Asymmetric protonation of enolic species: Dramatic increase in the selectivity with temperature and unexpected Eyring diagram

The palladium-induced cleavage of beta-ketosters and enol carbonates derived from alpha-alkylated 1-indanones and 1-tetralones in the presence of (+)-endo-2-hydroxy-endo-3-aminobornane led to (R)-alpha-alkylated indanones and tetralones with a large increase in the enantioselectivity (up to 38-40%) when the reaction temperature was raised from 21 to 45-70 degrees C. Thus, enantiopure 2-methyl-1-indanone was obtained at 52 degrees C. More than one inversion temperature has appeared in plotting the corresponding Eyring diagrams. (C) 1997 Elsevier Science Ltd. All rights reserved.