Is There Stereoelectronic Control in Formation and Cleavage of Tetrahedral Intermediates?

Abstract

Deslongchamps' hypothesis of stereoelectronic control states that preferential cleavage of a tetrahedral intermediate occurs when a leaving group is antiperiplanar to two lone pairs. It is argued that the evidence supporting the hypothesis is suspect. An alternative explanation is that product stabilities bias the results. A more suitable test is hydrolysis of cyclic amidines and related species. Product studies show substantial cleavage of the bond that is antiperiplanar to only one lone pair and syn to the other, especially in five- and seven-membered rings. Even in the most favorable cases, six-membered rings, antiperiplanar lone pairs provide <2 kcal/mol of transition-state stabilization.