Suppressed β-Effect of Silicon in 3-Silylated Monocyclic β-Lactams: The Role of Antiaromaticity

Abstract

The β-stabilizing effect of silicon substituent at C-3 on a C-4 cation and a radical in the 2-azetidinone systems is studied using NMR kinetics. While the β-effect is virtually nonexistent in the case of a cation, a foiled β-effect (only a 3-fold rate enhancement) is observed for a radical intermediate. From both the experimental and theoretical studies, it is demonstrated that antiaromaticity is playing the prime role in suppressing the β-stabilizing effect of silicon