The stereochemistry of the S[subscript N]2' reaction of ethylamine with 3-chloro-1-butene

Allylic compounds are known to react via nucleophilic substitution in which the double bond is displaced to another position in the compound (allylic rearrangement by the S_N2’ reaction). Theoretical and experimental work on the mechanism of this reaction is ambiguous and often contradictory. The reaction of optically active 3-chloro-lbutene-l-d (α-methylallyl chloride) with the primary amine, ethylamine, proceeds by an S_N2’ pathway that is stereoselectively syn. The allylic amine which results from the S_N2’ reaction of the above is first reduced by treatment with diimide and then ethylated using ethyl iodide. The optical rotation of the reduced, alkylated amine is then compared to that of a sample of the optically pure amine. This comparison shows that the reaction proceeds with syn stereoselectivity.