Kinetic Study of Reactions of a Ketone with a Dialkylmagnesium Compound and with Organomagnesate Species1

Abstract

The initial rate of formation of addition product from reactions of Np2Mg (Np = neopentyl) and phenyl tert-butyl ketone (1a) or o-methylphenyl tert-butyl ketone (1b) in benzene is proportional to [Np2Mg]0[1]1 when Np2Mg is in excess and to [Np2Mg]1[1]0 when ketone is excess. For either ketone, the rate is ca. 15-fold greater when ketone is in excess than when Np2Mg is in excess; regardless of which reagent is in excess, reactions of 1a are ca. 600-fold faster than reactions of 1b. 1H NMR absorptions of benzene-d6 solutions prepared with different Np2Mg/1b ratios indicate substantial formation of a 1:1 Np2Mg−1b complex, and when Np2Mg is in excess, some formation of a 2:1 complex. In THF as solvent, the initial rate of formation of addition product from Np2Mg and 1a is proportional to [Np2Mg]1[1a]1, and 1H NMR observations do not indicate Np2Mg−1b complexation. Formation of addition product from 1b and an organomagnesate solution prepared from KOMe and Np2Mg in benzene is 1−2 orders of magnitude faster tha...