Amines neighbouring group participate

You ve already met the most important ones—sulfides, esters, carboxylates. Ethers and amines (you will see some of these shortly) can also assist substitution reactions through neighbouring group participation. The important thing that they have in common is an electron-rich heteroatom with a lone pair that can be used to form the cyclic intermediate. Sulfides are rather better than ethers—this sulfide reacts with water much faster than rc-PrCl but the ether reacts with acetic acid four times more slowly than rc-PrOSC Ar. 

The effect of a heteroatom 0 to the oxirane ring has been studied in the reaction of monosubstituted oxiranes 131 and benzylamine. If X = 0, the reaction occurs via the transition state 132 with neighbouring-group participation. Neighboring-group participation has similarly been observed in the reactions of mono- and tri-substituted oxiranes and )3-substituted primary amines. The product ratio of the aminoalcohols formed from the reactions of a-vinyloxiranes and primary amines depends on the geometry of the oxirane.Base-catalyzed addition of oxiranes to oximes leads not only to 0-alkyl but to A -alkyl derivatives (Eq, 319). ... 

Now, consider this substitution reaction, in which OH replaces Cl but with a change in the molecular structure. The substitution goes with complete rearrangement—the amine ends up attached to a different carbon atom. We can easily see why if we look at the mechanism. The reaction starts off iooking iike a neighbouring group participation of the sort you are now famiiiar with (the carbon atoms are numbered for identification). 

Dingwall, J.G., Ehrenfreund, J., and Hall, R.G., Diethoxymethylphosphonites and phosphinates. Intermediates for the synthesis of a,P- and y-aminoalkylphosphonous acids. Tetrahedron, 45, 3787, 1989. Mohrle, H., and Vetter, W., Participation of phosphonate neighbour groups with dehydrogenations of amines, Z. Naturforsch., 43b, 1662, 1988. 

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