Stereoselection Parameters and Theoretical Model in the Enantioselective Protonation of Enolates with α-Sulfinyl Alcohols
作者:Gregorio Asensio、Pedro Aleman、Jesus Gil、Luis R. Domingo、Mercedes Medio-Simon
DOI:10.1021/jo981294y
日期:1998.12.1
The effects of the solvent, temperature, presence of Lithium salts in the medium, and acidity of the proton source on enantioselective protonation with alpha-sulfinyl alcohols 2a-e were studied. Stereoselectivity was generally enhanced when lithium bromide was present in the medium during enolization and also with the use of methylene chloride solutions. Conversely, the optimal reaction temperature varied with the alpha-sulfinyl alcohol used as a proton source, and its effect appears to be related to both the acidity of the proton source and the enolate structure. alpha-Sulfinyl alcohols 2a and 2b gave the best results when the reactions were carried out at -100 degrees C, while the optimal temperature with 2c was -78 degrees C. The same ee values were obtained with 2d and 2e at either -100 or -78 degrees C. In addition, an efficient synthesis of alpha-sulfinyl alcohols 2b and 2e is described.