β‐Elimination of an aziridine to an allylic amine: a mechanistic study

Abstract

The base-induced rearrangement of aziridines has been examined using a combination of calculations and experiment. The calculations show that the substituent on nitrogen is a critical feature that greatly affects the favorability of both α-deprotonation, and β-elimination to form an allylic amine. Experiments were carried out to determine whether E2-like rearrangement to the allylic amine with lithium diisopropyl amide (LDA) is possible. N-Tosyl aziridines were found to deprotonate on the tosyl group, preventing further reaction. A variety of N-benzenesulfonyl aziridines having both α- and β-protons decomposed when treated with LDA in either tetrahydrofuran or hexamethylphosphoramide. However, when α-protons were not present, allylic amine was formed, presumably via β-elimination.

Thermochemical Studies of Epoxides and Related Compounds

“…In some of the aziridines, the NH group can be either anti or syn to the alkyl substituent(s). The inversion barrier at the aziridine nitrogen is known to be on the order of 20 kcal mol –1 ; the stereoisomers interconvert at room temperature, , so the values tabulated reflect the energy weighted average determined by Boltzmann distribution.…”

“…8 Experimentally, β-elimination has been observed in few cases, such as when α-protons are not present. 9 The enhanced α-deprotonation of aziridines may be due to greater strain.…”

“…Unlike epoxides, aziridines treated with strong bulky base favor α-deprotonation over β-elimination, when nitrogen is substituted with anion-stabilizing substituents . Experimentally, β-elimination has been observed in few cases, such as when α-protons are not present . The enhanced α-deprotonation of aziridines may be due to greater strain.…”