STUDIES ON REACTION RATE DIFFERENCES BETWEEN ORGANOTRIFLUOROBORATES AND BORONIC ACIDS IN BINOL-CATALYZED CONJUGATE ADDITIONS TO ENONES

Organoboron compounds have become useful synthons in a variety of organic transformations. The combination of these reagents with organocatalysis first experienced major development in the area of asymmetric 1,4-conjugate addition reactions (Scheme 1). More recently, enantioselective organocatalysis has been successfully employed in combination with trifluoroborate reagents for novel organic transformations. However, no experimental mechanistic studies of these reactions have been reported. This thesis presents the experimental Hammett plot analysis of the organocatalyzed enantioselective conjugate addition of alkenyl, aryl, and heteroaryl trifluoroborate salts to chalcone derivatives with varying substitution at both the β-aryl and keto-aryl positions and compares the results to those previously observed when using boronic acids. The rate trend for the keto-aryl substitution diverges from that of boronic acid nucleophiles in that the keto-aryl substituent for trifluoroborate salts does not measurably impact reaction rate in a manner consistent with charge stabilization. In addition, variable temperature NMR in combination with quantitative thin-layer chromatography (TLC) analysis suggests that the reaction is minimally impacted by the low solubility of the trifluoroborate salts, thus the particle size and stir speed have a limited effect on reaction rates.