A new method for reductive coupling of carbonyl compounds to olefins

Article abstract of DOI:10.1016/s0040-4039(00)01034-0

Aromatic and aliphatic aldehydes and ketones react with AlCl₃-Zn in acetonitrile to yield olefins in good yield. (C) 2000 Published by Elsevier Science Ltd.

Full text of DOI:10.1016/s0040-4039(00)01034-0

Tetrahedron Letters 41 (2000) 6227±6229
A new method for reductive coupling of carbonyl
compounds to ole®ns
Dilip Kumar Dutta and Dilip Konwar*
Organic Chemistry Division, Regional Research Laboratory, Jorhat 785 006, Assam, India
Received 17 April 2000; revised 13 June 2000; accepted 20 June 2000
Abstract
Aromatic and aliphatic aldehydes and ketones react with AlCl ±Zn in acetonitrile to yield ole®ns in good
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yield # 2000 Published by Elsevier Science Ltd.
Keywords: reductive coupling; reductive cross coupling; aluminum, ole®ns.
1
The chemistry of aluminum has acquired renewed interest and in recent years the versatility of
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3
aluminum chloride has undergone a major increase. Despite the numerous methods available,
the reductive coupling and cross-coupling of aldehydes and ketones to ole®ns is a topic of current
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interest to organic chemists and is being pursued with sustained e€orts. Our interest in
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aluminum chemistry has led us to report here a novel utility of AlCl with Zn as an ecient
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reagent for the conversion of aldehydes and ketones to ole®ns (Scheme 1).
0
The addition of 1 equiv. of benzaldehyde ( 1a, R=Ph, R =H) to 2 equiv. of aluminum chloride
and zinc and heated to re¯ux under anhydrous condition in dry acetonitrile for 10 h gave stilbene
(
2a) in 92% yield (Table 1). Aliphatic and aromatic aldehydes and ketones a€orded (2a±i) in high
yields.
It was observed that under the reaction condition, mostly trans products were found when the
reactants were bulky in nature. Also, cross-coupling products could be prepared under the
reaction conditions (Table 2).
Scheme 1.
*
Corresponding author.
0040-4039/00/$ - see front matter # 2000 Published by Elsevier Science Ltd.
PII: S0040-4039(00)01034-0

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Table 1
Synthesis of Ole®ns (2a±j)
a,c
Table 2
a
Cross coupling reaction products (2j±l) (ratio of two carbonyl compounds 1:2)
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Regarding the mechanism of the reaction, we assume that single electron transfer (SET) from
the Al(0) to carbonyl compounds has occurred and this generates the dianion, presumably via a
ketyl like intermediate. The dianions bind to the aluminum particles, and subsequent homolytic
cleavage liberates the ole®ns and aluminum oxide.
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In conclusion, a new, cheap reagent comparable to McMurry's reagent, is reported for the
reductive coupling and cross coupling of carbonyl compounds to ole®ns.
Acknowledgements
The authors wish to thank Dr. J. S. Sandhu FNA, Director, Regional Research Laboratory,
Jorhat, Assam for his keen interest in carrying out this work.

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