TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 5255–5256
Indium-mediated carbonyl alkynylation
Jacques Auge´,* Nade`ge Lubin-Germain and Latifa Seghrouchni
Unite´ Mixte de Recherche CNRS-UCP-ESCOM ꢀSynthe`se Organique Se´lective et Chimie Organome´talliqueꢁ,
5 mail Gay-Lussac, Neuville-sur-Oise, 95031 Cergy-Pontoise, France
Received 3 May 2002; accepted 2 June 2002
Abstract—Indium mediates a Barbier-type reaction between alkynyl halides and aldehydes or ketones to give secondary or tertiary
propargyl alcohols. Secondary alcohols can be oxidised in situ according an Oppenauer process. © 2002 Elsevier Science Ltd. All
rights reserved.
Barbier-type carbonyl alkylation mediated by indium is
We have then formulated the hypothesis that the
ketone 2 came from the Oppenauer oxidation of the
transient indium alkoxide (corresponding to the alcohol
1) with the subsequent reduction of benzaldehyde into
benzylic alcohol. Such an oxidation during an alkynyla-
tion process was formally mentioned with vanadium
acetylides.4 The results presented in Table 1 confirmed
this hypothesis. The increase of the molar amount of
benzaldehyde allowed us to force the Oppenauer oxida-
tion, whereas an excess of phenylalkynyl iodide pre-
vented the oxidation (Table 1).
a
well-known reaction involving generally allylic,
propargylic or a-carbonyl halides.1 We report herein
Barbier-type reactions of alkynyl iodides with alde-
hydes or ketones mediated by indium powder (Scheme
1).
Relevant Barbier reactions were already described with
chromium chloride in DMF2 or samarium iodide in the
presence of hexamethylphosphoric triamide.3 Since
indium is tolerant of water, we investigated first the
reaction with aqueous solvents. In each case a reduc-
tion of the phenylalkynyl iodide used as the model was
obtained, which prompted us to study the reaction in
conventional organic solvents. The best yields were
obtained with dichloromethane at reflux but a mixture
of the propargyl alcohol 1 and the ketone 2 was
observed (Scheme 2).
In a typical experiment to produce exclusively propar-
gylic alcohol, indium powder (138 mg, 1.2 mmol) was
placed in a Schlenk tube under argon, followed by the
addition of dichloromethane (6 mL) and phenylalkenyl
iodide (228 mg, 1 mmol) and then benzaldehyde (53
mg, 0.5 mmol). The heterogeneous mixture was stirred
at reflux for 24 h. The reaction was quenched with a
sodium bicarbonate aqueous solution. The product was
extracted with ether, washed with brine, dried with
anhydrous Mg2SO4, concentrated under reduced pres-
sure, and separated with silica gel chromatography
using a mixture of cyclohexane and ethyl acetate as the
eluent, affording 1,3-diphenylprop-2-ynol in 83% yield.
OH
R1
R2
H2O
In
R1
R2
+
O
R
I
R
CH2Cl2
Scheme 1.
OH
O
Ph
H2O
In
CH2Cl2
+
+
Ph
Ph
I
O
Ph
H
Ph
Ph
1
2
Scheme 2.
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