Addition of hetero allenyl copper reagents to aldehydes: scope and behavior.
Cyanocuprates derived from propargylic amines or ethers react with aldehydes to give regioselectively the corresponding anti-homopropargylic alcohols with a high level of diastereoselectivity. Such selectivity could be obtained independently of the nature of the heteroatom (amine or ethers) or the acetylenic substituents. Excellent selectivities can be reached regardless of the aldehydes used, remarkably also with vinylic or acetylenic ones. A reactivity scale for the cuprates bearing different acetylenic substituents was established to be: SiMe3 >Ph> Et. The rate of the addition reaction to aldehydes was also found to be slowed down in the presence of HMPA underlining the crucial role of the Li counterion. DFT calculations have shown that the relationship between the rate and the acetylenic substituent is not connected to a possible metallotropic equilibrium but to the stability of the reactive allenic species compared to the less-stable propargylic isomer.
Vrancken
Emmanuel
E
Institut Fédératif de Recherche FR 2769, UMR 7611, Université Pierre et Marie Curie, 4 Place Jussieu, F-75252 Paris Cedex, France. vrancken@ccr.jussieu.fr
Alouane
Nacira
N
Gérard
Hélène
H
Mangeney
Pierre
P