Stereoelectronic control in the cleavage of tetrahedral intermediates in the hydrolysis of esters and amides

Abstract

A new stereoelectronic theory for the cleavage of the tetrahedral intermediate in the hydrolysis of esters and amides is presented. In this new theory, the precise conformation of the intermediate hemi-orthoester or hemi-orthoamide controls the nature of the hydrolysis products. It is postulated that the breakdown of a conformer of a tetrahedral intermediate depends upon the orientation of the lone pair orbitals of the hetero-atoms. Specific cleavage of a carbon-oxygen or a carbon-nitrogen bond in any conformer is allowed only if the other two hetero-atoms (oxygen or nitrogen) each have an orbital oriented antiperiplanar to the leaving O-alkyl or N-alkyl group. Experimentally, the oxidation of acetals by ozone and the acid hydrolysis of a series of cyclic orthoesters demonstrates clearly that there is indeed a stereoelectronic control in the cleavage of hemiorthoesters. Similarly, a study of the basic hydrolysis of a variety of N,N-dialkylated imidate salts shows that the same stereoelectronic control is operating in the cleavage of hemiorthoamides.