations because of
certain unique properties inherent to indium. Furthermore, indium metal is stable to boiling water or
alkali and doesn’t form oxides readily in air. Such special properties of indium indicate that it is perhaps
6
a promising metal for aqueous Barbier–Grignard type reactions. Even though indium has been used
7
extensively in carbonyl addition reactions, it has not been used for the substitution reactions of gem-
diacetates and acetals. Herein, we wish to report a mild and selective method for the synthesis of
homoallylic acetates through the allylation of gem-diacetates using indium metal and allyl bromide in
aqueous media. The mildness of the reaction conditions make it possible to use the indium metal for
mono substitution of diacetates without formation of any side products including aldehydes, pinacols and
∗
†
Corresponding author.
IICT Communication No. 4430
0
040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00242-2
tetl 16522

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696
Table 1
Mono-allylation of gem-diacetates with allyl indium bromide in aqueous media
homoallylic alcohols. The reaction of aromatic diacetates with an equimolar ratio of allyl bromide and
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indium metal in THF:H O (4:1), resulted in the formation of the mono-allylated products in good yields
2
while aliphatic and allylic diacetates gave homoallylic acetates in moderate yields. Furthermore, it is of
interest to observe that homoallylic alcohols were formed in good yields when diacetates were reacted
with allylic magnesium bromide in THF at room temperature. The formation of homoallylic alcohols

2
697
Scheme 1.
may be attributed to the hydrolysis of homo allylic acetates with magnesium in THF whereas no such
hydrolysis was observed by indium salts. Allylic magnesium bromides are known to react with esters
resulting in the regeneration of parent aldehydes which give addition products whereas allylic indium
bromide doesn’t react with esters forming substitution products. Although, we could not establish the
reaction mechanism by experiments, it may proceed as follows.
The reactions are clean and afford high yields of mono-substitution products at room temperature in a
short reaction time. The results summarized in Table 1 clearly indicate the generality of the reaction for
a variety of diacetates (Scheme 1).
In conclusion, we have described a new and efficient method for the synthesis of homoallylic acetates
in good yields in aqueous media. Indium is found to be effective and highly selective metal for this
transformation.
Acknowledgements
B.V.S. thanks CSIR, New Delhi for the award of fellowship.
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. Typical procedure: A mixture of indium powder (10 mmol), allyl bromide (12 mmol) and substrate 1c (10 mmol) in THF (16
ml) and H
the reaction was quenched with saturated ammonium chloride (20 ml) and extracted twice with ether (2×30 ml). The organic
extracts were washed with brine, dried over anhydrous Na SO and concentrated in vacuo to yield the crude product which
was further purified by column chromatography on silica gel (100–200 mesh), and eluted with ethyl acetate:hexane gradient
2
O (4 ml) was stirred at room temperature for 3.5 h, until completion of the reaction was observed by TLC. Then
2
4
1
mixture (2:8) to afford the pure product 2c as a colourless liquid. Representative data for compound 2c: H NMR (CDCl
.0 (s, 3H), 2.45–2.55 (m, 2H), 5.0–5.15 (m, 2H), 5.55–5.65 (m, 1H), 5.7 (m, 1H), 6.0 (s, 2H), 6.75–6.85 (m, 3H).
3
): δ
2