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Synlett 2005(13): 2098-2100  
DOI: 10.1055/s-2005-871962
LETTER
© Georg Thieme Verlag Stuttgart · New York

Regiocontrolled Carbometallation Reactions of Ynamides

Helena Chechik-Lankin, Shulamit Livshin, Ilan Marek*
Department of Chemistry, Institute of Catalysis Science and Technology, The Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32 000, Israel
Fax: +972(4)8293709; e-Mail: chilanm@tx.technion.ac.il;
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Publication History

Received 5 June 2005
Publication Date:
13 July 2005 (online)

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Abstract

The first carbocupration and copper-catalyzed carbomagnesiation reactions on diversely substituted ynamides is described here. This study shows that the linear regioisomer can be quantitatively obtained in the carbometallation reaction of N-substituted alkynes.

Key words

carbocupration - carbomagnesiation - ynamides - regiochemistry - enamides

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When the branched isomer was warmed to r.t., a β-elimination reaction occurs to lead to the corresponding alkyne.

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General Procedure for the Stoichiometric Carbocupration Reaction.
To a solution of CuI (2 equiv) in dry Et2O (10 mL) at -78 °C was added alkylmagnesium bromide (2 equiv). The reaction mixture was warmed to the indicated temperature and stirred for 30 min. Then, the reaction mixture was cooled to -78 °C and alkynyl amide 1 (1 equiv) in dry Et2O was added dropwise. The reaction solution was warmed to the indicated temperature and stirred for additional 90 min. After 90 min, the reaction was quenched by a 1:2 mixture of sat. soln of NH4Cl and NH4OH (30%) and warmed to r.t. The phases were separated and the aqueous phases were extracted three times with Et2O. The combined organic layers were washed with 1:2 mixture of sat. solution of NH4Cl and NH4OH (30%) and dried over anhyd MgSO4.

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General Procedure for Copper-Catalyzed Carbomagnesiation Reaction. To a solution of alkynyl amide (1 equiv) in dry Et2O (10 mL), copper salt (0.1 equiv) was added at r.t. The reaction mixture was cooled to -30 °C and alkylmagnesium bromide was added. Then, reaction mixture was warmed to r.t. and stirred for 90 min. After 90 min, the reaction was quenched by a 1:2 mixture of sat. soln of NH4Cl and NH4OH (30%) and warmed to r.t. The phases were separated and the aqueous phases were extracted three times with Et2O. The combined organic layers were washed with 1:2 mixture of sat. soln of NH4Cl and NH4OH (30%) and dried over anhyd MgSO4.