ABSENCE OF STEREOELECTRONIC CONTROL IN THE HYDROLYSIS OF FULLY AND PARTIALLY N-ALKYLATED CYCLIC AMIDINIUM IONS

Deslongchamps' hypothesis of stereoelectronic control states that pref erential cleavage of a tetrahedral intermediate occurs when a leaving group is antiperiplanar to two lone pairs. Yet substantial amounts of lactams were produced from hydrolysis of cyclic amidines, through clea vage of the exocyclic C-N bond that is antiperiplanar to only one lone pair and syn to the other. It may be that proton transfer catalyzes n itrogen inversion, leading to an intermediate with two antiperiplanar lone pairs, such that the product distribution is indeed consistent wi th stereoelectronic control. To exclude this possibility, three cyclic amidinium ions (1a,b,c) with methyl groups at both nitrogens were syn thesized, and their hydrolysis products in NaOD/D2O were analyzed by N MR. Although stereoelectronic control favors ring opening to amino ami de 3, substantial amounts (40-90%) of lactam 4 are again produced. To exclude the possibility that lactam formation is due to a steric effec t, hydrolysis of a cyclic N,N'-dimethyl amidine (2) was also studied, and 26-35% lactam is still produced. These results cannot be rationali zed by assuming reaction via a boat conformer, since the lone pair of the ring nitrogen does not become antiperiplanar even in the boat form . Thus stereoelectronic control is not operative in amidine hydrolysis .